Structural Concept (Play) to Reduce Well Targeting Risk: Rantau Dedap Case Study

Abstract

One of the biggest exploration risks to proving geothermal reserves is well bore targeting. Based on the strain structural pattern in the Rantau Dedap prospect an oblique convergent strike-slip faulting model was developed. The structure model shows that a dilatational fault system has formed as a result of dextral movement along Sumatra (Semangko) Fault System. Since subsurface permeability data is still limited, the surface structure data plays an important role in well targeting. Surface manifestations can reduce permeability risk for well targeting at the early exploration stage. Surface manifestations can confirm structure "play" model and prioritize faults for well targeting. After the conceptual has been constructed, combining all available information, the model compared to MEQ and other available subsurface data. MEQ shear wave splitting was used to confirm the major targets to reduce well targeting risk. Fault intersections and major strike slip faults could create zones of high fractures density, which are the best location for fluid flow particularly in a dilatational fault system. The distribution of geothermal manifestations is controlled by strike slip faults and their associated fractures particularly in NE-SW, NW-SE and N-S trends. Integration of the fault mapping results, structural interpretation, surface manifestations and MEQ shear wave splitting data allow faults or structures to be prioritized for well targeting. NE-SW, NW-SE and N-S extensional faults associated with fumaroles and hot springs are prioritized faults. NE-SW, NW-SE and N-S extensional faults which are not associated with surface manifestations are considered secondary targets.