Snorre Low-Salinity-Water Injection—Coreflooding Experiments and Single-Well Field Pilot

Abstract

Summary: Low-salinity (lowsal) waterflooding has been evaluated for increased oil recovery (IOR) at the Snorre field. Coreflooding experiments and a single-well chemical tracer-test (SWCTT) field pilot have been performed to measure the remaining oil saturation after seawaterflooding and after lowsal flooding. The laboratory coreflooding experiments conducted at reservoir and low-pressure conditions involved core material from the Upper and Lower Statfjord and Lunde formations. The core material from the Statfjord formations gave incremental recovery in the order of 2% of original oil in place (OOIP) by injection of diluted seawater. Similar amounts were produced during following NaCl-based lowsal injections. The same trend was observed in the high- and low-pressure experiments. No significant response to lowsal flooding was observed for Lunde cores. No response was normally observed during alkaline injection. The SWCTT field pilot was carried out in the Upper Statfjord formation. The average oil saturations after seawater injection, after lowsal seawater injection, and after a new seawater injection were determined; no significant change in the remaining oil saturation was shown. The measured in-situ value of remaining oil saturation after seawaterflooding was in agreement with previous special core analysis (SCAL) experiments. The measured effect of tertiary lowsal flooding from core experiments was in agreement with the SWCTT. Both measurements indicated only low or no effect from lowsal injection. It has been suggested that lowsal flooding has a potential for improved oil recovery in all clayey sandstone formations containing crude oil. The results from this work indicate that the initial wetting condition is a crucial property for the effect of lowsal injection.