Abstract
In fractured reservoirs, fluids injected Enhanced Oil Recovery (EOR) are channeled through the fracture zones and travel through highly permeable regions, failing to displace part of the oil, and decreasing oil recovery efficiency. To solve these problems, the conformance control technique is now widely used, as it allows the reservoir to be swept totally, similar to the ideal condition. In this context, polyacrylamide-based polymer gel systems can be used to block the high-permeability regions of the rock matrix, formingin situhydrogels that block the rock pores, avoiding the channeling of the fluids, and increasing the oil production. These polyacrylamide-based hydrogels can be crosslinked by inorganic (metal ions) or organic substances, and various systems are used for conformance control. Due to the greater stability of the bond formed between the polymer and the organic crosslinker, these systems are now used in higher temperature reservoirs. In order to produce hydrogels with higher resistance to severe salinity and temperature conditions, nanoparticles are applied to form systems with good mechanical resistance, and high thermal stability. These have presented promising results for conformance control.
Highlights
Oil production is crucial for the global economy and its demand tends to increase by 1.5% per year (El-Hoshoudy et al, 2017)
Gel systems based on polyacrylamide can be formed by crosslinking with organic compounds such as phenolformaldehyde, resorcinol-formaldehyde, hydroquinone – hexamethylenetetramine, N,N0-methylenebisacrylamide Polyethyleneimine (PEI), among others
Lashari et al (2018) studied the action of nanosilica as a reinforcement filler in systems formed by polymer based on polyacrylamide crosslinked by resorcinolhexamethylenetetramine, at temperature of 100 °C and salinity 51 984 ppm Total Dissolved Salts (TDS)
Summary
Oil production is crucial for the global economy and its demand tends to increase by 1.5% per year (El-Hoshoudy et al, 2017). Polymer hydrogels can be used as blocking gels, changing rock characteristics, and displacement mechanism, improving sweep efficiency, and leading to a higher oil recovery rate (Lakatos and Lakatos-Szabó, 2008) These systems are injected in the reservoir formation from an injection well or a producing well, typically with 5–15 ft. Of treatment are usually composed of a polymer and inorganic or organic crosslinking agent, and are divided into (a) two categories: in situ gels and Preformed Particle Gels (PPGs) (Lenji et al, 2018) In this method, in situ gels are injected into the reservoir to form a 3D gel network structure, under reservoir conditions (temperature, salinity, and pH) so as to efficiently block water currents and reduce permeability (Seright, 1991; Sydansk and Moore, 1992). The focus of this literature survey is the use of polymer hydrogels for water control treatment of oil reservoirs as “blocking gels” for in situ application
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