1. School of Geoscience and Surveying,China University of Mining and Technology,Beijing　 100083,China; 2. China United Coalbed Methane Ltd. ,Beijing 100011,China

Coalbed methane,shale gas and tight gas within coal measures exist simultaneously in many basins world- wide,with the successful exploration and development of specific gas respectively. However,the multi-layer / multi-un- conventional natural gas development in the same wellbore has not yet been systematically implemented. The realiza- tion of multi gas collaborative development will greatly improve the availability of underground resources and economic benefits. This paper systematically summarizes the development and understanding of hydrocarbon generation evolu- tion,gas reservoir occurrence,reservoir physical properties and production mechanism of coal bearing gas occurrence in typical basins in order to provide theoretical and methodological reference for unconventional gas multi gas co-pro- duction. The main progresses include ① the overpressure or micro-fissure during hydrocarbon generation of coal meas- ures is the necessary condition for gas diffusion and migration continuously to adjacent layers;② coal bearing gas sys- tem presents the characteristics of box sealing,continuous migration and accumulation,dynamic transformation and di- rectional accumulation and dispersion;③ static geological parameters such as strata combination,stress field,tempera- ture field and gas bearing property determine the recoverability,and dynamic parameters such as single / multi-layer phase permeability,reservoir pressure and liquid supply capacity determine the production performance;④ physical experiment and numerical analysis can simulate the interference factors of combined mining under ideal geological con- ditions,and reservoir pressure and permeability are the main factors affecting the seepage in drainage period and gas water production period;and ⑤ a reasonable drainage gas production process and scientific control of gas production speed can properly avoid or control the interference between layers and in the wellbore. The key in co-production re- search is “geology+engineering” dessert area selection. The key problems needed to be solved include ① the dynamic migration and accumulation process of superimposed multi type gas reservoirs in the geological evolution process,and the formation and recognition criteria of dominant reservoirs;② the complex gas-water distribution relationship and flu- id pressure system in coal measures,and how to ensure the effectiveness and scientific monitoring of stimulation meas- ures;and ③ the multi-layer combined production and drainage control system and productivity prediction method. The detailed works are to clarify the dynamic processes of coal measures sedimentary,reservoir diagenesis,hydrocarbon generation and migration,and gas-water occurrence and flow state. The technical sequences are geological selection, drilling and completion and reservoir protection,stimulation and transformation technology,drainage system and pro- ductivity prediction. According to the coexistence characteristics of multi-layered unconventional natural gas in coal measures in different areas,choosing appropriate technology to realize co-production within one wellbore will signifi- cantly reduce development costs,improve economic benefits and resource utilization.

LI Yong,WANG Yanbin,MENG Shangzhi,et al. Theoretical basis and prospect of coal measure unconventional natural gas co-production[ J]. Journal of China Coal Society,2020,45 (4):1406 -1418.