Mechanism and performance evaluation of a dual-crystal synergistic plugging system for high-temperature reservoir conformance control

Addressing steam channeling and water invasion in multi-cycle thermal recovery is now a critical challenge in heavy oil development. The study developed a high-temperature plugging system based on dual-crystal synergistic effects. The plugging agent, composed of calcium chloride, sodium sulfate, sodium carbonate, polymers, and dispersants, precipitates CaSO4 and CaCO3 crystals upon injection into the formation, synergistically sealing high-permeability channels. Experiments demonstrated that the agent effectively crystallizes within a temperature range of 60–200 °C. Displacement tests revealed well plugging performance under high-temperature conditions, with a core plugging rate of 99.3% at 150 °C and a permeability of 3195.6 mD, a breakthrough pressure gradient of 10.07 MPa/m, and a plugging strength of 4.70 MPa/m. The agent achieved effective plugging across a permeability range of 500–3000 mD. High-temperature stability experiments indicated that crystal consolidation slightly improved with aging time, confirming its long-term plugging capability. Further studies showed that the agent adapts well to high-salinity formation water, as increased salinity shortened crystallization time without significantly affecting plugging performance. Chemical compatibility tests revealed that small-molecule viscosity reducers had no notable impact on the agent’s performance, while polymers extended crystallization time at low temperatures, slightly reducing injectability. Therefore, the dual-crystal synergistic plugging agent demonstrates broad applicability. The study provides technical support for water control and production stabilization in the middle and late stages of heavy oil thermal recovery, highlighting the agent’s advantages of high-temperature resistance, strong plugging strength, wide permeability adaptability, and chemical compatibility.