2.1 SUMMARY OF THE GELAMA MERAH FIELD Geological Area
: Sabah Basin
Area
: Offshore Sabah
Country
: Malaysia
Reservoir Structure
: Anticlines
Coordinate
: Longitude 114 !"# $%&'4#( : Latitude $! ''# 4"&")#* 4"&")#*
+y,e +y,e of -ield
: Oil and gas
2.2 INTRODUCTION 2.2.1 REGIONAL SETTING
Gela.a Merah field is located in the offshore of Sabah Basin& /t 0as believed that the field is located nearby the Se.arang Asa. aya roduction roduction Sharing Sharing Contract Contract 0hich in (ast Malaysia at Sabah offshore& +his field 0hich is about 4! .iles 235.6 north0est of the Labuan Gas +er.inal is surrounded by shallo0 reed 0ith the 0ater de,th of '$ feet 2".6& +he location of the Gela.a Merah field is sho0n in the figure belo0& Sabah7 located in the northern ,art of Borneo7 lies at an i.,ortant 8unction bet0een the (urasian7 /ndo9Australian7 acific and hili,,ines Sea ,lates& +he Sabah Basin7 0hich is located in *orth est est of Sabah7 is .ainly offshore 0hile the other t0o basins cover so.e areas in the *orth (ast and South (ast of onshore Sabah& +he Sabah Basin contains 195. thic5 *eogene sedi.ents that 0ere de,osited de,osited 0ithin the dee, .arine and ,rogradatio ,rogradational nal shelf slo,e environ.ent& environ.ent& +here are si; tectonostratigra,hic ,rovinces are identified in Sabah Basin 0hich is Ra8ang Grou, -old9 +hrust Belt7 /nboard Belt7 Bara.
-igure 1&1 = Location of Gela.a Merah field
+he Geogra,hical Coordinate of Gela.a Merah is $! ° ''# 4"&") ° *7 114 ° !"# $%&'4 °(& +here are three 0ell on Gela.a Merah field 0hich is Gela.a Merah 17 Gela.a Merah S+91 and finally Gela.a utih& +he last and .ost recent tie9in to Sa.arang Asa. aya SC is fro. the nearby Su.anda5 field& +he fault that is occurred in Gela.a Merah is regional 0rench fault&
&1&1 late +ectonic Syste. +here are four .a8or tectonics event occurred in Sabah Basin that contribute to the fault align.ent> 16 develo,.ent and de,ositional during syn9riff ,hase2(ocene =Oligocene67 6transgression of deltaic de,osits of during late syn9riff ,hase2Late Oligocene9(arly Miocene67 '6 .ar5ed by tectonic ?uiescence during Middle Miocene7 and 46 /nversion and folding of tectonics during Middle Miocene9leistocene& +he tectonic setting and basin evolution of the Sabah Basin is very .uch related to the closing of the ,roto9South China Sea@ Ra8ang Sea& +he o,ening of the South China Sea since Oligocene causing .icrocontinents of
-igure &1& = +ectonic (vent of Sabah Basin
2.1.2 Exploration Opportuniti! +he e;,loration of Sabah Basin 0as carried out by nu.erous ty,e of oil co.,anies& A nu.ber of initiatives by (+RO*AS and SC contractors to test ne0 ,lay9ty,es and continuous studies to .ature ,lays have resulted in recent discoveries& +he success story begins 0ith the discovery of Gela.a Merah by Gela.a Merah 1 0ere drilled in Se,te.ber $$1& +hen7 seven .ore e;,loration 0ell 0ere drilled on the sa.e ,lay in the area bet0een $$1 until $$'& +o date7 t0enty9eight 2)6 develo,.ent 0ells have been drilled on Gela.a Merah area and the fields are currently on ,roduction& /n order to further e;,lore the hydrocarbon ,otential of this area7 a regional study 0ith se?uence stratigra,hic a,,roach 0as carried out in $$)& +he .ain ob8ective of this study is to generate stratigra,hic fra.e0or5 of Su.anda5 that can be correlated to the Sabah regional chronostratigra,hic fra.e0or5& +he generated stratigra,hic fra.e0or5 0ill hel, to facilitate inter,retation in the Bloc5 SB'1$ and surrounding areas& /n addition7 the study 0as also ai.ed to identify any u,side hydrocarbon ,otential for further e;,loration& +he a,,roach ado,ted in this study 0as based on (;;on#s techni?ues 2an agoner et& al& 1""$6 0hich defined Se?uence Boundary 2SB6 as a ,roduct of relative falls is sea level&
Seis.ic data and 0ell data 2logs7 cores biostratigra,hic data 0ere used to identify .a8or bounding surfaces in order to establish a fra.e0or5 in 0hich genetically related facies can be studied and a realistic de,ositional .odel can be constructed&
2.2 2"DIMENSIONAL CROSS IMAGING Contour line that is in surface .a, indicate the de,th of the area fro. to, vie0& Contour lines connect all the sa.e elevation ,oint and are used to illustrate relief on a .a,& Contour .a,s for e;,loration .ay de,ict geologic structure as 0ell as thic5ness of for.ations& By this contour7 the angle of a fault and 0here it intersects 0ith the for.ations and other faults as 0ell as 0here the for.ations ta,er off or sto, abru,tly can be sho0n& Basically7 geologist used iso,ach .a,s to assist in e;,loration 0or5 0hich is to calculate ho0 .uch ,etroleu. re.ains in a for.ation and to ,lan 0ays to recover it& +he range of de,th that ,lotted on to, of .a, is 0ithin 1'$$91)$$.& +here are a total of " layers of surface .a, 0hich are '&7 4&$7 !&$7 %&$7 3&$7 )&$7 "&$7 "&1 and "&& +he .a,s 0ere scaled as 1:!$. 0hich is in A' siDes& An identical scale of horiDontal and vertical are reco..ended for conventional cross section i.aging as sho0n belo0&
ertical (;aggeration 2(6 E value of one unit .easure.ent on the ForiDontal 2MA6scale value of the sa.e unit of .easure.ent on the ertical D E 1:!$ E 1
1:!$
Fi#ur 2.1 = Surface .a, for nit '&
+he de,th of cross section 0as dra0n to visualiDe the contour line in t0o di.ensional vie0s that is obtained fro. the surface .a,& +he vertical and horiDontal cross sections 0ere both ,lotted using Microsoft (;cel& +he ;9a;is re,resents the horiDontal line 0hile the y9a;is re,resent the thic5ness of each Done&
+he ater Oil Contact 2OC6 is found to be at 1!'!. +
2.$ %ETROLEUM SYSTEMS &'&1 Source Roc5 Success in the ,reservation of organic .atter in the * Sabah Basin see.s to be related to the high ,ri.ary terrigenous ,roductivity7 high sedi.ent accu.ulation rates and the resistant nature of the +y,e /// higher land ,lant 0a;es to o;idation and biodegradation& /nterestingly7 as .uch of the Sabah shelf tended to be o;ic during Middle Miocene7 it a,,ears that ano;ic de,ositional conditions 0ere not essential for organic .atter ,reservation& /n origin7 de,osited in generally o;ic environ.ents such as deltaic@,eat s0a.,s7 brac5ish .angrove s0a.,s and lagoons&
&'& Migration +he ti.ing of .aturation varies fro. Middle Miocene to the ,resent& Most of the area is still undergoing subsidence& Migration along faults is ,robably a .a8or .ethod of .igration though .any faults act as seals& So.e .igration through sedi.entary facies has ,resu.ably occurred7 es,ecially in an u, di, direction fro. condensed intervals&
&'&' Reservoir Roc5 Reservoir roc5s for Gela.a Merah field consist of interbedded sandstone 0ith thin shales layer of non9reservoir& ,,er shoreface sandstones of regressive ,arase?uence sets and fluvial and tidal sandstones filling incised valleys cut during lo0stands& +he de,ositional environ.ents for each sandstone reservoir differ 0ith the stratigra,hy& +he ,ri.ary de,ositional environ.ent7 burial diagenesis and .ineralogical contents of the reservoir sandstone ,lay an i.,ortant role in the ?uality of the reservoir in Sabah Basin& -or.ation that 0as de,osited during .iddle to u,,er Miocene contains reservoir roc5s that are de,osited in fluvial9deltaic7 coastal ,lain and shallo0 .arine environ.ent 2Madon M&7 1""46& +hese strata contains .ediu. to very fine grained sandstone 0ith ,orosity value that .ore than '$H and 1$$$.< ,er.eability value 2Bisho,7 $$6&
&'&4 +ra, Seals Most ,roducing reservoirs are anticlinal features& +his can be sho0n through the horiDontal cross of the contour .a, in -igure &'& Based on the location of basin it is either rollover anticlines ,roduced by gro0th faulting or anticlinal features associated 0ith .orris faults& So.e reservoirs are related entirely to sealing against faults& +he seals are either .arine flooding surfaces or faults 0ithin reservoirs& -urther.ore7 there are also stratigra,hic tra,s unrelated to anticlinal features according to the basin 0here the Gela.a Merah located&
-igure &' = ForiDontal Cross Section 2.& Strati#rap'( an) Corrlation +he correlation is done across 0ell Gela.a Merah91 2GM916 to 0ell Gela.a Merah91 S+1 2GM91 S+16& +o, and base sand unit correlation data are given for GM91 and GM91 S+1& Iuality chec5 of ga..a ray log res,onse is being used in order to identify the lithology of the for.ation& Sand and shale unit identification is done using ?uic5 loo5 .ethod& -igure &4 illustrates the stratigra,hic correlation fro. sand and shale distribution fro. the log res,onse&
GR: Figh 2radioactive for.ation69indicate shale
GR: /rregular readings 2lo0 high69indicate sand for.ation interbedding 0ith shale layers
GR: Figh 2radioactive for.ation69indicate shale
GR: /rregular readings 2lo0 high69indicate sand for.ation interbedding 0ith shale layers
GR: Lo0 for.ation6 indicate for.ation&
2clean 9 sand
GR: Lo0 2clean for.ation6 9 indicate sand for.ation&
GR: /rregular readings 2lo0 high6 9 indicate sand for.ation interbedding 0ith shale
-igure &4 : ell to, correlations using Ga..a ray log for GM91 and GM91 S+91
/t can be seen that the oil accu.ulation are distributed at a thic5 layer at Done "&$7 "&1 and "& as sho0n in the .ulti9layered reservoir in -igure &'& +he thin oil layered are sho0ed above the GOC is at Done '&7 !&$ and "&$ above the GOC level& tectonic .ight have caused another ,ossible u,lift that gives the Gela.a Merah the current anticlinal sha,e it has no0& +he hydrocarbon bearing reservoirs in Gela.a Merah area are re,resented by to,set < cross section and also ?uic59loo5 .ethod fro. the logs ,roven by Microsoft (;cel S,readsheet calculations
2.* Dpo!itional En+iron,nt
-igure &! =
-igure &% : Ga..a9ray log trends
/n Gela.a Merah field there are three ty,es of de,ositional environ.ent that can be found based on the sha,e of the Ga..a9ray logs& +he log is sho0n in the -igure &3&
-igure &3: Ga..a Ray Log of Gela.a Merah -ield
-urther infor.ation on the Ga..a Ray trend of Gela.a Merah field is stated in +able 1&
S'ap
Srrat)
En+iron,nt!
C(lin)r Re,resents unifor. de,osition
-ll S'ap -ining u,0ards se?uences
Lacustrine sands
Funnl S'ap Coarsening u,0ard se?uences
+able 1 : Sha,e of Ga..a Ray Log of Gela.a Merah -ield
+he ga..a ray log is often used to .easure the shaliness of a for.ation& /n reality the shaliness often does not change suddenly7 but occurs gradually 0ith de,th& Such gradual changes are indicative of the litho9facies and the de,ositional environ.ent of the roc57 and are associated 0ith changes in grain siDe and sorting that are controlled by facies and de,ositional environ.ent as 0ell as being associated 0ith the shaliness of the roc5& -igure &) analyses the sha,e of ga..a ray log res,onses for various de,ositional environ.ents&
-igure &) 9 Ga..a ray log
2. Strati#rap'( an) /ll Corrlation +he ,ur,ose of conducting 0ell correlation is to observe the lithology bet0een 0ells in the field& Sand unit 0as used in .a5ing the correlation bet0een 0ell& Fo0ever7 correlations based on sands can result in nu.erous correlation errors such as either adding sands that are not actually ,resent or in .issing sands that are 0hich 0ill lead to over9esti.ated and underesti.ated reserves& -igure &) sho0s the result of the sand layer in Gela.a Merah 1 and Gela.a Merah S+9 1 0ells 0hen co.,are using ga..a ray log&
/n conclusion7 both 0ell does not connected 0ith each other and it 0ill have their o0n ,etroleu. syste.7 reservoir and roc5 ,ro,erties& /n order to reduce the errors7 log data such as ga..a ray logs7 resistivity logs7 and neutron density logs 0ill hel, to i.,rove the results&
Based on -igure &"7 ga..a ray logs at the sa.e sand unit does not ,resent the sa.e lithology7 this is due to the different ty,e of reservoir characteristic bet0een each 0ell and the 0ell does not connected 0ith each other& By co.,aring 0ith resistivity logs at the sa.e sand units7 Gela.a Merah 1 and Gela.a Merah S+91 0ells sho0s the e;istence of the hydrocarbon in the sa.e sand units& Fo0ever7 the fluid ty,e is different 0hen co.,aring using neutron density logs&
2.0 GROSS ROC OLUME 3GR4 CALCULATION According to Ka.es et al7 the Gross Roc5 olu.e 2GR67 is the volu.e of roc5 bet0een a to, and base reservoir surface and above a 5no0n or ,ostulated hydrocarbon90ater contact in a geological tra,& e use the coordinate s?uare .ethod in deter.ining the area of the reservoir&
-igure '&$ = Area calculated by using grid s?uare counting
STOII% 5 00*6 7 GR 7 NTG 7 8 7 So 9 -o
(?& 2&16
here7 S+O//: Stoc5 +an5 Oil /nitially in lace7 S+B 33!) : Conversion factor fro. acre9ft to bbl GR : Gross Roc5 olu.e7 acre9ft *+G : *et to Gross Ø : orosity
So : Oil Saturation Bo : Oil -or.ation olu.e -actor7 bbl@S+B
GII% 5 &$*: 7 GR 7 NTG 7 8 7 S# 9 -# here7 G// : Gas /nitially in lace7 SC4'!%$ : Conversion -actor fro. acre9ft to ft' GR : Gross roc5 olu.e7 acre9ft *+G : *et to Gross Ø : orosity
Sg : Gas Saturation: Gas -or.ation olu.e -actor7 cu&ft@SC-
(?& 2&6
