Controlling factors for productivity of ultra-deep tight reservoirs in Keshen gas field, Kuqa depression

Keshen gas field in the Kuqa depression of Tarim Basin is a rare, ultra-deep, ultra-high pressure, and high-temperature fractured tight sandstone gas reservoir in the world. Low porosity and super-low permeability of matrix, fracture as the dominant seepage channel, large differences in the planar distribution of gas reservoir productivity, and difficulties in deployment of efficient development wells are key problems restricting the efficient development of gas field. Based on studying the geological characteristics of gas reservoir, the fracture system, the physical properties of matrix, reservoir microstructure, and the distribution of gas-water relationship, in combination with researches on the ground stress of reservoir, this paper systematically analyzes the difference between high-production and low-production wells in the main gas production area-Keshen 2 block from multiple perspectives, reveals the main geological factors controlling productivity and the factors influencing well drilling and completion, and proposes reasonable technical policies for the deployment, implementation, and development of efficient wells. The research results show that the development degree, occurrence, and effectiveness of fractures in the well bore and its periphery, mechanical characteristics of the reservoir, height of gas column and their matching relationships are congenital geological factors that restrict the productivity of gas well; faults in the periphery of well bore, fractures, interbeds, gas and water distribution, brought in well section, and reasonable technology policies made accordingly for optimization of perforated intervals and reservoir reform are the key factors that restrict the long-term high and stable well yield. Moreover, the physical properties and pore throat characteristics of matrix reservoirs also have a certain impact on productivity. Through a comprehensive analysis, it is believed that well spacing concentrated at high locations is the most direct and effective way to achieve the efficient development of this type of gas reservoir. © 2020, Editorial Office of ACTA PETROLEI SINICA. All right reserved.