Numerical Simulation of Enhancing Coalbed Methane Recovery by RF Heating with Small Spacing Well Pattern

In recent years, electromagnetic (EM) heating excitation technology has been widely concerned in the exploitation of Coalbed methane (CBM). However, the heating volume of a single antenna in a vertical well is limited and cannot meet the needs of large-scale development. From the perspective of multi-well and multi-antenna, this paper establishes a mathematical model of radio frequency (RF) heating coupled with EM field and temperature field of small-spacing well pattern, comprehensively analyzes the average temperature and heating efficiency of coal seam heated by RF, reveals the influence law of different well types on the temperature distribution of coal seam, and conducts sensitivity analysis on heating power, well spacing and well pattern layout according to the characteristics of well pattern. The results show that triangular well pattern heating has higher heating efficiency and heating rate. Increasing the RF heating power can improve the heating rate and heating range of the coal seam, but too high power will form high temperatures near the wellbore, resulting in downhole equipment or wellbore integrity failure. On the whole, the spacing of heating wells has little effect on the average temperature of coal seam. The larger the spacing of wells in 5 ∼ 9 m, the larger the heating range, but the worse the superposition effect of temperature. Finally, according to the different well pattern layout schemes in the same reservoir, the optimal scheme is well pattern 1. 1. INTRODUCTION CBM is a kind of unconventional gas in coal seams. Deep coal seam has the characteristics of low formation pressure, low permeability and weak gas saturation, which are the biggest challenges faced by coalbed gas exploitation (Gao et al., 2022). To overcome these challenges, engineers and researchers have proposed a number of methods, such as hydraulic fracturing, blasting, partial pyrolysis, solvent extraction, inert gas displacement, etc. (Guo et al., 2020). These methods can be divided into two categories: decompression and anti-reflection mechanisms. However, these approaches face environmental and economic challenges. In recent years, thermal stimulation technology has been widely concerned as an alternative method to increase natural gas production in unconventional reservoirs.