Temperature and Pressure Analysis of CO₂ Geological Sequestration in Low Permeability Reservoirs

Injecting CO₂ into underground formations for permanent storage is one of the key technologies for achieving carbon neutrality goals. Wellblock 38 in Wuqi Oilfield is the core area of the first domestic full-process CCUS demonstration project-the Yanchang Petroleum CCUS Demonstration Project, which has been injecting gas since 2014, now for a decade. The study of the migration state of CO₂ after injection into the formation and the dynamic changes in the temperature and pressure of the storage layer are crucial for the safety assessment of carbon storage projects. This study, based on core, geological and test data from the CCUS demonstration area in Wuqi Oilfield, utilized the TOUGH2/ECO2N software platform to construct a three-dimensional numerical model to simulate the plume state of CO₂ after injection into the formation and its impact on the temperature and pressure system of the formation. The results show that: CO₂ tends to migrate to the upper part of the storage layer. In the initial stage of CO₂ injection, the temperature around the well decreased sharply from 59.94 ℃ to 48.2 ℃ (a drop of 11.74 ℃), and the pressure increased from 12.6 MPa to a peak of 15.6 MPa (an increase of 23.81%). However, after 10 years of injection cessation, the temperature gradually returned to near the original value (60.2℃), and the pressure dropped to 12.8MPa (1.59% higher than the initial value). The temperature and pressure changes in the formation were more significant in the initial stage and gradually slowed down, eventually reaching a stable state. The impact of the injected CO₂ fluid on the overall temperature and pressure of the formation was relatively limited. This study quantified the temperature and pressure response thresholds for CO₂ storage in low-permeability oil reservoirs, revealing the coupling mechanism between the migration of supercritical CO₂ and the energy balance of the formation, providing theoretical support for the design of storage schemes and the optimization of monitoring systems in similar reservoirs.