Drilling Fluid

Mud is the lifeblood of drilling — one of the most critical factors in bringing a project to a successful conclusion. Preparing drilling fluid is therefore a science in itself. Its main ingredients are water and bentonite, but polymers are often added to obtain the required properties. Drilling fluid has six main functions:

1 – It carries the cuttings out of the bore

A bentonite-water mix has a density of 1.2–1.5 g/cm³. The soil particles ground by the cutters are suspended in the fluid and, thanks to its flowing consistency, carried out of the bore at the entry and exit points. This soil-laden mud is screened in recycling units and the cleaned fluid is returned to the system. The particles left on the screen carry extremely valuable information about the ground; the mud to be prepared and the operations to be applied are shaped by what these samples reveal.

Cracks and leak paths in the ground fill with bentonite after a while and an impermeable layer forms, which is essential for uninterrupted mud circulation. At the same time this process fills the cracks and consolidates the ground — a kind of ground rehabilitation.

2 – It keeps the bore stable

The bore wall is plastered by the fluid delivered under pressure. But like shotcrete in tunnel construction this is only temporary support; what really stabilises the bore is that it is full of fluid. The internal pressure of the drilling fluid overcomes the ground's tendency to collapse and the bore stays open.

3 – It provides hydraulic cutting

Fluid jetted into the ground under pressure disturbs and softens it, which makes the work of the mechanical cutters easier.

4 – It stops the equipment overheating

The friction of the bits against the ground generates heat that overheats the bits and the electronic locating devices inside them — an unwanted situation; the more sensitive electronics stop working above 50 °C. The drilling fluid absorbs this unwanted frictional heat and keeps the tools within their working temperature range.

5 – It lets the pipe be pulled in without damage

The bore, full of fluid specially prepared from an analysis of the ground, acts as a mud bath for the pipe to be installed and lets it be floated in. Friction between pipe and ground is reduced and the pipe is protected from damage.