Coal Reservoir Geological Modeling And Favorable Reservoir Prediction In And Around Weibei Coalbed Methane Field

Weibei Coalbed Methane(CBM)field,a monocline structure gentle dipping from southeast to northwest,is located in the eastern edge of the Weibei uplift in the Ordos Basin.The main minable coal seams in the study area are the Nos.3,5 and 11,among which the No.5 coal seam is the target layer of this study.This study focused on the CBM reservoir,and the researches included the advanced characterization of the regional structural characteristics and the coal reservoir development characteristics,and the 3D coal reservoir modeling.This study was concluded by a predication of the most favorable target area for the CBM exploration and production in the Weibei CBM field.Based on the theories of structural geology and seismic exploration technology,this study performed the interpretation of 2D seismic data,whose results were used to characterize the regional structural characteristics of the study area.Then,an analysis of the regional tectonic evolution history was completed by balanced cross-section technique.The results showed that the current structural characteristics in the study area were complex.There were numerous thrust faults and small-scale folds in Hancheng area in the north part,whereas there were many normal faults and less thrust faults appeared in Chenghe area in the south part.Three main tectonic movements including the Indo-Chinese,Yanshanian,and Himalayan orogeny had made an evident effect on the CBM accumulation in the study area.Among these tectonic movements,the serious deformation during the Yanshanian orogeny led to the formation of the major faulting system in the coal reservoir.The seismic data based constrained sparse spike inversion was made to characterize the regional and vertical distribution of the coal reservoir.The No.5 coal seam was thick and continuous with a thickness ranging from 1.5m to 10 m.The coal seam was relative thick in the north parts and in the west parts of the study area.Based on the above researches,3D structural modeling and gas content modeling were made to discuss the structural controls on the CBM accumulation.Results showed that well developed compressive structures,such as thrust faults and synclines,had made a key effect on the CBM accumulation.Other effects including the thickness and depth of the coal seam had also made positive influences on gas accumulations.Combing the analyses of the favorable tectonic positions and regional high gas-bearing zones,this study predicated the favorable target area for the CBM exploration and production.The most favorable tectonic positions were the northern and southeastern Hancheng area.The areas with the highest gas-content were the northern and middle Hancheng area,and the southwestern Chenghe area.The areas with most favorable coal reservoir were located in the northern and southeastern Hancheng area.