Page 169 - Gas Wettability of Reservoir Rock Surfaces with Porous Media

Effect of Gas Wettability on the Surface Properties CHAPTER 4 153

Table 4.17 Comparison of Conductivity of Cores With Different
Wettabilities

Item Water-wetting Cores Gas-wetting
Cores
Maximum gas saturation 74.85% 82.94%
Conductive path Continuous water, Water film, isolated
water film water
Conductive path under low gas Water film Water film
saturation
Conductive path under high gas Water film, air Isolated water, air
saturation
Effect of simulated formation Wetting phase Nonwetting phase
water

4.3.2.2 COMPARISON OF CONDUCTIVITY OF CORES WITH
DIFFERENT WETTABILITIES
The distinction in electrical conductivity of water-wetting cores and gas-
wetting cores is displayed in Table 4.17. The difference in conductivity of dif-
ferent cores is caused by a change in the surface chemical property of two
kinds of rock pores. The gas-wetting alteration agent is the fluorinated acrylate
polymer featuring extremely low surface energy and very strong adhesive abil-
ity. When it forms a film on the core surface, it reduces the surface energy of
the cores sharply, realizes hydrophobic and oleophobic gas-wetting features,
and affects the distribution of fluids in the pore, and ultimately, it affects
conductivity.

From Table 4.17, it can be seen that in irreducible water saturation, the electri-
cal resistance of water-wetting and gas-wetting cores is very high. However,
their conductive paths are entirely different. In water-wetting cores with low
water saturation, water-phase films are formed on the pore surfaces. The water
film is the conductive path. Its electrical resistance is relatively high for cross-
sectional areas of these water films that are small and long. In gas-wetting
rocks with extremely low gas saturation, the nonwetting-phase formation
water gets into or is located in dendritic pores in the form of isolated water,
and does not contribute to conductivity.

4.4 IMBIBITION PROCESS OF ROCKS
Imbibition is the process whereby under the effect of capillary force, wetting
phase is spontaneously imbibed into porous media to replace the nonwetting
phase [23]. When the imbibing direction of the wetting phase is the same as
the discharge direction of the nonwetting phase, it is called unidirection imbi-
bition (also known as consequent imbibition). When the imbibing direction
of the wetting phase is opposite to the discharge direction of the nonwetting