Experimental and field data analyses of ball sealer diversion
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Diversion methods are routinely used in both matrix acidizing and fracturing stimulation treatments. The diversion methods are categorized into chemical diversion and mechanical diversion. In this study, we focus on one of the classical mechanical diversion methods, ball sealers. Ball sealer diversion is used in cased and perforated wells to divert stimulation fluids by temporarily blocking perforation holes in the casing with rubber-coated balls. This diversion method can be very effective, particularly with high rate injection, but no general methodology is available to design ball sealer diversion, or to evaluate its effectiveness from the treating rate and pressure record. Although some design methodologies, such as the use of buoyant ball sealers to improve the ball sealer efficiency, have been suggested, no model has been presented for determining how many balls seat on the perforations. In this paper, experimental data from an extensive series of full-scale flow experiments conducted by BP were analyzed. We summarized several features of the ball sealer which are not presented in the literature. Also we used the procedure presented by Brown et al. (1963) to evaluate statistical nature of the ball behavior in the BP's experimental results. The BP experiments were designed to minimize scatter of data. However, the seating process was found to be statistical. Also we analyzed one field acid fracturing treatment where ball sealers were used as a diversion method. Then the analyzed data were compared to the BP experimental results. A similar trend in seating efficiency was observed. Copyright 2011, Society of Petroleum Engineers.
