Fracturing fluid cleanup by controlled release of enzymes from polyelectrolyte complex nanoparticles

Abstract

Guar-based polymer gels are used in the oil and gas industry to viscosify fluids used in hydraulic fracturing of production wells, in order to reduce leak-off of fluids and pressure, and improve the transport of proppants. After fracturing, the gel and associated filter cake must be degraded to very low viscosities using breakers to recover the hydraulic conductivity of the well. Enzymes are widely used to achieve this but injecting high concentrations of enzyme may result in premature degradation, or failure to gel; denaturation of enzymes at alkaline pH and high temperature conditions can also limit their applicability.In this study, application of polyelectrolyte nanoparticles for entrapping, carrying, releasing and protecting enzymes for fracturing fluids was examined. The objective of this research is to develop nano-sized carriers capable of carrying the enzymes to the filter cake, delaying the release of enzyme and protecting the enzyme against pH and temperature conditions inhospitable to native enzyme.Polyethylenimine-dextran sulfate (PEI-DS) polyelectrolyte complexes (PECs) were used to entrap two enzymes commonly used in the oil industry in order to obtain delayed release and to protect the enzyme from conditions inhospitable to native enzyme. Stability and reproducibility of PEC nanoparticles was assured over time.An activity measurement method was used to measure the entrapment efficiency of enzyme using PEC nanoparticles. This method was confirmed using a concentration measurement method (SDS-PAGE). Entrapment efficiencies of pectinase and a commercial high-temperature enzyme mixture in polyelectrolyte complex nanoparticles were maximized. Degradation, as revealed by reduction in viscoelastic moduli of borate-crosslinked hydroxypropyl guar (HPG) gel by commercial enzyme loaded in polyelectrolyte nanoparticles, was delayed, compared to equivalent systems where the enzyme mixture was not entrapped. This indicates that PEC nanoparticles delay the activity of enzymes by entrapping them. It was also observed that control PEC nanoparticles decreased both viscoelastic moduli, but with a slower rate compared to the PEC nanoparticles loaded with enzyme.Preparation shear and applied shear showed no significant effect on activity of enzyme-loaded PEC nanoparticles mixed with HPG solutions. However, fast addition of chemicals during the iv preparations showed smaller particle size compared to the drop-wise method. PEC nanoparticles (PECNPs) also protected both enzymes from denaturation at elevated temperature and pH.Following preparation, enzyme-loaded PEC nanoparticles were mixed with borate crosslinked HPG and the mixture was injected through a shear loop. Pectinase-loaded nanoparticles mixed with gelled HPG showed no sensitivity to shear applied along the shear loop at 25 °C. However, EL2X-loaded PEC nanoparticles showed sensitivity to shear applied along the shear loop at 40 °C.Filter cake was formed and degraded in a fluid loss cell for borate crosslinked HPG solutions mixed with either enzymes or...

A review of fracturing fluid systems used for hydraulic fracturing of oil and gas wells

“…Delayed release systems capable of delaying the activity of breakers or crosslinking of guar during the injection are another important focus of the oil and gas industry. 34,35,69,70 Slickwater Fluids The current focus of the industry is on the following items: Development of a system that can use less or no water, in order to address the concerns regarding high water volumes being used and also other concerns regarding near fracture damage. Development of gas-based fracturing systems and efficient fluid loss additives for smaller pore size formations are currently being pursued for this purpose.…”

“…Moreover, the industry is focused on development of environmentally‐ and equipment‐friendly breakers that can be applied at high temperatures and extremely low or high pH conditions. Delayed release systems capable of delaying the activity of breakers or crosslinking of guar during the injection are another important focus of the oil and gas industry …”

“…It is a function of yield stress and is caused by concentrated fracturing fluid and the conductivity of fracture. 7 To carry higher concentrations of enzyme breakers while delaying the reaction of breakers with guar-based fluid during the injection time and prevent premature degradation, Barati et al 34,35 developed a polyelectrolyte nanoparticle system that is capable of delaying the release of enzyme breakers and protecting the enzyme against alkaline conditions and elevated temperatures.…”

Stability Improvement of CO2 Foam for Enhanced Oil Recovery Applications Using Polyelectrolytes and Polyelectrolyte Complex Nanoparticles

“…This system has also been applied as a delivery vehicle for entrapping enzymes or chromium between their structures for hydraulic fracturing and gel treatment purposes, respectively. [16][17][18][19] For this paper, we used an optimized pH of polyethylinamine and dextran sulfate under a different salinity to develop the PECNP. The particle size and zeta potential are determined for the PEsurfactant system and the PECNP-surfactant system.…”

Polyelectrolyte complex nanoparticles for protection and delayed release of enzymes in alkaline pH and at elevated temperature during hydraulic fracturing of oil wells

“…However, the relatively large size of the capsules, which are usually designed to break open when the fracture recloses at the end of the injection, may result in incomplete degradation of filter cake 1, 6. Polyethylenimine (PEI)—dextran sulfate (DS) polyelectrolyte complex (PEC) nanoparticles originally developed for drug delivery applications7–9 and adapted for oilfield applications10–12 were hypothesized to be capable of entrapping, releasing, and protecting enzymes for fracturing fluids in a controlled manner. PECs are structures that form when aqueous solutions of polyanions and polycations are mixed together in nonstoichiometric ratios at low concentrations.…”