Coalbed Methane Reservoir Characteristics And Factors Affecting The Enrichment In Anze Area,Southeastern Qinshui Basin

Anze coalbed methane(CBM)field is located at the gently fold belt of the southeastern Qinshui Basin.The topography emerges a low-lying structure with the extending from east to west.The total area of Anze field is 1542 km~2.It is a developing CBM exploration and development field,which contains plenty of CBM resources.However,the present researches in this field is only limited to the aspects of the CBM formation and evolution process,but not the CBM reservoir characteristics,and gas accumulation mechanism.This study did a comprehensive investigation of the CBM reservoir geological properties,pores and fractures characteristics,gas-containing characteristics in the Anze field,and discussed the geological controls for gas accumulation.This study is important for exploration and production of CBM in the Anze field.Based on the updated drilling,logging and core data,this thesis investigated the thick and distribution features of the coal seam,coal geological characteristics,gas adsorption and gas-containing characteristics.Results show that the majority of experimental coal samples have medium ash yield,and low contents of moisture and volatile matters.Gas content and vitrinite reflectance are higher in the middle of the coal seam than that in the roof and bottom of coal seam.Based on 6 kinds(AC,GR,RT,etc.)of well logging data,this thesis established a method to identify and classify coal structure.Results show that vertically,undeformed coals and granulated coals are developed in the top and bottom,and the middle of the coal seam,respectively.Regionally,the undeformed and cataclastic coals are located in the northern and near A1 well in southern parts of the study area which structure is relatively simple and it is unfavorable for coalbed methane development.The granulated coals are mainly near the well A5 and A32 in the southern and near the fault F1 and fault F2 in south-central parts of the study area which is unfavorable for CBM development.This study used the data of core test and well loggings,and adopted the methodologies of R/S analysis and Matlab programming to discuss fracture development degree of CBM reservoir in the Anze area.As far as the degree and the heterogeneity of the coal fracture development,it is large in the fault development zone laid in the middle block,especially near the major fault F1 and F2.This study investigated the methane adsorption capacity of coal and its geological controls.It was found that high coal rank,low temperature and high pressure are favorable for gas adsorption on coals in the Anze field.This study investigated the CBM gas content and its geological influence factors.It was found that structure and the roof and floor lithology are two key factors to influence gas content.In the gentle structural area,gas content increases with increasing buried depth.Meanwhile,in the faulting area,gas content in the upthrown side of faults lower than that in the downthrown side of the fault.The mudstones and shales on the roof and floor of coal seam show extremely better sealing gas capacity than the roof and floor that are sandstones.