Dick Jacob Ligthelm

Low-Salinity Polymer Flooding: Improving Polymer Flooding Technical Feasibility and Economics by Using Low-Salinity Make-up Brine

Polymer flooding is a mature EOR technique, which is successfully applied in both sandstone and carbonate reservoirs. In ongoing polymer projects, make-up brine is either formation water, sea water or any available water sources like deep or shallow aquifers. In this paper we focus on the use of low salinity water as the make-up brine. The objectives of combining low salinity flooding (LSF) with polymer flooding are three-fold: • Using low salinity brine reduces the amount of polymer required to obtain the target viscosity, which may lead to significant cost reduction. • Combining the benefit of low salinity flooding with polymer flooding leads to higher oil recovery over conventional polymer flooding. • Enhancing the elasticity of polymers by using low salinity brine which may lead to reduced Sorw and increased oil recovery. In addition to the objectives mentioned above, the use of a low-salinity make-up brine can give other benefits, such as better polymer stability especially at high temperatures), lower sensitivity to polymer shear degradation, lower polymer adsorption and lower scaling and souring tendency. The paper will present 1- Experimental procedures for investigating the potential benefits of low salinity polymer on both the required polymer concentration and the oil recovery. 2- Experimental results for several field cases 3- De-risking activities that were undertaken to mitigate any potential negative impact of using low salinity polymer, in the areas of clay swelling, polymer shear sensitivity, mixing and adsorption. The paper concludes that low-salinity polymer flooding can significantly improve existing and anticipated polymer flooding projects by reducing polymer volumes and/or increasing oil recovery. Low-salinity polymer flooding provides opportunities to apply polymer flooding in high-salinity and high-temperature reservoirs, for which polymer flooding with produced or formation water would be technically unfeasible or uneconomic.

The Development of a Workflow to Improve Predictive Capability of Low Salinity Response

Low Salinity Waterflooding (LSF) is an emerging improved oil recovery (IOR) technology that has been shown to work in a number of cases, while sometimes – unexpectedly – no incremental oil production is observed. Industry has not yet reached consensus on the mechanism behind LSF, which precludes effective screening and prioritization of LSF candidate fields. In this paper a workflow is introduced that improves the way fields are screened for their LSF potential. It employs closely interlinked experiments and modeling work from the molecular scale to the macroscopic Darcy scale, thereby closing gaps that previously impeded the predictability of the low salinity effect. The new workflow is based on the notion that wettability is a surface phenomenon. Elucidation of the low salinity mechanism should thus not be based on bulk measurements, but rather on the characterization of surface compositions and forces. The main insights that follow from this work are:  Application of successful LSF leads to a wettability modification towards more water-wet, which is consistently observed at the atomic scale and at the core scale;  The surface alterations that occur during LSF correlate with macroscopic observations such as oil recovery from core plugs;  The time scales involved in wettability modification towards a more water-wet state can easily be long enough to lead to false negatives in common SCAL experiments; It is demonstrated that double layer expansion (DLE) is likely behind the low salinity mechanism, as processes involving cation exchange are expected to only occur long after breakthrough of the low salinity bank. Even though the workflow has been developed for LSF in sandstones, it is also being employed for LSF in carbonates. The fundamental insight that surface properties dominate the response does not only impact how LSF research and related SCAL experiments are being conducted, but impacts all other EOR processes relying on interfacial phenomena, as well as oil field science in general.