New insights into the genetic types and characteristics of the Ordovician marine fault-karst carbonate reservoirs in the northern Tarim Basin
The previously coined fault-karst reservoirs have become new exploration and exploitation targets and types of marine carbonate hydrocarbon reservoirs.However,these reservoirs are significantly different from conventional weathering-crust karst reservoirs and also show diverse reservoir types and structural characteristics themselves.By delving into the differences in the dissolution and tectonic fracturing of fault-karst reservoirs,we categorize these reservoirs into three types:the over-dissolved residual type,the fractured and highly dissolved type,and the highly fractured and weakly dissolved type.Investigations into these types of fault-karst reservoirs reveal that these reservoirs significantly differ in dissolution intensity,fracture and vug sizes,cumulative oil production,formation energy,and fracture-vug connectivity.Furthermore,the distribution of over-dissolved residual fault-karst reservoirs is influenced by both weathering crust unconformities and the longitudinal dissolution of fault zones.In contrast,the formation and distribution of the remaining two types,manifesting a minimal association with unconformities and tectonic locations,are primarily governed by the fracturing and dissolution intensity of dissolved fault zones.Specifically,large-scale caves occur in the cores of dissolved fault zones,gradually transitioning to fractured-vuggy and fractured reservoirs towards their both sides.
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