Features and classified hierarchical modeling of carbonate fracture-cavity reservoirs

Taking the Ordovician fracture-cavity carbonate reservoir of Tahe oilfield, Tarim Basin as an example, the fracture-cavity reservoir has been classified according to the type and size of reservoir space, and a 3-D geological model of fracture-cavity reservoirs was built according to their types and classes. Based on core, drilling, logging and seismic data, the fracture-cavity reservoir was divided into four types, namely cave, dissolved pore, fracture and Matrix block types, in which the cave was subdivided into two subtypes, large cave and small cave; and the fracture was subdivided into four subtypes, large scale fracture, meso-scale fracture, small scale fracture and microfracture. The large cave model was established using deterministic method via seismic truncation and pattern modification. The small cave model was built using the method of multiple-point geostatistical simulation with large cave model as the training image. The dissolved pore model was built using sequential Gaussian simulation. The large scale fracture model was established using the deterministic method of manual interpretation, meso-scale fracture model was built using deterministic method of ant tracking, the small scale fracture model was built using stochastic object-based modeling. The micro-fracture and Matrix block have no discrete distribution model established because of their poor storage quality. Then the different types of reservoir space models were merged into one model to get the discrete distribution model of typical fracture-cavity unit. The application in Tahe blocks 6 and 7 showed that this classified hierarchical modeling improved the reservoir model precision, guided the water-flooding effectively and advanced the development efficiency.