Formation Evaluation Aids Application Of Sequence Stratigraphy To Optimize Production Of The Means San Andres Unit, Andrews Co. , Tx. Available to Purchase

The Means San Andres Unit (MSAU) is located 50 miles northwest of Midland, Texas. Discovered in 1934 by Humble Oil, it was developed on 40-acre spacing by the mid 1950's and, after unitization, waterflooding began in 1963. The unit contains over 14,000 acres which produce from Permian Guadalupian age San Andres and Grayburg Formations at depths between 4200 and 4800 feet. The primary reservoir lithology is dolomite in the San Andres Formation and both dolomite and clastics in the Grayburg Formation. Daily production rates exceed 15,000 BOPD from over 500 active wells. The current C02 tertiary recovery project, initiated in late 1983, includes 366 of these wells in 189 injection patterns (Fig. 1). The Means San Andres Unit is located on the eastern margin of the Central Basin Platform. During Permian time the platform separated the shallow Midland Basin to the east from the deeper Delaware Basin to the west (Fig. 2). The Means Unit structure is a north-south trending asymmetrical anticline with a gentle west flank and a steeper east flank (Fig. 3). Four-way structural closure "exceeds 200 feet and the trapping mechanism is a combination type with reservoir facies pinching out to the west. In 1987 Exxon conducted a workshop to develop a new reservoir model for the MSAU San Andres Formation (Leary et. al., 1988) using the concepts of sequence stratigraphy. Geologists in the workshop interpreted seismic, described core, studied well logs, and used petrographic examination of thin sections to evaluate the sequence framework, depositional facies types, porosity types, and diagentic history of the San Andres Formation. In 1989 a follow-up project was initiated to increase the detail of the findings of the workshop and to apply them to field operations. This paper will briefly review the conclusions of the sequence stratigraphic workshop and discuss the results of the 1989 project emphasizing the importance of log analysis.