8 MARCH 2024 WorldWide Drilling Resource® HDD by Ronald B. Peterson Drilling Products Specialist, Mountainland Supply Company We have been talking “Drilling Fluid Maintenance” and we still have a way to go in future articles, but the focus of the magazine this month is Horizontal Directional Drilling (HDD), so we will take a break and discuss it. HDD is advancing a hole that is as the name indicates, horizontal, usually very shallow, and must be very carefully monitored using sophisticated equipment to make sure it is on target to reach the desired location. Very frequently these bores are drilled in an area where there are already several electrical, communication, gas, and water lines. The direction and location of the bit must be very accurate and precise to avoid causing issues with existing infrastructure in the area. The fluid properties and the testing procedures are similar in horizontal drilling and vertical drilling with a couple of exceptions. Calcium or hardness and pH still need to be identified, measured, and controlled at desirable levels. Calcium preferably below 200 ppm (parts per million), and pH between 8.5 and 9.5. Filtrate or water loss and filter cake are also still critical properties. Drilling fluid test procedures are basically the same, but some of the desired properties are different. A couple of viscosity related properties which will vary from vertical bores are viscosity, yield point, and gel strengths. Select a good, reliable, convenient source of make-up water, test it, and treat it as necessary. To get the desirable properties, add soda ash to adjust the calcium content and raise the pH as necessary. You will need a bentonite product designed to provide the correct properties for horizontal boring. Polymers may be necessary to achieve desirable filtration control properties, stabilize active formation clays and shales, and sometimes to provide carrying capacity. You may also need a lost circulation control material in very fragile formations. Viscosity is a measurement of the apparent thickness of the fluid or resistance to flow and can be a necessary evil. Viscosity is not an indication of carrying capacity of the fluid. It is resistance to flow, and you are trying to maintain flow. Gels, yield point, and viscosity - while related properties - are not the same. A thick fluid may not suspend cuttings, but a thin fluid can be designed to suspend cuttings. In horizontal drilling, flowability is the major concern. You are usually boring very close to the surface, so the ground is very fragile. High-viscosity fluid plus high solids content results in reduced flowability. Reduced flowability means more pressure will be required to move the slurry. High viscosity requires higher circulating pressures. High circulating pressures tend to break things and cause frac-outs (inadvertent flows), creating potential environmental and cosmetic concerns and/or humps in streets, highways, and driveways. This is never good! You need to suspend and carry the cuttings by building different properties related to viscosity. These properties are yield point and gel strength. Different bentonite products are designed to develop different drilling fluid properties; thus, they are designed for different drilling disciplines. Some provide high viscosities and others enhance the yield point and gels. Some polymers will give you a great deal of viscosity, but only a couple of them will give you an adequate yield point. Suspension is critical in horizontal directional drilling. Any solids generated need to be kept in suspension while in the borehole so they do not settle out and close off the bore. Gels are the tendency of the fluid to set up when idle. They need to be able to be broken easily so the fluid can flow again when disturbed. This ability is referred to as fragile gels. Equivalent circulating density (ecd) is a combination of the hydrostatic head and the pressure required to move the fluid. Fracture gradient is the pressure at which the circulating pressure exceeds the strength of the formation. If the ecd exceeds the fracture gradient, you will have a frac-out to the surface or into a stream, and/or an undesirable hump in an inconvenient location. Tooling in HDD is different from vertical drilling, as well. It is designed to advance the hole, but also to homogenize the cuttings and keep them in suspension. Tooling is also designed to help stabilize the bore. When you select drilling fluid additives, make sure they provide the properties you need to successfully complete the bore and install the product. If you have questions or concerns, contact your supplier to verify the products are fit for use in your application. Ron Ron Peterson may be contacted via e-mail to michele@worldwidedrillingresource.com DIR eranhenderson@gmail.com New & Used Tricones PDCs Drag & Claw Bits Drill Collars Bit Tipping Subs & Stabilizers HDD Bits & Reamers DTH Hammer & Bits Custom Fabrication Junk Mills / Fishing Tools Rod Henderson 661-201-6259 Eran Henderson 661-330-0790
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