Analysis on apparent permeability of shale matrix based on fractal theory
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TE311

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    Abstract:

    In order to characterize the apparent permeability of shale matrix and research its dynamic variation,apparent permeability model of organic and inorganic matter has been derived theoretically by considering absorption,slip,diffusion and seepage based on the fractal theory of tortuous capillary bundles and microscopic gas percolation mechanism. Thereby a fractal apparent permeability model of shale matrix is built by weighting the area factor. Reliability of this model was verified through experimental results and existing permeability calculation models,and then the effect of pore structure(pore size,porosity,fractal dimension),external environment(pressure,water saturation,effective diameter correction factors)and gas property on the apparent permeability of the shale matrix was quantitatively analyzed. The research results show that for the inorganic pore,with the decrease of formation pressure,the apparent permeability presents overall downward trend,which is influenced by the increase of water film thickness and the decrease of effective pore size,along with the increase of fractal dimension of tortuosity and the decrease of pore fractal dimension,and the gas slippage effect increases but the adsorption is still the main influential factor;for the organic pore,the permeability presents overall upward trend when the correction factor of effective diameter increases gradually with the desorption of shale gas,and the fractal dimension of tortuosity decreases while that of pore increases,and thus the slippage effect and Knudsen diffusion are enhanced in the small pore with low pressure;the variation of the apparent physical properties with the pressure and the adsorbed layer is different for the organic and inorganic matter,and the difference of permeability between the organic and inorganic matter is large. Therefore,the apparent permeability of the organic and inorganic matter in shale matrix should be calculated respectively to avoid errors brought by this difference.

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Li Yudan, Dong Pingchuan, Zhang He, Cao Nai, Wang Yang. Analysis on apparent permeability of shale matrix based on fractal theory[J]. Petroleum Geology and Recovery Efficiency,2017,24(1):92~99

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  • Received:
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  • Online: February 06,2017
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