Page 213 - Gas Wettability of Reservoir Rock Surfaces with Porous Media

Application of Gas Wettability CHAPTER 6 197

filtrate invades a reservoir, it chemically bonds with the surface of porous
media and has multipoint-connected stable adsorption with the rock surface.
The surface wettability is translated into oleophobic and hydrophobic low-
energy surfaces effectively, thereby reducing liquid-phase adhesion and dam-
age from water-blocks.

6.1.2.1 DAMAGE CAUSED BY WATER-BLOCK MECHANISM
Assuming the pore structure of reservoirs is regarded as a capillary bundle,
when liquid droplets or bubbles pass through the pore-throat, a severe Jamin
effect is generated, and the deformation resistance that needs to be overcomed
is [23]:

1 1
ΔP 5 2σ 2
R 2 R 1
In the formula,
ΔP: differetial pressure of curved interface, mN.
σ-oil/gas: tension of water interface, mN/m.
R 1 and R 2 : refer to the radius of curvature of the liquid film formed by two
phases, respectively, m.
It can be seen from the above formula that the capillary pressure is related to
the pore-throat radius of the porous media. The average pore radius of low
pore and low permeability reservoirs is significantly smaller than that of
medium and high permeability reservoirs, where the capillary effect is signifi-
cant. Therefore, water-block is more severe.

Based on the Young-Laplace equation, P c 5 2σ cos θ=r, capillary pressure P c is
reduced by decreasing the interfacial tension σ of gas and water, and increas-
ing the contact angle θ or pore-throat radius r. The frequently used water-block
resistance agent in drilling fluids reduces gas and water interfacial tension to a
small extent, and the surface tension of filtrates is normally greater than
30 mN/m. While during drilling, it is difficult to enlarge the pore-throat radius
of reservoirs. The pore-throat radius can remain undiminished to the highest
extent, by enhancing the inhibition capability of filtrates. Increasing the con-
tact angle can greatly decrease capillary pressure, and when the contact angle
is 90 degrees, the capillary pressure is zero.

6.1.2.2 PROCEDURE FOR PREPARING FCS-08
The purified acrylate monomers used earlier, fluorinated acrylate monomers
and anionic emulsifiers, were slowly dripped into 170 mL of deionized water
to conduct emulsification pretreatment until there was an even emulsion.
Then, it was transferred to a four-mouth flask mounted with a motorized
stirrer, condenser pipes, and nitrogen input device. The temperature of the
water bath was set at 80 C, and the initiator dripped for 3 hours to create a

reaction. The temperature of the emulsion obtained was reduced naturally to