GEOLOGICAL SUMMARYIntroductionTerang-1 was an exploratory wildcat well drilled in the western part of the kangean contract area. It was positioned to test a seismically, well-defined, faulted anticlinal feature located 48 kms southwest of kangean island in the east java sea.The well was drilled in a previously unexplored part of the contract area and as a result seismic and stratigraphic predictions were rather conjectural. Seismic horizon identifications were primarily based on ties to cities service MS 2-1a well, located 72 kms.west. additionally, the kangean islands outcrop sequence and regional facies considerations were utilized in the contruction of the stratigraphic prognosis.Primary objective of terang-1 were an early Pliocene limestone and a late Miocene coarse clastic sequence both interpreted to be developed within the limits of the large terang anticline. The former objective was correlated with porous, detrital limestone found in cities service MS 2-1A well, located 72 kms. West. Additionally, the kangean islands outcrop sequence and regional facies considerations were utilized in the contruction of the stratigraphic prognosis.Primary objectives of terang-1 were an early Pliocene limestone and a late Miocene coarse clastic sequence both interpreted to be developed within the limits of the large Terang anticline. The former objective was correlated with porous, detrital limestone found in Cities Service MS 2-1A. higher seismic amplitudes within the Pliocene and uppermost late Miocene and the presence of a flat seismic event underlying almost the entire area of mapped closure, were interpreted to indicate the presence of gas.The deeper late Miocene clastic sequence was postulated to has developed over an intra-late Miocene unconformity surface. Structure appeared to have developed within this section by late Miocene/early Pliocene times and potential sandstone reservoirs would have been ideally placed to trap hydrocarbons migrating updip from nature source rocks in deeper areas north and south of the prospect.The well was programmed to -9960ss. To investigate the nature of the largely unknown pre-late Miocene section which could include secondary objective sandstones and/or limestones.

The terang-1 well was drilled by the drilling barge Brinkerhoff-1( 40 above mean sea level). The well was spudded on march 24th,1982 and drilled to a total depth of 7444 KB into latest Early Miocene claystones and limestones. Total depth was reached on April 17th, 1982 and he well was plugged and abandoned as a non-commercial gas discovery on may 6th,1982.

Regional Geologic SettingThe Madura basin province of the east java sea is presently situated in a back-arc basin north of the ative java trench and java-lombok volcanic arc system. The north-northeast subduction of the Australian-India plate beneath the Java arc has generated compressional stresses into the back-arc region and resulted in reactivation, since Miocene time, of older Eocene-Oligocene back arc extentional fault systemsThe Madura-Raas/Sapudi-Kangean and Sepanjang Island chain are uplifted compression induced inversion features related to left lateral wrenching along the major boundary faults. The Kemirian Terrace, a present day submerged inversion feature is situated immediately south of Kangean Island and North of the terang-Sirasun fields. Inversion timingis from Miocene to recent with compressional stresses continuing to uplift segments of the islands and nearby structures.A deep water back-arc basin formed in Miocene to recent time between the Kangean-Kemirian Inversion high and the Islan arc of Bali and of Eastern-most Java. Present day water depths in the Madura Basin range from tens of meters on a shallow water re-entrant between Madura and Java to a thousand meters and more (>3000) between the Kemirian Ridge and the island of Bali.The Madura-Sepanjang zone has restricted clastics influx into the Madura Basin, except during Mid-late Miocene time when the Ngrayong and Paciran sandstones were deposited, and deep water pelagic carbonates and pelagic mudstone have dominated the sedimentary column.Inversion of the Kemiringan Ridge and continued crustal compression esulted in large scale normal faulting down to the south into the Madura Sub-basin. A large inversion feature, rooted in Eocene-Oligocene Ngimbang & Kujung shale formed a large back arc ridge underlying the Terang-Sirasun fields. This ridge is continuing to grow at present time since on lap onto the Terang structures is apparent at the seafloor.

TSB StratigraphyThe TSB fields are located in the southern of the Kangean PSC in present day water depths ranging from 300 to 1000. The southern Basin geologic history is difficult to interpret from the cretaceous basement through Oligocene section due to the absence of well penetrations and lack of deep seismic data in this section. However, nearby well control and limited deep seismic provides sufficient data to interpret this deeper section. Seven well penetrations and seismic provide a good data base from which to interpret the stratigraphy of the Miocene and younger section. However, nearby well control and li,ited deep seismic provides sufficient data to interpret this deeper section. Seven well penetrations and seismic provide a good data base from which to interpret the stratigraphy of the Miocene and younger section.Cretaceous sediments and metasediments, deposited within a fore-arc basin mlange complex are believed to floor the entire region and are considered to be peneplaned during the late cretaceous through early Eocene. Subsequent to peneplanation the Eocene through early Eocene. Subsequent to peneplation the Eocene through Oligocene was a period of extensional tectonics within the Madura Basin and Kangean PSC. Half graben systems formed with initial infill of fluvial and deltaic deposits of quartz sand,coal and carbonaceous shale during the Mid-Eocene through late Eocene forming the Ngimbang Clastics Member of the Ngimbang Formation. A marine transgression ensued during late Eocene time, and resulted in shallow and deep marine carbonates accumulating on the highs and in the low lying basins, respectively. These are reffered to as the Ngimbang Carbonate Member of the Ngimbang Formation.Following ngimbang carbonate deposition rapid regional subsidence occurred in the east java Java Sea and an extensive and thick accumulation of bathyal shale was deposited during the late Eocene, continuing into the early to middle Oligocene. This shale unit is comprised of the ngimbang shale member of the ngimbang formation of late Eocene age and kujung formation of Oligocene age. Upper Oligocene deposits vary from shallow water carbonates of the prupuh formation to deep water bathyal shales of the kujung and lower rancak formation.Lower Miocene to mid-miocene strata within the terang-sirasun region was encountered in the kemirian-1, Terang-1 and Arya-1 wells. In all wells a deep water facies comprised of interbedded claystone, siltstone and deep marine carbonates, with little to no reservoir character, was encountered.A regional tectonic event (N7-N14) during the mid-miocene restructured the sedimentary basins of the kangean PSC. The kangean island and kemirian ridge inverted, or was thrust upward at this time and sediments were shed off of the high into surrounding basins. The Terang-sirasun region of the Madura basin received deep water shales and silt stone and some thinlimestone beds during and subsequent to the inversion. The present-day structural configuration was established at the end of the mid-miocene inversion.Upper Miocene sediments within the Madura basin are deep water to shelf deposits of carbonates, claystone and siliciclastic sands. The structuring of the mid-miocene period had ceased, intervening lows were aggradationally filled and the upper Miocene cepu formation was deposited across a gently basinward (SE) dipping deep marine platform. The Cepu formation is comprised of argillaceous deposited as a transgressive blanket across the underlying angular unconformity.Overlying the cepu limestone is the upper Miocene to lower Pliocene Paciran Sandstone Member of the Mundu formation. Paciran sands are divided into two basinward prograding systems both of which coarsen upward from shales and silt stone to fine to medium grained sands. These sands were deposited within an outer shelf fan/delta complex and are really extensive within he Terang-Sirasun region. At Terang the upper Paciran sand package forms the lower reservoir interval and is comprised of angular to subangular quartz grains of fine grained fraction with a very small percentage of lithic grains (