Fracture development characteristics and their influence on water invasion of ultra-deep tight sandstone reservoirs in Keshen gas reservoir of Kuqa Depression, Tarim Basin

Abstract

Natural fractures are crucial factors influencing productivity and water invasion in the ultra-deep tight sandstone gas wells of the Keshen gas reservoir in the Kuqa Depression, Tarim Basin. Research on fractures is significant for understanding water invasion patterns and formulating effective water control strategies. This study investigated the development characteristics, distribution patterns, and water invasion characteristics of effective fractures using core samples, thin sections, conventional logging, imaging logging, production data, and well testing, as well as the influence of different fracture networks on water invasion. High-angle and nearly vertical shear fractures are the main fracture types. Vertically, the first member of Bashijiqike Formation (K1bs1) is predo-minantly characterized by completely filled fractures, which are ineffective fractures. Conversely, the second and third members of Bashijiqike Formation (K1bs2 and K1bs3) are mostly characterized by partially filled and unfilled fractures, which are effective fractures. Horizontally, the NNW-SSE striking effective fractures are concentrated in the western part of the gas reservoir and have larger average apertures. The eastern part has relatively deve-loped nearly E-W and NWW-SEE striking effective fractures with smaller average apertures. The more deve-loped and the larger the aperture of the effective fractures, the lower the initial water production from gas wells, with more production of condensate water. From production onset to water breakthrough, formation water is produced in various forms: sealed water, condensate water, movable water and pure formation water. The development stage, aperture and orientation of effective fractures are important factors affecting heterogeneous water invasion. Dense, highly effective fracture networks that are nearly parallel to the orientation of water invasion will accelerate the water invasion speed, resulting in significant water production and severely reducing gas well productivity. Integrating the development characteristics of effective fractures with individual well water invasion dynamics reveals three types of water invasion: rapid channeling along faults or dense fractures, slow coning along sparse fractures and slow uplift and invasion of edge-bottom water.

Keywords

• tectonic fractures
• dynamic characteristics of water invasion
• water invasion pattern
• ultra-deep gas reservoir
• kuqa depression
• tarim basin