Waterflooding has long been used as a secondary recovery method both in carbonate and sandstone reservoirs. However, in the mid-’90s the pioneering work by Yildiz and Morrow [1] showed that changing the brine composition can influence the oil recovery. Since then, the injection of so-called smart water with the correct salt composition and salinity has gained a lot of interest. Several groups have studied the mechanisms by which the improved oil recovery is achieved. At first, the research was mainly concentrated on sandstone reservoirs where extra oil recovered from low salinity flooding varied in the range of 5- 30 % of original oil in place [2]. However, several laboratory studies and field tests have confirmed its potential also in carbonate reservoir enhanced oil recovery. There are two main advantages compared to other enhanced oil recovery methods; (1) low cost and (2) less impact on the environment [3].
The underlying mechanism for low salinity flooding is not completely understood but it is related to complex crude oil/brine/rock interactions mostly between injected water and rock surface. For wettability alteration, the activation energy or energy barrier for the chemical reactions needed for wettability improvement to take place is crucial. Reservoir temperature plays an important role because activation energy is dependent on the temperature. Higher than 100 °C temperatures have shown to be more efficient [4].
To study the wettability alteration caused by low salinity water, contact angle measurements have been utilized [3]. In the study of Ding et. al. [3], the contact angles of different brine solutions were measured on the rock surface. To mimic the oil-wet state of the reservoir rock, the surface was aged in mineral oil. The water contact angle after the aging period was measured to range from 121° to 130°. To conduct the measurements with different brine solutions, the rock was immersed into mineral oil and the brine contact angles were measured through the oil phase.
As the smart water flooding happens at reservoir conditions, it is important to take that into account when contact angles are measured. To hear how temperature and pressure can also be considered in contact angle measurements, please watch the webinar by Prof. Xu.
[1] Yildiz, H.O. and Morrow, N.R., Effect of brine composition on recovery of Moutray crude oil by waterflooding, Journal of Petroleum Science and Engineering 14 (1996) 159.
[2] Anjirwala, H., Critical role of wettability alteration in improved oil recovery by low-salinity water in Sandstone rock – A theoretical approach, International journal for innovative research in science and technology 3 (2017) 2349.
[3] Ding, H., et.al., Macro- and Microscopic study of “smart water” flooding in carbonate rocks – An image-based wettability examination, Energy & Fuels (2019) Just accepted manuscript
[4] RezaiDoust, A., et.al., Smart water as Wettability Modifier in Carbonate and Sandstone: A Discussion of similarities/differences in the chemical mechanisms, Energy & Fuels 23 (2009) 4479.
Nanoparticles alone or integrated with conventional enhanced recovery processes have shown promising performance in improving oil recovery.
Studies show the influence of EOR agents on the reservoir rock wettability. Studies are not considering the reservoir conditions i.e. high pressure.
There are three commonly used wettability measurement techniques for oil reservoir characterization; Contact angle, Amott-Harvey, and USBM.
Most commonly used methods to study reservoir wettability are Amott-Harvey, USBM, and sessile drop contact angle.
Carbonate reservoirs are characterized as intermediate to oil- wet. Altering the wettability of the carbonates has been proposed as one of the main mechanisms for enhanced oil recovery.
Different enhanced oil recovery methods are used to alter the wettability of the reservoir rock. To study the wettability alteration at the reservoir conditions, an instrument where the measurements can be done at high pressures and temperatures are needed.
Unconventional oils, such as heavy oil, extra heavy oil, and bitumen, normally exist tightly on host solids such as rocks, sands and clay minerals. Successful liberation of unconventional oil from solids is essential for effective recovery.
In enhanced oil recovery wettability plays an important role as that determines the interactions between the solid (rock) and the liquids in the reservoirs (crude oil, brine). Wettability has been recognized as one of the key parameters controlling the remaining oil-in-place.