Like a chef, one must follow a recipe but make adjustments too.
By Jennifer Strawn
Mixing a good drilling mud is much like cooking an elaborate dinner from scratch. There is a lot of science and a little intuition involved.
You may start with a base recipe, but with experience—and evolving drilling conditions—you may find yourself making adjustments as you go. Maybe a pinch of that polymer and a dash of a specialty additive.
“I feel like I mix like a grandma cooks: A little bit of this and a shot of that,” says Richard Layman, MGWC, CVCLD, owner of Pure Water Well Inc. in Lachine, Michigan. “I’ve drilled in just about any formation, so I know what materials to mix and what it takes to get the job done.”
And like cooking, the order in which you add the “ingredients” matters in the quality of the end product.
Step 1: Treat your makeup water
The quality of your makeup water is one of the most important factors in mixing a good mud. If you don’t have good water, you won’t make good mud.
To get the most from your bentonite fluid, you should be using warm, soft water. Otherwise, you risk inhibiting the performance of the bentonite and any polymers you’re adding to it.
Because warmer water works the best, Layman has heard some drillers in cold climates run heated water into their water tanks at 100ºF or more.
“That’s extreme,” Layman argues, “but that’s what some people are willing to do to make the process easier for them. My water is 50 degrees and it definitely takes me longer to hydrate bentonite than it takes my cousins in Florida who have 70-degree water.”
You’ll also need to add soda ash to your water to soften it and raise its pH. The soda ash, which is sodium carbonate, will take the hardness and “tie” it up.
“While we put soda ash in some of our products to help buffer hard water conditions—as all of our competitors do—it doesn’t react the same as if you treat the hardness prior to introducing the clays,” says Stewart Krause of Wyo-Ben Inc. in Billings, Montana.
For pH, you’re looking for about 8.5 to 9. Typically, that is about a half-pound of soda ash per 100 gallons to about 1 pound per 100 gallons in extremely hard water.
“A lot of people will skip this step in the process and go right into mixing their bentonite,” says Gary Shawver, MGWC, president of Shawver Well Co. Inc. in Fredericksburg, Iowa. “I certainly don’t encourage it. Treating your water is going to make your bentonite mix much better and go a lot further than if you don’t.”
If you’re adding soda ash into the water and the pH doesn’t change, don’t be discouraged. It just means you need to put more in.
“It won’t adjust the pH until it satisfies the hardness,” Krause says. “It’s just one of those rules of thumb in the field.”
Step 2: Introduce your bentonite clays
Once you have your makeup water treated, it’s time to introduce the clay into the system. The type of clay varies—it could be a high-yield bentonite, an API-type material, or even a calcium bentonite if you’re working outside the United States. Typically, it will be an extended bentonite that increases the viscosity of the drilling fluid. This gives you gel strength, improves the carrying capacity of the fluid, and reduces fluid loss.
You add the bentonite before any other polymers or additives because these inhibit the swelling of the clay.
Add the clay slowly, get good agitation, and make sure the bentonite is fully hydrated.
“You don’t want to add the clay too fast,” Krause advises. “It will go out into the system, fall to the bottom, and you’ll continue to mix on top of that. You’re wasting material.”
Then, your solids will build up in your pit, so when you sweep the bottom it’s going to push that bentonite up and your fluid system is going to be way too thick.
The thickness of the mud you need will depend on what you’ll be drilling through. If you know you’ll be drilling in clays, you may want a little less bentonite in the mix.
If you’re drilling in sand, you’ll want to slow the annular velocity and use more bentonite to increase the viscosity.
“It really helps when you are starting out your mix to have an idea of what you’re going to be drilling into,” Shawver says. “But, we don’t always know. We log every hole, but each one can be a new adventure.”
Shawver says a 35-second Marsh funnel is a good place to start. Water runs out of a Marsh funnel at 26 seconds per quart, so you’re going to measure until it takes about 35 seconds for your fluid to run through the funnel.
“If, when doing this step, you see bentonite balls across the screen of the Marsh funnel, you’re not ready to drill with it,” Krause says. “It needs to be mixed more to get the total yield out of the material. Depending on the shear and the size of the system, that could take about 15 to 20 minutes, or on big systems maybe an hour.”
Step 3: Add your polymers as necessary
Now, you’re ready to add your polymers. Polymers are particularly helpful when drilling through clays to prevent clays from sticking together and bit-balling. Other polymers can also be added to mud to create a thinner, tougher wall cake when drilling in sand. Depending on your needs, this could be either a short-chain or long-chain polymer.
If you’re using a solids control system, you want to be very careful about the type of polymer you use because the screens will shake out the long-chain polymers.
Long-chain polymers will give you a lot of viscosity, which you may or may not need. If you don’t need it, a shortchain polymer may be preferable because you can keep more polymer in the system without creating a lot of viscosity. We are trying to encapsulate the drill cutting so it can be removed from the borehole as a larger particle rather than being dispersed in the fluid system, which will reduce the performance of the fluid and cause development issues.
Maintenance is really important when working with polymers as they get used up as you’re drilling deeper.
“At every two rods or every four rods—depending on the size of the hole you’re drilling—you need to add polymer back to the system,” Krause says. “The first guy on the site who’s going to know that you don’t have polymer in the system is the guy shoveling cuttings because they’re going to start sticking to his shovel where they didn’t before.”
If you only look at viscosity and aren’t thinking about how long you’ve been drilling, you might be setting yourself up for failure. The viscosity may not look any different because the formation solids build up the same viscosity. Meanwhile, your density is going up.
When increasing volume, you’re going to need to add soda ash, bentonite, and polymer just like the initial makeup. Krause recommends using a pre-mix tank for this so you don’t end up “playing catch-up” and stressing the borehole with varying mud properties.
“You may start drilling at a 40-second Marsh funnel,” he says. “All of a sudden you’ve watered it back and you’re drilling at 32. You try to build it back up, but maybe you’ve overcompensated and now you’re at 50. The hole sees a lot of different pressures without us adding to the issue. Remember some basic rules that never change: We are using the drilling fluid to remove cuttings and stabilize the borehole. One of the best ways to do this is to create a thin, tough wall cake while keeping the mud as light and thin as possible.
As you encounter different formations you’ll need to change your mud characteristics as you hit them, says Layman who serves on the National Ground Water Association Board of Directors.
“You can’t walk away from the controls,” he says. “You have to be on it and be sensitive to the formations. They don’t take 10 feet to change; they change instantly. You can be drilling in gravel and go into sticky clay in an instant.”
That’s why Krause carries a colander for pulling samples in his mud kit, “so I know what we’re in and adjust the mud accordingly.”
“Even if a driller isn’t pulling samples, I am,” he says. “If I see a change in the color of the cuttings, the nature of the cuttings, or even how fast we’re drilling—it all comes into play on what I’m going to put together. You’ll have these subtle changes and it’s tough to react.”
Most mud experts will say they want to see a surface system that’s four times the hole volume, but that’s rare for most water well drilling operations.
“Drillers want to drill as fast as they can drill,” Shawver says. “There’s nothing wrong with that because production is very important to the profitability of a drilling operation. But you need to allow your drilling fluid to work with the formation that your drill through.”
Step 4: Add specialty additives, if needed
Specialty additives include drilling detergents, dispersants, and loss circulation materials, which are added after your polymers.
Drilling detergents can be helpful if you have a really sticky clay. It can help prevent cuttings from sticking to your drill string.
“I’m not a huge fan of drilling detergents because it does reduce the surface tension,” Krause says. “It tends to break down those clays so they go into your system.”
Small additions are fine, but manufacturers typically don’t recommend more than a gallon per 1000 gallons at most for vertical drilling. For horizontal drilling, no more than 2 gallons per 1000 gallons is recommended.
Dispersants act as thinners when your mud is getting too thick. You want your mud to be thin enough that your flow patterns coming up the hole will still give you a good job cleaning the hole.
Loss circulation materials prevent the fluid from running off into the formation.
“If you’re still getting returns back and it’s just a partial loss where it’s just taking a little drink on you, simple steps like using a granular bentonite at the suction can work,” Krause says.
Small doses of fibrous material, mica, or cellophane will typically take care of loss circulation as long as it’s not a total loss. If you’re drilling a potable water well, you don’t want to use sawdust, cottonseed hulls, or anything that will biodegrade as it gets pushed into the formation and becomes food for bacteria.
If it’s a total loss, you’ve got to get your drill pipe out of the hole because it is no longer stable.
“I refer to it as that ‘sucking’ sound because not only do you lose all volume in your pit, but your volume in the hole drops and it truly gives you a sucking sound. This is the ‘come to Jesus’ time because there’s a danger of collapse at any given time.”
If you’re in an area prone to loss circulation, you can have a pill tank made up of viscous mud at about a 50-second Marsh funnel sitting alongside your rig. That way when you reach the loss circulation zone, you can quickly stir in any loss circulation material and inject that pill into the hole.
Dealing with artesian heads (flowing wells)
If you know you’ll be drilling in an area known for artesian flows, you may need a more heavily weighted mud to overcome higher artesian pressures. If you’re unprepared, you’re in danger of washing out on the hole or having your rig literally fall into the hole.
“You really need to do your homework before you get there,” Krause says. “You’re going to want to set surface casing—hopefully as close to where you’re going to hit the artesian flow as possible. If it starts flowing on you, you can shut that well in and control it.”
It will flow up the casing rather than eroding an open hole, so you can divert the water and let it flow until you can figure out how you’re going to handle it.
You’ll want to reach out to your mud person for help. You’ll need to know the estimated depth where you’re going to hit pressure and how much head pressure the formation has on it. They’ll help you calculate the mud weight and tell you how to mix it. Because the weight of the mud can be very high, they can instruct you on how to keep the pH up, and may even suggest a change in bentonites as well as dispersants to keep the mud thin.
“It’s very important when dealing with an artesian flow that we get it right,” Krause says.
Whether you’re a seasoned driller or someone just starting out or you’re drilling through heavy clays or sand, Shawver offers one golden rule you can take with you to any jobsite:
“Take your time, and let your drilling fluid do its job.”
Jennifer Strawn was the associate editor of Water Well Journal from 2004 to 2007. She is currently in the internal communications department at Nationwide in Columbus, Ohio. She can be reached at firstname.lastname@example.org.