Fushun Coal MinesCoalbed

Coalbed Methane Development and Utilization  in the Fushun Coal MinesCoalbed

    Methane Development and Utilization

    in the Fushun Coal Mines

    (1. Shenyang Coalbed Methane Development Centre, Shenyang 110015; 2. Fushun

    Coal Mining Administration, Fushun 113008)

    Abstract: The Fushun Coalfield has been mined for a whole century ever since

    1901. Its underground well methane extraction and utilization started in

    1952 and is one of the country’s earliest coal mines in doing so. In 1999,

    the total amount of methane extraction just in its Laohutai Mine reached

    128,811,000 m3 (in terms of 100% CH4), which accounts for 1/6 of the

    country’s total amount. In addition to domestic use by 170,000 city

    households, methane gas has also been used by mining area households, gas

    chemical industry and so on. The comprehensive efficiency reached 85%. Under

    the “control mining to protect city area” policy of the Fushun Coalfield,

    there are still 240 million tons of coal reserves beneath the city area and

    can not be exploited. Therefore, development of under city coalbed methane

    gas by surface boreholes approach has threefold significance, i.e. coal

    mines transformation, new energy source exploitation and environmental

    protection.

    Keywords: coalbed methane development and utilization, combination of

    underground drainage and surface development, commercial development

    evaluation

    1. Introduction

    The Fushun Coal Mines Coalbed Methane Development and Utilization Project

    has already been approved by the State Planning and Development Commission.

    This is going to be a demonstration project in comprehensive coalbed methane

    development and utilization by proper combination of underground mining well

    drainage and surface boreholes. It has already started operation, managed by

    a newly established Shunyang Coalbed Methane Development Limited Company.

    The new company is a joint venture from the Coal Mine Engineering Technical

    Limited Company of Fushun Coal Mining Administration, the General Shenyang

    City Coal Gas Company and the Liaoning Coalbed Methane Development Company.

    These three companies all together invested 47 million Yuan Renminbi at the

    first stage. In January 25 1999, Fushun City Planning and Development

    Commission formally agreed that an annually 50 to 100 million m3 of coalbed

    methane gas be supplied to Shenyang City in 20 years time. An agreement was

    thus signed between the General Shenyang Coal Gas Company and Fushun Coal

    Mining Administration. Shenyang City will accept an annually 50 million m3

    of coalbed methane gas before 2004 and then 100 million m3 after 2006 with

    the minimum calorific value of 7,000 Calorie/m3 and a rate of 1.4 Yuan/m3

    (equivalent to 8243 Calorie/m3 of calorific capacity). The implementation of

    the Fushun Coal Mines Coalbed Methane Development and Utilization

    Demonstration Project is divided into two stages. At the first stage,

    underground mining well drained coal gas from the Laohutai Mine (content of

    CH4 is 55-60%), mixed with liquid oil gas, will be sent to Shenyang City. At

    the second stage, methane gas extracted from surface boreholes, mixed with

    underground drained coal gas, will be conveyed to Shenyang City. Currently,

    construction of a 32 km long gas conveyance pipeline with a diameter of 377

    mm between Fushun City and Shenyang City, together with gas mixing and

    pressurization stations, is already undertaken. As a coalbed methane

    industry and commercial development project, it will be the first one in

    China, implemented by the Shunyang Coalbed Methane Limited Company.

    2. Coalbed Methane Resources in the Fushun Coal Mines

    The Fushun Coalfield is located in the south bank of the Yuhe River in

    Fushun City, Liaoning Province. It runs NEE and inclines from north to south

    with an angle of 300. It starts from the Guchengzihe River in the west and

    ends at the Dongzhouhe River in the east. The size of the coalfield is about

    40 km2 with a length of 18 km and width of 2~2.5 km. Early mining activities

    before 1949 was done without any formal planning. It became one of the

    largest coal bases in the country after large scale exploitation and

    construction after 1950. Its proved coal deposit amounts to 1,367,865,000

    tons with a guarranteed deposit of 834,046,000 tons in 1988. As required by

    the “control mining to protect urban area” policy, its Shengli Mine and

    Longfeng Mine have been closed one after another. At present, there are

    still 84,000,000 tons of exploitable geological reserves in the Jinggong

    Mine and Laohutai Mine, and 151,205,000 tons in the Xilutian Mine. In

    addition, there are 239,015,000 tons of coal reserves beneath the city area.

    Based on the coalbed methane content derived from statistical data of mining

    wells and experiment data from the explore well #2 drilled in 1998 jointly

    by Fushun Coal Mining Administration and China United Coalbed Methane

    Limited Company, it is estimated that the average coalbed methane content in

    the Fushun Coalfield is 15 m3/ton. The predicted cumulative coalbed methane

    reserve is 4,858,725,000 m3 in the Fushun Coal Mines, where 3,598,725,000 m3

    can be extracted by surface boreholes and 1,260,000,000 m3 by underground

    well drainage.

    3. Coalbed Methane Extraction and Utilization in the Fushun Coal Mines

    The current methane extraction in the Fushun Coal Mines is limited to the

    Laohutai Mine only. In 1999, coal production in the Laohutai Mine is

    3,600,000 tons, and the pure amount of methane extraction is 128,811,000 m3,

    where 109,815,000 m3 was butilized and 18,996,000 m3 emitted with a

    utilization ratio of 85%. The methane content of the extracted coal gas is

    53.8%. The general extraction approach is the combination of pre-extraction

    before mining, extraction during mining and extraction from already mined

    area. The gas collection and conveyance system includes three methane

    extraction stations and a 50,000 m3 wet gas cabinet in the Laohutai Mine, a

    50,000 m3 wet gas cabinet in the Shengli Mine, and the gas conveyance and

    distribution pipe network in the mining area. The extraction equipment is

    the Roze air blower and water-circulated vacuum pump. The present domestic

    methane users have reached 170,000 from Fushun City inhabitants and 50,000

    from the mining area (gas is supplied as a form of welfare scheme). A total

    of 6.5′108 m3 methane gas was supplied to the carbon black factory to have

    produced 8,770 tons of carbon black in 27 years from 1952 to 1978. Methane

    was also supplied to a formaldehyde factory with a daily capacity of 0.8-1.7

    tons set up in 1970 and methane power generators with a capacity of 1,500 kw

    introduced from Norway in 1990. Methane extraction and utilization of the

    Laohutai Mine in 1999 is summarized in Table 1.

    Table 1. Mining well methane extraction and utilization at the Laohutai Mine

    of Fushun Coal Mining Administration in 1999

    Month 1 2 3 4 5 6 7 8 9 10 11 12 Sum

    Total Amount extracted Mixed m3/min

    Concentration %

    Pure m3/min

    ′104m3 12881.1

    Pure amount supplied to city m3/min

    ′104m3

    Pure amount supplied to mining area m3/min

    ′104m3

    Pure amount supplied to boilers m3/min

    ′104m3

    Total Pure amount utilized ′104m3 10981.5

    Pure amount emitted m3/min

    ′104m3 1899.6

    4. Coal Seam Characteristics in the Fushun Coalfield

    Geological research in the Fushun Coalfield started much earlier and has

    reached a certain high level. In recent years, studies in the

    characteristics of its coal seams have also made good progress.

    4.1 Coal Seam Depth and Coal Quantity

    The maximum depth of the coalbeds in the Fushun Coalfield does not exceed

    1,200 m, dominantly 600-850 m. The principal target coalbed is the 本层煤 which

    has a poorly ventilate roof of oil shale and green shale. The thickness of

    this coalbed is 8-120 m with an average of over 40 m. The coalbed methane

    abundance value is more than 5′108 m3/km2 on average.

    4.2 Coal Quality

    Coal Physical Features

    Coal color is black with dark brown strips and has a very strong oil and

    glass lustre. The texture is hard but fragile, and easy to break into

    pieces. There are vertical and cross joints with a flat shell-like cutting

    section. In addition, amber exists in form of particles with strip shape or

    is scattered in the coalbeds in light yellow color. Types are dominated by

    semi shine coal with rare semi dark coal.

    Coal Rock Features

    本层煤 consists of humic coal and a bit of sapropelic coal. The sapropelic coal

    is concentrated at the bottom and appears in an independent layer with a

    depth of ±0.2 m. Coagulate is the dominant component in humic coal, usually

    over 80%, with rare 丝炭. Wood coal and wood 境煤 are often concentrated in this

    stratum, and can reach as much as 10% with less large spore but common small

    spore. The associated foreign substances in humic coal are rare, normally

    below 10%.

    Coal Type and metamorphism Factors

    Coal type belongs to the gas rich coal. The metamorphism factor in this

    coalfield is mainly regional thermal metamorphism. There is igneous rock

    intrusion below the coalbeds, by which the coalbeds were baked to evolve to

    natural coking coal. However, the igneous rock has no affects on 本层煤.

    Coal Quality Features

    Water content: generally 3-4% in 本层煤.

    Ash content: generally 8-15% in raw coal and 6-8% in fine coal, belongs to

    super low ash content.

    Volatile components: surphur content 0.37-0.73% with an average of 0.57% in

    raw and fine coal, belongs to low surphur coal; phosphorus content

    0.0034-0.076% with an average of 0.025% in raw coal and 0.004-0.05% with an

    average of 0.021% in fine coal, belongs to low phosphorus coal.

    Calorific capacity: generally 6,500-7,000 Calorie/kg with an average of

    6,692 Calorie/kg for raw coal and 7,000-7,200 Calorie/kg for fine coal.

    4.3 Porosity and Permeability

    The coalbed of 本层煤 has a higher permeability, generally in the range of

    0.54-3.8 m/d. It is 1.26 m/d in the Beilongfeng Mine with the porous volume

    of 0.0047 cm3/g and porosity of 10%. Moreover, well developed cuttings and

    joints are rarely filled with minerals. Hence, the well developed porous and

    good connectivity in 本层煤 in the Fushun Coalfield is thought to have the

    highest permeability all over the country.

    In 1982, a surface methane pre-extraction test well was drilled in the

    Laohutai Mine with a well depth of 821 m and coalbed thickness of 37 m.

    Although no breaking and other engineering measures were carried out on the

    coalbed, after water pumping a total of 254,925 m3 coalbed methane was

    extracted during the two years experiment time with an average daily gas

    production of 873 m3. This result reconfirmed the high permeability feature

    of the coalbeds in the Fushun Coalfield. Coal quality and porosity in the

    Fushun Coalfiled is given in Table 2.

    Table 2. Coal quality and porosity in the Fushun Coalfiled

    Items Mine Industrial analysis Porosity

    Mad Aad Vadf Dry coal Water contained coal

    Longfeng Mine 2.47 10.79 42.83 8.18 4.9

    Laohutai Mine 5.44 3.60 45.76 14.06 6.7

    Deep Pits 8.52 5.52 46.74 17.32 6.0

    4.4 Coal Seam Pressure

    Pressure inside the coalbeds increases with depth. According to the result

    from the explore well #2 in the Fushun Coalfield, the measured coalbed

    pressure is 8.2 Mpa at the depth of 926 m with a pressure gradient of 0.88

    mpa/100 m which belongs to higher negative pressure.

    4.5 Isothermal Absorption

    The isothermal absorption constants a and b are two important parameters in

    computation of the coalbed methane content and in deposit prediction. The

    overall average values of these two parameters are 39.4327 and 0.042893%

    respectively in the east part at the depth of 630 m in the Laohutai Mine;

    27.274 and 0.0724% respectively in the Longfeng Mine. They are in range of

    25.16-72.94 and 0.0478-0.566% respectively in the whole Fushun Coalfield.

    The isothermal absorption curve derived from sampling analysis at the

    explore well #2 shows that the critical desorption pressure reaches 4.6 Mpa

    when gas content is 12.9 m3/ton. This indicates that the coalbeds here have

    a rather high desorption pressure.

    5. Comprehensive Evaluation on Commercial Development of Coalbed Methane in

    the Fushun Coal Mines

    The pre-feasibility and feasibility studies were conducted by Fushun Coal

    Mining Administration and Shenyang Coal Design Institute, in which the whole

    project is planned in two stages. The first stage includes the construction

    of pipelines and auxiliary facilities. The methane gas extracted from mining

    wells, after mixing with liquid oil gas, will be sent to Shenyang City by

    the early 2001. The second stage, with an investment of 258 million Yuan

    Reminbi, is methane extraction by drilling surface boreholes to replace the

    mixing oil gas with coal gas.

    The implementation of the first stage of the project is through purchase of

    the extracted methane gas with a concentration of 55-60% from the Laohutai

    Mine by Shunyang Coalbed Methane Limited Company. According to the financial

    evaluation by experts, the profit of this project, once the two stages are

    completed, can be as high as 18% after tax under the assumed tax policy. The

    period of capital return is about 7.6 years. If cost rises 20%, the profit

    will correspondingly decrease 9%.

    A total of 32 boreholes are planned to be drilled at the second stage, i.e.

    the surface coalbed methane development stage, 16 of which will be drilled

    from 2001 to 2003 with 3 to be the test wells. It is estimated that single

    well daily methane production is between 3,000-4,000 m3/day and the yearly

    methane gas supply target of 20,000,000 m3 will thus be realized.

    Conclusions and Suggestions

    In terms of the underground coal well methane extraction of the Laohutai

    Mine in Fushun Coal Mining Administration, focus should be changed from

    traditional consideration of production safety into commercial utilization.

    In order to realize this transformation, gas extraction techniques need to

    be improved to increase extraction amount and improve methane quality (i.e.

    raise methane concentration). With more coal gas extracted, less oil gas

    will be used for mixing so cost reduced.

    Surface coalbed methane gas extraction wells should be optimistically

    designed before construction. With complete parameters of the relevant

    coalbeds collected from the test wells, a full set of development techniques

    for the production wells can then be set up. Special study should be carried

    out on the techniques of hydraulic breaking of coal seams and expert

    consultation should be sought before implementation.

    Surface development of coalbed methane in the Fushun Coalfield has the

    feature of small but rich. Its coalbed methane deposit has such favorite

    conditions as high abundance, high permeability and high desorption

    pressure.

    Coalbed methane development and its comprehensive utilization in the Fushun

    Coalfield owns a very big market. It is also facilitated by short conveyance

    pipelines, low gas rate and relevant preferential policies from the local

    government.

    Coalbed methane development and utilization in the Fushun Coalfield has a

    threefold function, i.e. production transformation of the mining area, new

    source of energy development and protection of the environment.