Recently, we presented the most popular Cascade webinar to date, Drilling 104: An Introduction to Rotary Drilling, providing newcomers and seasoned professionals with valuable insights into rotary drilling technology.
If you missed the live webinar, it’s now available to watch on-demand.
Participants submitted numerous questions covering various applications and scenarios. In this two-part blog series, seasoned drilling veterans share their expertise. You can read Part 1 here. Today’s post is Part 2.
1. What’s the Typical Productivity (Feet Per Day) of Rotary Drilling in Hard Rock Lithology?
The nature of the rock can make a big difference, but in hard and competent rock, you can expect between 200 and 350 feet per day. Using dual tube, it's not uncommon to achieve 600 to 800 feet per shift. In one project, we drilled 750 feet of 12.75 inch-diameter boring in a single shift. Overall, productivity varies widely, but in good conditions, 200 to 350 feet per shift is typical, depending on the borehole diameter.
2. What is the Greatest Depth You Have Drilled with a Rotary Rig?
In the environmental services industry, deep drilling is uncommon. At Cascade, the deepest we've drilled using rotary was about 2,200 feet. In a previous company, we went as deep as 3,000 to 3,500 feet. While deeper boreholes are rare, we have the equipment to handle them.
3. What is the Preferred Well Development Method(s) When Utilizing Mud Rotary?
Well development is crucial for ensuring a productive well. The best method involves:
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Completing drilling and allowing cement to cure.
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Evacuating heavy drilling fluids via airlifting.
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Using a double swab from the top to the bottom of the screen, aggressively swabbing and airlifting (six minutes per foot of screen).
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Adding a dispersant and blind swabbing from the bottom to the top of the screen.
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Airlifting and swabbing again from top to bottom.
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This thorough process ensures optimal well productivity.
4. When Using a Drilling Mud During Monitoring Well Installations, What Steps Can Be Taken to Ensure Representative Groundwater Samples?
Using a SimulProbe® is recommended. Once the bit reaches just above the desired sample depth, pull the drill out, run a SimulProbe sampler, and drive it into the undisturbed formation to obtain a water and formation sample. For more on groundwater sampling, refer to Sampling 102: 4 Ways to Collect Deep Groundwater Samples During Drilling.
5. What Are Typical Ranges for Air/Fluid Pressures During Operation?
Air or fluid pressure ranges depend on the method used—dual tube reverse, flooded reverse, or direct air. Higher psi is used the deeper you go. If using an air sub to assist with airlifting, lower pressure systems can be run. Foam or polymer can also lower the pressure needed by occupying borehole space.
6. Are There Any Types of Refuse That You Can’t Get Through Using Air Rotary Casing Hammer (ARCH) Drilling?
Yes, if drilling in a landfill and encountering an engine block or railroad steel, these can damage the drill bit. Drilling in landfills can be hit or miss, but sometimes moving a few feet can reach the required depth.
7. How Can You Best Identify the Water Table/Saturated Zone While Drilling?
When drilling where the borehole isn't full of fluids, it's easy to determine the water table by observing saturated cuttings or water at the surface. In fluid-filled boreholes, historical data and drill cuttings are indicators. Mud temperature changes can also indicate proximity to the water table. Setting a test well is a definitive method but incurs additional costs and time.
8. When Would I Need/Use Temporary or Permanent Steel Casing When Drilling?
Use casing anytime the formation won't stand open with direct air and you don't want to use mud. Temporary casing stabilizes the borehole during drilling.
9. What Are the Primary Factors That Determine What Rotary Rig Size Is Used?
The primary factors are the formation, required borehole depth, and diameter. Other considerations include project goals and budget. These criteria affect rig selection regardless of the drilling technology.
If you’d like to learn more about rotary drilling, be sure to watch Bryan and Mike’s webinar, Drilling 104: An Introduction to Rotary Drilling.
