Research On Occurrence And Exploitation Mode For Coalbed Methane Resource Of Xing-gong Coal Field

Xinggong coal field locates at the west of Zhengzhou city,and it has geographical advantages and abundant coalbed methane(CBM)resources.Studing on the occurrence and exploitation mode of the CBM resource in this area will provide a certain amount of backup resources for the central plains economic zone economic construction.Based on the data of coal and CBM geology in Xinggong coal field,numerical simulations and laboratory tests are both conducted to researches on the gas content and its influencing factors,CBM recoverability,and exploitation mode.The following congnitions are achieved.(1)Gas content in Xinggong coal field yields a situation of low in west and south,and high in middle-east and north.The main factors influencing gas content in this field are metamorphism,surrounding rock,structure,coal thickness and buried depth.(2)Macro cleat in the field is very few.Micro cleat is quite developed in vitrinite,while quite few in bright and dark coals.Permeability varies between 0.007m D and0.008m D,which is lower than the average value in China.The tested gas content is from 4.52m~3/t to 43.25m~3/t,with an average value of 16.15m~3/t.Langmuir volume is about 36.0m~3/t,and the gas saturation is between 24.57%and 85.5%,with an average value of 55.49%.Critical desorption pressure varies from 1.84 MPa to 0.34 MPa,and the average value is 1.15MPa.Ratio of critical desorption pressure to reservoir pressure is from 0.11 to 0.69.The calculated CBM reserouce is about 1731.79×10~8m~3,and the resource abundance is 1.92×10~8m~3/km~2.(3)As influenced by structure,coal is destroied heavily.Then virtual reservoir fracturing or indirect reservoir fracturing may be suitable in this area.During fracturing,active water should be selected as the fracturing fluid,and lightweight ceramsite can be chosen as the proppant.(4)During drainage progress,permeability is the key factor influencing the CBM drainage performance.If the fracturing can obtain a good permeability,CBM in this area will have a good exploitation value.Numerical simulation is conducted for single well in this area,and the highest gas production can reach 1700m~3/d,the cumulative gas production for ten years is 320×10~4m~3.Furthermore,well space is optimized,which shows that the space of 350×300m is most suitable in this area and can reach the highest gas production.