Overview: Offshore Facilities: Construction and Design (February 2007)
Authors: Valenchon Claude 
Published: February 2015

Oilfield operators aim at installing process equipment (e.g., separators) as close as possible to the well. For offshore development, this means installing process equipment on the seabed. After a difficult start more than 30 years ago in the Zakum field, this technology is becoming a reality for a growing number of fields under development.

Since the trial in 1970, the industry has developed equipment and systems for deepwater use, showing the level of reliability expected by operators. Such systems include multiphase pumps, electrical-power transport and distribution, connectors, valves, sensors, and controls, as well as means of installation and specialized tools (e.g., remotely operated vehicles). The relevant competencies to install and operate the subsea equipment successfully also were developed. Components and systems have been tested in laboratories, workshops, and finally the field. The Troll-C pilot in 350 m water depth in the North Sea and the vertical annular separation and pumping system on Marimba in 400 m water depth offshore Brazil have demonstrated that, after several years of operation, these technologies are field proven and can be repaired as needed with state-of-the-art subsea-intervention operations and tools. These pilots finally opened the way to fully industrial applications. Several operators are planning to use subsea processing, primarily to increase oil recovery of an existing field (e.g., Statoil's Tordis field in the North Sea) or to develop a new field by minimizing capital expenditures and increasing oil recovery (e.g., Total's Pazflor field offshore Angola and Shell's Perdido field in the Gulf of Mexico).

To illustrate the diversity of the technologies, the above two new-field subsea systems provide the same basic functions of gas/liquid separation and liquid boosting, but they are based on very different concepts. Total intends to use gravity separators and seabed boosting, whereas Shell chose to use an electrical-submersible-pump and caisson system with direct vertical access from the surface facility.

Deepwater developments seem to be an area of choice for subsea separation, with various problems linked mainly to oil quality, low wellhead pressure, debottlenecking of surface facilities to allow satellite additions, and unlocking of long tiebacks, all of which lead to increased oil recovery and reserves. But one also must not overlook the advantage that subsea-processing technologies could bring to Arctic and other harsh-environment developments.

No doubt the various participants of deepwater developments (i.e., operators; suppliers; and engineering, procurement, construction, and installation contractors) are ready for this new challenge in the offshore industry.

Offshore Facilities: Construction and Design additional reading available at the SPE eLibrary: www.spe.org

SPE 101000 "Managing Structural Integrity for Aging Platform" by N.W. Nichols, Petronas Carigali Sdn. Bhd., et al.

SPE 98489 "Development in Discharges and Emissions From Offshore Installations on the Norwegian Continental Shelf" by B. Jarandsen, Norwegian Oil Industry Assn., et al.

Available at the OTC Library: www.otcnet.org

OTC 18254 "Numerical and Experimental Investigations on Deepwater CALM Buoys—Hydrodynamics Loads," by C. Ricbourg, Principia R.D., et al.