Thermodynamic Characteristics and Impact Mechanisms of Core Barrels in Pressure-Preserved Coring Retrieval

Summary During pressure-preserved coring (PPC) retrieval, the core barrel’s pressure preservation performance is crucial for accurately assessing deep oil and gas resources. By accounting for the thermodynamic properties of the core, drilling fluid, and the variation in the core barrel’s working volume, we developed a thermodynamic model to predict temperature and pressure changes and to investigate the variation of thermodynamic parameters within the core barrel. A digital solution framework for the model was established using a fully implicit difference algorithm. Introducing the pressure preservation performance coefficient allowed us to evaluate the influence of key parameters—such as core length, drilling fluid density, and the core barrel’s height/diameter ratio—on pressure preservation. The model accurately predicts the thermal evolution during core retrieval and assesses the core barrel’s pressure preservation performance. Model predictions showed a relative error of less than 2.79% compared with laboratory measurements and less than 4.03% compared with field-collected data. During coring, the volumes of the core, drilling fluid, and core barrel increased by maximum values of 0.21%, 1.95%, and 1.00%, respectively. When ambient temperatures were high, adjusting the core length could improve pressure preservation. Given that various parameters affect core barrel design, it is recommended to increase the drilling fluid density, increase the height/diameter ratio of the core barrel, and keep the core barrel’s working volume below 20 L.