Mapping steam and water flow in petroleum reservoirs

Over the past 5 years, we have applied high-resolution geophysical methods (crosswell seismic and electromagnetics (EM), and passive seismic) to map and characterize petroleum reservoirs in the San Joaquin Valley and to monitor changes during secondary recovery operations. The two techniques provide complementary information. Seismic data reveal the reservoir structure, whereas EM measurements are more sensitive to the pore fluid distribution. Seismic surveys at the south Belridge field were used to map fracture generation and monitor formation changes due to the onset of steam flooding. Early results show possible sensitivity to changes in gas saturation caused by the steam flooding. Crosswell EM surveys were applied at a shallow pilot at Lost Hills for reservoir characterization and steamflood monitoring. Images made from baselines data clearly show the distribution of the target oil sands; repeated surveys during the steam flood allowed us to identify the boundaries of the steam chest and to accurately predict breakthrough. Applications of the EM techniques in steel-cased wells are at an early stage, but preliminary results at Lost Hills show sensitivity to formation resistivity in a water-flood pilot. Finally, passive seismic surveys during hydrofracture operations measured events corelatable in frequency content and magnitude with the size and orientation of induced fractures