Regionai seismostratigraphic study of the Tembungo area, offshore West Sabah

Transcription

1 Gel. Sc. Malaysia, Bulletin 32, Nvember 1992; pp Reginai seismstratigraphic study f the Tembung area, ffshre West Sabah SMAL CHE MAT ZN Petrnas Carigali Sdn. Bhd. Abstract: The Seism-stratigraphic study f the Tembung are, ffshre West Sabah prvided a depsitinal mdel fr the hydrcarbnbearing Stage VD turbidite sequence in the Tembung field. The mdel suggests that the turbidite sequence, characterised by an blique seismic reflectin pattern was depsited in a sedimentary bypass system tract as a result f wrench-related uplift f the Bunbury-St. Jseph area. The uplifted and subsequent remval f Stage VC-V A castal fluvimarine and lwer castal plain sediments during the Shallw Reginal Uncnfrmity fllwed by active Stage VD deltaic prgradatin prvided a huge vlume f sediment input t the cnfined Tembung depressin beynd the cntempraneus shelf edge. The deltaic sediments with gd reservir and surce rck prperties have cntributed t the hydrcarbn ptential f Stage VD turbidites in the Tembung field. NTRODUCTON The Tembung field which was discvered by Ess Prductin Malaysia nc. in 1971, is lcated ffshre West Sabah, 75.6 km t the NE fkta Kinabalu, EPM prduced hydrcarbns frm this field frm 1974 t 1986 and was then relinquished t PETRONAS which in tum appinted PETRONAS Carigali as the peratr. Carigali is nw ding the wrk-ver and field appraisal studies. The Tembung prductin blck is brdered by the SB 1 Explratin Blck t the suth and by the SB 2 Explratin Blck t the nrth (Fig. 1). PETRONAS Carigali is the partner in bth SB 1 and SB 2 explratin blcks. This reprt intends: OBJECTVE 1. T illustrate the established crrelatin between the il prducing turbidite sequence in the Tembung field and its prvinance, 2. T discuss the sedimentatin and tectnic histry f the study area, 3. T discuss the depsitinal mdel f the Tembung turbidite sequence and the hydrcarbn charging scenari f the field. Paper presented at GSM Petrleum Gelgy Seminar 1991

2 115 OO'E. 118 '. 117 '. ' OO'E. SB1 SABAH SCALE LEGEND.' -----======-----======j G.. Field, 5 1Km (2) 11 Field, Figure 1: Lcatin map f the Tembung il field.

3 REGONAL SESMOSTRATGRAPHC STUDY OF THE TEMBUNGO AREA, SABAH 111 STUDY TECHNQUE Reginal seismic lines cvering the Tembung field area were selected and interpreted. The fllwing seism-stratigraphic techniques were applied in the seismic interpretatin. Sequence bundaries and age determinatin The sequence bundaries were btained frm the well data drilled in the study area (Table 1). By transferring these sequence bundaries t seismic sectins, the mappable reflectrs representing the sequence bundaries were picked. The picked bundaries were further checked by crrelating them t the uplifted area where they nrmally became ersinal uncnfrmities. Once the sequence bundaries were cnfidently picked, the crrelatin were made thrughut the study area. The age f the sedimentary sequences culd then be inferred frm the SSB stratigraphic scheme (Fig. 2). Seismic facies and depsitinal envirnment interpretatin The distinctin f the varius seismicfacies based n the reflectin cnfiguratin was calibrated with the interpreted depsitinal envirnments and lith facies at the well lcatin. The depsitinal interpretatins made in this reprt were based n these calibratins and ther reginal data frm ffshre west Sabah. Structuratin Histry SESMO-STRATGRAPHC NTERPRETATON The Tembung-Bunbury area has undergne intervening phases f tectnic uplift and wrenching. Tw majr uplifts f reginal significance have resulted in the frmatin f the Deep Reginal Uncnfrmity (Base Stage VA) and Shallw Reginal Uncnfrmity (Base Stage VD) in early Middle Micene and early Late Micene times respectively. Table 1: Stage bundaries, in depth and tw-way time btained frm the well results in the study area. BASE BASE BASE BASE BASE WELL NAME STAGE VA STAGEVB STAGEVC STAGE VO STAGE VE Bunbury-2 6,65' (1.6) 875' (.55) S. Furius-1-6,524' (1.9) 4,659' (1.4) 2,689' (.85) 499' (.25) T embung ,44' (1.75) 2,681' (.85) Erb West ,4' (1.85) 3,511' (.95)

4 112 SMAL CHE MAT ZN!! PLANKTON K z:.. ZONES 5 TAGE 5 i.. i z u ZONES PAL YNO LOGCAL 5A BAH B! z K.. %,. FORAM CN g : X.., NN 21>- Z',.., cr N, r-!u 5712 E TL HOR lr:" 7 NN 11 11'11.., 7... cr 5., :1611!U NN ' SN 17 C 1 N H NN , r,'di: S. R. U N NN 1 N 14 " N '5 NN.1 ". Z N '.., NN 7 91' A,S '" S N" U. NN N 1 2 '11 N 9 NN - L.\l - D.R.U r '11 N NN SN 7 S : 1 N 11 cr NN zz.., 2S N 4 2S, NN 2S S.., ad.., NP 2S 121 Z N J.., cr 27 ][ U... S2 Z Z Z - NP C!). Z' SN 23 QUATERNA G NN. SOO N Z2 HOR 1 1. NN.. 2.., 2 N 21 NN SOO.., Z cr 3 NN F J U N r- 5.4 HOR n 4 :.N ' NN ' 141. N NN S l. > SN 2 11 >- 121 J t... S a:: cr NP 2S 52 '" 32 Figure 2: West Sabah stratigraphic scheme. 14

5 REGONAL SESMOSTRATGRAPHC STUDY OF THE TEMBUNGO AREA, SABAH 113 Ersins during these tw uncnfrmities and ther intermediate uncnfrmities resulted in the depsitins f the Stages V A-VC sedimentary sequences in thetembung-bunbury area (Fig. 2). tis inferred that the shelf-edge during Stages V A-C times was lcated t nrth f the Bunbury area. Wrenching and blck rtatin in the Bunbury-St. Jseph area ccurred in the Stage VD times (Fig. 3). Ersin in the uplifted area prvided a tremendus amunt f sediments depsited in the Tembung depcentre. Cmpressin and wrenching in the Stage VD time frmed the Tembung structure.,/ / / :) --\-""""1 s.wmend / / / / / /./,/ /" d s. Furiu_s C!2""!- Figure 3: Tectnic map shwing the lateral extent f pst SRU sinistral wrench faul ting in the Banbury - St. Jseph area.

6 114 SMAL CHE MAT ZN Sedimentatin Histry The depsitinal histry f this area culd be divided int three episdes; (1) Depsitin prir t thefrmatin f Shallw Reginal Uncnfrmity (SRU). (2) Depsitin in tpgraphic lw during the SRU times. (3) Depsitin after the structuratin ftembung. Pre Stage VD Sequences The nature f the Stage VA, B and C sediments in the St. Jseph-Bunbury area culd nt be cnclusively analysed since the area was severely wrenched and rtated. Hwever, their nature culd be bserved in the suth Furius area and ther inbard areas including Saracen Bank (Figs. 4 & 5). n the Saracen Bank and Suth Furius areas, Stage VA sequence is characterized by thick tpset packages f Lwer Castal Plain and CastaVCastal Fluvimarine envirnments grading int a clinfrm sequence f slpe what envirnment twards the nrthwest. These packages are verlain by lw angle clinfrm packages illustrating the rapid transgressive event at the end f the Stage VA time. Stage!VB represents the maximum transgressive perid in ffshre West Sabah (Bl & van Hm, 198). n the Saracen Bank area, this sequence is characterized by bttmset packages f Hllmarine t Bathyal envirnments. Stage VC clinfrm packages verlying the Stage!VB bttmset, represents the start f verall regressive perid in this area. The clinfrm packages are verlain by a massive nrthwest tpset utbuilding (Fig. 6). A similar nature f sedimentatin fr the Stage VA, B and C sequences was bserved in the Suth Furius Area and within the preserved wrenched blck in the Bunbury Area The apparent thickness f the three sequences is in excess f three secnds. This represented mainly by tpset packages grading t clinfrms in the dwndip psitin. The prximal ptins f these sedimentary sequences were erded. Depsitins ftke Stage VD Sequence a) Lwer Stage VD sequence Uplift and ersin in the Erb West area and the area t the west f Bunbury resulted in peneplenatin f these areas. This prvided sediments fr depsitin f the basal Stage VD sediments directly int the Tembung-Bunbury basin. This basin was wrenched Geft lateral mvement) and rtated in the early stage fsru. Massive ersin f the wrenched and uplifted Bunbury area, cutting int tpsets f the Stages VA,!VB and VC prvided a large amunt f sand-rich sediments feeding the turbidite system n the flank f the emerged area (Fig. 7). These sand bdies were blanketed by the Middle-Outer Neritic shales.

7 lis OO'E. 118 'E. 111 acre. p, Balambang P P.Malawall <\/ SABAH OO'N. LEGEND AT D HON/AT!:J HMN SCALE HN COL s OOKm.! LCP Figure 4: Palefacies develpment f the Stage VA Sequence.

8 115- OO'E. 118 OO'E_ 117 OO'E. O-OO'E. 7-'H. p_salambangpn - Sangg. P.Maawal' <c:> SABAH e-oo'n. SCALE.OOKra =======' c:====1 LEGEND -D BAT -HON/BAT HN D HN/HUN D COL LCP Figure 5: Palefacies develpment f Stage Ve Sequence.

9 ve seismic facies seismic facies Figure 6: Depsitin f the Stage VA,!VB and Ve Sequences.

10 118 SMAL CHE MAT ZN Figure 7: Wrench faulting pst S.R.D. frmatin. Seismically, the lwer Stage VD sequence is characterized by lw angle blique clinfrms (Figs. 8 and 9). The tpset unit f this package is nt preserved. This suggests that the tpset packages were nt develped and/r was erded and redepsited beynd the cntempraneus shelf-edge. Calibratin with Tembung 2 and 4 wells indicate that the lwer Stage VD reservir package ccurring within the basal c1infrm (fndfrm) facies. This clinfrm package cnsist f mainly marine shales. Theretically the blique c1infrm cnfiguratin represents a prgradatinal sedimentatin with high terrigeneus supply within a high energy envirnment during still stand r slw rising sea level. The fndfrm part f blique facies unit may cntain turbidite depsit (Sangree, 1977). Observatin f bth well results and seismic facies suggest that the Lwer Stage VD reservir sequence in the Tembung field were depsited as a turbidite sequence in a relatively shallw water envirnment by the still stand sedimentaryby-pass prcesses within a semi-cnfined basin. The basin is bunded by a lcal high t the nrth and by a synsedimentary grwth fault t the west (Fig. 1). This prduced a nrth-westward prgrading lateral discntinuus sand sheets f the Lwer Stage VD sequence. Therefre, the reservir crrelatin between the Tembung 2 and 4 wells shuld be crrelated as shwn in Figure 13 instead f Figure 12. b) Upper Stage VD Sequence The upper Stage VD sequence is characterized by a prgrading shallw marine sequence (Fig. 14). The tpset package prgraded ver the Tembung area and gradually graded int shingles and clinfrms, several kilmetres nrth f the structure. Wireline lgs frm the Tembung 2 and 4 wells indicate that the upper

11 REGONAL SEl SMOSTRATGRAPHC STUDY OF THE T EMBUNGO AREA, SABAH 119 UJ (J) C>..n c C>., c " Lf) f.d " f.d, Lf)..n.1:. L{) til <l,... as be ;j..c S <l E< C ;j..c as X1 <l...c:.s <l '-' <l ;j " Q) if] <l be as if] <ii '" as..c <l...c: "-< a Q) as S... <8.S u.- Q) ;j " :: Q)...c: be....c: '".- '-' Q) '" '-' 's ''" :; '" Q C' ci:i Q) '"'... C N M S-:J O::)3S 3 la11 1

12 12 SMAL CHE MAT ZN Figure 9: 3D seismic sectin shwing the dwn lap reflectr terminatins f Stage VD Sequence nt SRU in the Tembung field.

13 DELTA PROGRADATON -;--:-._ -- Figure 1: Depsitinal mdel f the Tembung turbidite.

14 .----_':::"""-,,'.'-'-' _-'--_-"!:! :,. t:..::..=" --"'",-;4::..=' '...:':..::";:.-t"-"..:.'...:'::..hi. ;=-"'!..'---...:':::"';.t.:."'!..'..!''!''':;,'o'!..(. f -en p t"" t (') :i r.zj.. t z Figure 11: W ell lcatin f the Tembung 2 and 4 in the Tembung field,

15 REGONAL SESMOSTRATGRAPHC STUDY OF THE TEMBUNGO AREA, SABAH 123 TEMBUNGO 2 TEMBUNGO 4 BASE STAGE VE Carbnate COF-FN COF-FN., c.. Figure 12: Lithstratigraphic crrelatin ftembung 2 and 4.

16 TEMBUNGO 2 TEMBUNGO 4 "'" -+---; BASE STAGE VE Carbnate COF-FN Figure 13: Time-stratigraphic and facies crrelatins f the Stage VD and VE Sequences in the Tembung field.

17 REGONAL SESMOSTRATGRAPHC STUDY OF THE T EM BUNGO AREA, SABAH 125 en Q) - u E en Q) en U--... C13 ' E Q) U ::l '- en -- E Q) :.= en.. c - u.- Q) C13 OUen- </ '.' Q)... 'J '.' PO<$> - en Q) Cll "C ai u Cll ::s - Cll U) bd <l...,. U)...,:3 : rjl p.. Cll Cl.-4 QJ Q) en c.. t2

18 126 SMAL CHE MAT ZN Stage VDpackage cmprises a carsening upward sequence which intum similarly suggest a prgradatinal depsitin. Bistratigraphic studies indicated that this unit was depsited in a shallw envirnment (COL-HN). This ccurred after the basin was filled by the lwer Stage VD sequence. Pst Stage VD Sequences The Stage VE represents a shallw marine basin infills depsit between the tw highs, Tembung and Bunbury. The she1f-edge during this depsitinal perid prgraded further nrthward, beynd thetembung structure. Stage VE carbnates unit was penetrated by mst f the wells in the Tembung fields, suggesting that the Tembung area was a high, away frm clastic influx, and favurable fr carbnate depsitin during the Stage VE times. GEOCHEMSTRY AND HYDROCARBON GENERATON Gechemical studies cnducted n the surce rcks and crudes frm the Sabah and Sarawak basins by several wrkers includingawang Sapawi (199), suggested that mst f the hydrcarbns in this regin were derived mainly frm land-plant surce rcks. N majr cntributin frm marine surce has s far been reprted. These studies als cncluded that the mst prlific area fr the develpment fland-plant surce materials is restricted t prximal depsitinal areas such as Lwer Castal Plain and Castal Fluvimarine envirnments. The surce rck quality and quantity deterirate with distance frm pale-castline (Fig. 15). Based n this cncept, the Tembung turbidite sequence which derived frm the prximal depsitinal sediments, can be expected t cntain substantial amunts f gd surce and reservir prperties brught dwn beynd the cntempraneus shelf-edge by the turbidity current. Surce rck data frm the Tembung field, i.e. frm A-6 well, shwed that the Lwer Stage VD Sequence is rich in surce rck. The Ttal Organic Carbn in this interval ranges frm 1. t 5 percent (Fig. 16). Maturity prfile studies, bth frm Vitrinite Reflectance Equivalent and Lpatin indicated that the Lwer Stage VD Reservir Sequence n the Tembung structure is in early maturity (Figs. 17 and 18). This sequence attained the il generatin windw in the deepest part f the Tembung basin (Fig. 19). The gas chrmatgraphy mass spectrmetry (GeMS) results fr bth crudes and extracts frm the LwerStageVD Sequence shwed the presenceftetracyclic, resin and lenane (Fig. 2). This suggested that the crudes and extracts f the Tembung prducing sequence are land-plant rigin. Althugh the avrulable GCMS data n extracts and crudes are nt identical, they seem t be f a similar rigin. Furthermre, extracts frm the underlying Stage VC Sequence shwed that this stage is f marine sediments (Fig. 21).

19 4'11. WO LEGEND N J"7':l L..:..:...:J AUA wrrw HUnVn.Y ii&+! CO/KrlrlATOf OF O"... C MTTY t Figure 15: Land-plant rganic matter distributin and maceral cmpsitin f the recent Baram delta Cafter Nagtegaal, 1989),

20 .. J z 5 a LTHOLOGY Ot ORGANC CARBO % OF ROCK 3 O'D 711 z a a 1, e HYDROCARBONS PPM OF ROCK EXTRACT % OF ORGANC CARBON f a: e 1:'" 111:'1!,le 2 3:' e 1 '.. > OL LKELY 11.1 MATURATON LEVEL OF RCHNESS wflj '" ORGANC MATTER eli.", f OL PRONE GAS PRONE i!! a t - i en MATUA TY HYDRO MATURTY ttyda c CARBON CAABON _ LEVEL PRODUCT LEVEL PRODUCT 2 " :':: t"'l;;,-c;';. -. i 71-]-_. --- '-== _.wr.._ "iw/.ly\'i!! - 11!UF- Wi. e. --- r-=t=--- t ib cz MATURE 15 :b- :.--j _ WATUR MNOR GA. r C':l ::t: t.zl f - LL 1 LEAN FAR jm;rae LEANAVER AVE u.s.pc)m:... OL-PAONE Gmln geal las Ll1HOLOOV BORE' SYMBOLS Figure 16: Surce rck data f Tembung A-S.

21 REGONAL SESMOSTRATGRAPHC STUDY OF THE TEMBUNGO AREA, SABAH' i J. J. c" :..., ( BASE VE 3 - a. w c 5 - \ \ \. BASE VD Upper - :: -:;:::: e \ "\ BASE VD Lwer VR (%) Figure 17: Depth vs VR f Tembung-4.

22 is Ti Me (H Y. ).., L._..!.. -.-,..l._.l''''t-...l",,....l.-.--h '!1,-_u,L.,..J...,.., l"'lijt".l_..j---'l ' " 11:1.'".,,' '''':' Lt '...,_ & ' ' '! "..,...' ""_"". "-,"_ \ t ( \ 111 i '\ \, /'.,,",..._ ,W"...,..._. '---a ' '",. j... ',:,.=...,..., " '! --.,"..,,',.' l \. / ",..,... ii, V -"'., ", i, " ' ''''',i"-,w,,_ ",,'''',' " l i'., i --,a.., i" - ' " " ",", ' J, '/,, ' ', ', \,,,' '11 '11 '! " ' \ 1, ', 11111/" " ',;,/ i,- " l --_.., "-" G G BASE D VD M BASE VC 6 E P T H... C: en a:: i!!: r (") ::: l"l z Figure 18: Maturity mdelling at the Tembung-2 lcatin.

23 t'l (5 en t'l Ul a:: S ]) E C5 en p 1:1 T H -< "'l ::z:: t'l ;? a:: ttl c:: 8 r.n 6; <:.&:l Figure 19: Maturity mdelling at the nrthern flank f the Tembung structure.

24 TEMBUNGO A-17 C C29 Oleanane 5D Tetracyclic R R 1 TEMBUNGO CRUDE OL 1 TEMBUNGO-2 686' C29 C3 5 Tetracyclic Oleanane 1 EXTRACTS FROM STAGE VD Figure 2: GeMS chrmatgraphs ftembung crude and extracts frm Stage VD Sequence.

25 TEMBUNGO A C C29 Oleanane 5 Tetracyclic R R 1 TEMBUNGO CRUDE OL TEMBUNGO-2 764'-767' R R 1 EXTRACTS FROM STAGE ve Figure 21: GCMS chrmatgraphs f Tembung crude and extracts frm Stage VC Sequence.

26 134 SMAL CHE MAT ZN Therefre, it is strngly believed that the il in the Tembung field were derived frm the intrafrmatinal surce f the same sequence in the Tembung dwn-flank area. CONCLUSONS Seism-stratigraphictechirlques were successfully applied, in delineating the sequence bundaries f SSPC stratigraphic scheme t the Tembung and the adjacent areas, and in establishing the depsitinal mdel fr the Micene Turbidite sequence in the Tembung field. The Tembung il prducing turbidite sequence is characterized by an blique clinfrm seismic reflectin pattern. This suggests that the turbidites were depsited in a sedimentary bypass system tract. S far, n turbidite prspect seen in this regin seems t be f a similar nature t that f the Tembung stage VD turbidites. The Tembung turbidite sequence is,unique with respect t its favurable hydrcarbn habitat in that the ersinal prducts f stage V A-VC lwer castal plain/castal fluvimarine sediments transprted dwn-slpe and depsited as turbidites cntained gd surce and reservir prperties. These turbidites were buried t depths with the il generatin windw in the flank areas f the Tembung structure. REFERENCES AWANG SAPAW AWANG JAML, MONA LZA ANwAR & ERC SEAH, P.K., Gechemistry f selected crude ils frm Sabah and Sarawak. Gel. Sc. Malaysia Bull., 28, BOL, A.J. AND VAN HOORN, B., 198. Structural Styles in Western Sabah Offshre. Gel. Sc. Malaysia Bull., 12, NAGTEGAAL, P.J.C., A Century f Petrleum Explratin in Sarawak and Sabah. Paper ASCOPE, Singapre. SANGREE, Seismic stratigraphy and glbal changes f sea-level. AAPG Mem. 26. Manuscript received 25th September 1992