Research on Forming Conditions and Enrichment Rules of Coal Bed Methane in West Henan

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1 2016 International Conference on Power Engineering & Energy, Environment (PEEE 2016) ISBN: Research on Forming Conditions and Enrichment Rules of Coal Bed Methane in West Henan Junmin Zhang 1, Yaming Yao 2, Jianjun Chen 3, Juanjuan Zhao 2, Fei Zhao 2 1 Department of Mining Engineering Xinjiang Institute of Engineering, Wulumuqi China 2 School of Resources & Environment North China University of Water Resources and Electric Power, Zhengzhou China 3 School of Earth Sciences and Engineering Xi an Shiyou University, Xi an China @qq.com, 2 yaoyaming321@163.com Key words: West Henan, bed methane, forming condition, resource evaluation, favorable area choosing Abstract. Based on the analysis of field geological characteristics, forming conditions and distribution law in such aggregation areas as Jiaozuo, Pingdingshan and Yima in West Henan, this paper studies macroscopic lithotypes of, microcal rock components and features of thermal evolution focusing on air content and influential factors, especially features of thermal evolution and influence of fault development on bed methane content. Main physical and chemical properties for bed methane, including gas saturation, desorption rate, crustal stress and critical pressure received special attention, including a contrast with main bed methane aggregation area in North China. After calculation, bed methane content in main blocks exceeds m 3, and thus Pingdingshan and Jiaozuo are ideal mining areas for bed methane in the future. Foundation items: Xinjiang science and technology projects of Xinjiang Uygur Autonomous Region( ) bed methane causing low rank enrichment regularity, fracturing technology, upper and lower joint exploration well comprehensive application technology development and demonstration, key points of scientific research in colleges and universities in Xinjiang Uygur Autonomous Region ( ) of project funding of Fukang City of Xinjiang bed methane efficient mining technology research. 1. Introduction Being unconventional natural gas, bed methane is generated from bed and mainly accumulated in bed in an absorbed state. With methane as the main component, mine becomes mashgas. On one hand, it is listed among one of calamities for mine safety production and excessive emission will cause climate warming; on the other hand, it is an efficient and clean energy. Exploiting bed methane will help make full use of the clean energy, improve conditions for mine safety production and protect atmospheric environment human beings depending on, killing three birds with one stone. Favorable block for bed methane development is a key groundwork, since its research results directly determine success or failure. Increase in bed methane exploration practices prove reservoir in China which is featured by low permeability, low pressure, low saturation, strong heterogeneity and high rank, resulting from common and strong stimulation in late period, with active deep process and strong activity as the root.

2 Medium-high metamorphic among resources in China is mainly distributed in North China -accumulation area Carboniferous Permian and Southern China -accumulation area Permian -bearing strata. Coal-bearing basin in these periods belongs to reformed basin, and thus it is difficult to choose favorable block for bed methane development and to conduct the related research urgently. 2. West Henan Coal Bed Methane Geological and Geochemical Characteristics 2.1 Geological and geochemical characteristics for bed methane in West Henan Covering Hebi, Anyang, Jiaozuo, Zhengzhou, Pingdingshan and Yima west of Beijing-Guangzhou Railway, West Henan -bearing area is the main production base for Henan. Upper Palaeozoic Carboniferous-Permian -bearing series has stable sediment, great thickness of bed and wide distribution, with and bed methane reaching one trillion cubic meters, which lays foundation for bed methane development and utilization. Currently the focus lies in Pingdingshan in the middle and Jiaozuo in north-central area. However, there are obvious differences in bed methane content, bed fracture distribution rule and texture, as well as bed methane adsorption/desorption due to low rank for Pingdingshan and high rank for Jiaozuo. As a result, different block choosing method will be adopted to offer data on recourses potential truly and objectively. 2.2 Stratum and Sediment West Henan Carboniferous-Permian is mainly -bearing clastic deposit against rivers-coastal wetland environment. Composed of gray, grey-green and grey-white sandstone, gray and dark grey mudstone as well as limestone with bed in between. With sediment depth of m, the stratum is divided into two systems, four series and six formations (refer to chart 1). Coal-bearing formations cover Carboniferous System Upper Series Taiyuan Formation, Permian System Lower Series Shanxi Formation, Xiashihezi Formation and Permian System Upper Series Shangshihezi Formation. Table 1. List of Main Coal Bed Depth in West Henan Shanxi Formation. bed no. (m) Ⅱ1 Ⅱ2 mine Min Max Average Min Max Average Shanmian Xin an Yiluo Yanlong Xinggong Xinmi Dengfeng Yuxian Linru Pingdingshan Jiaozuo

3 2.3 Coal Lithotypes Macroscopic Lithotypes of Coal According to underground observation for over 10 mines in Pingdingshan and Jiaozuo, petrography is mainly composed of bright and dull, followed by vitrain and fusain. As viewed from the longitudinal changes, the beds of Taiyuan and Shanxi Formation have similarities, with bright and semibright as the mainstay. Seen features of macroscopic lithotypes of various Carboniferous-Permian section as a whole, Shanxi Formation Ⅱ1 bed enjoys better lithotypes, with a simpler structure and being more favorable for bed methane generation and aggregation Microcal Rock Components After analyzing samples of Carboniferous-Permian main mines in West Henan, vitrinite content ranges from 44.6% to 99.67%, 60-80% being on average; fusinite content ranges from 0% to 52.8%, 10-30% being on average; exinite content is smaller than 2.0% on average. There is obvious regularity for vitrinite content changes, being high up and low down, the highest for Taiyuan Formation, and then Shanxi Formation, Xiashihezi Formation and Shangshihezi Formation respectively. 2.4 Features of Thermal Evolution There are gas, fat, coking, lean, meager and anthracite from low to high for main ranks, with regularity for space distribution. Coal rank decreases gradually from north to south for Ⅱ 1, Shanxi Formation. Jiaozuo, Yanlong-Xinggong falls into anthracite area, Xin an, Dengfeng, and Xinmi meager area, Shanmian, Yiluo, north Linru and Yuxian lean area, west Shanmian, south Linru and middle Pingdingshan coking and south Pingdingshan gas and fat. There is also a regularity for rank in a longitudinal direction. It takes a relatively decreasing trend for Taiyuan Formation, Shanxi Formation, Shangshihezi and Xiashihezi Formation from bottom to top. As for a single mine, rank for Taiyuan Formation is higher than Shanxi Formation, with a difference of less than one rank, and higher than Shangshihezi and Xiashihezi Formation with 1-2 rank (Fig. 2). Table 2. Change Features of West Henan Carboniferous-Permian Coal Rank. formation Taiyuan Formation Shanxi Formation Xiashihezi Formation Mine lot index volatile (%) Coal rank volatile (%) Coal rank volatile (%) Coal rank Pingdingshan No.13 Mine lean Coking Fat & coking Jiaozuo Encun 7.83 anthracit Yuxian Liangbei e Mine 9.42 anthracite Coking Xinmi Xinzheng Exploration Area meager meager Coking Xinggong Mine Field Jihe 4.33 anthracite 6.05 anthracite Xin an Mine Lot lean lean Coking

4 3. Coal Bed Methane and Influential Factors There are many factors restricting bed methane. Factors restricting bed methane content in the oilfields such as Jiaozuo, Pingdingshan, Xinggong and Xin an include evolution of metamorphism, effective overlying strata thickness over bed, structure conditions, macerals and ash yield after analysis and research. 3.1 Coal Evolution Coal in this area ranges from gas to anthracite. The higher metamorphism is, the more bed methane content there will be. Content of gas bed methane is four times of fat and coking. On one hand, as metamorphism is intensified, internal pore surface area gradually increases, leading to a greater adsorption to methane; on the other hand, being mainly tectonic, high-rank in the area has poor permeability, and thus bed methane is not easily desorbed, leading to a greater bed methane. Table 3. Statistics of Coal Bed Methane Content for Different Coal Rank in West Henan Shanxi Formation Ⅱ 1 Coal (according to Jiang Yongfu). Deep Mine lot Pingdingshan No.1, 4 and 6 Mine Yuxian Wangying Mine Linru Bishan No.2 Mine Pingdingshan No. 13 Mine Coal bed methane content(m 3 / t) Maximum Minimum Average Volatile flux(%) Coal rank (20) Fat (8) (8) (20) Coking Coking Coking Yuxina Lilou Mine (7) Lean Yuxian Mine Lot Dengfeng Gaocheng Lot Xinmi Mine Lot Xinmi Mine Lot Xinggong Mine Field Xinggong Huangzhuang Mine Field Liangbei Mine Quliang Peigou Jihe (19) Lean (6) (8) (4) Merger Merger Merger (16) Anthracite (11) Anthracite Jiaozuo Encun (15) Anthracite Average (sample number)

5 3.2 Effective Overlying Strata Thickness over Coal Bed After west Henan Carboniferous-Permian measures deposition, uplift and denudation process due to multiphase tectonic movement of Indo-Chinese, Yanshan and Himalayan caused a decreasing bed pressure and temperature, which destroyed the original absorption balance, formerly-generated bed methane began to desorb and resulted in lower methane content. According to bed methane reservoir mechanism, bed adsorbing capacity kept a dynamic balance with strata pressure. Despite settling and deposition again in later period, there is hardly any possibility for secondary hydrocarbon generation and another bed methane adsorption within an area with a burial depth less than 2000m. Consequently, Cenozoic sedimentary thickness is ineffective strata depth, namely strata depth without sedimentary thickness, rather than current bed burial depth, equals to effective overlying strata thickness over bed. 3.3 Faults and Fissures Development Faults and fissures also influence bed methane content. Northwest by west, northwest and northeast-trending faults cross cut the bed, derive many fissures and change bed permeability on one hand, and cause bed methane loss near faults or fissure-development zone, change the normal adsorption status dependent on effective overlying strata thickness over bed and make bed methane distribution complicated CH 4(m /t) H(m) fault zone Figure 1. Relation between Pingdingshan Coal Bed Methane Content and Effective Overlying Strata Thickness. Size of fracture and distance from the fault also influence bed methane to a different extent. Generally speaking, a large fracture or short distance means a low content, and vice versa.

6 gas content(m /t) ash content (%) Figure 2. Relation between Carboniferous-Permian Coal Ash Yield and Methane Content in part of North China. Research on West Henan and neighboring area shows that as vitrinite content increases, bed methane content also increases; meanwhile as ash yield increases, bed methane content will obviously decrease. In conclusion, bed methane is featured by the following: 1 Effective overlying strata thickness over bed is a main geological factor influencing bed methane; 2 Open fault and fracture cause great loss of bed methane and make the distribution complicated; 3Syncline structure is good for bed methane occurrence and its enrichment. 4. Main Physical and Chemical Properties for Coal Bed Methane and Distribution 4.1 Gas Saturation Isothermal adsorption experiment date for minable bed in various mines in West Henan indicates that Langmuir volume is m 3 /t and Langmuir pressure is Mpa (Fig. 4), among which Yanlong and Xinggong mine Ⅱ 1 bed has the largest Langmuir volume, being more than 45 m 3 /t, Pingdingshan mine has relatively low volume, being less than 22 m 3 /t in general and others keep at 25 m 3 /t. Isothermal adsorption takes a middle-low curve (Fig. 3). Coal bed gas saturation for West Henan -bearing area ranges from 26% to 91%, being 40-63% in general, which falls into less saturated bed. Pingdingshan bed, with well-preserved body structure, has a gas saturation of %, being higher than that in Liulin and Jincheng bed methane test area in North China. Thus based on this single parameter, Pingdingshan mine enjoys a better workability.

Table. 4. List of Coal Bed Adsorbability in West Henan (according to Jiang Yongfu). Mine lot Langmuir Coal Langmuir Equilibrium bed volume (m 3 pressure /t) humidity (%) (Mpa) Yuxian No.

39 Yanlong Jiaocun Mine Ⅱ 1 47.51 2.56 7.09 Xinggong Sanhe Mine Ⅱ 1 50.93 2.89 5.44 Pingdingshan No.8 Mine Ⅱ 1 20.28 1.59 Pingdingshan No.8 Mine Ⅱ 1 21.79 1.37 Pingdingshan No.8 Mine Ⅳ 2 17.01 1.

7 Table. 4. List of Coal Bed Adsorbability in West Henan (according to Jiang Yongfu). Mine lot Langmuir Coal Langmuir Equilibrium bed volume (m 3 pressure /t) humidity (%) (Mpa) Yuxian No. 5 Mine Ⅱ Dengfeng Xinxin Mine Ⅱ Bishan No.1 Mine Ⅱ Shanmian Caoyao Mine Ⅱ Xin an Mine Ⅱ Yanlong Jiaocun Mine Ⅱ Xinggong Sanhe Mine Ⅱ Pingdingshan No.8 Mine Ⅱ Pingdingshan No.8 Mine Ⅱ Pingdingshan No.8 Mine Ⅳ Pingdingshan No.811Mine Ⅱ Yuxian field Linru field Pin ding shan field Dengfeng field Shanmian field Figure 3. Isothermal Adsorption Curve for Main Coal Fields in West Henan (according to Fan Yongjie). Xinan fi eld 4.2 Rock Stress Determination Previous study shows that as effective rock stress increases, bed permeability usually takes an index decrease. As Fig. 5 shows, bed permeability decreases from μm 2 to μm 2 as effective rock stress increases from 2Mpa to 12Mpam, namely four orders of magnitude decrease of bed permeability corresponding to a 10Mpa increase of effective rock stress. Jiaozuo: with a burial depth of m, the maximum principal stress is MPa, and the minimum principal stress is MPa, with a difference of Mpa.

8 Desorption rate(%) Qinshui Basin: with a depth of m for middle and deep bed of No. 15, the minimum in-site horizontal principal stress is 7.45 Mpa, and with a depth of m for middle bed of Shanxi Formation, the minimum in-site horizontal principal stress is 15.5 Mpa. Permeability(md ) eff ective stress(m Pa) Figure 4. Relation between Coal Bed Permeability and Effective Rock Stress in North China. 4.3 Desorption ratio Desorption rate means the percentage lost gas quantity plus desorption quantity accounts for the overall methane. Changes in desorption rate reflect permeability, diffusivity and workability of bed methane. Based on more than 80 bed methane content materials by over ten Carboniferous-Permian mine exploration areas according to desorption standard set up by departments, desorption changes from 7% to 80%, being a large scope. It is mainly related to evolution of metamorphism (Fig. 5). Desorption rate is high at coking, with better permeability and pore connectivity, being favorable for bed methane depressurization, desorption and diffusion and thus a better workability V(%) Figure 5. Relation between Coal Metamorphism and Methane Desorption Rate.

9 The above analysis displays parameters influence bed methane workability in different ways and to a different extent, among which bed permeability is of the greatest significance. As it is known to all that the key for break-through in bed methane exploration in the areas like Liulin lies in its favorable permeability. 4.4 Critical Pressure Critical pressure refers to the pressure under critical state, namely the minimum pressure for gas liquefaction under critical temperature, and also the saturated vapor pressure of the liquor under critical temperature. Table 5. List of Critical Desorption Pressure for Coal Bed Methane Well in North China. Critical Theoretical Coal Measured gas desorption Area R0(%) recovery bed no. content(%) pressure ratio(%) (MPa) Shanxi Shaanxi Ordos Basin Yangquan Lu an Jincheng Hancheng Henan Jiaozuo Ⅱ Resources Calculation and Favorable Block Evaluation 5.1 Coal bed methane distribution Coal bed methane date for various mines and beds show that the methane content ranges from 1.36 to 33.63m 3 /t (Fig. 6). Form the graph, we can see that the bed methane content for Shanxi Formation ranks the highest, with a scope of m 3 /t for various mines, more than 12m 3 /t for Jiaozuo and Xinggong, m 3 /t for Pingdingshan, Dengfeng and Xinmi mine and less than 8m 3 /t for other mines. As for Shangshihezi and Xiashihezi Formation, bed methane contents ranges from 1.36 m 3 /t to 12.74m 3 /t, being 6.22m 3 /t on average.

10 Table 6. List for West Henan Carboniferous-Permian Coal Bed Methane Content. Coal field Taiyuan Formation Coal bed methane content(m 3 / t) Shanxi Formation Shangshihezi and Xiashihezi Formation Notes Shanmian /4.97(14) Coal bed Xionggong /24.84(26) Xinmi /9.15(25) Dengfeng /6.77(15) /18.08(32) Linru /5.32(17) /8.96(24) /3.43(12) Yuxian /14.81(29) /6.52(16) Pingdingshan /13.16(37) /8.04(19) methane content for Shanxi Formation is that for Ⅱ 1 bed Jiaozuo /23.25 (26) Limited bed distribution for Taiyuan Formation causes lower methane content. Shanxi Formation, with stable bed deposition, wide distribution and great depth, has the highest methane content, being the main group for bed methane evaluation and exploration, and Ⅱ 1 as the target bed for research. Thus this project conducts an in-depth research on its bed methane distribution. 1. Coal bed methane more than 20m 3 /t: mainly in Encun, Jiulishan in Jiaozuo, east of Xin an, north of Yanlong and Xinggong mine; 2. Coal bed methane ranging from 5 m 3 /t to 20m 3 /t: south of Shanmian, middle of Xin an, middle of Dengfeng and middle and north of Pingdingshan mine; 3. Coal bed methane less than 5 m 3 /t: north of Shanmian mine, west of Xin an, southern shallow buried area of Yanlong and Xinggong, south and northwest of Pingdingshan mine; 4. Ⅱ 1 Coal bed methane takes a decreasing trend in a north-south and east-west direction. 5.2 Resources Calculation Coal bed methane content mainly depends on resources and gas in bed. Based on hosting geological conditions for bed and change features of methane content, a precise estimation has been conducted for area with a burial depth less than 2000m. The result shows that bed methane content for weathered bed zone, with a burial depth of less than 2000m is m 3, including m 3 for methane weathered zone, with a burial depth less than 500m, m 3 for m, m 3 for m and m 3 for m. 5.3 Favorable Block Evaluation Viewed form resources in each block, it ranks Jiaozuo, Xinmi, Dengfeng, Xinggong, Linru, Pingdingshan, Shanmian and Xin an mine from high to low (Fig. 6).

11 Figure 6. Coal Bed Methane Content Distribution for Coal Fields in West Henan. There is a large change in resources abundance for West Henan Carboniferous-Permian, Jiaozuo field as the highest, being m 3 /km 2, and Shanmian field the lowest, being only m 3 /km 2 (Fig. 7). Figure 7. Coal Bed Methane Resources Abundance for Coal Fields in West Henan ( m). 6. Conclusion and suggestions 1. Carboniferous-Permian -bearing rock in West Henan enjoys superior -forming environment and contains large amount of bed methane resources, especially Shanxi Formation Ⅱ 1 with large thickness, wide distribution, ideal lithotypes and high methane content, being the main target interval for bed methane. 2. Among many factors influencing West Henan Carboniferous-Permian bed methane, rank comes the first, followed by effective overlying strata thickness over bed and faults. 3. Among many factors influencing workability of West Henan Carboniferous-Permian bed methane, there are permeability, strata pressure and desorption rate, permeability being the key. 4. Based on current economic and technological conditions for bed methane exploration, and after calculation for each block and depth interval, bed methane content for -bearing West Henan Carboniferous-Permian with a burial depth less than 2000m is m 3.

12 References [1] Jiang Yongfu, Tian Yun, Huang Jinzhen and etc. On Workability of Coal Bed Methane in West Henan Oil-bearing Area [J]. Henan Oil, 2001(4). [2] Yao Yaming, Zhang Liansheng, Qiao Guilin and etc. On Formation Conditions of Immature-Low Mature Oil in Zhoukou Depression [J]. Nature Gas Geoscience, 2010(5). [3] Qin Yong. Progess and Review of Chinese Coal Bed Methane Geological Study [J]. Geological Journal of China Universities, 2003(3). [4] Yao Yaming, Zhao Hongge, Yang Binyi and etc. Geological Features of Oil and Gas in Zhoukou Depression [J]. Journal of Northwest University (Natural Science Edition), 2004(3). [5] Zhao Qingbo. Geological Characteristics of Chinese Coal Bed Methane and New Exploration Field [J]. Natural Gas Industry, 2004(5). [6] Wang Dewei, Li Yuanjian, Fan Yunxia compiled. Exploration Potential of Coal Bed Methane in Henan province and Research on Mining [M]. Wu Han: China University of Geosciences Press, [7] Ye Jianping, Qin Yong, Lin Dayang as Chief Editor. China Coal Bed Methane Resource [M]. Xu Zhou: China University of Mining and Technology Press, [8] Liu Chenglin, Che Changbo, Fan Mingzhu and etc. Chinese Coal Bed Methane Geology and Resource Evaluation [J]. China Coal Bed Methane, 2009(3). [9] Wumanjiang. Eli, Yao Yaming, Zhang Junmin Complied. An Introduction to Energy Science [M]. Xi an: Shaanxi Science and Technology Press, 2013.

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