Understanding this simple approach can help you tackle challenges on the job.
By Jeff Blinn
A comment I’ve often heard from drillers is, “An engineered drilling fluid is too complicated and too expensive; I only need some mud!”
Fair enough if the driller has never been taught how to design a proper drilling fluid. So, let’s work through the design process, and if you can count to 5, you’re going to be in great shape. There are five steps to drilling fluid design to remember, and as a bonus, there are usually five primary drilling fluid additives used regularly in any given geographical area.
A Little Preplanning
Before we start to design a specific drilling fluid, a bit of preplanning is required. As discussed in a previous column, all drilling fluids are engineered to address the challenges presented by the geology the borehole is expected to intersect.
Will we be drilling coarse inert material such as sand and gravel or reactive fine-grained material such as clay? What drilling fluid functions will be most important to us—suspension, borehole stability, controlling lost circulation, or artesian flow? Is the aquifer easily plugged off and therefore sensitive to the solids and drill cuttings in the drilling fluid? Will we be drilling with a water-based fluid or will we be air/foam drilling?
Once we are armed with the answers to our questions and know what our engineered drilling fluid needs to accomplish, we can now design the fluid.
A Step for Each Finger
For this exercise, let’s assume we are using water as the base for our drilling fluid. We can look at air/foam drilling another time. So, look at your hand and see your five fingers.
1. The first finger represents step one and that is: Treat your makeup water. All water is not created equal. Just because you use potable water for mixing does not necessarily mean it is good for mixing drilling fluid.
According to the U.S. Geological Survey, the average water hardness around the United States is 250 mg/liter. Most drilling fluid additives do not mix well or develop their maximum properties when mixed in hard water.
All makeup water should be treated with soda ash to reduce the hardness level to 100 mg/liter or less. Drilling fluid additives also prefer a slightly alkaline solution (pH of 9-10) for maximum yield and effectiveness. Luckily for us, treating the makeup water with soda ash not only reduces hardness but also raises the pH into the 9-10 range. Step one uses product number one: soda ash.
2. Finger two, step two: Create suspension. All drilling fluids must be able to move drill cuttings away from the bit and suspend them in the drilling fluid as the fluid flows up the annulus to the surface.
Cuttings are moved by velocity and viscosity. If we could pump plain water fast enough, we could move all cuttings to the surface. Unfortunately, this is not possible due to pump limitations and the detrimental effects of high-velocity fluid eroding the borehole wall and fostering borehole instability.
Bentonite powder is the additive of choice to overcome these limitations. Bentonite as a drilling fluid additive has been around for more than 100 years. It effectively and economically creates viscosity, suspension, carrying capacity, filtration control, and borehole stabilization. Bentonite provides borehole stabilization by creating a thin impermeable filter cake on the borehole wall.
Step two gives us product number two: bentonite. Water, soda ash, and bentonite form a basic and effective engineered drilling fluid and most often is the base for more advanced fluid systems.
3. Third finger, third step: Protect the borehole. As good as our basic engineered fluid is that was created using steps one and two, it may not be robust enough at times to fully stabilize the wellbore. A little more glue may be necessary, so to speak, to help keep the formation from
falling apart. This is especially true in geologies that are inert and porous and permeable such as sand formations.
The class of products for this purpose is known as filtration control additives. They help keep formations in their native state by minimizing water wetting of the formation. They lower the filtration rate of the drilling fluid and thin and tighten and strengthen the filter cake, increasing borehole stability.
PAC polymers are the primary product used today for this purpose. Other filtration control additives are available but may be less effective than PACs. You guessed it; product number three: a PAC filtration control polymer.
4. Finger number four, step four: Protect the cuttings. So, why do we need to protect the drill cuttings when they are a waste product that we don’t want? We will drill the fastest when the drill bit cuts the formation and creates a cutting, and the cutting enters the flowing drilling fluid
and is transported to the surface and removed from the drilling fluid.
While being transported, we don’t want the drilling fluid to react with the cutting and alter it. This could be by physically breaking the cutting down into smaller pieces, or in the case of clay, allowing the surface to get water wet and swelling, becoming sticky, and in some cases, disintegrating entirely.
When the cuttings break down into small pieces, they are harder to remove at the surface and may be recirculated downhole with the fluid being pumped downhole. This increases the chances of plugging the water production zone and limiting the output of the completed well.
Clay-cutting swelling and stickiness present a different problem: bit balling and packing off around the drill string. Bit balling can bring a penetration rate to a near standstill and require a bit trip to remedy the problem. Packing off can completely stop circulation. If you can’t circulate your drilling fluid, you can’t remove cuttings and are stuck. Again, tripping out of the hole, if you can, is necessary.
To remedy the sticky swelling conditions PHPA polymers are recommended. Now we have four steps and four products.
5. Our fifth finger and step number five: Address unique needs in your area. The first four steps cover most normal drilling conditions, but every geographical area can have some unique challenges.
Some areas have lost circulation problems. On the other hand, your challenge could be artesian water flows. Maybe controlling viscosity is a problem and a thinning agent is needed. Or the sticky clay might need a soap or surfactant to help control the surface stickiness.
This step covers all the specialty products that may not be necessary every day or on every hole and includes lost circulation material (LCM); weighting material such as barite, thinners and dispersants; and soaps and detergents. Your fifth product could be the one product needed to address that special need in your home area.
I recommend every driller have a preplanning meeting or at least a conversation with themself to understand the challenges present on the next project.
Simple Roadmap to Drilling Fluid Design
There you have it, engineered drilling fluid design is right there in your hand. Your five fingers represent the five steps you need to follow. And your five fingers will also remind you of the five drilling fluid additives you will regularly use.
This simple roadmap to drilling fluid design helps us to remember what the fluid is required to do and what products to use to achieve our intended results.
As always, I recommend you contact your drilling fluids supplier and your preferred drilling fluid brands representative for their advice and expertise. They are happy to help you be successful.
I would like to revisit the comment I opened this column with: “An engineered drilling fluid is too complicated and too expensive; I only need some mud!”
I usually hear this after a driller calls me with a problem and I propose a solution. Usually they only call me, the mudman, as a last resort after everything else they have tried fails to get results.
And then they argue the proposed solution won’t work because they tried it once years ago and it didn’t work back then. And it might take a product that they never used before or needs to be mixed differently than what they’re used to or might cost more than a few bags of gel, or a dozen other excuses.
I often think, “Gee whiz, why did you call me for help in the first place?”
How do we resolve these differences? We start over again and ask questions.
What is the problem? When did it start? What were you doing before the problem began? What have you tried to fix it? How long has this been going on? When asking these questions for the second or third time, I’m trying to uncover any “Oh, by the way. . .” issues or event that the driller forgot or neglected to tell me the first time around.
Combining the original information with any new revelations, we can troubleshoot and understand the source of the problem. We uncover if the problem is truly drilling fluid-related or if is it operational, mechanical, or operator error. Of course, it’s never operator error!
If we agree on a drilling fluid solution, I work through the five steps of engineered drilling fluid design with the driller to troubleshoot the original fluid design. Did the driller treat their makeup water? How much bentonite were they using? Were any other products in the mix? What were their concentrations or how much did they use?
With this information, we employ the five-step design process to engineer a new drilling fluid design—the new recipe if you will. This new formulation will have the additives necessary to address the challenges presented by the geology of the area and in the concentrations required to give optimal drilling fluid properties to control the formations intersected during drilling.
What about the economics of engineered drilling fluids? Are they really too expensive to use? There is an upfront cost that you see when you write a check to your supply house. But what is the cost of fighting problems? Every extra hour on a job has fixed expenses.
In a worst-case scenario, overcoming problems might double or triple the time necessary to complete the well. This means you have two or three times the expenses for one well. A few extra dollars on the correct drilling fluid additives can save time and money in the long run.
By using this five-finger approach to formulating an engineered drilling fluid, I hope I have reduced the process to a simple user-friendly approach. I recommend every driller have a preplanning meeting or at least a conversation with themself to understand the challenges present on the next project and use this simple method to engineer the proper drilling fluid.
And don’t be a stranger; call your local mudman for advice.
Jeff Blinn has had a 40-plus year career as a professional drilling fluids engineer. Beginning with mud school in 1978, he has worked in many drilling disciplines including minerals exploration, water well, oil and gas, geothermal, geotechnical, and horizontal directional drilling. He has held positions as field sales engineer, engineering supervisor, account representative, technical services representative, and training manager. He can be reached at email@example.com.