A Smart Plugging System of Temperature-Sensitive Gels Based on Cellulose Ether

The smart plugging system of temperature-sensitive gels is a new type of colloid developed to enhance the recovery rate of hot water drive mining in thick oil reservoirs in China's Bohai Oilfield. Existing gel plugging agents exhibit poor adaptability under hot-water drive conditions, and the temperature fluctuations in the reservoir caused by hot water flooding make it difficult to effectively block the high permeability layers. The average reservoir temperature in the target block of the Bohai Sea is 50 °C-60 °C, the peak temperature can reach 100-110 °C when injecting hot water, and the conventional gel easily loses the plugging capacity. Thus, it is necessary to develop a smart plugging reagent that responds to temperature changes in the dominant channel. In this study, we used cellulose ether as the main agent and added auxiliaries, such as a reinforcing agent, a complexing agent, and a regulator, to form a temperature-sensitive gel system through physical cross-linking. Subsequently, injection performance, plugging performance, and scouring resistance as well as cooling and plugging removal performance experiments were conducted in porous media. The results demonstrated that the preferred system composition was cellulose ether 1 # (0.5%-1.0%) + nanosilica (0.2%) + HEDP·4Na (0.5%-1.0%) + urea (0-0.5%). The nanosilica reinforcing agent can enhance the gelation effect of the system. Moreover, HEDP·4Na forms a complex with calcium and ionic magnesium to form a multinetwork system that can enhance the elasticity of the system. Urea increases the gelation temperature, while an increase in the salinity reduces the gelation temperature. By adjusting the added auxiliary and degree of salinity, the system can be controlled to gel at 50-100 °C. Core experiments showed that the plugging rate of the system can exceed 96% under a permeability of 3000-7000 × 10^-3 μm², which indicates that it has a powerful plugging ability. After the formative gel was flushed by 11 pore volumes of injected water, the pressure was still stabilized above 4.5 MPa. After cooling and plugging removal at 52 °C, the water flooding pressure was reduced significantly, which reflects the ability of the system to temporarily block the dominant channel. Analysis of the fluid diversion performance showed that the system has an obvious water absorbing profile adjustment effect on the permeability ratio of 4-8.5, which provides a new significance for improving thick oil thermal recovery.