Evaluation and Modification of the Means San Andres Unit Waterflood

Abstract

Following detailed studies, the injection scheme of this unit was expanded to include interior injection as well as the original peripheral injection. The success of the project has borne out the peripheral injection. The success of the project has borne out the fact that a combination of engineering analysis and geological interpretation is far more effective in understanding performance than either study could be by itself. Overview Injection modifications made to the Means San Andres Unit waterflood in 1970 increased the gross unit oil production from 13,000 to more than 17,000 B/D during calendar 1970. Those modifications changed the waterflood scheme from an indirect peripheral waterflood to direct pressure support from peripheral waterflood to direct pressure support from interior injection. As a result, portions of the reservoir that previously were not effectively flooded have been brought under direct waterflood. Other portions of the reservoir that had been receiving some indirect support from the peripheral injection are now being flooded more efficiently because of the direct support from the interior injection. History The Means field is located in Andrews County, Tex.. about 15 miles northeast of the city of Andrews. Geologically, the field is on the eastern edge of the Central Basin Platform. It lies in a north-south trend of San Andres production stretching for more than 100 miles in West Texas. The trend contains several very prolific San Andres reservoirs, most of which are now under active waterflood. The means San Andres field was discovered in 1934. Early wells showed a potential exceeding 1,000 BOPD, with some as high as 5,000 BOPD. Although the center of the field was developed in the 1930's, complete definition of the field came slowly as development moved towards the relatively tight rock around the flanks of the field. The extreme southern part of the field was not developed until the part of the field was not developed until the mid-1950's after the introduction of hydraulic fracturing. The eastern part of the Means field was unitized as the Means San Andres Unit early in 1963. Water injection was started around the periphery shortly after unitization. The injection plan was designed to conform to the natural contours in the field. In an attempt to augment what was suspected to be a very weak natural water drive, the injectors were completed below the oil-water contact. Fig. 1 reflects the early response to the peripheral injection. The field had produced its allowable for several years, so the produced its allowable for several years, so the production response was not immediate. Very shortly production response was not immediate. Very shortly after the start of injection, however, the average GOR dropped significantly from 1,100 to about 350 scf/bbl only slightly greater than the solution GOR of 260 scf/bbl. The original bottom-hole pressure of about 1,800 psi had gradually declined to pressure of about 1,800 psi had gradually declined to about 950 psi at the start of water injection. During early water injection the average reservoir pressure increased to 1,150 psi, where it was maintained fairly stable during the relatively constant production times. The field produced little water during primary and early stages of injection. In fact, after production under a unit allowable commenced in 1965, the water production decreased considerably, and only recently production decreased considerably, and only recently has it increased to a significant value. After the 1967 Mid-East crisis with the attendant high market demand, the Unit reached the limit of its capacity for the first time. P. 1421