Geological Control Of Composite Reservoir Configuration And Permeability In Coal Measure

Chinese government and enterprise pay high attention to the potential development of coal measures gas.However,the development characteristics of coal measure composite reservoir are not clear,and the geological control factors of permeability are yet to be revealed.In view of this,taking the Damoguaihe Formation of the Lower Cretaceous in the Wujiu Depression in the east of Inner Mongolia as the research object,analyzing the exploration and development data of coalfield and coalbed methane,combining with the physical simulation experiment and numerical analysis,the configuration information of coal measure composite reservoir is extracted,and the mechanism of sedimentation-control and tectonics-control of composite reservoir permeability is discussed,and a dual-control prediction model of coal measure gas composite reservoir permeability is constructed.The following key innovation understandings were obtained:1)The characteristics of gas cyclic distribution of coal measures reservoir are revealed,and the control mechanism of its sequence stratigraphic structure is explained.According to the analysis of gas logging information,it is found that 2～4 independent gas-bearing systems are developed in Damoguaihe Formation in the study area.The sedimentary section with strong interbedding of coal seams and sandstone development is easy to form a large-scale gas-bearing system.The enrichment of thin-interbedded CMS is not only controlled by the development characteristics of coal reservoirs,but also closely related to the internal sealing conditions of coal measures.The geochemical characteristics of gas reveal that biogenic and thermogenic gas reservoirs are often formed in the intervals with shallow burial depth and high sand content of coal measures.2)The structural characteristics and types of coal measures composite reservoirs are revealed,and the geological control factors of basin filling are explained.Using Markov statistical models and other statistical models,quantitatively extract the information of coal measures reservoir types,and identify four types of coal measures reservoir configurations: multi seam interbedded,medium-multi seam interbedded,medium-few seam interbedded(with thick mudstone or sandstone),and few seam interbedded(with large spacing between adjacent coal seams).The correlation analysis shows that the geological factors controlling the configuration of the coal measures composite reservoir are the scale of the lake basin during the coal-accumulation period,the relative position in lacustrine basin,and the sedimentary system tract.3)The basic laws of fractures in coal measures composite reservoirs are revealed,and the coupling control factors of stress-strain and rock mechanical properties are explained.The true triaxial physical simulation test of similar materials shows that the geological phenomenon “the more obvious the characteristics of the thin-interbedded of coal measures,the higher the fracture development degree of its composite reservoir”,which is consistent with the fracture development law of non-coal measures reservoir.It is believed that this is the result of the coupling effect between the stress and strain incongruity of each rock stratum and the mechanical strength difference of different rock strata.And the coupling effect also affects the extensibility of natural fractures.4)The causality between fracture and permeability of coal measures composite reservoir is revealed,and the dual medium control mechanism of composite reservoir permeability is proposed.Based on the numerical analysis of RFPA3D-Flow,it is found that the permeability advantage of composite reservoir is mainly reflected in the direction of seepage along the strata(sedimentation-control)under the geological condition of weak tectonic stress transformation.If the tectonic deformation is strong,the dominant seepage direction is controlled by both the stress failure type and strength,as well as the composite reservoir configuration(sedimentation-control and tectonics-control).The analysis shows that the above geological phenomena are controlled by the coupling effect of fracture permeability and pore permeability of composite reservoir.5)The permeability dual-control prediction model of coal measures composite reservoir based on sedimentation-control and tectonics-control is constructed.In the prediction model,the sedimentation-control is mainly reflected in the proportion of different lithologies and the permeability of corresponding strata;the tectonics-control is mainly reflected in the thickness of each layer of composite reservoir,the mode of tectonic stress and the intensity of stress field.Combined with the geological conditions of the study area,the permeability prediction of coal measures composite reservoir is realized.This thesis contains 118 figures,39 tables and 235 references.