Coalbed Methane Enrichment Regulation And Favorable Area Prediction In Southern Wuxiang Exploration Block Of Qinshui Basin

The southern Wuxiang exploration block located in central of Qinshui Basin is rich in coal and coalbed methane(CBM)resources.In order to evaluate the exploration and development potential of CBM and guide the efficient exploitation of coal and CBM resources,this paper takes southern Wuxiang block as the research object.Based on the coalfield geology and CBM exploration data,and experimental test results in the study area,the sedimentary environments,geological stuctures,gas-bearing property,and coal seam occurrence characteristics were analy-zed,and the CBM favorable enrichment areas were evaluated comprehensively,the new unders-tanding and progress were achieved as follows:(1)Researched the coal measurres and sedimentary environment,and restored the lithof-acies paleogeography of southern Wuxiang Block.The results show:the tidal flat limestone and Sandstone-mudstone facies during the sedimentary period of Taiyuan Formation is develoed in north of this study area,and the peat swamp black mudstone facies and interdistributary bay m-udstone siltstone facies in the lower deltaic plain during the sedimentary period of Shanxi For-mation are developed the south of the study area;the most favorable facies belts of coal seam development is located in the peat swamp areas of the tidal flat and interdistributary bay.The15~#and 3~#coal seams have the same occurrence pattern,and both are monoclinic structures extending NNE and trending W,and their buried depth shallows gradually from the middle to the two sides,in which the thickness of 15~#coal seam increases gradually from southwest to northeast,and 3~#coal gradually thickens from north to south as a whole.Based on the regional comparative analyses of the primary mineable coal seams in the southern Wuxiang block,this work founds the 15~#coal seam of the Taiyuan Formation generally thicken from southwest to northeast,and the 3~#coal seam of the Shanxi Formation has a thickening trend from north to south as well.(2)Summarized the geological control factors of CBM enrichmen in southern Wuxiang block from the aspects of structure,sedimentation and hydrology,results display that the gas content variation of 15~#and 3~#coal seams in this area is mainly controlled by structural complx-ity,coal seam thickness,buried depth and roof or floor lithologic characteristics.The normal fa-ults with poor sealing properties can lead to gas escape,while reverse faults tend to have better sealing properties.The coal seam thickness and burial depth are positively correlated with gas content in the study area.In addition,mudstone and sandy mudstone have good sealing ability to CBM;the groundwater runoff in the study area is weak,which is beneficial to the preservatio-n of CBM.(3)By means of the studies about controlling geological factors of CBM and coal reservoir characteristics,and using the multi-level fuzzy mathematics method,this work establi-shed the evaluation system and model of CBM enrichment,and predicted the CBM enrichment in the study area.Finally,the results show that CBM enrichment areas of 15~#and 3~#coal seams are mainly distributed surrounding exploration wells W26-W31-W41 in the northeast part and W5-W2-W1 and W27-W37 in the north central of the study area respectively.