Hydraulic fracturing is a widely used technology to enhance the productivity of low-permeability reservoirs. Fracturing fluids using guar as the rheology builder leaves aside residual polymer layers over the fractured surface, resulting in a restricted matrix to fracture flow, causing reduced well productivity and injectivity. This research developed a specialized enzyme breaker and evaluated its efficiency in breaking linear and cross-linked guar-polymer gel as a function of time, temperature, and breaker concentration targeting a high-temperature carbonate reservoir. The study began with developing a high-temperature stable galacto-mannanase enzyme using the "protein-engineering" approach, followed by the optimization of fracturing fluids and breaker concentrations measuring their rheological properties. The thermal stability of the enzyme breaker vis-a-vis viscosity reduction and the degradation pattern of the linear and cross-linked gel observed from the break tests showed that the enzyme is stable and active up to 120 °C and can reduce viscosity by more than 99%. Further studies conducted using a high-temperature high-pressure HT-HP filter press for the visual inspection of polymer cake quality, filtration loss rates, and cake dissolution efficiency showed that a 6 h enzyme treatment degrades the filter cake by 94−98% compared to 60−70% degradation in 72 h of the natural degradation process. Coreflooding studies, under simulated reservoir conditions, showed the severity of postfracture damage (up to 99%), which could be restored up to 95% on enzyme treatment depending on the treatment protocol and the type of fracturing gel used.
Hydraulic fracturing or hydro-frac fluids can impede well production due to the damage caused to the reservoir formation and fracture face, generated from adverse interactions with reservoir rock. Understanding the mechanisms of hydraulic fracturing, optimum treatment designs, and pumping/pressure profiles is critical for hydro-frac success. However, to realize the full potential of fracturing and the mitigation strategies for reservoir and fracture conductivity damage during and after its occurrence, fracturing must be considered during the design phase itself. This article provides a brief overview of hydro-frac techniques, including design, optimization, modeling, commonly used proppants, and fracturing fluid benefits and consequences based on critically reviewed case studies. However, the primary focus of this article is on the potential of fracture conductivity damage and the intrinsic mechanisms in hydraulic fracturing. The article presents updated information on various damage mitigation processes established through laboratory investigation and field implementation. The authors expect that the provided workflow in this article will be helpful to researchers and stimulate engineers to a great extent.
Hydraulic fracturing, commonly referred to as fracking, is a widely used technology to enhance the productivity of low-perm reservoirs and the aqueous-based fracturing fluids use guar as the rheology builder. Residual polymer layer over the fractured surface results in a reduced matrix to fracture permeability, causing reduced well productivity. This research aims to develop a specialized mannanase enzyme and evaluate its efficiency in degrading linear and cross-linked guar polymer gel as a function of time, temperature, and breaker concentration, to enhance the effectiveness of the fracturing process and yielding higher production. The study begins with developing high-temperature stable mannanase using "protein engineering" tools to minimize denaturation at high temperatures and the underlying formation chemistry, followed by optimization of polymer, crosslinker, and breaker concentration through the measurement of rheological properties at moderate to high temperature. Initial studies were conducted using HT-HP filter press and filter papers as porous media for visual inspection of polymer cake dissolution efficiency. Final conclusions were drawn from the simulated coreflooding studies, wherein the injection and production return permeabilities were investigated on post-fracture and enzyme-treated cores, where the breaker was mixed with the frac fluid applied once the frac fluid is in place. The thermal stability of the enzyme breaker vis-à-vis viscosity reduction and degradation pattern of linear and cross-linked gel observed from the break test showed that the enzyme is stable up to 250 °F and can reduce viscosity by more than 1800 cp (99% breaking ability).
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