Controlling effects of geological structure and hydrodynamics on gas occurrence

This paper is devoted to study the influence of geological structure and hydrodynamics on gas occurrence in Tangjiahe coalfield.Based on tests of gas parameters and geological data,the gas distributions of No.8 coal seam are analyzed.The analysis includes the controlling effects of geological structure evolution,tectonic stress field,and geological structure form on gas distributions.Also,hydrodynamic impact on gas generation-enrichment-storage process is analyzed using descriptive statistics and nonlinear regression.The results show that the gas content of east flank is 1.7 times of gas content of west flank.Gas of east flank contains lower volatile contents and higher vitrinite reflectance contents than the west flank.The depth of the east flank if larger than the depth of the west flank and is correlated with gas emission linearly.The roof lithology for east flank varies greatly while the roof of west flank is mainly composed of mudstone.The coal seam dip angle of east flank is 1.5 times of the dig angle of west flank.Gas permeability in east flank is higher than west flank because the geological tectonic evolution developed 0.2～0.4 m thick tectonic coal during coal-forming period.The east flank is located at an anticline flank in Dalianghui anticline and the main tectonic stress is compression,which is conducive to gas storage.During the coal-forming period,the hydrodynamic activity in west flank was strong,which results in slightly lower ground temperature of coal reservoir,slightly lower coal metamorphism,and poorer coal seam integrity than the east flank.In reserving period,due to gas migration opposite to water flow direction,hydraulic sealing occurred in east flank while hydraulic migration occurred in west flank.The hydrodynamic conditions of west flank go against gas storage.The study also found that the aquifer water inflow is related to face gas emission with a logarithmic relationship,which helps to reveal the mathematical relationship between water inflow and gas occurrence.