Geologic and Geomechanical Reservoir Simulation Modeling of High Pressure Injection, West Salak, Indonesia

Abstract

Awi 18-1 is an injection well drilled in the Cianten Caldera, near the western margin of the Salak (Awibengkok) reservoir in west Java, Indonesia. The initial well injectivity was low, so long-term hydraulic stimulation was conducted to improve the permeability and establish a better connection to existing natural fractures. A reservoir geologic model of the area was built by integration of surface mapping, log and core data, and well performance information.
The well penetrated pre- and post-caldera volcanics, the caldera ring fault intrusion and contact metamorphic zone, and marine sedimentary rocks. Permeability was found primarily near the caldera margin in pre-caldera lavas and ring fault intrusion along steeply dipping NNW to NE-trending fractures that were partially sealed by mineral precipitation.
A simulation model was developed from the reservoir geologic model to understand the injectivity evolution mechanisms and behaviors under different injection conditions, and also predict long term future injectivity performance using the Geo-Mechanical Reservoir Simulator (GMRS®). The model contains the completed interval of deviated Awi 18-1 and the model domain covers the majority of microseismic events observed during the course of the stimulation. It simulates injectivity evolution using heat and mass transfer in an elastic formation.
The model was history-matched by calibrating rock mechanical and fracture properties. A number of what-if operational scenarios were simulated to evaluate the effects on injection rate of injection pressure and temperature, well shut-ins, and injectate temperature variation. In the numerical experiments, better performance was observed through higher pressure and lower injection temperature. Temperature cycling or periodic well shut-ins temporarily increase the injectivity but the stimulated volume (created fracture volume) is simply proportional to the amount of the volume injected and its temperature.