四川盆地茅口组风化壳岩溶古地貌及勘探选区

针对四川盆地中二叠统茅口组顶部岩溶古地貌分布特征认识不清的问题,开展了岩溶储层的地质及地球物理响应分析,同时对全盆地200余口探井的茅口组开展了详细的地层对比,在此基础上利用印模法和残余厚度法2种古地貌分析方法开展了茅口组顶部古地貌形态的精细刻画,指出茅口组顶部发育岩溶洼地、岩溶斜坡和岩溶高地3种地貌单元,古地貌具有“三高地、两斜坡、两洼地”的特点,岩溶洼地地层保存基本完整,岩溶高地缺失茅口组四段和部分茅口组三段,岩溶斜坡的地层缺失介于岩溶高地和岩溶洼地之间。突破了前人对茅口组风化壳古地貌存在“两高地”的认识,根据这一新认识并结合烃源岩生烃强度特征将茅口组顶部风化壳岩溶储层划分为4个有利勘探区带。

Paleokarst landform of the weathering crust of Middle Permian Maokou Formation in Sichuan Basin and selection of exploration regions

In view of incomplete understanding on distribution characteristics of paleokarst landform of Maokou Formation in Sichuan Basin, we studied the geological and geophysical response of karst reservoirs and made a detailed stratigraphic correlation of more than 200 exploratory wells of Maokou Formation in the whole basin. Based on this, we depicted in detail Maokou Formation palaeogeomorphology by using two palaeogeomorphologic analysis methods, impression method and residual thickness method, and proposed that there developed three geomorphic units in Maokou Formation, karst depression, karst slope and karst highland, which are characterized by "three highlands, two slopes and two depressions". Formations of the karst depression are basically well preserved, and the Mao-4 section and a part of the Mao-3 section have been missing in the karst highland, while the hiatus of the karst slope is medium between the highland and the depression. This conclusion made a breakthrough at the previous understanding on Maokou Formation weathering crust paleo-geomorphology, which holds a "two highlands" view. On the basis of this new conclusion and characteristics of the hydrocarbon generating intensity of source rocks, four favorable exploration zones of Maokou Formation were proposed in the paper.