(1. Chongqing Research Institute of China Coal Science and Technology Group Chongqing 400037; 2. State Key Laboratory of Gas Disaster Monitoring and Emergency Technology Chongqing 400037)
The utilization of coalbed methane is an inevitable requirement to promote the safe, clean and economic development of coal mines, an important measure to reduce environmental pollution and an effective measure to increase energy supply. This paper mainly introduces the regional geological background and characteristics of Shuicheng mining area in western Guizhou, and analyzes the occurrence law and main controlling factors of coalbed methane in Shuicheng mining area. The research shows that the occurrence of coalbed methane in Shuicheng mining area is mainly affected by the inward oblique structure, the sedimentary environment in the layer and the sequence system tract, and the specific occurrence of coalbed methane is mainly controlled by the small structure, caprock, coal seam occurrence and coal quality. The research results can provide reference for the development and utilization of coalbed methane in western Guizhou.
Keywords: coalbed methane occurrence law, influencing factors of structural caprock
Fund Project: National Science and Technology Major Project 34 "National Coal Mine Coalbed Methane (Gas) Development Information Platform" (201zx05040-005-01).
About the author: Dong Guowei, 198 1 born, male, from Yuncheng, Shanxi Province, engineer, doctoral student, mainly engaged in the study of coal and rock gas dynamic disasters and gas occurrence law, Chongqing Research Institute of China Coal Science and Technology Group, No.55, Shangqiao Third Village, Shapingba District, Chongqing, 400037. Tel:/kloc-0 15923355967, e-mail: leng285@ tom. com
Analysis of main factors of coalbed methane occurrence in Shuicheng mining area of Qianxi
Dong Qixiang Qin Mu Guang Huang
(1. Gas and Fire Research Institute of Chongqing Research Institute of China Coal Technology Engineering Group Corporation, Chongqing 400037; 2. State Key Laboratory of Gas Disaster Monitoring, Prevention and Emergency Control, Chongqing 400037.
Abstract: The utilization of coalbed methane is an inevitable requirement to promote the safe development of coal mines, an important measure to reduce environmental pollution and an effective measure to increase energy supply. This paper mainly introduces the regional geological background and characteristics of Shuicheng mining area in Qianxi, and the coal-bearing strata in Shuicheng mining area in Qianxi. The law and controlling factors of coalbed methane accumulation in Shuicheng mining area of western Guizhou are analyzed and studied. The research shows that the coalbed methane accumulation is mainly influenced by syncline structure in Shuicheng mining area of western Guizhou. In plane, coalbed methane reservoir formation is mainly influenced by sedimentary environment and sequence system tract, and coalbed methane reservoir formation is mainly controlled by local mine structure, caprock and coal. The characteristics of coalbed methane reservoir parameters are measured and analyzed. The development and utilization technology of coalbed methane at present is introduced. The research results can be used as a reference for the development of coalbed methane in western Guizhou.
Keywords: coal seam; CBM accumulation rule; Structure; Cover; influencing factor
1 Overview of Shuicheng Mining Area in Qianxi Area
Guizhou Shuicheng Mining (Group) Co., Ltd. (hereinafter referred to as "Shuicheng Mining Area") is located in the northwest section of Liupanshui coalfield. Shuicheng mining area is mainly engaged in coal mining. The coal measure stratum in the mining area is Longtan Formation (Xuanwei Formation) of Upper Permian. According to geological structure and mining conditions, the mining area is divided into seven independent mines from northwest to southeast (mostly built in the early 1970s): ① Sheng Yuan Coal Mine; ② Dawan Coal Mine; (3) Naluozhai Coal Mine; ④ Wangjiazhai Coal Mine; ⑤ Okawa Coal Mine; 6 hongqijing; All landowners Laoyingshan Coal Mine.
Sheng Yuan coal mine and Dawan coal mine are located in Ertang syncline, Hongqi coal mine, Dachuanbu coal mine, Wangjiazhai coal mine and Naluozhai coal mine are located in Dachuanbu syncline, and Laoyingshan coal mine is located in Xiaohe syncline. See figure 1 for the structural outline of Shuicheng mining area.
Figure 1 Structural Outline of Shuicheng Mining Area
The strata exposed in Shuicheng Mining Area are: Upper Permian Emei Mountain Basalt (P 12), Upper Permian Longtan Formation (P22), Lower Triassic Feixianguan Formation (T 1), Middle Triassic Jialingjiang Limestone (T2) and Quaternary Topsoil (Q). Main coal seams 1, 2, 4, 7, 8, 9, 1, 13.
2 regional geological background of Shuicheng mining area in western Guizhou
Shuicheng is located in the southwest edge of Yangtze landmass. It is not only controlled by the tectonic evolution of Yangtze plate, but also by the evolution of Shuicheng fault depression zone. There are mainly NW-trending structures, NE-trending structures and nearly EW-trending structures in this area [1] ~ [4].
Panxian-Liupanshui fault, Shuicheng fault and Shizong-Guiyang fault control the occurrence of coal seam and coalbed methane in Longtan formation in Shuicheng mining area. Yanshan movement in the coal-bearing strata in the late Late Permian caused a large area of folds in the coal-bearing strata, which laid the outline of the coal-controlling structure in the later period. Himalayan movement caused cracks in coal-bearing strata, which had a certain impact on the enrichment of coalbed methane [2]. See figure 2.
The NE-trending synsedimentary faults played a leading role in controlling the late Permian sedimentary pattern in Guizhou, while the differential subsidence superposition of near-EW-trending synsedimentary faults and NEE-trending synsedimentary faults further complicated the sedimentary pattern, forming a sedimentary coal accumulation pattern of "East-West Zoning and North-South Zoning". This led to the emergence of delta tidal flat environment and muddy subtidal environment in Shuicheng mining area in western Guizhou [2]. See figure 3.
Fig. 2 Outline map of main basement faults in Late Permian in Guizhou Province
In the southern part of Late Triassic, Shuicheng area was a continental denudation area. The lithofacies palaeogeography of Huobachong period is basically similar to that of Banan period. In the Second Bridge Period of Late Triassic, Shuicheng area entered the stage of continental deposition, with denudation in the east and inland lake environment in the west, and a set of lacustrine clastic rocks with coal deposits developed, but only coal lines and thin coal seams were formed.
Fig. 3 Late Permian sedimentary environment map of Shuicheng mining area
3 occurrence law of coalbed methane in Shuicheng mining area in western Guizhou
Shuicheng mining area is divided into three coalbed methane geological structural units, namely, coalbed methane geological unit 1: Ertang syncline, including Sheng Yuan Coal Mine and Dawan Coal Mine; Coalbed methane geological unit 2: Okawabe syncline. The mines included in this structural unit are Hongqi Coal Mine, Dachuanbu Coal Mine, Wangjiazhai Coal Mine and Naluozhai Coal Mine. Coalbed methane geological unit 3: the syncline of the small river, and Laoyingshan Coal Mine is in this structural unit.
The main factors affecting the occurrence of coalbed methane in coal seam are faults, folds, caprocks, occurrence state of coal seam and coal quality.
3. Influence of1structure on coalbed methane occurrence
Ertang syncline, Dachuan syncline and Xiaohe syncline control the occurrence of coalbed methane. The structure of Xiaohe syncline is the most complex, with large dip angle of coal seam and concentrated tectonic stress, which is easy to form gas outburst. Dachuan syncline from south to north Okawabe coal mine → Wangjiazhai coal mine → Naluozhai coal mine has increased structural complexity and coalbed methane content. The structure of Ertang syncline is relatively simple, the axis of syncline is buried deeply, and the coalbed methane is larger than the two wings.
Fig. 4 Relationship between coalbed methane content in Ertang syncline 1 1 coal seam and mudstone thickness in coal seam floor.
3.2 Influence of caprock on coalbed methane occurrence
The caprock is controlled by sedimentary environment and sequence system tract. The content of coalbed methane in Shuicheng mining area generally increases with the increase of mudstone content in the roof and floor of coal seam. The caprock is one of the reasons that affect the occurrence of coalbed methane in Shuicheng mining area, but the influence is relatively small. Take Ertang syncline as an example, as shown in Figure 4. The main coal seam 1 1 and 13 were formed in the late period of transgressive system tract, close to the maximum flooding surface, and the main coal seam 1 was located in the middle and late period of transgressive system tract [5] ~ [7].
3.3 Influence of coal seam occurrence state (coal thickness) and coal quality characteristics on coalbed methane occurrence
The content of coalbed methane in coal seam increases with the increase of coal seam thickness, but the correlation coefficient is not high.
The methane pressure in coal seam increases with the decrease of floor elevation and the increase of buried depth of coal seam, and the correlation coefficient is high. Take Ertang syncline as an example, as shown in Figure 5.
In syncline, coal seam gas pressure decreases with the increase of coal seam dip angle, which accords with the general law of coal seam gas pressure and coal seam dip angle, but the correlation is not high.
There is little difference in the metamorphic degree of coal quality in Shuicheng mining area, which has little influence on the occurrence of coalbed methane.
3.4 Influence of Aquifer on CBM Occurrence
The aquifer of coal measures strata and its overlying strata in Shuicheng mining area is weak in water-rich, and the aquifer has little influence on the occurrence of coalbed methane.
Fig. 5 Relationship between pressure of coalbed methane and buried depth in Ertang syncline 1 1 coal seam.
3.5 In the regularity area of coalbed methane occurrence in Shuicheng mining area, Ertang syncline, Dachuan syncline and Xiaohe syncline control coalbed methane occurrence, and Xiaohe syncline has the most complicated structure, large dip angle of coal seam and concentrated tectonic stress, which is easy to form gas outburst; Dachuan syncline from south to north Okawabe coal mine → Wangjiazhai coal mine → Naluozhai coal mine has increased structural complexity and coalbed methane content. The structure of Ertang syncline is relatively simple, the axis of syncline is buried deeply, and the coalbed methane is larger than the two wings.
Stratigraphically, 1 1 3, 13, followed by No.7, No.8, No.9, No.4 and No.2 are the largest coalbed methane near the maximum water flooded surface in Shuicheng mining area.
Through the analysis of structure, sedimentation, coal seam occurrence, coal quality and other factors, it is found that the coalbed methane reserves in the same geological unit are mainly controlled by buried depth and elevation, and the correlation coefficient is generally greater than 0. 7. The content of coalbed methane in coal seam increases linearly with the increase of buried depth and decreases with the decrease of altitude. Local areas are controlled by small structures, roof and floor lithology, coal thickness and coal quality, and the correlation coefficient is basically less than 0. 7.
4 main conclusions
(1) Panxian-Liupanshui fault, Shuicheng fault and Shizong-Guiyang fault control the occurrence of coal seams and coalbed methane in Longtan Formation in Shuicheng mining area.
(2) Ertang syncline, Dachuan syncline and Xiaohe syncline control the occurrence of coalbed methane, and the axes of Xiaohe syncline, Dachuan syncline and Ertang syncline are larger than their wings.
(3) Stratigraphically, 1 and 13 coal seams near the maximum water flooded surface in Shuicheng mining area have the largest coalbed methane, followed by1coal seam, followed by 7, 8, 9, 4 and 2 coal seams.
(4) Comprehensive analysis of factors such as structure, sedimentation, coal seam occurrence and coal quality shows that in the same geological unit, the occurrence of coalbed methane in the same coal seam is mainly controlled by buried depth and elevation, and locally controlled by small structure, roof and floor lithology, coal thickness and coal quality.
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