An Experimental Study of the Influence of the Preflush Salinity on Enhanced Oil Recovery Using Silica-Based Nanofluids

Tola Sreu,Ronald Nguele,Yuichi Sugai,Kyuro Sasaki

doi:10.3390/en14216922

Abstract

The underlying effect of preflush salinity and silica nanofluid (Si-NF) on oil production is examined. The influence of salinity on the stability of Si-NFs is studied. A series of sand-pack floodings evaluating oil production was conducted at different concentrations of preflush salinity (0 to 4 wt.%), followed by the injection of a Si-NF (0.5 wt.%) at the trail of which postflush water was injected. The effluent water and solids were collected and analyzed using X-ray fluorescence (XRF). Interfacial tension (IFT) and contact angle measurements were conducted on the Si-NF in the presence of salinity to confirm the effect. The Si-NF became unstable and formed precipitate in the presence of salinity. The sand-pack flooding showed that when the preflush salinity was increased, the displacement efficiency (ED) using the Si-NF and postflush injection was increased (ED = 44%). The XRF of the precipitated effluent revealed that the preflush salinity and Si-NF caused mineral leaching, which triggered pore clogging. The IFT value reduced from 13.3 to 8.2 mN/m, and the wettability was altered to be more strongly water-wet when the salinity increased. The primary mechanisms of oil recovery using the Si-NF after preflush salinity is attributed mainly to the clogging mechanism. This clogging helps block the high-perm area, shift the fluid flow to the oil-trapped zone, and free the oil out. Other contribution mechanisms are IFT reduction and wettability alteration.

Highlights

silica oxide nanofluid (Si-NF) started to precipitate from day 2, and the amount of sedimentation reached
Si-NF started to precipitate from day 2, and the amount of sedimentation reached the maximum on day 3
In the control experiment, we found a minor change in the contact angle when salt was added into the Si-NF

Summary

Introduction

Up to 75% of oil in place remains underground at the end of primary and secondary oil production, with a significant portion trapped within the narrow pore throats. This is because the capillary forces which keep the oil droplets attached to the rock surface are so strong that neither the natural energy of the oil-bearing matrix (primary production) nor the injection of water and/or gas (secondary production) can overcome them. These capillary forces are subsequent to the interactions between the surface charges of the formation rock and the polar groups of the stranded oil [1]

Methods

Results

Conclusion