Impact of ultra-thick fracture-cavity reservoirs and fluid phase behavior on development strategies for Shunbei ultra-deep fault-controlled condensate gas reservoir, Tarim Basin

The Shunbei No. 4 fault zone in the Tarim Basin is the largest fault-controlled, strip-shaped, vertical, and ultra-thick fracture-cavity condensate gas reservoir in China. This gas reservoir is characterized by ultra-deep burial, ultra-high temperature and pressure, complex fracture-cavity structures, and intricate phase behavior of reservoir fluids, posing significant challenges to the selection and adjustment of scientific development strategies. To clarify the impact of reservoir architecture and supercritical complex fluid phase characteristics on the development technical policies of this gas reservoir, methods including fine geological characterization of fracture-cavity reservoirs and non-equilibrium phase behavior study of supercritical condensate gas were employed, combined with the production dynamics during gas reservoir exploitation, to analyze the controlling effect of reservoir-fluid coupling on development technical policies, clarify the pore-fracture-cavity development characteristics in fault-controlled reservoirs both in depth and along the long axis direction, and reveal the controlling effect of complex reservoir geological characteristics on the distribution of condensate oil and gas in accumulation and development units. The study indicated that under ultra-high temperature and pressure conditions, during the depletion production stage from initial pressure to dew point pressure, the recovery degree of condensate oil and gas could simultaneously reach 30%. By measuring the non-equilibrium gravitational settling relaxation phenomenon during the depletion stage from dew point pressure to maximum retrograde condensation pressure, it could be deduced that the relaxation time within the fault-controlled reservoir could reach 3 months. Additionally, the controlling effect of gravity segregation and phase evolution stratification of the gas-gas two-phase system during the gas injection process was explored, and the non-equilibrium diffusion time for gas injection was determined to exceed one year. It further clarified the different influencing mechanisms of fluid distribution differences in the northern, central, and southern sections of the gas reservoir on development strategies, as well as the effect of gas injection location selection on the effectiveness of gas injection displacement. Based on the above research findings, a three-stage development approach tailored to this type of gas reservoir is proposed, providing technical support for the formulation of development strategies for the Shunbei ultra-deep fault-controlled condensate gas reservoir, as well as serving as a reference for the efficient development of similar ultra-deep fault-controlled fracture-cavity condensate gas reservoirs.