Quantitative calculation method for coal and rock adsorbed gas content

Abstract

The invention discloses a quantitative calculation method for coal and rock adsorbed gas content. First, logging information is preprocessed; then, fixed carbon content and formation pressure are calculated, a quantitative relation drawing board between the coal and rock adsorbed gas content and a coal rank, a burial depth, temperature and pressure is established, and a vitrinite reflectance function and a regression coefficient between impact factors and Langmuir pressure are obtained; lastly, a dynamic adsorption calculation model of the coal and rock adsorbed gas content is established based on a Langmuir equation, and logging data and parameters are introduced into the dynamic adsorption calculation model for calculation to obtain the coal and rock adsorbed gas content; coal and rock gas characteristics are evaluated according to the coal and rock adsorbed gas content obtained through calculation. According to the quantitative calculation method, quantitative influence on the coal and rock adsorbed gas content by multiple factors under the formation condition is studied sufficiently, experimental data are utilized for scaling to the logging information under the shaft, the dynamic adsorption calculation model of the coal and rock adsorbed gas content based on the logging information is established, and the calculation accuracy of the adsorbed gas content is improved.

Description

technical field [0001] The invention belongs to the technical field of coalbed methane exploration, and in particular relates to a quantitative calculation method for the content of adsorbed gas in coal rock. Background technique [0002] The quantitative calculation method of the content of adsorbed gas in coal rock is the key and main technical problem in the evaluation of CBM reservoirs. The use of logging data to calculate its content has become an important approach, and its calculation accuracy directly affects the decision-making of CBM exploration and development. To this end, domestic and foreign researches have been carried out on the calculation methods of gas adsorption in coal and rocks, and some calculation models have been established, including the Langmuir model (Langmuir equation), the Freundlich empirical model, the neutron incremental model, and the BP neural network model. [0003] Among them, the Lanshi equation is the most widely used, and its formula ...

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Problems solved by technology

[0011] The limitation of this equation is: under actual formation conditions, the V that characterizes the maximum adsorption capacity of coal rock L The Rankine volume is not fixed, it is affected by various factors such as coal rank, buried depth, temperature, pressure, etc. The experimentally determined V L Only reflects the adsorption capacity of coal rock under the experimental conditions; P L Lange stress is similarly affected

These models have great application limitations. First, the laboratory conditions are different from the actual stratigraphic conditions of coal and rock burial, and the models are not completely suitable for dynamically changing burial conditions. Second, the existing models consider fewer factors and cannot be compared Accurately describe the influence of various objective factors underground on the gas adsorption capacity of coal rocks

Therefore, the applicable conditions of the existing model are relatively strict, and the influencing factors considered by the model are relatively simple. When evaluating the coal-rock adsorbed gas content under the dynamic change of formation conditions, the calculation error is relatively large

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