Delayed Breaker Systems To Remove Residual Polymer Damage in Hydraulically Fractured Reservoirs

Abstract

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.

Progress and Prospects of In Situ Polymer Gels for Sealing Operation in Wellbore and Near-Well Zone

“…Mannanase-II has been reported to remain active in the range of 40−70 °C. 155 Ghosh et al 156 developed a thermally activated enzyme breaker with a temperature resistance of 120 °C, whose main ingredient is galactomannanase, which was able to degrade 94−98% of the filter cake formed by cross-linking HPG guar with sodium tetraborate at 120 °C in only 6 h. They compared the effect of this enzyme with several acid gel-breaking agents such as chlorous acid, sodium bromate, and diammonium peroxidisulfate. At 148.8 °C, the breaking time of the enzyme was longer, taking 24 h, but it produced the least amount of residue.…”

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

“…Abdelrahim et al revealed the residual damage mechanism of fracturing fluid. 64 The main problem is the intrusion of polymers into pore throats, increasing the level of binding water between rock pores and the surface of proppants. In addition, due to the adsorption of fluids, the matrix expands and the pore space decreases, resulting in a decrease in fracture conductivity.…”

“…69 The MAS-1 polymer synthesized by Zhang et al was used in core-damage experiments, and the results showed that the permeability damage rate was between 12.64%−17.62%. 70 Ghosh et al 64 used the enzyme breaker developed to break the cross-linked HPG fluid and regained the matrix fracture permeability to 80%−95%. 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%.…”

“…The incomplete breaking of polymers can have a negative impact on increasing production, as they can bridge the pores of proppant packs and rocks, ,, blocking flow channels, especially in low-permeability reservoirs. Abdelrahim et al revealed the residual damage mechanism of fracturing fluid . The main problem is the intrusion of polymers into pore throats, increasing the level of binding water between rock pores and the surface of proppants.…”

“…In addition, due to the adsorption of fluids, the matrix expands and the pore space decreases, resulting in a decrease in fracture conductivity. To reduce the damage left by the polymers, the gel breakers (such as oxidants or enzymes) are used to break the polymer. − However, the activity of the enzymes is strongly influenced by the external environment, causing limited effects. The oxidants are used at high concentrations, which is not environmentally and technically safe .…”