Abstract

The Shafter Lake (San Andres) Field in Andrews County, Texas, produces on the eastern side of the Central Basin Platform from the upper San Andres and lower Grayburg formations, part of the lower Permian (Guadalupian). The field has produced about 58 million barrels of oil since discovery in 1930. Development of the field began in earnest around 1944. Expansion of the field area continued into the early 1980s. Today the field has about 700 producing wells over approximately 24,000 acres. This presentation illustrates the core results and production of the Dow Hall #3H operated by Trey Resources in the northern portion of the field.

The San Andres is a relatively heterogeneous platform carbonate that until recently has been produced vertically. The reservoir ranges from a subtidal, peloidal dolopackgrainstone with intergranular, moldic, and intercrystalline porosity to intertidal flat peloidal dolowacke-packstone with abundant fenestral porosity and is responding well to unconventional technology. The lower section of the reservoir transitions into the Residual Oil Zone. Petrophysical models of the reservoir were developed from logs including resistivity, spectral gamma ray, neutron-density, and sonic. Bulk volume water and water saturations indicate the boundary with the residual oil zone. The seal is a regional exposure and erosional surface in our lease area which is in the lower Grayburg. It contains red sandy clay -mudstone and clay-rich siltstones interbedded with sandy dolowackestones, and is identified by the lack of porosity due to anhydrite occluding the porosity. The Dow Hall #3H IP’d at 347 BOPD, 80 MCFD, and 791 BWPD. Cumulative production is 63,806 barrels. Net reservoir thickness was mapped and a volumetric estimate of recoverable oil is 288,892 bbls.