Characteristics of natural fractures and their influence on dynamic gas and water distribution in Xinchang gas field

The characteristics of natural fractures in the second member of Xujiahe Formation in Xinchang gas field were studied using core, logging and production data. The responses of natural fractures of different types were determined using conventional logging data, by which we evaluated the influence of various fracture types on dynamic gas and water distribution, and discussed their geologic origin. Tectonic and diagenetic fractures are predominant in the Xujiahe reservoirs in Xinchang gas field. Most of the tectonic fractures are shear fractures, which can be classified into high angle, oblique and low angle fractures according to their inclination angles. The diagenetic fractures are mainly bedding fractures with a good effectiveness, and contribute greatly to reservoir physical properties. The dynamic gas and water distribution and fracture development in the study area were closely related to the development degree and type of fractures. The reservoirs which mainly develop low angle fractures (especially bedding fractures) or network fractures produce water or meet high water cut rapidly, while reservoirs with high angle fractures show a high and stable gas yield rate. Permeability anisotropy caused by natural fractures of different types controlled the dynamic gas and water distribution in the study area.