(China United Coalbed Methane Co., Ltd. Beijing 1000 1 1)
Based on the study of regional structure, coal-bearing strata, coal seam quality and coalbed methane drilling in the project area, the achievements of gas bearing, permeability, reservoir pressure and its gas control factors in Baode block are emphatically summarized, and the exploration and development targets of coalbed methane in Baode are pointed out.
Keywords: exploration and development target of coalbed methane in Baode block
New progress in exploration and development of coalbed methane in Baode block, Shaanxi Province
Jiagaolong
(China United Coalbed Methane Co., Ltd., Beijing 1000 1 1)
Abstract: The structure, coal-bearing stratum, coal seam, coal rank and drilling data in this area are studied. The gas content, permeability, pressure, gas saturation and their controlling factors of reservoir are analyzed. The target area for exploration and development of coalbed methane resources in Baode block in the eastern margin of Ordos Basin is delineated.
Keywords: Baode block; Coalbed methane exploration; Development goals
1 overview
The coalbed methane field in the eastern margin of Ordos basin is located near the Yellow River in Shanxi, Shaanxi and Mongolia, including Zhungeer in Inner Mongolia, Shenfu in Shaanxi and Hedong coalfield in Shanxi. The gas field is 480km long from north to south and wide from east to west 15 ~ 80 km with a total area of 23000km2.
The eastern margin of Ordos Basin is an important coking coal and power coal production base in China. There are not only abundant coal resources here, but also abundant coalbed methane resources. It is one of the basins with the best coalbed methane resources and development conditions in China, and it is also the most active exploration area. Known as "San Juan of China" by geologists at home and abroad.
Hedong CBM field is explored by domestic enterprises such as North China Petroleum Bureau and Changqing Petroleum Exploration Bureau of the former Ministry of Geology and Mineral Resources, and foreign companies such as American CBM, Enron, Phillips, Arco, Chevron Texaco (CVX), Lowell, BHP Billiton (BHPB) and Sino-Australian Energy (SGE).
Zhungeer coalbed methane project area is located in the north of the gas field, with a total area of 6853km2, of which: Zhungeer Block 2817km2; ; Shenfu block is 2998km2；; Hequ block is 560km2；; Baode Block is located in the south of the project area with an area of 478km2 (Figure 1).
From June 5, 2000 to 10, Zhonglian Company and Texaco Company signed three CBM product sharing contracts in Shenfu Zhungeer, Shaanxi Province and Baode, Shaanxi Province. In June, 2004, Chevron Texaco and BHP Billiton completed the transfer agreement of shallow blocks with coal seam depth of1000 m m. ..
Bhp Billiton Company started CBM exploration in September 2004, and completed the construction of five CBM parameter wells ZG-2, ZG-3, ZG-4, SF- 1 and BD- 1 in the north. In 2005, CBM exploration was carried out in Baode Block, and five CBM parameter wells BD-2, BD-3, BD-4, BD-7 and BD-8 were completed. The horizontal well group operation was carried out around BD-4, and the horizontal well L 1 directional interval was completed. As of August 2006, the directional intervals of vertical well V 1 ~ V4 and horizontal well L 1 ~ L4 have been completed.
Table 1 Zhungeer CBM Project Construction Drilling Coring Test List
2 Geological achievements
2. 1 geological structure
The geotectonic structure is located in the middle abdomen of North China Plate, that is, Hedong Block on the eastern edge of Ordos Block, bordering Lvliang Uplift in the east, Yinshan Plate Edge Belt in Inner Mongolia in the north and Qinling Plate Edge Belt in western Henan in the south. The gas field shows a transitional basin-edge structure type.
Lvliang uplift on the east side of the plot exposes the coal seam to the surface; There are Tianjiashiban fault and Qingshuichuan fault in the north; There is an asymmetric anticline structure (deflection) in the west of Gaoshiya-Haojiazhai, with gentle east wing and steep west wing. The dip angle of Gaoshiya village can reach 40, which has a great influence on the buried depth of coal seam and gas content.
The interior of the block is characterized by a monoclinic structure inclined at a small angle to the west. There are NNE secondary anticlines (such as Miaogoumen anticline and Tianjiazhai anticline) in Shenfu block in the west. The anticline structure controls the accumulation of coal-formed gas, and Tianjiazhai anticline may become a gas storage structure, which deserves attention.
2.2 coal-bearing strata
Coal-bearing strata include Upper Paleozoic Carboniferous benxi formation, Taiyuan Formation, Lower Permian Shanxi Formation and Lower Shihezi Formation. Only benxi formation and Xiashihezi Formation have coal lines, and the main coal seams are located in Taiyuan Formation and Shanxi Formation.
Taiyuan Formation: the bottom boundary is K 1 sandstone, and the top boundary is the bottom of K3 sandstone. It is a coal-bearing series composed of clastic rocks, carbonate rocks and coal seams, and is dominated by shallow delta deposits controlled by rivers. The thickness of this group is 70 ~ 1 10m, with an average thickness of 95m.
Shanxi Formation: The lower interface is K3 sandstone, and the upper interface is the bottom of K4 sandstone of Xiashihezi Formation. It is a set of coal-bearing measures mainly composed of rivers and shallow lakes, and composed of grayish white sandstone, sandy mudstone and coal seam, with a general thickness of 35 ~ 90m and an average thickness of 70m.
2.3 Coal seam and coal quality
There are 7 coal-bearing strata in Taiyuan Formation, of which No.8 and No.9 coal seams are the main coal seams, with thicknesses of 0.40 ~ 3.50m and 2.20 ~ 4.30m respectively. Two layers of coal are often merged with 10 coal seam, and the general trend is "thick in the north and thin in the south", and the thickest in the north of Baode block can reach 17m m.
There are five coal-bearing strata in Shanxi Formation, of which No.4 and No.5 are the main coal seams with thicknesses of 0.40 ~ 5.50 m and 0.50 ~ 3.50 m respectively, and they are often combined, showing a general trend of "thick in the north, thin in the east and thin in the west". The thickness of coal seams in the north of Baode Block can reach11m.
The main coal seams in Hedong gas field are long flame coal, weak caking coal, 1/2 medium caking coal, gas coal, fat coal, 1/3 coking coal, coking coal, lean coal and anthracite from north to south. Baode block is represented by No.4-5 and No.8-9 coal seams, and the coal is mainly gas coal. The test results of coal quality in Hedong coalfield are shown in Table 2.
Table 2 Coal quality characteristics of main coal seams in Hedong coalfield
2.4 gas content and its control factors
The gas content of coal seam in Hedong gas field increases gradually from north to south and from east to west, and the gas content is 4. 15 ~ 23.0m3/t, with an average of12.64m3/t. According to the test results of five coalbed methane wells in Baode block, the gas content of No.4-5 main coal seam is 2 ~ 8m3/t, and that of No.8-9 main coal seam is 2 ~ 8m3/t.
Table 3 List of Coal Reservoir Characteristics in Baode Block
According to the study of hydrocarbon generation history, the main gas generation stage is middle-low metamorphic bituminous coal gas generation stage, and the change of coal seam gas content is mainly controlled by regional metamorphism.
2.5 Permeability
Hedong gas field is mainly gas coal, fat coal, coking coal and other moderately metamorphic coals. Cleavage and fracture are developed in coal, and the permeability of coal seam is high, with the maximum permeability reaching 453mD and the average value being 3.2 MD
According to the test results of five coalbed methane wells in Baode block, the permeability of main coal seam is generally 2.4～8mD.
2.6 Reservoir pressure
The pressure of coal reservoir in Hedong gas field is mostly negative pressure, and the pressure gradient of No.8 coal seam in LXC 4 well in Linxing block is 0.988 MPa/100 m; The pressure gradient of No.9 coal seam in Sanjiao SG- 1 Well is 0.143mpa/100m; The pressure gradient of No.9 coal seam in Shilou SH-2 well is 0.409 MPa/100 m. ..
According to the test results of coalbed methane wells in Baode block, the reservoir pressure in most areas is negative pressure, and only the vicinity of well group BD-4 is normal pressure.
2.7 adsorption and saturation
Langmuir volume of coal (maximum adsorption capacity):14,438+0 ~ 35.52m3/t in Linxing block; Shilou block is 10.64 ~ 35.85m3/t, and the test results show that the coal reservoir has strong adsorption capacity.
Gas saturation of coal reservoir in Linxing block: 3.5 ~ 79.2%; Shilou block has an average of 63.4%; Baode block is not saturated enough.
3 CBM exploration and development work
3. 1 Baode target area
Including south-central Baode block and Shenfu block, with an area of about 1500km2. According to the characteristics of coal reservoirs and the preservation conditions of coalbed methane in this area, the parameters of exploration target area are determined: the single-layer thickness of main coal seam is greater than 5m, the reservoir depth is generally less than 1500m, the gas content is generally greater than 5 ~ 8m3/t, the permeability is generally greater than 1mD, and the gas saturation is generally greater than 50%.
Figure 1 Target Area of CBM Exploration and Development
(Coalbed methane field in the eastern margin of Ordos Basin)
Baode target area is a gentle slope zone, the depth of coal reservoir is generally 300 ~1200m, and there is a very thick coal reservoir. The single-layer thickness of the main coal seam can reach 10m, with high gas content and permeability, and it is the main exploration and development target area in the north of the gas field (Figure 1).
3. 1. 1 exploration and development of Baode target area
The first horizontal well group in Baode block is near BD-4 well, because its gas content is 4 ~ 8m3/t and its permeability is 5 ~ 8md, which can meet the requirements of horizontal well development. The well group design consists of 8 wells, 4 vertical wells and 4 horizontal wells, and the medium radius drilling technology (MRD) is adopted (Figure 2). It is expected that the horizontal well group will achieve good results.
Schematic diagram of radial drilling (MRD) in Figure 2.
Fig. 3 Schematic diagram of exploration and deployment in Baode target area.
3. 1.2 exploration and deployment of Baode target area
In 2006, three exploration wells, BD-9, BD- 10 and BD-6, were deployed in Baode block, which were located in the deep north, deep west and shallow middle east respectively. Arrange 25km seismic data acquisition, as shown in Figure 3.
In 2007, it is planned to deploy three exploratory wells in the south of Baode Block, namely BD- 12, BD- 13 and BD- 14.
3. 1.3 CBM exploration scheme in Shenfu block
In 2006, SF-2 well was located in the middle-east of Shenfu block, that is, in the deep part of Baode Well Group (the well depth was about 1000m). Well SF-3 in 2007 depends on the exploration results extending westward in 2006.
3.2 Other target areas of gas field in the eastern margin of Ordos Basin
Sanjiao target area: including the northern part of Sanjiao and the central and western part of Sanjiao block, Liulin block and the northern part of Shilou block, covering an area of over 2000km2. The low-angle monoclinal zone with moderate buried depth of coal seam in the target area is beneficial to the storage of coalbed methane; No.4-5 and No.8-9 coal seams are thick, and the cumulative thickness exceeds10m; Coal seam gas content is generally above 65438+1100m3/t; The permeability is high, and most CBM wells are above 10mD. The pressure of coal seams in this area is high, and most of them are overpressure strata. The average reservoir pressure gradient of No.4-5 coal seam in Sanjiao area is1.1MPa/100m, and that of No.8-9 coal seam is1.02mpa/100m. The gas saturation of coal seam is also high, generally reaching about 80%. In addition, the degree of coalfield geological exploration in this area is high, the depth, thickness and coal quality of coal seam have been proved, and the parameters of coal reservoir have been known more. A set of construction technology suitable for the geological characteristics of this area has been gradually explored, and nearly 40 coalbed methane wells have been constructed. The average daily gas production of Huangkou Well Group (5 wells) is 4300m3, and the maximum daily gas production of a single well is 5400m3. The average daily gas production of Sanjiao Well Group (9 wells) is 4500~6000m3, and the maximum daily gas production of a single well is 6800m3. This target area is the first choice for exploration and development of coalbed methane in Hedong gas field (Figure 1).
Jixian target area: located in the middle of Jixian block, with an area of 1300km2. The buried depth of coal seam in the target area is moderate; The thickness of No.5 main coal seam is 3.0~7.5m, that of No.8 main coal seam is 3.0~8.8m, and the total thickness of coal seam is16m; ; The degree of coal metamorphism is moderate, and the vitrinite reflectance Ro is1.1.5 ~1.97%, which is mainly composed of coke and lean coal. The mudstone of the Upper Shihezi Formation overlying the coal seam can be used as a regional caprock. Coal seam gas content 1 1 ~ 23.4m3/t, gas saturation 76.5% ~ 90.8%. Changqing Petroleum Bureau has drilled 6 coalbed methane wells in this area, among which Jishi 1 well has the characteristics of high pressure, high permeability, high gas content and high saturation. It has been pumped continuously for more than one month, and the daily gas production is more than 2800m3, and the daily gas production of Well Jishi 5 is more than 6000m3. This area is a promising exploration and development target area in the next step (Figure 1).
refer to
[1] Sun Maoyuan, Huang Shengchu. 1998. handbook on development and utilization of coalbed methane. Beijing: Coal Industry Press.
[2] Sun Maoyuan. 2000. Development and utilization of coalbed methane in China and foreign cooperation. Beijing: Coal Industry Press.
Cheng Baozhou. 1992. Late Paleozoic sedimentary environment and coal accumulation law in Shanxi. Taiyuan: Shanxi Science Press.
Gui xuezhi. 1993. late Paleozoic coal accumulation law and coal resources evaluation in Hedong coalfield. Shanxi: Shanxi Science Press.
Ye Jianping, Terry and Dayang Lin. 1998. CBM resources in China. Xuzhou: China University of Mining and Technology Press.
Jiang et al 2002. Analysis of coalbed methane accumulation conditions in Daning-Jixian area. New progress in geological evaluation and exploration technology of coalbed methane in China.