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Geomechanics and Engineering
  Volume 29, Number 2, April25 2022 , pages 145-154
DOI: https://doi.org/10.12989/gae.2022.29.2.145
 


Influence of complex geological structure on horizontal well productivity of coalbed methane
Bing Qin, Zhan-Shan Shi, Wei-Ji Sun, Bing Liang and Jian-Feng Hao

 
Abstract
    Complex geological conditions have a great influence on the mining of coalbed methane (CBM), which affects the extraction efficiency of CBM. This investigation analyzed the complicated geological conditions in the Liujia CBM block of Fuxin. A geological model of heterogeneities CBM reservoirs was established to study the influence of strike direction of igneous rocks and fault structures on horizontal well layout. Subsequently, the dual-porosity and dual-permeability mathematical model was established, which considers the dynamic changes of porosity and permeability caused by gas adsorption, desorption, pressure change. The results show that the production curve is in good agreement with the actual by considering gas seepage in matrix pores in the model. Complicated geological structures affect the pressure expansion of horizontal wells, especially, the closer to the fault structure, the more significant the effect, the slower the pressure drop, and the smaller the desorption area. When the wellbore extends to the fault, the pressure expansion is blocked by the fault and the productivity is reduced. In the study area, the optimal distance to the fault is 70 m. When the horizontal wellbore is perpendicular to the direction of coal seam igneous rock, the productivity is higher than that of parallel igneous rock, and the horizontal well bore should be perpendicular to the cleat direction. However, the well length is limited due to the dense distribution of igneous rocks in the Liujia CBM block. Therefore, the horizontal well pumping in the study area should be arranged along the direction of igneous rock and parallel plane cleats. It is found that the larger the area surrounded by igneous rock, the more favorable the productivity. In summary, the reasonable layout of horizontal wells should make full use of the advantages of igneous rock, faults and other complex geological conditions to achieve the goal of high and stable production.
 
Key Words
    CBM; horizontal well drainage; intrusive igneous rock; pressure distribution; sealing fault
 
Address
Bing Qin,Wei-Ji Sun and Bing Liang : Institute of Mechanics and Engineering, Liaoning Technical University, Fuxin 123000, China
Zhan-Shan Shi: Institute of Mining, Liaoning Technical University, Fuxin123000, China;
Liaoning Academy of Mineral Resources Development and Utilization Technical and Equipment
Research Institute, Liaoning Technical University, Fuxin 123000, China
Jian-Feng Hao: Institute of Mining, Liaoning Technical University, Fuxin123000, China
 

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