Fractures Development Characteristics and Their Effect on Productivity in Tight Sandstone Reservoirs, Keshen Gas Field, Kuqa Depression

Abstract

Abstract

Keshen gas field is a typical tight sandstone reservoir where fractures universally developed. According to outcrop observation, drilling core analysis, normal well logging, imaging logging and well test data combined with using Geoframe software interpretation platform, fractures development characteristics and their effect on deliverability of Bashijiqike formation tight sandstone reservoirs in Keshen gas field are analyzed herein.

The results indicate that the structural fractures are mainly developed in tight sandstone reservoirs of Keshen gas field. And the structural fractures are mainly composed of high dip-angle fractures(greater than 60°), and oblique fractures. By interpretation of the imaging logging image using Geoframe software, it shows that the fractures of the first and the second member of Cretaceous Bashijiqike formation in study area are developed relatively better, and the predominant fractures strike is close to S-N direction which is perpendicular to the fault strike and parallel to the current maximum principle stress axis, followed by near E-W trending fractures. In effective fractures concentrated interval, corrected fracture density (FVDC) has an average value of 13.3A/m and FVAH has an average value of 1.56mm. Combining with core observation, fractures approaching S-N strike direction have a longer vertical extension. As a whole, fractures are characterized by high fracture density, minor fracture opening degree and long vertical extension. The impact of fractures on single well productivity is mainly reflected in improving reservoir permeability, followed by oil saturation. Due to the high connectivity of fractures, their influence on permeability are far beyond matrix porosity, especially in low-porosity and low-permeability tight sandstone reservoirs. The permeability in study area are mostly distributed between 0.01μm² and 0.1×10^-3μm². About an order of magnitude improvement can be achieved by fractures development. Build up open flow potential and the number of fractures relational model using well test data. It shows that fracture density and total fracture numbers have the best correlation with production index. And in single well oil testing interval, open-flow capacity increases as the fracture density increases.

AAPG Datapages/Search and Discovery Article #90260 © 2016 AAPG/SEG International Conference & Exhibition, Cancun, Mexico, September 6-9, 2016