Study on structure and hydrologic gas control role of coalbed methane gas field in Yanchuannan Block

Based on a structure study of a coal bed methane gasfield in Yanchuannan Block, in combination with the water quality analysis of No. 2 seam, logging a s well as analysis and chemical test information, the paper discussed the structure and hydrogeological conditions affected to the control role of the coal bed methane d eposition. The study showed that a monoclinal structure and reverse fault sealed decided two different hydrogeological units developed in the study area with different h ydraulic gas contral features. Tanping structure zone was located in a weak runoff area and was shallow in a deposition depth and low in a pressure gradient. The struct ure zone was gas controlled with the hydraulic sealing. The seam water had a low mineralization and a weak alkalinity and the water type had Na+- HCO3type features. Wanbaoshan structure zone was located in a detention area with a deep deposition depth. The pressurized water was sealed and the pressure gradient was high. The s eam water had a high mineralization and a weak acidity. The water was in Ca (2 +) - Cltype features. The seam was air controlled with hydraulic sealing. No. seam in Wanbaoshan structure zone had a gas content of 15. 3 m3/ t in average. Tanping structure zone had a gas content of 9. 2 m3/ t in average. The coal bed methane depo sition condition in Wanbaoshan structure zone was better than Tanping structure zone.