37 OCTOBER 2024 WorldWide Drilling Resource® Drilling Fluid Circulation by Ronald B. Peterson Let’s talk about drilling fluid circulation methods and applications. The drilling fluid circulation method is how we clean the borehole, remove the cuttings, control any borehole pressures, and maintain the integrity and stability of the borehole. The various methods of circulation include: nothing, air and the various iterations of air, and mud. The formations to be drilled, any anticipated downhole pressures, and the drilling equipment used will play into the decision you make in determining the circulation method that will be the most effective to drill the hole, remove the cuttings, maintain borehole stability, protect the anticipated production zones, and optimize the final well production. A fluid, by definition, is anything that flows and takes the shape of the container it is in. A fluid can be liquid or gaseous. If you are drilling the borehole with a vibrasonic rig and the borehole has adequate integrity, you may be able to complete the borehole without using any drilling fluid. Air is usually the fastest method of circulation. This is due to the fact that air is the lightest fluid. This means it exerts the least hydrostatic pressure on the bottom of the borehole and allows cuttings to come off of the bottom of the borehole, clearing it so the bit can continue to generate more cuttings. Air is also the highest energy circulating environment with hole velocities of 1000 to 3000 feet per minute. The high energy characteristics of air drilling require the formation be stable and competent, even though it may be fractured (vugular). Water is often injected into the air stream during air drilling to help suppress the dust. When air by itself will not keep the borehole clean, you can thicken the air by injecting a fluid containing water and a foaming agent. The foam generated from this injection fluid then becomes the cutting carrying agent and you can reduce the amount of air used in drilling the borehole. This will also reduce costs since you will need less fuel to run your air compressor. The next step in air drilling is to add a polymer to your injection fluid which will make the air still thicker and reduce the air requirements even more. Stiff foam by reducing the energy required to clean the borehole, also helps maintain the stability of the borehole. If one of the air methods will not maintain borehole stability, you can go to a casing advance system if you have the correct equipment, or use a properly designed drilling fluid. This is a brief synopsis of drilling fluid circulation methods. They continue to evolve and change as the available equipment and applicable chemistry changes. Always remember, “A man has to know his limitations,” but he doesn’t have to be defined by them. He can raise the bar. Working together, it is amazing where we can go. Let’s enjoy the trip! If you have any questions on drilling fluids or if you have another topic you would like addressed, please remember this column is ours. Your input helps me make it of value to you. It needs to be an interactive tool. I need your feedback. Please send your suggestions to Michele (below) and she will get them to me. Ron Ron Peterson may be contacted via e-mail to michele@ worldwidedrillingresource.com WTR Note from the Publisher: Have you taken a few minutes as each of these issues of WWDR arrive, and you read through it, to see how Ron Peterson focuses on the topics we present each month? Hmmmm . . . Makes one think, doesn’t it? He has the knowledge ~ He is willing to share his knowledge with you ~ each month. Go ahead, ask him a question. I’ll bet he knows the answer.
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