Fault-related fractures characteristic of Kijang fault at Wayang Windu Geothermal field

Understanding the characteristic of permeability in the reservoir is a challenge in order to enhance well targeting success ratio. The permeability of a geothermal field is often related to the structure control and/or the rock type of the reservoir. The availability of interconnected fractures as the secondary permeability in the reservoir is believed to give larger contribution to the production instead of matrix permeability. This study is aimed to gain more insights of fractures characteristic related to Kijang fault zone, as one of the most productive fault zone in the Wayang Windu geothermal field. Kijang fault zone is a NE-SW trending interpreted fault located at the northern part of the field, where the wells with the highest production rate are located. Better understanding of the permeable fractures related to the fault is expected by having further analysis of geologic and geophysics data. The approach using borehole image as main data and using both microearthquake focal mechanism and shear-wave splitting as support data for beyond the wells concluded NE-SW dominant fracture orientation. The dominant fracture orientation derived from borehole image ranged from N 40°E to N 50°E, while from microearthquake analysis ranged from N 30°E to N 50°E.