(Exploration and Development Research Institute of China Petroleum Daqing Oilfield Co., Ltd., Daqing 1637 12 1)
Abstract: Hegang Basin is one of the main coal-producing basins in Heilongjiang Province, which is rich in coal resources. In 2009, the successful deployment and construction of Meihe 1 well in Daqing Oilfield is of great significance for understanding the coalbed methane resources and resource potential in Hegang Basin. Based on the drilling and seismic data of coalfields and oil fields, the reservoir-forming conditions of coalbed methane in Hegang Basin are analyzed. Through the analysis of the structural conditions of earthquake and other data, it is considered that the extensional faults in Hegang basin are developed in multiple stages, reviewed and overlapped, which is not conducive to the preservation of coalbed methane. According to the data of coalfield drilling and Hemei 1 well, the characteristics of coal seams in Hegang Basin are analyzed. It is considered that the coal seams of Nanshan Mine, Xinyi Mine and Niaoshan Mine are relatively thick, with the cumulative thickness generally greater than 60m, and the single-layer thickness of main coal seams is greater than 10m. The buried depth of the main coal seam is moderate, and the buried depth of the main coal seam exposed by Hemei 1 well is above 1000m; The coal rank is moderate, mainly gas-fat coal, which increases eastward with the increase of buried depth; Through the statistical analysis of the drilled coalbed methane wells, the gas content in Hegang coalfield is low in the south and high in the north, which can meet the industrial mining standards. The analysis of reservoir characteristics of Hemei 1 well shows that most coal seams in Hegang Basin have poor physical properties, and only a few coal seams develop cleavage, which is suitable for mining coalbed methane. To sum up, it is considered that Nanshan Mine, Xinyi Mine and Niaoshan Mine in Hegang Basin have good enrichment potential, and the resources of the three mining areas are estimated, with considerable reserves of 303.75× 108m3. Comprehensive analysis shows that the development of structural coal, insufficient exploration efforts and unclear exploration methods caused by extensional faults in Hegang Basin are the core problems that restrict the breakthrough of coalbed methane exploration in Hegang Basin.
Key words: Hegang basin; Coalbed methane; Reservoir forming conditions; Quantity of resources
Potential Analysis of Coalbed Methane Resources in Hegang Basin
Wang Shihui, Wang Youzhi, Xu Chengwu
(Exploration and Development Research Institute of China Petroleum Daqing Oilfield Company, China Daqing 1637 12 1)
Abstract: Hegang Basin is rich in coal resources. It is one of the main core production basins in Heilongjiang Province. Well HM- 1 is a well successfully designed and constructed in Daqing Oilfield in 2009, which is of great significance for understanding Hegang coalbed methane resources and resource potential. By studying the drilling data and seismic data of coalfields and oil fields, the conditions of coalbed methane accumulation in Hegang Basin are analyzed. The development of tensile faults in Hegang basin is not conducive to the storage of coalbed methane. Based on the data of coalfield and HM- 1 well, the characteristics of coal seams in Hegang Basin are analyzed, and it is concluded that the coal seams in Nanshan District, Xinyi District and Niaoshan District are thicker. The cumulative thickness is generally greater than 60 meters. The thickness of the main coal seam can reach 10 meter or more. The buried depth of main coal seams is moderate, in which the buried depth of HM- 1 well is above 1000 meters. Ro of coal is in a suitable range. Most of them are gas-fat coal. With the deepening of buried depth, the coal rank increases eastward. Through the analysis of the drilled coalbed methane wells, we find that the gas potential in the south of Hegang Basin is low and that in the north is high. These data meet the standards of industrial production exploration. Through the study on the reservoir characteristics of HM- 1 well, it is shown that most reservoirs have poor physical properties and only a few have developed coal seam cleavage. To sum up, Nanshan belt, Xinyi belt and Niaoshan belt in Hegang basin have good enrichment potential. In order to estimate the resources in these three areas, we found that the reserves are very large, which is 303.75× 108m3. Comprehensive analysis shows that the development of structural coal caused by extensional faults, insufficient exploration efforts and unclear exploration methods of structural coal are the core problems that restrict the breakthrough of coalbed methane exploration in Hegang Basin.
Key words: Hegang basin; Coalbed methane; Reservoir forming conditions; Scope of resources
1 river basin overview
Hegang basin is located at the junction of Xiaoxing 'anling and Sanjiang Plain in Heilongjiang Province, and it is distributed in the north-south direction. It starts from vegetable fields in Sifang Mountain in the north, reaches Alingda River in the south, reaches Li Yong-Shuyuan area in the west, and reaches Xinhua-Yuantoushan line in the east, with a length of about 100km from north to south and a width of about 28km from east to west. Coal resources in Hegang basin were developed earlier. From north to south, there are mining areas 10, industrial reserve 16× 108t, with recoverable reserves of 8×108t.
2 CBM exploration and development status
With the continuous breakthrough of exploration theory and development technology of coalbed methane in the United States, the research and development of coalbed methane in more than 30 important coal-producing countries in the world has been promoted [2 ~ 4]. 1989, the implementation of the United Nations Environmental Protection Agency's assistance project "Development of coalbed methane resources in China" officially kicked off the research on surface development of coalbed methane in China. Compared with the successful development of coalbed methane basin in the United States [5 ~ 7], Hegang basin has become one of the important coal seam exploration areas.
Hegang area realized the commercial utilization value of mine gas earlier. 1984 drainage gas as high-quality fuel, 1992 began to enter the practical stage of residents. At present, only Nanshan Mine has realized the comprehensive utilization of gas drainage [8 ~ 9].
The exploration of coalbed methane in Hegang basin began at 1998. China United CBM Company, Heilongjiang Provincial Planning Commission, Hegang Mining Bureau, Heilongjiang Coal Management Bureau and hegang Municipal Government jointly built two CBM parameter wells and production test wells (HE-0 1, HE-02) in Junde and Xing 'an areas. In 2002, Zhonglian CBM Company, Heilongjiang Provincial Planning Commission and Heilongjiang Coalfield Geology Bureau conducted exploration in Nanshan, Xinyi and Niaoshan, and arranged four CBM parameter wells and production test wells (He Shen 3, He Shen 4, He Shen 5 and He Shen 6), and constructed a reference well (He Shen 3) in advance. In 2009, Zhonglian Coalbed Methane Company constructed a test well in Xinyi area, and conducted a drainage test on the well. The daily gas production reaches 65,438+0,400 m3/d. ..
A major gas explosion occurred in Hegang on June 5438+065438+1October 2 1 day, 2009. In order to implement the spirit of the instructions of the leaders of provincial and oil companies and reflect the social responsibility of Daqing Oilfield, with the original intention of reducing safety accidents and solving environmental pollution, Daqing Oilfield built three coalbed methane evaluation wells in Xinyi Mine and Niaoshan Mine from 2009 to 20 10, and achieved good results.
With the increase of coalbed methane exploration, the resource prospect of Hegang basin has been clearly understood. After full analysis and research, Nanshan, Xinyi and Niaoshan mining areas are determined as the key targets for future exploration and development. However, due to the complex reservoir-forming conditions, it has brought certain difficulties to exploration.
3 Analysis of reservoir-forming conditions
3. 1 structural features
Regional structure affects the generation and enrichment of coalbed methane by controlling its generation and occurrence. Therefore, a correct understanding of the regional structural characteristics of coalfields is the basis for analyzing the occurrence law of coalbed methane resources.
3. Structural characteristics of1.1region
Hegang basin is located in the northwest of Jiamusi massif, with Mudanjiang fault in the north-south direction in the west and Yilan-Yitong fault in the southeast (figure 1). The basement of the basin is mainly composed of pre-Paleozoic Mashan Group, Heilongjiang Group deep metamorphic rock series, Proterozoic mixed granite and Variscan granite. Hegang basin is composed of four first-order structural units, which are Hongqi fault depression, Lianerling-Fuerjihe uplift, Baoquanling fault depression and Duluhe uplift in turn from west to east, showing "depression-uplift alternation" on the whole.
Figure 1 Hegang basin structural zoning map
3. 1.2 Structural characteristics of coalfield area
Hegang coalfield is a monoclinic structure with an inclination of 65438+05 ~ 35. Affected by the rigidity of the basement, the folding in the basin is weak, and the fault structure is well developed, mainly normal faults, which can be divided into groups of north-south, east-west, north-northeast, north-west and north-northwest. There are many faults, many stages, mutual cutting and interweaving, which leads to complex and mixed fault structural styles.
The openness of tensile faults is not conducive to the preservation of coalbed methane. Due to stretching, the vicinity of the profile becomes a low-pressure area due to the release of tectonic stress, and a large amount of methane adsorbed in the coal seam decomposes and escapes from the profile, which has a destructive effect on coalbed methane reservoirs.
3.2 Characteristics of coal-bearing strata
3.2. 1 coal seam thickness
The main coal-bearing stratum in Hegang coalfield is Chengzihe Formation of Lower Cretaceous with a total thickness of 730 ~ 13 10m. There are more than 40 layers of coal in the coalfield, including 36 minable and partially minable coal seams. The main minable coal seams [10] include 3 #, 1 1 #, 15 #, 17 #, 18 #, 2 1 # and 22 #.
Fig. 2 Statistical histogram of average coal seam thickness of Chengzihe Formation in Hegang Basin
Judging from the development of coal seams in the whole region, the continuity of coal seam thickness is good and the resource potential is great. On the whole, Xinyi Mine gradually becomes thinner from south to north, in which coal seams with a thickness greater than 60m are mainly distributed in Xinyi, Nanshan and Niaoshan Mines, while Xing 'an and Junde Mines are only locally developed (Figure 5). The cumulative thickness of coal seam exposed by Hemei 1 well exceeds 100m, so Xinyi Mine has a good exploration prospect.
3.2.2 Buried depth of coal seam
The western edge of coal seam in Hegang Basin is shallow buried, even exposed to the surface, and gradually buried eastward, but the thickness of coal seam becomes thinner. According to the coalfield drilling data and the coal seam situation revealed by Hemei 1 well (Figure 4), the maximum buried depth of coal seam is shallow, which is 1000m, and there is no drilling control outside the mining boundary. According to seismic interpretation, it is estimated that the maximum buried depth can reach 2000m m. The buried depth of coal seam in Hegang Basin is moderate, which is beneficial to the exploration and development of coalbed methane [5].
Fig. 3 Comparative Distribution Map of Main Coal Seam Profiles in Hegang Basin
Fig. 4 histogram of coal seam thickness and buried depth of Hemei 1 well.
Grade of coal
Under the same geological conditions, it is generally believed that the gas content in coal seam increases with the increase of coal metamorphism. Hegang coalfield is dominated by medium-low metamorphic gas coal and fat coal, and the coal rank increases with the increase of buried depth from west to east. Due to the intrusion of Yanshanian magmatic rocks, thermal contact metamorphism occurred in coal seam, and the metamorphic degree of coal gradually increased from south to north (Figure 4). Junde and Xing 'an mining areas are mainly gas coal and long-flame coal, while Fuli, Nanshan and Xinyi mining areas in the middle are fat coal, and Niaoshan mining area becomes coking coal. There are lean coal and anthracite in the east of Xingshan mining area (Figure 6). Therefore, the gas content of coal seams in Hegang Basin is high in the north and low in the south.
3.3 Coal seam gas content
By analyzing the test results of Well HE-0 1 and Well HE-02, it is found that the gas content in each coal seam is low. The gas content in Well HE-0 1.14 ~ 2.41m3/t, with an average of 2.3m3/t. The gas content in Well He 02 is relatively high, ranging from1.06 ~ 5.0/.
According to the test results of Hemei 1 well, the content of coalbed methane is high. Twenty-three samples were analyzed in Hemei 1 well, and the gas content was basically greater than 2m3/t. The gas content in the 620 ~ 654m interval was above 5m3/t, the highest was 9.3m3/t, and the methane concentration was above 80%, which reached the industrial standard.
Fig. 5 cumulative thickness distribution of coal seams in Hegang basin
Fig. 6 Coal rank distribution map of Hegang Basin 1 1 # coal seam
3.4 Physical characteristics of coal reservoir
Physical factors mainly include porosity, permeability, cleavage, adsorption capacity, reservoir pressure, analytical pressure and so on. According to previous research results, Hegang Basin has low porosity and permeability [1 1]. Through the observation of 23 samples from Hemei 1 well, it is considered that the structural coal in Xinyi mining area is mainly dark coal with a small amount of bright coal, and the coal body structure is broken, mainly pulverized coal with a small amount of fragments, and cleavage cannot be observed (Figure 7). In the table 1, the interval 65 1.73-652. 13 has high gas content, reaching 9.3m3/t, with gas saturation of 67%, high reservoir pressure and analytical pressure, which is suitable for coalbed methane fracturing and drainage analysis.
Fig. 7 Photo of coal rock types and cleavage cracks in Hemei 1 well.
Table 1 Hemei 1 Well Reservoir Physical Parameters Table-Reservoir Pressure is the value estimated according to the pressure gradient of 0.77 MPa/100 m.
4 Coalbed methane resource prediction
By analyzing the basic geological conditions in Hegang area, combining with the previous research results and the relevant data of Hemei 1 well, it is considered that Xinyi, Niaoshan and Nanshan areas are the most favorable areas for coalbed methane exploration in the future. Considering the current mining capacity and economic factors, the coalbed methane resources in Xinyi, Niaoshan and Nanshan mining areas are predicted with 1500m as the boundary. The reserves of coal resources in Nanshan Coal Mine are 9.03× 108t, the reserves of coalbed methane are 139.5× 108m3/t, the reserves of coal resources in Xinyi and Niaoshan Mining Areas are 22.32× 108t and the reserves of coalbed methane are164.2.
5 conclusion
(1) On the basis of fully analyzing the measured data of Hemei 1 well, the basic geological characteristics, buried depth, thickness, metamorphic degree, gas-bearing property and reservoir characteristics of Hegang Basin are systematically studied, and it is considered that Hegang Basin has the potential to become an important CBM development base. At present, the key factors restricting the breakthrough in Hegang Basin are insufficient exploration efforts and unclear understanding of structural coal exploration methods.
(2) The coal seams in Hegang Basin are mainly gas coal and fat coal, with a moderate evolution degree; The gas content and gas saturation are relatively low, but the coal seam is thick and the spacing between layers is small, which can make up for the lack of gas source caused by the low evolution degree. Coal and rock are mainly pulverized coal, which is seriously broken, which brings great challenges to the later fracturing reconstruction process; The strong transformation in the later period of the basin, the development of extensional faults and the wide distribution of tectonic coal are double-edged swords for coalbed methane exploration. Tectonic coal can not only become a high concentration area of coalbed methane, but also destroy the accumulation of coalbed methane.
(3) Although Hegang Basin is structurally relatively fractured, there are abundant coalbed methane resources in Nanshan, Xinyi and Niaoshan mining areas in the middle, with considerable reserves. The successful drilling of Hemei 1 well proves that Daqing Oilfield has the strength to develop coalbed methane, mastered relatively mature coalbed methane exploration methods, and established the confidence to achieve a breakthrough in coalbed methane industry as soon as possible.
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