Engineering Features of the Schuler Field and Unit Operation

A summary of the reservoir engineering and related geologic data on the Schulerfield, Union County, Arkansas, is presented here in a manner intended tointerest both technical and nontechnical readers. The Cotton Valley formation and the Reynolds oolite are oil-productiveformations in the Schuler field, but the Jones sand pool, at a depth of 7500ft., developed with I46 wells on 20-acre spacing, is the reservoir of principalinterest. The Jones sand sandstone reservoir is an anticlinal trap typically gas-drive ordepletion type in performance. The core analyses from 88 per cent of the wellsdrilled, together with drilling time and electric-log data, yield an accurateestimate of the "productive" sand thickness and its areal distributionover the pool. Accurate production statistics, monthly reservoir-pressuresurveys, and bottom-hole sample analyses when correlated by the "material-balance equation" show unusually good agreement with thatprinciple. Estimates of oil initially in place made by the material-balancemethod and the sand-volume method are in good agreement at 1I6 to I20 millionbarrels. The reservoir-pressure history of the pool reflects the reaction of areservoir to production, proration and secondary-recovery practices. The cost of the extensive program of reservoir study in the Jones sand pool hasbeen estimated, in order to emphasize the value derived from such an investmentthrough better understanding of a reservoir's reaction to productionpractices. Unit operation of I40 of the I46 Jones sand wells made possible an effectiveunitized gas injection pressure-maintenance program. Reservoir-pressure declinewas arrested, natural flow was maintained, and pumping and lease equipment wereconserved. An increased ultimate recovery of 20 million barrels beyond theestimated 34 million barrels primary recovery is indicated at present. Extension of the Jones sand unit to include the undeveloped Cotton Valleyformation will permit additional recovery of otherwise uneconomic reserves ofoil through wells no longer required in the Jones sand operations. Introduction The Schuler field comprises approximately 4000 acres in and about sec. 18, T.Ig S., R. 17 W. in west central Union County, Arkansas. Three reservoirs areproductive of oil and gas: the Cotton Valley formation, the Jones sand, and theReynolds oolite section of the Smackover limestone. The Jones sand pool is themost important reservoir from an engineering viewpoint. It possesses thetraditional and somewhat classic characteristics usually associated with ananticlinal trap. Development and operations have followed the dictates ofadvanced 'engineering practices. maintenance operation now being carriedout. T.P. 1605