PROSPECTS FOR MEDIUM-DEEP NATURAL GAS EXPLORATION FIELD IN WEST SICHUAN AREA

The developed degree of the Caledonian weathering crust directly affects the developing of related reservoirs, and paleogeomorphology palys a decisive part in the development of secondary pores. In view of the importance of the Caledonian fossil weathering plane, the paleogeomorphology is divided into karst highland, karst slope and karst depression three paleogeomorphological units in this paper, and four shortcomings existing in the former paleogeomorphological restorstion methods such as the residual thickness method, the standard method, etc. are analysed. On this basis, the sequence stratigraphy method to restore paleogeomorphology whose kernel content is regional unconformable planes with isochroneity is suggested. The authors use this method to restore the Caledonian paleogeomorphology of Zhanhua area in the Jiyang Depression and analyse the karst development features of two different paleogeomorphological units in this area, 991 Buried Hill in karst highland and Gudao Buried Hill in karst depression. Results show that the sequence stratigraphy method can accurately restore the Caledonian paleogeomorphology and predict the developed zones of secondary pores, and at last direct hydrocarbon exploration related to karst.