Study Of Coalbed Methane Enrichment Law In South ShiLou Block

South Shilou block is located in the southern section of Jinxi fault-fold belt in the eastern margin of Ordos Basin.Under the influence of Lishi fracture from east side,structures are complex in the block.Generally,depth of main coal seam from Carboniferous-Permian is deeper than 1200m,and the deepest depth is more than2000m.So the difficulty of CBM`s exploration and development were increased.This paper aimed to analysis the coal seam development status,coal reservoir`s characteristics and geological conditions,and then to find out the main factor which controlled CBM enrichment.Paper achieved the following results and understanding:The main coal seams in South Shilou block were 3#coal seam from Shanxi group and 9#coal seam from Taiyuan group which belonged to lean coal.With low ash content and high gas content,the coal seams`gas content was 10.82?20.04m~3/t.And their thickness was thin.3#coal seam thickness was 0.38?3m,average 1.56;And 9#coal seam thickness was 1?5.24m,average 3.3m.The depth of main coal seams was great.The shallowest depth of 3#coal seam was about 1200m,and the deepest was more than 2000m.9#coal seam was 50m deeper than 3#.From bottom to top,sedimentary facie of Taiyuan group was transited from epicontinental sea-barrier-lagoon system to tidal flat-lagoon system.Peat swamp mainly developed in the former system,which contained barrier islands,tidal flat,lagoon.And among them,tidal flat was advantageous for coal accumulation.From bottom to top,Shanxi group was transited from lower delta plain to upper delta plain,and peat swamp mainly developed in the latter,which contained distributary channel and interdistributary.And between them,interdistributary was advantageous for coal accumulation.South Shilou block was located near the intersection of provenance coming from north and south.Meanwhile,the block was mainly affected by north source.Coal seams of Shanxi group developed better in the north block,and because of deeper water,they were poorly developed in the south block.Tectonic framework named double uplift and double concave controlled the structure and depth of coal seams,thereby affecting their air content.The highest gas content area was in wide shaft portion of Shilou anticline.Followed by wings of Shilou anticline,the worst areas were near faults.With greater depth,3#coal seam gas content was first increased and then decreased,and the critical depth was about1400m.Sedimentation controlled the coal thickness and closed conditions,and thereby affecting CBM enrichment.Interdistributary and tidal flat were advantageous for coal accumulation.With large thickness and high gas content,coal seams in these microfacies were CBM rich region.9#coal`s roof and floor were mostly shale-shale combinations,and 3#coal was less.Generally,9#coal gas content was greater than 3#coal.