Sandstone Acidizing Design With a Generalized Model
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SummaryAcidizing of sandstones with HF/HC1 mixtures is most frequently applied to remove near-wellbore damage, often in reservoirs with considerable vertical heterogeneity. A previously presented model for such processes in which an organic resin diverting agent was used has been extended to account for any type of particulate diverting agent and to allow for injection of multiple sequences of acid and diverting agent at either constant rates or constant bottomhole pressures (BHP's). When used to design treatments for a typical U.S. gulf coast reservoir, the model has shown that the optimal treatment strategy depends on both diverting-agent efficiency and the desired depth of live acid penetration and that relatively high injection rates appear advantageous for the conditions imposed by the model.A general model of diverting-agent behavior was developed from filtration theory. A single parameter, the specific cake resistance, is needed to model the diverting-agent behavior in the acidizing simulator. Calculation procedures to determine this parameter from laboratory tests of diverting agents were developed. These tests are either constant-rate, constant-pressure, or variable-rate and variable-pressure experiments; in each case, the specific cake resistance can be extracted from the experimental data. These procedures allow the efficiencies of various diverting agents to be compared on an equal basis.The sandstone acidizing model was used to design a treatment for a typical gulf coast sandstone reservoir. On the basis of an overall skin factor for the well, various assumptions were made about the distribution of formation damage around this multilayered completion. Treatment results were found to be fairly sensitive to the details of the damage distribution, suggesting that the skin factor alone may not be an adequate design parameter.
