Reseach On Reservoir Characteristics And Quantitative Diagenetic Facies Of Xujiahe Formation In Southern Sichuan Basin

The Southern Sichuan Basin could be divided into the western, central, southwestern, and southeastern Sichuan low and steep structural area, which has a long history oil and gas exploration. According to the record of industrial gas wells, the Xujiahe Formation has excellent hydrocarbon potential. However, due to the lack of main control factors, spatial distribution of reservoir, reservoir evaluation is relatively lacking. This study is focus on the Xujiahe Formation reservoir, combined with former studies, the wild outcrop observation data and oil field data, summarize and analysis main control factors and evolution mode, and quantitative analysis of diagenetic facies, the following conclusions has gotten:(1) Reservoir rocks composition maturity of Xujiahe Formation sandstone is high, there are feldspar lithic sandstone, lithic feldspar sandstone, lithic sandstone and lithic quartz sandstone, content of matrix is low, cements include calcite, dolomite, siliceous cement, chlorite, kaolinite, siderite. The type of reservoir spaceis mostly composed of primary grained pore, in-grain dissolution pore, micro crack.(2) According to the drill core physical properties, Xujiahe Formation reservoir is a low-porosity and low-permeability reservoir. The physical properties are controlled by sedimentary sandstone original composition and distribution of sedimentary face.(3) Compaction is the primary factor causing destruction of reservoir pores, cementation further leads to the density of reservoir, dissolution and tectonic disruption increases the porosity and permeability of reservoir to some extent. We believe diagenetic stage is in middle diagenesis A stage to the middle diagenesis B stage based on the research study.(4) By calculating the reservoir rock compaction coefficient, cementation coefficient and coefficient of dissolution, with the Q type cluster analysis method to classify reservoir rock according to the similar variable factors, diagenetic facies of the 2nd member of Xujiahe Formation are divided into strong compaction- strong cementation facies, strong compaction- medium cementation facies, strong compaction- weak cementation facies, medium compaction- weak cementation facies, weak compaction- weak cementation facies in five kinds of diagenetic facies quantitatively. Liminating the coefficient of the dissolution which is not relative with surface porosity of sandstones and diagenetic facies of the fourth member of Xujiahe Formation are divided into strong crush solid cementation facies and crush real weak cementation phase in the cementation facies, medium voltage solid cementation facies, medium voltage equals the real weak cementation in 5kinds of diagenetic facies quantitatively. The study found that the diagenetic facies distribution is obviously controlled by interstitial material, the plastic debris and the distribution of sedimentary facies, which mainly developed in the underwater distributary channel of delta front.