Gas Analysis Handbook



DATALOG DATALOG 1999 199 9

Hydrocarbon Evaluation and Interpretation Interpretation

T2

Hydrocarbon Evaluation Evaluation and Interpretation Version 2.0

Written by the Training Department of DATALOG David P. Ha!er

"### Data$og This This manua manuall is for for the the sole sole use use of partic particip ipan ants ts in the Datal Datalog og Hydrocarb Hydrocarbon on Evaluation Evaluation and Interpretation training Interpretation training course. Datalog, 3030 9 th St SE, algar!, Al"erta, Al"erta, ana#a T$G 3%9 Tel &'03( $'3)$$$0* +acsimile &'03( $'3)$-$* e")site e")site http/.#atalog.a".ca http/.#atalog.a".ca




Hydrocarbon Evaluation and Interpretation

0





%O&T'&T( SECTION 1

INTRODUCTION

5

SECTION 2

HYDROCARBON COMPOSITION AND CLASSIFICATION

9

2."

Petro Petro$e) $e)m m %ompos %ompositi ition on and %$assif %$assifi*at i*ation. ion..... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........... ............. ............. .......... ... #

2.2 (at)rated Hydro*arbons or A$!anes.................... A$!anes...... .............. .............. .............. .............. ............... ........ ...... .. "0 $.$.1 araffin............................................................................................................................. 10 $.$.$ 4aphthenes... 4aphthenes....... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ .......... ............. .......... ... 1$ 2.+

,nsat)rated Hydro*arbons or Aromati*s................... .............. .............. ............... ............. .."-

2.-

AP Gravity %$assifi*ation........ .............. ............... .............. .............. .............. .............. ........ ......."/ .

SECTION 3

SAMPLING, DETECTION AND MEASUREMENT

17

+." 3.1.1 3 .1 .$

'tra* 'tra*tin ting g Gas Gas fro from m the Dri$$ing Dri$$ing 1$)id.. 1$)id...... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ......... .......... ..... " Agitator Agitator T!pe Gas Traps... Traps....... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ......... ........ ... 1The Gasi5ar# T2 6 7uantit ati8e Gas in 2u# 2easurement........................ 2easurement.......................................... .................. $'

+.2 3.$.1 3.$.1 3.$.$ 3.$.3 3.$.' 3.$.< 3.$.; 3.$.;

Gas Dete*tion and 3e*ording......... .............. .............. ............... .............. .............. ................ .......... ...... 2# The atal! atal!tic tic om" om"ust ustion ion or ot ire ire Detec Detector. tor.... ...... ...... ...... ...... ...... ...... ...... ..... ..... ...... ...... ...... ...... ...... ...... ...... ...... ...... ....... .... $9 Thermal on#ucti8 on#ucti8it! it! Detecto Detector.... r........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ......... ........ ... 3$ +lame :oni5ation :oni5ation Detector Detector &+:D(.... &+:D(........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ .......... ...... 3' :nfrare# :nfrare# Detector. Detector..... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ......... ........... ............. ............. ........ 3; Total Gas Detector Detector Summar!.. Summar!...... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ .......... ............ ............. ......... .. 3 =n)mann =n)manne# e# Total otal Gas Gas Dete Detecti ction on S!st S!stem ems.. s..... ...... ...... ...... ...... ...... ..... ..... ..... ..... ...... ...... ...... ..... ..... ...... ...... ...... ...... ...... ...... ...... ...... ....... .... '0

+.+ 3.3.1 3.3.$ 3.3.$ 3.3.3

Gas %hromatography............ %hromatography............ ............... .............. .............. .............. .............. .............. ........... ..... ....... -2 . hromatographic hromatographic Operation.... Operation........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ...... '$ The igh igh Spee Spee# # Ther Thermal mal on#u on#ucti cti8it 8it! ! hrom hromato atogra graph... ph...... ...... ..... ..... ...... ...... ...... ...... ...... ...... ...... ..... ..... ...... ...... ...... ... '3 TD >ersus +:D hromatograph?. hromatograph?..... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ .......... ...... ''

+.-

,nits ,nits of 4eas)r 4eas)reme ement.. nt...... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ .......... ............. ............. ......... ... -

SECTION 4 -."

SURFACE GAS EVALUATION EVALUATION

49

(o)r* (o)r*es es of of Gas Gas at ()r ()rfa* fa*e.... e........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ......... ........... ............. ............. ........ 50 ..

-.2 %hange %hangess in Phase Phase.... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ .......... ............ ............. ........ 5+ . '.$.1 Temperature emperature onsi#erati onsi#erations.... ons........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ...... <3 '.$.$. ritical ritical oints... oints....... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ .......... ............ ...... <; '.$.3 '.$.3 hase hase hanges hanges in omple@ omple@ etro etroleu leum m 2i@tures. 2i@tures... ..... ...... ...... ...... ...... ...... ...... ...... ..... ..... ...... ...... ...... ...... ...... ...... ...... ..... ..... ...... ... ;0 -.+

3e$ated 3e$ated Termino ermino$og $ogy... y....... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ .... /+

SECTION 5



ORIGINS OF GAS



65

1





%O&T'&T( SECTION 1

INTRODUCTION

5

SECTION 2

HYDROCARBON COMPOSITION AND CLASSIFICATION

9

2."

Petro Petro$e) $e)m m %ompos %ompositi ition on and %$assif %$assifi*at i*ation. ion..... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........... ............. ............. .......... ... #

2.2 (at)rated Hydro*arbons or A$!anes.................... A$!anes...... .............. .............. .............. .............. ............... ........ ...... .. "0 $.$.1 araffin............................................................................................................................. 10 $.$.$ 4aphthenes... 4aphthenes....... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ .......... ............. .......... ... 1$ 2.+

,nsat)rated Hydro*arbons or Aromati*s................... .............. .............. ............... ............. .."-

2.-

AP Gravity %$assifi*ation........ .............. ............... .............. .............. .............. .............. ........ ......."/ .

SECTION 3

SAMPLING, DETECTION AND MEASUREMENT

17

+." 3.1.1 3 .1 .$

'tra* 'tra*tin ting g Gas Gas fro from m the Dri$$ing Dri$$ing 1$)id.. 1$)id...... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ......... .......... ..... " Agitator Agitator T!pe Gas Traps... Traps....... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ......... ........ ... 1The Gasi5ar# T2 6 7uantit ati8e Gas in 2u# 2easurement........................ 2easurement.......................................... .................. $'

+.2 3.$.1 3.$.1 3.$.$ 3.$.3 3.$.' 3.$.< 3.$.; 3.$.;

Gas Dete*tion and 3e*ording......... .............. .............. ............... .............. .............. ................ .......... ...... 2# The atal! atal!tic tic om" om"ust ustion ion or ot ire ire Detec Detector. tor.... ...... ...... ...... ...... ...... ...... ...... ..... ..... ...... ...... ...... ...... ...... ...... ...... ...... ...... ....... .... $9 Thermal on#ucti8 on#ucti8it! it! Detecto Detector.... r........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ......... ........ ... 3$ +lame :oni5ation :oni5ation Detector Detector &+:D(.... &+:D(........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ .......... ...... 3' :nfrare# :nfrare# Detector. Detector..... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ......... ........... ............. ............. ........ 3; Total Gas Detector Detector Summar!.. Summar!...... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ .......... ............ ............. ......... .. 3 =n)mann =n)manne# e# Total otal Gas Gas Dete Detecti ction on S!st S!stem ems.. s..... ...... ...... ...... ...... ...... ..... ..... ..... ..... ...... ...... ...... ..... ..... ...... ...... ...... ...... ...... ...... ...... ...... ....... .... '0

+.+ 3.3.1 3.3.$ 3.3.$ 3.3.3

Gas %hromatography............ %hromatography............ ............... .............. .............. .............. .............. .............. ........... ..... ....... -2 . hromatographic hromatographic Operation.... Operation........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ...... '$ The igh igh Spee Spee# # Ther Thermal mal on#u on#ucti cti8it 8it! ! hrom hromato atogra graph... ph...... ...... ..... ..... ...... ...... ...... ...... ...... ...... ...... ..... ..... ...... ...... ...... ... '3 TD >ersus +:D hromatograph?. hromatograph?..... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ .......... ...... ''

+.-

,nits ,nits of 4eas)r 4eas)reme ement.. nt...... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ .......... ............. ............. ......... ... -

SECTION 4 -."

SURFACE GAS EVALUATION EVALUATION

49

(o)r* (o)r*es es of of Gas Gas at ()r ()rfa* fa*e.... e........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ......... ........... ............. ............. ........ 50 ..

-.2 %hange %hangess in Phase Phase.... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ .......... ............ ............. ........ 5+ . '.$.1 Temperature emperature onsi#erati onsi#erations.... ons........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ...... <3 '.$.$. ritical ritical oints... oints....... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ .......... ............ ...... <; '.$.3 '.$.3 hase hase hanges hanges in omple@ omple@ etro etroleu leum m 2i@tures. 2i@tures... ..... ...... ...... ...... ...... ...... ...... ...... ..... ..... ...... ...... ...... ...... ...... ...... ...... ..... ..... ...... ... ;0 -.+

3e$ated 3e$ated Termino ermino$og $ogy... y....... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ .... /+

SECTION 5



ORIGINS OF GAS



65

1





5."

%$assi %$assifi*a fi*atio tion n of Gas Gas (o)r (o)r*es *es.... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ .......... ......... ... /5

5.2

Liberated Liberated Gas................ Gas........................... ..................... .................... ..................... ..................... ..................... ..................... .......................................... ................................ //

5.+ <.3.1 <.3.1 <.3.$ <.3.$ <.3.3 <.3.3 <.3.'

Prod Prod)*e )*ed d Gas........ Gas............ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ......... ............ .............. .......... ... /# erma ermanent nentBB on#it on#ition ionss of =n#er" =n#er"ala alance. nce.... ..... ..... ...... ...... ...... ..... ..... ..... ..... ...... ...... ...... ..... ..... ...... ...... ...... ...... ...... ...... ....... ....... ...... ..... .. ;9 Tempora emporar! r! on#it on#ition ionss of =n#er" =n#er"ala alance. nce.... ...... ...... ..... ..... ...... ...... ...... ..... ..... ..... ..... ...... ...... ...... ..... ..... ...... ...... ...... ....... ....... ...... ....... ....... ... -0 ro#uc ro#uce# e# Gas from from :mpermea :mpermea"le "le +orma +ormatio tions.. ns.... ..... ...... ...... ...... ...... ...... ...... ...... ..... ..... ...... ...... ...... ...... ...... ....... ....... ...... ...... ....... .... -0 Similar Similar 2echanisms.. 2echanisms...... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ .......... ........ -$

5.-

3e*y*$e 3e*y*$ed d Gas..... Gas......... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ .......... ............ ........ + ..

5.5 <.<.1 <.<.1 <.<.$

%ontam %ontamina inatio tion n Gas........ Gas............ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ......... ........... ........ 6 .. The A##ition A##ition of etro etroleu leum m ro#u ro#ucts cts... ...... ...... ..... ..... ..... ..... ...... ...... ...... ..... ..... ...... ...... ...... ...... ...... ...... ...... ..... ..... ...... ...... ...... ....... ....... ...... ..... .. -9 Oil %ase# %ase# 2u# S!stem S!stems... s....... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ...... 0

SECTION 6

QUANTITY AND COMPOSITION OF RECORDED GAS

5

/." ;.1.1 ;.1.$

1ormat 1ormation ion %onsid %onsidera eratio tions. ns..... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........... .............. ............. .......... .... 65 orosit! orosit! an# Gas Saturation... Saturation....... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ .......... ............ ........ .. < Effec Effecti8e ti8e orosit! orosit! an# ermea"il ermea"ilit!. it!..... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ .......... ............. .............. ....... ;

/.2

Ho$e Depth.. Depth...... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ......... ......... .... #0

/.+ ;.3.1 ;.3.1 ;.3.$ ;.3.$ ;.3.3 ;.3.' ;.3.<

Dri$$ing Dri$$ing %onsi %onsider deratio ations. ns..... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........... ............. ...... #" Cate Cate Of enetra enetration tion an# ole ole Diamet Diameter.. er.... ..... ..... ..... ...... ...... ...... ..... ..... ...... ...... ...... ...... ...... ...... ...... ..... ...... ....... ...... ....... ....... ...... ...... ..... .. 91 %it T!pe T!pe an# Cesul Cesultin ting g Drille Drille# # utting uttings... s...... ...... ...... ...... ...... ...... ..... ..... ...... ...... ...... ...... ...... ...... ...... ..... ..... ...... ...... ...... ...... ...... ...... ...... ..... 9; oring..... oring......... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ .......... ............ ........ .. 9+lorate +lorate.... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ .......... ............. .......... ... 9 Differential Differential ressure............... ressure......................... ..................... ..................... ..................... ..................... .................... ..................... .......................... ............... 101

/.;.'.1 ;.'.$ ;.'.3

1$)id 1$)id nvasi nvasion on and 1$)shi 1$)shing. ng..... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ......... ........... ............. ............. ......... ... "0+ :n8asion :n8asion an# +iltration.. +iltration...... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ......... ............ ............ ..... 103 +lushing.... +lushing........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........... ............. ........ 10; +lui# +lui# :nflu@es. :nflu@es..... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ......... ............ ......... 111 111

/.5 ;.<.1 ;.<.$ ;.<.3 ;.<.'

4)d Type and and 3heo$o 3heo$ogy. gy..... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ......... ...... ""5 . 2u# T!pe.... !pe........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ......... ........... ............. ......... .11< 2u# Densit!. Densit!..... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ .......... ............ ............. ............. ...... .11; 2u# Temperature.. emperature...... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........... ............. ............. ............ ..... 11>iscosit iscosit! ! an# Gel Strength..... Strength......... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ .......... ............. ......... .. .11

/./ ;.;.1 ;.;.1 ;.;.$ ;.;.3

()rfa* ()r fa*ee %onsid %onsidera eratio tions.. ns...... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ......... ....... ""# .. Desig Design, n, Effi Effici cienc enc! ! an# Locat Location ion of the Gas Gas Trap. Trap.... ...... ...... ...... ...... ...... ...... ...... ..... ..... ...... ...... ...... ...... ....... ....... ...... ....... ...... .119 The Gas Sample Sample Line..... Line......... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ .......... ............ .......... .... 1$$ Losses Losses of Gas to the Atmospher Atmosphere.... e........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ .... 1$3

SECTION 7

EVALUATION EVALUATION OF LIBERATED AND PRODUCED GAS

129

."

7asi* 7asi* Definit Definition ions.. s...... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ......... ........... ............. .......... ... "2#

.2 -.$.1 -.$.1

7a*!gro 7a*!gro)nd )nd Gas..... Gas......... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ......... ........... ............. ............. ........ "2# .. Statio Stationar nar! ! an# ircul irculatin ating g %acg %acgrou roun#s. n#s.... ...... ...... ..... ..... ...... ...... ...... ..... ..... ...... ...... ...... ...... ...... ...... ...... ..... ..... ...... ...... ...... ...... ...... ..... 130





$




-.$.$


+ormation +ormation %acgroun %acgroun#..... #......... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ .......... ...... 13<

.+

nterp nterpre retat tation ion of of 7a*!gr 7a*!gro)n o)nd d Gas... Gas....... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ....... ... "+

.-

(ho (ho 'va$)a 'va$)atio tion.. n...... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ...... "-0 ..

.5

Gas &orm &orma$i8 a$i8ati ation. on..... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ......... ........... ...... "-

./ -.;.1 -.;.1 -.;.$ -.;.$

'va$)a 'va$)atio tion n of of Pro Prod)* d)*ed ed Gas..... Gas......... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ......... ........... ............. ............. ......... ... "5/ Seale Seale#B, #B, O8erpre O8erpressu ssure# re#,, erme ermea"l a"lee +orma +ormatio tions.. ns..... ..... ..... ...... ...... ...... ..... ..... ..... ..... ...... ...... ...... ..... ..... ...... ...... ...... ...... ...... ..... 1<=n#erc =n#ercomp ompact acte# e# shales shales ith ith a trans transiti itional onal pressu pressure re increa increase.. se..... ...... ...... ...... ....... ....... ...... ...... ....... ....... ...... ..... 1<9

. -.-.1 -.-.$ -.-.$ -.-.3 -.-.3 -.-.' -.-.' -.-.<

%onne* %onne*tio tion n Gas...... Gas.......... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ .......... ............. ......... "/" .. auses auses of onnection onnection Gas..... Gas......... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ .......... ......... ... 1;1 one one of increa increasing sing format formation ion pressu pressure re #ue to un#erco un#ercompa mpacti ction... on...... ...... ...... ....... ....... ...... ....... ....... ...... ..... .. 1;; =n#er" =n#er"alan alance# ce# permea permea"le "le 5ones. 5ones.... ...... ...... ...... ...... ...... ...... ...... ...... ...... ..... ..... ...... ...... ...... ...... ...... ...... ...... ..... ..... ...... ...... ...... ....... ....... ...... ...... ... 1;Shape, Shape, #ura #uration tion an# an# timing timing of of conne connecti ction on gas gas pea.. pea..... ...... ...... ...... ...... ...... ..... ..... ...... ...... ...... ...... ...... ...... ...... ...... ...... ..... .. 1; Ceporting Ceporting of onnection onnection Gases... Gases....... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ .......... ........ 1-1

.6 -..1 -..$

Trip Gas..... Gas......... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ .......... ............. .......... ... "5 The occurrence occurrence of Trip Trip Gas..... Gas......... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ......... ........... .......... .... 1-< :nterpretation :nterpretation of Trip Trip Gas...... Gas.......... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ......... ..... 10

.#

9e$$y 9e$$y Gas..... Gas......... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ......... ........... ............. ........... .... "6/

SECTION 

CHROMATOGRAPHIC CHROMATOGRAPHIC ANALYSIS ANALYSIS

193

6."

Gas 3atio 3atio Ana$ysi Ana$ysis... s....... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ .......... ............. ....... "#+

6.2 .$.1 .$.$ .$.3 .$.' .$.' .$.< .$.<

Gas 3atio 3atio P$ot P$ot )sing )sing *hr *hroma omato togra graphi* phi* va$)e va$)ess of methan methanee thr thro)g o)gh h pen pentan tane... e....... ........ ........... ......."#"#=se of the Catio Catio lot... lot....... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ .......... ........ .. 19< E8aluation E8aluation of Oil %earing %earing ones... ones....... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ......... ..... 199 E8aluation E8aluation of Gas %earing %earing ones... ones....... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ .... $00 re#ic re#ictio tion n of on#ens on#ensate ate %earing %earing ones ones... ...... ...... ...... ...... ...... ...... ...... ..... ..... ...... ...... ...... ...... ...... ...... ...... ..... ..... ...... ...... ...... ...... ...... ..... $01 ompar ompariso ison n ith ith Drille Drille# # utting uttings... s...... ...... ...... ...... ...... ...... ..... ..... ...... ...... ...... ...... ...... ...... ...... ..... ..... ...... ...... ...... ...... ...... ...... ...... ...... ....... ...... $03

6.+ .3.1 .3.$ .3.3 .3.'

Wetn etness ess:: 7a$an* 7a$an*ee and and %har %hara*t a*ter er 3atio 3atio Ana$ys Ana$ysis... is....... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ....205 etness etness Catio Catio &h(...... &h(.......... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ .......... .......... .... $0< %alance %alance Catio... Catio....... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ......... ....... .. $0=sing =sing %h ith ith h....... h........... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ......... ........... ...... $0 haracter haracter Catio... Catio....... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ......... ........... ...... .$11

6.-

Oi$ ndi*at ndi*ator. or..... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ......... ......... .... 2"-

6.5

Limitat Limitation ionss to to Gas Gas 3ati 3atio o 'ffe* 'ffe*tive tivenes ness... s....... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ......... ........ ... 2"/

SECTION 9 #." 9.1.1 9.1.$ 9.1.$ 9.1.3 9.1.'



FLUORESCENCE ANALYSIS ANALYSIS

225

%onve %onventi ntiona ona$$ f$)or f$)ores* es*en* en*ee as as a e$$site e$$site eva$) eva$)ati ation on pro*e pro*ess.. ss...... ........ ........ ........ ......... ........... ............. .............. ......... ..22/ 22/ Sample Sample reparation.. reparation...... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........... ............. ............. ......... .. $$; +luore +luoresce scence nce olou olourr an# %right %rightnes ness.. s..... ...... ...... ...... ..... ..... ...... ...... ...... ...... ...... ...... ...... ..... ..... ...... ...... ...... ...... ...... ...... ...... ..... ..... ...... ...... ..... $$ +luoresce +luorescence nce Distri"uti Distri"ution.... on........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ......... ....... .. $$9 Sol8ent Sol8ent ut...... ut.......... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........... ............. ............ ...... $30



3




9.1.< 9.1.;


Cesi#ue Cesi#ue.... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ .... $31 Sampling Sampling the mu#...... mu#.......... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ......... ............ ............. ............ ...... $31 ;)antit ntitat ativ ivee 1$) 1$)ores*en*e Te Te*hni hni<)eT4..................... ............................... ..................... ..................... ................................... ......................... 2+2

#.2 #.2

SECTION 1!

CASE STUDIES AND APPLICATIONS APPLICATIONS

239

"0." Geoste Geosteerin ering g Hori8ont Hori8onta$ a$ We$$s We$$s ,sin ,sing g Gas 3atio 3atio (ign (ignat) at)re res.... s........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ...... ..2-" 2-" ase 1 Geostee Geosteering ring using gas ratios..... ratios......... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ......... ........... ............. ............. ......... ... $'3 ase $ Geostee Geosteering ring using gas ratios..... ratios......... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ......... ........... ............. ............. ......... ... $'' ase 3 Geostee Geosteering ring using gas ratios..... ratios......... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ......... ........... ............. ............. ......... ... $'< ase ' Geostee Geosteering ring using gas ratios..... ratios......... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ......... ........... ............. ............. ......... ... $'; "0.2

%ase %ase 5 'stab$i 'stab$ishin shing g Prod) Prod)*ti *tion on Potent Potentia$ ia$ from from 4)d 4)d Logging Logging Data.... Data......... ............ ............. ............. .......2-6 2-6

"0.+

%ase %ase /

Determ Determinat ination ion of Gas=Oi$=W Gas=Oi$=Wate aterr %onta %onta*ts. *ts..... ........ ........ ........ ........ ........ ........ ........ ........ ........ .......... ............. .......... ...2525-

"0.-

%ase %ase 

3eserv 3eservoir oir and 1$)id 1$)id dentif dentifi*at i*ation ion from from Gas 3atio 3atio Ana$ysi Ana$ysis.... s........ ........ ........ ........ ........ ........ ....25 25

"0.5 ,sing ,sing Gas 3atio 3atioss to dent dentify ify 4is*ib 4is*ib$e $e 1$oods. 1$oods..... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ .......... ........... ..... 2/0 ase  :#entificat :#entification ion of a misci misci"le "le floo#.. floo#...... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ .......... ............. .............. .......... ... $;1 ase 9 :#entificat :#entification ion of a misci misci"le "le floo#.. floo#...... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ .......... ............. .............. .......... ... $;$ "0./ Predi*t Predi*tion ion of Gas >one >one Prod Prod)*t )*tivi ivity ty ith ith s)bse s)bse<)e <)ent nt D(T D(T res)$ res)$ts. ts..... ........ ........ ........ ........ .......... ............ ......2/2/ase 10 ro#ucti8e Gas one................ one........................... ..................... ..................... ..................... ..................... ..................... ............................... ..................... $;' ase 11 4on)pro#ucti8e gas 5one..................... 5one............................... ..................... ..................... ..................... ..................... .................... ..................... ........... $;"0.

1ra*t)re dentifi*ation........... .............. .............. .............. .............. ............... ........... ...... ........... ........... ...... 2/# .

"0.6

%ase %ase "2 Predi* Predi*tio tion n of a Tight: Tight: ,npro ,nprod)* d)*tiv tivee Gas >one... >one....... ........ ........ ........ ........ .......... ............. ............. ............. .......2+ 2+

"0.#

%ase %ase "+ 'viden* 'viden*ee and and 'ffe* 'ffe*tt of 1$)sh 1$)shing ing on gas respo response nsess and and ratio ratios.... s........ ........ ........ ........ ......... ....... ..25 25

"0."0

%ase "- The 'ffe*t of Heavier Oi$s on Gas 3atio Ana$ysis..... ............... .............. ............ ......... ...26 26

"0.""

%ase "5 The 'ffe*t of 4)d Vis*osity on Gas 4eas)rements.................. .............. ........... ...... .....26" 26"

"0."2

%ase "/ Determination of %hanging Oi$ Gravity thro)gh a 3eservoir........ ................ .......... ........2626-

"0."+

%ase " Predi*tion of the Approa*h to Dep$eted 3eservoir........... .............. .............. .....26/ 26/

APPENDI" REFERENCES





27

'



DATALOG 1999


H?D3O%A37O& 'VAL,ATO& A&D &T'3P3'TATO&

(e*tion "

&T3OD,%TO&

The "asis of mu# logging is the #etection, measurement an# e8aluation of h!#rocar"on flui#s an# other gases, that are containe# ithin the #rilling flui# & mud ( an# #rille# cuttings returning from the ell"ore an# relating this to a specific #epth an# litholog! that has "een penetrate# through #rilling.

This "asic principle ena"les an e@perience# mu# logger to rapi#l! #etermine a range of in8alua"le information as the ell is "eing #rille#/ )

    

Cecognition of h!#rocar"on "earing 5ones. Determination of reser8oir flui# t!pe, gra8it! an# contacts. E8aluation of reser8oir pro#uction potential. re#iction an# e8aluation of formation pressure. An essential component to ell safet! in the #etection of ics an# the a8oi#ance of "loouts.

The anal!sis of h!#rocar"on flui#s an# resulting #ata, together ith other mu# logging techniFues such as #rilling #ata e8aluation an# cuttings anal!sis, greatl! assists ell e8aluation in man! #ifferent applications/ )

     



:#entification of h!#rocar"on "earing 5ones that shoul# "e further teste#. :#entification of 5ones that ma! otherise go un#etecte# "! ireline or other measurements. ell planning in terms of mu# eight, ic tolerance an# casing points. Alternati8e to LD in the geosteering of ells. :#entification of misci"le floo#s. :#entification of thin "e#s an# fracture porosit!.

DATALOG 1999


<



DATALOG 1999


oe8er, in or#er for formation an# h!#rocar"on "earing 5one e8aluation to "e of an! "enefit, se8eral consi#erations ha8e to "e ma#e/ )



%! hat mechanisms can gas enter the #rilling flui#?



o much of the in situB h!#rocar"on flui#, release# from the formation, is #etecta"le at surface?



o representati8e is the h!#rocar"on composition at surface to the composition, at #epth, in the potential reser8oir?



o #o #ifferent con#itions an# factors influence the amount of gas #etecte# an# the resulting measurement?



Does the gas interpretation correlate ith other in#icators?

ith all these possi"le factors an# 8ariations taen into consi#eration, the anal!sis of h!#rocar"ons #etecte# at surface is recogni5e# as "eing an important metho# in pro8i#ing rapi# an# in8alua"le information in terms of real)time ell e8aluation.

+or meaningful interpretations of gas #etecte# at surface to "e ma#e, the mu# logger or ellsite geologist must first "e a"le to #etermine the source of the gas an#, secon#l!, assess the influences that coul# affect the magnitu#e or composition of gas seen.

This information must "e presente# in such a a! that it can "e rea#il! un#erstoo# an# e8aluate#, not onl! hile the ell is "eing #rille# "ut also at an! time in the future hen ells are "eing re)e8aluate# or correlate#.

:n the preparation of a h!#rocar"on log, or mu# log, the mu# logger must first "e aare of the #ifferent mechanisms "! hich gas can originate from the formation an# enter the #rilling flui#. These #ifferent origins shoul# "e clearl! i#entifia"le from the log, thus pro8i#ing concise information as to formation porosit!, permea"ilit! an# pressure. Gas originating from the formation must also "e separate# from gas that originates from other sources.

Data, or information, shoul# "e pro8i#e# that clearl! informs the user a"out con#itions, or changes in con#itions, that influence the amount of gas #etecte# in or#er for consi#ere# e8aluations to "e #ran from the log.



DATALOG 1999


;



DATALOG 1999


The aim of this course an# manual is to/ )





:#entif! the 8arious mechanisms an# h!#rocar"ons can enter the #rilling flui#.



:#entif! an# #iscuss all of the 8arious con#itions that pla! a part in #etermining the final gas recor#ing in the logging unit.



:llustrate the operation an# measurement of total gas #etector t!pes an# the comparison to chromatographic measurement.



:n8estigate recent a#8ances in technolog! an# e8aluation techniFues.



:llustrate ho real)time an# #epth)"ase# gas tren#s an# information can "e interprete# an# e8aluate#.



Sho ho gas ratio #ata is calculate# an# illustrate ho this #ata can, hen use# correctl!, gain an accurate profile of potential reser8oirs.



:llustrate, ith the help of case stu#ies an# e@amples, ho h!#rocar"on interpretation an# e8aluation can "e use# in man! #ifferent applications.

DATALOG 1999

influences


"!

hich

-



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

DATALOG 1999






DATALOG 1999



(e*tion 2

2."

H?D3O%A37O& %O4PO(TO& A&D %LA((1%ATO&

Petro$e)m %omposition and %$assifi*ation

Petroleum is the term that is applie# to an! h!#rocar"on, hether gas, liFui#, or soli#, that occurs naturall! in the earthBs crust. As ell as h!#rocar"ons, petroleum ma! also contain 8aria"le "ut minor amounts of impurities, such as car"on #io@i#e, sulphur an# nitrogen.

:n liFui# form, petroleum is t!picall! referre# to as crude oil , hich ma! "e compose# of a comple@ mi@ture of h!#rocar"ons 8ar!ing in molecular si5e an# eight. hen reco8ere# to surface, the h!#rocar"on compoun#s can "e separate# through refining an# #istillation to !iel# a 8ariet! of petroleum pro#ucts.

%! #efinition, h!#rocar"on compoun#s are those that consist of h!#rogen an# car"on atoms. These compoun#s, the simplest of hich are the h!#rocar"on gases, can "e classifie# into $ t!pes, #epen#ing on the molecular "on#ing of the car"on atoms.

4%



1. Saturate# !#rocar"ons

compoun#s that possess one single co8alent "on# "eteen the car"on atoms

$. =nsaturate# !#rocar"ons

compoun#s possessing #ou"le "on#s "eteen the car"on atoms

A co8alent "on# results from the simultaneous attraction of to nuclei for a share# pair of "on#ing electrons. A #ou"le co8alent "on# occurs hen to pairs of electrons are share# "! to atoms.

DATALOG 1999


9



DATALOG 1999

2.2


(at)rated Hydro*arbons or A$!anes

These compoun#s consist of short chains of car"on atoms saturate# ith h!#rocar"on atoms that occup! all a8aila"le car"on "on# positions.

The car"on atom chains ma! "e straight, "ranche# or c!clic, gi8ing rise to 3 series of alanes. The straight an# "ranche# series are non as Paraffins an# the c!clic series as Naphthenes.

2.2.1

Paraffin

araffin is the most common form of h!#rocar"on, hether foun# in liFui# cru#e oil or in a gaseous state. The group inclu#es to of the alane series, the straight an# "ranche#)chaine# car"on atoms.

The straight chaine#, or normal , alanes are gi8en "! the folloing general formula an# are illustrate# in +igure $.1

n $n  $ here n ranges from 1 to 10, the paraffin mem"ers are methane &1(, ethane &$(, propane &3(, "utane &'(, pentane &<(, he@ane &;(, heptane &-(, octane &(, nonane &9( an# #ecane &10(.

hromatographic gas anal!sis at ellsite usuall! e@ten#s from methane through pentane, since hea8ier mem"ers of the series ill, t!picall!, remain in a liFui# state at surface pressure an# therefore "e un#etecta"le as a gas. 2inor amounts of he@ane can sometimes "e #etecte# "ut reFuires a longer anal!sis time. This o"8iousl! restricts the #epth resolution of acFuire# #ata hich is necessaril! reFuire# for effecti8e reser8oir e8aluation.

ertainl!, at normal surface temperature an# pressure, methane through "utane ill e@ist as gases an# are easil! #etecte#. At am"ient pressure, pentane con#enses into a liFui# state at a "oiling point of 3;  &Ta"le '.$(, so #epen#ing on the temperature of the circulating mu#, is normall! e@tracte# as a gas. Am"ient temperature ill control hether part, or all of the pentane re)con#enses "ac to liFui# form an# goes un#etecte#. (tr)*t)re



DATALOG 1999

&ame

Abbreviation


1orm)$a

10



DATALOG 1999


2ethane

1

'

Ethane

$

$;

ropane

+igure $.1

3

3

4ormal %utane

n'

'10

4ormal entane

n<

<1$

The normal alanes of the paraffin group

The "ranche#, or iso, chain series of alanes ithin the paraffin group are gi8en "! the same general formula as the straight chaine# series an# are illustrate# in +igure $.$

n $n  $

The "ranche# alanes contain four or more car"on atoms, therefore commenceB from iso) "utane through to the hea8ier h!#rocar"ons. hromatographic #etection at ellsite is t!picall! restricte# to the iso)"utane an# iso)pentane mem"ers.

(tr)*t)re

&ame

:so %utane



DATALOG 1999

Abbreviation

i'

1orm)$a

 '10

11


:so entane

i<

 <1$



DATALOG 1999


+igure $.$

The "ranche# or iso) alanes of the paraffin group

A further isomer of entane is calle# 4eo entane. 2olecularl!, ' car"on atoms each occup! one of the a8aila"le "on#s on the < th car"on atom in the group. As ith the other alanes, each a8aila"le "on# on the outer ' car"on atoms is occupie# "! h!#rogen. This isomer is illustrate# "elo in +igure $.3

4eo entane

+igure $.3

2.2.2

4<

<1$

4eo entane isomer

Naphthenes

4aphthene is the name gi8en to the thir# group of the alane series &+igure $.'(. ar"on atoms in this group are close# chaine# an# again saturate# ith h!#rogen atoms occup!ing e8er! a8aila"le "on# position. The names alrea#! gi8en to the paraffin series are prefi@e# ith c!cloB to #istinguish the naphthene series i.e. c!clopropane, c!clo"utane, an# ha8e the general formula/ )

n $n

(tr)*t)re



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&ame

1orm)$a


1$



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+igure $.'

!clopropane

 3;

!clo"utane

 '

!clopentane

 <10

The naphthene group of alanes

Since there are $ less h!#rogen atoms than ith the normal or "ranche# alanes, molecularl!, the naphthenes are slightl! lighter than the paraffins.

T!picall! associate# ith higher #ensit! cru#e oils, onl! c!clopropane an# c!clo"utane normall! remain in the gaseous state at surface pressure an# temperature. =nfortunatel!, since the molecular eight is so similar, the! are anal!5e# "! chromatographs as if the! ere propane or "utane from the paraffin series. Slo separation at lo pressures is reFuire# to #istinguish "eteen naphthene an# paraffin. This time constraint is o"8iousl! impractical at ellsite.

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13

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2.+

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,nsat)rated Hydro*arbons or Aromati*s

Similar to c!clo)alanes or naphthenes, the aromatic series comprises close# chaine# car"on atoms. =nlie the alanes hoe8er, the aromatics are not h!#rogen saturate#, i.e. h!#rogen atoms #o not occup! e8er! a8aila"le "on#. The series is usuall! onl! a minor component to cru#e oils, "ut the most common aromatic, "en5ene &+igure $.<(, is ne8ertheless present in most petroleum compoun#s.

The series has the general formula

(tr)*t)re

+igure $.<

n $n ) ;, ith %en5ene "eing ;;

&ame

1orm)$a

%en5ene

;;

Toluene

 ;<3

The aromatic group

%en5ene is the simplest aromatic compoun#, a close# chain, or ring, of si@ car"on atoms. Alternating single an# #ou"le co8alent "on#s lins the car"on atoms. This "en5ene ringB forms the "asis of further compoun#s in the aromatic series. Since the car"on atoms are unsaturate#, "on#s unoccupie# "! h!#rogen atoms are free to "e taen up "! further car"on atoms. Thus, outsi#e of the close# ring, as shon in +igure $.<, further aromatics such as toluene &one "en5ene ring  one  3( comprise one or more "en5ene ring together ith one or more  3 elementsB occup!ing the free "on#s. 4ote that 3 also forms the final lin in the straight)chaine# alanes. %en5ene is e@tremel! solu"le, in fact this group is often referre# to as the solu"le h!#rocar"on group. :t has "een i#entifie# that this can pro8i#e a 8er! useful e8aluation parameter, in that it

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1'

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is more su"Hect to flui# mo8ements an# can therefore "e an in#ication as to the pro@imit! to a h!#rocar"on source. =nfortunatel!, the same characteristic, "en5eneBs high solu"ilit!, also maes it e@tremel! #ifficult to e@tract from the #rilling flui#, so that it has ne8er "ecome a component to normal ellsite anal!sis.

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1<

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2.-

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AP Gravity %$assifi*ation

A classification of cru#e oil, "ase# on the #ensit! or specific gra8it! &gmcc( of the oil, is #efine# "! the American etroleum :nstitute &A:( an# i#el! use#.

igh A: gra8it! oils ha8e a high content of the gasoline h!#rocar"ons & ' to 10(.

The A: gra8it! is #efine#, at 1;  an# atmospheric pressure, "! the folloing formula/ )

A: I

1'1.< ) 131.< SG

The larger the A: rating then the lighter the oil. The A: rating can "e 8isuall! appro@imate# "! the colour of the oil or "! the colour of the fluorescence un#er ultra)8iolet light/ )

Gravity

Type

%o$o)r

1$)ores*en*e

Lo A:

hea8! oil

#ar "ron to "lac

re# "ron to orange

2e#ium A:

me#ium oil

me#ium to green "ron

!ello, gol#, green

igh A:

light oil

colourless, light

"lue &pale "lue is often interprete# as hite un#er => light.

on#ensate

8iolet or ultra)8iolet &non)8isi"le(

4ote, that at that the lo A: en#, the intensit! of the fluorescence ma! "e so lo that it ma! not "e 8isi"le. At the high A: en#, particularl! hen #ealing ith con#ensate flui#s, the fluorescence ma! "e in the ultra)8iolet range of the spectrum, again not 8isi"le ith the nae# e!e. These limitations ill "e #iscusse# in more #etail in Section 9.

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1;

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(e*tion +

+."

(A4PL&G: D'T'%TO& A&D 4'A(,3'4'&T

'tra*ting Gas from the Dri$$ing 1$)id

The main reFuirement in pro8i#ing effecti8e ellsite gas anal!sis is that of a continuous, uninterrupte# e@traction an# measurement of the gas entraine# ithin the #rilling flui#. +rom the point of 8ie of ell safet!, this ena"les changes to "e rapi#l! i#entifie# an# the appropriate action taen. +rom an e8aluation point of 8ie, it again ena"les changes in formation or gas 8olume an#or composition to "e accuratel! i#entifie# an# relate# to the e@act #epth of its li"eration. This is important in applications such as the i#entification of reser8oir gasoilater contacts, the #etermination of specific 5ones to "e teste# or fracture#, an# the geosteering of hori5ontal ells on the "asis of gas ratio anal!sis pro8i#ing a cheaper option to #onhole LD tools. hate8er form of gas e@traction is use#, the important consi#erations are/ )



o efficient is the gas e@traction?



o Fuantitati8e is the gas measurement?



:f the sample is #ilute# in air, ho #oes the gas)in)airB measurement relate to the total 8olume of gas hel# in the mu#?



Does a surface gas measurement "ear an! relation to the 8olume of gas in the formation?

3.1.1

Agitator Type as Traps

The trap, or #egasser, is positione# in the returning mu# stream, t!picall! in the shaer "o@ &hea#er "o@ or possum "ell!(, in or#er to ha8e a continual flo of nel!B returning mu# from hich to e@tract a consistent as possi"le gas sample.

Agitator t!pe traps ha8e "een historicall!, an# are still, use# i#el! in the in#ustr!, principall! "ecause the! are relati8el! cheap, mechanicall! an# operationall! simple, although reFuiring a certain amount of maintenance.

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The trap operates "! #raing in mu#, t!picall! from an orifice at the "ase of the trap c!lin#er. The mu# is then su"Hecte# to e@treme agitation from a rotating "la#e, or agitator, to "rea out an# e@tract the #issol8e# gas together ith the free gas "u""les entraine# in the mu#. Once free from the mu#, the gas is lifte# to the top of the trap "! a constant flo of air circulate# through the trap from the logging unit. The gasair mi@ture is then carrie# on to the #etectors in the mu# logging unit. This t!pe of suction is necessar! since methane is the onl! h!#rocar"on gas that is lighter than air. ea8ier h!#rocar"ons ill not rise on their on accor#, so reFuire lifting "! the air floing up through the trap. >ariations ha8e "een use#, here"! the mu# is first #ran off from the shaer "o@, then passe# to a 8essel here agitation is applie# to "rea gas out of solution. Although i#el! use#, this con8entional trap #oes ha8e certain limitations that lea#s to concern o8er the accurac! an# relia"ilit! of su"seFuent gas measurements an#, ultimatel!, that potential pro#ucti8e 5ones ma! "e "!passe#/ )



>aria"ilit! in gas measurement ith operating con#itions such as mu# flo rate, in# spee# an# #irection. hanges in florate lea# to a change in mu# le8el &in the shaer "o@( an# therefore the 8olume of mu# "eing sample#. hile this lea#s to the possi"ilit! of more gas "eing e@tracte# from a larger 8olume of mu#, the increase in mu# 8olume also e@erts more loa# against the agitator, #ecreasing its efficienc!. Although a significant factor, immediate or significant changes in mud level should never present an operational problem, since, whenever a change in flowrate occurs, the first priority of the mudlogger should be to reset the height of the gas trap. oe8er, the shaer "o@ is Fuite a tur"ulent en8ironment so that there are continual minor fluctuations in the mu# le8el, lea#ing to inconsistent operation of the trap an# therefore of the amount of gas e@tracte#. A##itional effects, as a result of florate changes, ill "e #iscusse# in section ;.3.' in#, on entering the air intae, ill increase the #ilution of the gasair sample lea#ing to a re#uction in the gas measurement. :n fact, research "! Te@aco an# the Gas Cesearch :nstitute &SLA, June 1993( has shon that a in# spee# as lo as  mph, #irectl! into the port, can lea# to a <0K #rop in the gas 8alue. Again, while this is quite an alarming statement, wind is not such an operational hazard !n most modern day rigs, certainly offshore vessels, the flowline and sha"ers are enclosed or protected Even where open, the mud level is usually sufficiently below the top of the sha"er bo# to provide protection to the air inta"e. oe8er, shoul# the trap "e e@pose# to in#, then 8ariations in spee# an# #irection can "e a maHor effect on gas #ilution that cannot "e o8erlooe# so that e8er! effort shoul# "e ma#e to pro8i#e some protection.



The effect of trap loa#ing, here gas is actuall! e@tracte# from the mu# at a greater rate than it is "eing e8acuate# from the trap. This lea#s to a "uil# up, or concentration, of gas ithin the trap that ill tae a longer time to "e completel! e8acuate#. This can result in erroneousl! high gas measurements e@ten#e# o8er a longer perio# of time, possi"l! masing

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changes in gas 8olume o8er the same perio#. This pro"lem has "ecome more pronounce# o8er recent !ears ith the impro8e# efficienc! of gas traps. Although e@traction of lo 8olumes of gas has impro8e#, the higher 8olumes lea#ing to trap loa#ing #oes create a pro"lem, especiall! for engineers ho are concerne# a"out mu# con#ition an# ell control. 

The potential of losing gas as a result of the agitation process. As the gas is "roen out of solution, a proportion of the free gas "u""les ma! "e carrie# straight out of the trap "! the e@pelle# mu#. The significance of this ill 8ar! ith the rotational spee# of the agitator, trap immersion #epth an# mu# properties, all of hich #etermine the pattern of the mu# flo through the trap.



The efficienc! of gas e@traction is #etermine#, to a large #egree, "! the rotational spee# of the agitator. This, naturall!, lea#s to concern from operators hen #ifferent spee#s ¬ to mention o8erall trap #esign an# t!pes of #etectors "eing use#( lea# to 8aria"le gas measurements from #ifferent ser8ice companies, maing ell correlation #ifficult.



The other pro"lem ith rotational spee# is that, e8en for a gi8en rpm, the e@traction efficienc! is relati8e to in#i8i#ual h!#rocar"on components. ea8ier h!#rocar"ons are more solu"le an# therefore more #ifficult to "rea out of solution. ith lighter h!#rocar"ons, not onl! is a significantl! smaller 8olume hel# in solution, "ut the! are also easier to "rea out. Therefore, for an! gi8en composition, the e@traction of light h!#rocar"ons is liel! to "e more complete than that of the hea8ier components.



2u# t!pe an# rheolog! also pla!s an important role in the efficienc! of the trap. The hea8ier or more 8iscous the mu#, the sloer the rotation of the agitator an# the less efficient the gas e@traction. This, again, amplifies the effects #ue to the relati8e solu"ilit! of #ifferent gas components. Oil "ase# s!stems ill hol# a much greater Fuantit! of gas, especiall! the hea8ier components, in solution.

Se8eral of these limitations are eliminate# or re#uce# "! the gas trap use# in the Te@acoGas Cesearch :nstitute patente# 7G2 T2 &7uantitati8e Gas 2easurement( s!stem. The sensiti8it! to changes in florate an# mu# le8el are minimi5e# "! the interior #esign of the trap an# rotational spee#. The trap e@haust "eing "eneath the mu# surface eliminates 8ariations in air #ilution an# gas loss.

electric motor airgas sample to anal!sis agitator e@tracting entraine# gas

am"ient air Direction of mu# flo, entering mu# e@it port shaer "o@ from the floline Hydrocarbon Evaluation and Interpretation  DATALOG 1999

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+igure 3.1 T!pical gas trap assem"l!

DatalogBs agitator trap &+igures 3.1 an# 3.$( comprises a c!lin#rical trap ith mu# intae from the "ottom an# a com"ine# port for mu# e@haust an# air intae, hal8e a! up. The gas sample is #ran to the mu# logging unit, from the top of the trap, "! air "eing pumpe# at a constant rate of ' scfh &stan#ar# cu"ic feet per hour(. The agitator has a tripo#B configuration, hich, in comparison to a single or crosse# "la#e, is more efficient at lo immersion le8els an# less suscepti"le to fluctuations in the mu# le8el. :t is poere# "! an electric or air motor that, #eli8ering 1-$< rpm, pro8i#es 8er! efficient agitation an# gas e@traction.

The location an# positioning of the trap is o"8iousl! 8er! important an# the folloing points shoul# ala!s "e o"ser8e# &+igure 3.$(/ )



The trap shoul# "e site# #irectl! here the mu# enters the shaer "o@, not off to the si#e here the mu# ma! ha8e "een stan#ingB for a perio#, all the time losing gas to the atmosphere, an# not representati8e of the lagged depth.



There must "e a sufficient #epth of mu# in or#er that the trap can "e set at the correct #epth for ma@imum efficienc!. The trap shoul# not "e o"structe# "! cuttings "uil# up in the shaer "o@.







The e@it port shoul# "e positione# #onstream so that mu# &agitate# an# li"erate# of an! gas( is not rec!cle# "ac into the trap.



:f the shaers are not enclose#, e8er! effort shoul# "e ma#e to ensure that the air intae is not e@pose# to changes in am"ient in#.

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+igure 3.$


T!pical trap assem"l!

Gi8en that a resulting gas measurement represents the gas)in)air 8olume, the Fuestion remains as to ho this compares to the gas)in)mu# 8olume. Depen#ing on the efficiencies an# limitations #iscusse# a"o8e, it is clear that a proportion of the entraine# gas ill remain in the mu# an# "e rec!cle#. Of the gas that is e@tracte# from the mu#, su"seFuent processes can, also, occasionall! lea# to erroneous &a"solute( measurements. 

The length of the gas sample line, "eteen trap an# #etector, lea#s to a #ela! in gas responses, sometimes as long as se8eral minutes.



T!pical pol!flo tu"ing is no non to a"sor" the hea8ier h!#rocar"ons until a saturation point is reache#. hen gas le8els in the sample re#uce, the a"sor"e# h!#rocar"ons can then "e #esor"e# an# release# "ac into the sample line.



!#rocar"ons ma! arri8e at surface, in the hot mu#, as a gas. Once e@tracte# an# su"Hecte# to the col#er am"ient temperature in the gas sample line, the hea8ier components ma! con#ense into liFui# form an# therefore not "e #etecte#.

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The 8olume of air in the trap, sample line an# #r!ing 8essels lea#s to a large #ilution of the e@tracte# gas. Such #ilution can cause e@ten#e# an# #ampene# gas responses ith poorer sho #efinition. Accurac! can therefore "e lost in the i#entification of thin "e#s an# fractures for e@ample.



>ariations in gas response #ue to fluctuations in sample pump rate can "e cause# "! flui#s con#ensing in the gas line, free5ing of the gas line etc, so that the s!stem reFuires a high #egree of maintenance in or#er for consistent operation.


As a result of all the pro"lems associate# ith agitator t!pe traps, as #escri"e# a"o8e, it is clearl! recogni5e# "! mu# loggers an# ellsite geologists that the resulting gas measurement is e@tremel! Fualitati8e, so that e8aluation has to "e "ase# on relati8e changes in gas response. >arious metho#s ha8e "een use# to attempt to Fuantif! the gas)in)air measurement, to impro8e the Fualit! of gas #ata. ro"a"l! the most accepta"le is "! cali"rating, or appl!ing a correction factor, to the gas)in)air 8alue from an actual gas)in)mu# 8olume. This can "e o"taine# "! taing a mu# sample from the floline, then remo8ing all h!#rocar"ons ith a steam still, or as ith the Te@acoGC: 7G2 s!stem, a microa8e still, an# measuring the gas 8olume. The theor! is that ha8ing o"taine# a Fuantitati8e measurement of the gas 8olume in the mu#, it can "e #irectl! eFuate# to the 8olume of gas in place in the reser8oir, there"! o"taining a measurement of apparent gas porosity. This can "e achie8e# "! #etermining the ratio of cuttings to the mu# 8olume &the rate of penetration an# hole #iameter #etermines the 8olume of roc that gas is li"erate# from, an# the florate #etermines the 8olume of mu# that the gas is li"erate# into(, together ith e@pansioncompressi"ilit! factors of the #ifferent gas components.

hilst this is goo# theor! an# the #esire# en# goalB, there are pro"lems associate# ith the process of o"taining an accurate Fuantitati8e con8ersion/ ) :f the mu# sample is taen from an!here other than the "ell nipple hen the mu# first  returns to surface, the gas)in)mu# measurement ill not "e accurate since losses to atmosphere ill ha8e occurre# &especiall! the light en# components(. 

A goo# Fualit! sample is #ifficult to o"tain, ith a true gas)mu# ratio, if the mu# is gas cut an# "u""ling.



o often shoul# the mu# sample "e taen? A ne con8ersion factor ill "e reFuire#, as minimum, hene8er there is change in gas 8olume, gas composition, mu# rheolog! an#or temperature, florate etc. :n other or#s, hene8er there is a change in actual gas measurement or in an! parameters that affect the gas measurement, a ne correction factor shoul# "e applie#. :n realit! this means, for effecti8e Fuantification of gas measurements, corrections ha8e to "e applie# on a real)time "asis. This is o"8iousl! impractical at ellsite.

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$$

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E8en gi8en i#eal circumstances, ith the mu# sample taen from "ell an# a freFuent cali"ration factor #etermine#, the measurement ill still not account for changes in gas saturation of the mu# &i.e. not #irectl! eFuating to the gas li"erate# from a gi8en 8olume of roc( #ue to/ )



+lushing of formations that lea#s to the #isplacement of formation flui#s aa! from the formation su"seFuentl! to "e #rille#. The li"erate# gas 8olume recor#e# at surface ill therefore "e less than the true gas 8olume of the formation.



The influence of "orehole influ@es, so that pro#uce# flui# floing from the formation a##s to the li"erate# gas 8olume for a unit 8olume of roc.



ole ashouts in the "orehole can lea# to a #ecrease in the gas saturation of the mu#, since, as mu# circulation is #istur"e# through the ashe# out area, the gas is #isperse# in a larger 8olume of mu#.

Although these situations can "e rea#il! i#entifie# at ellsite, hen the! occur the! cannot "e accounte# for Fuantitati8el!. :n such situations, it remains 8er! #ifficult, in practice, to relate surface measurements to the gas 8olume in place in the formation, so that, relati8e changes in 8olume an# flui# t!pe is still a 8er! important component of ellsite e8aluation.

3.1.2

The as!i"ard T# $ %uantitative as in #ud #easure&ent

Cather than tr!ing to appl! corrections to the inconsistent an# Fualitati8e gas measurement pro8i#e# "! the agitator trap an# sample line s!stems, Datalog ha8e intro#uce# an e@traction s!stem that eliminates "oth of these maHor sources of error. The sensor ors on the principle of gas &hether free or in solution( passing through a gas permea"le mem"rane positione# in the returning mu# stream. noing the e@change capacit! of the mem"rane, an# "! measuring the 8olume of gas that has passe# through the mem"rane, the 8olume of gas in the mu# can "e mathematicall! #etermine#. The Gasi5ar# T2 &+igure 3.3( pro8i#es continual, quantitative gas measurement #irect from the returning mu# stream for the first time in the histor! of mu# logging an# ellsite gas anal!sis. The s!stem pro8i#es actual gas percentage "! 8olume so that the specific 8alues of recor#e# gas are no 8er! significant an# meaningful.

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$3

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signal

e@plosion proof unit housing #etector, pump an# anal!sis eFuipment

ca"le

Sensor ith gas permea"le mem"rane

+igure 3.3

fle@i"le hose carr!ing gas sample to #etector

The Gasi5ar# T2



The sensor is insensiti8e to changes in the mu# le8el, pro8i#ing continuall! accurate gas measurements, regar#less of florate 8ariations, an# alloing more effecti8e ell correlation.



The Gasi5ar# s!stem pro8i#es a Fuantitati8e measurement of the gas entraine# in the #rilling flui#. Accuratel! noing the gas percentage, "! 8olume, in the mu# lea#s to further applications in Fuantitati8e gas e8aluation such as the #etermination of apparent gas porosit! an# the #etermination of the #egree of gas cut mu#.



Since the #etector is locate# at the point of installation, there are minimal transit #ela!s "eteen gas e@traction an# gas measurement. This rapi# response time lea#s to much "etter #epth resolution an# more accurate #etermination of formation tops an# contact points for e@ample.



Greater sensiti8it! results from the sampling mechanism. Onl! 8er! small Fuantities of gas an# air are reFuire# "! the s!stem, so that there is no o8er)#ilution of the gas sample in large air 8olumes resulting in #ampene#B, poorl! #efine# responses. This #egree of sensiti8it! pro8i#es more effecti8e formation e8aluation in situations such as the i#entification of thin "e#s or fractures an# in the #etermination of minor changes in porosit! or permea"ilit!.

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%ecause there is no gas trap, there are no erroneousl! high gas measurements associate# ith trap loa#ing. Although geologists are 8er! aare of the Fualitati8e aspects of gas measurements, engineers are 8er! frustrate# ith gas reports of 0 or 90 percent, for e@ample. :f that as the true 8alue, there oul# "e no mu# column in the annulus an# the ell oul# ha8e "lon outM 4o, engineers ill "e pro8i#e# ith the e@act 8olume of gas in the mu#, a 8alua"le component to ell control.




The Gasi5ar# sensor is not effecte# "! changes in mu# #ensit! or 8iscosit!.



The sensor can "e positione# #irectl! in the floline to minimi5e the error of lighter gases "eing lost to the atmosphere. Similarl!, it can "e mounte# in the pump suction line so that the 8olume of gas "eing rec!cle# in the s!stem can "e accuratel! #etermine#.



The carrier air is #rie# at the point of intae, "efore it reaches the sensor. There are therefore no pro"lems ith h!#rocar"ons "eing a"sor"e# "! #r!ers an# filters an# not "eing recor#e#.



The gas sample is heate# #uring its transit to the gas #etector, so that the hea8ier gases ill not con#ense to liFui# form an# go un#etecte#.



The Gasi5ar# is not effecte# "! hether gas is free or #issol8e#, an# is therefore accurate in oil "ase# s!stems here gas is pre#ominantl! in solution. E8aluation onsi#erations

The Gasi5ar# s!stem #oes not #ifferentiate as to hether the gas in the mu# is present as free gas "u""les or as #issol8e# gas. :t is not su"Hect to the irregularities of agitator traps hen "reaing gas out of solution, cause# "! 8ar!ing h!#rocar"on composition, 8ar!ing "u""le si5e, mu# temperature an# 8iscosit!. This principle #oes contri"ute, hoe8er, to #ifferences in gas measurements &than oul# ha8e pre8iousl! "een e@perience# ith agitator traps( that nee# to "e un#erstoo#.

General Differences &+igure 3.'( 

One thing that e8er! ellsite operator is familiar ith, from agitator traps, is the gas rea#ing falling to 5ero hen connections are ma#e. This is simpl! #ue to the fact that the mu# le8el #rops in the shaer "o@ so that the trap is no longer in the mu#. This is not seen ith the Gasi5ar# &see 3.'A(. Although the gas le8el falls, it #oes not go to 5ero since there is still am"ient gas in the floline surroun#ing the sensor, hich ill pass through the mem"rane. :t is also possi"le that the mu# #oes not completel! 8acate the floline o8er the #uration of the connection, so that gas is still measure#.



Gas responses are Fuicer as a result of the faster transit time from sensor to #etector &3.'%(.

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Sharper an# "etter #efine# changes are seen in the gas response &3.'(. This results from the smaller 8olume of air in the s!stem. ith agitator traps, the gas is #ilute# in a large 8olume of air so that responses "ecome smeare#B or #ampene#B o8er an e@ten#e# time inter8al.



Large gas 8alues, of -0K or 0K for e@ample, are common ith agitator traps "ut not recor#e# "! the Gasi5ar#. These large 8alues result from trap loa#ing, here gas is e@tracte# from the mu# at a Fuicer rate than it is "eing 8acate# from the trap. The concentration therefore "uil#s up in the trap, lea#ing to erroneousl! high 8alues that tae a longer perio# of time to "e completel! 8acate# from the trap. >alues recor#e# "! the Gasi5ar# are a true measurement of gas 8olume in mu#.


A

GasWi8ard T4

Agitator Trap

% 1 minute inter8als

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+igure 3.'.

T!pical #ifferences in gas response of the Gasi5ar#.

ater)%ase# 2u# S!stems 

Gas 8alues are t!picall! loer than those recor#e# "! the agitator trap as a result of the trap loa#ing #escri"e# a"o8e. This is particularl! true for larger gas 8alues, in e@cess of 10K.



+or loer gas concentrations, hen #ealing ith principall! methane, gas 8alues are liel! to "e 8er! similar. :f the Gasi5ar# is installe# in the floline at the "ell nipple, hoe8er, rea#ings ill "e higher since gas that oul# otherise escape to the atmosphere, "efore the mu# reaches the shaer "o@, is "eing #etecte#.



Gas composition ma! also cause a #ifference in response. :f hea8ier oil is "eing sample# ith a greater proportion of hea8ier en# gases &propane through pentane( present, the response ill "e higher ith Gasi5ar#. This is "ecause a greater proportion of these components is in solution an# not efficientl! e@tracte# "! agitator traps. This ill mae no #ifference to the Gasi5ar#, since it #oes not matter hether gas is in solution or present as free gas.

Oil %ase# 2u# S!stems 

Gasi5ar# rea#ings are t!picall! higher than those recor#e# "! con8entional agitator traps. This is simpl! a result of gas phase. Oil has a much higher "u""le point than ater so that gas #oes not "rea out of solution until a higher saturation is reache#. Oil "ase# mu# arri8ing at surface therefore has a far greater proportion of #issol8e# gas. This, as e ha8e seen, #oes not influence the Gasi5ar# measurement since #issol8e# an# free gas are e@tracte# alie, "ut it can lea# to inefficient e@traction an# loer measurements ith agitator traps.

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Gas Dete*tion and 3e*ording

Once the gas sample has "een passe# through 8arious arrangements of filters an# #r!ing agents in or#er to remo8e moisture an# contaminants, it is route# to the gas #etectors. T!picall!, these ill inclu#e an instrument for measuring the total gas an#or total com"usti"le gas an# a chromatograph to pro8i#e a precise "rea#on of the gas.

Tota$ Gas 4eas)rement

+irstl!, it shoul# "e recogni5e# that no gi8en #etector t!pe has overall superiorit! o8er the others. Each has their on particular "enefits an# each has their limitations. Detector response an# measurement 8aries accor#ing to the particular gas propert! that is "eing anal!5e#, "e it com"usti"ilit!, thermal con#ucti8it! or ioni5ation energ!. :n or#er for effecti8e e8aluation of Total Gas measurements, the user shoul# "e aare of the capa"ilities an# limitations of in#i8i#ual #etectors an# the 8ar!ing response that can "e e@pecte# hen there are changes in gas concentration or composition.

3.2.1

The 'atalytic 'o&bustion ('') or Hot !ire *etector latinum

This is the earliest an# simplest gas #etector use# ire in the mu# logging in#ustr!. :t is still a i#el! use# #etector for total gas measurement. The sensor contains a 8er! fine platinum filament em"e##e# in a "ea# of alumina to hich, a catal!tic mi@ture is applie# &+igure 3.<(. A current is passe# through the #etector coil, raising its temperature to a 8alue at hich h!#rocar"ons ill "e o@i#i5e#. The gas sample is passe#, at a constant rate, through the com"ustion cham"er an# the tin! fraction of gas coming into contact ith the filament is "urnt off, releasing heat that then further heats the filament an#, in #oing so, increases itBs electrical resistance. The filament forms one si#e of an Alumina electrical heatstone "ri#ge circuit so that the %ea# an# change in resistance pro#uces a potential atal!st #ifference across the circuit. This can "e measure# an# cali"rate# in terms of the com"usti"le gas concentration. +igure 3.< atal!tic om"ustion The  #etector is cali"rate# in terms of K E2A &EFui8alent 2ethane in Air(. T!picall!, a Detector concentration of "eteen 1 an# $K methane is use# for cali"ration. The #etector pro8es to "e 8er! accurate for lo concentrations of methane.

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As the molecular eight increases, hoe8er, hea8ier h!#rocar"ons pro#uce a 8ar!ing response &than that pro#uce# "! methane( from the #etector, proportional to their calorific energ!. The hea8ier the h!#rocar"on, the greater the response gi8en "! the #etector. The 8aria"le responses are #etaile# in Ta"le 3.1 an# as can "e seen, the response "! "utane, for e@ample, oul# "e almost #ou"le that pro#uce# "! the same 8olume of methane.

The response of the #etector is also effecte# "! 8ariations in gas concentration &+igure 3.;(. 2ethane respon#s linearl! to
At a concentration of 100K methane, the response oul# "e 5ero since there is no o@!gen to allo com"ustion. This pro"lem is amplifie# if the proportion of hea8ier h!#rocar"ons is greater, since the hea8ier the molecule the more o@!gen is reFuire# for complete com"ustion.

Gas 2ethane Ethane ropane i)%utane n)%utane !#rogen Sulphi#e Ta"le 3.1

Cesponse &relati8e to 1( 1.000 1.'- 1.1$ 1.93 1.-10 $.'<;

Celati8e atal!tic om"ustion responses

2o#ifications can "e ma#e in terms of increase# #ilution ith a non Fuantit! of air in or#er to measure higher gas 8olumes. This ensures that the gasair mi@ture is ept "elo the L.E.L in or#er to maintain as linear response as possi"le an# allos concentrations of up to 100K E2A to "e measure#.

A further mo#ification can "e ma#e, "! re#ucing the temperature of the filament, so that methane is not com"uste#. This pro8i#es a recor#er for hea8ier gases onl! an# can therefore "e use# as a wet gas or gas richness in#icator. Again, hoe8er, the molecular eight an# #ifferent Detector responses from the hea8ier gases lea#s to inaccurac!. Cesponse

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oncentration in Air

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+igure 3.;


!#rocar"on com"ustion ith the atal!tic om"ustion #etector

 A#8antages   

Linear response at lo concentrations. >er! relia"le, ro"ust an# cheap. +amiliarit! an# ease of use.

 Disa#8antages    



The resistance of the filament changes o8er time #ue to constant "urning an# ear. The filament can "e poisone# an# ma#e less sensiti8e, to h!#rocar"ons, "! corrosi8e gases. The sensor reFuires regular re)5eroing an# cali"ration. 2easurements are su"Hect to non)linearit! as gas composition changes #ue to #ifferent reaction rates, heat generate# an# resulting filament temperature changes. This ill affect su"seFuent com"ustion rates an# instrument response.

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3.2.2


Ther&al 'onductivity *etector (T'*)

Similar to the  #etector, the Thermal on#ucti8it! Detector operates "! a! of a filament forming one si#e of a heatstone "ri#ge circuit ith changes in resistance representing changes in the concentration of gas.

=nlie the  #etector, hoe8er, hich measures the temperature increase #ue to com"ustion, the TD ors "! measuring the cooling effect on an element #ue to the thermal con#ucti8it! of the gas. The #etector has to sensing elements. One is enclose# in air pro8i#ing the controlB against hich, the response #ue to the gas sample on the secon# element is compare# &+igure 3.-(.

The thermal con#ucti8it! of a gas is #epen#ent on its molecular inetic energ!. Different gases therefore ha8e a 8ar!ing cooling effect, pro#ucing #ifferent responses from the #etector. 2ethane has a positi8e response &1.$<@ the response gi8en "! air, at 0 ( an# is t!picall! use# as the cali"ration me#ium ith the measurement "eing e@presse# in terms of K E2A &as ith the  #etector(. A methaneair mi@ture ill ha8e a linear response all the a! to 100K methane, maing it an i#eal #etector for measurement of large methane concentrations associate# ith h!#rocar"on gas 5ones.

sample

Ceference +igure 3.-

Acti8e

Schematic of the Thermal on#ucti8it! #etector elements

oe8er, linearit! an# accurac! of the TD is lost hen other gases are intro#uce# to the mi@ture. All other h!#rocar"on gases, e@cept methane, ha8e a loer thermal con#ucti8it! relati8e to air, pro#ucing a re#uce#B response from the #etector &Ta"le 3.$(. The #egree of error is o"8iousl! #epen#ent on the proportion of the hea8ier h!#rocar"ons to the methane concentration. Ethane, for e@ample, at 0 , results in N the response of air & 3< of that of methane( an# ill cause a loer sensor output for the eFui8alent concentration. A #rop in the total gas 8alue, or

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rather, in the rate of increase, can therefore ha8e to possi"le causes* either a #rop in methane concentration, or, an increase in the proportion of hea8ier h!#rocar"ons.

GAS

Thermal on#ucti8it! &relati8e to Air( 0 100

Air 2ethane Ethane ropane %utane entane 4itrogen ar"on Dio@i#e Acet!lene !#rogen elium

Ta"le 3.$

1.00 1.$< 0.-< 0.< 0.<< 0.<$ 0.99 0.;0 0.--.0 <.9

1.00 1.'< 0.90 0.-0 0.;; 0.< 0.99 0.-0 0.< ;. <.<

Thermal con#ucti8it! of gases relati8e to air

Similarl!, non)com"usti"le gases also pro#uce a 8aria"le response from the #etector. +or e@ample, car"on #io@i#e an# h!#rogen sulphi#e "oth ha8e a loer cooling effect than either air or methane hereas gases such as h!#rogen an# helium pro#uce a large positi8e response.

Although #etrimental to h!#rocar"on e8aluation, the #etection of these gases is eFuall! important in the #rilling of a ell/ )

car"on #io@i#e  h!#rogen sulphi#e helium

ell an# personnel safet! fracture #etection in geothermal applications

TD A#8antages 

2easurement to 100K methane concentration. Detection of non)com"usti"le gases.   Long life, cheap an# relia"le. TD Disa#8antages   



>aria"ilit! of response #ue to the presence of other gases. oor sensiti8it! "elo concentrations of 0.1K. oor 5eroB sta"ilit! since the #etector is sensiti8e to flo.

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3.2.3


+la&e Ioni"ation *etector (+I*)

The +lame :oni5ation Detector, similar to the , operates "! a! of gas com"ustion. =nlie catal!tic com"ustion, hoe8er, here onl! a fraction of the gas is "urnt off, the +:D relies on complete com"ustion of the gas sample. assing the sample through a proportionall! larger h!#rogen flame, hich has the a#8antage that an! heat generate# through gas com"ustion is negligi"le hen compare# to the heat generate# "! the h!#rogen flame, ensures this. This pro8i#es a constant temperature an# com"ustion rate an# ensures a uniform response at all concentrations.

The +:D respon#s to the ioni5ation process that occurs hen the high flame temperature "reas #on the car"on)h!#rogen "on#s.

' methane

3) 



3)

3

e)



electron

The meth!l anion & 3)( pro#uce# #uring the initial com"ustion is attracte# to an ano#e that surroun#s the flame. :n #oing so, it #ischarges an electron, "ecoming neutral, an# completes com"ustion.

The h!#rogen cation is attracte# to a catho#e, here it gains an electron to "ecome neutral an# com"usts further &+igure 3.(.

earth

A

 om"ustion ham"er &catho#e( 

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Air

Sample !#rogen

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+igure 3.

Schematic of a +lame :oni5ation Detector

This ionic transfer across the com"ustion cham"er, representing the num"er of molecules "urning, completes an electrical circuit. The resulting current flo, proportional to the concentration of organic 8apour, can "e measure# an# cali"rate# in terms of h!#rocar"on concentration.

As ith the other #etectors, methane is t!picall! the cali"ration me#ium ith the result "eing e@presse# in terms of K E2A. =nlie the other #etectors, hoe8er, the response is #ue to the num"er of car"on)h!#rogen "on#s "eing "roen an# is therefore proportional to the car"on content. :.e. ethane an# propane ill pro#uce tice an# three times, respecti8el!, the response that methane pro#uces.

The +:D therefore pro#uces a Fuantitati8e measurement of gas richness an# E2A "ut, as ith the other total gas #etectors, is una"le to #etermine hether a change in measurement is as a result of changing 8olume or changing composition.

+:D A#8antages  

=niform an# linear measurement of gas richness. E@cellent sensiti8it! an# range from a fe parts per million to 100K.

+:D Disa#8antages     

3.2.,



The h!#rogen reFuirement maes the sensor unnecessaril! #angerous. E@pensi8e No response to non$hydrocarbons Electronicall! comple@. %aseline #rift ith the presence of impurities, reFuiring re)5eroing.

Infrared *etector (I+-)

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A further total gas #etector, not commonl! use#, is the infrare# #etector. !#rocar"ons &as ell as other gases( ha8e a ell)#efine# a"sorption spectrum signature in the infrare# region of the electromagnetic spectrum. The #etector &+igure 3.9( contains an infrare# source an# a p!ro) electric sensor. The infrare# stream passes, in#epen#entl!, through to cells, one containing the sample gas an# the other containing a reference gas.

Gas Sample ell +ilter :nfrare# Source

Detector

Ceference ell

+igure 3.9

:nfrare# Detector schematic

Alternatel!, the infrare# energ! from the to cells pass through a filter, selecte# to remo8e all "ut the specific spectrum freFuenc! that h!#rocar"ons a#sor", to the infrare# #etector. %! comparing the energ! le8els emitte# from the to cells, the #etector can #etermine the energ! a"sorption from the sample gas, hich can "e cali"rate# in terms of h!#rocar"on concentration.

The :+C #etector cell length #etermines sensiti8it! an# range, ith a range of 0 to 100K methane possi"le. oe8er, the energ! emitte# is a function of molecular "on#ing, so that the output increases in response to hea8ier h!#rocar"ons. This error can "e minimi5e# "! the filter selection "ut each h!#rocar"on has a slightl! #ifferent a"sorption spectrum, so that a filter ith a "est fittingB freFuenc! range has to "e chosen &+igure 3.10(. :ntensit! Cange of filter

1

$

+reFuenc! +igure 3.10

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:#eali5e# schematic of h!#rocar"on an# filter freFuenc! range


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:+C A#8antages  

A range of 0 to 100K is possi"le. There is no ear or #egra#ation #ue to poisonous gases.

:+C Disa#8antages    

The #etector gi8es a non)linear output. :nterference from other gases. The #ifferences in car"on)car"on an# car"on)h!#rogen "on#ing gi8es continuous "an#s of o8erlapping a8elengths, pre8enting precise concentration measurement. E@pensi8e

3.2.

Total as *etector /u&&ary

Effecti8e formation e8aluation ith total gas #etectors #oes reFuire a goo# nole#ge of the #ifferent responses that can "e e@pecte# ith the #ifferent #etector t!pes. On the "asis of com"ustion,  an# +:D #etectors ill ala!s gi8e proportionall! higher responses as the content of hea8ier h!#rocar"ons increases. ith ' or < times the response of methane gi8en "! "utane an# pentane content, +:Ds ill gi8e larger responses than the  hen hea8ier components are present. :n certain situations, these responses ma! appear to "e erroneousl! large #ue to the hea8ier composition, as illustrate# in Ta"le 3.3. urel! on the "asis of h!#rocar"on e8aluation, the +:D is the most effecti8e total gas #etector since it #oes pro8i#es a linear, Fuantitati8e measurement of h!#rocar"on content, in terms of eFui8alent methane. oe8er, lie ALL total gas #etectors, the +:D cannot #istinguish "eteen specific h!#rocar"ons an# flui# t!pe. This, together ith the #isa#8antages of the instrument comple@it! an# the reFuirement of h!#rogen #o not mae it the automatic choice for total gas #etection. Each #etector t!pe has itBs on particular merits an# limitations.

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T #etectors are e@tremel! effecti8e for gas 5one #etection #ue to the linear response of methane up to 100K. ith the a##ition of hea8ier components, the response is loer than those responses gi8en "!  an# +:D #etectors, "ut ill o"8iousl! remain positi8e in most situations. ith certain flui# t!pes, hoe8er, o8erall response ma! "e 8er! small #epen#ing on the relati8e changes of methane an# hea8ier components. :n the case of hea8ier oil for e@ample, the methane content an# response ma! #ecrease "ut the increase in response gi8en "! the hea8ier components ma! not "e sufficient to gi8e an o8erall significant response.

Actual omposition K 2ethane Ethane ropane %utane TOTAL Ta"le 3.3

< ; 3 1 #5

TD response <.0 3.; 1.' 0.' #0.-

 response <.0 .9 <.' 1. "0"."

+:D response <.0 1$.0 9.0 '.0 ""0.0

omparison of E2A responses of total gas #etectors

Essentiall!, total gas anal!sis pro8i#es a 8er! useful, continuous, recor#ing of "ul gas 8olume ith a Fualitati8e anal!sis of gas richness an# of relati8e changes in gas 8olume "eteen #ifferent formations an#or reser8oirs. :t also pro8i#es an in8alua"le safet! monitoring s!stem. oe8er, accurate Fuantitati8e anal!sis an# e8aluation of changing flui# t!pe is not possi"le since it cannot pro8i#e an a"solute "rea#on of the actual composition of the gas mi@ture, hether h!#rocar"ons, com"usti"le or non com"usti"le. +or this e ha8e to loo to gas chromatograph!.

An! total gas measurement is #epen#ent on the particular sensor t!pe an# relati8e response to #ifferent concentrations an# compositions.

%enefits 

Total gas #etection is effecti8e hen 5ones are ell #ocumente# or hen onl! one flui# t!pe is e@pecte# &i.e. chromatographic anal!sis is not reFuire# to #etermine contacts(. Therefore, it is i#eal for gas ells an# #e8elopment ells.



:t can assist the ellsite geologist or mu# logger in picing core points an# formation tops.



Total gas #etection can "e utili5e# in a stan#)aloneB ellsite monitoring s!stem &see "elo( hen a full logging unit is not reFuire#.



:t pro8i#es an essential component to ell safet!.

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

:t pro8i#es a "acup to chromatographic anal!sis.


Limitations 

an not #istinguish h!#rocar"on compoun#s or i#entif! flui# t!pe.



ersonnel not un#erstan#ing the #ifferences in operation an# resulting measurement.

hen using a gas chromatograph, as a "ac up Datalog use a total gas s!stem that incorporates "oth a atal!tic om"ustion #etector an# a Thermal on#ucti8it! #etector. +or itBs accurate an# linear response at lo le8els of gas, the  #etector is use# for concentrations of "elo '.0K E2A. :f the gas e@cee#s this le8el, the s!stem automaticall! sitches to the use of the T #etector "oth for itBs capa"ilit! of measurements of up to 100K E2A an# "ecause it pro8i#es "etter safet! monitoring in the #etection of non)h!#rocar"on gases. hile the T #etector is pro8i#ing the measurements, the  #etector is automaticall! sitche# off to minimi5e ear on the filament, so prolonging itBs life an# accurac!. 3.2.0

n&anned Total as *etection /yste&s

As mentione# a"o8e, hen a full logging s!stem is not reFuire# or arrante# &gas ells, #e8elopment ells(, total gas #etection can "e incorporate# in a stan#)aloneB, eas! to operate ellsite monitoring s!stem. This gi8es the operator a cheaper alternati8e to a manne# mu# logging unit an#, in situations here the "u#get #oes not pro8i#e mu# logging, ena"les the operator to maintain an effecti8e safet! an# e8aluation tool.

This unit, hich can "e operate# "! a ellsite geologist, pro8i#es the folloing "enefits/ )      



Assist in picing core points an# formation tops. an "e automate# ith lagge# gas #ata an# COBs. ro8i#es continual printout an# #ata storage. ost effecti8e #etermination of porosit! an# formation pressure changes. :n8alua"le ai# to ell safet!. ro8i#es insurance against ireline tools not "eing a"le to "e run or against E)log #ata "eing effecte# "! su"seFuent formation in8asion.

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+igure 3.11


The Geologger, DatalogBs stan# alone gas #etector

2inimal training can re#uce the one #ra"ac, in that, hen total gas s!stems are the responsi"ilit! of the ellsite geologist, e@perience in unit operation an# interpretation of resulting measurements ma! not "e holl! sufficient. DatalogBs total gas monitoring s!stem, the Geologger &+igure 3.11( incorporates a catal!tic com"ustion #etector, ith automate# #ilution to eep the gas sample "elo the loer e@plosi8e limit, pro8i#ing total gas measurement from 0 to 100K E2A. The s!stem is complete ith a real)time #ispla! an# har# cop! printout &+igure 3.1$(. Data is store# an# a8aila"le in LAS format maing it compati"le ith geological strip log softare.

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+igure 3.1$




Ceal)time printout from The Geologger

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Gas %hromatography

3.3.1

'hro&atographic peration

Gas chromatographs can operate on the "asis of an! of the #etector t!pes alrea#! #escri"e# "ut ha8e the capa"ilit! of ph!sicall! separating in#i8i#ual components of a gas mi@ture. T!picall!, to#a!, either the +:D or TD #etector t!pe is use#.

%eing a"le to #etermine the e@act concentration of in#i8i#ual h!#rocar"ons, as ell as other gases, allos for/ )   

Determination of reser8oir flui# t!pe. :#entification of gas, oil an# ater contacts. :#entification of changes in oil gra8it! or gas #ensit!.

This maes the chromatograph an in8alua"le tool hen #rilling e@plorator! ells here little is non a"out the regional geolog! or reser8oir characteristics.

=pon sample inHection, separation of in#i8i#ual compoun#s an# gases occurs as the sample is passe# through columns containing a me#ium that has #ifferent retention rates for compoun#s of #ifferent chemicalph!sical properties. :n#i8i#ual components are then passe# through the #etector here the! are anal!5e# an# measure#. The in#i8i#ual gas peas are integrate# to #etermine the area "eneath the resulting cur8e. This 8alue is then e@presse# as an a"solute concentration "! comparison ith a cali"rate# 8alue &i.e. a gi8en area correspon#s to a gi8en gas 8olume(.

The particular gases that are anal!5e# "! the chromatograph #epen# on se8eral factors/ )    



The separating me#ium use# in the columns. The carrier gas carr!ing the gas sample through the columns. The pressure an# temperature of the columns. The length of columns an# separation time alloe# i.e. in the case of alanes, the longer the time alloe# for each sample to pass through the columns, the hea8ier the alanes that can "e separate#.

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ith all chromatographs, samples ha8e to "e separate# an# anal!5e# "efore a further sample can "e taen. Although this ma! allo more h!#rocar"ons to "e measure#, the #isa#8antage of a longer separation time is that sampling is less freFuent. This is a 8er! significant #ra"ac in gi8en situations/ )    

3.3.2

hen #rilling rates are fast. :n the #etection an# anal!sis of fracture gas. recise i#entification of formation tops or reser8oir contacts. :#entification of thin formation stringers.

The High /peed Ther&al 'onductivity 'hro&atograph

olumn

+igure 3.13

Detector

The porta"le, micro), high spee# gas chromatograph

Datalog uses a state of the art, porta"le, high spee#, micro)chromatograph &+igure 3.13( that anal!ses 1 to < in less than 30 secon#s. This spee# of elution is in8alua"le for accurate #etection of reser8oir contacts, formation tops, thin stringers, coal seams an# fractures, an# is facilitate# "! the small si5e of #etector so that onl! a small sample 8olume nee#s to "e inHecte# &+igure 3.13(.

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The chromatograph ors on the thermal con#ucti8it! principle so that the stan#ar# columns also accuratel! monitor non)com"usti"le gases such as nitrogen an# car"on #io@i#e, ithout interfering ith h!#rocar"on e8aluation. This is a "ig a#8antage o8er com"ustion "ase# chromatographs & or +:D(, especiall! in un#er"alance# #rilling &using nitrogen( or geothermal applications. The columns, t!picall! ' to < m of micro)tu"ing, an# the t!pe of carrier gas are selecte# #epen#ing on the reFuirements of the particular operation. 4ormall!, helium is the carrier gas use# in h!#rocar"on #etection, pro8i#ing a much safer alternati8e to h!#rogen. %ut, for e@ample, argon carrier gas an# specific columns can "e use# to #etect helium an# other inert gases in geothermal applications. The chromatograph use# in stan#ar# applications contains to in#epen#ent columns that anal!5e methane, ethane, nitrogen, o@!gen an# car"on #io@i#e, an# propane through pentane &+igure 3.1'(.

Some of the #istincti8e features of the chromatograph inclu#e/ )

    

3.3.3

The lo inHection time &t!picall! 30 6 <0 millisecon#s( pro8i#es a small sample that can "e anal!5e# through to pentane in un#er 30 secon#s. onstant column temperature is softare controlle#. ali"ration is performe# for each in#i8i#ual compoun# "eing #etecte#* therefore calculate# concentrations are a"solute. Operates from a fe parts per million through to 100K. eroing of the "aseline is #one automaticall! hen each sample is inHecte#.

T'* 4ersus +I* 'hro&atograph5

:t is a commonl! hel#, "ut mistaen, "elief that Thermal on#ucti8it! chromatograph! is inferior to +lame :oni5ation. oe8er, the micro)chromatograph #oes not ha8e the limitations associate# ith a T total gas #etector. 

The 8ariation in response ith air flo is not a factor since the gas sample is carrie# through the columns "! helium at a constant pressure, or rate. Each time a sample is inHecte#, the response #ue to the carrier gas is automaticall! measure#, pro8i#ing a 5eroB against hich, the gas responses can "e measure#. Therefore, an! 8ariations in the "aseB rea#ing are cancelle#.



>aria"le response #ue to #ifferent gases is not a factor, since gases are separate# an# anal!5e# in#i8i#uall!.

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The micro)#etectors pro8i#e a linearit! that is compara"le to +:D chromatographs. The importance, here, is the si5e of the #etectors 6 the smaller the! are, the faster the response an# the more linear the measurement.


olumn A

composite !%&N %

olumn %

'( ') i'*

n'*

i'+

n'+

'%

'!%

10 1!

+igure 3.1'

$0 2!

elution time &secon#s( hromatographic column anal!sis

30 3!

One pro"lem that ALL t!pes of chromatograph ha8e is non)linearit! an# possi"le column o8erloa#ing resulting from gas 8iscosit! an# sample si5e.

Gas 8iscosit! has an o"8ious effect on the rate at hich gi8en gases ill flo into the inHector. +or a gi8en inHection time, a #ou"ling in gas 8olume ma! not result in tice the recor#e# measurement since not all of the gas ma! ha8e ha# sufficient time to flo into the inHector. This non)linearit! can "e minimi5e#, or re#uce# to 5ero, "! lengthening the inHection time an# alloing more time for the gas to flo. oe8er, this presents another possi"le pro"lem, in that, "! increasing the time an# alloing more gas to enter the column, the ris of o8erloa#ing the column or reaching the full)scale limit of the amplifier is increase#. olumn o8erloa#ing occurs hen there is a larger 8olume of gas than the column can retain, so that the response is not #irectionall! proportional to the gas concentration. ith the TD micro)chromatograph, the operator easil! recogni5es this con#ition since sample chromatograms can "e 8iee#. Amplifier sensiti8it! an#or inHection time can "e a#Huste#

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accor#ingl! so that full range measurement is maintaine#. :n this a!, the chromatograph can measure up to 100K gas, hereas +:DBs ten# to ha8e a ma@imum saturation threshol#, a"o8e hich the! are no longer a"le to measure the gas.

ith linearit! compara"le, the onl! significant #ifference "eteen an +:D an# TD micro) chromatograph is that an +:D can #etect gas le8els to the parts per "illion &pp"( an# maintain linearit!, hereas the TD has a loer #etecta"le limit of "eteen 1 an# 10 parts per million &ppm(. This le8el of accurac! is more than sufficient for ellsite gas chromatograph!.

A further operational consi#eration is the carrier air emplo!e#. The TD chromatograph uses helium hich is inert an# hich can "e supplie# at a constant pressure. The +:D reFuires air as a carrier gas an# also a h!#rogen suppl! to maintain a constant flame. Air is t!picall! supplie# "! the rig an# reFuires filtering an# #r!ing to pro8i#e pure, #r! air. !#rogen is t!picall! supplie# "! generators, rather than "! compresse# c!lin#ers hich create a safet! concern. !#rogen generators reFuire a high #egree of maintenance to ensure that the! are operating safel! an# pro#ucing a constant suppl! rate. An! slight 8ariation in the rate an# pressure at hich the h!#rogen is "eing supplie# ill result in an inconsistent flame si5e. This ill alter the com"ustion rate of the #etector an# mean that the cali"ration is inaccurate.

!#rogen generators are also a large safet! concern, since, in the e8ent of a leaage, highl! com"usti"le gas is leaing into an enclose# or area. ith a nae# h!#rogen flame alrea#! present in the chromatograph, or ith the possi"l! of a cigarette "eing lit, e@plosions are a real #anger an# the! have happene#.

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,nits of 4eas)rement

Ta"le 3.' shos the con8ersion "eteen the 8arious units t!picall! use# in the oilfiel# to report gas Fuantit!.

arts per 2illion &ppm(

ercentage &K(

1 10 <0 100 1000 10,000 100,000 1,000,000

0.0001 0.001 0.00< 0.01 0.1 1.0 10.0 100.0

Ta"le 3.'

Gas =nits &ana#a(

0.1 0.< 1 10 100 1000 10,000

Gas =nits &=.S.A(P

0.$ 1 $ $0 $00 $000 $0,000

Gas unit con8ersion chart

P 4% man! companies a#opt their on gas unit con8ersion.

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Gas Analysis Handbook

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