Description

The most distinctive feature of an oil or gas drilling operation is the drilling rig or "drilling rig". Simply put, this is basically the rig that operates the drilling tool and drives the whole thing.

Drilling for oil or gas is done with a bit attached to a series of drill pipes called the "drill string". The bit is driven into the earth while rotating, crushing the rock.
In "traditional" drilling, the entire drillstring rotates. For this purpose, in the middle of the drill floor is the "rotary table", which is brought into rotary motion during drilling. One lowers the drillstring through the opening in the centre of this rotary table. The rotary motion is transferred to the drillstring by a hexagonal tube; called a "take-away rod" or "kelly". Each time, a new drill pipe is screwed onto the previous one, making the drilling go deeper and deeper.

Nowadays, there are drilling systems, in which the only rotary motion is transmitted to the chisel. This is then no longer done by the rotary table in the drilling floor but by a turbine just above the chisel. The drill string itself then hangs stationary.
The drilling speed is controlled both by the rotational speed of the chisel and by the weight on the chisel. To do the latter, the lower drill pipes are extra thick and heavy. These extra-heavy pipes are called "heavy rods" or "drill collars".

Because the drill bit is wider than the drill pipe, an annular space is created between the drill pipe and the wall of the borehole.
During drilling, a mixture of water, special types of clay and chemicals is pumped down through the hollow tube column. This rinse or "mud" flows back up through the space between the drill pipes and the wall of the borehole. This cools down the drill bit, transports the stone dust to the surface, more or less plugs up the walls of the borehole and - very importantly - the weight of the mud keeps the well pressure under control.
Already during drilling, the mud is maintained at surface quality. For this purpose - among other things - drilling cuttings are continuously removed from the cuttings. The drill cuttings give the indication of the composition of the drilled layers

When the bit becomes so blunt that it needs to be changed, all drill pipes are pulled out of the borehole. After replacing the bit, they are lowered back into the borehole. Such an operation is called 'round trip' and is a time-consuming and heavy job for the drilling staff. For a 2000-metre well, the round trip often needs to be repeated up to 100 times.

At the drilling rig, which we visit, the "round-trip" operations are highly automated. This not only saves time but also requires a much lighter physical effort from the people.

An oil or gas well cannot just be drilled all at once but must be done in stages

Location

NAM location Witten (near Assen)

Organiser

Northern Region

Name and contact details for information

Further information from Anne-Marie Oudejans at the e-mail address below.

amoudejans@planet.nl