With ever increasing costs of drilling fluids and their disposal, solids control seems to be a hot topic for a long time now.
Maximizing the use of the fluid while minimizing the volume to be disposed of is the ultimate goal. For contractors running larger rigs, solids control equipment is an essential part of the operation and is usually paired with the rig at purchase. Mid-size rigs can also benefit, depending on what type work they are doing and location size.
Most of the larger operators are keenly aware of the key components and how they work, which makes selection of equipment fairly straightforward. Smaller operations need to fully understand what they expect out of the system before purchase and not just buy the cheapest unit available.
Over sizing the unit is not a bad thing (within reason). Remember the manufacturer is probably rating the capacity at constant flows with perfect mud, which rarely happens in the field. Under sizing the unit will sour you on the idea of recycling fluid with poor fluid going back down the bore causing hole problems or just slowing down the operation for the cleaning system to catch up.
Good mud properties are essential to efficient boring and production drilling but shouldn’t be limited by the solids control system. Maintaining viscosity and flow volume required to remove cutting from the bore is key to completing a successful bore. A drilling fluid program designed to meet both requirements of efficient drilling as well as being easy to recycle is the goal. Get with your fluid supplier for recommendations based on them understanding you will be using a solids control system and its capacity. Formations will dictate not only the additives that are used to make up the fluid but also some changes to the settings on the solids system. Sizing screens is important to manage for reclaimers so as to not overload the cones or the system as a whole.
A basic understanding of mud and its objective can be simple but crucial to the success of your bore. You want your mud to have the viscosity to carry your cuttings out of the hole and into your return pit. Here you want it to start dropping out solids before it is pumped to the reclaimer.
The order of operation when mixing mud is water, soda ash, bentonite, dry polymers, then liquid additives. You want to understand the quality of your water because it makes up 97 percent of your drilling fluid. The goal is to have a Ph of 8.5 and your total hardness as low as possible. Soda ash will bring your Ph up. Typical water sources like a fire hydrant are at a seven on the Ph scale. If there is Hardness from calcium, the soda ash will neutralize what it can.
The next step is adding your bentonite. You want to know a little about the formation you will be drilling into, so you have a viscosity number to shoot for. You want to build much of your viscosity with bentonite. It is the cheapest way. Bentonite particles are the building blocks for your additives to work with. The more you have, the better they will perform. I typically recommend a PAC polymer at this point. PAC polymers are contaminant resistant. Meaning they will work in nearly all conditions. They give you good gel strengths that will still allow you to drop your solids once the mud has made it to the return pit, they have great fluid loss properties to protect the formation and cuttings from taking on water from your mud. PAC works great with reclaiming systems. Now if you find the conditions still need a better yield and higher viscosity to carry large dense material and support the bore you could add a bio-polymer.
One you have reached your desired viscosity, you can add your liquid clay inhibitors, lubricants or detergents. Clay inhibitors and liquid PAC’s will change the rheology of your mud, so please be aware.
Now let’s talk about the reclaimer itself. Reiterating, you don’t want to show up to a job and not have enough capabilities to clean your mud. Know your limits and don’t out drill your mud.
The reclaimer uses a shaker screen filtration system and de-sanding and de-silting cones (a cyclone effect). When choosing a screen size, you must have some knowledge of what is coming up from down hole. The scalping screen should have a rather large mesh size, maybe a 60 or 80. Under the de-sanding cones you should have 160 to 180 mesh screen. Finally, under the de-silting cones you should have 200 to 220 mesh screens. The screens are important to know and inspect daily, as the sand and silt can act like sandpaper and rub the information off and rub holes through the screen itself.
The tanks that the mud filters into are called a clean tank and a dirty tank. You should understand how to combine them and recirculate them. the de-sanding and de-silting cones work on the largest particle running through the system, so if you recirculate the mud within itself, you will remove the next largest particle size. This is great to do on down time.
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The last part of solids control is testing. The information you will test for are viscosity, mud weight, sand content, Ph and total hardness. You can test all of these with a basic mud testing kit. All reclaiming systems should come with one. In addition to knowing yourself what is going on, you can reach out to your mud engineer and give him the information so you can discuss and mud program that will work best for your situation.