High Permeability Prediction Study Of Coal Reservoir In Daning-Jixian Area In The Eastern Of Erdos Basin

The amount of coalbed methane resources in Daning and Jixian area is rich.This area is also the favorable one in Eastern Ordos Basin CBM development.However the area geological conditions is complex,coal seam buried large depth.What's more,the coalbed methane enrichment factors and high permeability region distribution is unkonwn.To sovle the problem above,this paper carries out a systematic study.Through the analysis of sedimentary environment,coal reservoir cap rock development,hydrogeological conditions,structural characteristics,pointes out the favorable areas in Daning and Jixiang area.The analysis suggests that Guyi-Yaoqu anticline belt and eastern slopes are the favorable area for coalbed methane enrichment.Field reconnaissance,and observe forty joint fissure points in research area,statistics the joint fissure devolopment condition.There are five groups plane shear and two groups tension joint.The dip rangs from 63°-90°,average 72°.According to the cutting relationship between the joint fissure,the research area experienced a total of two ancient tectonic stress,Yanshan period and Himalayan period.The Yanshan period of the maximum principal stress was NWW direction,Himalayan maximum principal stress was NNE direction.Through the structural trend analysis,Yanshan period established the basic structural pattern,forming a northeast trending faults and folds.Himalayan period changed Yanshan tectonic framework partly,and formed the local NW-SE trending faults and folds.Predicting the coal seam fracture belts under the ancient stress efect by the structural main curvature method,and point out that the structure curvature values generally distributed between 0.1x 10-4and 2.6×10-4 in Daning and Jixian area.The structure curvature values is higher in Guyi and Yaoqu area than others,so it is possible to form fracture belts.ANSYS finite element simulation software is used to establish three-dimensional geological models and divide finite element mesh.Then in conjunction with the structural evolution and hydro-fractures monitoring data of coalbed methane wells,the reasonable constraints are exerted on the finite element model boundaries.By means of inverting the limited well point stress inner geological model,the boundary forces are obtained.Finally,the stress distribution of research area is concluded.With the above mentions,Griffith failure criterion and Coulomb-Navier failure criterion are applied to predict the tension fractures and shear fractures in the research area respectively.The stress distribution map can predict the distribution of high permeability areas by analyzing cleat and fracture distribution statistically.