Page 34 - Gas Wettability of Reservoir Rock Surfaces with Porous Media

18 Gas Wettability of Reservoir Rock Surfaces with Porous Media

the yield is increased by more than 10 times, recovery speed is improved sig-
nificantly, and the water cut is almost zero. They believe that the dominant
mechanism of gas-wet alternation for water plugging happens when the wetta-
bility is changed from strong water-wet into neutral gas-wet: The power driv-
ing water towards the bottom of the well is relatively weak, which reduces the
water content, leading to an increase in the yield and recovery speed. Further,
by changing the wettability of rocks, the water cut of horizontal wells can be
controlled, and the purpose of decreasing water and increasing oil yield can be
realized. The research results once more prove that water alternation is a feasi-
ble option for water plugging.

In 2011, Ma Dong et al. [40], based their experimental study of gas injection
production on the gas wettability principle, which states that gas-wet alternation
can change the capillary pressure from gas-displacement resistance into dynamic
pressure in order to improve the efficiency of gas-displacing-oil. N 2 and CO 2
were used as air sources in the experiment, with low permeability cores from
the Changqin oil field, and cationic fluoride (perfluoroalkyl methacrylic acid
copolymer) as the gas-wet alternation agent. They conducted gas-displacing-
water experiment of the core prior to and after gas-wet alternation to study the
effects and enhancement of gas-wet alternation on oil recovery. The experimen-
tal results indicate that the saturation of residual water after gas-wet alternation
decreases, and the recovery caused by CO 2 displacement is higher. However, in
the earlier stages of displacement, the speed of water production caused by N 2
displacement is faster. The above experimental results indicate that gas-wet alter-
nation can improve the recovery of gas-displacing-water.
In 2012, Huang Qiliang et al. [41,42], discussed the possibility of using the
gas-wet alternation method for coal-gas exploration and improving gas extrac-
tion, based on successful research and development of gas-wet alternation
agents. They calculated intermolecular forces in gas-wet alternation agents,
changes in interfacial tension, and the CA of the corresponding three-
component system in the molecular simulation. The gas-wet alternation agent
was synthesized on the basis of molecular simulation, and relevant perfor-
mance parameters including CA were measured. A dynamic prediction method
for gas extraction was being primarily studied. It is believed that the influenc-
ing factors for gas extraction and the dynamic one are mainly permeability,
relative permeability, fracture development degree, and mining measures.
Finally, they discussed the possibility of using gas-wet alternation for improv-
ing gas extraction (coalbed methane). They concluded that gas-wet alternation
theory and technique have better applications future in oil exploration
(including coalbed methane, namely gas), including drilling, completion, acid-
ification, fracturing, water plugging, and improving recovery in gas displace-
ment. For example, adding gas-wet alternation agent in drilling fluids and
completion fluids can reduce the amount of these fluids invading the gas res-
ervoir, so that the damage to strata is relieved. When a gas-wet alternation
agent with a certain concentration is added during the acidification and frac-
turing process, the wettability of rocks near the well bottom or artificial