Instructions for drilling operations

The hydrocarbon prospects, the objects of exploratory drilling, are deeply buried. These prospects are often at depths of 2,000 to 4,000 m, sometimes as much as 6,000m (the equivalent of 20 Eiffel Towers!). To get there a hole has to be drilled. The derrick (or mast) is the support for the drilling system. It is a metallic tower thirty or so meters high, which is used to introduce the drilling pipes vertically. At the end of the first drilling tube, is the drilling tool, in general a tri-cone (trepan) equipped with teeth or very hard steel pastilles.

The drill bit has very hard steel teeth or inserts.

The trepan attacks the rock, a little by applying pressure, but above all by turning at high speed: it pulverises the rock into small pieces. As the drill bites deeper into the substratum, a new nine meter drill pipe is added. It is screwed to the preceding one. And so the well progresses. The set of drill pipes with its trepan is called the drill train. For very hard rocks, the teeth of the trepans are not strong enough. Tools are then used that are made out of a single block set with diamonds; nothing resists them!

To avoid collapse of the hole, a large hollow steel cylinder is inserted along its full length (like the drill pipes, it is fed down in segments and screwed one to another). It is the tubing. Once the tubing is installed, the drilling restarts, but the diameter of the hole has become smaller: the tubing that has just been inserted occupies space and reduces the initial diameter of the hole. Thus a drill hole of 50 cm diameter at the start can be reduced to 20 cm after the insertion of several tubes.