Drilling fluids (also drilling mud or English drilling mud ) are liquids that are pumped through the borehole when drilling . There are two basic types of drilling fluids - water-based and oil-based drilling fluids.
A drilling fluid is usually a bentonite- water mixture, which is processed into a suspension using a high-speed special mixer. Aids, usually polymers , are also added to the suspension for targeted control of the rheological properties . To increase the density, bentonite can be replaced by heavy spar ( barium sulfate ).
Drilling fluids are mainly used to stabilize a borehole, to clean the bottom of the borehole and to remove the drilled soil material ( cuttings ).
In addition, they dissipate the considerable frictional heat generated on the drill bit and thus cool and lubricate the drilling tool. In addition, they reduce the frictional resistance for drill bits and rotating drill rods and dampen their vibrations.
Flushing fulfills an important task in determining inflows (oil, gas and water) from the drilled rock formation and in controlling the formation pressures . The density of the drilling fluid is based on the drilling depth and the expected formation pressures. If the hydrostatic pressure of the drilling column ( mud pressure ), which is dependent on the density of the drilling fluid, is lower than the formation pressure of the rock drilled deep down, gas or liquid ingress into the borehole and eruptions of borehole fluids and gases, oils or water (blowout ) come. On the other hand, if the mud pressure is too high, the surrounding rock can be torn open and mud can be injected into the rock. These mud losses are also to be avoided as they can lead to borehole instabilities.
By adding additives to drilling fluids, formation damage can be prevented by building up a good filter cake or B. prevent absorption of filtrate by the formation.
The drilling fluid is sucked in from the mud tanks by the mud pumps and transported through the drill rods at high pressure. If an underground drill motor is installed in the boom, this is partly driven by the flush. The mud then exits the drill bit at high speed and carries the cuttings through the annulus to the surface. On the surface, the drilling fluid is through various systems - such as E.g .: desander , desilter , degasser , shaking sieve and decanter - processed and re-entered into the rinsing tanks.
- Hans-Joachim Bayer, HDD Practice Handbook: Terms and bandwidth of HDD, HDD machines and accessories, practical reports, HDD market partner, Essen: Vulkan-Verl., 2005, p. 17
- Glossary on drilling fluid on Heidelbergcement.com
- The procedure ( page no longer available , search in web archives ) Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. on Stadt-Zürich.ch
- Peter Hatzsch: Tiefbohrtechnik , Enke, Stuttgart 1991, ISBN 3-432-99511-3 , pp. 59-61