Abstract: Fracture cave type reservoirs are special and complicated ones. The materials equilibrium equation for the reservoirs differs from the one of conventional reservoirs greatly. Based on the basic principle of materials equilibrium for reservoirs, the materials equilibrium equation is established for fracturecave type reservoirs. Compared with the material equilibrium calculating method of conventional reservoirs, the features of stratum pressure changing and elasticity expanding is considered in the new method, the coefficient of compressibility introduced, meanwhile, the two phase factor of oil and water in fracture cave type reservoirs is considered which makes the new materials equilibrium method be not only able to express the release process of stratum elastic energy, but also to describe water invasion phenomenon. The related curve solving method is applied, as a result, the reserves calculating accuracy is improved greatly. Taking fracture cave unit S of a certain oil field as example, its production performance data are used to verify the new method, the results show using the new calculation method of the materials equilibrium equation can accurately calculate the reserves of fracture cave type reservoirs.

Key words: fracture cave type reservoir, materials equilibrium equation, geological reserve, coefficient of compressibility, calculation method