MAPPING STEAM AND WATER-FLOW IN PETROLEUM RESERVOIRS

During the past 5 years, we have applied high-resolution geophysical m ethods [crosswell seismic and electromagnetics (EM) and passive seismi c] to map and characterize petroleum reservoirs in the San Joaquin Val ley and to monitor changes during secondary-recovery operations. The t wo techniques provide complementary information. Seismic data reveal t he reservoir structure, whereas EM measurements are more sensitive to the pore-fluid distribution. Seismic surveys at the South Belridge fie ld were used to map fracture generation and monitor formation changes caused by the onset of steamflooding. Early results show possible sens itivity to changes in gas saturation caused by the steamflooding. Cros swell EM surveys were applied at a shallow pilot at Lost Hills for res ervoir characterization and steamflood monitoring. Images made from ba seline data clearly show the distribution of the target oil sands; rep eated surveys during the steamflood allowed us to identify the boundar ies of the steam chest and to predict breakthrough accurately. Applica tions of the EM techniques in steel-cased wells are at an early stage, but preliminary results at Lost Hills show sensitivity to formation r esistivity in a waterflood pilot.