Experimental Study On Acid-diversion Ability Of Strong Heterogeneous Carbonate Reservoirs

In the process of acidizing,the problem of uneven acidification is becoming prominent due to the reservoir heterogeneity.The development and application of diversion acid is the key to solve this problem.In recent years,the effect of diversion acid was analyzed by the differential pressure and flow through parallel coreflooding experiments at home and abroad.However,the quantitative characterization of the shape of wormhole in low permeability core was ignored.Researchs show that there are three points need to be further studied about the performance evaluation of diversion acid: Firstly,the digital quantitative characterization method has not been formed in the performance evaluation of diversion acid;Secondly,the maximum permeability ratio of three common diversion acids can be diverted remains unclear;Thirdly,whether the diversion effect under different permeability conditions for the same permeability ratio is the same remains to be further studied.In this paper,an experimental study on acid diversion performance of strongly heterogeneous carbonate reservoir is carried out around above three issues.Based on the images of wormhole of low permeability cores after parallel coreflooding experiments,the maximum diversion permeability ratio of three diversion acid was explored.The diversion ability of foam acid,VES acid,and foam-based VES acid were 7.84,9.84,and 14.95,respectively;By mean of digital characterization,a set of experimental method for evaluating acid diversion performance based on the maximum differential pressure ratio of high permeability cores,the improvement of permeability and dimensionless wormhole length of low permeability cores were proposed.Based on this method,the effects of three acids at the maximum diversion ratio were evaluated.Studies show that at the maximum diversion ratio,for foam acid,the improvement of low permeability core is 13.09% and the length of wormhole is 2.07 cm,and the maximum differential pressure ratio of high permeability core is 7.88.For VES acid,the improvement of low permeability core is 39.24%,the length of wormhole is 3.48 cm,the maximum differential pressure ratio of high permeability core is 21.92.For foam-based VES acid,the improvement of low permeability core is 54.28%,the length of wormhole is 5.07 cm,the maximum differential pressure ratio of high permeability core is 30.54.This article further explores the effects of different permeability conditions on the diversion performance of three diversion acids.From the perspective of diversion ability,the different permeability conditions have little effect on the diversion ability of foam acid,and with the permeability increases,the diversion ability of VES acid and foam-based VES acid was improved by 20.85% and 48.47%,respectively.From the perspective of diversion effect,with the permeability increases,the length of wormhole and the improvement of permeability of three diversion acids increased,and the diversion effect also increased.The degree of influence of permeability conditions on three diversion acids is ranked as follows: foam-based VES acid> VES acid> foam acid.The research and understanding of diversion acid performance is of great theoretical and practical significance for the development and implementation of the conversion to acid system and the acidification scheme for transformation of strongly heterogeneous carbonate reservoirs.