IMAT DP 

“Offshore”, when used in relation to hydrocarbons, refers to operations undertaken at, or under the, sea in association with an oil, natural gas or condensate field that is under the seabed, or to activities carried out in relation to such a field. Offshore is part of the upstream sector of the oil and gas industry.

Offshore activities include searching for potential underground crude oil and natural gas reservoirs and accumulations, the drilling of exploratory wells, and subsequently drilling and operating the wells that recover and bring the crude oil and/or natural gas to the surface.

Offshore exploration is performed with a variety of DP ships, floating drilling units, drillships, semi-submersible installations and jack-up installations.

DP systems have become more sophisticated and complicated, as well as more reliable.

Computer technology has developed rapidly and some vessels have been upgraded twice

with new DP control systems. Position reference systems and other peripherals are also improving and redundancy is provided on all vessels designed to conduct higher-risk operations.

At the surface (either on the seabed or above water) offshore facilities are designed, constructed, commissioned and operated to process and treat the hydrocarbon oil and gas. Permanent oil and gas installations and plant include subsea wellheads and flowlines, offshore platforms and tethered floating installations. Other facilities include storage vessels, tanker ships, and pipelines to transport hydrocarbons onshore for further treatment and distribution.

There are various types of installation used in the development of offshore oil and gas fields and subsea facilities, these include: fixed platforms, compliant towers, semi-submersible platforms, jack-up installations, floating production systems, tension-leg platforms, gravity-based structure and spar platforms.

Dynamic positioning (DP) is a rapidly maturing technology, having been born of necessity as a result of the increasing demands of the rapidly expanding oil and gas exploration industry in the 1960s and early 1970s.

The demands of the offshore oil and gas industry have brought about a whole new set of requirements. Further to this, the more recent moves into deeper waters and harsh environment locations, together with the requirement to consider more environmental-friendly methods has brought about great development in the area of Dynamic Positioning techniques and technology.

The first vessel to fulfil the accepted definition of DP was the “Eureka”, of 1961, designed and engineered by Howard Shatto. This vessel was fitted with an analogue control system of very basic type, interfaced with a taut wire reference. Equipped with steerable thrusters fore and aft in addition to her main propulsion, this vessel was of about 450 tons displacement and length 130 feet.

It is interesting to note the diversity of vessel types and functions using DP, and the way that, during the

past twenty years, this has encompassed many functions unrelated to the offshore oil and

gas industries. Operation with Dp ship is not limited to only to oil and gas industry but other conventional marine operations have found benefit in using DP system, example: Passenger ships, yacht, tankers,naval ship, Heavy-Lift Vessels, Crane Barge or Crane Vessel, ice breakers…..etc etc

A list of activities executed by DP vessels would include the following:

• exploration drilling (core sampling)
• production drilling
• diver support
• pipelay (rigid and flexible pipe)
• cable lay and repair
• multi-role
• accommodation or “flotel” services
• hydrographic survey
• pre- or post-operational survey
• wreck survey, salvage and removal
• dredging
• rockdumping (pipeline protection)
• subsea installation
• lifting (topsides and subsea)
• well stimulation and workover
• platform supply
• shuttle tanker offtake

Floating production (with or without storage)

• heavy lift cargo transport
• passenger cruises
• mine countermeasures
• oceanographical research/coring
• seabed mining

DP is also used in

• rocket launch platform positioning
• repair/maintenance support to military vessels
• ship-to-ship transfer and
• manoeuvring conventional vessels

• Vessel is fully self-propelled; no tugs are required at any stage of the operation
• Setting-up on location is quick and easy
• Vessel is very manoeuvrable
• Rapid response to weather changes is possible (weather vane)
• Rapid response to changes in the requirements of the operation
• Versatility within system (i.e. track-follow, ROV-follow and other specialist

functions)

• Ability to work in any water depth
• Can complete short tasks more quickly, thus more economically
• Avoidance of risk of damaging seabed hardware from mooring lines and anchors
• Avoidance of cross-mooring with other vessels or fixed platforms
• Can move to new location rapidly (also avoid bad weather)

• High capex
• Can fail to keep position due to equipment failure
• Higher day rates than comparable moored systems
• Higher fuel consumption
• Thrusters are hazards for divers and ROVs
• Can lose the position in extreme weather or in shallow waters and strong tides
• Position control is active and relies on the human operator (as well as equipment)
• Requires more personnel to operate and maintain equipment