塔里木盆地奥陶系碳酸盐岩古岩溶作用与储层分布

在塔里木盆地奥陶系海相碳酸盐岩中识别出同生岩溶、风化壳岩溶、埋藏岩溶三种不同类型的古岩溶作用，综合分析认为它们是控制奥陶系碳酸盐岩储层形成的关键要素。同生期大气淡水选择性溶蚀颗粒碳酸盐岩所形成的粒内溶孔、铸模孔和粒间溶孔等，为储层提供了基质孔隙，储层分布受大气成岩透镜体控制，通常呈透镜体沿台地边缘高能相带断续分布。与风化壳岩溶作用有关的碳酸盐岩储层在区域上主要展布于奥陶系碳酸盐岩裸露的古潜山分布范围内，垂向上则局限于奥陶系碳酸盐岩侵蚀不整合面以下200 m深度范围内。根据风化壳岩溶的垂向与横向发育特征，指出其储层垂向上主要分布于地表岩溶带的覆盖角砾岩、垂直渗流岩溶带和水平潜流岩溶带内，平面上主要发育于岩溶高地边缘、岩溶斜坡区、岩溶谷地上游区、岩溶残丘等古地貌单元。埋藏岩溶作用常与有机质热演化过程中伴生的有机酸溶蚀碳酸盐矿物有关，往往沿原有的孔缝系统进行，具有期次多、规模不等的特点，是碳酸盐岩储层优化改造的关键因素之一。

Paleokarstification and Reservoir Distribution of Ordovician Carbonates in Tarim Basin

Three types of paleokarstification,including syndepositional,weathering-crust,and buried ones,are distinguished in Ordovician marine carbonate within Tarim basin.It is synthetically considered that the paleokarstification is a key factor of the formation of Ordovician carbonate reservoirs.Intragranular and intergranular solution spaces and moldic pores formed by syndepositional meteoric fresh-water selective dissolution,are provided matrix porosity for the carbonate reservoir.These reservoirs are controlled by meteoric diagenetic lens in the distribution and are generally developed along the high-energy platform margin facies in the shape of discontinuous lenticle.The carbonate reservoirs related to weathering karstification are regionally distributed within ancient buried hills of exposed Ordovician carbonate,and are vertically limited within 200 meters below erosional unconformity interface of Ordovician carbonate.Based on vertical and lateral development characteristics of weathering karstification,it is directed that karst-type reservoirs are largely distributed within cap rubblerock of surface karst,vertical vadose and horizontal phreatic zones in the vertical direction,and generally developed at karst upland margin,karst slope,upstream karst valley,and karst hammock in the region.Burial karstification is generally related to the dissolution of carbonate minerals resulted from organic acid by which the thermal evolution of organic matter accompanied,is commonly proceeded along previous pore and fissure system,is characterized by more stages and various scales,and is a key factor for the optimized reworking of carbonate reservoir.