Pore-Scale X-ray Imaging of Wetting Alteration and Oil Redistribution during Low-Salinity Flooding of Berea Sandstone

Abstract

Observations over a range of scales show that lowering the salinity of injected water can alter the wetting state of a rock, making it more water-wet. However, there remains a poor understanding of how this alteration affects the distribution of fluids over the pore and pore-network scale and how this wetting alteration leads to oil recovery. In this work, we observe how oil and brine redistribute in the pores of rocks in response to low-salinity flooding. We use X-ray μ-CT scanning to image tertiary lowsalinity waterflooding in two Berea sandstone cores. The wetting state of one core is altered with exposure to crude oil. We characterize the wetting state of both samples using imagery of fluid−solid fractional wetting and pore occupancy analysis. In the unaltered rock, oil saturation, fractional mineral area covered by oil, and size distribution of oil-filled pores remain constant between high-salinity flooding and subsequent low-salinity floods. In contrast, in the altered sample, we observe a shift in the mineral area covered by oil after low-salinity flooding toward decreasing coverage, consistent with a change to a less oil-wetting state. This change is also reflected in the observed variation in fluid pore occupancy. The wetting alteration results in the redistribution of 22% of oil within the rock, but an additional recovery of just three percentage points. The success of low-salinity waterflooding depends on both a wetting alteration and a pore structure, which facilitates the production of mobilized oil.

Pore-scale processes in tertiary low salinity waterflooding in a carbonate rock: Micro-dispersions, water film growth, and wettability change

“…X-ray imaging has been previously used to study LSW [49][50][51][52][53], with only a few studies on carbonate rocks [27,[54][55][56]. Using micro-CT imaging, Qin et al [57] compared high and low salinity flooding at reservoir conditions.…”

X-ray Imaging of Clathrate Hydrates as Gas Storage Materials: Absorption Contrast of Low-Density and Low-Absorption Materials Using Energy-Dependent X-ray Computed Tomography

“…Likewise, it has strong potential for applications in material sciences, such as salt or mineral hydration, and geological phenomena, such as fluid migration in fractures within shale . In addition to acquiring knowledge on these materials, this work has implications for industrial applications of non-destructive observation , and may enable numerical simulation of various physical processes in digital objects. − …”

Pore-Scale Investigation of the Ion-Tuned Water Effect on the Surface Properties of Limestone Reservoirs

“…This was done to ensure the visibility of the water droplet in oil. Literature has shown that the effect of the modified salinity brines on oil recovery can be hindered, unless the initial oil-wet conditions are achieved . That is why, in each case, the acidity of the mixture was adjusted to a TAN of 1.5 mg KOH/g by using stearic acid to ensure that oil-wet conditions are established during the aging process. , The interfacial tension (IFT) of each mixture with seawater has been tested using the pendant drop method and is presented on Figure .…”