Analysis On Geological Control Factors And Models Of Coalbed Mathane In The Eastern Segment Of South Margin Of Junggar Basin

The southern margin of the Junggar Basin is a middle and low-rank coal mining area in China.The area is rich in coalbed methane resources and has great potential for exploration and development.However,for a long time,there is a lack of overall research on factors controlling coalbed methane enrichment in the eastern section.Based on the analysis of geological data and field surveys,combined with laboratory experiments,the paper comprehensively explored the influencing factors of coalbed methane enrichment in the coal reservoir characteristics,structural characteristics,sedimentary conditions,and hydrogeological conditions in the study area,and summarized Coalbed methane enrichment model in this area.Obtained the following main research results:(1)The quasi-Southern part of the structure is relatively complex.Affected by the overthrust of the southern Pogda complex anticline,it shows tight anticlines and synclines,and the faults are mostly high-angle reverse faults.In the foothill depression,the early and middle Jurassic coal-bearing rock series and coal seams were developed.The Xishanyao coal seam has an average thickness of 80 m and a coal seam depth of 800~1200m.The thickness of the coal seam in the Badaowan Formation is 20~80m,and it is generally characterized by the thin thickness of the west and the east.(2)The degree of coalification in the region is relatively low(Ro:0.38 to 0.95%)and varies greatly in the plane.The macro coal type is mainly semi-dark coal and semi-bright coal,with high vitrinite content,low Ash features.The pore type of coal is dominated by micro and small pores,and the endogenous fissures are more developed.The Rankine volume of the coal reservoir is 17.6~24.82m~3/t,and the gas content is generally 9.08~16.12m~3/t.The coal reservoir is mostly undersaturated.(3)The coal-bearing stratum in the western part of the study area is the Xishanyao Formation,which is generally a low-water receding system area.The coal seam develops in the environment of the lower delta plain and the front of the shallow water delta.Coal seam roofs are mostly siltstone,and high-angle fracture development is common and is not conducive to the preservation of coalbed methane.The coal-bearing strata of the Badaowan Formation in the east of the Sigong River developed in the low-water-entrance system domain and is a sub-facies of the shore-shallow lake.The top and bottom of the coal seam is thick mudstone,which is conducive to the enrichment of coalbed methane.(4)The structural characteristics of the study area and hydrodynamic closure conditions affect the enrichment of coalbed methane.The coal-bearing strata in the east of the Urumqi region are controlled by the syncline of the Badaowan Bay.At the same time,the sealing of the high-angle reverse fault cross-section prevents the coalbed methane from escaping through the cross-section;the southeastern area of Fukang City is affected by the Fukang syncline,and the gas content in the core is greater than the two wings.At the same time,the hydrothermal closure of the aquifer system in the south slope of the inclined rock was formed.The west of Dahuang Mountain is under the control of the Huangshan-Shuanggong River,and is cut by reverse faults to form a fault seal.(5)The coalbed methane enrichment under the coupling mechanism of tectonic evolution,coal accumulation environment and hydrodynamic conditions mainly manifests as follows:1)coalbed methane is mostly enriched in different forms of syncline structures;2)high angle faults are associated with coalbed methane Accumulation plays a role in sealing;3)Hydraulic plugging restricts the relationship between gas and water saturation.Based on this,three kinds of coalbed methane enrichment models are concluded:three models of syncline-rich reservoirs,hydraulic plugging syncline reservoirs,and fault-closed reverse-steering reservoirs under the influence of high-angle faults.