Containing, Disposing of Drilling Mud and Drilling Cuttings
Drilling mud — a mixture of water and bentonite clay (usually) we use to advance a borehole into the subsurface. When planning a project, drillers normally have some idea about the type of mud and additives they will use, and it usually includes bentonite, soda ash and water. There are many additives for so many different purposes that it can be overwhelming, but these additives are often necessary to successfully complete the bore. We have additives to control fluid loss, inhibit swelling clays, add extra viscosity, enhance gel strength and so on. We can add polymers or even drill the borehole with bio-polymer (non-clay) drilling fluids.
Years ago, when drilling wells, the standard procedure was to dig an earthen pit for containment of the drilling fluids. At the end of the project, we spread the excess fluids and cuttings on the project site and backfilled the pit. It was easy to see where the drilling mud was spread because the grass/plants seemed to be greener. Times have certainly changed, and the option to dig an earthen pit and spread the cuttings and excess mud on the ground surface is over. Most drillers now utilize above ground drilling fluid cleaning and recirculating/recycling systems. This leads to complications on the site; for example, how do we contain and dispose of the drill cuttings and fluids?
A word of caution: Read the contract!! Drillers should avoid taking ownership of the drill cuttings and fluids. This material originates from the owner’s property and the ultimate responsibility of the materials should be left up to the owner. The driller can assist with storage and disposal but should not contractually be made the owner or generator of the waste. It is acknowledged that most contracts pass this on to the contractor, and many accept the waste disposal without a second thought. That is a danger that can cost a tremendous amount, particularly if there is contamination, either man-made or naturally occurring. But that is for another article.
Now, let’s get down to the fun stuff. First, the drill cuttings. Most above ground fluids systems utilize shale shakers and/or de-sanding/de-silting cones to remove solids from the mud. The solids are sent down chutes off the side or back of the equipment, while the scalped/cleaned fluids drop into the underlying tanks. We can use small, normally 3-cubic-yard tip bins to catch the solids and then transport the material to a roll off, or place a roll off directly below the chute. Most drillers I know prefer 20-cubic-yard roll offs for containment. Solids from the fluids system can be relatively dry or very “soupy,” depending on the drilling fluid and subsurface conditions. So the roll off containers should be “water tight.” A caution about roll off containers: When ordering the containers from the vendor, be very specific about how you will be using them. Make sure the vendor understands that you need non-leaking containers. Also ask for liners to be placed in the roll offs. Finally, very carefully inspect the containers when they arrive at the site. Mud leaking from a storage bin may “contaminate” the ground surface, can cause traction problems for personnel and equipment, and will make a nice tidy drill site look very ugly.
One other very important item about containment of drill cuttings: You can only fill a roll off container to the half way point with solids. If you fill it to the top, get ready to figure out how to pull half of the material out, because the container will be too heavy to move. Speaking of movement, now that the roll off is half full what do you do with it? Before it can be hauled off and disposed of, the material must be tested. What tests? Good question. You may have to test the material to comply with federal, state and local regulations. Remember the comment about the contract you signed? Hopefully the testing, transport and disposal of the cuttings are the responsibility of the owner (or the consultant).
On to the mud. If everything goes perfectly on the project, you won’t have to change out or dump your mud halfway through the drilling. So, once the borehole is drilled, then what? Most of the drillers I know opt to place the drilling fluid/mud into open top, water tight roll offs. Wouldn’t a 20,000 gallon “frack tank” be easier? No. Remember, when you return the tank it must be clean. If you dump mud in the tank, the solids will settle out and then what? How do the solids get removed from a frack tank? In the worst case, you or the tank rental company will place a person in the tank to wash out the solids. Guess what? That’s a confined space and a very expensive proposition.
Now that you have drilling mud in the tank, what do you do with it? Couple of options. Maybe you could find a place that will take the material as a slurry. In that case, a vacuum truck could come in, suck the tank dry and haul the material off for disposal. Don’t forget about the testing. Again, I hope the contract states that it is the consultant’s/owner’s responsibility. If you can’t find anyone to take the mud as a slurry, now it may be time to solidify the fluid in the tank. There are lots of materials that could be utilized for that purpose, including additional bentonite, sawdust, fly ash and myriad chemicals that will solidify the mud. (Portland cement is a bad choice, by the way.) Another note: Even the best recyclers may discharge cuttings that won’t pass a paint filter test, so even the solids may need to be solidified before hauling. Remember, once the material is solidified, it must be tested before disposal.
Couple of other cautions at this point. “Dirty water” from the mud thinning process, decon, well development and testing should be kept as a separate waste stream. Trying to solidify water is very expensive and time consuming. Finally, be very careful with “wash out” water from grouting operations. Cement has a very high pH and the water from cleaning pumps, hoses and drill rods will have a high pH and may need treatment before disposal or mixing with other waste streams on site.
I hope the above is not “clear as mud.” Just understand that times have changed and we just can’t dump stuff on the ground anymore, even if the well is for a potable water supply. Go into the project with a firm understanding of the containment, transport and disposal of all of the drilling generated waste streams, including the drilling mud. Read the contract carefully and make the owner/consultant responsible for the containment, storage, testing, transport and disposal of all drilling generated wastes, including the drilling fluids and well development and testing water.
David S. Bardsley is business development manager for Directed Technologies Drilling. For more Bardsley columns, visit www.nationaldriller.com/bardsley.