Characteristics Of Coalbed Methane Distribution And Development Mode In Liulin Block

Liulin block is located in the middle of HeDong coalfield of Ordos Basin.It is characterized by its numerous coal seams,large thickness,high gas content,favorable geological conditions and large potential for coalbed methane development.Based on the collection and analysis of geological data,this paper discusses the characteristics of coal reservoir,existence features of CBM and the control factors influence the occurrence of CBM in this study area.Meanwhile,this paper studies and analyzes the development mode of CBM in Liulin block by numerical simulation and analogy.The main results include:?1?The main coal seams are No.3+4,No.5 and No.8+9 in Liulin block,which are dominated by meager lean coal and coking coal;the lnhotype of coal are dominated by vitrain and clarain;the coal types are bright coal and semi-bright coal;the organic maceral are vitrinite group,followed by inerting coal group.The coal structure is mainly composed of fragmented coal and primary structural coal.The pore structure of coal is mainly micro and small pore,and the cleating is more developed.The permeability of coal reservoir changes greatly,mainly concentrated in 0.01²4.8mD,The pressure gradient is 4.13×10^-311.2×10^-3MPa/m.The reservoir pressure of the coal seam belongs to under-pressure to normal state,and the gas saturation is 37.74%⁹9.60%.The change is large and it belongs to under-saturation state.?2?In this area,the adsorption capacity of CBM is medium.The No.8+9 coal seam has the strongest adsorption capacity and followed by No.3+4 coal seam.And the No.5 coal seam has relatively weaker storage capacity.The coal seam has high gas content and has favorable conditions for development of CBM.?3?This paper analyses the factors of affecting CBM occurrence from four aspects:regional structure,roof and floor lithology,coal seam burial depth and hydrogeological conditions.The roof and floor lithology,coal seam burial depth and hydrogeological conditions have a greater impact on the occurrence of coal bed methane,while the influence of structural conditions is relatively small.?4?In the study area,the No.3+4+5 coal seam of Shanxi Formation in the North area and the No.8+9 coal seam of Taiyuan Formation in the southwest area are separately developed.While the No.3+4+5 coal seam of Shanxi Group in the southeast and the No.8+9 coal seam of Taiyuan Formation should be put to develop.The optimal branch spacing of multi-branch horizontal wells is 300m when it is adopted.Under the current exploitive technical conditions,the vertical well spacing is more suitable at300⁴00m for CBM development by the analogy and numerical simulation methods.However,combined with the different numerical simulation results of well spacing,the best well spacing is 350m×300m for the development of CBM in this area.