Novel Drag-Reducing Agents for Fracturing Treatments Based on Polyacrylamide Containing Weak Labile Links in the Polymer Backbone

Abstract

Abstract Water-soluble polymers have found extensive use in the oil and gas industry. For instance, high molecular-weight polymers are very efficient drag/friction-reducing agents and viscosifiers. Unfortunately, the adsorption of the polymer on the reservoir formation reduces the effectiveness of the recovery of oil and gas from tight low-permeability formations, such as shale. The availability of water-soluble polymers containing weak links in the backbone of the polymer that can be degraded upon experiencing a certain trigger, such as temperature, pH, or reducing agent, would be very advantageous. Because of the ability of weak links to degrade under certain conditions, such polymers can be used for their intended application and afterwards be degraded in a controlled and predetermined way. The resulting lower molecular-weight fractions of that polymer lead to reduced viscosity, quick partitioning in the water phase, and they are also less likely to adsorb onto formation surfaces. Additionally, no oxidizers need to be pumped to break or clean the deposited polymer, thus, saving time and money. It has been proved that using a bifunctional reducing agent containing degradable groups and oxidizing metal ion as a redox couple is a facile method to initiate the free-radical polymerisation and build degradable groups into the backbone of the vinyl polymers. Temperature-degradable but hydrolytically stable azo groups showed the most desirable results. The presence of azo groups in the backbone of the synthesized polyacrylamide (PAM) was confirmed by rf-NMR spectra and differential scanning calorimetry (DSC). The degradation behavior of the PAM with temperature-sensitive azo groups was characterised using gel permeation chromatography (GPC) system and proved the multiple labile links were built into the polymer backbone. It was also found that PAM with azo links in the polymer backbone is as good a drag-reducing agent as pure PAM. However, PAM with azo links in the backbone loses its drag-reduction properties once subjected to elevated temperature, which for some applications is viewed as an advantage.