Modeling of Multiphase Flow with the Wellbore in Gas-Condensate Reservoirs Under High Gas/Liquid Ratio Conditions and Field Application

Summary Due to the deeper burial depths of gas-condensate reservoirs, temperatures and pressures are much higher than in conventional reservoirs, resulting in the wellbore usually having a high gas/liquid ratio. The retrograde condensation phenomenon is often observed during the production process of such gas-condensate wellbores. Especially when heavy components are present in the gas-condensate wellbore, the appearance of wax particles occurs, and complex multiphase flow characteristics, with gas, liquid, and solid phases mixed flow, are formed. This leads to a serious threat to the safety and production within the wellbore in the gas-condensate reservoir under a high gas/liquid ratio, and even wellbore region blockage. The wax appearance and dynamic changes caused by retrograde condensation are fully considered in this study; through coupling the multiphase flow characteristics of a gas-condensate wellbore with the phase transition process, a mathematical model was established to predict multiphase flow in a gas-condensate wellbore. This model reveals the phase behaviors and wax appearance characteristics within the wellbore in the gas-condensate reservoir under a high gas/liquid ratio. As the wellbore depth decreases, phase changes occur in sequence with decreasing molecular weight, appearing in liquid and solid phases. The wax particles of the solid phase are mainly composed of C33* (C33–C40) and C25* (C25–C32), while the liquid phase formed by the retrograde condensation is primarily composed of C17* (C17–C24) and C9* (C9–C16). In addition, it establishes a general correlation between pressure drop, temperature drop, and wellbore depth in high gas/liquid ratio condensate wellbores, and the model’s error is controlled within a 5% range by validating with actual data. Finally, the model calculation results determined the flow pattern transition process as follows: From single-phase gas flow at the bottomhole to gas-liquid phases mist flow and gas-liquid-solid phases mist flow toward the wellhead, and in conjunction with the supercritical state of light hydrocarbons to provide an explanation for change characteristics of pressure drop at the transition boundary between different flow patterns.