A Modeling Approach for Optimizing Waterflood Performance, Slaughter Field Chickenwire Pattern

Abstract

Listen

Translate article

A two-dimensional areal simulation indicated significant trapping of oilbetween center and off-center producers in this unique waterflooding pattern. For typical conditions, the predicted ultimate recovery of 41 pattern. Fortypical conditions, the predicted ultimate recovery of 41 percent of originaloil in place was increased to 44.6 percent by drilling percent of original oilin place was increased to 44.6 percent by drilling additional producers betweencenter and off-center producing wells. Introduction The 3,200-well Slaughter field is one of Texas' major fields. It is on theNorth Basin Platform in West Texas, approximately 35 miles west-southwest ofLubbock. The field was discovered in April, 1937, and most drilling took placein the late 1940's. It produces 32 degrees API sour crude from the San Andresproduces 32 degrees API sour crude from the San Andres dolomite formation ofPermian age at an average depth of 5,000 ft. The formation is relativelyheterogeneous; it structure is a monocline, dipping at less than 1 degrees tothe south-southeast. The field covers an area of approximately 100,000 acresand currently has 2,311 producing wells and an estimated 903 water injectionwells. The producing rate of 113,000 BOPD (July, 1972) ranks fourth in Texas. Cumulative production to Jan. 1, 1972, was 464 million bbl. production to Jan.1, 1972, was 464 million bbl. Field discovery and bubble-point pressure was1,710 psia at 1,250 ft (subsea). Except for several minor gas injectionprojects, the field produced by a solution gas drive until waterfloodingoperations commenced during the mid 1960's on many leases. The field is notbeing produced as one fieldwide secondary recovery unit but consists of a groupof smaller units and cooperating lease floods. Water injection operations arecurrently being conducted on practically every major lease or unit. A uniquespacing exists in much of the field since that part of West Texas wasoriginally surveyed in the Spanish land measurements of hectares, labors, andleagues. A large portion of the field was developed with a density of fivewells per labor (35.4 acres per well). Four wells usually were drilled atlocations 440 to 500 ft from the respective labor lines and a fifth well wasdrilled in the center of the labor. Many of the early Slaughter Fieldwaterflood projects started as cooperative lease-line injection projects orperipheral waterfloods. These were later converted to a unique pattern when itwas determined that an increased pattern when it was determined that anincreased injection-to-producing-well ratio was necessary for more effectiveflooding in this low-permeability reservoir. Fig. 1 shows the two-injector, three-producer pattern that Slaughter Field operators call the pattern thatSlaughter Field operators call the "chicken-wire" pattern. The patternresults in six injectors enclosing three producing wells. A repeating developedchickenwire pattern results in a net injector: producer ratio of 2:3 duringsecondary operations as producer ratio of 2:3 during secondary operations asopposed to a ratio of 1:1 for the conventional five-spot pattern. Thechickenwire pattern resulted in an intensification of flooding. However, it wasnot obvious whether or not this was the optimum pattern or to what degreewaterflood recovery might be influenced by previous unbalanced injection. Evenwith this intensified injection pattern, most flood rates would be relativelylow and the projects long-lived. Thus, it was decided several years ago to do amodel study of a typical area of the field. This study would investigate theeffects of imbalance and additional drilling or well conversions on rates andultimate recovery. JPT P. 757