Abstract:
In the high-steep structural belt of the eastern Sichuan Basin, gas reservoirs of the Maokou Formation in Wolonghe structure block were discovered between the 1980 s and 1990 s by following the exploration model in South Sichuan. The natural gas production reached 44.13×10
8m
3, accounting for 72.57% of the explored reserves. However, no major exploration breakthroughs have been made in recent years. By analyzing the influencing factors of reservoir development, it is determined that the Maokou Formation reservoir in Wolonghe structure block is mainly reformed by later karstification and dolomitization. Among them, dolomitization plays a role in construction of the reservoir, and the karst fracture-cavern body is the key to finding gas reservoirs of the Maokou Formation in the study area. But the application effect of conventional prediction methods for karst reservoir is not good, and it is difficult to predict the regional distribution of karst reservoir thickness. The seismic prediction technology put forward for karst reservoirs in this study include the following analytical steps. (1) According to the development condition of karst geology, paleogeomorphology research is carried out to delineate the favorable areas for karst reservoir development. (2) Based on the geophysical response characteristics of karst reservoirs, a new seismic prediction technique of karst is developed to further delineate the karst development zones in the favorable karst areas. (3) According to the logging response characteristics of karst reservoir, the development zone of karst reservoir is adopted as the facies control condition, and the P-wave velocity data volume of karst is obtained through the facies-controlled stochastic inversion. (4) The regional distribution regularity of karst reservoirs is quantitatively characterized by integrating paleogeomorphology, development zone and P-wave velocity body of karst. The research results show that the time domain thickness and reservoir thickness of the predicted karst coincide with those of the drilled wells up to 88%, which effectively realizes the seismic prediction of the karst reservoirs of the Maokou Formation in Wolonghe structure block. The seismic prediction technology of karst reservoirs helps to open up the prospects for exploration of the Lower Permian Maokou Formation in Sichuan Basin.