Abstract
A field in southern Oman has been identified for conducting an alkaline surfactant polymer (ASP) pilot project to enhance oil recovery. The potential benefit from ASP flooding had been estimated to be significant, based on coreflood investigations and single-well tests. The ASP pilot was initiated to derisk and support the financial investment decision for full-field implementation.
The vertical saturation estimates were obtained through state-of-the-art nuclear magnetic resonance (NMR) technology in the observation well, which was completed with fiber-reinforced plastic (FRP) casing and located midway between the injector and a producer of the pilot. Laboratory ASP flood experiments demonstrated that NMR response is insensitive to the chemistry of ASP/polymer solutions. The tool response provides salinity-independent inference for saturation profiling. These characteristics of NMR technology make it a suitable saturation monitoring tool for fields applying chemical enhanced oil recovery (EOR).
The pilot was executed with several phases, starting with pre-ASP waterflooding. This was followed by ASP slug injection, which, in turn, was followed by polymer chase and, ultimately, by chase water injection.
The base vertical saturation profile was established during the last stage of the pre-ASP waterflooding phase. The time-lapse vertical saturation profiles facilitated estimation of incremental desaturation during and after every stage of the injection phases. The dedicated multiphase flowmeters for each producer have also provided realtime oil production profiles to quantify the incremental oil production.
During the ASP pilot, NMR indicated the formation of an oil bank and desaturation due to ASP. This paper discusses the results of NMR during ASP pilot and the insights that NMR brings into understanding of subsurface performance and vertical sweep due to ASP.
