WorldWide Drilling Resource

12 MARCH 2022 WorldWide Drilling Resource® Hammers / Bits / Tooling by Ronald B. Peterson Drilling Products Specialist, Mountainland Supply Company This month, we will briefly discuss the downhole assembly, including hammers, bits, collars, and tooling; along with their interaction with drilling fluids. Fluids are by definition, anything that flows and takes the shape of its container. Fluids can be either gas or liquid. When drilling with a hammer, fluids are often simply air - although it is somewhat compressed. In hammer drilling, the fluid or air has multiple purposes. You need to have sufficient air to trip the hammer and make it strike the bottom of the hole firmly enough to cause it to fail or break and create cuttings. It then passes around the bit, cleaning the cuttings created by the hammer action - this is from the bottom of the hole to ensure the hole is clean so more cuttings can be created by future hammer blows. The air then has to move up the inside of the drill pipe fast enough so it can carry the cuttings with it to the surface. When drilling with a conventional bit, the air goes down the drill pipe, around the face of the bit, and up the annulus of the borehole. The air in this case actually has to have a higher volume to carry the cuttings up the hole, since there is typically more space in the annulus. This results in a need for larger volumes of air to clean the hole. When circulating the air up from the open hole at the volumes and speeds required, it can be very erosive to the borehole and cause borehole instability, so it works best if the borehole is very competent. There are two ways to clean the borehole - velocity and viscosity. One of the ways to reduce the amount of air required, is to make it thicker by adding a foaming agent and/or a polymer so it can better carry the cuttings out of the hole. This also reduces the potential erosion of the borehole. When drilling conventionally with a fluid, the basic ingredient used in water well drilling is water. Like air, there are still two ways to clean the borehole - velocity and viscosity. The water, just like the air, can be made thicker by adding the proper additives to it. This reduces the velocity of the fluid and helps maintain borehole stability. In reverse circulation, the drilling fluid goes down the annulus, around the face of the bit, and up the inside of the drill pipe. In conventional circulation, the fluid goes down the drill pipe and up the annulus. In either case, the fluid must cool and lubricate the bit, clean the bottom of the hole, and carry the cuttings back to the surface. In any case, the drill pipe will have lower velocity and the collars (bottom hole assembly) will have a higher velocity. This is simply a thumbnail sketch of the interaction of the hammers, bits, drill string, and bottom hole assembly. We will discuss more specifics in other articles. Feel free to contact me or your drilling fluids professional for more detail. Ron Ron Peterson may be contacted via e-mail to michele@worldwidedrillingresource.com WTR

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