Seismic Monitoring of a Steamflood at South Casper Creek Oil Field, Wyoming

JOHNSTON, PHIL, DOO-SUNG LEE, and FRANK MARTENS, Unocal, Brea, CA, and NOBORU WACHI, Japan National Oil Company, Chiba, Japan

Repeat three-dimensional (3-D) seismic surveys and repeat cross-well seismic surveys were used to monitor fluid flow in a steamflood EOR pilot project at South Casper Creek oil field, Wyoming. The reservoir is a sandstone 160 ft thick at a measured depth of 2700 ft.

Baseline 3-D and cross-well seismic surveys were shot prior to steam injection in the study area. Steam injection was started, and seven months later monitor surveys were shot using identical survey parameters and geometries. Traveltime delays up to 10 msec are present in the cross-well monitor survey compressional wave arrivals, and traveltime delays up to 8 msec are present in the 3-D monitor survey arrivals. These delays are due to the lower compressional velocity of reservoir rock heated by steam flooding.

Differences between tomographic images from the baseline and monitor cross-well surveys are used to infer the position of the steam flood in a cross-section between the two wells. Differences between isochron maps from the baseline and monitor 3-D surveys are used to infer the position of the steam flood in map view. Cross-sectional and map images of the steam flood position agree. This indicates interwell details of fluid flow in a 160-ft-thick reservoir at a depth of 2700 ft can be successfully mapped by seismic methods.

AAPG Search and Discovery Article #91009©1991 AAPG-SEPM-SEG-SPWLA Pacific Section Annual Meeting, Bakersfield, California, March 6-8, 1991 (2009)