Publications

Interpreting geological fault configurations is still an obstacle in the Bunyu Area, although the area has high hydrocarbon production. Seismic data, the main data for fault interpretation in this area, has a low signal to noise ratio due to high absorption of wave energy from loose sand and coal at and near the surface and also complex geological structure. The old 2D seismic datasets from 1970 through until 2005 are difficult to interpret due to the low resolution. As a consequence, the fault configuration is difficult to map, and this results in uncertainty both in terms of hydrocarbon trap configuration and migration pathway interpretation. In order to have a better fault interpretation, data integration of FMI log, gravity, passive seismic, earthquake, and the latest seismic data are used to optimize the geological interpretation. Drilling induced fractures and borehole breakouts in FMI logs provide the understanding that the maximum stress in the Bunyu Area is coming from a NE-SW direction. This direction is the same as the focal mechanism from 2015 Tarakan earthquakes. This corresponds with the displacement of the Sempurna and Mangkalihat strike slip faults which are the key controlling geological structural systems in the Tarakan Basin. Besides that, regional gravity shows an en echelon and horsetail splay structure which contributes to the evidence that today the Bunyu Area is controlled by a strike slip fault system. New high resolution 2015 gravity and new 2D seismic data covering the Bunyu Area shows more specifics about the fault configuration. Based on the Riedel Shear model applied to the new gravity data, an R’ antithetic fault configuration is easily recognized as very dominant in the southern part of the Bunyu Area. This fault configuration in the southern Bunyu Area can also be interpreted easier using the new 2015 2D seismic data combined with the magnetotellurics data. By overlying the new gravity, time structure map, and new passive seismic data, it is apparent that the high value passive seismic anomaly in the southern part of Bunyu Area is localized on the pop-up structure that is driven by R’ antithetic faults. The low passive seismic anomaly in the middle part is not related with R’ fault configuration. Based on this analysis, potentially there are more hydrocarbons trapped in the southern part than middle part of Bunyu Area. Fault related structures are interpreted as an important factor in the hydrocarbon migration pathway in the Bunyu Area, and it can be interpreted by using integrated borehole and geophysical data.