Controlled Waterflooding, Means Queen Reservoir

Abstract

Abstract Controlled, balanced waterflooding techniques evolved from thorough planning in Humble Oil and Refining Co.'s 16,000-acre Means Queen five-spot water flood project as the logical solution to reservoir, proration, ultimate recovery and economic factors associated with secondary recovery operations. To achieve the goals of maximum oil recovery and minimum water production, the effectively controlled water flood requires an accurate and detailed reservoir description, planned rates of injection and production, accurate per-well performance data and monthly comparison of actual-to-theoretical performance to monitor water flood behavior and efficiency. Methods for accomplishing these requirements were preparation of a reservoir isopach describing the pore volume around each well; allocation of each well's producing or injection rate on the basis of PV fractions; installation of individual well metering equipment on both injection and producing wells; and development of a computer program, both to compare performance data monthly and provide schedules and records. The current success of the project demonstrates the effectiveness of these methods in combination with control procedures developed from reservoir performance. Secondary recovery has exceeded primary on some leases with current water-cuts of only 40 per cent. Ultimate secondary recovery is expected to be at least twice primary. Introduction The concept of controlled, balanced waterflooding evolved from a deliberately planned program of data gathering and analysis. For example, a planned coring program was incorporated in primary development to obtain basic reservoir data. This type of basic data could not have been secured, at any reasonable price, after primary development had been completed. Also, accurate secondary performance data have been obtained by the planned use of metering equipment and pressure interference tests. This project presented the problems of efficiently operating a prorated five-spot waterflood with varying spot sizes (a factor of 3:1) and varying spot PV (a factor of 10:1) to obtain maximum oil recovery while producing a minimum amount of water. In reviewing industry water-flooding activity, it was found that for various reasons (lack of sufficient reservoir data, mechanical conditions of wells, presence of multiple producing stringers open to common wellbores) only a moderate degree of control was exercised in carrying out most waterflood operations. Secondary recovery from many of these floods is approximately equal to primary, although secondary recovery up to two times primary recovery might have been possible under controlled waterflooding. Published and unpublished laboratory studies, as well as theoretical recovery calculations, indicate that more oil probably should be recovered if a more efficient displacement could be achieved, which should result in a longer period of maximum allowable producing rates and reduced water cycling. The potential for improved profit through controlled operations, where applicable, is substantial. For example, if secondary oil recovery in the Means Queen project could be increased by an amount equal to only 10 per cent of ultimate primary, an additional 1 million bbl of oil would be recovered. The decision was made to attempt a controlled waterflood in the Means Queen project. A balanced waterflooding concept, with a maximum degree of waterflood control exercised at the individual well level and with continuous monitoring of performance, was adopted to try to achieve the controlled operations desired. Reservoir CharacteristicsThe geographical location of the Means (Queen sand) field in northern Andrews County, West Texas, is shown in Fig. 1. Geologically, it is one of three separately prorated Queen fields in a single reservoir which lies on the eastern edge of the Central Basin Platform and extends into the Midland Basin of West Texas. These fields cover a combined area of about 35,000 acres with the Means (Queen sand) field covering about 16,000 acres. The reservoir, partially structural and partially stratigraphic, is a sand formation composed of two stringers occurring at a depth of about 4,100 ft. Log and core data in Fig. 2 are typical of the average reservoir characteristics. The lower sand member is the main producing zone since the upper sand is productive over very limited areas in the Means (Queen sand) portion of the reservoir. JPT P. 1385ˆ