GETZ, BOYD STEVEN, Getz Geological Services, Bakersfield, CA
ABSTRACT: Use of Resistivity Electrofacies and Geologic/Engineering Analyses to Understand Performance Differences in Two Adjacent McKittrick Field Steam-Drive Projects
Several empirical approaches were employed in a comprehensive geologic/engineering review of the 9Z and 16Z Amnicola sand steam-drive projects located in the "northeast area" of the McKittrick oil field. These included (1) resistivity electrofacies mapping, (2) three-dimensional temperature distribution analysis, (3) analysis of the preflood production history, and (4) mapping of numerous steamflood parameters on a per pattern basis. The purpose of the study was to determine why there were large differences in performance between the two contiguous projects.
The original 16Z Amnicola sand steam drive was initiated in August 1975 by Chevron U.S.A. The drive consisted of 22 inverted five-spot patterns covering 96 ac in the northeast corner of Sec. 16 and northwest corner of Sec. 15, T30S, R22E. Favorable production response led to the 9Z lateral expansion, which consisted of 16 additional patterns covering 75 ac in the southwest corner of adjacent Sec. 9, T30S, R22E. It was later found that although the 16Z project had been very successful, the 9Z project did not perform nearly as well.
Several findings and conclusions resulted from the study: (1) electric log resistivities could be effectively used to map reserves, (2) a strong downdip aquifer existed which prevented some patterns from effective heating, (3) updip well production was being lost due to premature steam breakthrough, (4) steam was migrating into and being lost to a large, low-pressure secondary gas cap, and (5) the 16Z project had produced an incremental 46% of original oil in place at a cumulative steam-to-oil ratio of 4.3, whereas the 9Z project had produced 25% of original oil in place at a cumulative steam-to-oil ratio of 7.7. The principle reasons for the poorer performances included (1) lower reservoir quality as indicated by the resistivity mapping, (2) higher dip (35 degrees vs. 12 degrees at 1 Z), leading to a more rapid premature steam breakthrough in upstructure producers as well as steam migration and heat loss to the secondary gas cap, and (3) the detrimental effects of a previous fireflood adjacent to the 9Z project.
A series of recommendations were implemented as a result of the study. These extended the economic life of both projects until steam injection was discontinued in June 1990. The major strategies included (1) drilling of several strategically located infill wells to tap areas with the greatest remaining reserves potential, (2) establishment of a lateral expansion program to the south and east to add new reserves and create new heating fronts in historically "cool" areas, (3) implementation of selected steam quality and rate reductions and discontinuation of injection in highly uneconomic patterns, (4) conducting of high-volume cyclic steam jobs in cool downdip areas to stimulate nonresponsive individual and adjacent wells, and (5) converting selected producers to water injectors and co verting some injectors to producers in attempt to lessen steam loss to the secondary gas cap.
AAPG Search and
Discovery Article #90992©1993 AAPG Pacific Section Meeting, Long Beach,
California, May 5-7, 1993.