Issues That Can Occur While Drilling Wells
“There are no perfect drill holes, or drill rigs.” I have heard this more than once from multiple drillers. What does it mean?
First, not all geology is conducive to drilling. The local geology of a drill site can vary greatly, whether it changes gradually over a large area, or rapidly on an area as small as a drill pad. The materials that are being drilled through can change from soft to hard, loose to solid, or dry to wet. Each one poses a different set of challenges that must be overcome through knowledge, experience and the correct equipment choice. Underground faults can complicate matters even more. When faults are present, the geology can change drastically in a short distance. Therefore, engineers can only estimate what material the rig will be drilling through and prepare accordingly. LWS is onsite to assist with seeking answers and solving problems onsite in real time.
For example, sand is one of the softer materials to drill through. However, hole cave-ins and flowing sands can complicate drilling and has done so on several LWS projects, which I’ll explain later. On the other end of the hardness scale, materials like basalt, volcanic tuff, or granite are extremely hard and can be very slow and difficult through which to drill. Component wear and tear and equipment failure due to drilling through hard materials can also occur. Delays on past projects have occurred for these exact reasons. A robust geology review can help to identify problem zones and aid in the correct equipment choice.
Drilling in sand may sound fairly straightforward. Sand in general is not a cohesive material. During one LWS monitoring well drilling project, while drilling with a hollow-stem auger, approximately 20 feet below ground surface (“bgs”) the driller noticed a pinching of the drill bit. This was due to a cave-in at 10 feet bgs. Much of the material above the drill bit had caved in and was impeding the progress of the bit. The drill string had to be pulled out and then re-drilled through the cave-in. Sometimes water, or other fluids that can help stabilize the borehole, can be added to help with this situation. However, when native water quality is a critical issue, such as in environmental boreholes, LWS tries to avoid introducing foreign fluids, so as to avoid contamination of the formation. For additional information on water quality check out the LWS blog on Water Quality. In general, a good rule of thumb when drilling in sand is to progress slowly, keep the area around the auger free of debris, and watch for flowing sand issues. Cave-ins can be even more troublesome in deeper holes, mainly due to the time, effort, and associated costs involved in rectifying the situation.
Photo 1: 16 failed bolts on the drill head.
Photo 2: Close-up of one of the failed bolts after it was extracted.
On the other hand, the correct rig for the project is vitally important when drilling in hard material. LWS consults with drilling companies prior to the initiation of the field drilling program to discuss what materials are expected to be encountered during drilling. However, sometimes the geology can present unforeseen problems. When the geology encountered is unexpected, drilling times can be significantly affected if the drilling rig is not the right type of rig for the geology. For example, on a recent project where limited local geologic information was available, the rig struggled in advancing the borehole because the rig encountered large zones of clay instead of the expected geology, which swelled and pinched the bit causing it to struggle. As a result, there was an equipment fatigue failure, with bolts connecting the core barrel to the drill head eventually shearing, see Photos 1 and 2. Because the geology was more suited for a reverse circulation rotary rig with a downhole hammer, the change in equipment was made to more efficiently drill the boreholes. Additionally, the amount of heat, stress, and abuse drill rigs endure is a recipe for the degradation and failure of one, or multiple, components over time.
All in all, the correct rig and associated equipment can make or break a drilling project. Make sure you chose the right contractor and equipment for the geology. LWS is always here to offer advice and consult on your project.
If you are in need of a field drilling project to develop a groundwater monitoring plan, production well, and/or water quality sampling plan, LWS can help with your groundwater well needs. Feel free to give us a call (303-350-4090) or email our team members.
Bruce Lytle bruce@lytlewater.com
Chris Fehn chris@lytlewater.com
Ben Bader ben@lytlewater.com
Anna Elgqvist anna@lytlewater.com
Dan Rowe dan@lytlewater.com
Marlena McConville marlena@lytlewater.com
