Publications

Jemuduk-1ST1 is an exploration well located in block SK301A, offshore Sarawak that tested a rollover anticlinal structure confined by growth faults within the Rajang Delta. The well, drilled by PETRONAS in 2013, yielded non-economical results, with gas shows throughout Cycles VI-VIII clastic reservoir objectives. A comparison of the pre-drill well prognoses and post-drill well results reveals that the targeted reservoirs are thicker and better-developed than expected, considering the perceived mud-proneness of the Rajang Delta system. A total 350 m gross thickness sandy intervals, with porosity of 16-25 %, was encountered and high gas readings were recorded. Based on these observations, the reservoirs were suspected to have been previously charged with hydrocarbons but failed to trap any significant accumulations. Consequently, a study using Fluid Inclusion Stratigraphy (FIS) was performed and this shows moderate FI responses with several visual petroleum inclusions throughout the wellbore. Such outcomes suggest that the reservoirs have been charged with migrated hydrocarbons. To lend further support to this finding, an analysis of the FIS results from the Kebabangan-1 oil discovery well was undertaken, where a distinctive zone of no FI responses overlying the well's primary reservoir was observed indicating an effective top seal. In contrast, such observations have not been recorded in the well Jemuduk-1ST1. With thicker reservoir sections, a post-drill Fault Seal Analysis (FSA) demonstrated evidence of cross fault sand-to-sand juxtapositions and the lack of fault sealing capacity: this is considered the key reasons for the absence of hydrocarbon accumulations. In conclusion, Jemuduk-1ST1 has proven a working hydrocarbon charging system, albeit with poor fault seal capacity due to the unexpected sandier lithology encountered. The study’s outcomes have positive implications for the Rajang Delta exploration, apart from proving an active hydrocarbon charging mechanism, it also suggests the possible presence of potential sandy sedimentary fairways development, down-dip in the deepwater Bunguran Trough, and ultimately enhances the prospectivity of the relatively under-explored Rajang Delta.