Page 35 - Handbook Of Multiphase Flow Assurance

Systematic approach to solving flow assurance problems 29

Deepwater production
Deepwater reservoirs tend to be at pressure higher than bubble point thus undersaturated
and can be pre-salt or subsalt. In addition to the above problems, this adds the problems of
asphaltene deposition in flowlines and deepwater wells. High salt content in produced water
may also affect the potential for scale deposition and limit the types of chemicals which may be
brought in contact with produced water without forcing salt to precipitate out of the water as
scale.
Both onshore and subsea production of oil and gas experience flow assurance issues. The
key distinction between the two is the remoteness of subsea equipment. The remoteness of
deepwater fields makes fixing any issues much more complex subsea, requiring the devel-
opment and use of new technologies and significantly more planning in the project develop-
ment stage not unlike a space station. Attempts to design one piece of equipment and to build
many have mostly been uneconomic because the reservoirs and fluids vary from well to well
and from zone to zone. However, subsea tree pressure ratings have become standardized in
5000 psi increments.
Flow assurance as a discipline started with the needs of subsea production. With the ad-
vent of subsea and then deepwater production hydraulic restrictions to flow such as liquid
holdup began to affect production causing flow instabilities. Currently the horizontal wells
experience similar flow instability and may benefit from the experience accumulated in sub-
sea production.

Systematic approach to solving flow assurance problems

The knowledge of all possible flow assurance issues and their interdependence may help
correctly identify and treat a problem.
Many other aspects of flow assurance exist that are not listed above among threats such
as flow performance of various artificial lift methods, performance of various restriction pre-
vention and blockage remediation technologies, multiphase boosting, controlling high fluid
temperature and these will be discussed further.
Some of the flow assurance threats may appear in any location of the production system:
from reservoir pores and production well perforations to topsides or surface process equip-
ment to export or water injection pipelines and injection well perforations.
These threats are known to happen onshore or offshore, in surface or topsides lines, in
fluid separation process equipment or LNG liquefaction process, flares or any other location
where conditions allow any of these threats to appear.
Temperature, pressure and fluid composition dictate where one or more of these threats
will appear. Therefore it is common to overlay curves showing where each threat may appear
(known as phase boundaries) on the Pressure-Temperature chart showing where vapor and
liquid coexist (known as a phase diagram or a phase map).
The phase diagram may be regarded by a practicing engineer as a map. The more detailed
and accurate is the knowledge about fluid and environment properties, the better flow assur-
ance strategy may be developed using that map. Flow assurance analysis may rely on very lit-
tle knowledge, utilizing rules of thumb or common perceptions about flow assurance threats