Paleo-karstification of the Ordovician carbonate reservoirs and the relationship with fractures in the Halahatang area of Tarim Basin

The Ordovician reservoirs in the Halahatang area of Tarim Basin are carbonate reservoirs and the storage space is karstic vugs and fractures. Types and characteristics of paleo-karstification in the Ordovician carbonate reservoirs were comprehensively analyzed by outcrop study, core observation, thin section analysis, SEM-CL spectrum and SEM-EDS analysis. Coarse-clast collapsed chaotic breccia facies, fine-clast transported chaotic breccia facies, highly disturbed strata facies and undisturbed strata facies were identified in the Xikeer outcrop by outcrop analog. Chaotic breccia related to paleo-caves was found in different formations of the Ordovician under core observation. The Ordovician reservoir experienced three types of paleo-karstification, including penecontemporaneous karstification, weathering karstification and buried karstification. Different karstic vugs demonstrated different SEM-CL spectrums. Widely developed fractures in the reservoir have a significant influence on burial karstification. On one hand, factures promoted karstification by connecting stylolite networks; on the other hand, fractures induced karstification by carrying deep hydrothermal fluids into the reservoir.