CBM Desorption Model and Stages Based on a Natural Desorption Experiment

Area of Science:

• Earth Science
• Geology
• Energy Resources

Background:

• Coalbed methane (CBM) desorption is key to understanding gas recovery mechanisms and well productivity.
• Accurate modeling of CBM desorption is essential for analyzing CBM well performance.

Purpose of the Study:

• To establish a CBM desorption model using experimental data from the Qinshui Basin.
• To quantitatively identify CBM desorption stages and their relationship with well productivity.
• To analyze factors influencing CBM adsorption time and its impact on steady production.

Main Methods:

• Collected CBM natural desorption experimental data from 64 coal samples.
• Developed a CBM desorption model: V = a*t/(t + b).
• Quantitatively identified four CBM desorption stages and correlated them with well production phases.

Main Results:

• A significant functional relationship exists between CBM desorption time and cumulative quantity, described by the model.
• The CBM natural desorption process was divided into startup, sensitive, steady, and decay stages.
• CBM adsorption time decreased with increased desorption rate, gas content, and vitrinite/inertinite ratio.

Conclusions:

• The four identified desorption stages correspond to well production stages: pressure drop, steady production, and decline.
• Optimizing the ratio of adsorption time to gas content is crucial for extending the steady production stage of CBM wells.
• Understanding these relationships can improve CBM well productivity and resource utilization.