Shale apparent permeability prediction method based on pore structure characteristics
A technology of pore structure and prediction method, applied in permeability/surface area analysis, prediction, measurement device, etc., can solve the problems of inability to predict the apparent permeability of shale reservoirs, and the inability to predict the apparent permeability of porous media, etc. achieve high prediction accuracy
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Embodiment 1
[0136] Example 1-Apparent Permeability Model for Gas Transport in Microchannels
[0137] The gas transmission mode is determined by the channel characteristics and gas characteristics, and the Knudsen number is generally used as the criterion for gas transmission mode. The Knudsen number is defined as the ratio of the mean free path of gas molecules to the pore diameter, and its expression is:
[0138]
[0139] In the formula: Kn is Knudsen number, dimension 1;
[0140] λ is the mean free path of gas molecules, m;
[0141] k b is the Boltzmann constant, 1.38×10 -23 J.K. -1 ;
[0142] T is the absolute temperature, K;
[0143] σ is the average collision diameter of gas molecules, m;
[0144] p is the pore pressure, Pa;
[0145] d is the diameter of the channel, m;
[0146] The mean free path of gas molecules is positively correlated with temperature, and negatively correlated with pore pressure and mean collision diameter of gas molecules. Table 1 shows CH 4 、C ...
Embodiment 2
[0216] Example 2 - Shale Apparent Permeability Model Considering Effective Stress Effect
[0217] The microchannel apparent permeability model established above in (1) is for a single microchannel with a specific pore diameter. For porous media, it is assumed that the gas transmission channel is composed of a number of micropores with a certain tortuosity and pore size distribution, and the micropores are composed of substances that do not have the ability to pass through the gas, that is, the capillary bundle model. It is specifically assumed that the pore diameters of microchannels in porous media are d 1 , d 2 ,...,d i , the number of microchannels corresponding to the corresponding pore diameter is N 1 , N 2 ,...,N i . The following discussion is for a porous medium with a unit mass; the apparent permeability of a microchannel with a specific pore diameter is expressed as Kapp, d i , then the microchannel gas flow rate can be expressed according to Darcy's law as
...
Embodiment 3
[0270] Example 3 - Shale Apparent Permeability Model Considering Effects of Effective Stress and Matrix Shrinkage
[0271] The shale apparent permeability model considering the effective stress established in (2) above is for the gas flow process with constant pore pressure and variable effective stress. During the decompression and gas production process of shale reservoirs, as the pore pressure decreases, the adsorbed gas on the pore surface will be desorbed into free gas, the shale matrix will shrink, and the pore size will become larger. The matrix shrinkage effect will enhance the gas transport capacity of the pores. The correction coefficient of matrix shrinkage permeability is used as the correction coefficient of matrix shrinkage to the apparent permeability of porous media. The matrix shrinkage permeability correction factor is
[0272]
[0273] Where: ω s is the partial coefficient of permeability of shale organic matter shrinkage effect, dimension 1;
[0274]...
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