High-Temperature Stable Specific Enzyme for Guar Polymer Based Fracturing Fluid Degradation

Abstract

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).

Review on High-Temperature-Resistant Viscoelastic Surfactant Fracturing Fluids: State-of-the-Art and Perspectives

“…71 Abdelrahim et al studied the damage of the residual fracturing fluid to the core through the coreflooding experiment. 72 The results indicated that the residual fracturing fluid may reduce the permeability of brine injection by 99% or more. Even after 48 h of aging and back-flowing, the oil recovery permeability significantly still decreased.…”

“…The retained permeability of the metal-cross-linked synthetic polymer fluid tested by Lee et al with a temperature resistance of up to 232 °C is less than 80% . Abdelrahim et al studied the damage of the residual fracturing fluid to the core through the core-flooding experiment . The results indicated that the residual fracturing fluid may reduce the permeability of brine injection by 99% or more.…”

Residual Damage, Its Consequences, and Remedial Measures on Post Hydrofrac Well Productivity: Learnt Lessons

“…Most fracturing fluids use an optimum dose of guar-based polymers (guar and its derivatives). The guar derivatives most commonly used in fracturing fluids include carboxymethyl guar (CMG), hydroxypropyl guar (HPG), and carboxy Methyl hydroxypropyl guar (CMHPG), with each having unique properties [23]. It is of paramount interest to select the correct type of guar at an optimized concentration when designing fracture treatments to deal with the rheology and temperature constraints.…”

“…These modified guar derivatives gained popularity because of their unique properties, such as high molecular weight (ranging from 1 to 2 MD), helping to generate high viscosity at low concentration, quick hydration, stability at a higher temperature, and a greater pH range (pH 4.5-10). They also crosslink with metals, biocompatible, biodegradable, and non-toxic nature [23].…”

“…It also demonstrated a wider range of temperature (40-65 • C) and pH (7-8.5) tolerance, making it suitable for application in sallow carbonate formations. The development of a protein-engineered galacto-mannanase enzyme that works at temperatures as high as 120 • C and a pH range from 6-8.5 has been tested successfully in carbonate reservoirs [23]. The breaker system can degrade the damaging polymeric residues on the fracture face and regain matrix-fracture permeability to the extent of 80-95%.…”