The evaluation of coalbed methane (CBM) resources is the basis for planning CBM development and utilization. In the light of the success ful experiences of CBM development in China and the characteristics th at CBM is co-generated, co-stored and co-exploited with coal seams, th e paper points out that, in the near future, the evaluation of CBM is of practical significance only when it is based on the recoverable res erves of coal. On the basis of large quantities of gas adsorption cons tants, porosity and coal property data of coal seams in various coal m ining areas and field measured methane pressure of coal seams, the pap er calculates methane content of coal seams and puts forward the evalu ation results of CBM resources in the main mining areas of China. The total available reserves and extraction reserves of CBM in the main co al mining areas of China are ª©4,730ª±34ªª billion mª¬3 and 1387ª±86 b illion mª¬3, respectively. ª©1 Significanceªª and Status of CBM Resources Evaluation The evaluation of CBM resources is the basis for planning the deve lopment and utilization of CBM and an important basis for ventilation and gas management work in mine production as well. From the point of view of CBM development, the contents of evaluation shall include the total quantity of resources, recoverable resources, occurrence of gas sources and the difficulties of gas recovery. According to the research results of related research institutes a nd scholars in recent years, the CBM resources in bituminous and anthr acite coal fields down to 2000 m underground alone are about 30-35 tri llion mª¬3. This result is basically derived from the formula Q=M¡Áq ( where, Q - CBM resources, mª¬3; M - coal reserves, t; q - CBM content, mª¬3/t) and based on 5 trillion tons of the national total coal resou rces. This evaluation result of the total CBM resources is of great si gnificance in understanding the general situation of CBM resources in China and macro planning and management. However, according to many ye ars' of research and practical production experiences, especially the experience of coal mine gas drainage, in addition to the characteristi cs of being co-generated and stored with coal seams (coal seam is not only the gas source rock but also the gas reservoir), CBM also has the characteristic of being co-exploited with coal seam. Only when coal s eam is directly mined or affected by mining can CBM emits in great qua ntity (naturally or extracted). It may also be one of the reasons why in recent years, 90% of the CBM exploratory wells tested by the depart ments concerned in China have not obtained ideal gas output. Therefore , in the near future, it is of practical significance to evaluate CBM resources on the basis of recoverable coal reserves. Coal resources ar e widely distributed in China. The gas production and storage conditio ns and CBM preservation environment vary greatly. The actual CBM conte nt in different areas and different coalfields varies greatly so that we can not use a unified standard of CBM content to estimate CBM resou rces. Moreover, the CBM development needs to be carried out on a certa in scale. The production form of small mines is technically and econom ically unsuited for developing CBM. Therefore, we think in the near fu ture, the evaluation of CBM resources based on the main coal mining ar eas of China is of great significance in guiding the development and u tilization of CBM. ª©2 CBMªª Resources in the Main Mining Areas of China 2ª±1 Method for Determining CBM Content The determination methods for CBM content are mainly the direct me thod (including using special sealed coal core sampler to take coal sa mples from geological exploratory boreholes to directly determine and calculate gas content according to the gas desorption law) and the ind irect method (according to gas adsorption characteristics, porosity an d analysis parameters of coal samples and in combination with gas pres sure of coal seam to calculate gas content of coal seam). Because the indirect method is relatively simple and easy to operate in sampling a nd determination, it is commonly used at present in coal mines to dete rmine gas content of seams in China. When the indirect method is applied, main parameters to be determi ned in laboratory on coal samples include: methane adsorption isotherm and adsorption constant (a,b) of coal sample; coal porosity (F), prox imate analysis data (moisture, ash content, volatile matters, etc.). I n calculation of gas content of coal seams, the actual measured value or speculative value of gas pressure at the specific locations in coal mines shall be used. The paper gives the results of CBM content in so me of the main mining areas, which are calculated gas content of coal seams based on the gas adsorption constant, porosity, coal analysis da ta of different coal seams in various coal mining areas and with refe rence to the field measured gas pressure value of coal seams and infer red pressure gradient value. 2ª±2 CBM Resources in the Main Mining Areas As mentioned above, in consideration of the ª©co-generation,ªª ª©c o-storageªª and co-exploitation characteristics of CBM with coal seams , in calculation of CBM resources, we have used the available coal res erves of mining areas so that the quantities of CBM resources obtained are called available CBM reserves. The calculated CBM resources based on available coal reserves of coal mines in production or under const ruction are the reserve ready for extraction(RRE). Table 1 CBM Resources in Main Mining Areas of China No. Mining Area Coal Rank Adsorption Volume (mª¬3/t combustibles) Average value Porosity (%) Average value 1 Kailuan fat,gas 14.46 3.93 2 Fengfeng lean,coking,fat 19.17 9.93 3 Yangquan anthracite 34.48 4.58 4 Xishan meager,coking,fat 22.52 4.66 5 Xuangang coking 15.28 7.11 6 Baotou coking,fat,gas 20.77 14.38 7 Fushun gas,long-flame 24.44 3.36 8 Fuxin long-flame 21.11 13.29 9 Beipiao coking,gas 20.48 3.02 10 Tiefa gas,long-flame 23.50 3.54 11 Shenyang anthracite,coking,lean 45.52 13.61 12 Jixi coking 20.44 5.40 13 Huainan coking,gas 17.64 6.32 14 Huaibei meager,coking,gas 19.80 8.03 15 Pingxiang anthracite,lean,coking 21.79 9.80 16 Fengcheng coking,fat 21.41 5.83 17 Pingdingshan coking,fat 20.48 5.21 18 Jiaozuo anthracite 38.71 9.40 19 Hebi anthracite,meager,lean 27.24 6.50 20 Zhengzhou anthracite,meager 32.66 10.06 21 Lianshao anthracite,meager,lean 30.22 10.39 22 Baisha anthracite 30.08 11.20 23 Furong anthracite 29.62 8.43 24 Panzhihua meager coal,lean coal,coking coal 19.16 9.85 25 Nantong meager,lean,coking 19.06 7.56 26 Zhongliangshan meager,lean,coking 21.04 7.80 27 Tianfu meager,lean,coking 20.29 8.49 28 Songzao anthracite 30.55 8.23 29 Liuzhi meager,lean,coking 24.0 7.80 30 Panjiang coking,fat,gas 16.32 7.83 31 Shuicheng coking,fat,gas 14.83 9.03 32 Tongchuan meager,lean,coking 27.73 9.91 33 Hancheng anthracite,meager,lean 19.64 8.14 34 Jingyuan gas 18.37 5.86 35 Shizuishan coking,gas 17.12 9.56 36 shitanjing anthracite,meager,coking 11.64 6.80 37 Wulumuqi long-flame 19.91 10.07 Table 1 Continued Gas pressure (MPa) Actual measured maximum value Inferred to 1500m CBM content inferred to 1500m (mª¬3/t) CBM resources (100 Mmª¬3) Available RRE 2.65 4.20 14.91 654.9 654.9 1.2 4.20 19.08 514.7 354.1 2.3 6.45 28.06 4947.9 1123.5 6.45 19.17 2344.2 917.0 6.45 15.30 148.1 99.4 1.58 5.85 17.88 58.6 44.3 4.6 5.52 19.52 165.8 113.9 1.32 5.40 19.90 203.2 153.8 8.25 12.76 14.11 19.3 19.3 4.10 10.20 21.18 425.8 359.9 2.9 9.9 31.81 50.8 30.5 5.0 10.5 18.48 468.2 330.3 4.1 10.05 20.27 3106.4 796.4 2.8 10.05 19.24 1115.7 400.3 8.4 22.85 45.5 41.1 8.4 23.24 65.8 23.4 5.85 15.68 418.6 343.5 1.4 5.85 31.78 956.9 185.7 1.2 5.85 29.32 323.8 155.0 1.75 10.5 33.44 1026.7 234.1 3.4 11.1 26.81 63.4 63.4 1.7 13.67 36.91 44.9 44.9 3.2 7.95 26.48 187.6 153.7 6.0 13.24 56.8 54.4 6.0 16.4 23.61 58.3 38.2 4.5 14.3 24.40 21.4 21.4 8.0 16.61 25.50 74.1 74.1 3.2 7.40 27.02 208.7 186.8 2.0 7.5 25.85 340.0 83.2 2.4 11.1 17.02 1283.3 234.9 11.1 17.02 772.7 175.5 1.1 4.20 19.08 327.5 178.1 1.1 4.20 17.84 407.4 180.6 10.5 18.69 198.1 143.7 7.5 15.58 71.8 43.0 7.5 12.76 157.4 94.8 7.5 21.20 391.6 220.6 The CBM resources of main coal mining areas in China are shown in Table 1. The distribution of CBM resources in various mining areas is described in the following. The coal mining areas with the available CBM reserves above 100 bi llion mª¬3 are: Yangquan, Huainan, Xishan, Panjiang, Huaibei and Zheng zhou; The coal mining areas with the available CBM reserves between 50-1 00 billion mª¬3 are: Jiaozuo, Shuicheng, Kailuan and Fengfeng; The coal mining areas with the available CBM reserves between 10-5 0 billion mª¬3 are: Jixi, Tiefa, Pingdingshan, Hancheng, Wulumuqi, Liu zhi, Tongchuan, Hebi, Songzao, Fuxin, Jingyuan, Furong, Fushun, Shitan jing and Xuangang. Mining areas with RRE above 50 billion mª¬3 are: Yangquan, Xishan, Huainan and Kailuan. The coal mining areas with RRE between 10-50 billion mª¬3 are: Hua ibei, Tiefa, Fengfeng, Pingdingshan, Jixi, Panjiang, Zhengzhou, Wulumu qi, Songzao, Jiaozuo, Hancheng, Tongchuan, Shuicheng, Hebi, Fuxin, Fur ong, Jingyuan and Fushun. Yangquan coal mining area is the richest in coalbed methane resour ces in China with the available CBM reserves and CBM resource ready fo r extraction at 494ª±79 billion mª¬3 and 112ª±35 billion mª¬3 respecti vely. The total available CBM reserves and RRE in the main mining areas of China are 4730ª±34 billion mª¬3 and 1,387ª±86 billion mª¬3,respecti vely. The provinces and autonomous regions with the total available CBM reserves in the main coal mining areas above 100 billion mª¬3 are: Sha nxi,Anhui,Henan,Guizhou,Hebei,Shaanxi,Heilongjiang,Inner Mongolia,Liao ning,Gansu and Sichuan. The provinces and autonomous regions with the total CBM reserves f or extraction in the main coal mining areas above 50 billion mª¬3 are: Shanxi,Henan,Hebei,Anhui,Heilongjiang,Liaoning,Guizhou,Sichuan and Sh aanxi. Similarly,the main coal mining areas in Shanxi province also have the richest CBM resources with the total available CBM reserves and to tal RRE of ª©2394ª±52ªª billion mª¬3 and ª©426ª±03ªª billion mª¬3,resp ectively. 3 Issues Concerning CBM Development in China 3ª±1 Technical Selection for Key Areas of Development The focal points of CBM development in the near future should be o n the existing production mining areas. Because the geological conditi ons and CBM resources in these mining areas are relatively clear and r eliable,some successful experiences have been obtained in the developm ent work,there are many ways for utilization of resources after recov ery and less investment is needed. For instance,the development of CBM in the near future can be focused on the coal mining areas with certa in basis for CBM development,such as Fushun,Yangquan,Songzao,Nantong,T ianfu,Zhongliangshan,Liuzhi,Tiefa,Panjiang,Shuicheng,Jiaozuo,Shitanjin g,Huaibei and Huainan. Of course,from long point of view,to reach the goal of 10 billion mª¬3/a,it is necessary to exploit CBM on a large sc ale in large virgin coalfields. The research work that needs to be car ried out at present is to solve the bottleneck problems in the surface recovery of CBM on a commercial scale in the near future. 3ª±2 To Increase Mine Gas Drainage Efficiency with Great Efforts For coal seams within the limit of mining areas,the comprehensive drainage methods of working seam,adjacent seam,pre-mining gas drainage ,gas draining while mining and gob gas drainage shall be practiced,bor eholes rationally positioned,gas draining time extended and borehole d ensity increased so as to greatly increase the gas drainage efficiency and increase mine gas drainage efficiency to above 30-40%. 3ª±3 Recovery Rate of CBM Under the condition of atmospheric pressure (0ª±1MPa),the residual gas quantity is about 10% of the total content (See Fig. 1). Moreover ,the diffusion losses of gas during mining and developing process can not be eliminated. Therefore,before the enrichment and utilization tec hnology of low concentration gas can be effectively solved,the recover y rate can not be higher than 50% when the mine gas drainage is taken as the main method for CBM recovery. As to the large commercial scale CBM recovery in virgin coalfields by surface wells,it is very necessar y to consider the influence of desorption coefficient,which is mainly based on gas well pressure. Under the condition of effective water dis charge and the pressure is below 0ª±5MPa,the desorption coefficient ca n be above 0ª±5%. Figª±1 CBM content versus volatile matter at atmospheric pressure 4 Conclusion The main coal mining areas in China have abundant CBM resources,wi th the total available CBM reserves reaching 4730ª±34 billion mª¬3 and total RRE reaching 1387ª±86 billion mª¬3. The coal mining areas riche st in CBM resources are Yangquan,Huainan,Xishan,Panjiang,Huaibei,Zheng zhou,Jiaozuo,Shuicheng,Kailuan and Fengfeng. Because CBM resources are different from conventional natural gas resources,the occurrence cond itions of CBM resources in China are also different from that in the c ountries which have successful development experiences,such as the US, therefore,the CBM development in China should be focused on the existi ng production coal mining areas. Under the premise of accelerating the installation of mine gas drainage equipment and intensify mine gas dr ainage,we must ensure the achievement of the near-term objectives of C BM development. Hence,the evaluation of CBM resources based on the act ual measured data of coal seams in mining areas is of important practi cal significance to the planning and guidance of CBM development. Many mining areas in China,such as Yangquan,Fushun,Songzao,which have abun dant and reliable CBM resources and have already obtained successful e xperience in CBM development and utilization,shall be taken as the key areas for the investment on CBM in the near future.