A Discussion of the Low Salinity EOR Potential for a North Sea Sandstone Field

Abstract

AbstractDue to the lack of an exact chemical understanding of the mechanism for enhanced oil recovery by low salinity water flooding in sandstones, predictable EOR effects based on actual reservoir parameters have not been possible to obtain.Recently, we published a new chemical mechanism for the low salinity effect, which is in line with experimental documentation so far. In this paper, the results for low salinity lab experiments related to an offshore field in the North Sea are discussed in relation to the new chemical knowledge. The important reservoir parameters for the actual field are: total clay content 8-16 wt%, crude oil acid and base numbers 0.13 and 0.85 mgKOH/g, respectively, formation water salinity 201 000 ppm, and reservoir temperature 130 °C. The reservoir has been flooded with seawater, and the question is: "Is it possible to increase the oil recovery by injection of diluted seawater as the low saline fluid?" In most cases, the cores were first flooded with formation water in a secondary process followed by diluted seawater, 1600ppm, in a tertiary process. The extra oil recovery varied between 0–6% of OOIP. In light of the newly published mechanism, the results are discussed in terms of: Clay content: type and amountpH: initial and change in pHConcentration gradient in the most active cation, Ca2+Initial water saturation and composition.Effects of aging and flooding temperature.For a given system, the low salinity EOR effect appeared to be strongly linked to the change in pH. Low initial pH, created by the presence of CO2, increased the adsorption of polar components onto clays, which normally will lead to enhanced oil recovery due to the low salinity water flooding effect.