In
CO2 flooding, the dissolution of CO2 in produced
fluid may change the stability of crude oil emulsion, thereby affecting
the design/operation of the gathering pipeline and oil–water
separation. The purpose of this study is to investigate the stability
change of crude oil emulsion and its mechanisms after the dissolution
of CO2. The stability of the CO2-dissolved crude
oil emulsions is determined with a self-made apparatus. The mechanisms
of the stability change are uncovered from interfacial properties
and bulk viscosity. It is found that the stability of the crude oil
emulsions is visibly reduced with an increasing dissolved quantity
of CO2. This is partly attributed to the fact that dissolved-state
CO2 can lessen the interfacial dilational modulus and increase
the loss angle markedly, thus lowering the structural strength and
elasticity of the interface. Meanwhile, the dissolution of CO2 in crude oil can reduce its viscosity, resulting in easier
collision of droplets. In view of these experimental results, it can
be inferred that the gathering and subsequent dewatering of produced
liquid become easier after CO2 flooding is applied in oil
fields.
As
a kind of enhanced oil recovery technology, CO2 flooding
is being employed more and more widely in oil fields. In CO2 flooding produced fluid, crude oil, water, and CO2 are
transported simultaneously, and part of the fluid may be emulsified.
The dissolving of CO2 may affect the kinetic stability
of the emulsion formed in the mixed fluid and change the effective
viscosity of the fluid as well. In this study, the solubility of CO2 in the water-in-crude oil emulsion was measured, and the
variation of water/crude oil interfacial viscoelasticity was probed
after the dissolution of CO2, so the influence of CO2 dissolution on emulsion stability and its mechanism could
be uncovered. After the stability of the mixed fluid was verified,
a viscosity measuring equipment was designed according to the principle
of energy dissipation. With the help of this equipment, the effects
of the CO2 solution pressure, temperature, oil/water ratio,
and shear intensity on the effective viscosity of the mixed fluid
were explored. The results reveal that the CO2 dissolution
worsens the stability of the water-in-crude oil emulsion. The mechanism
lies in the structural weakening of the interface by the action of
the dissolved CO2 besides its viscosity-reducing effect.
The effective viscosity of the CO2–water–crude
oil mixed fluid decreases exponentially with the increasing CO2 solution pressure. Moreover, the viscosity reduction effect
of the dissolved CO2 on the mixed fluid is more pronounced
than on the pure crude oil.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.