Page 233 - Gas Wettability of Reservoir Rock Surfaces with Porous Media

Application of Gas Wettability CHAPTER 6 217

declines, and the injection pressure grows, which does not satisfy the require-
ment of oilfield injections, while significantly affecting the production of the
corresponding wells. To solve this technical problem, oilfield enterprises
reduce the pressure and increase the injection rate.
Currently, the main measures for reducing pressure and increasing injection
adopted in China and overseas are acidification and fracturing conducted on
water wells and adding chemical agents, including clay inhibitors and bacteri-
cides, etc. However, these measures still don’t overcome the problems exposed
during the injection process in low- and extra-low-permeability reservoirs.
Also, the cost of improving the quality of injected water with chemical agents
is higher. For example, when acidifying and fracturing wells, the injection
pressure is greatly decreased and the injection quantity is increased signifi-
cantly, but the period of effectiveness is short lived. Hence, the injection pres-
sure increases again to much higher values and the quantity injected decreases
to extremely low values, or even to zero.
Based on development trends in China and overseas, Buckley and Leverett
knew the importance of altering the wettability of rock surfaces in water injec-
tion reservoirs during water injection as early as 1941. Later, several researchers
studied the effects of wettability on capillary pressure, relative permeability,
initial oil saturation, residual oil saturation, electrical property of oil reservoirs,
and increasing production of oil and gas wells, and some increase has been
observed.
In 1998, Yan Jienian’s research with natural cores showed that when the wetta-
bility of core surfaces in reservoirs was altered unfavorably, the water injection
recovery decreased by more than 40%. In 2004, Wu Jiangping et al. studied
the water injection process, and the effects of bacteria and suspended solids in
injected water, on the wettability of reservoir rocks. In 2005, He Haifeng et al.
studied the influence of injected water on the wettability of reservoir rocks
and obtained the key factors affecting wettability. In 2006, Sun Zhiguo et al.
applied polysilicic nanomaterial to water injection in low-permeability reser-
voirs, which had an increasing injection effect. In 2008, Sun Renyuan et al.
studied the inhibition of swelling in polysilicic nanomaterials as compared to
clay minerals. In 2006, He Hongpu et al. studied the development of water-
injection of surfactants improving low-permeability reservoirs. Experimental
results indicated that appropriate surfactants decreased the injection pressure
in low-permeability reservoirs by 26.6%. They also showed that there was an
increase in oil-displacing efficiency by 0.7%, and the overall relative perme-
ability of oil and water phases was elevated. In 2006, Cheng Yamin et al.
realized that pressure decreased when there was an increase in water-injection
in low- and extra-low-permeability reservoirs. This was possible due to the
synergistic effects of nanomaterials and surfactants used in the preparation of
water-based nano-polysilicon emulsion through evenly dispersed super-
hydrophobic, nano-polysilicon kernels on the water surface, with a com-
pounded surfactant like super-hydrophobic nano-poly emulsion as the