Experimental Study on the Throttling Characteristics of High-CO

During the surface gathering and transportation of CO2-enhanced oil recovery (CO2-EOR) under ambient temperature conditions, pressure drops caused by valves or elbows result in significant throttling effects in multiphase flows with high CO2 content, which critically impact the safe operation of the gathering system. Using a high-pressure sapphire autoclave experimental setup, this study analyzes the effects of phase state, CH4 content, gas-liquid ratio, and water content on the throttling characteristics. The results indicate that under ambient temperature conditions, the final throttling temperature of liquid CO2 is primarily influenced by the final throttling pressure, with no significant correlation to the pressure drop. For throttling without phase change, liquid CO2 exhibits a weaker throttling effect, with a throttling coefficient (Di) of approximately 0.6℃/MPa, whereas gaseous CO2 demonstrates a stronger effect, with Di ranging between 10-12℃/MPa. Furthermore, the influence of CH4 content on the throttling temperature drop varies with the initial pressure. At high initial pressures (16 MPa), Di is approximately 1.3-5.4℃/MPa, and the addition of CH4 enhances the throttling effect of the mixed gas. At lower initial pressures (5 MPa and 4 MPa), Di is approximately 3.4-11.9℃/MPa, and the addition of CH4 weakens the throttling effect. An increase in the gas-liquid ratio and a decrease in water content both lead to a greater throttling temperature drop, with the gas-liquid ratio having a particularly significant impact.