Play model and hydrocarbon transport of carbonate reservoirs in Lower Ordovician on Northern Slope of Tazhong area

摘要

The Northern Slope of the Tazhong area is one of the important areas to increase reserve and production in carbonate reservoirs in the Tarim Basin, west China. But in the complex superimposed basin, multiple-stage charging from multiple-sources, and mixed sources in different proportions have resulted in the complexity of oil-water relationship. Major controlling factors and play models are not clear, which has brought great difficulties to exploration. Therefore, it is necessary to study hydrocarbon generation, migration, accumulation and distribution, and recognize the dynamic process of hydrocarbon accumulation. Our research on geology, petrology and geochemistry of trace elements indicated that controlled by the key elements of cap rock, karsted weathering crust reservoir bed and strike-slip faults, accumulation of hydrocarbons in the lower Ordovician on the Northern Slope of the Tazhong area is characterized by vertical zonation and horizontal section-wise distribution. Transport framework of fault-unconformity-karsted fracture and void was established by our research on the static characteristics of faults, unconformity and karstification. Hydrocarbon migration parameters of V/Ni ratio and physical properties of oil indicated that strike-slip faults developed in the lower Ordovician were important migration pathways in the vertical direction. Hydrocarbons migrated up to the unconformity and then were charged towards both sides of the fault, like letter T. Through the analysis of matching between play elements and reservoir formation, the play model "Letter T charging through strike-slip faults, and multiple-stage reservoiring with earlier oil and later gas" was established. According to the model, the deeper formations under the Yingshan formation could be a new worthy exploration target.