Designing gas injection projects in naturally fractured reservoirs requires special considerations which, in turn, relies on knowledge of the fracture network. Characterization of the fracture network involves delineation of important physical characteristics, such as fracture spacing, fracture orientation, fracture conductivity (of both natural and hydraulically induced fractures). Of equal significance is understanding the transfer mechanisms between oil and gas in the rock matrix and injected water and gas present in the fracture network.
Integration of fracture characterization with results obtained during experimental investigation of transfer mechanisms is a key step for history matching and predicting reservoir response to water or gas injection. This paper describes the steps taken in two important areas of 1) fracture characterization and 2) fluid exchange from fracture to matrix as a precursor for design of a 10 acre CO2 pilot in the naturally fractured Spraberry Trend Area.
Fracture and matrix characterization are based on oriented vertical and horizontal core taken from Upper Spraberry reservoirs. Fluid exchange mechanisms are investigated in reservoir plugs and whole core at reservoir temperatures and pressures. Results of imbibition/wettability and CO2 gravity drainage experiments are presented. History matching Spraberry waterflood performance and predicting performance. under CO2 injection is presented based on integration of reservoir characterization and laboratory experimentation.