Subsea Production Systems
Subsea production system consists of subsea completed well, seabed wellhead, subsea production tree, subsea tie-in to flowline system, and subsea equipment and control facilities to operate the well. It can range in complexity from a single statellite well with a flowline linked to a fixed platform, FPSO (Floating Product, Storage and Offloading), or onshore facilities, to several wells on a template or clustered around a manifold that transfer to a fixed or floating facility or directly to onshore facilities.
As the oil and gas fields move further offshore into deeper water and deeper geological formations in the quest for reserves, the technology of drilling and production has advanced dramatically. Conventional techniques restrict the reservoir characteristics and reserves that can be economically exploited in the deep waters now being explored. The latest subsea technologies have been proven and formed into an engineering system, namely, the subsea production system, which is associated with the overall process and all the equipment involved in drilling, field development, and field operation. The subsea production system consists of the following components:
- Subsea drilling systems;
- Subsea Christmas trees and wellhead systems;
- Umbilical and riser systems;
- Subsea manifolds and jumper systems;
- Tie-in and flowline systems;
- Control systems;
- Subsea installation.
Some subsea production systems are used to extend existing platforms. For example, the geometry and depth of a reservoir may be such that a small section cannot be reached easily from the platform using conventional directional drilling techniques or horizontal wells.
Based on the location of the tree installation, a subsea system can be categorized as a dry tree production system or a wet tree production system. Water depth can also impact subsea field development. For the shallower water depths, limitations on subsea development can result from the height of the subsea structures. Christmas trees and other structures cannot be installed in water depths of less than 30 m ( 100 ft). For subsea development in water depths less than 30 m (100 ft), jacket platforms consisting of dry trees can be used.
The goa of subsea field development is to safely maximize economic gain using the most reliable, safe, and cost-effective solution available at the time. Even though wet well systems are still relatively expensive, their attraction in reducing overall capital expenditures has already been made clear. Subsea tie-backs are becoming popular in the development of new oil and gas reserves in the 21st century. With larger oil and gas discoveries becoming less common, attention has turned to previously untapped, less economically viable discoveries.
In Subsea field development, the following issues should be considered:
- Deepwater or shallow-water development;
- Dry tree or wet tree;
- Stand alone or tie-back development;
- Hydraulic and chemical units;
- Subsea processing;
- Artificial lift methods;
- Facility configurations (i.e., template, well cluster, satellite wells, manifolds).
The subsea system is associated with the overall process and all equipment involved in the arrangement. It is designed in such a way that safety, environment protection, and flow assurance and reliability are taken into consideration for all subsea oil and gas exploitation. Subsea distribution systems consist of a group of products that provide communication between subsea controls and topside controls for all equipment via an umbilical system.
Subsea distribution systems may include, but not be limited to, the following major components:
- Topside umbilical termination assembly (TUTA);
- Subsea accumulator module (SAM);
- Subsea umbilical termination assembly (SUTA), which includes:
- Subsea Distribution assembly (SDA);
- Hydraulic flying leads (HFLs);
- Electric flying leads (EFLs);
- Multiple quick connector (MQC);
- Hydraulic coupler;
- Electrical Connector;
- Logic caps.
The subsea survey for positioning and soil investigation is one of the main activities for subsea field development. As part of the planned field development, a detailed geophysical and geotechnical field development survey together with soil investigation is performed. The purpose of the survey is to identify the potential man-made hazards, natural hazards, and engineering constraints of a proposed subsea field area and pipeline construction; to assess the potential impact on the biological communities; and to determine the seabed and sub-bottom conditions.
- Establishing vertical route profiles, a contour plan, and the seabed's features, particularly any rock outcrops or reefs;
- Obtaining accurate bathymetry, locating all obstructions, and identifying other seabed factors that may affect the development of the selected subsea field area including laying, spanning, and stability of the pipeline;
- Carrying out a geophysical survey of the selected subsea field and route to define the shallow sub-seabed geology;
- Carrying out geotechnical and laboratory resting in order to evaluate precisely the nature and mechanical properties of soils at the selected subsea field area and along the onshore and offshore pipelines and platform locations;
- Locating existing subsea equipment (e.g., manifold, jumper and subsea tree), pipelines, and cables, both operational and redundant, within the survey corridor;
- Determining the type of subsea foundation design that is normally used for subsea field development.
Installation and Vessels
The development of subsea production systems requires specialized subsea equipment. The deployment of such equipment requires specialized and expensive vessels, which need to be equipped with diving equipment for relatively shallow equipment work, and robotic equipment for deeper water depths. Subsea installation refers to the installation of subsea equipment and structures in an offshore environment for the subsea production system. Installation in an offshore environment is a dangerous activity, and heavy lifting is avoided as much as possible. This is achieved fully by subsea equipment and structures that are transmitted to the installation site by installation vessels.
Subsea installation can be divided into two parts: installation of subsea equipment and installation of subsea pipelines and subsea risers. Installation of subsea equipment such as trees and templates can be done by a conventional floating drilling rig, whereas subsea pipelines and subsea risers are installed by an installation barge using S-lay, J-lay, or reel lay. This includes special vessels that can run the trees and rigless installation. Subsea equipment to be installed is categorized based on weight, shapes (volume versus line type), dimensions, and water depth (deep versus shallow).
 C. Haver, Industry and Government Model for Ultra-Deepwater Technology Development, OTC 2008, Topical Luncheon Speech, Houston, 2008.
 C.W. Burleson, Deep Challenge: The True Epic Story or Our Quest for Energy Beneath the Sea, Gulf Publishing Company, Houston, Texas, 1999.
 M. Golan, S. Sangesland, Subsea Production Technology, vol. 1, NTNU (The Norwegian University of Science and Technology), 1992.
 Minerals Management Service, Deepwater Gulf of Mexico 2006: America’s Expanding Frontier, OCS Report, MMS 2006-022, 2006.
 J. Westwood, Deepwater Markets and Game-Changer Technologies, presented at U.S. Department of Transportation 2003, Conference, 2003.
 FMC Corporation, Subsea System, http://www.fmctechnologies.com/en/SubseaSystems.aspx, 2010.
 H.J. Bjerke, Subsea Challenges in Ice-Infested Waters, USA-Norway Arctic Petroleum Technology Workshop, 2009.
 International Standards Organization, Petroleum and Natural Gas Industries-Design and Operation of the Subsea Production Systems, Part 1: General Requirements and Recommendations, ISO, 2005, 13628-1.
 International Standards Organization, Petroleum and Natural Gas Industries-Design and Operation of the Subsea Production Systems, Part 6: Subsea Production Control Systems, ISO, 2000, 13628-6.
 M. Faulk, FMC ManTIS (Manifolds & Tie-in Systems), SUT Subsea Awareness Course, Houston, 2008.
 C. Horn, Flowline Tie-in Presentation, SUT Subsea Seminar, 2008.
 S. Fenton, Subsea Production System Overview, Vetco Gray, Clarion Technical Conferences, Houston, 2008.  P. Collins, Subsea Production Control and Umbilicals, SUT, Subsea Awareness Course, Houston, 2008.