What is the difference between an oil rig and an oil platform?

You often hear reference to oil rigs and platforms, and sometimes people will say, that wasn't a platform, it was a rig; or the opposite. So why do the terms cause so much confusion? As usual, it is because there is some crossover in the terminology. But if you understand the underlying mechanics, you will be much clearer.

The short answer:
~ A platform is a permanent structure fixed to the seabed.
~ A rig is moveable platform, which is moved into place by barges and then secured in each location temporarily.

The long answer:
1. Platforms
Firstly, let's look at platforms.  They have three main parts; the jacket (the legs which are secured in the sea/ocean), the deck (a large flat surface area), and the modules (crew quarter blocks, drilling aparatus, storage containers etc. which are fixed to the deck).

A basic fixed platform is fixed in a permanent position on the seabed with anchors (as above) and is not intended to move. It provides a long-term, stable facility from which a lot of oil can be produced because it can host so much equipment and crew. As a result, they tend to be build in locations with known long-term oil deposits.

However, there are other types of platform which are similar. Compliant Towers (below) are like fixed platforms, but have more narrow, flexible jackets, meaning they move with the wind and waves. There are also tension-leg, subsea and SPAR varieties, as well as numerous other iterations and combinations of the above.

2. Rigs
Generally rig refers to a jackup rig. This is a moveable platform with very tall legs, which can be jacked up and down, meaning it can be towed into place and then lowers its legs into the seabed, creating a stable but temporary platform from which drilling or other work can take place. They tend to be used for smaller oil deposits and shallower water.

So why the confusion?

Well, the thing is, as you'll see from the above, jackup rigs, are moveable platforms, so you might see an incident where, for example, their platform is damaged. This would lead to references to 'the platform'. In the same way, fixed drilling platforms will have equipment onboard called the drill rig (the gear which actually drills into the seabed). So the word rig could be used in reference to a platform sometimes too.

A Brief Guide to Tugs and Towing

Tugboats are small but very powerful vessels which were developed to specifically assist other vessels (by pushing or towing them from a to b, moving them around in canals or harbours, fire fighting etc.). 


Today they are more advanced than ever and can perform a multitude of tasks but the basic construction of a simple harbour tug remains broadly as the following diagram. You will notice a towage rope for assisting other vessels and heavy 360o fendering (the tyres)

TERMINOLOGY
- A tug is always a boat, and not a ship. The craft began their lives as relatively small vessels and so will forever be categorized as such, even though today many are very large vessels.
- A tug tows other vessels using a towage or towing line (when a piece of rope is used) or a wire (when some form of metal rope is used).

TYPES



General Harbour Tugs - The most common form, they perform a multitude of general assistance tasks around ports and harbours. Generally small and do not venture far from the harbour or port limits.


SDMs (Ship Docking Modules) - These are very specialised little tugs used to help moor other small vessels, normally yachts, in tight marinas. Because they need to be so versatile and gentle with their charge they look a little bit like padded floating saucers.


Ocean-Going Tugs - These are much larger tugs used to tow vessels over a long journey in potentially hazardous seas.


AHTS (Anchor Handling Towage Supply) Tugs - These vessels provide support for offshore structures in the energy industries, both old and new. They are specially built to be able to raise huge anchors belonging to offshore rigs, tow vessels and platforms where necessary and carry supplies out to them.

CONTRACTS


For a look at the principal contracts involved in Towage work see this article.