Method for calculating maximum coal-bed gas adsorption value based on coal rank and temperature-pressure gradient ratio

Abstract

The invention provides a method for calculating the maximum coal-bed gas adsorption value based on the coal rank and the temperature-pressure gradient ratio. The method comprises the following steps that when the equal buried depth is changed, the ratio of the ground temperature change numerical value dT to the pressure change numerical value dP is defined as the temperature-pressure gradient ratio, it is represented that the maximum reflectivity R<o, max> of a vitrinite and the temperature-pressure gradient ratio are utilized to calculate the maximum coal-bed gas adsorption value, and the maximum coal-bed gas adsorption value includes at least one of the critical buried depth H<c>, the critical pressure P<c> and the critical adsorption quantity V<c>, wherein the maximum reflectivity R<o,max> of the vitrinite is within the range of 0.65% to 2.50%, the temperature-pressure gradient ratio is within the range of 1.92 to 5.0, the ground temperature change numerical value dT is within therange of 2.5 DEG C / hm to 3.5 DEG C / hm, and the pressure change numerical value dP is within the range of 0.70 MPa / hm to 1.30 MPa / hm. Compared with related technologies, the method for calculating themaximum coal-bed gas adsorption value based on the coal rank and the temperature-pressure gradient ratio is easy and convenient to use and high in precision.

Description

technical field [0001] The invention relates to the field of calculation methods for coalbed methane adsorption extremes, in particular to a method for calculating coalbed methane adsorption maximums based on coal ranks and temperature-pressure gradient ratios. Background technique [0002] Coal bed adsorption gas contains more than 80% of the total gas content, and the main component is methane. The adsorption capacity and adsorption characteristics of coal rock reservoirs are important basis for coal bed methane geological evaluation. In the study of coalbed methane, the Langmuir isothermal adsorption theory is mainly used to characterize its adsorption behavior, and the isothermal adsorption and desorption of coalbed methane are theoretically completely reversible. At present, coalbed methane is mainly developed and utilized according to the mechanism of "drainage-depressurization-desorption-diffusion-seepage". Therefore, the adsorption and desorption behavior characteri...

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Problems solved by technology

[0004] However, in related technologies, there are only qualitative analysis and semi-quantitative estimation of the critical depth Hc

At the same time, the semi-quantitative calculation also needs Langmuir volume (VL), Langmuir pressure (P L), adsorption temperature, vitrinite reflectance, moisture content, ash yield, vitrinite content, inertinite content and other parameters, which also makes the existing technology not easy to use

Moreover, there is no method to calculate the critical pressure Pc and the critical adsorption amount Vc, and there is no method to link the temperature-pressure gradient ratio with the maximum reflectance of vitrinite

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