Acid fracturing pilot in the porous limestone reservoirs of Halfaya Oilfield

The Mishrif oil reservoir in Halfaya Oilfield of the Middle East is a monoblock anticlinal oil reservoir of strong heterogeneity, and its stimulation scale is limited due to the influence of bottom water when the acid fracturing pilot is carried out at the edge of the structure. The reservoir rocks are lithologically pure, which is not beneficial to the nonuniform acid etching in the process of acid fracturing. The Young’s modulus is low and the shielding capacity of stress barriers is poorer, which are not beneficial to the extension of fracture length and the control of fracture height. The crude oil is emulsified seriously after the acid/rock reaction, which is not beneficial to the flow back. Numerical simulation and experimental results show that the adoption of acid fracturing technology of multi-stage alternating injection and the optimization of injection technological parameters base on reservoir characteristic can increase the operating distance of acid/rock reaction and realize nonuniform acid etching; the support technology of fiber for temporary plugging and fluid loss control and mutual solvent for emulsion breaking and flow back promotion address the problems of great fluid loss in the process of fracturing and difficult flow back after the fracturing; and the closed acidizing in the last stage enhances the flow conductivity near the well. The “crosslinked fracturing fluid+gel acid” system is selected, which slows down the acid/rock reaction velocity effectively. Its application effect in Well MF3 is excellent. The length of the effective etched fractures is up to 80 m and the tested oil production rate of single well is 317 t/d, which indicates remarkable reservoir stimulation effect. The research results provide the effective engineering technology and method for the production of similar reservoirs in the Middle East.