core, rotary coring, core samples

C is for Conventional Coring | Rotary Coring

By: Gillian Hogarth | 0 Comment

Mineral exploration Conventional Coring Ayrshire

What it is?

Conventional rotary coring is the method of taking a core sample from the ground using the rotary drilling technique.

Why you would do it?

Rotary coring provides essential information for exploration and evaluation of ground strata. Coring allows us to collect an undisturbed near perfect sample of the ground in areas of interest to the client.

Conventional rotary coring is a better way of sampling the ground than more common techniques such as destructive drilling i.e. open Hole and down the Hole hammer (DTH)

When would you do it?

We were asked by a client to drill exploration boreholes as they required a better understanding of the coal measures ground strata/ rock formation, in this specific area. The boreholes were shallow 30m maximum so the most cost effective way of carrying out the project was to use a conventional coring system with air mist. Air mist was used as the water supply on the site was scares and the rock was known to be badly broken.  We used a PDC core bit combined with a 412 core barrel which performed great and produced a perfect 74.6mm core sample.

Who would need this?

This type of work is regularly requested by companies involved in infrastructure projects such as construction, pile design, tunnelling and geological interest (mineral exploration) it also is widely used by government bodies such as BGS, EA and water authorities.

How would you do it?

To carry out a successful core run to obtain a good quality core sample there are many factor to consider. First of all you need to look at the ground of which you are trying to recover. Once this information is gathered you need to piece together the best coring system to carry out the works.

The core barrel comes in a variety of sizes, ranging from an average of 75.7mm to 146.3mm these core barrel dimensions produce a core size of around 47.7mm to 115.7mm. Smaller or larger sizes can be obtained for more specialist projects.

Core bits come in a wide variety of specification ranging from the PDC for the softer formations through to diamond impregnated for the hardest formations and can work with water or air mist flush medium.

These core bits normally come with a serial code. The codes allow us to identify the different strengths. Note you should always seek advice from the bits supplier in regards to suitability for bit strength to ground formation.

 

Scott Burt from Geotechnical Engineering Services a trading division of Drilcorp Ltd commented that “A wireline coring system maybe more efficient and cost effective when reaching greater depths as conventional coring becomes slower.”

Coring is an art and is not something you can learn overnight. There are a lot of key factors in carrying out a successful core run. Rotation speed, torque pressure, weight on bit, bit selection and flush pressures all have a key role in producing a Class A core sample. These key factors are used in different ways depending on ground formation all this considered it’s the driller reactions to ground changes within the core runs that really helps towards a good quality 100% recovered core ( a driller is only as good as his tool rig selection is very important hydraulic control is a must when trying to recover softer materials as a driller you never stop learning when it comes to coring technics )”