Summary
Chemical demulsifiers are routinely added in the oil field to effectively
resolve water-in-crude-oil emulsions. As used in the common bottle test,
demulsifiers, in effect, probe or interrogate emulsion stability
strength. Emulsion stability, in turn, is defined by no fewer than three
parameters: water drop, oil dryness, and interface quality. All three
parameters are direct outputs of the bottle test, and, collectively, all three
provide a more complete picture of emulsion stability, as opposed to the use of
any singular parameter.
By selecting a wide variety of demulsifiers and by performing a standardized
bottle test, emulsion stability from a variety of sites can be quantified and
compared. By coupling bottle test results with corresponding crude oil
analytical data, fundamental questions concerning factors governing emulsion
stability can be quantified. The results show that solid content, not
asphaltene content or any other crude oil parameter investigated, is by far the
best single predictor for gauging emulsion stability. Furthermore,
statistical analysis through partition trees shows that emulsion stability is
most aptly described using several crude oil parameters, as opposed to one
single factor.
Introduction
Crude oil characterization remains a challenging proposition. Many
crude oil characterizations are based on a separation scheme [e.g.,
distillation (Speight 1998), chromatography (ASTM D4124 2003; McLean and
Kirkpatrick 1997c), and precipitation (Akbarzadeh et al. 2004)], a bulk
property of the fluid [e.g., viscosity, American Petroleum Inst. (API) gravity,
and surface tension), or a combination of properties. The intent of most
characterizations is to relate some property or group of properties back to the
fluid’s behavior in production or refining. Establishing a valid
cause-and-effect relationship can lead to greater confidence when assessing the
economic and technical risks associated with new projects or modifications to
existing systems.
As related by Hopf (2000), crude oil characterization played a strong role
in the development of organic chemistry. For example, the cage
hydrocarbon adamantine—a classic in skeletal construct—was first isolated in
minute amounts (0.0004%) from petroleum in 1933, 8 years before a synthetic
confirmation. The characterization of crude oil has thus developed, both
one molecule at a time and by groups of molecules. Fractionation into
saturates, aromatics, resins, and asphaltenes (SARA) remains the most common
method for classifying crude oils by groups. A variety of techniques
exist for classifying crude oils by SARA analysis. Two recent advances in
SARA characterization center on the use of high-performance liquid
chromatography (Fan et al. 2002) and infrared and near-infrared spectroscopy
(Aske et al. 2001). The most studied petroleum group is the asphaltene
fraction, which is an ensemble of molecules defined by both solubility and
insolubility properties (Pfeiffer and Saal 1940) and certain general features
regarding structure and atomic composition (Koots and Speight 1975).
Recently, a process for quantifying the overwhelming molecular complexity of
crude oil has been illustrated by high-resolution mass spectroscopy (Marshall
and Rodgers 2004). Such quantifications are providing a fingerprint with which
to compare and contrast crude oils. This technique is quite an
advancement that holds unprecedented potential. While certain atomic
arrangement information is still not possible with mass spectroscopy, the
ability to rapidly amass and store crude oil information for any molecular
parameter holds great promise.
Additionally, Buckley (1999) pointed out that the characterization of crude
oil and asphaltenes in particular is on the basis of not just the output of
laboratory methods, but also by process conditions that influence the
solubility parameter and ultimate fate of the asphaltenes (Wang et al.
2004). Such an operational definition clarifies the need to couple crude
oil properties (i.e., characterizations) with crude oil behavior in the
field. The industrial practice of establishing and managing such critical
relationships ultimately falls under the realm of flow assurance. Flow
assurance can be divided into the deposition of solids (e.g., hydrates, waxes,
asphaltenes, and scales) and disturbed fluid behavior (e.g., foaming and
emulsification) (Fu 2000). The latter of these areas is the focus of this
study.
© 2006. Society of Petroleum Engineers
View full textPDF
(
644 KB
)
History
- Original manuscript received:
14 December 2004
- Revised manuscript received:
30 November 2005
- Manuscript approved:
11 December 2005
- Version of record:
20 August 2006
View Cart
