Development and Utilization of Coalbed Methane 
in Tiefa Mining Area

Liu Dongcai, Li Guojun
Tiefa Coal Industry (Group) Limited Liability Company

1. Brief Introduction to Tiefa Mining Area
Tiefa mining area is located within the boundaries of Tiefa, which is situated at the juncture of Tieling and Faku and is about 100km to the northeast of Shenyang, Liaoning province. In this mining area, there are four separated coal basins under its jurisdiction, i.e. Tiefa Coal Basin, Kangping Coal Basin, Kangbei Coal Basin and Changtu Coal Basin exploration area. The total coal bearing area is 618 km2 and the proven coal reserves are 2.259 billion tons, accounting for over one third of the total coal reserves of Liaoning province. The types of coal are: longflame coal and gas coal, belonging to high quality steam coal. 

Over 42 years’ development and construction since 1958, Tiefa mining area has become one of the key coal production bases in China with the annual production capacity reaching 15 Mt. With the approval of Liaoning provincial Party committee and provincial government, Tiefa Mining Administration was reformed to Tiefa Coal Industry (Group) Limited Liability Company (Tie Coal Group Company or Tie Coal Group for short) on October 20, 1999. It has been chosen for three times in succession as the National Ten-Good Enterprise of the Coal Industry in Science and Technology Advancement. In December of 1999, it passed the authentication of the ISO9002 quality system.

2. Coalbed Methane Resources of Tiefa Mining Area
Among the four coal basins under the jurisdiction of Tiefa mining area, Tiefa Basin and Kangping Basin are under development and construction. The former has 7 production mines and the latter has one production mine and one mine under construction. Kangbei Basin and Changtu Basin exploration area have not been developed yet.

2.1 Occurrence Conditions of Coalbed Methane
Tiefa Basin is a completely concealed basin. The occurrence conditions of coalbed methane are relatively good. The burial depth of coal is fairly deep and the thickness of the overlying strata, generally 40-800m, increases gradually from north to south. In the coal formation, there are 3-5 layers of 5-8 m mudstone playing the role of coverage and storage.

The cleats of the basin have experienced the process of expansion first and compression later and belong to the closed group structure, thus playing the role of certain sealing to coalbed methane.

The main coal bearing strata of Tiefa Basin is the Fuxin formation of upper Jurassic series. This is a set of continental facies coal-bearing series with 30-40 coal bearing seams. This formation mainly has two coal-bearing sections: upper section and lower section, and each contains 10 coal seams. The 6 main workable seams in the upper coal section are: No.2, No.3, No.4, No.7, No.8, No.9 and No. 10 coal seams, and the 6 main workable seams in the lower coal bearing section are: No.12, No.13, No.14, No.15, No.16 and No.17 coal seams, which are suitable for the surface or underground recovery of coalbed methane from adjacent seams.

The main coal types are high quality longflame coal and gas coal. The cleats in the coal seams are well developed. The occurrence of coalbed methane is mainly in the adsorption state and supplemented by the free state. The methane content is 89.15%-98.00%.

2.2 Quantity of Coalbed Methane Resources
Of the two coal basins under development and construction in Tiefa mining area, only Tiefa Basin now possesses the conditions for development and utilization of coalbed methane. The striking length of Tiefa Basin from south to north is 29.5 km, the width from east to west is 17.4 km and the area is 513.3 km2. By the end of 1999, the recoverable coal reserve of Tiefa Basin was 1.318 billion tons (The statistical figure of the end of 1997 was 1.346 billion tons.).

2.2.1 Total Amount of Coalbed Methane Resources 
The evaluation of coalbed methane resources of Tiefa mining area was conducted in June 1996 and May 1995 by Xi’an Branch and Fushun Branch of China Coal Research Institute. The final checked quantity of coalbed methane resources of Tiefa mining area is 23.512 billion m3, of which, Tiefa Basin has 18.722 billion m3 and Kangping Basin has 4.79 billion m3. Table 1 shows the calculation results of the quantity of coalbed methane resources in Tiefa Basin. Fig.1 is the distribution chart of coal seams and coalbed methane in Tiefa Basin. Fig. 2 shows the proportion chart of coalbed methane resources of Tiefa Basin.

The present checked total amount of coalbed methane resources of 23.512 billion m3 does not include the amount of coalbed methane resources in non-workable coal seams below 0.8m and that in the surrounding rocks. If this portion of resources times a factor of 1.25, the quantity of coalbed methane resources of Tiefa Block would be 18.722 billion x 1.25 = 23.4 billion m3.

2.2.2 Amount of Recoverable Coal Resources in Tiefa Basin
The coal seams in Tiefa Basin have low permeability, 0.1-0.2md, and coalbed methane is mostly in the adsorption state. Therefore, the development and utilization of coalbed methane can only be carried out under the influence of mining operation and the recovery rate can not be very high. 

According to analysis of the quantity, recovery rate and drainage rate of coalbed methane resources suitable for different extraction methods, it is determined that the recoverable amount of coalbed methane resources suitable for surface vertical well development in the primary coal seams is 2.01 billion m3 and that suitable for the surface vertical gob well development is 3.61 billion m3. Therefore, the recoverable amount of coalbed methane resources in Tiefa Basin is 5.615 billion m3. Of course, this figure is relatively conservative. With the gradual improvement of the mining technology, the level of coalbed methane recovery technology will be gradually enhanced and the recovery rate and drainage rate will increase. Therefore, this figure has the potential to increase. 

3. Status of Coalbed Methane Development and Utilization in Tiefa Mining Area

3.1 Status of Coalbed Methane Development in the Mining Area

Since its development and construction in 1958, up to now, Tiefa mining area has had 8 production mines and one mine under construction. Of the these coal mines, 7 production coal mines are in Tiefa Basin, which are all high gassy mines and equipped with the mine gas drainage system for degassing. Table 2 gives the list of gas drainage equipment of 7 mines in the mining area. Table 3 shows the detailed system of the main gas drainage pipeline of various mines. By the end of 1999, the pure methane drainage was close to 40 Mm3.

3.2 Situation of Coalbed Methane Utilization in the Mining Area
7 mines in Tiefa Basin are all high gassy mines and equipped with mine gas drainage system for degassing. Altogether there are 10 gas drainage pump stations. Four residential areas in Tiefa mining area have set up the coalbed methane utilization system. In the mining area, there are 7 gas holders with the total storage volume of 107,500 m3, 50 km of gas pipelines with the diameter above 150mm. The coalbed methane users in the mining area have reached 26,000 households. By October 2000, a 29km long coalbed methane pipeline, 325x7mm in diameter, will supply gas to 110,000 households in Yingzhou district of Tieling. In addition, it will supply 20 Mm3 gas to Tieling every year and 15,000 and 40,000 households in Qinghe district and Kaiyuan, respectively. At present, the utilization rate is only 25%. After gas is supplied to Tieling, the utilization rate will reach above 50%. However, there will still be some surplus gas to be discharged to the air.

4. Prospect of Coalbed Methane Development and Utilization in Tiefa Mining Area

4.1 Prospect of Coalbed Methane Development in the Mining Area

In addition to the above mentioned 10 sets of complete gas drainage systems, the Tiefa mining area has matured technologies for coalbed methane development. Over 40 years of development and construction of the mining area, many valuable and matured gas drainage technologies and methods have been explored. The UNDP and APEC demonstration projects of coalbed methane development and utilization achieved successes successively, laying down a good foundation for the development of coalbed methane in the mining areas of the same category.

With the continuous scaling up of the mining area, there are more and more technical routes for gas drainage. A dozen of technical methods for gas drainage have provided reliable technical guarantee for the development of coalbed methane in Tiefa mining area. These methods include the full-area sealing process, induction process, the process of burying tube at the triangle point in the back of gob area in the retreat mining, roof gas roadway process, tailing way process, oblique crossing drilling in return air entry and intake entry, surface vertical gob well process, horizontal in-seam longhole drainage process, drainage in the methane concentrated zone, in-seam pre-drainage process, fracturing process and downward hole drainage process, etc. The development regularity of coalbed methane in Tiefa mining area has been clearly understood. Fig. 3 is the schematic diagram of the zoning of upper roof and gas along the perpendicular line of coal seam.

4.2 Prospect of Coalbed Methane Utilization in the Mining Area
Tiefa mining area is close to Shenyang, a large industrial city. The development of coalbed methane in the mining area will play a very important role in the economic development of Shanyang and city group in Shanyang. Liaoning provincial government has already put the engineering project of coalbed methane development and utilization in the mining area into one of 26 economic growth projects of the province. By the end of 2000, the number of coalbed methane users of Tiefa mining area will reach 136,000 households (of which, 26,000 households in the mining area and 110,000 households in Yingzhou district of Tieling), the annual gas consumption will reach 28 Mm3 and the recovery amount of coalbed methane in the mining area by the end of the year is estimated to reach 40 Mm3. In the development plan of coalbed methane of the mining area, the annual recovery quantity is estimated to reach 50 Mm3 and the service life is 110 years. Thus it can be seen that the development of coalbed methane resources in Tiefa mining area will have a good prospect.


4.3 Analysis of the Utilization Efficiency of Coalbed Methane

The selling price of pure coalbed methane (heating value 8,750 kcal/m3) is 1.78 yuan/m3, then the sales income is 89 million yuan based on the annual total recovery amount of 50 Mm3. The selling price is 0.712 yuan/m3 based on the heating value of 3,500 kcal/Nm3, then the sales income is 35.6 million yuan based on the annual total recovery amount of 50 Mm3.

It is estimated that beginning from the end of 2000, the users of coalbed methane of Tiefa mining area will reach 136,000 households and pure coalbed methane consumption will reach 28 Mm3. If the selling price is 0.712 yuan/m3, the sales income would be 19. 936 million yuan.

5. Problems that Need Attention and Solution

5.1 Problems that Need Attention

Coalbed methane is the associated resource that coexists with coal and is released during the process of coal mining. Therefore, the development of coalbed methane in the mining area must be combined with the overall planning of coal mining and realize the rational development and utilization. The mining and development of these two resources must match each other.
The development of gas drainage in the seven existing gas drainage mines in Tiefa mining area is rather uneven. This is not only due to some objective factors and but also due to the unfavorable conditions caused by the subjective factors, which all need to be solved. For Daxing Basin with large gas reserves, the net amount of gas drainage per year reached 19 Mm3, accounting for about 50% of the total amount of the mining area. However, Xiaonan Basin has relatively high gas content and large gas emission, all gas has to be emitted to the air because the amount of air distribution during the mining period was excessively high.
The organization structure for the development of coalbed methane is not perfect and there is no capability to coordinate all mines. Hence, it can not meet the needs of large development of coalbed methane.

5.2 Problems that need to be solved

● Changes of ideology: Because coalbed methane is a new and developing energy industry, the development and utilization of this new energy is a good thing to the country and people and is extremely beneficial no matter in terms of safety and resources or in terms of environmental protection. But we must realize that the current price of coalbed methane is a little low, the cost is relatively high and moreover, there are various kinds of tax that must be taken into account. As a result, coalbed methane developers could only make very little profit. Therefore, we suggest the government departments concerned give incentive tax and credit policies to support its development.

● Input into the development of coalbed methane: As mentioned above that the development of coalbed methane in Tiefa mining area is not even. There are both objective and subjective factors. But the key problem is the financial problem. In the long-range development plan, the surface development must account for one third of the total amount of development. But the cost for the surface well drilling is high so that it needs high input of funds. Although the underground development accounts for two thirds of the total development, drilling machines used in all the mines are equipped of low level domestically or internationally. Only the equipment in Daxing mine is a little higher in technical level. Hence, funds are also needed for replacement. 

● Financial input into the utilization of coalbed methane: Currently, there are 7 mines in Tiefa mining area doing gas drainage with 10 sets of CH4 drainage systems. Only Daxin, Dalong, Xiaonan and Xiaoming Basins have connected the positive pressure gas supply to the network. The rest of mines, such as No.1 mine, No.2 mine and Xiaoqing mine, have not been connected to the network and need financial input. The reason is that although No.1 and No.2 mines are old mines, methane of low concentration and high flow still can be recovered from the gob areas, which can be mixed with the appropriate proportion of gas of high concentration and high flow from other mines for supplying to customers.

● The surface metering installations are not perfect and most of them are manually controlled. From the long-term view, this is not beneficial to management and regulation. Therefore, funds are needed for the establishment of the general station and sub-stations of coalbed methane monitoring network in the mining area so as to promote the application of computer for accurate and convenient measurement. And, this will also benefit the mutual regulation between tank farm, pipeline and mine pump station.