Study On Prediction Method Of Coal Reservoir Permeability In Southern Qinshui Basin

Qinnan region is considered to be one of the regions with the most potential of coalbed methane exploration and development, which cover an area of about 2922 square kilometers, including Zheng Zhuang blocks, Anze blocks and so on. But the development practice shows that single well production of CBM wells is relatively low and the economic benefit is not high in the study area and the surrounding area. It is difficult to achieve a large area and scale of commercial exploitation due to the lack of understanding of the characteristics of coal reservoir, as well as the lack of targeted drainage scheme and single reservoir reconstruction technology.This paper conducts the research to the physical characteristics of coal reservoirs using a variety of methods and various geological data in Zheng Zhuang- Anze block of QinNan basin. Plane heterogeneity distribution characteristics of reservoir physical property be identified, such as buried depth, coal thickness,gas contain, critical desorption pressure and porosity. The change and the control mechanism of the reservoir physical property of the thick coal seam in the vertical was revealed.In this paper, the physical parameters of the core are measured by using the multi- parameter core measuring system with three axial confining pressure, high temperature and high pressure. The results show: The porosity index m is related to the porosity structure. The porosity index of coal samples with extremely development of fractures tends to 1.0 The porosity index is around 1.6 of coal samples with massive matrix porosity. The porosity index of other type coal sample is 1.6~1.1In previous large studies and on the basis of existing geological data, based on the simplified Archie formula of fracture porosity, fracture occurrence, triple porosity exponent model m, radial fracture extension coefficient are introduced, gradually establish a fracture porosity formula,which more accord with the dual pore medium characteristics of coal reservoir. Combining with the darcy’s law and dual laterolog deducing new fracture permeability calculation model. On this basis, the coal reservoir to ooze south region to evaluate fracture permeability. The results showed that fracture porosity presents a strong correlation with the well test permeability. Fracture porosity was calculated by the dual laterolog iterative method, in which the fracture distortion coefficient Kr was introduced. The predicted fracture permeability is generally low in the Zhengzhuang area, ranging from 0.01 mD to 0.37 mD, with an average of 0.07 mD. The planar permeability is strongly heterogeneous. The regional distribution of permeability is mainly controlled by burial depth and in-situ stresses. The fracture permeability of the coal reservoir in the vertical direction is in the range of 0.005 to 0.680 mD, decreasing significantly with increasing burial depth.Integrated gas content、critical desorption pressure and buried depth, coal body structure, and the study area is divided into three categories: favorable development blocks of coal reservoirs in the study area in central and southwestern north edge, second-rate coal reservoir has the development in the region. The disadvantage of coal reservoir distributed in the edge of east and west in the study area.