Pet r o Sc C ou ourse N ot es roph ph ysics M S
5.
WIRELINE LOGGIN G
5.1
What is a Wire lin line Log
W ir eline Logging
A log is a continuous r ec ecor ding of a geophysical par ameter along a bor ehole. W ir eline logging is a conventional f or m of logging that em ploys a measur ement tool 0 sus pended on a ca ble or wir e that sus pends the tool and carr ies the data back to the 620 . These logs ar e tak en between face sur f dr illi illing e pisodes and at the end of dr illing. R ece ecent developments also allow some measur ements to be made dur ing dr illing. The tools r equir ed to mak e these measur ements ar e attached to the d r ill str ing behind the b it, and do not use a wir e r elying 630 r adio on band-width instead low communication of data thr ough the conductive dr illi illing mud. S uch data is called i lling) f or MW D (measur ement while d r rilli sim ple dr illi illing data, and LW D (logging w hile d r i lling) f or measur ements analogous rilli 640 to conventional wir eline measur ements. MWD and LWD will not b e cover ed b y this oduced cour se, although the logs that ar e pr od acter istics, in this way have ver y similar char ac even though they have been obtained in a com pletely diff er ent way.
G AMM A R AY (GR) AP I UNITS
650 shows a ty pical wir eline log. In this case it is a log that r e pr esents the natur al gamma r adioactivity of a f or mation. N ote that de pth is arr anged ver tically in f eet or metr es, and the header contains the name of the log cur ve and the r ange. This exam ple o f data. N ote also that 660 ra ck o shows a single t r no data sym bols ar e shown on the cur ve. S ym bols ar e r etained to r e pr esent discr ete cor e data by convention, while continuous measur ements, such as logs, ar e r e pr esented by smooth cur ves. Figur e 5.1 shows o nly 50 eal logs ar e of ten much m of bor ehole, but r ea 670 longer (thousands of metr es), and contain ple cur ves on a single tr ac ack such as multi p ple tr ac ack s. this, and multi p F igur e 5.1
Fig. 5.1 Exam ple of a Gamma R ay Log
100
Pet ro ph ysics M S c C ourse N ot es
W ir eline Logging
Figure 5.2 A ty pical log set
Pet ro ph ysics M S c C ourse N ot es
W ir eline Logging
Figure 5.3 Land logging vehicle
Figure 5.4
O ff shor e logging ca bin
Figure 5.5 Inside the logging unit
Pet ro ph ysics M S c C ourse N ot es
W ir eline Logging
Data is tr ansmitted to the sur face thr ough the wir e and r ecor ded digitally. Moder n tools sam ple the f or mation at inter vals f r om 2.5 mm f or the high def inition imaging tools to a bout 15 cm f or the sim pler tools, so f or a com bination tool with sever al d iff er ent logs, ther e may b e as many as 100,000 individual measur ements per metr e over a log r un of u p to say 2000 m. De pending on the logging s peed, data tr ansmission r ates may be as high as 200 kbits per second. This data is su b jected immediately to a r udimentar y analysis b y po wer fu l p r ocessor s and d is played so that the q uality o f the measur ements can be check ed. The data is also r ecor ded onto digital (DAT) ta pe and tr ansmitted to the contr olling off ice of the logging com pany by satellite f or in- de pth analysis. A ty pical dr illing and logging histor y f or a well might be as shown in Ta ble 5.1. N ote that the logs ar e r un in each section bef or e casing tak es place. When each log is r un, the oper ator ensur es that some measur ements ar e included opposite the pr eviously cased section a bove the log r un as a test that the ng corr ectly and to p r ovide a local d e pth f ixed po int to hel p tie the d e pths f or each log tools ar e wor ki tool together . Whenever a bor ehole is logged in sections the oper ator also ensur es that ther e ar e over la p sections so that the logs can be tied together accur ately, and r e peat sections to check log quality and consistency. Table 5.1 A ty pical dr illing and logging histor y. Proce dure
Dr ill C ase Dr ill Log C ase Dr ill Log Log Log C ase Dr ill Log Log Log Log
D rill Bit Size
(inches )
Casing Diame ter (inches )
25
-
20 17.5
-
-
-
-
13.375
12.25
-
-
-
-
-
-
-
-
9.625
8.5
-
-
-
-
-
-
-
-
-
De pth
Tools
(m s ub se a s urf ace ) 300- 400 300- 400 400- 700 700- 400 300- 690 700- 1400 1400 - 680 1400 - 680 1400 - 680 690- 1390 1400- 2100 2100- 1380 2100- 1380 2100- 1380 2100- 1380
ISF - Sonic- GR /1
ISF - Sonic- GR /2 F DC - CN L/1 HDT/1
ISF - Sonic- GR /3 F DC - CN L/2 HDT/2 DLL/1
that the logs ar e r ecor ded dur ing the withdr awal of the tools f r om the well, that some tools wer e r un sever al times at diff er ent de pth inter vals and that these r uns have been coded consecutively, that ther e is an o ver la p of d ata, and that the lower log r uns include p ar t o f the p r evious casing at their top. N ote also that the most tools ar e r un in the ar ea that is ex pected to be of gr eatest inter est (i.e., the r eser voir). F or tool codes see wir eline oper ator s manuals.
N ote in Ta ble 5.1
Eff or ts ar e made at all times to ensur e that the logs ar e of the highest quality. Methods of ensur ing that logging quality is high include (a) mak ing r e peat sections of log measur ements over shor t sections that contain both low and high measur ed values, ( b) mak ing over la p measur ements of the pr evious
Pet ro ph ysics M S c C ourse N ot es
Tr ack 1
W ir eline Logging
Dep t h
Tr ack 3
Tr ack 2 10
0 10 3610
0
20
r
a e n i L
3600 0
10 3610
1
100
10
1000 c i m h t i r a g o L
3600 0
10 3610
1
10
0
10
d i r
b y H
3600
Figure 5.6 Log pr esentation gr ids. N ote that the AP I f or mat def ines par ticular dimensions f or each tr ack, and an over all width of 8.25 inches.
5.4
Tools
Ther e ar e a plethor a of logging tools now availa ble in the oil industr y. Ther e can be s plit into the f ollowing ty pes:
•
•
Standard ope n-hole
tools (diame te r 3 to 4 inches ) These r ange f r om the sim plest cali per tool to the sophisticated imaging and N MR tools and have ver tical r esolutions f r om 2.5 mm to over 30 cm. Slim hole tools (diame ter 1.6875 to 2 inches ) These ar e slimmer ver sions of the standar d tools, and ar e used wher e standar d tools ar e too thick. A pplications of these tools ar e in s pecialist logging thr ough dr ill- pi pe or coiled tu bing, and in small scale holes used in the water industr y.
Pet ro ph ysics M S c C ourse N ot es
•
•
•
W ir eline Logging
Ce me nt-logging tools These ar e s pecial ver sions of those tools that wor k thr ough cement casing that ar e optimized to wor k under these conditions. Production tools These ar e s pecialist tools f or r unning dur ing the pr oduction of hydr ocar bons f or measur ing pr essur e and f low r ate, and ar e always of the slim- hole var iety to f acilitate their inser tion into a pr oducing well. LWD tools These tools ar e designed to connect into the dr ill str ing and communicate data to the sur face thr ough the dr illing mud.
A summar y of some of the main standar d open- hole tools is given in Ta ble 5.2. Dr illing r igs ar e ex pensive and can of ten amount to almost 10% of the total dr illing costs. The time r equir ed to r un wir eline logs eff ectively delays the dr illing oper ation leading to gr eater ex pense. To minimize this ex pense tools ar e bo lted together f or lower ing do wn the bor ehole. All wir eline tools ar e designed to be com bined in this way and ther e ar e many possi ble com binations, some which ar e as long as 30 m. Each tool in the com bination has its own measur ement- sensitive r egion, which measur es a given f or mation at a s pecif ic de pth at diff er ent off set times. The data has to be de pth shif ted to account f or this. This is do ne in the d ata acquisition vehicle with inf or mation a bout the instantaneous s peed and dimensions of the tool com bination. Even using com binations, it is common f or as many as thr ee log r uns to b e made in the same section of the bor ehole with diff er ent com binations of tools. If this is the case, one tool is included in all com binations to act as a r ef er ence to which the other s might be com par ed f or de pth matching pur poses. This tool is commonly the gamma r ay tool (GR). shows an exam ple standar d op en- hole logging tool. N ote that it is a neutr on por osity tool, which is com bined with a gamma r ay tool. The loops at each end cover scr ew thr eads to ena ble it to be com bined with other tools of similar design. F igur e 5.7
wher e the gener al geology is well k nown and dr illing is chea per , only a f ew logs may be r un. This is because ex pense can be s par ed as inf or mation concer ning the su bsur face is not har d to come by. However , and per ha ps counter - intuitively, off shor e a f ull set of logs is of ten carr ied out even when ther e ar e no hydr ocar bon shows. This is because dr illing is so ex pensive that r elatively f ewer wells will be dr illed, and hence the maximum d ata must b e squeezed o ut of each well r egar dless almost o f the cost. If ther e ar e no hydr ocar bon shows, the well d ata will still b e ver y usef ul f or corr elation with other wells that do show hydr ocar bons, will hel p to constr ain the extent of neigh bour ing r eser voir s, as well as adding to the inf or mation a bout the gener al geological str uctur e of the ar ea. O n land,
Pet ro ph ysics M S c C ourse N ot es
W ir eline Logging
Figure 5.7 A C om pensated N eutr on Sonde (C N S )
Length Diameter Weight in air R ange φ R esolution Ver t. R esolution Investigation De pth
3.87 m (12.68 f t) 95 mm (3.74 in) 109 k g (240 l b) pu - 3 to 100 l Better than 0.05 pu at 20 pu 750 mm (30 in) 260 mm (10.2 in)
Pet ro ph ysics M S c C ourse N ot es
Table 5.2
C ommon open- hole
Tool
W ir eline Logging
tools and their uses
Phys ical M eas ureme nt
Use
Comments
Tem per atur e
Bor ehole tem per atur e f or r esistivity
C orr ected
Logging conditions
Tem per atur e (BHT)
with Hor ner plot
calculations. P r essur e (P R ESS )
F luid
pr essur e
F luid
pr essur e f or f or mation volume
Incor por ated in R F T
f actor calculations.
C ali per (C AL)
Bor ehole diameter
Data quality, in situ str ess tensor ,
Availa ble in 2, 4, or multi-
lithology and
ar m ver sions.
per mea bility indicator
Lithology
Gamma R ay (GR)
N atur al r adioactivity of
S hale indicator and
de pth matching
C an r ead
thr ough casing.
the f or mation. S pontaneous P otential (SP )
P er mea ble beds
Does not wor k in conductive
potential.
R esistivity of f or mation water
muds, or off shor e.
Velocity of an elastic
Eff ective (connected) por osity
C om paction,
S and/shale inter face
Poros ity S onic
(BHC , LSS )
wave in the f or mation.
gas and vugs,
cali br ation of seismic data.
Density (FDC ,
Bulk density of the
LDT)
f or mation.
N eutr on (S N P ,
Hydr ogen concentr ation
Total por osity (shale incr eases
CN L)
in the f or mation.
measur ed por osity, gas r educes
Total por osity
Used to calculate synthetic seismogr ams. C an r ead
thr ough casing.
measur ed por osity) Res istivity
S im ple electr ic log
R esistivity of f lushed,
(S N , L N , Lat)
shallow and dee p zones
can’t be used in oil based
r es pectively.
muds, pr one to invasion.
Induction Logs
C onductivity of the
(IES , ISF , DIL,
f or mation.
DISF , ILm, ILd)
Used in water satur ation calculations.
C onductivity and
r esistivity in oil
N ow obsolete,
Focussed
not f ocussed,
devices.
based muds, and hence calculation of
Use in oil based and f r esh
water satur ation.
water muds. R ange of de pths of investigation. (Ver tical r esolution 5- 10 f t.)
Later ologs
R esistivity of the
R esistivity in water based muds, and
Focussed
(LL3, LL7, DLL,
f or mation.
hence calculation of water satur ation.
Use in salt water based
devices.
muds. R ange of de pths of
LLs, LLd)
investigation.
(Ver tical
r esolution 2- 4 f t.) R esistivity of mudcak e
Indicator of per mea bility.
(ver tical r esolution a bout 1
and f lushed zone.
Detector of thin beds.
f t.)
Micr o- later olog
R esistivity of f lushed
Measur es R XO
N ot
(MLL)
zone.
P r oximity Log (P L)
R esistivity of f lushed
Micr olog (ML)
mudcak es. Measur es R XO
R esistivity of f lushed
f ocussed log
zone.
N ot
good if invasion is
small.
zone. Micr o- s pher ically
good with thick
Measur es R XO
Par t of DLL- R XO
tool.
(MSF L) Imaging Logs Ther e is a r ange of imaging logs based u pon sonic, visual, electr ical and N MR measur ements that ar e
beyond the scope of this cour se.
