Research On The Characteristics Of Movable Fluid In The Pore-Fracture Network System Of Dolomitic Tight Reservoirs

Argillaceous dolomite and dolomitic mudstone reservoirs extremely developed in the Qingxi sag of Jiuquan basin,which belong to the typical fractured dolomitic tight oil reservoirs of low porosity and low permeability.The research on the set of dolomitic tight oil reservoir has important significance.The pore and throat structure of reservoir is carefully studied through core observation,SEM,casting slice,nuclear magnetic resonance,high-pressure mercury injection and micro-nano CT techniques,so as to further characterize the characteristics of the movable fluid in the research area and summarize 4 types of reservoir structure patterns.Finally,the result of reservoirs classification is confirmed by the datas of micro-nano CT techniques.The lithology of dolomitic tight oil reservoir in the Xiagou formation,Qingxi sag,Jiuxi basin is mainly argillaceous dolomite and dolomitic mudstone.The mean porosity of the argillaceous dolomite samples is 3.064% and the mean permeability is 2.091 mD.The microcracks,the grain margin fractures and the residual intergranular pores are mainly developed in the argillaceous dolomite.The mean porosity of the dolomitic mudstone is 2.569% and the mean permeability is 1.464 mD.The interlayer pore of clay mineral,microcracks and the intergranular pore of pyrite are mainly developed in the dolomitic mudstone.The unimodal and doublet type are two main types dolomitic reservoirs pore size distribution in the study area.The size distribution of the unimodal type is from 0.010?m to 0.050?m,and the distribution of the doublet type is 0.010~0.030?m and 0.100~1.000?m.The movable fluid of dolomitic tight oil reservoirs in the research area is mainly controlled by the pore throat which size range is from 0.100?m to 0.500?m.The movable fluid saturation of the 0.100~0.500?m pore-throat radius is generally high.The reservoir structure in the study area is divided into 4 types,based on the standard of movable fluid saturation.The movable fluid saturation of the I type reservoir structure is greater than 35%.The movable fluid saturation of the II type reservoir structure is between 25% and 35%.The movable fluid saturation of the III type reservoir structure is between 20% and 25% and the movable fluid saturation of the IV type reservoir structure is less than 20%.In order to verify the accuracy of the reservoir classification,Micro-nano CT experiments were carried out on the three rock samples of Long104-02,Liu4-06 and Liu102-06 in the study area.From qualitative and quantitative perspectives,the correctness and scientificity of reservoir classification results is proved by the pore-fracture network structure.