Characteristics of Facies-Controlled Karst Reservoir and Exploration Orientation of Mid-Permian Maokou Fm., Sichuan Basin

Abstract

Karst reservoir of Mid-Permian Maokou Fm. widely exists in the whole Sichuan basin with many high-productivity gas wells. The main controlling factors and distribution of Karst reservoir are not so clear so far, which leads to the less-proved natural gas reserve and poor development. On the base of plenty of drilled wells data, researches were conducted on tectonic evolution, sedimentary and reservoir characteristics, Karst paleo-geomorphology, patterns of hydrocarbon accumulation and preservation conditions and so on. Research results are as follows. First, Karst reservoir of Mid-Permian Maokou Fm. in the Sichuan basin is characterized by multiple phases. Early stage facies-controlled weathered crust and later stage fault-related Karst reservoir are main two reservoir styles. Second, comparing the typical Karst in the Tarim basin, the early weathered crust controlled by sedimentary facies with larger area, shorter erosion stage, weaker erosion degree and thinner reservoir net pay. The peak clump unit and dissolve mound unit are the best palaeo-geomorphology units. The former unit developed bedding fracture-cave karst reservoir and shallow karst usually were situated on dissolve mound unit. Finally, fault-related karst reservoir developed high-steep structure zone of eastern and southern Sichuan basin and Daxinchang area of western basin. Syncline areas of eastern and southern Sichuan basin, central basin and Jiulong mountain of western basin developed weathered crust karst reservoir. The next exploration will aim to the peak clump and dissolve mound units in syncline zones.