Conception of key technologiesfor low-negative carbon emission reduction in the process of coalbed methane development from the CBM well,coal mine and goaf

The realization of the “dual carbon”goal and the large-scale commercial development of coalbed methane ur- gently require some new technologies. Coalbed methane development with carbon dioxide capture utilization and storage (CCUS)technology is systematically analyzed. Based on coalbed gas bioengineering, some key technologies for low-negative carbon emission reduction in the process of CBM development, coal mine gasextraction, and goaf CBM de- velopment are discussed and prospected.In the stage of CBM development, converting coalbed methane development into coal measure methane development and converting conventional hydraulic fracturing into large-scale fracture network reconstruction are effective ways to realize the commercial development of coalbed methane.Liquid-phase CO2 and micro- bial culture solutionare used as working fluids for reservoir modification, the integrated fracture network reconstruction of coal-measure gas reservoirs and the multiple stimulation effects of CBM based on CO2 are realized, including the res- ervoir modification under the combined action of microorganisms and CO2 , carbon dioxide to displace methane. This pro- vides a new way for CBM production enhancement and low carbon emission reduction. Meanwhile, the CO2 biomethana- tion and geological storage achieve a negative carbon emission reduction.Therefore, for the development of coalbed meth- ane, CO2 can increase its production.For the storage of CO2, the coal reservoir is the best destination. In the under- ground gas extraction stage in coal mines, according to the mechanism of permeability improvement from the frac- ture generation of hard coal, and the capacity and permeability enhancement of soft coal through unloading coal and pressure relief, and related theories,the first-generation technology of hydraulic strengthening, i.e., hydraulic fracture, and the second-generation technologies of hydraulic strengthening including the technology to increase permeability and yield of integrated drilling and stamping, the solid-liquid two-phase hole sealing technology for three blocks and two in- jections, the increase production technology of old hole repair and increase permeability, and the technology of downhole automatic drainage, slag discharge and gas flooding are proposed. This technological system can realize the transformation of gas extraction from "regular extraction to the quick, economical, pure and clean extraction". The quality and quantity of gas extraction have been improved greatly, achieving to access low-carbon energy, and to re- duce methane emissions. In addition, the closed coring device for integrated drilling and sampling is developed, which can accurately determine the gas content. Coal seam permeability evaluation technology based on low-speed non- linear seepage is established.In the development stage of CBMin goaf,fly ash is considered to be the material of choice for enhancing coalbed biogas production, filling gobs for subsidence reduction and realizing CO2 mineralization and stor- age.In the goaf with gas trap conditions, microbial culture solution, fly ash and CO2 are injected into the goaf to achieve microbial methanation of coal and CO2 , so as to obtain low-carbon energy. After the gas drainage is completed, a large amount of CO2 and fly ash are injected into the goaf.The calcium and magnesium plasmas in fly ash and goaf wa- ter combine with dissolved CO2 to form carbonate cementation from fly ash, realizing CO2 mineralization and sequestra- tion and goaf solidification and sedimentation reduction. This is of great significance in terms of low carbon and nega- tive carbon emission reduction and ecological environment.The low-negative carbon emission reduction technology system for the whole process of coalbed methane combined well-ground extraction is based on coalbed methane production stimulation and the CCUS and provides some new development ideas for the realization of carbon neutrality goals.