Influence of geological and technological Parameters on the Efficiency of acid treatments in carbonate reservoirs: Experimental and statistical study

Acid treatment technology has become widespread in the development of carbonate layers in oil fields. Virtually every well in the history of its production has been acid treated downhole, ultimately providing millions of tons of incremental oil production globally. Despite the considerable amount of theoretical and practical research devoted to this technology, the problem of controlling the efficiency of acid treatments remains topical. In this connection, the purpose of this paper is to study the influence of known and available in field conditions geological and technological parameters on the efficiency of acid stimulation in carbonate reservoirs. Laboratory studies (in free volume, filtration and X-ray tomography tests) using two hydrochloric acid compositions and carbonate rock samples of the same geologic age from oil fields of Perm krai to determine the dependencies were performed. Acid treatments were modeled by varying technological parameters (volume, rate and pressure of injection of acid compositions, reaction time of acid with rock) under thermodynamic conditions corresponding to reservoir properties. Statistical processing of empirically obtained data allowed us to note the predominant role of technological parameters to achieve a successful result of acid stimulation. Multivariate statistical models describing the process of formation of acid treatment efficiency in carbonate reservoirs have been developed. It was found that the reservoir stimulation efficiency varies in direct proportion to the increase in the injection pressure of the acid composition and the volume of agent used due to the development of wormholes. The efficiency of acid treatment at dolomite content in the rock is significantly lower, which requires increasing the rate of composition injection and reaction time to achieve the highest stimulation result. Thus, the paper provides a basis for further development of the process of controlling the effectiveness of acid treatments in carbonate reservoirs of oil fields.