Reduced Polymer Loading, High Temperature Fracturing Fluids using Nano-crosslinkers

Abstract

Abstract In the quest to discover more natural gas resources, considerable attention has been devoted to finding and extracting gas locked within tight formations with permeability in the nanoto microdarcy range. The main challenges associated with working in such formations are the intrinsically high temperature and high pressure bottom hole conditions. For formations with bottom hole temperatures around 350-400°F, traditional hydraulic fracturing fluids that use crosslinked polysaccharide gels, such as guar and its derivatives, are not suitable because of significant polymer breakdown in this temperature range. Fracturing fluids that can work at these temperatures require thermally stable synthetic polymers such as acrylamide-based polymers. However, such polymers have to be employed at very high concentrations in order to suspend proppants. The high polymer concentrations make it very difficult to completely degrade at the end of a fracturing operation. As a consequence, formation damage by polymer residue can block formation conductivity to gas flow. This paper addresses the shortcomings of the current state-of-the-art high temperature fracturing fluids, and focuses on developing a less damaging, high-temperature stable fluid that can be used at temperatures up to 400°F. A laboratory study was conducted with this novel system which is comprised of a synthetic acrylamide-based copolymer gelling agent and is capable of being crosslinked with a nano-sized particulate crosslinker (nano-crosslinker). The laboratory data has demonstrated that the temperature stability of the crosslinked fluid is much better than a similar fluid lacking the nano-crosslinker. The nano-crosslinker allows the novel fluid system to operate at significantly lower polymer concentrations (25 to 45 pptg) when compared to current commercial fluid systems (50 to 87 pptg) designed for temperatures from 350°F to 400°F. This paper presents results from rheological studies which demonstrate superior crosslinking performance and thermal stability in this temperature range. This fracturing fluid system has sufficient proppant carrying viscosity, and allows for efficient cleanup using an oxidizer-type breaker. Low polymer loading and little or no polymer residue are anticipated to facilitate efficient cleanup, reduced formation damage, better fluid conductivity and enhanced production rates. Laboratory results from proppant-pack regained conductivity tests are also presented.