The depression of
the current global oil market makes the majority
of chemical EOR projects worldwide nearly unprofitable, especially
in China. Therefore, economic alternative methods and technologies
must be quickly developed. This proof of concept research evaluates
a chemical flooding method using pre-formed mild O/W emulsions, which
were produced by saponification between a low-cost alkali (NaOH) and
a petroleum acid-rich oil. Our focus was first given to the dynamics
of the saponification with an aim to quantify alkali consumption.
Afterward, the composition of the crude oil before and after the reaction
was characterized using a Fourier transform ion cyclotron resonance
mass spectrometer (FT-ICR MS) to determine the preferred compounds
in saponification. The physiochemical properties of the generated
emulsions were further investigated through direct measurements of
rheology, morphology, particle size distribution, and stability. Particular
attention was placed on the oil displacement mechanisms of the emulsions
at pore level. The results showed that fatty acids, naphthenic acids,
and aromatic acids were clearly partitioned on the FT-ICR MS spectra
of the crude oil, while the C16 and C18 fatty acids (DBE = 1, DBE
represents equivalent double bond number) were predominantly saponified,
which accordingly produced mild O/W emulsions (pH ≈ 7.0). The
viscosity, morphology, and stability of the emulsions were found to
strongly depend on the oil–water ratio. The displacement dynamics
of three stable emulsions observed in a visual micromodel revealed
that the O/W emulsion flooding can enlarge the sweep area and also
notably reduce the residual oil saturation when employed as an EOR
mode. Emulsification/entrainment, blocking, and stripping were three
dominant pore level driving forces for this emulsion flooding. Phase
inverse from O/W to W/O occurred when the emulsion of O/W = 3:7 was
used and finally caused injectivity issue.
The depression of the current global oil market renders the majority of chemical EOR projects worldwide unprofitable, especially in china. Therefore, economic alternative technologies must be quickly developed. This paper evaluated the potential of a smart pre-formed emulsion flooding EOR in Block 9 based on the reaction between alkali and highly acidic crude oil. The static properties and dynamic displacement behaviors of the emulsion were thoroughly investigated. Particular emphasis was placed on the relationship between emulsion stability, droplet particle/pore radius matching, and EOR efficiency. The experimental results showed that the petroleum acids of the crude oil reacted with alkali (NaOH), and producing neutral emulsions (pH≈7.0). The emulsion rheology and morphology were strongly dependent on oil water ratio. From the economic point, the oil/water ratio of 0.5:9.5 was used to prepare two types of O/W emulsions (unstable and stable emulsions) with different particle sizes. The core flooding tests proved that a higher pressure during emulsion injection was generated than that of water injection due to Jiamin effect induced by the dispered oleic phase. As a consequence, the oil recovery factor was further improved by 6-17%. High matching factor and emulsion stability accounted for more significant EOR effect as we observed.
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