Abstract: A Permanent 3-D VSP Array for Time-Lapse Reservoir Monitoring at Lost Hills, California
CORNISH, B., Halliburton Energy Services, Houston, TX; J. MINEAR, Consultant, Houston, TX; WILLIAM KEMPNER, Chevron USA Production Co, Bakersfield, CA; T. NEMETH, Chevron Petroleum Technology Company, New Orleans, LA
A permanent, 40-level, 3-component geophone cable was installed by Halliburton in a temperature observation well near Chevron's Lost Hills Oil Field steam pilot. The permanent nature of the array emplacement and its proximity to the reservoir were expected to improve image quality and repeatability and to reduce the cost of repeated time-lapse reservoir monitoring surveys. A baseline data set was recorded in 1998 during a 3-D surface seismic survey conducted by Chevron using the same sources and the same recording system as the surface acquisition. We selected a subset of 45 sources located within a radius of 800 feet of the observation well for 3-D VSP processing.
The processed 3-D VSP forms a pre-stack depth-migrated data cube rather than a 2-D profile as would be obtained via traditional methods. The cube measures 800 ft on the sides by 2000 ft in thickness and is analogous to a surface-acquired data volume but incorporates the advantages of the downhole receiver array. The borehole imagery supports a maximum frequency of 65-70 Hz as compared to the 50-60 Hz result for the surface data. Both frequencies are considered quite good for the San Joaquin Valley. Spatial resolution improvement with the 3-D VSP data allowed bin size to decrease by up to 50% relative to the surface survey.
Subsequent to a 1999 repeat 3-D VSP survey, reflection character changes and velocity increases are being observed that are consistent with those noted by Langan et al. (2000, this meeting) in a time-lapse crosswell seismic imaging experiment.
AAPG Search and Discovery Article #90911©2000 AAPG Pacific Section and Western Region Society of Petroleum Engineers, Long Beach, California