Numerical Simulation Research on Hydraulic Fracturing Promoting Coalbed Methane Extraction

Fan Yongpeng,Yang Li,Huo Zhonggang,Hao Jinwei,Shu Longyong,Gan Feng

doi:10.1155/2021/3269592

Fan Yongpeng, Yang Li + Show 4 more

Open Access

https://doi.org/10.1155/2021/3269592

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Abstract

Although hydraulic fracturing technology has been comprehensively investigated, few scholars have studied the influence of hydraulic fracturing on the effect of coalbed methane (CBM) extraction, and few considered the interaction between water and CBM in the research process, which is not conducive to guiding the engineering design of hydraulic fracturing wells. In this work, a hydraulic-mechanical-thermal coupled model for CBM extraction in hydraulic fracturing well is established; it combines gas-liquid two-phase infiltration, where nonisothermal adsorption is also considered. The COMSOL Multiphysics software is used to carry out the numerical simulation study of the CBM extraction process in hydraulic fracturing well and analyze the influence of coalbed permeability, initial methane pressure, and fracture length on CBM extraction in hydraulic fracturing well, and the results show that the hydraulic-mechanical-thermal coupled model for CBM extraction can be used for CBM extraction research in hydraulic fracturing well. The initial coalbed permeability, initial gas pressure, and fracture length all affect the migration speed of CBM to surface well in different ways and have a greater impact on the CBM production rate of hydraulic fracturing well. The greater the initial coalbed permeability and methane pressure are, the longer the fracture length is and the greater the CMB production rate of hydraulic fracturing well is. The change trend of coalbed permeability during the extraction process of surface fracturing well is directly related to the state of the reservoir. The factors of stress, temperature, and CBM desorption jointly determine the increase or decrease of coal seam permeability.

Highlights

In order to increase the production of coalbed methane (CBM) and promote the utilization of CBM resources, hydraulic fracturing technology is widely used in surface well CBM extraction projects [3, 4]
A hydraulic-mechanical-thermal coupled model for CBM extraction in hydraulic fracturing well is established; it combines gas-liquid two-phase infiltration, where nonisothermal adsorption is considered. e COMSOL Multiphysics software is used to carry out the numerical simulation study of the CBM extraction process in hydraulic fracturing well and analyze the influence of coalbed permeability, initial pressure, and fracture length on CBM extraction in hydraulic fracturing well
In order to verify the accuracy of the model, the methane production rate data of LA-019 surface fracturing well in Yuwu Coal Mine was compared with the numerical simulation data

Summary

Introduction

→oqfgco al−, kg/m3; ρ (k/μ)Δp is is the fluid density in the fluid seepage velocity in the coalbed, m/s; k is the coalbed permeability, m2; μ is the dynamic viscosity of gas, Pa·s; p is coalbed pressure, Pa. Bottom elevation of surface well where φ is the porosity; ρga is the gas density under standard conditions, kg/m3; ρs is the density of coal skeleton, kg/m3; ρg MgP/RT is the methane density in the coal seam, kg/m3; T is the coal seam temperature, K, m3/kg; Mg is the gas molar mass, kg/mol; R the gas molar constant, J/(mol·K); Vcg is the gas adsorbed per unit mass of coal volume [15]. MPa m2 Pa·s mPa·s 1/K m3/kg MPa MPa− 1 K− 1 K J/(kg·K) J/(kg·K) J/(kg·K) W/(m·K) W/(m·K) W/(m·K) J/mol

Experiments Experiments Experiments Experiments Experiments Experiments

Model Validation

Numerical Simulation of Methane Extraction in Hydraulic Fracturing Well

Findings

Conclusions