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中奥陶统马家沟组由内源沉积岩及由岩溶作用改造的碳酸盐岩-岩溶角砾岩组成。硬石膏结核溶模孔,晶间溶孔是最主要的储集空间:孔隙度为0.08%～18.60%,平均2.86%;渗透率为(0.001～1343.4)×10-3 m2,平均0.63×10-3 m2。马家沟组碳酸盐沉积物(岩)经历的成岩作用有压实、压溶、白云石化、交代、溶蚀、岩溶和去白云石化等。经全岩样品分析较低的18O值和Sr含量以及较高的Mn、Fe含量说明白云石受到淡水淋滤和埋藏深度的影响明显。充填于溶蚀孔、缝和砾石间孔、缝中的白云石胶结物18O和13C值较低,说明形成于裸露期的风化壳岩溶作用阶段,受埋藏作用、淡水淋滤和有机质影响较大。储集岩以低孔、低渗、强非均质性为特征。
The Middle Ordovician Majiagou Formation consists of endogenous sedimentary rocks and carbonate-karst breccias altered by karstification. The anhydrite nodules dissolve in the pores, and the intergranular dissolution pores are the most important reservoir space: the porosity is 0.08% ~ 18.60% with an average of 2.86%; the permeability is (0.001 ~ 1343.4) × 10-3 m2 with an average of 0.63 × 10 -3 m2. Diagenesis experienced by carbonate sediments (rocks) in the Majiagou Formation is compacted, pressured, dolomitized, interpreted, dissolved, karstified and de-dolomitized. The lower 18O value and Sr content as well as the higher Mn and Fe content of the whole rock samples indicate that dolomite is significantly affected by freshwater leaching and burial depth. The 18O and 13C values of the dolomite cements filled in the pores, seams and gravels of the dissolution holes and seams are lower, indicating that the weathering crust karst formed during the bare period is burial-affected by freshwater leaching and organic matter. Reservoir rocks are characterized by low porosity, low permeability and strong heterogeneity.