The mineral bentonite can be found all over the world. It is formed from weathering volcanic ash. Bentonite is a mixture of various clay minerals. It consists of 60-80% of montmorillonite. Further accompanying minerals can include quartz, mica, feldspar, pyrite or also calcite.
Primarily its exceptional properties are noteworthy: when stirred into water, as it demonstrates a so-called thixotropic reaction. It reacts as a fluid when mechanically stressed, i.e., shaken or stirred. However, it hardens in quiescent condition because its viscosity increases.
The most common use of bentonite is in drilling fluids. The bentonite in the flush fluid lubricates and cools the cutting tools whilst protecting against corrosion. As the drilling fluid generates hydrostatic pressure in the borehole, it hinders fluid and gas penetration. Conveying, sealing, supporting Although these drilling fluids are also used for simple drilling such as wells, their true potential is only demonstrated for demanding tasks such as drilling for oil and natural gas sources and exploration on drilling platforms.
The drilling liquid conveys the drill cuttings to the surface. When the purge pumps have idle periods, the thixotrophy of the bentonite hinders the stone material from dropping back into the drilled shaft.
As a flush fluid, bentonite seals the drilled shaft from water ingress downwards and at the sides of the shaft. The mineral forms a firm sludge cake on the bore wall which provides the borehole with additional stability. The fine bentonite particles enter the bore wall, swell and harden. Depending on the constitution of the ground structure, fine and coarse particles are needed.
The requirements of the bentonite particles are not unusual, but nonetheless critical. API 13A “Specification for Drilling Materials” precisely regulates the technical data for the bentonite in the drilling fluid.
A leading manufacturer of drilling grade bentonite in the Middle East supplies oil and gas producers worldwide. Since 2005, he has been using a NEUMAN & ESSER grinding system for bentonite grinding. The bentonite manufacturer selection was made for a cyclone configuration with a PM 20U4 pendulum mill and an SDR radial classifier 1200 for coarse grinding from 15–25% > 63 μm.
Frank Verreck, Area Sales Manager at NEUMAN & ESSER explains: “The arguments in favor of this investment were this system’s high throughput performance of nearly 18 t/h and reliable reproducibility of the product fineness as well as the outstanding selectivity. That was important for the customer. The system can be used for highly precise setting of the particle sizes, enabling precise predictions of the properties of the drilling fluid. This rules out unpleasant surprises at the oil and gas producers.”
What finally convinced the Middle East bentonite manufacturer of our mills and classifier systems was their impressive wear protection provided by the mill. The impurities in bentonite cause increased stress, attrition and wear and tear in the mill. Nonetheless, the abrasive feed material does little to harm the mill. All the components of the grinding system are designed to be robust and wear resistant.
