Page 12 - Gas Wettability of Reservoir Rock Surfaces with Porous Media

Introduction

Surface wettability of reservoir rocks with porous media is a key factor in con-
trolling fluid flow and distribution in porous media. It is as important as
porosity, permeability, pore structure, and fluid saturation, and is a key charac- xi
teristic of fluid found in reservoir rocks [1]. Buckley [2] was the first to recog-
nize that wettability had a significant impact on water displacement effect, in
1942. Subsequent research over the century related to surface wettability of
reservoir rocks show that wettability of reservoir rocks has a certain influence
on core property analysis, including capillary pressure, relative permeability,
water drive dynamics, electrical properties, adsorption, cation exchange capac-
ity, Zeta potential, expansion, and dispersion, tertiary recovery factor, irreduc-
ible water saturation, and residual oil saturation [3 13].
In general, wettability refers to a liquid’s tendency to extend or adhere to a
solid surface in the presence of an immiscible fluid. In other words, it refers to
the phenomenon of a liquid flowing along a solid surface under molecular
force [1].
In discussing wettability, the study object is a three-phase system of immisci-
ble solid phase, liquid phase, gas phase, or another liquid phase. Wetting
(fluid) and nonwetting phases (other fluid) in two kinds of liquids are always
present, relative to solid phase’s surface. The phase that can spread along a
solid surface is called wetting phase (fluid), while the other phase is called
nonwetting phase (other fluid). In most cases, gas phase is nonwetting phase.
For example, in a water-air-glass system where water can spread on the glass
surface, water is a wetting phase while air is nonwetting phase; that is, water
Preferential wets glass surface. Under special conditions, gas phase can also be
a wetting phase. For example, in a mercury-air-glass system where mercury
cannot spread on a glass surface, mercury is a nonwetting phase while air is a
wetting phase. In this case, air selectively wets the glass surface.
Whether a solid can be wetted by a liquid is always relative to the other gas or liq-
uid phase. If a phase can wet solid phase, the other phase cannot wet solid phase.
We place a bubble, using a dropper, at the bottom of the solid in a liquid, as
shown in Fig. 1. If the liquid selectively wets the solid, the liquid’s contact
0
angle will be less than 90 . Obviously, supplementary angle θ (5180 -θ) can

0
also be taken as the bubble’s contact angle, so θ . 90 . If gas selectively wets

the solid, the liquid’s contact angle will be more than 90 (θ . 90 ), and bub-

0 0
ble’s contact angle will be less than 90 (θ , 90 ). In both cases, θ 1 θ are

equal to 180 .