2 research outputs found
Accurate Determination of the CO<sub>2</sub>–Brine Interfacial Tension Using Graphical Alternating Conditional Expectation
A newly
developed CO<sub>2</sub>–brine interfacial tension
(IFT) correlation based on the alternating condition expectation (ACE)
algorithm has been successfully proposed to more accurately estimate
the CO<sub>2</sub>–brine IFT for a wide range of reservoir
pressure, temperature, formation water salinity and injected gas composition.
The new CO<sub>2</sub>–brine correlation is expressed as a
function of reservoir pressure, temperature, monovalent cation molalities
(Na<sup>+</sup> and K<sup>+</sup>), bivalent cation molalities (Ca<sup>2+</sup> and Mg<sup>2+</sup>), N<sub>2</sub> mole fraction and CH<sub>4</sub> mole fraction in injected gas. This prediction model is originated
from a CO<sub>2</sub>–brine IFT database from the literature
that covers 1609 CO<sub>2</sub>–brine IFT data for pure and
impure CO<sub>2</sub> streams. To test the validity and accuracy of
the developed CO<sub>2</sub>–brine IFT model, the entire dataset
was divided into two groups: a training database consisting of 805
points and a testing dataset consisting of 804 points, which was arbitrarily
selected from the total database. To further examine its predicted
capacity, the new CO<sub>2</sub>–brine IFT correlation is validated
with four commonly used pure CO<sub>2</sub>–pure water IFT
correlations in the literature, it is found that the new CO<sub>2</sub>–brine IFT correlation provides the comprehensive and accurate
reproduction of the literature pure CO<sub>2</sub>–pure water
IFT data with an average absolute relative error (% AARE) of 12.45%
and standard deviation (% SD) of 18.57%, respectively. In addition,
the newly developed CO<sub>2</sub>–brine IFT correlation results
in the accurate prediction of the CO<sub>2</sub>–brine IFT
with a % AARE of 10.19% and % SD of 13.16%, respectively, compared
to two CO<sub>2</sub>–brine IFT correlations. Furthermore,
sensitivity analysis was performed based on the Spearman correlation
coefficients (rank correlation coefficients). The major factor influenced
on the CO<sub>2</sub>–brine IFT is reservoir pressure, which
has a major negative impact on the CO<sub>2</sub>–brine IFT.
In contrast, the effects of CO<sub>2</sub> impurities and salt components
in the water on the CO<sub>2</sub>–brine IFT are in the following
order in terms of their positive impact: bivalent cation molalities
(Ca<sup>2+</sup> and Mg<sup>2+</sup>), CH<sub>4</sub>, N<sub>2</sub>, and monovalent cation molalities (Na<sup>+</sup> and K<sup>+</sup>)
Interaction between Surfactants and SiO<sub>2</sub> Nanoparticles in Multiphase Foam and Its Plugging Ability
To
improve the stability of foam fluids, SiO<sub>2</sub> nanoparticles
and trace amount of Gemini cationic surfactant were combined with
the main foaming agent, nonionic surfactant, to form a tricomponent
multiphase foam. The stability of the multiphase foam was assessed
through two parameters of half-life time and dilational modulus. The
interaction between surfactants and nanoparticles were studied though
surface tension, adsorption amount, and ζ potential measurement.
The effects of saline ions and temperature on foam stability were
also investigated. The plugging ability of the tricomponent multiphase
foam was assessed using a sandpack model. The optimized tricomponent
multiphase foam was 10 times more stable than corresponding foam without
nanoparticles in terms of half-life time and also resisted to saline
and temperature to a certain degree because the adsorption of nanoparticles
at the interface improved the mechanic strength of foam film. The
tricomponent multiphase foam showed more excellent plugging ability
in porous media than foam without nanoparticles during flooding. The
adsorption of cationic surfactant not only changed the surface hydrophobicity
of the SiO<sub>2</sub> nanoparticles, but also promoted the adsorption
of APG molecules. Combined the results of Gemini C<sub>12</sub>C<sub>3</sub>C<sub>12</sub>Br<sub>2</sub> replaced by CTAB or SDS, and
C<sub>12</sub>C<sub>3</sub>C<sub>12</sub>Br<sub>2</sub>/SiO<sub>2</sub> replaced by pretreated partially hydrophobic SiO<sub>2</sub> nanoparticle
(H15), it is deduced that the in situ surface modification by cationic
adsorption to a suitable hydrophobicity was a key step in multiphase
stability. Compared with the pretreated partially hydrophobic SiO<sub>2</sub> nanoparticle, more SiO<sub>2</sub> nanoparticles were distributed
at the air/liquid interface and utilized effectively in the tricomponent
multiphase foam