The impact of an active strike-slip fault to the principal horizontal stress orientations and fluid flow in the Karaha Bodas Geothermal Field, Indonesia

Abstract

The Karaha Bodas field is located in an active tectonic region which consists of complex volcano-stratigraphy and structural framework. To determine the best strategy for its development, we studied its tectonic setting and how it correlates with the productivity of a well using the geologicalevidence in a production well called WELL-A. The geological structure analysis from the image log data in WELL-A includes the identification of the maximum horizontal stress orientation along the well from the
orientation of the drilling-induced fractures, including borehole breakout and drilling-induced tensile fractures or DITF. The maximum horizontal stress orientation is also determined from caliper data using the maximum and minimum size of the caliper to define the breakout or washout interval along the borehole. This image log analysis shows evidence of a rotation in the maximum horizontal stress in the reservoir rocks from N235°E to N200°E, which is strongly believed to be caused by the active NE-SW strikeslip Candramerta fault that was targeted by WELL-A. This active fault is also interpreted to contribute to production from the well as the response in the production log that is acquired in this well indicates a significant mass flow changeat the fault. Overall, both the drilling-induced tensile fracture and caliper-breakout analysis capture the stress trend rotation and suggest the present-day principle horizontal stress orientation is directed NE to NNE. This is also similar to the
regional stress data that suggest the maximum horizontal stress in West Java is oriented north-northeast.