Page 176 - Gas Wettability of Reservoir Rock Surfaces with Porous Media

160 Gas Wettability of Reservoir Rock Surfaces with Porous Media

unidirectional self-oil-adsorption and unidirectional self-water-adsorption of
cores that are treated by the gas-wetting alteration agent of the same concen-
tration are compared, and it is found that unidirectional self-oil-adsorption
and unidirectional self-water-adsorption present the following features.
1. Unidirectional self-adsorption gas recovery decreases gradually;
2. Speed of self-adsorption liquid reduces gradually, and then increases
when balance is achieved;
3. Gas recovery of unidirectional self-oil-adsorption of cores is higher than
that of unidirectional self-water-adsorption;
4. Speed of unidirectional self-oil-adsorption is higher than that of unidi-
rectional self-water-adsorption;
5. For the core treated by gas-wetting alteration agent of same concentra-
tion, the gas wettability of gas-oil-rock system is weaker than that of
gas-water-rock system.

4.4.3 Reverse Imbibition Process of Cores
4.4.3.1 EXPERIMENTAL PROCEDURE OF REVERSE
SELF-ADSORPTION OF CORES
For the same group of samples (four core columns and two core pieces) treated
by gas-wetting alteration agent solutions of same concentration, the bubble cap-
ture test method of gas/water and gas-oil systems, and self-water-adsorption and
self-oil-adsorption were carried out. The remaining two core columns were used
for experimenting with self-water-adsorption and reverse self-oil-adsorption. The
difference between reverse self-adsorption experiment and one-way self-adsorp-
tion experiment is that the reverse self-adsorption experiment requires the entire
core column to be sunk into the self-adsorption liquid phase.
During the experiment, the liquid seeps into the cores. So, the gas in the cores
is displaced and core mass increases. When the core mass doesn’t change any
longer, the core is taken out and the water or oil attached to the surface is
removed and weighed immediately. The core mass at this moment is recorded
as M water or M oil . When the cores are vacuumed and saturated with water or
0
0
oil, they are weighed again and the masses are recorded as Mv water or Mv oil .
The saturation of reverse self-adsorption captured gas calculated with the for-
mula (4.13) and formula (4.14) is as follows:

Mv water 2 M 0 water
Water 2 gas 2 rock system: S 0 5 3 100% (4.13)
gas-water ρ water V
Mv oil 2 M 0 oil
Oil 2 gas 2 rock system: S 0 5 3 100% (4.14)
gas-oil
ρ V
oil
In the formula, S gas-water —saturation of one-way reverse self-water-adsorption
0
captured gas, %. S gas-oil —saturation of one-way reverse self-oil-adsorption cap-
0
tured gas, %.