A material assessment has been completed for a polyethylene liner to be utilised in polymer injection enhanced oil recovery. The assessment includes determination of the effect of representative exposure to the service fluids on the critical mechanical design properties for the polymer liner, comparative assessment of environmental stress cracking potential and a radial collapse resistance analysis to provide early design stage liner wall thicknesses. It was concluded that the material was suitable for use in the service environment tested, with the preprocessing of the liner material undertaken and suitable design input selection.
In brownfield oil and gas locations operators seek to identify cost-effective, low risk technologies which can extend the economic producing life of the field. One enhanced oil recovery (EOR) or tertiary recovery technique is the introduction of water-soluble polymer species to the reservoir via the water injection (WI) system.
Polymer injection EOR enables improved oil recovery by improving the sweeping efficiency of existing water flood recovery systems (Hinkley and Brown, 2017). Addition of water-soluble polymers reduces bypassing present in traditional WI where the injected water short-cuts from injection to production wells leaving regions of oil saturated rock unrecovered (Needham and Doe, 1987).
In addition to the injection of water-soluble polymer the injection of surfactants has been recognised since the 1970s (Healy & Reed, 1974) as a method of improving oil recovery. The effect of the surfactant is to lower the interfacial tensions between the oil and water phases and enables formation of an "oil bank" (Samanta, Ojha, Sarkar and Mandal, 2011) which is then pushed through the reservoir by the polymer injection EOR fluid and has the capability of increasing oil recovery significantly (Hill, Reisberg and Stegemeier, 1973; Larson and Hirasaki, 1978; Shah and Schechter, 1977).
Polymer lining technology now has a proven track record and can demonstrate an active field life of greater than 25 years in the water injection environment. These pipelines have typically had maximum operating temperatures of approximately 60°C, and the fluid composition has been based on seawater with additional chemical injection as necessary on the project. Where additional chemical injection is required the purposes typically include oxygen scavenging and inhibitors of various kinds, to the authors knowledge polymer liners have not been used in EOR applications, at least in the offshore environment. Where additional species are included in the injection fluid a chemical compatibility assessment of the liner material with the injected species under the operating conditions must be conducted. In some cases, assessment can be achieved utilising published chemical compatibility tables and results, such as those contained within ISO/TR 10358, but where results are not available or suitable analogues cannot be identified in published tables then physical testing can be conducted.
