Solids Control for Mineral Core Drilling
In a perfect world every core rig would have a full suite of solids control equipment which would reduce their mud problems, and improve productivity. In the real world that scenario is unrealistic as the site footprint is often too small, the equipment is too expensive and there is not enough available power or people to keep it going. A high percentage of diamond core rigs have no solids control beyond a couple of settling pits.
Is this a problem? Well, the build-up of undesirable low gravity solids in the drilling fluid can cause poor hole conditions, stuck rods, poor penetration and lost meters.
What can we do about it? Basically there are three routes to tackle the problem.
Method 1. Dilution
Basically one just adds water and this of course reduces the percentage of the solids in the fluid and improves the settling factor.
Using settling pits alone means you are usually to some extent using method 1, dilution
Method 2. Solids Control
Here is a basic overview of solids control equipment.
Shakers/mud cleaners – With 200 mesh screens they can remove solids down to about 75 microns.
Hydrocyclones/Desilters/Desanders – These can remove solids down to 15-20 microns in theory, but take a lot of TLC to achieve that kind or performance
Normal Centrifuge – These can remove solids down to about 5 microns or if high speed even a little further. In a way the most suited for diamond core drilling
So what’s the problem with these? Well let’s look at them one at a time.
Shakers in general are too big for the normal core rig and their solids cut is insufficient. They can also use a fair amount of power.
Hydrocyclones. For those of you who are mud engineers please explain to the others how you keep them working! I certainly have never succeeded and used to keep a welding rod in my back pocket to unplug them. To me these are too labour intensive and untrustworthy.
Centrifuges are good, have a solids cut which is about right, however usually quite expensive and they need a minder. A centrifuge does not run on its own it requires an operator. Tell me if I am wrong.
To have a closed loop system, quite a few companies have been offering systems which have a combination of shakers, hydrocyclones and even centrifuges. At the end of the day, you still end up with solids and liquid and I believe there are simpler approaches via good house-keeping and an increased use of mixing tanks and better settling tanks.
I am not saying that there is no place for solids control, I am just highlighting that from my perception there is nothing in the market at the moment which is fit for purpose and recognises the realities of how we operate and where we operate. Most systems are just oilfield hand me downs!!
Method 3: Chemical control.
The solids can be flocculated and coagulated and allowed to settle out. Interestingly enough, while we use settling we tend not to give it a chemical boost to improve the process. This offers significant improvements. In fact, a little flocculant prior to the fluid entering one of the solids control units can dramatically improve the performance and the cut. Even the cut on a 200 mesh shaker screen can be considerably enhanced if the solids are aggregated before crossing the screen.
So where are we? Until a small, reliable, cost effective solids control unit hits the market in this present downturn, I guess many of us will make do with good settling pits/sumps (longer the run the better) and perhaps a good above ground mixing tank and separate suction tank. I would also like to recommend that to just give your fluid that extra little edge you consider the use of a flocculant to ensure a much higher rate of solids settlement.