Novel Nanocomposite Fiber-Laden Viscoelastic Fracturing Fluid for Coal Bed Methane Reservoir Stimulation

Abstract

As coal has strong adsorption characteristics and well-developed natural fracture systems, an improper choice of fracturing fluid can result in significant challenges for coal bed methane exploitation, including damage to the coal formation and ineffective creation and propagation of hydraulic fractures. Viscoelastic surfactant (VES) fracturing fluid has become a preferred option because of its easy flowback and the resultant minimal damage. A novel nanocomposite fiber with substantially improved functional and structural properties was synthesized by introducing nanoparticles into conventional polyester fiber. Subsequently, a nanocomposite fiber-laden VES (NFVES) fracturing fluid was developed and evaluated in the laboratory. The results show that the fiber disperses well in the fluid and that the addition of a small amount (0.5%) of fiber substantially enhances the proppant-carrying capacity of the fluid. To achieve a proppant-carrying capacity equivalent to a standard VES, the surfactant concentration can be decreased from 2.5% to 1%, which not only reduces costs but also significantly lowers adsorption of the surfactant by the seam and rock surfaces. In addition, rod micelles with less surfactant added are more easily broken. Addition of 0.7% nanocomposite fiber reduced the tube friction by 20% at shearing rate of 5000 s−1. The nanocomposite fiber also effectively prevents backflow of the proppant and mitigates leak-off of fluid and aggregation of coal scraps. Continuous degradation of the fiber occurs over time at formation temperatures, thus reducing the potential damage to the coal seam. The strong performance of this NFVES fracturing fluid in the laboratory evaluations indicates the great potential and development prospects for coal bed methane reservoir stimulation using this fluid.