Page 282 - Enhanced Oil Recovery in Shale and Tight Reservoirs

EOR mechanisms of wettability alteration and its comparison with IFT 259

Looyestijn and Hofman (2006) found that the quantitative NMR wetta-
bility index I w shows a good agreement with the USBM index, as shown in
Fig. 9.32.
Liu and Sheng (2019) used the NMR technique to study the effect of
surfactant on wettability alteration. The cores were initially saturated with
oil. Heavy water imbibed into the cores. Since heavy water did not have
NMR signal but oil had some signal strength, the NMR signal amplitude
decreased as more heavy water imbibed. Fig. 9.33 shows the NMR ampli-
tude at different imbibition time for heavy water and the heavy oil of
different surfactants at two surfactant concentrations of 0.01% and 0.1%.
The following observations can be made.
First, those subfigures all show that the cores have two T 2 peaks, first one
representing small radius pores, and the second large radius pores. The sub-
figure a shows that heavy water could hardly imbibe the small pores; as more
heavy oil imbibed into large pores, more oil with NMR signal was displaced
out, and the T 2 amplitude decreased with time.
The subfigures b and c show the T 2 amplitude when heavy water with
surfactant IAE at 0.01% and 0.1% imbibed into the cores, respectively.
Because the surfactant could change the wettability from oil-wet to

Figure 9.32 Comparison of NMR wettability index and USBM index (Looyestijn and
Hofman, 2006).