Evaluation of Acid Treatments from Pressure Build-Up Analysis

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Abstract
Published in Petroleum Transactions, AIME, Volume 216, 1959, pages 38–43. Abstract A method has been developed for evaluating acid treatments in fractured limestone fields by breaking down pressure drawdown into three component parts:pressure differential across "skin" near the borehole face,pressure differential due to flow resistance in the coarse communicating fissures andpressure differential between the fine voids and the coarse fissures. It is apparent that in most successful acid treatments the first term, skin resistance, has been reduced or eliminated. Further, it is often possible to estimate the volume of coarse fissures associated with the second term, coarse fissure flow resistance. In cases where this volume is comparable with practical acid volumes it seems likely that this resistance also may be attacked with a suitably retarded acid. Introduction Acid treatment has been successfully applied as a general practice in the limestone wells in the Mara/ Maracaibo districts of Venezuela for some 10 years. At the same time the need has been felt for a more precise method of:evaluating the effect of an acid job andselecting wells which should benefit from an acid treatment. The following method, based on an analysis Of build-up curves for wells producing from fractured limestone, provides a means of forecasting the effect acid will have on a well and in many cases the probable order of production rate increase which may be expected. In certain cases it is also possible to calculate the fissure volume through which the acid has to be displaced for best results. Various approximations are introduced in the method, but within the limitations of these the analysis gives an indication of how a well, whether previously acidized or not, may be expected to respond to acid treatment.

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