塔中地区北部斜坡带下奥陶统碳酸盐岩风化壳油气富集特征

Characteristics of hydrocarbon enrichment in the Lower Ordovician carbonate rock weathering crust on the northern slope zone of Tazhong area

塔里木盆地塔中地区北部斜坡带下奥陶统发育大型碳酸盐岩风化壳。对风化壳储层及其成藏条件的研究表明,风化壳储层类型以次生溶蚀孔洞形成的低孔、低渗储层为主,储层主要发育于下奥陶统顶部,分布范围与古构造活动形成的不整合面形态具有较好的对应关系。断裂及裂缝的发育对改善风化壳储层具有重要作用,形成了纵向上叠置、横向连片、沿岩溶斜坡部位广泛分布的风化壳储层。断裂和不整合面构成的输导体系控制了风化壳的油气运聚成藏,储层发育程度控制了风化壳的油气富集程度,多期油气充注与风化壳储层非均质性造成了风化壳油气赋存的差异性。

A large-scale Ordovician carbonate weathering crust was developed on the north slope of Tazhong area in Tarim basin. Studies on the weathering crust reservoirs and its reservoiring conditions show that the reservoirs feature in low porosity and low permeability dominated by secondary solution pores and cavities. They are mostly developed on the top of the Lower Ordovician and have an excellent correspondence relationship with the morphology of the unconformity surface. Reformed by the development of faults and fractures, the weathering crust reservoirs were widely distributed along the karst slope vertical superimpositon and horizontal connection. The hydrocarbon carrier system which is composed of faults and unconformities controlled the migration and accumu-lation of hydrocarbons ; and the development of reservoirs controlled the enrichment of oil and gas in the weathe-ring crust. Multiphase charging and heterogeneity of the reservoirs caused the differences of oil and gas occur-rence.