Java Field is located in the North West Java Basin that is one of the hydrocarbon prolific basins in Indonesia. The most of oil and gas in this area was produced from Jatibarang volcanic reservoir that consist of volcanic rock such as tuff, pyroclastic breccia, and lava andesite. In general, volcanic rocks have been ignored because a perceived lack of reservoir quality. Fractures were detected in the Jatibarang volcanic formation which enhanced porosity and permeability allowing hydrocarbon production. To exploit this type of reservoir to the fullest, comprehensive study must be done including determination of distribution and orientation of fault and fractures, possible migrations, and trap of hydrocarbon. Fractures identification and distribution modelling has been carried out in Java field with a combination of seismic interpretation by post-stack seismic geometrical attributes extraction, wireline log, imaging log and cores. A well log interpretation technique on the artificial neural network concept has been developed for evaluation of the volcanic rock reservoir and it was calibrated with imaging log and sidewall core data. Detailed petrophysical and petrographycal analysis have shown that the volcanic facies of Jatibarang formation is characterized by several types of tuff, andesite breccia, and andesite-basalt lava. The tuff facies is the best reservoir that has a multiporosity types with a range value of total porosity 6-19%, secondary porosity index value is 2-12% and average of fracture permeability value is ± 42,90 mD. The formation evaluation analysis of several productive well in Java field suggested that the distribution of productive well is mainly controlled by distribution of fractures beside by distribution of volcanic facies. The fractures in study area has three general orientation that is N-S, NNW-SSE and NE-SW trend strike of fractures. The all of fracture subsets were generated by polyphase tectonic event interpreted by N-S compressive stress during Mio-Pliocene and originally thought to be an extensional regime of the Cretaceous-Oligocene Meratus System that was rejuvenated during Pliocene. The N-S trend of conductive fractures is a potential open fractures that have ability to save and flow the hydrocarbon. Regarding the orientation of potential fractures, a horizontal well lateral from west to east is suggested for producing potential fractured volcanic reservoir in order to penetrate perpendicular to strike of productive fractures. This study can be analogue for all of unexplored volcanic reservoir, so this type of reservoir can be future target for hydrocarbon plays in Indonesia.

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