Study On Features Of Coal Reservoir Of Southern Yan Chuan Block Of Ordos Basin

Coalbed methane (CBM) is a kind of clean energy which is adsorbed in coalbed. There is abundant coal resources in China and the CBM reserves is a considerable figure. Exploitation of CBM not only provides energy but also has important significance on improving safe production level of coal mines and also can protect the atmosphere.Southern Yan Chuan block is one of the main blocks which Sinopec exploits for CBM. Southern Yan Chuan is located in the interchange of Weibei uplift and Jinxi fold belt. The coalbed's structural form of Carbonic- Permian is a single anticline and some parts have the flexible fold feature. The area has lots of coal beds in Carboniferous and Permian. The NO.2 and NO.10 coal-beds are wildly and stably distributed in the research area. As the coal quality is good and the thickness of the coal beds is thick, NO.2 and NO.10 are the main target coal-beds for exploitation of coal resources and CBM. The buried depth of the two coal beds is less than 1500 m in general, increases from southeast to northwest and has the outcrop of the two coal beds in the southeast of the block.In the area the coal is the mid-high rank and the main macroscopic coal types are semi-bright coal. The coal porosity is low and the tested average porosity is 3.4%, but the specific surface area is high. As the CBM is absorbed in the coalbed, the coal matrix specific surface area is more important than the porosity. In total, the permeability is poor, the permeability of NO.2 coalbed is 0.0124-0.1698 md and NO.10 is 0.026-0.2265md. There is a high permeability (higher than 0.1md) in the middle of the block.The two coal beds are low-ash coal which is advantage for absorbing more gas in coal. The core test and drainage data have proved the gas content is high, higher than 13m3/t. During the research, it is found the error between the tested gas content and the real gas content is a little great. After the comprehensive calibration, the max gas content is larger than 30m~3/t and the saturation is generally larger than 85%. The fact implicates that the tectonic effect on the CBM pool is weaker. .Generally speaking, NO.2 and NO.10 coal beds in southern Yan Chuan area are the best exploration and development target. And the drainage data from well Yan 1 and others have proved the area has potential for commercial exploitation.The tectonics in this area is simple. The main controlling factor of gas-bearing properties is pressure. The gas content increased with the increase of pressure in certain rang. It can be found from the test data that the west platform area and the east platform area are in the different pressure system, the pressure coefficient in west platform area is 0.76-0.87MPa/100m and in east is 0.40-0.48MPa/100m. It is also found from the 12 parameter wells that there is a good relationship between the gas content and buried depth/ thickness of coalbed, the correlation coefficient achieves 0.82. This relationship should be examined in the all area.The total resource of CBM in the area is 523.44×10~8m~3, resource of CBM is 357.7×10~8m~3 in NO.2 coalbed and is 165.74×10~8m~3 in NO.10 coalbed resource. The CBM reservoirs can be divided into three kinds according to the buried depth and permeability: type I favorable area, type II favorable area and type III favorable area. Type I favorable area mainly exists in the middle area of the block and contains lots of resource. The resource of NO.2 coalbed in type I favorable area is 137×10~8m~3 and accounted for 38% of the whole amount resource of NO.2 coal. Type I favorable area is probably the favorable area to production capacity.Through the analysis and research in this block, it is considered that the area has the value of commercial development. And the block is probably to become the first CBM commercial pilot area in Sinopec. The main development area should be type I favorable area and the area should be continues to extend. In order to obtain the drainage data and drainage experience the small well group drainage should be used at first. In the northwest of the block, the deepest buried depth area of coalbed, exploration for CBM should be continued.