Key Geological Controls to Formation of Coalbed Methane Reservoirs in Southern Qinshui Basin of China: II, Modern Tectonic Stress Field and Burial Depth of Coal Reservoirs

摘要

Based on the comprehensive research to the various information, the characteristics of the modern tectonic stress field in the southern Qinshui Basin was found out, and the high interrelation of the physical properties of the coal reservoirs to the stress field were revealed. As the main stress difference increases, the reservoir permeability enhances in a exponent and the pressure gradient increases in a logarithm. At the same time, the permeability reduces and the reservoir pressure enhances with increasing the crustal stress gradient. The wall gaps of the natural fissures in the coal reservoirs are theoretically functioned to the magnitude and direction of the crustal stress, and the effect of the main stress difference to the wall gap and permeability is showed in two polar patterns. This interrelationship is just the essential reason why the permeability of the main reservoirs in the Qinshui Basin enhances with increasing the main stress difference. Moreover, the reservoir permeability drops generally in a negative exponent that converges about at the 800 meters of the burial depth.