Drilling fluid pumps
The mineral bentonite is found all over the world. Bentonite is formed through the weathering of volcanic ash. It is a mixture of various clay minerals and consists of 60–80 per cent montmorillonite. Other minerals found alongside bentonite include quartz, mica, feldspar, pyrite and calcite.
The unusual properties of bentonite are particularly noteworthy: when stirred into water, it exhibits what is known as thixotropic behaviour. It behaves like a liquid when subjected to mechanical stress, such as being shaken or stirred. When left undisturbed, however, bentonite solidifies because its viscosity – that is, its thickness – increases.
Use of bentonite in drilling fluids
The bentonite in the drilling fluid lubricates and cools the cutting tools and protects against corrosion. By generating hydrostatic pressure in the borehole, the drilling fluid prevents the ingress of liquids and gases.
The drilling fluid transports the cuttings to the surface. When the circulation pumps are stopped, the thixotropy of the bentonite prevents the rock material from sinking back into the borehole.
Used as drilling fluid, bentonite seals the borehole against water. It prevents water ingress from below and from the sides. The mineral bentonite forms a solid mud cake on the borehole wall, which further stabilises the borehole. The fine bentonite particles penetrate the borehole wall, swell and solidify. Depending on the nature of the soil, fine and coarse particles are required.
These pumps from DYNASET have been specially developed for pumping drilling fluids.
