AAPG GEO 2010 Middle East
Geoscience Conference & Exhibition
Innovative Geoscience Solutions – Meeting Hydrocarbon Demand in Changing Times
March 7-10, 2010 – Manama, Bahrain
Geophysical Monitoring of Steam Flood in from Omani Heavy Oil Field
(1) OXY, Muscat, Oman.
Occidental is conducting a geophysical monitoring program to aid optimization of production from a heavy oil field in central Oman. The Permian age Gharif reservoir consists of three stacked sandstone units spread over a gross interval of about 50 meters with average porosities of 30%. Oil recovery is stimulated by steam injection into each of the three reservoirs to lower oil viscosity. Steam injection and production alter reservoir properties such as temperature, pressure and saturation. A 4D modeling study was carried out to investigate the impact of these reservoir changes on compressibility and rigidity of the rocks. Synthetic seismic models were derived from our understanding of the reservoir rock properties combined with the history matched reservoir models. The modeling predicts a change in the reservoir interval velocities of approximately 10-15%, resulting in a change in acoustic impedance that should be large enough to observe in surface seismic data. Modeling also suggests that changes in the reservoir properties will be localized close to the steam injectors and that these anomalies could be strong enough to identify in surface seismic without time lapse differencing. A crosswell tomography survey was acquired through a well that injects steam into all three reservoirs. The cross well survey confirms a reduction in reservoir interval velocity by 10% associated with the steam injection. Comparison of the crosswell tomography cross section with the equivalent predicted velocity section from the reservoir simulation highlights differences between the reservoir simulation prediction and how steam is actually affecting the reservoir. Petrophysical and production surveillance data have helped our understanding of these differences. The crosswell tomography helped in assessing the connectivity vertically between the three reservoirs and horizontally between the study wells as the resolution is higher in the cross well than in the surface seismic. The crosswell tomography and modeled seismic response also serve to calibrate the surface seismic response which is needed to highlight field wide lateral reservoir changes. Information gained from geophysical monitoring that is correlated with observation and production data is important for monitoring steam movement in the subsurface and optimizing field production.