Relative Permeability Measurements to Quantify the Low Salinity Flooding Effect at Field Scale

摘要

In the last few years it has become widely accepted in the industry that Low Salinity Flooding (LSF) works by changing reservoir wettability towards a more water-wet state. Most of the published experimental data to quantify the LSF effect focus on comparing ultimate recovery of low salinity (LS) and high salinity (HS) waterflooding experiments either in secondary and/or tertiary mode. A wide range in incremental oil recovery is reported in the literature, from 0 to more than 20% of OIIP. To assess the potential of LSF and to enable upscaling of the LSF benefit to reservoir scale, the relative permeability curves for HS and LS brine should be determined. In only a few published cases, the experimental data was interpreted using numerical simulations to derive relative permeability curves for both low and high salinity water. So far all of the LSF corefloods reported in the literature have been done using the unsteady state (USS) coreflooding method. Unsteady state corefloods are appropriate in evaluating the LSF potential qualitatively and to de-risk for potential formation damage due to clay swelling. However, USS corefloods can only measure the relative permeability curves after water breakthrough and they are sensitive to heterogeneities in the core samples. The steady state (SS) coreflood method, on the other hand, is less sensitive to sample heterogeneity and can measure the relative permeability curves over a wide saturation range. In this paper we will present the experimental procedures and data measured during SS LSF core floods using less homogeneous core samples from a sandstone reservoir. Details of the experimental procedures to quantify the LSF effect were published earlier (Masalmeh et al. 2014). In this study a combination of USS and SS coreflooding experiments using in-situ saturation monitoring were performed, accompanied by spontaneous imbibition tests. Numerical simulation of the experimental data was used to extract the LS and HS relative permeability curves. While the Amott and USS experiments unequivocally showed a very clear positive LSF effect with no formation damage, SS corefloods tests were performed to better quantify the effect. The result of the tests, - to our knowledge - are the first to be reported in the industry for LSF on real rock material, allow extracting reliable relative permeabilities and enable upscaling of the LSF effect to field scale.