The onshore Seria field in Brunei Darussalam has been producing oil for over 80 years and is approaching the end of primary production. Estimated remaining oil-in-place volumes are significant enough to consider enhanced oil recovery techniques. Alkaline-Surfactant-Polymer (ASP) flood is under investigation as a potential method to increase the recovery in the field. Sand pack and core flood experiments indicate that remaining oil saturations may be reduced sufficiently to warrant commercial application of ASP flood technology in the Seria field. To assess feasibility of this process under reservoir conditions, a single-well, multi-zone injection test using Log-Inject-Log (LIL) techniques was executed. The objectives of this test were to determine injectivity of ASP fluids and to estimate changes in residual oil saturation (Sor) in the near-wellbore region. This paper discusses the preparation, execution, and learnings associated with the LIL activities employed to assess chemical effectiveness of the ASP slug.
Standard open-hole logs were acquired in a newly drilled well to confirm static reservoir properties and to determine the current oil saturation. The original LIL logging program included Schlumberger’s Reservoir Saturation Tool (RST) in pulsed neutron spectroscopy mode (also known as carbon/oxygen or C/O logging) as the primary evaluation method to quantify changes induced by ASP flooding. This was initially supplemented by the slim Cased-Hole Formation Resistivity (CHFR) tool and further supplemented by RST sigma logging and additional cement bond logging to identify sweep outside of perforated intervals. The use of multiple logging tools and the integration of logging results provided corroborative evidence for reduction in oil saturation outside of perforated intervals resulting from acid/brine, polymer/brine and ASP/brine injection as well as valuable insight into changes in the near-wellbore region that would otherwise be missed using a single logging method.