In water injector wells, continuous injection can wash gravel from the annulus around the screen, especially if the rate of injection generates a pressure above the fracture threshold. The voids created after the washout are sometimes filled by an influx of formation sand during shut-in operations. This sand accumulation consequently reduces the injectivity when the injection operations resume. A solution to prevent such washouts is needed to maintain sand control and injectivity throughout the life of water injector wells.
As a solution to this common problem, we propose a new fiber based product that reinforces the gravel and/or proppant pack. The fibers have an outside layer that is activated by temperature to form a bonded fiber network that locks the gravel in place. The fibers can be used with any type and size of proppant. The key benefit is that the fibers can withstand the cyclic loading of stress inherent to the shut-in and restart of injection operations, which are typically performed several hundred times during the life of an injector well.
Our experimental study showed that the drag force of injected water easily displaced the gravel in the annulus into the fracture, whereas when gravel is reinforced with the fibers it withstood the drag force even at high injection rates (e.g., at 100 B/D per 0.5-in.-diameter perforation). We performed several experiments to evaluate the strength of the pack under cyclic stress conditions. After 30 cycles, the pack strength remained unaffected. The fiber chemistry was tailored for compatibility with commonly used fracturing fluids and brines. We found that the fibers remained connected in an interconnected network even after long-term interaction with seawater. We also studied the interaction of fibers with screens and other downhole equipment that comes in contact with the fibers during gravel placement. The laboratory results of that study showed the fibers do not create any issues with proppant placement or tool functionality during the sand control operation.
Our experimental study also showed the fibers provided an effective solution for preventing gravel washout in water injector wells, thereby supporting the sand control and injectivity for the life of the well.