Page 180 - Gas Wettability of Reservoir Rock Surfaces with Porous Media

164 Gas Wettability of Reservoir Rock Surfaces with Porous Media

Theoretical analysis and experiments confirm that preferential liquid-wetting
of porous rock surface in gas reservoirs can be translated into preferential
gas-wetting, which has a significant effect on maintenance or increase capac-
ity in gas reservoirs or condensate gas reservoirs. Recent gas wettability
focuses mainly on qualitative studies with macro experiments on core
displacement, etc. To observe the effect of gas wettability on the fluid flow
process in pores, this chapter conducted microscopic visualization study of
gas wettability, adopting single and straight capillaries, respectively, and
etched-glass network model. It follows the flow interface of fluids, and
studies the influence of gas wettability on the displacing front and fluid
distribution. Finally, the effects of gas wettability on fluid permeability
and oil recovery were studied based on core displacement experiments of
different gas wettability.

5.1 GAS WETTABILITY OF SINGLE-STRAIGHT
CAPILLARY
Single-straight capillaries are the simplest micro model for wettability stud-
ies, and have been used earlier to study fluid fluid solid interactions. This
model enables effective and intuitive observation of wettability. Under quasi-
static conditions, micro experiments on mutual displacement by gas water
systems and gas oil systems, respectively, were conducted in single-straight
capillaries, to study the influence of gas wettability on displacement and
fluid distribution.

5.1.1 Water-Displacing-Gas in Capillaries
5.1.1.1 EXPERIMENT THEORY
5.1.1.1.1 Evaluation of Gas Wettability in Single-straight
Capillaries
When a single-straight capillary is treated with a fluorocarbon polymer gas-
wetting alteration agent solution of different concentrations, it presents differ-
ent gas wettability. To evaluate gas wettability of the inner wall surface of
capillaries intuitively and accurately, the sessile drop method was adopted,
along with the water-displacing-gas process under quasistatic conditions. This
is because wettability evaluation by sessile drop method is the process of water
displacing air on the solid surface, which is similar to the process of water dis-
placing gas under quasistatic conditions. As the sessile drop method requires
level, smooth, and even test substrates, quartz slide surfaces made of the same
materials as quartz capillaries, and treated with gas-wetting alteration agent
solutions of same concentrations, were used to represent the gas wettability of
the inner wall surfaces of the capillary.