Page 26 - Gas Wettability of Reservoir Rock Surfaces with Porous Media

10 Gas Wettability of Reservoir Rock Surfaces with Porous Media

In 2011, Li Kewen et al. [22], conducted experiments on the effects of gas-wet
alternation on water blockage in condensate reservoirs. They cemented the
core of artificial sandstone into a double-layer core with epoxy resin. The
upper layers with low-porosity and low-permeability simulated gas reservoirs,
and those with high-porosity and high-permeability at the bottom simulated
the bottom aquifer. The study evaluated the influence of gas-wet alternation
on the water breakthrough time and water flow of the gas reservoirs with self-
designed experimental facilities. Experimental results indicate that when the
wettability of reservoir rocks transforms into preferential gas-wet state, water
breakthrough time is delayed, gas recovery without water increases, and water
intrusion into the gas reservoir decreases.

1.2.2 Research Status of Gas Wettability in China
Research on gas wettability in China started relatively late. It gradually turned
into the study of “gas wettability” from the concept of “neutral-wet” or “inter-
mediate-wet.” It is generally believed that the wettability of rock can be distin-
guished based on the CA of water on the solid surface, θ. Normally, when
θ , 75 degrees, it is called hydrophilic or water-wet; when 75 degrees
# θ , 105 degrees, it becomes neutral wettability; and when θ $ 105 degrees,
it becomes oleophilic or oil-wet.
In 2005, Wang Fuhua [23,24] conducted an analysis on effects of wettability
on oil and gas drilling and developing and proposed that the drilling and
completion fluids do not only meet the requirements of normal practice of
drilling and reservoir protection, but also improve the productivity of oil and
gas wells. They developed a MMH dual polymer drilling fluid system, which
makes the surface of reservoir rocks neutral wet when exposed to fluids or its
filtrate. Field application indicates that the system possesses special rheological
properties, has excellent lubrication, and ensures borehole wall stability, as
well as other significant functions for protecting reservoirs and enhancing oil
recovery. Successful application of this technique may enhance oil recovery by
4%-10%. Wang Fuhua holds that intermediate wettability plays an important
role in oil and gas drilling and development engineering.
1. Intermediate wettability improves the stability of drilling fluid: The wet-
tability of solid grain surface in drilling fluid affects the type and stabil-
ity of emulsified drilling fluid. Normally, solid grains with strong water-
wet and strong oil-wet surfaces are present in the wetting liquid sepa-
rately, and solid grains with intermediate-wet surface are present at the
interface of oil and water.
2. Intermediate wettability is favorable in decreasing friction in drilling tools
and improving the penetration rate: Starting with drill antimud packs,
PDC drill surface is processed with a fluoropolymer to make the wettabil-
ity of the drill surface intermediate or oil-wet. The average penetration
rate can be increased by more than double during mudstone drilling.