The Process of Pressure, Temperature, and Phase State Changes Within Supercritical CO2 Buried Pipelines During Micro-Leakage

Within the carbon capture, utilization and storage (CCUS) chain, buried CO2 pipelines are an indispensable engineering solution under complex topographic conditions. Experimental investigations show that leakage from buried supercritical CO2 (sCO2) pipelines features a two-stage pressure decline: an initial rapid drop driven by high leaking medium mass flow, followed by a linear decrease governed by homogeneous liquid CO2 vaporization. Notably, the choking flow effect homogenizes linear pressure drop rates across distinct experimental conditions. Leakage orifice diameter is a dominant factor for pipeline temperature distribution: small orifices yield consistent temperature drop rates at different vertical pipeline positions, while larger ones cause faster cooling at the pipeline bottom, forming significant vertical temperature gradients that intensify closer to the leakage orifice. Leakage direction and initial pipeline pressure are key regulators of leakage dynamics: vertical upward leakage (0°) leads to faster pressure drops due to the reduced soil resistance, and elevated initial pressure not only intensifies the pressure drop rate and amplifies CO2’s endothermic effect but also modulates the phase transition pathway of sCO2 during leakage.