Nanomaterials-Enhanced High-Pressure Tolerance of Borate-Crosslinked Guar Gels

Abstract

Abstract Borate-crosslinked guar gels are widely used for hydraulic fracturing treatment of wells at temperatures of about 100-300°F due to their advantages such as low cost, ability to reheal upon shearing and operational simplicity. These fluids, however, may lose some or even all of the gel viscosity under sufficient high pressure, especially at elevated downhole temperatures. Although this process could be reversed when the pressure and/or temperature drops, it may potentially cause adverse operational issues such as proppant screenout where the proppant cannot be placed. Recently we found during the lab research studies that the viscosity loss of the borate-crosslinked guar fluids under high pressure could be mitigated with a number of novel nanomaterials. This paper examines three specific nanomaterials. These enhancing nanomaterials were applied to the borate-crosslinked guar gels as a liquid additive, with dosages typically at about 0.02%-0.12% by weight. In one example, the addition of 1 gpt of nanomaterial-I (0.02% active nanomaterials) enhanced the borate-guar fluid viscosity by about six times at the pressure of 8000 psi. In another example, when 2 gpt of nanomaterial-II (0.04% active nanomaterials) was added, the fluid viscosity was enhanced by about nine times under a pressure of 8000 psi. As the result, the viscosity boosted by nanomaterial-II under high pressure was more than enough for the fluid to function normally to render fractures and transport and place proppant. Other nanomaterials including nanomaterial-III also significantly reversed the high pressure-induced viscosity loss for the borate-crosslinked guar fluids. These nanomaterials may have rendered more attractive interactions among the guar polymer chains, thus stabilizing the crosslinking of the fluids when the borate-guar bonding was reduced under elevated pressure and temperature. The detailed results of the lab tests at high pressure, as well as fluid chemistry will be discussed in this paper.