Abstract: The fault-karst reservoirs in the southern Tuoputai block of the Tahe oilfield exhibit a high initial production capacity, but a sharply declining production in the late development stage due to serious water flood and rapid water breakthrough occurred in many wells. There is no efficient simulation method for this phenomenon. Based on the karst features, seismic characteristics, actual well-reservoir configuration, and three-zone structure of fault-karst reservoirs, a grid-like fragmented structure of the fault-karst reservoirs was proposed. Accordingly, by combining the automatic fault extraction (AFE) technology with the ant body attributes, the fracture indicator was derived for characterizing the grid-like fragmented reservoir. Tensor attributes were used for characterizing the karst-vug reservoir, and a dual-porosity compositional model was established for numerical simulation. The results indicate that the grid-like fragmented structure serves as the primary flow channel in fault-karst reservoirs. The fracture indicator is better applicable to characterize the grid-like fragmented structure than AFE and maximum likelihood, and it is highly compatible with tensor attributes in water source zone but poorly compatible in other areas. Compared to single-porosity model, the dual-porosity model based on the grid-like fragmented structure can offer higher matching accuracy and better reflect the production performance of the fault-karst reservoirs.

Key words: southern Tuoputai block, fault-karst reservoir, serious water flood, grid-like fragmented structure, geological modeling, fracture indicator, dual-porosity model, numerical simulation