An Analysis of Large-Scale Flooding in the Fractured Spraberry Trend Area Reservoir

Abstract

Introduction The Spraberry Trend oil reservoirs, producing from a very tight fractured sand, have been characterized by a rapid decline in reservoir pressure and oil producing rate and by production of only a small fraction of estimated original oil in place. Almost all original areas of development are now in the stripper stage or have been abandoned. Although it was considered unlikely that this solution gas-drive reservoir would lend itself readily to conventional methods of secondary recovery, a great deal of effort has been devoted to developing techniques which would utilize the unusual characteristics of the reservoir rock and its fracture system to increase ultimate oil recovery. A single five-spot pilot water flood was initiated in the west central portion of the Spraberry Trend Area reservoir during March, 1955. A combination analytical and numerical method employing high-speed computing equipment was utilized to analyze results of this pilot flood. With field behavior as the criterion for the analysis, orientation of the major fracture system, ratio of the permeability parallel and perpendicular to this trend, and relationship of the observed recovery from the center producing well of the pilot flood to that which might be achieved under large-scale flooding operations were determined. Information developed during analysis of the pilot water flood was then used to develop a flooding program for a 40-section area in the western portion of the field. From this work, it was concluded that the analysis procedure has considerable utility in analyzing flooding operations in a fractured reservoir and a relatively high pattern efficiency can be achieved in the area studied if the proper flooding pattern is chosen. Attempts to Develop Recovery Techniques The first attempt to develop a new recovery technique was a process designed by The Atlantic Refining Co. to utilize the principle of water imbibition. Laboratory work and the subsequent field trial demonstrated that water injected into the fractures could be imbibed spontaneously into the matrix rock by capillary action with the concurrent expulsion of oil into these same channels from which it could be produced by the surrounding wells. The second example of the research effort to increase oil recovery was work performed by Humble Oil and Refining Co. It was determined that with an intensive and inter-connected system of fractures, water injected into the formation could flood simultaneously a large number of matrix blocks. Water invading the matrix with the concurrent discharge of oil into the fractures would rapidly increase oil content and reduce water content of the effluent in the fractures moving toward the producing wells. To evaluate the potentialities of this type flood, a single five-spot pilot water flood was put into operation March 8, 1955.