Simulation of Flow Effects during Acidizing in Carbonate Oil Reservoirs

The acidizing and the acid fracturing are the most common and effective methods of well stimulation for carbonate reservoirs. These technologies permit cleaning and extending pore channels and creating new channels and fractures. The new mathematical model of acidizing in carbonate reservoir is presented. It accounts for two-phase flow of oil and acid water solution, kinetics of rock dissolution and porosity increasing. It is suggested that the salt generated by the reaction dissolves in water and the carbon dioxide is oil and water soluble. The permeability is assumed to be porosity dependent. Both acidizing and acid fracturing are considered. Numerical solution of the problem is obtained. Some analytical results are derived using the characteristic method for quasilinear equations. The model allows investigating dimensions of the acid penetration zone, the duration of the dissolution reaction and the needed length of the shut-in period. It makes possible to optimize the acid treatment design. On the basis of the obtained solution the efficiency of acid treatment and acid fracturing is estimated by calculation of the achieved skin-factor. Some real cases are analyzed, field and calculated data are in good agreement.