Mixing and Handling of Drilling Fluids

Products function as they should, so be sure you know how to properly do things.

By Ronald B. Peterson

A fluid is defined as anything flowing and tending to take the size and shape of its container. When we talk about drilling fluids, we are talking about whatever your circulating medium is. Sometimes it is
air; sometimes it is air with additives; and sometimes it is water with additives as needed. It can be more exotic in other drilling disciplines on occasion.

The physical properties of both air and water can be modified to facilitate our needs and enhance our drilling project. It should be designed to improve our performance, minimize our problems, and improve our profitability.

Drilling fluid additives are anything altering the chemical or physical properties and characteristics of the fluid.

Products will only function for us and perform as they should if they are properly mixed.

Proper mixing will:

  • Activate the products’ functions. We need to make sure the desirable properties of each additive are fully activated.
  • Enhance the ability to achieve the desired fluid properties. By activating the function of the products we will be able to achieve and maintain the desirable properties of the drilling fluid.
  • Ensure full performance of the drilling fluid additives. We need to have adequate shear in the mixing equipment and time for the additive to mix. This will maximize the product’s yield and performance. This will also reduce the potential for any unintentional un-yielded product to be introduced to the borehole.

We need to make sure we achieve the maximum potential of each additive so we get the full value of the drilling fluid and its impact on our drilling operation. We do not want unyielded additives to cause us to waste money and reduce our profitability.

We have spent a lot of time researching the project and making sure we know what we need to maximize our overall performance and minimize any potential problems. Now we should make sure that time and effort were well spent.

The Requirements

Drilling fluids require:

  • Planning of the project, which we have already done as the first step.
  • A well-designed drilling fluids system with adequate capacity, solids control equipment, and baffling. The drilling fluid needs to be designed based on the available drilling fluid equipment as well as the anticipated lithology and challenges in the borehole.
  • A good source of product-friendly make-up water. The water needs to be low in calcium—less than 100 mg/L, low in chlorides—less than 500 mg/L, low in chlorine—less than 100 mg/L, and preferably have a pH of ±9.0. We may need to add soda ash in order to achieve those parameters. The average tap water across the U.S. is more than 200 mg/L calcium with a pH of ±7.0.

Products need to be added in the correct order:

  • If a product is used to adjust the chemical properties of the water, then it needs to be added first to ensure those properties are adjusted before any additives which would be impacted by the properties of the water are introduced.
  • Bentonite products need to be added next and must be given adequate shear and time to hydrate before any other additives are introduced.
  • Polymer products can be added next. One of the inherent properties of polymers is they will inhibit the hydration and yield of other products as well as activate sections of the borehole.
  • Dry products must be added before liquid products. Polymers need to have adequate shear to assure hydration, but not so much as to break down the individual polymer chains, which can change their properties. Always mix dry polymers first since they require less initial shear and more time to fully hydrate. Allow them enough time to fully hydrate before you add any liquid polymers. Liquid polymers require more shear but less time to hydrate.
  • All drilling fluid additives mix best when mixed slowly. This provides them enough time to fully hydrate.

Have Time

We’re always in a hurry to get things done, but one of the most critical things in any mixing operation is adequate time to allow the products to shear and mix.

We need to make sure we achieve the maximum potential of each additive so we get the full value of the drilling fluid and its impact on our drilling operation.

My father frequently said, “If you don’t have time to do it correctly the first time, how will you find time to do it over?” And then there are the costs involved in doing things twice. I know I always feel like I go faster sometimes if I slow down.

If we get in a hurry at the beginning and don’t take the time to properly mix our drilling fluid, we will fight hole instability at the top of the borehole the entire drilling operation.

A properly designed drilling fluid has properties built into it to stabilize and minimize problems in the most fragile and sensitive section of the borehole. Sometimes it is better and more cost effective to design the casing program to cover that section of the borehole—so we don’t need to worry about it.

If that is not an option, the alternative is to design the drilling fluid to provide that level of protection. Be careful not to ask a drilling fluid to do something it’s not capable of.

We may encounter the need to mix drilling fluid to maintain our desired properties, but don’t feel we have the time required. In order to keep drilling progress moving ahead, we must maintain our volume with fresh water and allow it to cascade past water-sensitive and fragile portions of the borehole, destabilizing them, and ultimately slow or halt our drilling progress.

I am a firm believer in a prehydration or premix system. A prehydration system will provide a backup volume of fluid on location that is fully mixed with the desired properties so it can be introduced into the borehole immediately if and when needed to minimize the possibility of allowing the drilling fluid properties to get out of the desired range due to time constraints in mixing. A prehydration system is an insurance policy on the success of your project.

I would like to close by emphasizing this is our column. If you have a topic you want to see discussed, let me know.

Until we meet again.

Ronald B. Peterson was hired in 1977 by Baroid Industrial Drilling Products as a field service representative and has worked in various positions for the company, including as an account rep and manager. He can be reached at ron.peterson@halliburton.com.



Tooling Up
To help meet your professional needs, this column covers skills and competencies found in DACUM charts for drillers and pump installers. DO refers to the drilling chart. The letter and number immediately following is the skill on the chart covered by the column. This column covers: DOB-1, DOB-3, DOB-4, DOD-2, DOE-2, DOE-13 More information on DACUM and the charts are available at www.NGWA.org.