22 MAY 2021 WorldWide Drilling Resource® Mud Balance and Pumps by Ronald B. Peterson Drilling Products Specialist, Mountainland Supply Company “Will the use of a mud balance while drilling affect the life of the pump and the performance of the well?” I was at the California Ground Water Convention banquet when the gentleman sitting next to me casually asked that question. Fortunately, over the years I have learned to think before I answer questions as there may be underlying issues at play. So I answered, “It depends.” (To buy time and get some background.) He then wanted to know what it depended on. I answered that it depends on why you were weighing the drilling fluid and what actions you planned on taking when you obtained the results. He responded that mud people often talk about mud weight, but not how it impacts the performance of the well and the life of the pump. Thinking about it, I realized we are guilty as charged. We talk about the impact on the drilling operations and the borehole, but do not carry it forward to the performance of the well upon completion. Water has a weight of 8.34 pounds per gallon or a density of 1.0; anything higher is due to other material in the water. The other material can be dissolved or colloidal. You can have a very viscous drilling fluid with a weight between 8.34 and 8.6 pounds per gallon. If the weight is higher than 8.6, it is either because we have added material to the fluid to increase the weight or because we have incorporated drilled solids into the fluid. Increased mud weight can cause many problems including increased wall cake thickness in the borehole, increased wear on the circulating system components, and increased hydrostatic pressure on the borehole. During the drilling process, the increased hydrostatic pressure on the borehole will result in a higher potential for drilled solids to be pushed into the aquifer, and higher potential for loss of circulation. It will also result in a reduced drilling rate because the higher hydrostatic pressure results in a greater chip hold-down pressure, which makes it harder to remove the bit chips from the face of the borehole and slows the advancement of the borehole. Higher drilling fluid weight also results in increased pumping cost and greater fuel consumption. During the completion phase, higher solids and the possibility of a thicker wall cake may cause problems in running casing. The higher mud weight and density will also increase the buoyancy of the casing, making it more difficult to float the casing into the borehole. Drill solids are typically the single largest contaminant in a drilling fluid system. A borehole 9.875 inches in diameter drilled to a depth of 200 feet with an average specific gravity of the solids at 2.65 would produce 17,578 pounds, or nearly 9 tons of solids. The weight or density of the drilling fluid is determined by using a mud balance, which can be obtained from your drilling fluid supplier. The desirable mud weight is as low as possible while still controlling any anticipated pressures, artesian flows, and/or borehole stability issues. The mud balance has four scales on it to report the weight. The weight can be reported in pounds per gallon (lbs/gal), specific gravity, pounds per cubic foot, or pounds per square inch (psi) per 1000 feet of depth. The accuracy of the mud scale can be verified by weighing water, which should be at 8.34 lbs per gal. The mud weight can be used to calculate the hydrostatic head of the drilling fluid, calculate the total solids content of the drilling fluid, and determine the efficiency of any solids control equipment you are using. To calculate the hydrostatic head, use the following formula: Hydrostatic Head (psi) = Drilling fluid or mud weight (lbs/gal) x depth (feet) x .052 To calculate the solids content, you can use the following formula: % (percent) solids* = (Drilling fluid or mud weight (lb/gal) - 8.3) x 8 *Assumes 2.6 specific gravity of solids So why do we care? During the drilling process, unless we take specific measures to control the drilling fluid weight, drilled solids may be broken up or dissolved and become incorporated into the drilling fluid system. A high drilling fluid weight, as mentioned earlier, can push those solids out into the production zone of the well, which will result in the need for longer development time and the need for higher amounts of energy to effectively develop the well. Solids pushed out into the aquifer production zone can also result in stubborn turbidity levels, which can be recurring over time and reduce the life of the pump. The accumulation of drilled solids into the drilling fluid is very seldom, if ever, a good thing. Increased solids make it difficult to control the density and the flow properties of the drilling fluid. Increased solids reduce the life of the drill bits and other surface equipment related to drilling fluid circulation. Increased drilled solids will result in higher volumes of fluids to dispose of after the well is drilled and the related disposal costs. Increased solids result in a greater risk of differential sticking and may result in issues during the grouting and/or cementing operations. The use of a mud scale to monitor the weight of the drilling fluid system and the other related potential issues is always a good thing to incorporate into the drilling operation. It is one of the first steps to take in ensuring the success of your drilling operation and the ability to provide a more problem-free water well to the client. The best way to minimize the buildup of solids in the drilling fluid system is the use of appropriate solids control equipment. So in short, the answer to the question: “Will the use of a mud balance while drilling affect the life of the pump and the performance of the well?” is YES. If you have questions about this topic or if you have another topic you would like me to address, please contact Michele (below) and she will let me know. If I don’t know the answer, I will find someone who does and is willing to share. We work in an amazing industry and have a tremendous resource base to pull from. Ron Ron Peterson may be contacted via e-mail to michele@worldwidedrillingresource.com Publisher’s Note: Have a chat with Ron at the Second Annual WorldWide DownHome DrillFest™in Branson, Missouri, August 16-18, 2021. WTR
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