A Designer Water Process for Offshore Low Salinity and Polymer Flooding Applications

Abstract

Abstract Low salinity water flooding is getting much wider attention in the oil industry since it is highly cost-competitive compared to other conventional EOR methods. Water desalination and hardness removal are the keys to its success for effective oil recovery. However, conventional seawater desalination methods provide almost fresh waters that could be incompatible with resident reservoir clays and hence may not be suitable for direct injection into the reservoir. In this paper, we describe a novel "designer water" desalination scheme that is capable of providing the desired injection water composition to suit the specific formation. Thus, this process could potentially avoid clay-swelling, and at the same time mitigating other critical issues such as reservoir souring and unfavourable wettability modification to more oil-wet state. Selected examples are given to conceptually demonstrate how various water streams generated in the designer water process would help to move the injection water quality point away from the clay flocculation region for different reservoir clay types. Polymer flooding is another promising avenue for low salinity water applications. The use of low salinity water in polymer flooding processes considerably reduces the amount of dosing chemicals required to achieve a target polymer solution viscosity. This favourably impacts chemical procurement, transportation, storage, and handling (mixing and hydration) requirements and operating costs in offshore environments. The effect of injection water salinity on polymer concentration requirements is shown for different polymer solution viscosities. These data indicate about 5-10 times lower consumption of polymer in low salinity water when compared to seawater. As a result, a high-level facility engineering study was performed to assess the cost savings associated with low salinity water in offshore polymer flooding. The study results show that polymer flooding with low salinity water is economically more beneficial compared to seawater polymer flooding. It could be possible to pay out the incremental desalination costs within a 4-year project time frame due to the large savings associated with chemical costs and polymer facilities costs in low salinity polymer flooding. When the reservoir fits the criteria for low salinity flooding, then the additive effect of lower waterflood remaining oil saturation compounds with the benefit of polymer flood improved oil recovery due to better reservoir sweep. This means that low salinity water flooding can synergize well with polymer flooding to drive unit technical cost down and oil recoveries up.