A successful steam injection vertical expansion was recently implemented in California's Midway Sunset Field using slimhole injection wells. Slimhole injectors were chosen over conventional injectors to reduce capital investment. This cost savings enabled the drilling of additional injection wells which were used to optimize steam placement based on reservoir architecture.
Two vertical expansion designs were compared at a fixed cost using either conventional or slimhole steam injectors. The conventional well design used ten injection wells and three temperature observation wells. The steam drive targets were two steeply dipping turbidite depositional lobes that contain multiple vertically segregated sand bodies. Conventional well locations were picked based on the upper primary reservoir, compromising injection location in the lower secondary reservoir.
The slimhole plan was selected because of its advantages. It consisted of thirty-eight injectors and ten temperature observation wells. The capital cost for the slimholes was about the same as the conventional program. Approximately three slimhole injectors could be drilled for the cost of one conventional injector. With additional wells, injector locations were optimized for both the upper primary and lower secondary reservoirs. These additional injection wells provided improved profile control and steamflood management of the individual sand bodies within each reservoir. As a result of the vertical expansion, incremental production has increased steadily since project start-up.
The section 2F (T11N/R24W) property covers 220 acres and is located in the Midway Sunset Field near Maricopa, California (Fig.1). The field was discovered in the early 1890's and primary production on the property began in 1917. In 1965, when primary production was no longer profitable, cyclic steam stimulation was initiated. Due to decreasing cyclic steam response, an infill and replacement well program was started in the early 1970's with cyclic steam continuing as the EOR method. In 1983 an up dip, staggered line drive, steam injection project was initiated to process two of the reservoirs on the property. In 1992, steam injection was terminated in the lower of the two reservoirs when it became uneconomical. An expansion into a stratigraphically higher reservoir was undertaken in 1990 based on the success of the previous drives. This project never responded. Excess steam capacity in 1992 led to the project discussed in this paper, which is a mid dip, line drive vertical expansion using slimhole injectors.