Rock sampling difficulties

[killswitchengage]

Hi
It happened to me in the past and it may happen for my incoming projects , we had many problems drilling in a rock that caused our core drilling and bits to be damaged . What are the criteria to be respected for the choice of the drilling tools ? if i am right i believe it has to do with the chemical constituents mainly carbon and Tungsten ?

 

[MotorCity]

I know nothing about drilling rock samples, but perhaps your problem could be alleviated by using some sort of drilling fluid or lubricant?

 

[GeoPaveTraffic]

The choice of drill tools is an art. Good drillers maintain a variety of bits and choose their bit based on the materials being drilled.

In no particular order there are three main items that affect rock coring:

1. Cutting material. As you pointed out different material is used for the cutting teeth on core bits including carbide and diamond. Generally any material will cut softer rock, but harder rock generally requires diamond bits.
2. Size of the cutting teeth. In general larger teeth are used to cut softer rock such as most shales since that helps prevent the bit from becoming blocked off. However, if harder rock is encountered the larger teeth can be sheared off.
3. Type of drilling fluid. Usually, water or a bentonite/water mixture is fine for rock coring. When coring rock that tends to swell on contact with water, a polymer drilling fluid is often used to reduce the amount of swell.

Other items such as rotational speed of the bit, size of the equipment, water flow, and down pressure can also dramatically affect coring. In the end, it all comes down to have a good drill company and drill operator.

Mike Lambert

 

[killswitchengage]

Thank you both
GeoPavTraffic you are right advice n°2 is very interesting . Does diamond bits with deep chiseled carvings fair better than flat bits with diamond powder ?

 

[GeoPaveTraffic]

Killswitchengage, It depends on the type of rock being cut. In very hard rock I've seen bits that are almost smooth do very well. In shales, I've seen bits with what looked like pencil erasers sticking out of them used to great effect. The worst conditions are interbedded hard and soft rock. Once saw a very good rock driller struggle for days in interbedded shale and hard sandstone.

Mike Lambert

 

[killswitchengage]

That's very informative i will root that in mind

 

[fattdad]

There are side-discharge bits. There are bottom-discharge bits. There are impregnated diamonds. There are set diamonds. There is soft matrix. There is hard matrix.

These variations are based on the fact that these distinctions affect the drilling rate. In a very hard rock, you may want a softer matrix. That way, the matrix gets out of the way to reveal more of the diamond surfaces. In a soft rock you may want a harder matrix to control bit wear.

I never quite knew when to use impregnated versus set diamond bits. Then again, impregnated bits are less expensive!

Lots has changed since I spent countless hours logging rock core.

f-d

ípapß gordo ainÆt no madre flaca!

 

[killswitchengage]

Very helpful f-d thanks

 

[Okiryu]

Not an expert for rock drilling but we use these diamond bits for limestone rock:

https://www.ybm.jp/Product/Tools/sharkbit.htm

I did not know that they come from North America:

http://www.fordia.com/types-produits/core-bits/

With just water as drilling mud,these bits have been performing well for us.

 

[killswitchengage]

Yea they are called impregnated diamond bit just like f-d said thanks