Waterflood Stimulation for Fractured Limestone of the Austin Chalk

Abstract A process for treating older wells completed in the Austin chalk has produced impressive production increases in wells which had previously been fracture stimulated using water-based, sand-laden fracturing fluid. The process utilizes high volumes of water pumped at high rates (more than 25 bbl/min). Termed ‘waterflood stimulation,’ this technique has helped rejuvenate wells which had experienced major production declines since the original fracturing treatment. Incorporated in the treatment fluid are surfactants, diverting agents, weak acids, and friction reducers. Based on analysis of 3 years of treatment results, ‘waterflood stimulation’ appears to provide a waterdrive production mechanism, as evidenced by well response. Austin Chalk completions have typically been characterized by high initial production followed by rapid production declines. Reservoir characteristics of the Austin Chalk indicate that production is dependent on the fracture system, both natural and created, rather than on the actual rock matrix. Methods have been developed to help determine feasibility of ‘waterflood stimulation’ on an individual well basis. Factors to consider include cumulative production and gas:oil ratio. Guidelines for treatment rates and volumes have also been developed based on well parameters and field experience. Other, similar-type reservoirs may also be receptive to this form of treatment. Subject paper will present case histories from approximately 20 wells, descriptions of reservoir characteristics, evaluation criteria for candidate wells, and treatment design and operation with production data before and after treatments.