History Match Analysis of the Little Creek CO2 Pilot Test

Abstract

Production and pressure data from the Little Creek CO2 miscible pilot test are history matched using a miscible flood simulator. Simulated recovery is dominated by gravity segregation of CO2 and crossflow of oil. A new pseudorelative permeability technique, which decouples gravitational and viscous fingering effects, is developed and used in the history match. Introduction A limited number of carbon dioxide miscible pilot tests have been completed or have enough history to permit a meaningful evaluation. Noteworthy tertiary examples include the SACROC, Twofreds, and Willard tests in west Texas and the Little Creek test in Mississippi. SACROC, Twofreds, and Little Creek were producing pilots; of these, the Little Creek pilot is best suited for a thorough analysis to identify those factors that influenced tertiary oil recovery. The test was well confined and small, with one injector and three producers.The primary objective of this work was to determine the controlling factors in the Little Creek CO2 flood by history matching pressure and production data with a four-component, miscible flood simulator. Additional objectives were to (1) develop, demonstrate, and employ a pseudorelative permeability technique for simulating three dimensional miscible performance with two-dimensional calculations and (2) project performance for different-size CO2 slugs than that tested at Little Creek. Field Description and History The characteristics and history of the Little Creek field are documented elsewhere. A limited discussion of the field is presented here for completeness.The Little Creek field is in the Lower Tuscaloosa trend of southwestern Mississippi. It was discovered in 1958. A peripheral line-drive waterflood was conducted from 1962 to 1970, and CO2 was injected into the pilot area from Feb. 1974 to Feb. 1977. Of the 102 million bbl (16.2 x 10(6) m3) of oil initially in place, 25 million bbl (4.0 x 10(6) m3) were produced by primary depletion and 22 million bbl (3.5 x 10(6) m3) were produced as a result of waterflood operations. More than 120,000 bbl (19 000 m3) were produced in the pilot test.The reservoir's pay zone is the 10,750-ft (3280-m) Lower Tuscaloosa Denkman sand, which is Cretaceous in age. The reservoir is controlled stratigraphically, being limited by rapid sand pinchout on the flanks. The reservoir is said to have "remarkably uniform rock properties ... (with) no correlative high permeability zones." The reservoir responded very well to water injection, reportedly "flooding out uniformly ... going to 100% water within 3 months of flood-front breakthrough and conformance was estimated to be 90%" Table 1 lists average rock and fluid properties.The CO2 miscible pilot test was conducted against a pinchout along the eastern edge of the field. As shown in Fig. 1, the pattern is essentially one-quarter of an inverted nine-spot on 40-acre (16-ha) spacing. The pilot area was confined by five backup water-injection wells whose purpose was to prevent migration of fluids out of the test pattern. JPT P. 2042＾