The recovery of heavy oil is challenging due to its high viscosity. Especially in water flooding, the high viscosity of heavy oil induces a high water/oil mobility ratio, resulting in frequent channeling and fingering. In the present work, the viscosity reduction in heavy oil caused by foaming agents is studied. Among the studied foam systems, the KX-048 foaming agent had the best oil viscosity reduction performance. It also shows excellent foaming performance, including large foam volume, long foam half-life, and high foam comprehensive index. With the reduction in oil viscosity, the KX-048 foaming agent decreases the foam/oil mobility to 0.28, which is beneficial for controlling gas channeling and fingering in foam flooding. Moreover, Foam flooding experiments in heterogeneous sand-pack models indicate that KX-048 has excellent efficiency in improving oil recovery, especially in the low-permeable tube. The chosen KX-048 foaming agent could provide a promising pathway for improving heavy oil recovery.

Excessive water production remains one of the most intractable challenges threatening the economic and sustainable development of oil production worldwide. In situ crosslinking polymer gel systems have been widely adopted as cost-effective chemical solutions for water shutoff and conformance control in oilfields. However, the excessively fast gelation kinetics of conventional gel systems at elevated temperatures severely hinders their application in deep, high-temperature reservoirs. To address this gap, this work systematically evaluates a novel Cobalt(II) (Co(II))-crosslinked polymer gel system developed for water control in high-temperature reservoirs. The effects of polymer type, Co(II) concentration, salinity, temperature, and pH on the gelation time, sol–gel transition behavior, and long-term thermal stability of the system were comprehensively investigated. Compared with the most widely used Cr(III)-crosslinked polymer gel systems, the Co(II)-based gel system exhibits a significantly prolonged gelation time at 130 °C, and the gelation time is positively correlated with the molar content of 2-acrylamido-2-methyl propane sulfonate (AMPS) in the polymer backbone. For instance, the gelation time at 130 °C can be remarkably delayed to 16 days when using the AMPS-rich polymer SAV-10. A unique and distinguishing feature of this polymer/Co(II) gel system is its fully reversible thermoresponsive sol–gel transition behavior. Unlike Cr(III)- and Zr(IV)-crosslinked gels, which form permanent and irreversible gels once crosslinked, the Co(II)-based gel system can crosslink into a robust bulk gel at high temperatures and reversibly switch back to a low-viscosity polymer solution when the temperature drops. For example, the SAV-28/Co(II) mixture forms a stable gel at 130 °C and fully reverts to a flowing polymer solution when the temperature is reduced to 80–85 °C. Furthermore, the SAV-10/Co(II) gel exhibits exceptional long-term thermal stability at 130 °C in both 5% NaCl brine and reservoir formation water, with no observable gel volume loss or syneresis after 100 days of high-temperature aging. The combination of tunable delayed gelation, unique thermoreversible sol–gel transition, and excellent high-temperature stability makes this Co(II)-based gel system a promising candidate for water control in oil and geothermal reservoirs, particularly for targeted plugging in the far-wellbore region and other advanced applications requiring dynamic and reversible fluid diversion.