Publications

Reservoir depletion due to hydrocarbon production changes the pore pressure and the absolute stress magnitudes operating in the field. In stress sensitive reservoirs, particularly in carbonates, pressure depletion may alter the geomechanical stresses of rock and can cause natural fractures within the reservoir to be reactivated due to their critical stress state. Slip along these critically stressed fractures will rupture the seal and could cause the natural fractures to become conduits for fluid-gas flow, which could change how we understand or model production. In some situation, enhanced production performance could occur, however, depending on the reservoir, stress state, fault orientations and depletion history, some of these critically stressed fractures could extend into the water leg and drive water upward through the gas-oil reservoir. We believe the latter may have occurred in the Gunung Kembang field, Indonesia.Gunung Kembang has been producing oil since 1992 and gas since 2002. The reservoir pressure has already depleted almost 300 psi from its original state. Evidence of natural fractures were detected in a well drilled during the early stages of field development, however, they may not have been critically stressed. During the 2004 drilling campaign there is evidence to suggest that critically stressed natural fractures may have contributed to severe losses while drilling and premature water breakthrough during production.This paper presents an analysis of the impact that reservoir depletion could have one the natural fractures in the Gunung Kembang field. Image data, drilling experiences, well test analysis and also production profiles were used to construct a geomechanical model with specific applications to the mechanical behavior of the natural fractures in the reservoir. We found compelling evidence that natural fractures do play a role in reservoir production, however, their role is more related to premature water breakthrough. The important asset management concept is to identify well for future development that avoids trajectories that could exacerbate premature water breakthrough in the Gunung Kembang Field.