A Calculation Method of Apparent Permeability Considering Shale Pore Size Distribution Characteristics

Abstract

The invention discloses a shale pore size distribution feature-considered apparent permeability calculation method. According to the method, a mercury injection experiment (nitrogen adsorption) and the like are carried out on a shale core to obtain a capillary diameter size and a distribution frequency under atmospheric pressure; apparent permeability of each capillary is established while the fact that multiple flow states, such as continuous flow, slip flow and the like, exist in free gas is considered; through summarizing the distribution frequencies of capillaries with different diameters,a method for calculating the apparent permeability in a shale reservoir scale is obtained; and through further considering influences, on shale reservoir apparent permeability, of reservoir water saturation and pressure sensitive effect, a reservoir pore apparent permeability calculation which considers comprehensive influences of multiple factors is finally established. According to the method,characteristics of shale reservoirs are sufficiently combined, the influences, on shale reservoir apparent permeability, of pressure sensitivity and water containing are considered at the same time, and experimental data and a theoretical model are combined, so that the calculation results can reflect the apparent permeability of shale reservoirs more correctly.

Description

technical field [0001] The invention relates to the field of shale gas development, in particular to a method for calculating apparent permeability considering shale pore size distribution characteristics. Background technique [0002] A large number of pores are developed in shale reservoirs. Shale reservoirs are rich in organic matter, clay minerals, and the micro-nanoscale pore structure determines that methane exists in shale reservoirs as adsorbed gas, free gas, and dissolved gas at the same time. Shale gas flow is jointly driven by multiple physical fields such as pressure, wall collision, and molecular concentration. In micropores and mesopores, methane is dominated by desorption-Knudsen diffusion and slip flow, while in macropores it is dominated by viscous flow, Knudsen diffusion and slip flow. The desorption and diffusion process of adsorbed gas in nanopores is slow, and the free gas diffusion and seepage resistance are large, resulting in extremely low methane g...

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Problems solved by technology

This method cannot truly reflect the influence of different capillary diameter combinations on the apparent permeability of shale

Xu et al. (P Xu, B Yu. Developing a new form of permeability and Kozeny–Carman constant for homogeneous porous media by means of fractal geometry[J]. Advances in water resources, 2008,31(1):74-81) considered that shale The size distribution of reservoir capillary has fractal characteristics. The fractal theory is used to calculate the apparent permeability of shale gas in slip flow in the capillary, but the influence of various flow states in the shale capillary is ignored.

However, the above-mentioned methods for calculating the apparent permeability of pores in shale reservoirs do not consider the influence of water saturation and stress-sensitivity effects on apparent permeability, resulting in large errors in the calculation results.

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