Coalbed methane extraction in multibranch horizontal wells: evolutions of reservoir characteristics with different geometric parameters

ABSTRACT

Despite effective application of multibranch horizontal wells (MBHW) in the development of coalbed methane (CBM) fields, fewer studies have explored the variation of coal reservoir parameters under MBHW CBM extraction with different geometric parameters, which markedly restricts the maximum MBHW productivity. This study aims to develop a thermal–hydraulic–mechanical (THM)-coupled model, including coal deformation, gas migration, and thermal transport. Using the finite element simulation software, COMSOL Multiphysics, we analyzed the main geometric parameters of MBHW, including branch structure, branch angle, branch length, and branch quantity on the reservoir pressure, gas production, and reservoir temperature. In the entire CBM extraction process, the reservoir pressure and temperature at various points in the coal seam declined gradually; the closer to the wellbore, the faster the decline of the gas pressure and temperature in the coal seam. Typically, the cumulative gas production proportionally increases with an increase of branch length. The impact of the branch quantity on the productivity of unit length wellbore correlated with the extraction time. When the extraction time was relatively short (within 500 days), the gas production rate unit length of the wellbore increased gradually with an increase of the branch quantity.

KEYWORDS:

• Multibranch horizontal well (MBHW)
• CBM extraction
• geometric parameters
• reservoir characteristics evolution
• Thermal-Hydraulic-Mechanical (THM)-coupled model

Acknowledgments

We would like to thank American Editor (www.mjeditor.com) for providing linguistic assistance during the preparation of this manuscript. The authors are grateful to the reviewers for discerning comments on this paper.

Disclosure Statement

The authors declare no competing financial interest.

Additional information

Funding

The work was funded by National Natural Science Foundation of China [51604144].

Notes on contributors

Nan Fan

Nan Fan is a Ph.D. candidate at Liaoning Technical University, main engaged in coalbed methane recovery.

Jiren Wang

Jiren Wang is a professor at Liaoning Technical University and academician of the Russian Academy of Natural Sciences. He is engaged in teaching and research in the fields of mining engineering and safety science andengineering.

Cunbao Deng

Cunbao Deng is a professor at Taiyuan University of Technology and a member of the Mine Ventilation Professional Committee of the China Coal Industry Labor Protection Science and Technology Society.

Yongliang Mu

Yongliang Mu is a Ph.D. candidate  at Liaoning Technical University, specializing in coalbed methane recovery.

Yongpeng Fan

Yongpeng Fan is a Ph.D. candidate  at Liaoning Technical University, mainly engaged in the exploration and development of coalbed methane.