Experimental Study on the Throttling Characteristics of High-CO₂ Content Produced Fluids

During the surface gathering and transportation of CO 2 -enhanced oil recovery (CO 2 -EOR) under ambient temperature conditions, pressure drops caused by valves or elbows result in significant throttling effects in multiphase flows with high CO 2 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, CH 4 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 CO 2 is primarily influenced by the final throttling pressure, with no significant correlation to the pressure drop. For throttling without phase change, liquid CO 2 exhibits a weaker throttling effect, with a throttling coefficient ( D i ) of approximately 0.6℃/MPa, whereas gaseous CO 2 demonstrates a stronger effect, with D i ranging between 10-12℃/MPa. Furthermore, the influence of CH 4 content on the throttling temperature drop varies with the initial pressure. At high initial pressures (16 MPa), D i is approximately 1.3-5.4℃/MPa, and the addition of CH 4 enhances the throttling effect of the mixed gas. At lower initial pressures (5 MPa and 4 MPa), D i is approximately 3.4-11.9℃/MPa, and the addition of CH 4 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.