Synthesis of hydrophobically modified polyacrylamide and investigation of its behaviour in porous media

• Main Author: Zabihi, Hassan
• Other Authors: Diaz, Pedro ; Orrin, John
• Published: London South Bank University 2017
• Subjects: 620
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.734083

Approximately half of the world oil production is a result of water flooding. A major concern in this process is the mobility control of the injected phase with unfavourable fluid mobility ratio, channelling through permeable zones and, fingering effects can occur leading to an early water breakthrough and an inefficient flooding. Technically, it is possible to improve the flooding efficiency by applying enhanced oil recovery (EOR) processes (e.g. polymer flooding, steam injection and surfactant flooding). EOR processes intend to improve the sweep efficiency by reducing the mobility ratio between injected and in-situ fluids and/or to improve the displacement efficiency by reducing the capillary and interfacial forces. Polymer flooding is an enhanced water flooding process in which the water/oil mobility ratio is lowered by adding watersoluble polymers to water to increase its viscosity. The most applied polymer for EOR processes is the synthetic partially hydrolyzed polyacrylamide (HPAM). Several field projects have been carried out utilising HPAM, and the observed trend is that these polymers show low shear stress stability, and low salt tolerance. They are also sensitive to elevated reservoir temperature. Additionally, polymer retention and adsorption affect the rheological properties of the polymer solution significantly and reduce permeability. Therefore, polymers with greater salinity resilient and temperature resistance are needed. Hydrophobically modified polyacrylamide is a type of associative polymers that has been introduced to oil field applications as an alternative to HPAM for the past two decades. The main characteristics of these polymers are their significant enhancement of water viscosity compared with the conventional polymers such as HPAM, and their salinity tolerance and temperature resistance that would be more important in the real application. In this project, phenyl-polyacrylamide (PPAM), a hydrophobically modified polyacrylamide is studied as a potential viscosifier in waterflooding process. PPAM is synthesised by free radical micellar copolymerisation. The synthesised copolymer was characterised and the polymer composition was determined. Viscosity average molecular weight of copolymer was measured, and the rheological behaviour of the polymer was investigated in both, distilled water and NaCl solution and the results were compared with those obtained for HPAM. Greater viscosity values were observed for PPAM in distilled water and saline brine than HPAM. Comparative flow experiments for polymer solutions were carried out in sand packs to investigate the interaction of polymer, sand, and brine, and also to study the effect of the shear rate on viscosity of the polymer in-situ. The polymer solutions exhibited a shear thinning, shear thickening and degradation behaviour at different shear rates. The experiments were further carried out to investigate the polymer retention at different polymer concentrations, and brine salinity, and the results were compared with those from conventional hydrolysed polyacrylamide. Greater polymer adsorption was observed at higher brine salinity for HPAM than PPAM, however, polymer adsorption for PPAM is slightly greater than HPAM in distilled water. Oil displacement tests were further conducted through consolidated core samples (Benthemier sandstone). The reduction of permeability to water was estimated, and oil recovery was measured. A greater permeability reduction to water was observed for PPAM than HPAM solution at low salinity which is not desirable, however, oil recovery at higher concentration of PPAM was greater than HPAM. In summary, PPAM can be used as a good alternative to conventional HPAM due to strong viscosity behaviour in high salinity and temperature. Intermolecular association of hydrophobic monomers in copolymers of PPAM form a bulky structure which causes great viscosity enhancement of polymer solution in distilled water. PPAM solubility in high salinity water is proven to be greater than HPAM and the results from polymer precipitation tests showed much less polymer precipitation for PPAM than HPAM in high saline brine. Moreover, the results for temperature effect on polymer viscosity demonstrated stronger temperature resistance for PPAM than HPAM.