Geophysical & Geological

7/25/2019 Geophysical & Geological

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Chapter I : Geophysical & Geological Data

1.1. Regional Geological Setting

1.1.1.Tectonic Setting

The Centaury PSC is located on the eastern margin of the South Sumatra

Basin in a region comprising of multiple NNE-SSW trending horst and

graben features, which were initiated in Palaeogene times

Figure 1-1 - Centaury PSC: regional tectonic setting

!n the Centaury area, the "erang and #etaling $ighs form the main horstbloc%s with the "erang and #etaling &eeps forming the inter'ening grabens()igure * These horsts were sources of sediment into the basins until theywere e'entually submerged and carbonates de'eloped on the old highs Thearea was then sub+ected to "id-"iocene transpressional and then furthersubsidence


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Figure 1-2 - Centaury loc!: "ocal tectonic setting

This transpressional phase is also associated with a regional tilt towards

the southwest and the uplift of the Sembilang $igh to the northeast,followed by a considerable amount of erosion in the past few million years

1.1.2.Stratigraphy

The stratigraphy of Centaury Bloc% ()igure * can be described as follow

Pre-Tertiary ase#ent metamorphic roc%s such as schist and phylliteare the dominant basement roc%s in Centaury PSC area The basementproduction eld in the south is mostly comes from thic% granitic sections

$i%-"ate ocene ' "o(er )ligocene*"ahat For#ation:The early syn-rift .ahat )ormation is conned to the graben areas o'erlain by allu'ial fandeposits and capped by thic% lacustrine shales, which form ma+or oil-pronesource roc%s !ts thic%ness reaches more than /000 m in the SouthSumatra basin depocenters to the south, while on intermediate horstfeatures the unit is absent The thic%ness of the .ahat can 'ary rapidly ina lateral sense with thic% accumulations close to faults

"ate )ligocene - arly $iocene*Talang +!ar For#ation ,T+F TheT1) lies uncomformably on the .ahat )ormation and was deposited in ano'erall bac%stepping, transgressi'e system tract with 2u'ial channel sandspassing up into shallow marine deltaics, which encroach onto the

basement highs Coals and shale pro'ide potential gas prone source roc%s


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and the o'erlying Pendopo marine shale pro'ides a regional seal and apotential oil-prone source roc%

arly $iocene*aturaa ,RF an% Gu#ai For#ations ,G/F: Thecarbonate platform buildups of the B3) represent the continuation of the

transgressi'e phase of the T1) depositional system The o'erlying 4umaishales represent the drowning e'ent and pro'ide a regional marine shaleseal o'er the entire area Two transgressi'e ma5ima are recogni6ed withinthe 4umai separated by a short li'ed phase of regression (NN7-NN8* Thisregressi'e phase resulted in sub-aerial emergence of the B3) reefs andsubse9uent poro-perm enhancement !t also caused widespread depositionof a basal clastics member in the Centaury area, which probably formsthief beds to se'eral dry holes drilled for B3) ob+ecti'es ("erang :,#etaling-/, etc* !n addition, these conduits pro'ided a means forhydrocarbon migration into o'erlying 1B) sands

$i%-"ate $iocene*+ir ena!at ,+F an% $uara ni# For#ations

,$F:The rst signicant in2u5 of 1B) sands is indicati'e of the ma+orregional "id "iocene regression, which results form a large deltaic unitprograding from the northeast The 1B) is composed mostly of marineshales and marginal marine sands, which pro'ide reser'oirs in East#etaling and Tempino )ields The "E) consists predominantly of abundantcoals and sandstones, with occasional de'elopment of tu;s, alldemonstrating continuation of a ma+or regressi'e cycle


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Figure 1-0 - Centaury PSC Stratigraphic Colu#n


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The appraisal wells drilled after Beta-: were designed only to penetratethe three main reser'oirs that pro'ed oil in the 1B) sands $ence, thethree well T&or "uara Enim usually encounteredabo'e 1B) These formations encountered from surface to around :00m ateach well, co-incident with an unconformity on the seismic line Thelithologies are predominantly composed of claystones with bloc%ysandstones of 'arying thic%nesses from :m up to ::m The claystones inthis formation appear as light grey-yellowish grey in colour and aregenerally amorphous, 9uite stic%y, with traces of pyrite and carbonaceousspec%s The sandstones in the #asai are composed of clear-translucent9uart6 grains, which are loose to occasionally consolidated with moderate-well sorting 4rains are ne to medium and are generally 9uite rounded,

with traces of blac% carbonaceous material The sands ha'e beenobser'ed as 'ery ne grained in parts and locally grade to silt

+ir ena!at F# : 1ir Bena%at formation consist of claystones,sandstones and siltstones

The claystones were light grey to light oli'e grey in colour, generally 'erysoft and amorphous, with accessory minerals such as pyrite, carbonaceousmaterial appearing as both spec%s and micro-laminae They weregenerally 9uite micaceous with rare pale bluish green chlorite 2a%esobser'ed in some beds "icrofossils were present in the formation and the

most recogni6able were foraminifera

The sandstones were predominantly identied as argillaceous sandstone,which consisted of clear to translucent 9uart6 grains, with some rare o;-white 9uart6 grains, pac%ed into a poor to moderately sorted clastsupported structure The pore spaces between the grains appeared tocontain argillaceous material with some additional degree of 'isibleporosity 4rains were generally 'ery ne to medium, with some rare thinbeds of coarser grained sands These coarser grains, most commonlyappeared as loose particles ha'ing being washed free when drilled Thegrains were predominantly sub-angular to sub-rounded and mostly sub-rounded in shape Sorting was generally poor to moderate, with occasional

well sorted 'ery ne sandstones appearing in thinly laminated beds Traceminerals of glauconite, fossil fragments and debris were also obser'ed

Siltstones are generally bloc%y to sub-bloc%y, friable, soft to rm andoccasionally 9uite stic%y when hydrated They display poor 'isible porositybut good inferred porosity due to water retention Siltstones also occur asthinly laminated beds within the shales and claystones, and cansometimes be 9uite calcareous 3are thin coal beds were identied inBeta-/, appearing as blac% to dar% brownish blac% in colour with an earthyluster They were rm and 9uite brittle, ha'ing a woody te5ture and a subbloc%y to bloc%y shape, occasionally splintering into sub-ssile fragments


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433

533

633

433

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433

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633

433

533

633

033 033 033 033

GR +)73GR +)73GR +)73GR +)73

Figure 1- - eta Fiel% stratigraphic cross section through (ell logs

eta-eta-eta-eta-

eta-eta- eta-

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1.1.0.Depositional niron#ent

The depositional facies of Beta )ield (1ir Bena%at )ormation* was

interpreted by utili6ing con'entional core data, cutting samples, log cur'epattern and borehole image log interpretation To begin, lithofacies weree5amined to determine the depositional facies The lithofacies wasclassied into si5 facies based on roc% te5tures, mineral composition,sedimentary structures and bioturbation intensity ()igure *


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Figure 1-4 ' "itho;acies Classia#ple ;ro# eta-

Based on facies association, Beta )ield is interpreted as shallow marine too;shore deposit &etails of the interpreted depositional facies are

described in the )igure

: .ower Shoreface, !ntensi'ely bioturbated 'ery ne grainedheterolithic sandstone facies are interpreted as being deposited in alower shoreface en'ironment 1 mi5ed association of 'ertical andhori6ontal trace fossils are indicati'e of a medium to low energy marineen'ironment

The presence of medium-grained sandstone (particularly at the top of ?-@A0* is interpreted as the result of a transgressi'e ra'inement thatrewor%ed the upper part of the sand, which impro'ed the reser'oir9uality

/ ;shore Transition, ?oophycos ichnofacies obser'ed in this lithofaciesis indicati'e of a low energy marine en'ironment Therefore, part of thebioturbated mudstone and laminated shale is thought to ha'e formed inan o;shore transition en'ironment

@ ;shore, The massi'e shale facies is interpreted as being depositedin an o;shore en'ironment ery few storm e'ent deposits and?oophycos ichnofacies are indicati'e of a constant sedimentation rate ina low energy marine en'ironment

Figure 1-6 - Interprete% se?uence o; surroun%ing eta Fiel%

)rom the image log interpretation, the o'erall deposition setting isconsidered to be a shallow marine low angle clastic ramp, probablysloping to the south based on bidirectional N-S tidal currentsinterpreted from minor cross bedding found on the )"! log Thesediment pro'enance is interpreted from the north based on thestudy of other wells in the area The facies belts mo'ed up and

down this ramp in response to eustacy, with 'ery little if anytectonic control, as indicated by the 'ery uniform and highly


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correlatable nature of the sedimentary pac%ages, which also tendsto indicate that the main sands are continuous sheets throughoutthe eld

1.1..Petroleu# Syste#

Source an% $igration : 3egional studies indicate thathydrocarbons are deri'ed from se'eral di;erent source roc%s, )igure notably the lacustrine shales of the .ahat )ormation (oil-generating*, nearshore coals and coaly shales of the T1) (gas-generating*, and nearshore T1) marine shales (oil-generating* 1tthe basin centre, T1) can e5ceed up to D00m at "erang deep4eochem study at Beta-: well indicate that the T1) section has a

TC of between :-/

Charging and migration of this reser'oir was pro'en by the Beta-:disco'ery well .ateral migration is interpreted to be from the north

to northwest area Some local 'ertical migration would ha'eoccurred through the faults associated with the Beta Structure Thethic%ness of the source roc% 'aries depending on the position at thebasin

Reseroir : The main reser'oir in the Beta area is the 1ir Bena%at)m ()igure *

3eser'oirs comprise stac%ed nearshore marine sands, which ha'ebeen intersected in almost all wells drilled in Beta area There are'e main 1ir Bena%at reser'oir at Beta prospect (%nown as ?-@A0, 3-

:0, ?-870, ?-770 and ?-D70* 3eser'oir continuity is widespread atthe Beta structure E5cellent correlation of the reser'oirs occursbetween all four wells drilled in the Beta structure ()igure *

Trap :The trap component of the Beta Structure is a @-way dip,closed anticline that is bounded by NW-SE faults on the southernpart of the structure, and also di'ided by some smaller NE-SWe5tensional faults The trap formed during Pliocene-Pleistocenecompression 1 free water le'el has established the minimumtrapping conguration

Containment/Seal :Containment in the Beta Structure was rst

pro'en in the Beta-: well, where the intra 1ir Bena%at shales werefound to be good top seals for the 1B) reser'oirs


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Figure 1-5 - +ir ena!at Palaeogeography


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1.1.4.Play Concept

The 1B) play comprises of stac%ed nearshore marine sands in latecompressional faulted anticlines, sourced 'ertically from underlying .ahat(minimally present in Beta* and T1) shales and coals 1ll wells drilled in

the Centaury PSC ha'e encountered oil shows within the 1B) Specicallyin Beta the 1B) sands ha'e demonstrated commercially producti'e'olumes on the structural highs of the sand formations 1dditionally, theWest Berau, East #etaling and Tempino )ields ha'e pro'en oil in placewithin their 1B) sands

Figure 1-9 - Centaury PSC sche#atic play types

1.2. Geophisical InterpretationThis Plan of &e'elopment benets from the regional wor% detailed in thesection on the $istory of the Centaury PSC, together with the analysis ofwell and seismic data from within the PSC The predominant source of dataoriginates in the Beta disco'ery and appraisal wells

1.2.1.Seis#ic Data@ase

Se'eral legacy 'intages of /& seismic cross the Beta )ield While thesepro'ide a gross structural trend, 9uality is generally poor There are alsoma+or concerns related to the static solution for these lines The /007'intage seismic data ac9uired by mega Carigali gi'es a regionalCentaury PSC co'erage with good 9uality of seismic data, but it is only Flines (appro5 /-@ %ms line spacing* o'er Beta structure that gi'es limitedinterpretation 1t late /0:0 mega Carigali was ac9uired another :80%ms of /& Seismic lines which about = lines were inll at Beta area Theseare the grey and red lines shown in )igure lder 'intages are shown in

pin%


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4eophysics well control was limited to the Beta-: disco'ery well and thethree appraisal wells (Beta-/, @ G 8* The West Berau well (:F@=* issituated to the southwest on the same structure but no data is a'ailablefor this well 1 comprehensi'e logging suite e5ists for each of the Betawells $owe'er, signicant washouts compromise the 9uality of acousticlogs and hence the seismic-well tie 1 6ero-o;set SP was ac9uired in bothBeta-: and Beta-@ while the other Beta wells ha'e ade9uate chec%shotco'erage


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Figure 1-7 - eta Fiel% "ocation $ap an% Data@ase

1.0. eta Fiel% Seis#ic Interpretation

1.0.1.Aell Ties

Well ties were established for the four Beta-wells using the electric log andwell seismic (chec% shot G SP* data Spectral analysis was done for Beta-:, / and @ ()igure * and then simplied to a 3ic%er 80 $6 minimum phase(pea% onset corresponds to an increase in acoustic impedance - 3e'erseSE4* wa'elet This 3ic%er wa'elet was used in the generation of syntheticseismograms for the Beta wells


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Figure 1-13 - Aaelet e>traction - eta-2

&ue to areas of se'ere washout raw acoustic logs were unsuitable forsynthetic generation )ortunately, corrected logs were generated as partof a borehole stability study These were used to generate 6ero-o;setsynthetics for each well

The Beta-: e5ploration well was drilled near the crest of the structureWhile a SP was run in this well, a poor tie is achie'ed The syntheticseismogram was deri'ed using 3ic%er wa'elet, with a limited Hstretch and

s9uee6eH, a reasonable good match with the seismic is achie'ed

eta-

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Beta-/ was drilled downdip some 700m to the south of the structural crest,and was found to be 7m deep to prognosis 1 chec%shot sur'ey wasac9uired in the well 1 //ms bul% shift is re9uired to achie'e a good tie

The bul% shift suggests that there are issues with the static solution for theseismic in this areaBeta-8 was drilled prior to Beta-@ The main ob+ecti'e was to core the oilreser'oirs encountered in Beta-: The well came in :0 m updip toprognosis (I7m higher than Beta-: instead of 7m deeper* Jsing the 80$6 3ic%er wa'elet, the synthetic seismogram ties well with the seismic(07P1.0:7, )igure *

Figure 1-11 ' "ine 34P+"314 : eta 2* Seis#ic Aell Tie

Beta-@ was drilled to test the sealing capacity of a NNE-SSW fault thatdi'ides the structure !t intersected the reser'oir le'els some 7m deep toprognosis and only encountered oil at the ?-870 le'el Notwithstanding thesporadic poor hole condition, a good tie was achie'ed with SP andseismic line 07P1.0D8 ()igure *

Beta-Beta-8

R-13


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Figure 1-12 - "ine 34P+"36 : eta-0 Seis#ic Aell Tie

1 tuning thic%ness calculation has been done for the datasetK for thedominant fre9uency of 80$6 and a 'elocity of //00m>s gi'es a wa'elengthof 7Dm and a tuning thic%ness ( >8* of :8m This mean that the seismiconly can di;erentiate beds with minimum thic%ness of :8m1.0.2.Ti#e InterpretationBased on a re'iew of the acoustic response at the wells and the /007seismic data, three ma+or seismic mar%ers were chosen for eld-widemapping These correspond to the 3:8 (Top !ntra 1B)*, ?-770 (tight sand*and 3: (Base 1B)* These three seismic mar%ers represent the mostreliable mar%ers close to the ma+or reser'oir units (?-@A0, ?-870 and ?-D70, )igure * and being regionally e5tensi'e in both the wells and within

the seismic control3eser'oir le'els were not pic%ed directly as a consistent seismic charactercould not be established within the e5isting well control

Beta-

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Figure 1-10 - eta Aell Correlation ,(ith synthetic trac!

Beta- Beta- Beta- Beta-

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The shallowest mar%er pic%ed o'er the eld is the Top 1ir Bena%at)ormation !t is mapped as an angular unconformity within the rst :00 msof the data The pic% is compromised by low fold at this depth4enerally the three seismic mar%ers were laterally continuous pea%s Theseismic in crestal area is of slightly lower fre9uency than the 2an%s and insome parts of the sur'ey the surface seismic is degraded by near surfacestatics issues The ?-770 tight sand re2ection is higher amplitude and islaterally more continuous than the other e'ents and formed the basis forthe structural interpretation 3:8 (top !ntra 1B)* and 3: (base 1B)* ha'econtinuous pea% seismic re2ectance, but are not as clear as the ?-770tight sand These e'ents are less consistent in their seismic response but apic% has been established for all 1reas of lowest condence include thearea to the north of the Beta-:>8 wells (line 07P1.-0:7* and the crestalarea of line 07P1.-0:@&ue to the steep dips and commensurate poor migration of the /& data,signicant miss-ties are present in the dataset 1 pragmatic approach tothese has been adopted absolute 'alues of dip lines are always honored

abo'e the 'alues on the stri%e data where a discrepancy occurs

1.0.0.+ttri@ute +nalysis

1lthough as mention abo'e the calculated tuning thic%ness is :8m whichis some of the reser'oir are below the tuning thic%ness, the seismicattribute still can be generate to control the lateral distribution - 1ppendi5: static modeling (properties distribution*

The 4amma ray log was chosen due to the log can show the sand pac%agewhich is characteri6ed by negati'e amplitude )urther is the seismicattributes ie, amplitude, fre9uency and phase were crossplotting with 43log and founded the dominant fre9uency is the most appropriate attribute

to guide the spread laterally


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Figure 1-1 Cross Correlation Aell "og ,GR an% Seis#ic +ttri@ute,Do#inant Fre?uency

Figure 1-14 - Do#inant Fre?uency Seis#ic +ttri@ute $ap

:@8 Time Structure !nterpretationThe Beta structure is a NNW-SSE trending compressional anticline The

anticline forms in the hanging wall of a large re'erse fault to the SW Thisfault trend continues to the SE to the #ali Berau )ield The re'erse fault is


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limited to the west by a NE-SW fault 1 number of NNE-SSW trendinge5tensional faults splay o; the re'erse fault in what appears to be acomple5 response to de5tral transgression and cloc%wise rotation,associated with the NW-SE thrust fault The e5tensional faults di'ide theanticline into a series of rotated bloc%s, each of which sets up a small, faultdependent closure ()igure* The Beta )ield occupies an ele'ated grabenwithin this trend and a west-hading fault separates the main part of theeld from Beta-@ (although pressure data suggests that communicationbetween the fault bloc%s occurs* There is signicant uncertainty as towhether some or all of the faults on the structure lea%, but free waterle'els established during the appraisal program conrm that the structuralclosure is substantially larger than the closure based on the hydrocarbonsencounteredThese e5tensional faults are debated to be seal or lea%, from the+u5toposition it is possible to be seal Beta-@ compartment most li%ely tobe a lea%ing fault due to %nown from pressure data the )W. sits at similardepth West Berau compartment most li%ely to be a sealing fault die to

WB-: well is lies under Beta )W. and still producing oil

Figure1-16- Fault Pattern aroun% the eta Fiel%

The time interpretation generated structure framewor% that consist oftime structure maps of three seismic mar%ers and fault plane that used forfurther stage ne e5ample of time structure maps are seen below ()igure*


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Figure 1-15 - Top Intra +F ,R1 Ti#e Structure $ap1.0.4.Depth Conersion

Two (/* methods were hired to con'ert the time to depth structure map)irst is the simplest method use a trend line (e9uation* from wells thatpenetrated The second method is trending line calculated use #riggingE5ternal &rift "odel (#E&* 3egarding all Beta wells were located at thecrestal area, both techni9ues gi'es similar depth con'ersion at the crestalarea, the di;erences appears on the uncontrolled area - 2an% area

The rst methodK use a'erage 'elocity data from the wells ()igure * togenerate the trend for the depth con'ersion away from the wells

Beta-

Beta-

Beta-

Beta-


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Figure 1-19 - Ti#e s. Depth ;or the eta (ells

The second method is calculating the regression line using #rigging

E5ternal &rift (#E&* methods

Beta Time Depth Chart

Beta-: TWT

(s*

Beta-/ TWT

(s*

Beta-@ TWT


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Figure 1-17- D Interpolation : 8-443 Ti#e s Depth

The main di;erences of two depth structure output from both techni9uesare located at 2an% area, which is no well control 1t the crestal areawhere the oil accumulation the depth resulted similar

Figure 1-23 - 8-643 Depth DiBerences @et(een ?uation an% D#etho%s

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$ence the nal depth structure maps were calculating the a'erage depthfrom both methods

1.0.6.eta Fiel% Depth StructuresJnderstanding the layering of Beta structure and thin reser'oir, to createstructure maps at reser'oir le'el the depth con'erted seismic mar%ers andfault information (polygons* were imported into modelling pac%age and a@& structural model was generated By calibrating the seismic mar%erswith the well data a set of stratigraphic surfaces including all the mainreser'oir le'els could be generated !t is important to note that theresulting maps are only 'alid if the stratigraphy is conformable)inal depth structure map, as shown )igure to )igure below respecti'ely,

Figure 1-21 - 8-093 Depth Structure $ap (ith latest FA"

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Figure 1-22 - R-13 Depth Structure $ap (ith latest FA"

Figure 1-20 - 843 Depth Structure $ap (ith latest FA"

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Beta-

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1.. Aell Drilling Result

1..1.eta-1Beta-: was spudded on 8 "arch /00= and reached a T& of /@00 m #B(//ADm T&SS* on /8 "arch /00= in PreLTertiary )ractured Basement

The well disco'ered hydrocarbons with C/rich dry gas in a thin D meterbasal sand o'erlying basement and shallow light oil of the 1ir Bena%at)ormation (1B)* clastics The 1B) oil was identied as the primaryreser'oir in a forward sense

The sedimentological interpretation of the 1B) section and 4umai sectionof Beta-: represents two main progradational se9uences with 2oodinge'ent (parase9uence set boundary* at D70m The sands are arranged as aseries of stac%ed parase9uences within the progradational se9uences!ndi'idual parase9uences range in thic%ness from /7 m to =7 m Eachse9uence comprises o;shore muds prograding to low energy sandyshoreface from :/A:m L D70m and D70 L 8DA m The progradationcorresponds to a facies change from highly laminated o;shore muds to the

shaly and bioturbated sand facies Sands are interpreted as mi5ed lowerand middle shoreface, while heterolithics associated with laminated sandfacies are interpreted as tidal sand 2atsPalaeocurrent analysis indicates that within the shoreface deposits of the1B) in both the wells the a6imuth of sand beds and cross-bedding of theshoreface deposits gi'es an o'erall south easterly to southerly directionindicating the palaeoshoreline to be NE-SW 'arying to ENE-WSW1B) sands porosity 'aries from :D to /@ Water saturation is D0 to =7for oil reser'oir

1..2.eta-2Beta-/ was drilled as a down2an% appraisal well to establish the oil-water

contacts of the three oil bearing sands production tested in the Beta-:wellBeta-/ intersected the 1B) sandstone reser'oirs appro5imately /@mdowndip of the original Beta-: disco'ery well The top of ?-@A0 and ?-870were appro5imately //m downdip from Beta-: while the ?-D70 wasappro5imately /Fm downdip showing the southern 2an% is steeper thanpredicted 1n e5cellent correlation e5ists between the Beta-: and the Beta-/ appraisal well and, as such, reser'oir continuity has been establishedSand porosities range from :7 to /@

1..0.eta-

Beta-8 was drilled as a crestal well some :=7m NW of Beta-: well Themain ob+ecti'es were to obtain whole core and )"! image logs forcalibration and to complete the well as a potential producer The wellcame in some :0m shallow to prognosis (I7m higher than Beta-: insteadof 7m deeper*1n e5cellent correlation e5ists between the Beta-8 to Beta-: disco'ery welltogether with Beta-/1n coring program within @ main oil inter'al was done for

@=/7 L @A87 m"& with 7A reco'ery

@A87 L @F/ m"& no reco'ery of hydrocarbon sand

8@D7 L 8DD m"& 6ero reco'ery

D/A7 L D@=7 m"& no reco'ery of hydrocarbon sand D8@@ L D8F m"& with F= reco'ery


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The main reason for this poor reco'ery is due to failed mechanical corecatcher 1lso, the formation is too soft and washed out from the corechamber while drillingThere are no other signicant obastacles while drilling the Beta wells 1llwells were shallow, and no o'erpressure or signicance temperaturegradient change was obser'ed The only problem occured while drillingthe wells is the presence of 4umbo as the intra shale facies of 1ir Bena%at

That swelling clay slower the drilling operation of Beta appraisal wells,hence it is suggest to impro'e the mud system use for future drilling willhelp resol'e the problem

1...eta-0Beta-@ was drilled to test the sealing capacity of a NNE-SSW fault thatdi'ides the structure The result of the drilling show that the compartmentbetween Beta-@ area (Central* and Beta-:,/,8 (West* has a pressureconnection for the reser'oirs !t is tested using the "&T and resulted that

the water gradient line up in the same trend between this / compartmentThe Beta-@ well intersected the sandstone reser'oirs appro5imately /0mdowndip of the original Beta-: disco'ery well The top of ?-@A0 and ?-870were appro5imately :8-:Am downdip from Beta-: while the ?-D70 wasappro5imately @@m downdip f the three ma+or reser'oirs, only ?-870resides abo'e the )W. at depth 887m T&SS 1n e5cellent correlatione5ists between the Beta-: disco'ery well and the Beta-/, 8 and @ appraisalwells as such that reser'oir continuity has been established Sandporosities range from := to /@

1.4. Core Description & +nalysis

1.4.1.Si%e Aall CoreThe sidewall cores ha'e been ta%en at Beta-:, Beta-/, Beta-@ and Beta-8!n Beta-:, total of @0 sidewall cores (SWC


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mud system to a more saline 2uid to help reduce water in'asion into theformation Ne'ertheless the cores still drilled too 9uic%ly indicating softformation which meant the formation had been a;ected by the 2uidin'asion despite higher salinities !n total only two partial cores werereco'ered from the run which those samples are not the formation roc%s!n Beta-8, the "SCT tool was run only in the A-:>/ hole The "SCTprogram called for two runs whereby the rst run would attempt to corethe rm formations with the second run attempting what were belie'ed tobe softer formation in the ?870 sands Jnfortunately the reco'ery onsurface was 'ery poor with only one fully reco'ered core and F partialfragmented cores obtained The second "SCT run was cancelled

1.4.2.Conentional CoreThe core description was conducted by PT Corelab !ndonesia and the resultwas incorporated with the other analysis to support the o'erall interpretationof facies, sedimentology and depositional en'ironment605.3 ' 67.0 #eters

&escription This inter'al is composed of 'ery ne- to ne-grained sandstonethat is mainly bioturbated and burrowed !dentied burrows includeOphiomorpha, and possibly Rosselia, Teichichnus, and Zoophycus Planarbeds and ripples are locally preser'ed Contacts between depositional unitsare scoured The sandstone is tightly cemented with calcite between D88=and D87@@ meters Bioclasts are mainly pelecypods1'erage porosity is /87F (range O A0@ L /FA@* and a'erage air#lin%enberg permeability (#inf* is :// md (range O 000@ L :08 mdK medianO 7D7 md* 1'erage grain density is /DD g>cc (range /D@ L /DF g>cc*629.4 ' 605.3 #eters&escription Core reco'ery was 'ery poor in this inter'al 3eco'ered materialis clay-rich, unlithied, and contains no 'isible sedimentary structures or

burrows !t does not resemble any other portion of the described cores056.42 ' 059.79 #eters&escription This inter'al is composed mainly of thinly interlaminated shaleand 'ery ne- to ne-grained sandstone "edium-grained sandstonebetween @==/ and @==@7 meters is less common 4radational to scouredcontacts separate depositional units !nterlaminated sandstone and shale arerippled, with clay drapes, to hea'ily bioturbated Bioclasts include pelecypodsand benthic foraminifera The medium-grained sandstone bed is oil-stained,bioturbated to cross bedded, with scattered bioclasts and shale rip-up clasts1'erage porosity is /7@@ (range O /08A L @7/=* and a'erage air#lin%enberg permeability (#inf* is @F7 md (range O D@@ L 8F7D mdK median

O 87/ md* 1'erage grain density is /D8 g>cc (range /7F L /DF g>cc*054.64 ' 056.42 #eters&escription This thin inter'al is composed medium-grained sandstone that isoil stained Jnoriented shale rip-up clasts indicate that the sandstone hasbeen bioturbated S%eletal fragments include pelecypods The sandstone iswea%ly to moderately lithied, calcareous, and has a scoured basal contactwith underlying sediments1'erage porosity is @0:D (range O /:0: L @870* and a'erage air#lin%enberg permeability (#inf* is 7D: md (range O 078A L :@7: mdK medianO D@8 md* 1'erage grain density is /DA g>cc (range /D7 L /=0 g>cc*052.4 ' 054.64 #eters&escription This inter'al is comprised of argillaceous sandstone that is

bioturbated to rippled, with millimeter-thic% sandy laminae and clay drapesThese sediments are relati'ely uniform in this inter'al


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1'erage porosity is :FF@ (range O :D=A L /0/@* and a'erage air#lin%enberg permeability (#inf* is 0:8@ md (range O 0007 L 07=/ mdKmedian O 0:80 md* 1'erage grain density is /D/ g>cc (range /D: L/D8 g>cc*

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