In Situ Stress and Stress Regime in

In Situ Stress and Stress Regime in

the Offshore Part of the Northeast Java Basin

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INTRODUCTION

.QRZOHGJHRI in situ stress is very important in hydrocarbon exploration to the production stage. It ZLOOSURYLGHDEHWWHUXQGHUVWDQGLQJRISUHVHQWGD\

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UHVHUYRLU GUDLQDJH DQG IORRGLQJ IOXLG IORZ LQ IUDFWXUHGUHVHUYRLUVK\GUDXOLFIUDFWXULQJDQGIDXOW seal breach.

7KH RQVKRUH SDUW RI WKH 1RUWKHDVW 1( -DYD Basin is tectonically located in a very active region )LJXUH+RZHYHUWKHUHLVVWLOOOLWWOHNQRZQDERXW the LQ VLWX VWUHVV LQ WKLV EDVLQ 7KH in situ stress FRQVLVWV RI WKUHH FRPSRQHQWV LH YHUWLFDO VWUHVV PLQLPXPKRUL]RQWDOVWUHVVDQGPD[LPXPKRUL]RQWDO VWUHVV7KLVVWXG\DLPVWRDQDO\]HWKH stress regime DQGWKHPDJQLWXGHRIWKHVHVWUHVVHVLQWKHRQVKRUH SDUWRIWKH Northeast Java Basin on a regional basis XVLQJGDWDIURPWZHOYHZHOOV)LJXUH

ABSTRACT - ,Q VLWX VWUHVV LV LPSRUWDQW LQ WKH SHWUROHXP LQGXVWU\ EHFDXVH LW ZLOO VLJQL¿FDQWO\ HQKDQFH RXU XQGHUVWDQGLQJRISUHVHQWGD\GHIRUPDWLRQLQDVHGLPHQWDU\EDVLQ7KH1RUWKHDVW-DYD%DVLQLVDQH[DPSOHRI DWHFWRQLFDOO\DFWLYHEDVLQLQ,QGRQHVLD+RZHYHUWKH LQVLWXVWUHVVLQWKLVEDVLQLVVWLOOOLWWOHNQRZQ7KLVVWXG\

DWWHPSWVWRDQDO\]HWKHUHJLRQDO LQVLWXVWUHVVLHYHUWLFDOVWUHVVPLQLPXPDQGPD[LPXPKRUL]RQWDOVWUHVVHV magnitude and orientation, and VWUHVVUHJLPHLQWKHRQVKRUHSDUWRIWKH Northeast Java Basin based on twelve wells GDWDFRQVLVWRIGHQVLW\ORJGLUHFWLQGLUHFWSUHVVXUHWHVWDQGOHDNRIIWHVW/27GDWD7KHPDJQLWXGHRIYHUWLFDO 6_v DQG PLQLPXP KRUL]RQWDO 6_hmin VWUHVVHV ZHUH GHWHUPLQHG XVLQJ GHQVLW\ ORJ DQG /27 GDWD UHVSHFWLYHO\

0HDQZKLOHWKHRULHQWDWLRQRIPD[LPXPKRUL]RQWDOVWUHVV6_hmaxZDVGHWHUPLQHGXVLQJLPDJHORJGDWDZKLOHLWV PDJQLWXGH ZDV GHWHUPLQHG EDVHG RQ SRUH SUHVVXUH PXGZHLJKW DQG WKH YHUWLFDO DQG PLQLPXP KRUL]RQWDO VWUHVVHV 7KHVWUHVV UHJLPH ZDV VLPSO\ DQDO\]HG EDVHG RQ WKH PDJQLWXGH RILQ VLWX VWUHVV XVLQJ $QGHUVRQ¶V IDXOWLQJ WKHRU\ 7KH UHVXOWV VKRZ WKDW WKH YHUWLFDO VWUHVV 6_v LQ ZHOOV WKDW H[SHULHQFHG OHVV HURVLRQ FDQ EH GHWHUPLQHG XVLQJ WKH IROORZLQJ HTXDWLRQ 6_v ] ZKHUH LV LQ SVL DQG ] LV LQ IW +RZHYHU ZHOOV WKDW H[SHULHQFHG VHYHUH HURVLRQ KDYH YHUWLFDO VWUHVV JUDGLHQWV KLJKHU WKDQ RQH SVLIW 6_v ] 7KH PLQLPXP KRUL]RQWDO VWUHVV 6_hmin LQ WKH K\GURVWDWLF ]RQH FDQ EH HVWLPDWHG DV 6_hmin ], ZKLOH LQ WKH RYHUSUHVVXUHG ]RQH 6_hmin ] 7KH PD[LPXP KRUL]RQWDO VWUHVV 6_hmax LQ WKH VKDOORZDQGGHHSK\GURVWDWLF]RQHVFDQEHHVWLPDWHGXVLQJHTXDWLRQV6_hmax ]and S_hmax ], UHVSHFWLYHO\:KLOHLQWKHRYHUSUHVVXUHG]RQH6_hmax ]7KHRULHQWDWLRQRI6_hmax LVa1(6:ZLWKD VWULNHVOLSIDXOWLQJ stress regime.

Keywords Northeast Java Basin, in situ stress, stress regime.

SCIENTIFIC CONTRIBUTIONS OIL AND GAS

Reserach and Development Centre for Oil & Gas Technology

“LEMIGAS”

-RXUQDO+RPHSDJHKWWSZZZMRXUQDOOHPLJDVHVGPJRLG

,661H,661 VOL. 44 NO. 2, AUGUST 2021

DATA AND METHODS A. Geological Setting

1. Tectonic and Stratigraphy

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7KHVWXG\DUHDLQFOXGHV5HPEDQJ=RQH5DQGX EODWXQJ=RQHDQG'DQGHU+LJK7KHGHHSHVWSDUWRI WKLVEDVLQLVWKH.HQGHQJ]RQHDIROGHGWKUXVW]RQH is indicated by a negative Bouguer gravity anomaly )LJXUH

7KHVWUDWLJUDSK\RIWKHNortheast Java Basin is VKRZQLQ)LJXUH7KHROGHVW&HQR]RLFIRUPDWLRQ LQWKLVEDVLQLVWKH1JLPEDQJ)RUPDWLRQDV\QULIW 0LGGOH(RFHQH±(DUO\2OLJRFHQHGHSRVLWFRQVLVWVRI ODFXVWULQH±GHOWDLFVDQGVWRQHVDQGPXGURFNVLQWKH lower part and deep marine mudrocks with turbidite sandstone intercalations in the upper part. It is one RIWKHPDLQUHVHUYRLUVLQWKHNortheast Java Basin.

0HDQZKLOHWKH\RXQJHVWVHGLPHQWDU\VHTXHQFHLVWKH

/LGDK)RUPDWLRQZKLFKFRQVLVWVRIFOD\GHSRVLWHG in an enclosed marine environment.

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B. Data Availability

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C. Vertical Stress

Vertical stress at a given depth is simply stress due to its overlying sediment. Vertical stress in the onshore area is calculated by integrating density log DVDIXQFWLRQRIGHSWKE\XVLQJWKLVHTXDWLRQ

:KHUH6_v is vertical stress, is bulk density RIVHGLPHQWVJLVJUDYLWDWLRQDODFFHOHUDWLRQDQG]

is depth.

7KHGDWDVRXUFHIRUREWDLQLQJYHUWLFDOVWUHVVLV WKHGHQVLW\ORJ8QIRUWXQDWHO\WKLVORJLVQRWDOZD\V available over the entire well interval, and its quality LVYHU\PXFKDIIHFWHGE\KROHUXJRVLW\DVIRXQGLQWKH VWXG\DUHD0RVWRIWKHGHQVLW\ORJVRIZHOOVRQWKH RQVKRUHSDUWRIWKHNortheast Java Basin are either QRWFRPSOHWHXSWRWKHVXUIDFHRULQSRRUFRQGLWLRQ GXHWRWKHSUHVHQFHRIKROHHQODUJHPHQWFDXVHGE\

washout and caving, especially in the upper section where the lithology is dominated by unconsolidated material, and also in the limestone section. Caliper ORJZDVXVHGWRVHOHFWWKHJRRGGHQVLW\ORJ,IWKH FDOLSHUORJLQGLFDWHVWKHSUHVHQFHRIKROe enlargement, WKHQWKHGHQVLW\ORJGDWDZHUHHOLPLQDWHGIURPIXUWKHU

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By using this relation, the increase in vertical VWUHVV6_vWKURXJKGHSWK]IROORZVWKLVHTXDWLRQ

SHUIRUPHGE\SXPSLQJWKHGULOOLQJPXGLQWRDZHOO ,Q)LJXUHLWFDQEHVHHQWKDWDWWKHEHJLQQLQJRI the test, the pressure inside the borehole will increase OLQHDUO\DVWKHPXGYROXPHLVLQFUHDVLQJ$W3RLQW

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WKHIRUPDWLRQEUHDNGRZQ)%3LVUHDFKHGDQGLQ WKLVVWDJHWKHIUDFWXUHVZLOOSURSDJDWHDQGXQWLOD certain time, the pressure in the wellbore will be relatively constant because the mud will escape into the IUDFWXUHV$IWHUWKLVVWDJHWKHSXPSLVWXUQHGRIIDQG WKHSUHVVXUHZLOOGURS7KHSRLQWZKHUHWKHSUHVVXUH VWDUWVWRGURS3RLQW'LVUHIHUUHGWRDVWKHLQVWDQWDQHRXV VKXWLQ SUHVVXUH ,6,3 7KH SUHVVXUH LQVLGH WKH ZHOOERUHFRQWLQXHVWRGHFUHDVHDQGWKHIUDFWXUHVZLOO FORVHDJDLQ7KHIUDFWXUHFORVXUHSUHVVXUH)&3LV GHWHUPLQHGE\WKHµGRXEOHWDQJHQW¶PHWKRGLHWKH FURVVSRLQWEHWZHHQWKH,6,3OLQHDQGWKHVWDELOL]HG SUHVVXUHOLQHSRLQW(:KLWHet al.VWDWHG WKDW ,6,3 DQG )&3 DUH WKH EHWWHU HVWLPDWHV RI WKH PLQLPXPKRUL]RQWDOVWUHVVWKDQWKH/23EHFDXVHWKH /23LVDIIHFWHGE\VWress perturbation and the hoop stress surrounding the wellbore when inducing or RSHQLQJDIUDFWXUH

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D. Minimum Horizontal Stress

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SUHVVXUHLVDQDO\]HGEHIRUHGHWHUPLQLQJWKHYDOXHRI this stress in this study.

Considering the pore pressure condition, the SRZHU UHJUHVVLRQ RI DYDLODEOH /27 GDWD IURP DOO ZHOOVZDVXVHGDVWKHSUR[\IRUPLQLPXPKRUL]RQWDO VWUHVV7KLV PHWKRG KDV EHHQ XVHG E\ %UHFNHOV YDQ(HNHOHQWRHVWDEOLVKPLQLPXPKRUL]RQWDO VWUHVVGHSWKUHODWLRQLQVHYHUDOVHGLPHQWDU\EDVLQV 7KLVPHWKRGLVFRQVLGHUHGWREHUHDOLVWLFLQRUGHUWR DYRLGIDFWRUVDIIHFWLQJ/23DVGLVFXVVHGDERYH7KH DYDLODEOH/27LVWKHQUHODWHGZLWKGHSWKZLWKWKH IROORZLQJSRZHUHTXDWLRQWRHVWLPDWHWKHPLQLPXP KRUL]RQWDOVWUHVV6_hminYDOXH

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Maximum Horizontal Stress

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available in two wells and in a very limited depth interval.

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Volume of Mud Pumped

E. Stress Regime

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RESULTS AND DISCUSSION A. Vertical Stress

$V PHQWLRQHG EHIRUH WKH ¿UVW WKLQJ WR GR LQ constructing vertical stress is editing the density log

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HGLWLQJLVVKRZQLQ)LJXUH7KHGDWDLVWDNHQIURP ZHOOQXPEHU7KHFDOLSHUORJLQGLFDWHVDJRRGKROH condition in general, with some minor hole enlargement LQVHYHUDOVHFWLRQV7KHUDZGHQVLW\GDWDFRQWDLQVRPH spikes, either unreasonably high or unreasonably ORZ$IWHU HGLWLQJ VRPH EDG GDWD SRLQWV EDVHG RQ the above criteria, we have edited the density log as VKRZQLQWKHULJKWSDQHORI)LJXUH

%\XVLQJHTWKHYHUWLFDOVWUHVVIRUDOOZHOOV LQWKHVWXG\DUHDLVVKRZQLQ)LJXUHD,WFDQEHVHHQ that the vertical stress in the study area is less than RQHSVLIWH[FHSWIRUZHOOQXPEHUVDQG7KHVH two wells have experienced severe erosion that the section with lower density values has been eroded.

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:KHUH6_vLVLQSVLDQG]LVLQIW B. Minimum Horizontal Stress

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VFDWWHUHGDQGLQWKHUDQJHRIQHDUO\WRXFKLQJDYHUDJH YHUWLFDO VWUHVV )LJXUH 7KH /27 GDWD RI ZHOO QXPEHULVJUHDWHUWKDQ/27GDWDIURPRWKHUZHOOV It may also be related to severe erosion experienced by this well.

,JQRULQJ /27 GDWD RI ZHOO QXPEHU DQG considering the pore pressure condition, the equations IRUUHODWLQJPLQLPXPKRUL]RQWDOVWUHVV6_hminZLWK GHSWK]LQWKHVWXG\DUHDDUH

:KHUH6_hminLVLQSVLDQGLVLQIW(TLVIRU K\GURVWDWLF]RQHVZKLOHHTLVIRUWKHRYHUSUHVVXUHG ]RQH7KH UDWLR RI PLQLPXP KRUL]RQWDO VWUHVV DQG YHUWLFDOVWUHVV6_hmin6_vLQK\GURVWDWLF]RQHVIURP WRIWDQGIURPWRIWLVLQWKH UDQJHRIWRDQGWRUHVSHFWLYHO\

0HDQZKLOHWKHUDWLRRIPLQLPXPKRUL]RQWDOVWUHVV DQGYHUWLFDOVWUHVV6_hmin6_vLQWKHRYHUSUHVVXUHG]RQH WRIWUDQJHVIURPWR

C. Maximum Horizontal Stress and Stress Regime

,QRUGHUWRHVWLPDWHWKHPDJQLWXGHRIXVLQJHT WKHSRUHSUHVVXUHDQGPXGSUHVVXUHXVHGIRULQGXFLQJ WHQVLOHIUDFWXUHVPXVWEHNQRZQ)LJXUHVKRZVWKH HVWLPDWHGEDVHGRQGULOOLQJLQGXFHGWHQVLOHIUDFWXUHV

)LJXUH

'LDJUDPVKRZLQJ/27GDWDLQDOOZHOOVFRORUHGER[DQG WKHLQWHUSUHWHGDYHUDJHPLQLPXPKRUL]RQWDOVWUHVV$YHUDJH6_{hmin ୦୫୧୬}ൌ ͳǤͲͷͻͻœ^{଴Ǥଽ଺ଷ}

_୦୫୧୬ ൌ ͲǤ͹ͶͶ͸œ^{ଵǤ଴ଶଶ଼}

EOXHDQGRUDQJHGLDPRQGV,WLVFOHDUWKDWWKHstress UHJLPHLVVWULNHVOLSIDXOWLQJVLQFH6_+PD[>S_v >S_hmin . 7KHUHIRUHHTFDQEHXVHGWRHVWLPDWHWKHLQWKH depth interval where image log data are not available.

/LNHWKHYHUWLFDODQGPLQLPXPKRUL]RQWDOVWUHVVHV WKHUHODWLRQRI6_+PD[DQGGHSWK]FDQEHZULWWHQ DVWKHIROORZLQJHTXDWLRQ

)LJXUH

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KRUL]RQWDOVWUHVV$YHUDJH6_+PD[QXPEHUVDQGLQGLFDWHZHOOQXPEHUV

WKHUDQJHRIWRDQGWRUHVSHFWLYHO\

0HDQZKLOH7KHUDWLRRIPD[LPXPKRUL]RQWDOVWUHVV DQGYHUWLFDOVWUHVVLQWKHRYHUSUHVVXUHG]RQH WRIWUDQJHVIURPWR

7KHRULHQWDWLRQRIWKHPD[LPXPKRUL]RQWDOVWUHVV ZDV DQDO\]HG EDVHG RQ LPDJH ORJ GDWD IURP WZR ZHOOVLHZHOOQXPEHUVDQG)LJXUH%RWK LPDJHORJVLQGLFDWHWKDWWKHRULHQWDWLRQLVa1(6:

$VDOUHDG\PHQWLRQHGEHIRUHZHOOQXPEHUVDQG H[SHULHQFHGVHYHUHHURVLRQWKDWWKHVHFWLRQZLWK ORZHUGHQVLW\YDOXHVKDVEHHQHURGHG7KLVFDXVHVWKH YHUWLFDOVWUHVVRIWKHVHZHOOVWRH[FHHGWKHYDOXHRI RQHSVLIWZKLOHWKHRWKHUZHOOVGRQRW7KHDYHUDJH YHUWLFDO VWUHVV 6_v RI WKHVH WZR ZHOOV FRXOG EH DSSURDFKHGE\WKHIROORZLQJHTXDWLRQ

:KHUH6_+PD[LVLQSVLDQG]LVLQIW(TLVIRU WKHVKDOORZK\GURVWDWLF]RQHWRIWHT LVIRUWKHRYHUSUHVVXUHG]RQHWRIWZKLOH HTLVIRUWKHGHHSK\GURVWDWLF]RQHJUHDWHUWKDQ IW7KHUDWLRRIPD[LPXPKRUL]RQWDOVWUHVVDQG YHUWLFDOVWUHVV6_+PD[6_v LQWKHK\GURVWDWLF]RQHV IURPWRIWDQGIURPWRIWLVLQ _ୌ୫ୟ୶ൌ ʹǤͶͳͻ͵œ^{଴Ǥଽସଷଶ}

_ୌ୫ୟ୶ൌ ͸͹Ǥ͹Ͷ͵œ^{଴Ǥହଷ଺ଶ} _ୌ୫ୟ୶ൌ ʹǤͶͻͲʹœ^{଴Ǥଽଷଽ଺}

_୴ ൌ ͳǤͲͷͻͻœ^{଴Ǥଽଽ଼ଶ}

:KHUH6_vLVLQSVLDQG]LVLQIW

)LJXUH

,PDJHORJDQGLQWHUSUHWHG6_+PD[ and S_hminRULHQWDWLRQLQDZHOOQXPEHUDQGEZHOOQXPEHU

)LJXUH

'LDJUDPVKRZLQJWKHDYDLODEOH/27SUHVVXUHWHVWGDWD'67DQGPXGZHLJKW LQZHOOQXPEHUVDQGFRPSDUHGWRDYHUDJH6_v6_hminDQGSRUHSUHVVXUHLQRWKHUZHOOV

)LJXUH VKRZV WKDW LQ WKHVH WZR ZHOOV WKH reservoir pressure is mostly hydrostatic, though, in some depths, the reservoir pressure is depleted.

Nevertheless, the mudweight used during drilling indicates that these two wells experienced slight RYHUSUHVVXUH7KH/27GDWDRIZHOOQXPEHUVWLOO have the same pattern as the average S_hminRIRWKHU ZHOOV LH LQ WKH RYHUSUHVVXUHG ]RQH LW FRLQFLGHV with the vertical stress.

)LJXUHVDQGVKRZWKDWWKHUHDUHQROHDNRII test data in the deep hydrostatic or pressure reversal ]RQH7KXVWKHLQWKLVLQWHUYDOFDQQRWEHFDOLEUDWHG +RZHYHU $GGLV KDV GHPRQVWUDWHG WKDW SRUHSUHVVXUHUHGXFWLRQLVUHODWHGWRWKHVLJQL¿FDQW GHFUHDVHRIPLQLPXPKRUL]RQWDOPDJQLWXGH7KHUH IRUH WKH UHDO DYHUDJH 6_hmin in this study could be lower than the interpreted average S_hmin.

CONCLUSIONS

,QWKHRQVKRUHSDUWRIWKHNortheast Java Basin, WKHYHUWLFDOVWUHVV6_vLQZHOOVWKDWH[SHULHQFHGOHVV HURVLRQLVORZHUWKDQRQHSVLIWLHFDQEHGHWHUPLQHG XVLQJ WKH IROORZLQJ HTXDWLRQ 6_v ], where S_vLVLQSVLDQG]LVLQIW+RZHYHUZHOOVWKDW experienced severe erosion have a vertical stress JUDGLHQWKLJKHUWKDQRQHSVLIW6_v ] 7KH SRUH SUHVVXUH FRQGLWLRQ LQ WKLV EDVLQ FDQ EH JHQHUDOL]HG LQWR WKUHH ]RQHV VKDOORZ K\GURVWDWLF ]RQH IURP WKH VXUIDFH WR a IW RYHUSUHVVXUHG ]RQHIURPaWRIWDQGGHHSK\GURVWDWLF ]RQHLQGHSWKVJUHDWHUWKDQaIW7KHPLQLPXP KRUL]RQWDOVWUHVV6_hminLQWKHK\GURVWDWLF]RQHFDQ be estimated as S_hmin =], while in the over SUHVVXUHG]RQH6_hmin ]7KHPD[LPXP KRUL]RQWDO VWUHVV 6_hmax LQ WKH VKDOORZ DQG GHHS K\GURVWDWLF]RQHVFDQEHHVWLPDWHGXVLQJHTXDWLRQV S_hmax ] and S_hmax ], respectively.

:KLOHLQWKHRYHUSUHVVXUHG]RQH6_hmax ]. 7KHLQWHUSUHWHGstress regime in the onshore part RI WKH 1RUWKHDVW -DYD %DVLQ LV VWULNHVOLS IDXOWLQJ since the S_hmax > S_v> S_hmin0RUHRYHUWKHUHVXOWRI image log analysis indicates that tKHRULHQWDWLRQRI S_hmax LVa1(6:

ACKNOWLEDGEMENT

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