Currently, with continuous innovation of gas-condensate reservoir development technology, the production of gas-condensate and light oil has rapidly increased, making gas-condensate play an important role in the global petroleum industry. However, due to the deeper burial depths of gas-condensate reservoirs under high gas-liquid ratio condition, temperatures and pressures are much higher than conventional reservoirs. At the bottom of the wellbore, the gas-condensate system typically exists in a gaseous state. The retrograde condensation phenomenon is often observed during the production process of such gas-condensate wellbore. Especially when heavy components are present in the gas-condensate well,the appearance of wax particles, and complex multiphase flow characteristics with gas, liquid, and solid phases mixed flow are formed. These complex phase change characteristics of multi-alkanes coupled with multiphase flow patterns may have varying degrees of impact on production operations, from minor to severe.
Based on existing phase equilibrium models of multi-alkanes, this study fully considers wax appearance and dynamic changes in gas-liquid ratio caused by retrograde condensation. By coupling the multiphase flow characteristics of gas-condensate wells with the phase change process of gas-liquid-solid components under high gas-liquid ratio conditions, a mathematical model was established to predict multiphase flow in gas-condensate wells. This model not only reveals the phase change behaviors and wax appearance characteristics in gas-condensate wellbore with high gas-liquid ratio but also determines the critical wellbore depths at which the gas phase transitions to the liquid phase and wax appearance. It reliably predicts the composition of gas-liquid-solid phases at different wellbore depths. As the wellbore depth decreases, phase changes occur in sequence with decreasing molecular weight, appearing liquid and solid phases. The wax particles of solid phase are mainly composed of C33* (C33 to C40)and C25*(C25 to C32), while the liquid phase formed by the retrograde condensation is primarily composed of C17*(C17 to C24)and C9*(C9 to C16).
Additionally, it establishes a general correlation for predicting pressure drop, temperature drop, and wellbore depth in high gas-liquid ratio condensate wells, 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 bottom to gas-liquid phases mist flow and gas-liquid-solid phases mist flow towards the wellhead, and in conjunction with the supercritical state of light hydrocarbons to provide an explanation for the relationship between multiphase flow structure and wellbore pressure drop.
