Abstract

Cyclic steam injection has been used in California since the 1960s. It has been used as a commercial technique to recover oil from diatomite since the mid-1990's. This paper is a synopsis of the analysis and interpretation of over three years of steam injection flow rate, pressure and temperature data from Santa Maria Energy's (SME) cyclic steam injection pilot project in the diatomite zone in the Sisquoc formation on the Careaga Lease in the Orcutt Oil Field, Santa Barbara County, California.

The pilot consists of 19 cyclic steam injection wells configured in a 4x5 matrix spaced about 120 feet apart producing from a depth of about 925 feet. Operating practices are used specific to Careaga Lease geologic and reservoir features that include a tailored range of steam injection rates and steam volumes for each steam injection cycle. Comprehensive surveillance and steam injection management protocols are in place for maintaining a safe and reliable operation. The discussion that follows examines data gathered automatically at each well and their real time analyses.

Cycle-by-cycle analyses of steam injection and soak periods for all SME wells show (a) no indication of fractures being induced and (b) that large skin effects are present during steam injection in this project. The latter calls into question use of the tubing wellhead pressure as an indicator of the reservoir pressure while injecting steam.

Based on the analysis and interpretation of the data, it appears that mechanisms, such as differential thermal expansion of the heated rock and its fluids, are likely to be occurring within the geologic setting of this project to an extent not seen in more permeable rocks and could be favorably affecting the overall production response. Other possible effects are also cited.

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