Characteristics Of Cambrian And Ordovician Deep Dolomite Reserviors In Tazhong Area, Tarim Basin

Carbonate rock is a kind of important oil and gas reservoirs.In worldwide, more than half of the oil and gas resources are contained in the limestone and dolomite. The strata of dolomite are lower Ordovician and Cambrian in Tazhong area of Tarim Basin. Dolomite is susceptible to transformed of physical and chemical factors and become the good oil and gas reservoir. However, trap types of dolostone reservoirs for oil and gas are diversity.They are more difficult in the exploration and development. The understanding on origin of dolostone and the master control factors of high-quality dolomite reservoirs is of great significance to dolomite hydrocarbon exploration.Based on the comprehensive analysis of previous studies, According to carbonate petrology, sedimentary palaeogeography, petroleum geology and seismic and well logging interpretation technique, we study the Cambrian and lower Ordovician dolomite reservoir.Through the observation of outcrops and cast thin section identification, dolomites in the study area are divided into the following categories according to the construction characteristics and special structure. The rock types include crystalline dolostone, residual limy dolostone, residual-grain dolomite, hidden algal dolomite and breccia dolomite.Cast thin section observation showed, kinds of cracks and dissolved pores had a high degree of development in lower Ordovician Dolomite in Tazhong area. Filling component were mortar,dolomite and bitumen. Corrosion of fluid can make crack expand. Dolomite grains adjacent to the cracks usually had high idiomorphic degree. Dolomite had development of intercrystalline solution openings and intragranular pores. Cast thin-section analysis showed, limestone pore space is greatly increased under transformation of dolomitization, had potential to be a high quality reservoir.Dolomite most experienced diagenesis in the formation process in Cambrian to Ordovician in Tazhong area. Diagenesis is one of the decisive factors in carbonate reservoir. It has two sides obviously transformation for carbonate reservoir. Filling, compaction, cementation, recrystallization made destruction of the original effective pore and reduce the porosity and permeability of reservoir. Pressure solution and dolomitization made expansion of effective porosity and the formation of new holes. There was a correlation between different depositional system tracts divided on the basis of sea-level and diagenesis. This correlation can be reflected by the diagenesis effect of different types of system tracts.