Exploring Rocks, Minerals, and Petroleum with Thin Section Preparation

The primary function of exploration is to gather pertinent data required to capitalize on the most favorable opportunities offered by various areas. To obtain high-quality samples for the direct measurement of reservoir and rock properties, coring is regarded as the most effective method.

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Most core samples are procured by drilling with specialized drills into a substance such as sediment or rock utilizing a hollow steel tube, known as a core drill. These core samples are subjected to Core Analysis to acquire detailed petrophysical data.

The core samples can also be prepared as thin sections to analyze the rock samples acquired from drilling and to study the rock properties and their relationship with oil and gas reservoirs.

Thin sections offer geologists the opportunity to scrutinize the pore structures, grain size, and orientation of the rocks, thereby providing valuable insight into the permeability and porosity of the reservoir rocks and the possibility of oil and gas accumulation.

To prepare thin sections, a thin sliver of rock is sliced from the sample with a diamond saw and ground optically flat. It is then placed on a glass slide and further ground smooth using progressively finer abrasive grit until it is reduced to a thickness of only 30 μm.

The technique employed in this process involves the use of the Michel-Lévy interference color chart. In general, quartz is utilized as a gauge to determine the thickness since it is one of the most abundant minerals.

When inserted between two polarizing filters that are positioned at right angles to each other, the optical characteristics of the minerals in the thin section cause a change in the color and intensity of the light observed by the viewer.

Different minerals possess unique optical properties; thus, most rock-forming minerals can be easily distinguished. For instance, plagioclase is a clear mineral that exhibits multiple parallel twinning planes. On the other hand, the large blue-green minerals are clinopyroxene with some exsolution of orthopyroxene.

Recommended Equipment for Thin Section Preparation

The ‘KemTech Geo’ represents a precision machine for cutting and grinding thin sections of petrographic and rock samples, capable of performing both processes with speed and accuracy.  

On the cutting module, the slide-mounted specimen is fixed on a holder via vacuum and sectioned up to a thickness of 0.5mm. Water cooling during cutting avoids deformation and heat degradation.

On the grinding module, the grind position can be adjusted, with an encoder displaying the grinding position on the HMI to 0.001 mm resolution, ensuring high precision.

The ‘KemTech III Thin Section Lapping Machine’ is specifically designed to lap and polish thin sections mounted on glass slides to a thickness of 30 microns.

The integrated peristaltic dispenser allows for metered dosing of conventional and/or diamond abrasives, which are applied to the lapping plate to achieve the desired results.

The Kemet Lift-Off Disc system offers a rapid and efficient means of switching between the lapping and polishing stages of the process. The Kemet line of Geological sample preparation equipment is capable of accommodating both high and low-volume production.

Preparing thin sections requires highly specialized equipment and skills as the specimen is extremely thin, generally around 30 microns, for observations with Polarizing Microscopes with transmitted light.

In conclusion, thin sections play a vital role in the exploration of minerals and petroleum, providing valuable insights into the properties and characteristics of rocks and minerals. This information is instrumental in enabling geologists to make informed decisions regarding mineral and petroleum exploration.

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This information has been sourced, reviewed and adapted from materials provided by Kemet International Ltd.

For more information on this source, please visit Kemet International Ltd.

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