Case Study of Stevens Sand Horizontal Well

Abstract

SPE Members Abstract The Yowlumne horizontal well was completed in March 1991 at a measured depth of 14,005' (11,253' true vertical depth). The 2252' horizontal lateral developed a thin Stevens Sand interval that could not be economically developed using vertical wells. The increased pay exposure and drainage radius from a horizontal well provided higher rates and reserves, at lower capital and operating costs, than vertical wells. The horizontal well has produced at more than three times the rate of previous vertical wells in this part of the Yowlumne field. At the time it was completed, the Yowlumne horizontal well was the most ambitious horizontal drilling project undertaken onshore in California. The well is noteworthy because it exploited a thin sandstone oil column in an active waterflood, and has an effectively cemented completion. This paper provides a comprehensive analysis of the projects design and results in three areas: reservoir engineering, drilling and completion. Introduction The Yowlumne field is located near the southern end of the San Joaquin Valley, about 25 miles south of Bakersfield, California (Figure 1). Yowlumne is one of a series of giant light oil fields which produce from the Upper Miocene age Stevens formation. Other giant Stevens fields in this trend include Buena Vista, Elk Hills and North Coles Levee. The Stevens formation is locally known as the Yowlumne Sand, occurring at an average depth of 12,000' (Figure 2). The Yowlumne Sand is a turbidite deposit. The channel facies occurs in Yowlumne Unit "A", at the southern end of the field (Figure 3). The Unit "B" deposit, in the northern end of the field, is primarily a fan facies. However, the horizontal well was drilled in a high energy channel near the updip pinchout of the Yowlumne Sand in Unit "B". The Yowlumne field was discovered in 1974 by Texaco at the southern tip of what later became Unit "A". Development spread northward, reaching what later became Unit "B" in 1976. The field was competitively developed during primary production by seven operators. Primary production peaked at over 26,000 barrels of oil per day (BOPD) in 1978. Unit "A" was unitized for purposes of waterflooding in 1979. The waterflood was extended to the rest of the field in 1982, after Unit "B" was formed. The waterflood was very successful, with peak production of more than 23,000 BOPD in 1986. Ultimate recovery is projected to be 107 million barrels of oil (40% of the original oil in place). P. 549^