Page 78 - Gas Wettability of Reservoir Rock Surfaces with Porous Media

62 Gas Wettability of Reservoir Rock Surfaces with Porous Media

In the gas-liquid-solid system, the solid/gas interface energy and solid/liquid
interface energy uniformly contributes to the three wettability types of the sys-
tem in the effect form of A. The greater γ SG is, the smaller γ SL is, and the
greater γ SG 2 γ SL is, the more it contributes to wettability. The contribution of
the liquid surface energy to the three wettability processes vary; bigger γ LG is
good for adhesional wetting, smaller γ LG makes for spreading, and the size of
γ LG has no bearing on soaking.
Whether it is adhesional wetting, soaking, or spreading, changes in interface
include disappearance of solid/gas interfaces and generation of solid/liquid
interfaces, spontaneous progress conditions of various wetting types can be
expressed with work of adhesion A. The greater the work of adhesion A, the
stronger the ability of liquid wetting the solid surface and the weaker the gas
wettability is. For example, A directly reflects ability of liquid to replace gas on
a solid surface during the soaking process.
In addition, the involved wetting type is determined theoretically. Whether
wetting preceded is determined when the value of the relevant interface energy
is known, and the required wetting effect can be reached through changing
corresponding interface energy. However, in practice, in the three wetting types
involving gas/liquid/solid, only γ can be easily measured. Thus it is really
LG
difficult to determine the wetting type by various spontaneous progress condi-
tions of above wetting types.

In conclusion, it is necessary to discuss the relationship of gas wettability of
the solid surface and the surface free energy, work of adhesion, and free energy
on the liquid surface (interface) in the solid-liquid-gas system. It is also neces-
sary to study the effect of free energy on the solid surface and that of liquid
surface (interface) on gas wettability.

2.4.2 Effect of Surface (Interface) Free Energy on Gas
Wettability
2.4.2.1 THEORETICAL STUDY OF THE EFFECT OF SURFACE (INTERFACE)
FREE ENERGY ON GAS WETTABILITY
2.4.2.1.1 Studying Influence of Surface (Interface) Free Energy
on Gas Wettability by Sessile Drop Method
1. Theoretical study of the effect of free energy of solid surface on gas wettability
With regard to solid phase, when fluidity of atoms and molecules on the
surface in the gas-liquid-solid system is weak, the ability of gas to wet a solid
surface is related to the surface free energy of the solid. In the air, Owens two--
fluid process model can be used to establish the relationship between surface
free energy of the solid and contact angles of the liquid.

Surface free energy calculated with Owens two-fluid process [33]:
d
γ 5 γ 1 γ P s (2.19)
s
s