Research progress,key scientific issues,and prospects of segmented fracturing and pressure relief gas drainage technology for coal seam roof horizontal wells

The segmented fracturing and pressure relief gas drainage technology in the horizontal well of the coal seam roof is a key means to guide the efficient gas extraction in deep, high gas, soft and low permeability coal seams.Based on this, a full lifecycle development concept for the segmented fracturing, pressure relief,and gas drainage engineering of the coal seam roof horizontal well is proposed, including three stages: early scientific planning, mid-term engineering construction, and later safety management.This paper summarizes the research progress on the full life cycle development of segmented fracturing and pressure relief gas drainage in coal seam roof horizontal wells, constructs an overall research framework for key scientific issues related to segmented fracturing and pressure relief gas drainage in coal seam roof horizontal wells, and looks forward to its future development direction.The results show that the expansion of segmented fracturing cracks in the horizontal well of the coal seam roof is extremely complex due to geological factors, construction parameters, and physical properties.It is urgent to comprehensively evaluate the primary and secondary relationships under the influence of multiple factors in crack expansion, and reveal the mechanism of coal seam roof fracturing crack expansion under the influence of multiple factors.Exploring the critical relationship between the coupling of stress, water, temperature, and coal factors on the promotion and inhibition of coalbed methane adsorption, desorption, and migration, and establishing an optimal model for coalbed methane adsorption and desorption under multiple critical indicators, is the key to achieving efficient coalbed methane extraction.At present, there is insufficient research on the residual water from coal seam roof fracturing in terms of polluting water sources, inhibiting gas drainage,and dangerous accumulation, and there is a lack of management experience and technical support in a "Chinese style" approach.Guided by the development concept of the entire life cycle of coal seam roof fracturing engineering, this paper analyzes its high water consumption, fracturing fluid selection and potential pollution, reasonable selection of proppants, air pollution and seismic risks, and puts forward corresponding policy and regulatory formulation ideas.Realizing real-time and accurate monitoring of multi crack competition expansion in complex environments, revealing the mechanism of segmented fracturing and cross interface crack expansion of coal seam roof under the influence of multiple factors, constructing an effective radius evaluation model for segmented fracturing crack expansion of coal seam roof horizontal wells, exploring the water and gas migration law under the dual anisotropy conditions of three-dimensional stress and coal body structure, achieving advanced detection of potential danger areas for water and gas aggregation during fracturing of coal seam roof horizontal wells,and establishing a refined evaluation model for the effect of segmented fracturing,pressure relief, and gas drainage in coal seam roof horizontal wells is currently a key scientific problem that urgently needs to be solved.Finally, the development direction of precision,coordination, intelligence, comprehensiveness, and demonstration of segmented fracturing and pressure relief gas drainage technology for coal seam roof horizontal wells was discussed.