Acid fracturing technology forcing fracture to propagate downward in carbonate reservoirs

Considering the strong heterogeneity of carbonate reservoirs, it is very difficult to reach the reservoir at the lower part by conventional acid fracturing due to restrictions of drilling technology and geological conditions if the borehole is relatively far away from the reservoir. This paper, based on the mechanism of artificial interlayer controlling fracture propagation path, puts forward an idea where floating type of diverting agent forms high artificial barrier layer before forcing longitudinal downward propagation of acid fracture. A special floating type of diverting agent TBA of ultra-low density and high temperature and high pressure resistance is developed, which has a density of 0.37 g/cm3, pressure-bearing capacity of 140 MPa and keeps stable at 260 ℃. The floating type of diverting agent TBA is studied with respect to the floating law, and digital modeling is used to optimize the time of floating and dosage of TBA to obtain the control parameters of acid fracturing that effectively forces the fracture to propagate downward as far as possible until reaching the reservoir. This acid fracturing technology has been tested in 4 wells in carbonate reservoirs in Tarim basin with excellent effect.