Overcoming Challenges in Fault-Vuggy Condensate Gas Reservoirs: A Simulation-Based Approach

Fault-Vuggy condensate gas reservoir is a new type of condensate gas reservoir with abundant resources. It is also a significant emerging field for increasing oil and gas reserves and production in China[1–3]. Characterized by diverse media, complex structures, strong heterogeneity, and rapid decline rates, these reservoirs have not yet been developed on a large scale either domestically or internationally. Compared to conventional sandstone reservoirs, their development faces the following challenges: 1. The geological conditions are highly complex, featuring multi-scale, strong heterogeneity, and strong randomness. The reservoir space is primarily composed of fracture surfaces and their interconnected broken bodies, with fractures, and pores, interwoven into a complex multi-scale reservoir structure. Various types of reservoirs, including strike-slip fault zones, fault-controlled bodies, cave-like bodies, and chaotic bodies, exhibit significant spatial heterogeneity. 2. The reservoirs also face extreme geological conditions, such as ultra-high temperature, ultra-high pressure, and supercritical pressure, which further complicate development. The fluid belongs to the condensate gas reservoir category, and retrograde condensation is evident during the development process. The phase transition of the fluid runs through the entire development process, making exploitation difficult, especially in ultra-deep and complex geological conditions, where component gravity differentiation and nonequilibrium behavior are observed. 3. Most successfully developed condensate gas reservoirs to date are clastic condensate gas reservoirs, which typically employ depletion development or gas injection circulation exploitation. However, due to their unique geological conditions, fault-vuggy condensate gas reservoirs cannot directly apply traditional development technologies. To address the complexity of fault-vuggy condensate gas reservoirs, the research team adopted a quantitative analysis method integrating modeling and numerical simulation during both depletion and pressure-maintaining stages. The research contents include: 1. Considering the multi-scale and strong heterogeneity of the reservoir, a seepage model for fractured-vuggy condensate gas reservoirs was established, accounting for stress-sensitive, non-isothermal, and non-equilibrium phase behavior. 2. Focusing on the phase evaluation of non-equilibrium phase behavior, the phase characteristics of gravity differentiation and non-equilibrium phase behavior were deeply investigated under ultra-high temperature and ultra-high pressure conditions through experiments and numerical simulation. 3. Considering the pressure-sensitive characteristics, the deformation process due to fractures and caves was evaluated. Combined with reservoir and fluid characteristics, numerical simulation of fracture-cavity elements was conducted to achieve model establishment, production history matching, and gas injection simulation.