In Tahe oilfield of Xinjiang, China, the carbonate reservoir displays poor porosity and permeability in its matrix, while the fracture-cave formation is distributed in a random, discreet and discontinuous way. As the oil recovery with water injection mechanism shows, the water injection curve of the carbonate reservoir differs from that of the sandstone reservoir. For discontinuous carbonate reservoirs, the reservoir type can be determined from the shape of the water injection curve. For karst-cave reservoirs with high permeability, on the other hand, the new theoretical model of the water injection process can be adopted to calculate the volume of a single cave or a multiple of caves, crude oil, and formation water. The calculated results agree well with the practical results.