Negatively Charged Polyelectrolyte-Complex Nanoparticles Using Pei/pvs for Encapsulation of Fracturing Fluid Breakers

Abstract

AbstractHydraulic fracturing treatment is a stimulation technique in low-permeability reservoirs and tight rock formations. It involves pumping large quantities of fluids into the well at extremely high pressure. Due to hydraulics, it creates small cracks in the rock formations called fractures, allowing reservoir fluids such as natural gas, petroleum and brine to flow out of tight formations. Nanotechnology leads the research direction especially in the field of hydraulic fracturing. This paper/poster presents a novel approach for improving the fracture cleanup process, using negatively charged assembled polyelectrolyte-complex (PEC) nanoparticles as a technique for targeted and controlled release of enzyme breakers. Our previous work (Alhajeri et al. 2021) showed that positively charged PEC nanoparticles using the Polyethylenimine-Dextran Sulfate system can produce stable nanocontainers for enzyme breakers during the hydraulic fracturing process. However, negatively charged PEI/DS nanoparticles showed a significant loss of fracture clean-up efficiency due to the high pH level over the encapsulated enzyme that led to denaturing. In this study, negatively charged PEC nanoparticles were formed by the mixture of polyethyleneimine (PEI) and poly(vinlySufonic acid) (PVS) in nonstoichiometric amounts to encapsulate breakers. It is hypothesized that PEI/PVS system would provide a higher controlled release of breaking agents with high loading capacity due to lower toxicity levels. The development of negatively charged PECs nanoparticles was examined. The nanoparticles were assembled by means of alternate electrostatic adsorption of a polyanion (PVS) and a polycation (PEI). Enzyme-breaking agents were introduced into the PECs during the complexation process. A screening test of the PEI/PVS PEC loaded with enzyme was conducted based on particle size, polydispersity, and zeta potentials. The most stable PEC structure was selected for Enzyme viscometric assays to measure the entrapment efficiency (EE,%). Results from this study demonstrated a proof of concept that negatively charged PEC nanoparticles using PEI/PVS can be used to encapsulate fracturing fluid breaks, minimize premature degradation of fracturing fluids, and provide protection from inhibited surroundings at downhole conditions. In addition, the negatively charged PEC nanoparticles show higher particle stability in terms of smaller particle sizes (>200 nm) and zeta potential (> - 40 mV) for more than 94 hours, thus; improving fracturing clean-up efficiency. The general goal of this study is to develop nano-sized particles loaded with enzyme breakers capable of functioning within fracturing fluids during fluid leak-off into the reservoir matrix, filter cake development, and hydraulic fractured area.