Page 286 - Enhanced Oil Recovery in Shale and Tight Reservoirs

EOR mechanisms of wettability alteration and its comparison with IFT 263

Figure 9.35 Interfacial tensions and wetting angles at equilibrium.

where the subscripts s, w,and o represent solid phase, water phase, and oil
phase, respectively. According to Eqs. (9.49) and (9.50), cosq ws ¼ ecos q os .
So, the oil contact angle q os ¼ p q ws . For a water-wet rock, the

water-wetting angle is less than 90 , and the oil-wetting angle is higher

than 90 .Therefore,we have Conclusion 1:
In a water-oil-solid system (a liquid-liquid-solid system), a water-wetting
angle or an oil-wetting angle on a core can be used to determine the
wettability.
In an air-liquid-solid system, the preceding two equations become

s as s ws
cosq wsa ¼ (9.51)
s wa
s as s os
cosq osa ¼ (9.52)
s oa
by replacing o by a and replacing w by a, respectively in those two equations.
The subscript “a” is added to represent the presence of air. Generally, a rock
is more liquid-wet than gas-wet. Thus, both cosq wsa and cosq osa are positive.
From the preceding two equations, we have

s as s ws s as s os s as ðs oa s wa Þ s ws s oa þ s wa s os
cosq wsa cosq osa ¼ ¼
s wa s oa s wa s oa

s as ðs oa s wa Þ s ws ðs oa s wa Þþ s wa ðs os s ws Þ
¼
s wa s oa
ðs oa s wa Þðs as s ws Þþ s wa ðs os s ws Þ
¼ :
s wa s oa
(9.53)