Lithofacies Description and Fracture Evaluation of an Unconventional Reservoir in Indonesia: Critical Role of Borehole Imaging in a Geothermal Reservoir Characterization

Chitale, D. V. (Vivek)¹, Ramon Sanchez² (1) Halliburton Energy Services, Houston, TX (2) Halliburton Energy Services, Jakarta, Indonesia

Role of an electrical borehole image becomes especially critical in reservoir characteri­zation when the only other well data available are gamma- and temperature logs! The chal­lenge becomes even bigger when the reservoir to be characterized is non-conventional and it contains geothermal energy! This paper reports such a case history documenting a suc­cessful application of borehole imaging in characterizing geothermal reservoirs of Indonesia.

An Operator in Indonesia deployed extended range micro-imager (XRMI), a current gen­eration imager to describe complex volcanic reservoirs containing geothermal energy. Operational considerations allowed neither mud logs nor wireline logs except gamma ray and temperature. Borehole images were interpreted to accurately describe the litho-facies and diagnose fractures holding the geothermal energy. Image interpretation software called “sculpturing” (Chitale et. al. 2004) was used to quantify the fractured porosity.

This paper shows how XRMI and the software “sculpturing” achieved characterization of the andesite reservoirs containing geothermal energy, which was done without any help from other logs except gamma- and temperature. Further, the borehole images differentiat­ed reservoirs from shales or impermeable rocks, which proved crucial for the Operator since the common shale indicator- gamma log was affected by radioactive minerals in the vol­canics. Borehole images also enabled core-like description of the litho-facies thereby saving costs of conventional coring in a tough borehole environment. Thus, borehole imaging proved critical in the reservoir development efforts and significantly reduced the E&P risks for the Operator in these geologically complex areas of Indonesia.