Drilling rig selection is crucial. Offshore drilling is always a technical challenge. As the hunt for offshore hydrocarbons moves to further more remote and deeper waters, the technical challenge ever increases.
Offshore drilling for the exploration and production of hydrocarbons, both oil and gas will always start with an engineer making a selection of drill rig.
The type of drilling rig used will be dependent on a number of factors:
- Geographical location of the well
- Depth of water the rig will operate
- Depth to be drilled
- Heat and pressure of the well.
Types of Drilling Rigs
Once these factors have been considered, the engineer from the offshore oil and gas exploration and production (EP) company will traditionally hire the services of a specialised drilling company, and normally their drilling rig. Drilling rigs can come in the form of:
- A Jack-up Rig
- A semi-submersible Rig
- A Drill Ship
Each type of drilling rig will have its pros and cons:
Jack-up Drilling Rig
These kind of drilling rigs are more often the older drilling rigs in operation.
They typically operate in shallower water, depths of 250ft (76m) – 400ft (122m) and drill up to depths of 35,000ft (10,670m).
They are normally not self propelled and require tow from tugs to move from one drill location to the next. On longer moves, the services of a heavy lift ship may be required, although this is an expensive option. Jack-up drilling rigs are typically the cheapest drilling rigs to hire.
Semi-submersibles or semis as they are more often known are typically newer and seen as a next generation of drilling rig compared to a jack-up.
Through design, they are regarded as true deep water drilling rigs, typically drilling in water depths up to 7000ft (2130m) and drilling to depths of 35,000ft (10,670m), although the latest generation of semi-submersible drill rigs can operate at greater depths than this.
Like jack-up rigs, they too are not normally self propelled and also need tugs to be moved them from one drill site to the next or a heavy lift ship on longer duration moves. Unlike jack-up rigs however, they also have the added expense of having to employ anchor handling ships to help secure them in place to the sea floor.
Due to a semi-submersible’s design, they are more stable under tow, however the services of a heavy lift ship would still likely be sought if moving greater distances i.e. the Gulf of Mexico to Europe.
Some of the most modern generation of semi drilling rigs have been built with dynamic positioning systems, allowing them to work without the need for anchors.
The latest generation of drillships are seen as ultra-deepwater, and through the ever increasing need to reach hydrocarbons in tougher more remote locations, drillships are often seen as the only viable option.
Because of this, much of the latest ground breaking technology will go into a new build drillship. The benefit of using drillships over semis is the manoeuvrability, as it is able to not only move from one drill site to the next under its own steam but, at great distance and speed- typically 14knts as opposed to 4knts of a semi under tow.
This would take weeks off of a typical journey from the Americas to Europe or vice versa, equating to less operational down time. Also due to natural design, size and therefore storage, drillships are also able to stay fully self-sufficient for much greater periods of time.
For example in 2012, Stena Drilling launched the Stena IceMax, the world’s first drillship capable of drilling in ultra-deepwater within arctic conditions. As arctic and more harsh and remote hydrocarbon reserves become more viable, the likely hood of further harsh environment, self sufficient drillships being launched remains strong.
Fixed Platform Drilling
Drilling operations taking place in shallow waters on older fixed platforms will often have their own drilling facilities.
In this case the exploration and production company will traditionally hire in the services of a drilling company to conduct both maintenance activates and drilling operations on their fixed platform drilling rig. This arrangement is most common within the North Sea.Last updated on 05:35PM - 22/08/16