Heat-Generating Expandable Foamed Gel Used for Water Plugging in Low-Temperature Oil Reservoirs

Polymers are often used for chemical water plugging. When the reservoir temperature is lower than 50 degrees C, the reaction between polymers and cross-linking agents is very slow, which extensively prolongs the gelation time and even leads to unsuccessful gelation. To overcome such problems, a foamed-gel system that is capable of spontaneous in situ heat generation was developed. The optimal system was identified through the orthogonal test using the gel strength, gelation time, and gel volume as indexes. The test shows that, when the ambient temperature is fixed at 30 degrees C and the pH value is 6.8, the system performs well. Under such circumstances, the gelation time is 40 h, the gel strength reaches the G grade, and the volumetric expansion ratio at 10 MPa exceeds 130%. Nuclear-magnetic-resonance-based T-2 spectra indicate that the foamed gel injected into the rock can effectively plug large pores and, therefore, offset the heterogeneity. It is also found that the foamed gel has great capacity for volumetric expansion-based water plugging. The synchronization between gelation and gas generation is the key to the heat-generating foamed gel. Experiments suggest the properties of the developed heat-generating expandable foamed gel can be manipulated by adjusting pH values to satisfy varied requirements for placement in different reservoirs.