Summary
Before the development of a field, it is worthwhile to determine the
characteristics of crude-oil emulsions. This may be even more important if the
wells are to be equipped with electrical-submersible pumps (ESPs) which can
create a shearing environment resulting in tight emulsions. One such study was
conducted to determine the characteristics of emulsions from a cluster of oil
fields planned for development. The proposed development is to produce from
three fields and several different reservoirs. The central processing facility
(CPF) will process ≈500,000 B/D oil and 50,000 B/D of water. Previous
studies determine the impact of ESP on emulsions and on the ESP design
(horsepower) and the possibility of demulsifier injection downhole. The
emulsion properties are also necessary for the design of central wet crude
handling facilities. A series of emulsion tests was conducted with crudes from
different reservoirs at bottomhole and surface temperatures, range of water
cuts, and shearing conditions. The results are provided in terms of “relative”
tightness of emulsions from different reservoirs. The viscosities of various
emulsions were also determined. The results indicate that demulsifier injection
facilities will be needed at the wet crude handling facilities and possibly in
wells from one reservoir that has a high asphaltenic and viscous crude. This
paper provides a framework of laboratory emulsions studies that can provide
valuable information for the design of CPFs before they are built. This paper
also discusses some practical aspects of demulsifier treatment programs,
including demulsifier selection and optimization and methods to prevent
emulsion problems.
Introduction
An important aspect during oilfield development is the design and operation
of wet crude handling facilities. The crude oil is partially stabilized
(separation of associated gas) and separated from the produced water. The
characteristics of the oil/water mixture are important during the separation
process. The produced water must be separated from the oil, treated, and
disposed properly. The sellable crude oil also must comply with certain product
specifications including the amount of basic sediment and water (BS&W) and
salt.
The incoming oil/water mixture may be loose and the water may separate
easily, or it may be produced in the form of an emulsion. A regular oilfield
emulsion is a dispersion of water droplets in oil. Emulsions can be difficult
to treat and may cause several operational challenges in wet crude handling
facilities and gas/oil separating plants (GOSP). A typical GOSP is shown in
Fig. 1. Emulsions can create high-pressure drops in flowlines, lead to an
increase in demulsifier use, and sometimes cause trips or upsets in wet crude
handling facilities. The problem is usually at its worst during the winter
because of lower surface temperatures. The emulsions must be treatedto remove
the dispersed water and associated inorganic salts to meet crude specifications
for transportation, storage, and export and to reduce corrosion and catalyst
poisoning in downstream-processing facilities.
“Crude-oil emulsions” is a broad area, and several books have been written
on the subject. For in-depth details and further reading on the subject matter,
the reader is directed to the textbooks (Schramm 1992; Sjoblom
2000)1-2 and website addresses (Sjoblom, Kilpatrick, Masliyah,
Wasan, Yarranton) provided in the references.
For the design of a GOSP in a new field, it is important to understand the
type of emulsion it will handle and to measure its characteristics. How is the
field demulsifier treatment program designed? What kind of demulsifier will be
suitable, and what kind of facilities should be included in the design package?
This paper provides an example for one such study that was conducted to
determine the characteristics of emulsions from a cluster of oilfields planned
for development. It also discusses some practical aspects of demulsifier
treatment programs that should be useful for the practicing engineer dealing
with emulsions, either regularly or on a limited basis. A field emulsion
treatment program is discussed and, more importantly, methods to prevent
emulsion problems are highlighted. Finally, practical aspects of demulsifier
selection and optimization are included.
Emulsion Characterization
The focus of the study was to characterize the emulsions from the new fields
in terms of their relative tightness. This particular field development
consisted of three oil fields that were to be developed together and the crude
processed in a CPF (Fig.1). Each field will produce from several different
reservoirs. The properties of these crudes are provided in Table 1.
Crude oil samples were collected from Field A (Arab-A, B, C, Hanifa and
Hadriya reservoirs), Field B (Arab-D and Fadhili reservoirs) and Field C
(Arab-A, B, C, and D reservoirs). None of the fields is on production at
present and the oil samples were collected from shut-in wells at the wellhead.
Some of the samples did not contain any water and the emulsions were simulated
with water collected from the same reservoirs in nearby fields.
© 2007. Society of Petroleum Engineers
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History
- Original manuscript received:
25 June 2006
- Revised manuscript received:
9 November 2006
- Manuscript approved:
20 November 2006
- Version of record:
20 March 2007
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