pH-Responsive Supramolecular Gelling Agents Used in EOR and Their Potential as Fracking Fluids

摘要

Hydraulic fracturing is an important method to recover shale oil and gas that has drastically increased U.S. energy production in recent decades. Shales are low permeability formations where natural resources are trapped, and require a well-planned hydraulic fracturing process and a highly developed fracturing (fracking) fluid for efficient oil/gas recovery. In this study, a pH-responsive solution synthesized by supramolecular assembly of maleic acid and an amino-amide in an aqueous media is described as a potential fracking fluid owing to its mobility control, proppant carrying and settling capacities. Previous investigations on this solution system had shown its large potential to replace displacement fluids in EOR due to pH-tunable and reversible viscosity behavior. The main working mechanism is that; the initial viscosity of injected solution is kept at moderate/high values to easily transport proppants and easily inject the fluid; and then decreased when the solution reaches a position near fissures for settling of proppants. It has been reported by rheology tests of the developed fracking fluid, which consists of the supramolecular solution and proppants (silica sand), viscosity can be changed about 1600 times from pH 3.8 to pH 8.3 in a reversible fashion at only 2 wt.% concentration. On the other hand, sedimentation studies indicated that the sedimentation speed of the silica proppants decreased around five orders of magnitude from pH 4 to pH 8, again in a reversible way. Furthermore, experimental studies revealed that the developed supramolecular solutions have both reversible pH-responsive properties, and tolerance against high salinities and elevated temperatures. Another outstanding property of these supramolecular solutions is their self-healing feature which enables them to disassemble and reassemble upon exposure to extreme shear stresses, while polymer viscosifying agents the fracking fluids degrade and break up under similar conditions. The supramolecular assembly system discussed in this study has a promising potential to become next-generation fracking fluids with its outstanding properties including but not limited to pH-sensitivity, reversible viscosity, high proppant transfer capacity, tolerance to high temperatures and salinity, self-healing behavior, environmental friendliness and sustainability.