Compound acid fracturing method for carbonate reservoir

The invention provides a compound acid fracturing method for a carbonate reservoir. The method comprises steps as follows: (1) a pad fluid stage: a surface cross-linked acid is injected into a stratum with the displacement ranging from 1.0 m /min to 3.0 m /min; (2) a main sand adding stage: fracturing fluid gel and sand are mixed and injected into the stratum with the displacement ranging from 4.0 m /min to 5.5 m /min; (3) a closed acidizing stage: a closed acid is injected with the displacement ranging from 4.0 m /min to 5.5 m /min, a sand-carrying fluid formed by mixing the fracturing fluid gel with the sand is fed into the stratum in a displacement manner, and when a formed artificial fracture is longer than 130 m, the closed acid is continuously injected with the displacement reduced to range from 1.0 m /min to 1.5 m /min; (4) a displacement stage: a displacement fluid is injected with the displacement ranging from 1.0 m /min to 1.5 m /min. The total volume of the injected fluids is in a range of 680-750 m , and ratios of the volumes of the injected fluids to the volume of total fluids injected into the stratum are as follows: in procedure (1), the surface cross-linked acid accounts for 40%-45%; in procedure (2), the sum of the fracturing fluid gel and the sand accounts for 45%-50%; in procedure (3), the closed acid accounts for 4%-5%; in procedure (4), the displacement fluid accounts for 6%-10%. With the adoption of the method, the flow conductivity of the fracture and the productivity of an oil well are greatly increased.