Reservoir Characterization and Waterflood Performance Evaluation of Granite Wash Formation, Anadarko Basin

The Granite wash formation in the Anadarko basin is classified as a tight-gas play and is located along the Texas ? Oklahoma border. It has a complex mineralogy and consists of stacked-pay series of tight sands. Our zone of interest is the liquid-rich Missourian Wash B interval in Wheeler County in which two horizontal wells have been drilled. The purpose of this research is to characterize the reservoir through geologic modeling and determine the feasibility of a waterflood using simulation studies.

A set of field data was provided by the operator and other necessary parameters were obtained through publicly available field studies and literature. The final objective is implementing advanced reservoir simulation to integrate well log data, PVT data, diagnostic fracture injection test and microseismic analysis into a plan of development.

The Missourian Wash B formation has a maximum net pay thickness of 50ft. The target sand is laterally continuous which makes it an ideal horizontal drilling prospect. The wells are stimulated by multi-stage hydraulic fracturing. The initial production gas-oil ratio is 1800 scf/stb and PVT reports indicate presence of an oil reservoir above bubble point pressure. PVT correlations show that the 42? API oil and potential injection water at the reservoir temperature have almost the same viscosity. All these factors point towards the formation being a good waterflood candidate.

Well log analysis was performed to obtain porosity and saturation estimates. The microseismic mapping report provides a good overview of the well completion efficiency. Laboratory PVT data was tuned to predict reservoir fluid behavior by parameter regression and component lumping. An isotropic black-oil simulator by Computer Modeling Group Ltd was selected for our work. The reservoir model was validated by sensitivity studies and history matching of production rates was performed.

Simulation result of waterflood implementation by utilizing offset horizontal wells as injectors is analyzed, and three different plans of development are discussed. It is seen that the overall response to waterflooding is poor due to low formation permeability leading to low water injectivity. But a greater reservoir area can be drained if production is initiated from additional horizontal wells. A well-spacing of four horizontal wells in 600 acres section is recommended. The stimulated reservoir volumes of adjacent wells should be close to each other for effective reservoir drainage.