The mathematical model of two-phase displacement of oil by an acid aqueous solution in the neighborhood of a well and a hydraulic fracture is created. It takes into account the kinetics of acid dissolution of a carbonate rock. The proposed model allows us to investigate the penetration of the active admixture and the changing of the reservoir characteristics during the solution injection and after well shut-in for reaction.
The effect of well acidizing and acid fracturing are estimated. It is shown that neglecting the two-phase nature of the flow leads to the underestimation of the treatment effect. At given process parameters the needed length of the shut-in period for reaction and dimensions of the acid penetration zone are estimated.
The control of such parameters as the injection rate and the chemical reaction rate makes possible to reach the maximum treatment effect at the given solution volume. 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.