Fluid Properties, Components Key to Drilling Jobs
I have had great success drilling around the world with multiple types of mud drilling in water well, exploration and construction. Not once did I think it was just a good day of drilling; the success came from understanding the basic components of drilling fluids. There is no such thing as good and bad days of drilling — just days we impact the downhole structures more. That understanding allowed me to build the right fluid for the project.
I don’t believe that you have to be a mud engineer to build a good drilling fluid. The first time I sat through a mud school, I was overwhelmed. The only thing I can remember from that first school was my father whispering, “Where the hell do we have room for a premix tank?” Ironically, two of his sons went on to become Baroid mud engineers. My younger brother, Chad Yordy, is the Baroid IDP lead for the Midwest and Northeast. He is an excellent mud engineer.
Although I have had extensive oilfield fluids training by Baroid, the actual key to my success is staying current with innovations in drilling fluids and techniques. Staying in touch with my local mud engineer, and other mud engineers around the world, helps me stay current. I adopt the new products and implement them into what has worked in the past to build my custom drilling fluids plan. The key to executing a plan is understanding the three essential components of freshwater drilling fluids and how to utilize the fourth specialty component. This article goes over these components, as well as the critical characteristics each contributes to a successful fluid and, ultimately, a successful drilling job.
Critical Components & Characteristics of Freshwater Drilling Fluids:
The first component, and easiest to overlook, is water. Wyoming sodium bentonite drilling gel requires contaminant-free water. Makeup water requires a calcium hardness less than 100 ppm, chlorides (salt) content less than 500 ppm, and chlorine less than 50 ppm. Utilize calcium hardness test strips and pH test strips to understand the properties of your makeup water.
Calcium hardness is easy to eliminate by using soda ash. When soda ash is introduced, a chemical reaction occurs where the calcium hardness is lowered and pH is raised to a maximum of 10. It is essential to understand that soda ash will only remove calcium hardness. If soda ash is introduced and the hardness does not go down, it is another form of hardness contamination.
Makeup water with salt is more complicated to treat; the best case is to find a freshwater source with a salt content below 500 ppm. If it is the only water source available, your option is to use an alternate type of clay called attapulgite. I have used Baroid IDP’s ZEO-GEL and Tunnel-GEL SW products with great success.
Chlorine content is not a typical issue, but if you encounter chlorine content of more than 50 ppm, your options are to allow UV light to dissipate the chlorine, use aeration, or utilize an additive that will deplete or bind up the chlorine content. Freshwater drilling fluids are typically 97 percent water and need to be contaminate-free.. Bentonite and polymers require being free of pollutants and a pH of 8.5 to 10 to change water into a drilling fluid with useful properties. Invite your local mud engineer and have them take a look at your makeup water.
The second component of a freshwater drilling fluid is the NSF-approved additive that augments the characteristics of water and changes it to a drilling fluid. I use the term additive because new technology has made it possible to build a freshwater drilling fluid without bentonite that still has the characteristics of lubricity, suspension and filtration control. These three characteristics help us develop a drilling fluid that will minimize the impact caused by drilling. The additive, whether it’s the old school Wyoming sodium bentonite or the new school all-polymer systems, first and foremost needs lubricity. We require a fluid that can lubricate the bit and tooling to keep them cool and help prevent erosion from abrasive solids. Water by itself does not have functional lubricating characteristics. I learned this the hard way in college when my roommates and I made a “slip ‘n slide” with a tarp and flowing garden hose. I believed water was acting as a lubricant, but at the end of the day, I had friction burns. In reality, alcohol was the internal lubricant that allowed me to believe the water was working. To get the best efficiency and life out of bits, pumps and tooling, the fluid needs good lubricity characteristics.
The ideal drilling fluid will assist the mud pump in moving drill solids uphole to the surface and suspend solids when the pump is not active. Commonly, we use Wyoming sodium bentonite as a suspension agent and, depending on the type of drilling gel chosen (high-yield, medium-yield or low-yield), the suspension characteristic can be temporary to long-term. In vertical drilling applications, a drilling fluid needs to have enough suspension to achieve adequate circulation in the hole and then allow settling of cuttings in the pit. That is why, in many vertical applications, the drilling gel of choice is high-yield. When it is necessary to use medium-yield 140- to 180-barrel or low-yield 90-barrel yield “oil field drilling gel,” mechanical solids control is required to remove suspended solids. The lower the barrel yield, the more bentonite platelets are available to help carry the cuttings to surface. High-yield drilling gel is specifically designed with specialty polymers to extend the yield. These polymers allow for fast mixing of a viscous mud with just enough suspension to carry cuttings, yet will still enable those cuttings to settle out on the surface. Medium- and low-yield gels take more time to mix and have higher suspension characteristics because the gel has not been extended as far apart with polymers.
Beyond bentonite, suspension characteristics can be achieved or enhanced by specialty polymers and loss circulation material. Often, these specialty polymers are designed with starches and are a nutrient source for bacteria — therefore, not NSF approved. However, some new ones are rolling out to the market that can be NSF approved. Another option is NSF-approved loss circulation materials like Baroid’s N-Seal and Fuse-IT. Both products can help increase carrying capacity in bentonite- and polymer-based fluids.
Let’s talk about viscosity … or commonly known as the Big Thick Fat Monster. Viscosity is an old school drilling fluid component. In a 21st-century drilling fluid, it should be viewed as the total result of a drilling fluid incorporated with drill solids. When I was driller, I believed that I needed to thicken or thin my mud to solve drilling issues. In reality, thick and thin are poor descriptions for drilling fluid. A fluid that is visually thick can be loaded with solids. Alternatively, it could be contaminated and the thick visualization is caused by bentonite platelets flocculating, thus creating a fluid incapable of suspension.
Then there were times I purposely created super thick mud by using a PHPA to sweep a hole. The increased viscosity happened because the PHPA crosslinked with drill solids, creating a cottage cheese look. Then I would try adding water to thin my mud back down. Neither solution was effective in drilling. If you ever get the golden ticket to attend a Baroid IDP week-long mud school in Houston, you will join the club in chanting “soda ash, soda ash, soda ash” and “viscosity is the resistance to flow.”
The characteristics of viscosity and suspension are confused every day. To drill a borehole, we require suspension. But to maintain flow, we do not need viscosity. Low viscosity drilling fluids can have excellent suspension. High viscosity drill fluids increase the flowability of the mud which, in turn, requires more horsepower to move the fluid. The maximum output rating of centrifugal pumps is based on water. Therefore, the higher the viscosity, the less pump volume is available. If you are using a piston pump, sure, you can pump more viscous drilling fluid, but when that fluid incorporates with new drill solids created by the bit, the higher resistance to flow creates downhole fractures and blowouts. Resistance to flow can be the difference in the path of least resistance being up the borehole or laterally out the side of the hole.
Viscosity is a change in the water characteristics when adding bentonite and polymers. The goal should be to add what is necessary to clean the hole, not what appears to look necessary. A Marsh funnel kit or rheometer can help you better understand necessary viscosity. Your local mud engineer has these tools, but I suggest you purchase a funnel and mud balance.
Filtration control is the third, and most critical, component of any drilling fluid. Borehole stability is 100 percent dependent on preventing drilling fluid from saturating the surrounding geology. Good drilling fluid will create a filter cake in the borehole that is 2⁄32-inches thick, leaving the borehole outside of that untouched. Sodium bentonite alone does not have excellent filtration control. The most effective way to increase filtration control is with a PAC, or polyanionic cellulose branched polymer. These branched polymers help bring the bentonite platelets together, creating a tighter filter cake. These stronger filter cakes prevent fluid from moving through the borehole wall, preventing destabilization of porous zones and stopping water from reacting with clays and shales. In the past, PAC polymers have been incredibly hard to mix, but new dispersible technologies have made these products very easy to incorporate into any system.
The second half of hole stabilization is inhibiting reactive soils disturbed by the bit’s cutting action. PHPA polymers, or partially hydrolyzed polyacrylamide, are used for clay and shale inhibition. The long-chain polymer wraps around the reactive cutting, preventing the hydration reaction that causes clays and shales to swell, become sticky or break down. PHPAs are often misused as a viscosity booster to assist in sweeping a borehole. Although the high viscous sweep may help clean the borehole, it is nearly impossible to return the fluid to a manageable viscosity. PHPAs come in various molecular weights. The higher the weight, the longer the chain and more viscosity created when mixed. These polymers are invaluable when used correctly for drilling reactive formations and should be incorporated into all drilling programs. I have had great success with low molecular weight PHPAs such as Baroid IDPs EZ-MUD GOLD.
Understanding the three basic components of lubricity, suspension and hole stability will make you successful 80 percent of the time. For that other 20 percent, we move from basic to complex drilling fluids and utilize specialty components. Loss circulation material can be added to a fluid to increase infiltrations control, stabilize a borehole or plug off a void. These materials also make an excellent way to sweep a hole without adding a PHPA, creating an unusable viscous fluid. The next specialty product assists in drilling reactive soils by changing the charge of the fluid. Wetting agents and surfactants help drill clay and shale by removing the clay’s characteristic sticky charge or by coating the tooling, thus preventing the reactive soil’s ability to attach. Finally, we can change fluid properties with dispersant. Ideally, these products should be used for development and breaking down bentonite gel.
Understanding the essential components is an excellent first step. The next step is to test your drilling fluid properties and interpret the results. A basic slurry test kit with a Marsh funnel, sand content, mud scale and water quality test strips can take you to the next level. The ability to explain your drilling fluid properties to your mud engineer is invaluable. Once you get comfortable with the basic test, you can move on to the filter press and rheometer. Ten years ago, it was difficult to create a universal drilling fluid able to drill a wide range of geologies. Product improvements and innovations have allowed us to develop fluids that utilize all four components. Twenty-first century drilling fluids will minimize the impact of the drilling process by stabilizing the borehole through inhibiting reactive soils, plugging porous structures and effectively cleaning all cutting from the hole. Drilling no longer has to be disruptive.