Thermally assisted gas oil gravity drainage (TA-GOGD) is a mechanism used to enhance heavy-oil recovery from naturally fractured reservoirs. TA-GOGD works by injecting steam into the fractured reservoir, heating oil in the rock matrix, reducing oil viscosity and accelerating gravity drainage. Microseismic monitoring of this process is an uncommon practice. Here we develop a workflow to characterize induced seismicity due to thermal expansion and subsequent stress/strain alteration in a heavy oil field in the Sultanate of Oman. Microseismic monitoring is designed to better understand the effectiveness of TA-GOGD in field development and risk mitigation. The field is comprised of highly fractured, low permeability and high porosity, stacked carbonate rocks forming a domal shape. Around 7200 events were detected from April-2011 to July-2015, using a network of 13 vertical borehole, each equipped with 8 3C-geophones. The frequency of microseismic events correlates well with periods of injection. Among several tested velocity models, a 3D heterogeneous velocity model provides results with the lowest location errors, which are on average 15 meters. Events are clustered around existing faults indicating reactivation of the fault system at locations where steam injection is taking place and there is little evidence of microseismicity in the overburden.
