3D SEISMIC IN A MATURE PRODUCING AREA: RESULTS AND ECONOMICS OF THE 1997 COALINGA NOSE/GUIJARRAL HILLS 3D SEISMIC SHOOT

3D Seismic was used by a small independent oil and gas operator to evaluate the East Coalinga Extension, Pleasant Valley and Guijarral Hills oil fields in Fresno County, California. A major emphasis of the project was to determine if there bypassed reserves in fields that had been abandoned decades ago. In addition to enhancing the interpretation of structural and stratigraphic trapping mechanisms in the area, producing characteristics of each reservoir were used in conjunction with the 3D seismic to evaluate the migration of the produced fluids. From the seismic data, increased amplitude responses from gas saturation were seen in most of the reservoirs that produced. These increased amplitudes helped delineate different aspects of the fields such as compartments in reservoirs that were once thought continuous, and bypassed oil reserves in areas that were thought to have been completely swept by water. A second major emphasis behind the 3D seismic shoot was to look for new structural and stratigraphic features that had not been previously distinguished in the area. Complex faulting in the Cretaceous sediments proved to be the biggest surprise encountered in the 3D interpretation. These faults had previously not been mapped due to the area’s sparse Cretaceous well control but were found to have a large influence on the trapping mechanisms and production in the shallower horizons.

Recent drilling in the area both confirmed and contradicted the interpretation of the 3D seismic. The greatest risk for the oil and gas operator is whether or not 3D seismic in the older, produced areas and subsequent drilling based on this seismic discovers economic oil production. A discussion of the economics for this project is presented.