Page 107 - Gas Wettability of Reservoir Rock Surfaces with Porous Media

Gas-wetting Alteration Agent and Gas-wetting CHAPTER 3 91

Table 3.5 Effect of Fe 31 on Gas Wettability Alteration
31
Fe Concentration (mg/L) 0 100 500 1000 5000 10000 15000 20000
Contact angle ( ) Brine 138 137 32 30 66 79 107 129

N-decane 79 40 10 0 0 0 0 0

Table 3.6 Effect of Temperature on Gas Wettability Alteration
Temperature ( C) 20 40 60 80

Contact angle ( ) Brine 133 132 138 132
N-decane 93 83 77 60

31
It can be seen from Table 3.5 that when the concentration of Fe is very low
31
(500 mg/L), gas wettability is greatly weakened. As the concentration of Fe
increases, the contact angle of core surface to water gradually increases and
hydrophobocity is somewhat recovered. However, oil is spread out on the
core with strong oil-wetting, and has not recovered. It was observed that the
core surface treated with Fe 31 turns yellowish-brown, and the surface was
unevenly treated. As the concentration of Fe 31 increases, the color of core sur-
face gradually becomes lighter. This is because high concentration of
Fe 31 solution develops colloids, which affects the absorption of Fe 31 on the
rock surface, and Fe 31 with higher concentration develops sediments, which
prevents the absorption of Fe 31 on the rock surface. It is concluded that the
existence of Fe 31 is really not conducive to the alteration of gas wettability of
the core, and Fe 31 content must be tested before conducting actual operations.

3.1.3.2 EFFECT OF TEMPERATURE ON GAS WETTABILITY
The core was treated with different methods at different temperatures, and the
gas wettability of the treated core was measured, as shown in Table 3.6.
It can be seen from Table 3.6 that when the temperature is increased from
20 Cto80 C, the hydrophobicity of the core remains essentially unchanged.

Wettability of the core caused by oil is somewhat increased; however, the
degree of increase is small. When the temperature is increased to 80 C, the

contact angle to oil is reduced from 93 to 60 degrees, and it is still intermedi-
ate gas-wetting state. Thus, this method can be used to prepare a gas-wetting
core at a high temperature of 80 C.

3.1.3.3 EFFECT OF PH VALUE OF TREATMENT SOLUTIONS ON GAS
WETTABILITY
The pH value of the treatment solution was adjusted and the same treatment
method for the core was used, following which the gas wettability of the trea-
ted core was measured, as shown in Table 3.7.