Approach to Optimization of Acid Treatment in Oil Reservoirs

Abstract

The mathematical model of two-phase displacement of oil by an acid aqueous solution in the neighborhood of a well and a hydraulic fracture [1] was used for investigation processes of optimization acidizing and acid fracturing. It takes into account the kinetics of acid dissolution of a carbonate rock. The proposed model allows us to improve the process of searching and selecting the best design for acidizing and acid fracturing.The effect of well acidizing and acid fracturing are estimated. It is shown possibility to find the best value of such parameters as the speed of injection, speed of reaction and volume of acid mixture injected into a well during acidizing and acid fracturing. At given process parameters in the real case is shown importance of studying the process of interval treatment including the possibility of optimizing the design of each of the treated intervals.The control of such parameters as the injection rate, the chemical reaction rate and the volume of injected acid makes possible to reach the maximum treatment effect at the given solution volume. Also calculations showed that in the case of the acid fracturing the significant slowing of the reaction rate may lead to large leakage of unreacted acid into the reservoir, extending the penetration zone, but also reducing the effects near the fracture and thus worsening the result of treatment.The created model was applied to numerical calculations for real cases. Field and calculated data are in good agreement. Using of this approach allows us to find the ways for new possibilities in improving design of acid treatments and understand the current status of the proposed design. IntroductionAcid treatment is the widely used and effective method of recovery stimulation for oil reservoirs in carbonate rocks. This method makes possible both to clear and extend the porous channels and fractures, to stimulate fluid inflow from the reservoir and to create new voids by dissolving the minerals forming the rock. At the same time acid treatment is an inexpensive and sufficiently simple technology. Process design schemes of the process differ in recipes of compositions, volumes of reagents, the injection rate and pressure, the use of additives for acceleration or deceleration of chemical process.During acid fracturing, the carbonate rock is pickled by acid composition nonuniformly. And the fractures developed by acid fracturing do not require to be fixed by a propping agent since even after closing they have higher conductivity due to the wormholes formed.In the basis of presented paper put a model of the two-phase displacement of oil by an aqueous acid solution [1]. The problem of the design optimization is solved by finding the functions extremums of additional growth of oil rate and NPV (Net present value) depending on the acid volume. Thus it is shown the possibility of growth of effectiveness such effects as acidizing and acid fracturing.