Insights into the intimate link between nonlinear rheological characterization and the rupture behavior of polymer gel in model fractures

Abstract

A deep understanding of how fluid flows through the polymer gels has significant implications for achieving effective gel treatments in fractured reservoirs. This study aims to investigate the behavior of brine breakthrough from the gels in model fractures and relate the rupture behavior to the rheological properties of the gels. The underlying mechanisms for different gel rupture behavior are also elaborated. The effect of the injection rates, the aperture of tubes, and the gel properties on the rupture pressure of the gel were also studied. The results show that the rupture pressure of gel is highly dependent on the flow rates, and the rupture pressure is decreased with increasing the aperture sizes. It is also found that the polymer gel with a higher amount of crosslinkers has a high G’ value yet exhibits a low rupture pressure. From the visualization experiments, we found that brine is more likely to penetrate through the gel along the weak network structures, and a narrower channel would be formed at a higher injection rate. Moreover, various rheological measurements were conducted to characterize the gel properties. The results reveal that the maximum differential pressure the gel can withstand is highly dependent on the microstructure and the toughness of the gel. The defect structures, such as large cavities or cracks, would lead to a low yield stress of polymer gel, which is more susceptible to fracturing. The texture properties of the polymer gel can be interpreted by the shapes of Lissajous curves. The flexible gel shows a “banana-shaped” curve at high strain, a typical response for rubber-like materials. The toughness of the gel can significantly improve the pressure for water breakthrough. The degree of the brittleness of the polymer gels can be characterized by the reduction rate of the maximum elastic stress. The results presented in this study allow us to select an appropriate gel for water shutoff in fractured reservoirs by rheological methods, which are more robust and cost-effective.