Deep Coal Bed Methane Recovery Factor Calculation
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Solution Overview
Problem
Current methods for determining the recovery factor of deep coal bed methane wells do not consider the influence of free gas, making them unsuitable for deep CBM where both free and adsorbed gas coexist, and are either arbitrary, data-intensive, or complex to apply.
Innovation Solution
A method involving PVT experimental data, isothermal adsorption data, and Langmuir parameters to calculate the recovery factor, considering both free and adsorbed gas contents, using a model that incorporates deviation factors and pressure relationships to determine the recovery factor effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the desorption method or isothermal adsorption curve method is used, then the recovery factor of adsorbed gas can be determined, but the influence of free gas on the recovery factor cannot be considered
Solution Approach 1:
The patent combines the desorption method and isothermal adsorption curve method into a unified approach that simultaneously considers both adsorbed gas and free gas. The material balance equation integrates adsorbed gas content (Gad) and free gas content (Gf) to calculate the total recovery factor, making the method applicable to deep CBM reservoirs where both gas phases coexist.
2Reliability
If the gas reservoir numerical simulation method is used, then the influence of heterogeneous geological characteristics and seepage characteristics can be comprehensively considered, but a large number of data are needed and the research process is complex
Solution Approach 1:
The patent extracts the essential parameters from the complex numerical simulation approach, retaining only the critical elements needed for recovery factor calculation. By focusing on adsorbed gas content, free gas content, and material balance principles, the method achieves reliable results without requiring extensive geological data or complex simulation processes.
Solution Approach 2:
Instead of using complex forward simulation to predict recovery factor, the patent inverts the approach by using material balance equations that directly calculate recovery factor from measured parameters (adsorbed gas content, free gas content, pressure data). This inverse method simplifies the research process while maintaining reliability.
3Loss of time
If the analogy method is used, then the recovery factor can be predicted in the early development stage, but the prediction is arbitrary and less reliable
Solution Approach 1:
The patent transforms the arbitrary analogy method into a quantitative calculation method by introducing specific parameters (adsorbed gas content Gad, free gas content Gf, Langmuir pressure PL, Langmuir volume VL). These parameter changes enable early stage prediction while significantly improving reliability through mathematical modeling rather than qualitative analogy.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method provides a simple, reliable, and practical approach to determine the recovery factor, considering both free and adsorbed gas, overcoming the limitations of existing methods and offering strong operability and application value.
Implementation Method 1
obtaining isothermal adsorption experimental data, an adsorbed gas content G0ad and a free gas content G0f at the original formation pressure and an original temperature for the deep coal rock
Data Source
AI summary
A method for determining a recovery factor of a deep coal bed methane (CBM) well includes steps of: (1) collecting an original formation pressure and pressure-volume-temperature (PVT) experimental data of the CBM well, and establishing a relationship table between pressure and deviation factor; (2) obtaining isothermal adsorption experimental data, an original adsorbed gas content and an original free gas content for the deep coal rock; (3) according to the isothermal adsorption experimental data, determining Langmuir's pressure and Langmuir's volume; (4) determining an abandoned formation pressure in CBM well exploitation; (5) obtaining a deviation factor at the original formation pressure and a deviation factor at the abandoned formation pressure; and (6) according to the original formation pressure, the original adsorbed gas content, the original free gas content, the Langmuir's pressure, the abandoned formation pressure, the above deviation factors, the recovery factor of the CBM well is calculated.