Is Rotary Drilling Right for Your Project?
Apr 17, 2018 -
The selection of any drilling technology is dependent on a number of factors, both on and offsite. Timeline, budget, goals, and lithologies all heavily weigh into the project manager’s decision to opt for one drilling technology over another. Whether you’re facing a geotechnical or environmental project, the selection of the correct drilling technology has never been more important.
Rotary is often the drilling technology of choice when strength and depth are needed. The various rotary drilling technologies Cascade utilizes provide both power and versatility, thus helping to keep even the most challenging and costly projects on time and within budget. Read on for the various benefits of each rotary drilling methodology, as well as a practical example of the effectiveness this technology had for one Arizona client.
Advantages of Rotary Drilling
Why Should You Use Rotary Drilling?
- Rotary methods can effectively advance through both hard and soft lithology
- Depth & Diameter
- Capable of larger diameter bore-holes, rotary can also achieve deeper depths compared to direct push and auger drilling
- There are several combinations and variations of the rotary technology, each of which offers unique advantages with respect to lithology and site goals
Rotary drilling relies on a sharp rotating drill-bit with significant downward pressure to cut through the subsurface. Depending on the substrate, the drill casing is advanced as the hole is cut to keep the borehole open. Cascade offers four different rotary methods; air rotary, mud rotary, dual rotary, and reverse circulation technologies.
Air Rotary works very well in hard rock conditions. Plus, it has a low environmental impact and a maximized penetration rate to reduce drilling cost per foot. Additionally, air rotary provides good borehole cleaning capacities as well as clean cutting samples, with no infiltration of drilling fluids into the formation. This reduces well development time.
Mud Rotary is the preferred method in unconsolidated, alluvial and loose geological formations. This method builds a mud cake on the perimeter of the borehole that keeps loose deposits stable during drilling. There is an added benefit to mud caking process because it can seal off water-bearing zones and formations. Although mud rotary has a lower comparative cost and higher comparative production, there is a higher cost of well development and the additional burden of properly managing and disposing of the investigation derived waste.
Dual rotary Is the preferred method where there are unconsolidated formations like sand, gravel, and boulders. The rotary head has its own feed system and raises and lowers independently of the lower drive, advancing the casing as needed. The casing can be advanced ahead of the drill bit to minimize aquifer cross contamination, loss circulation, and eliminate borehole stability problems. The cost per foot is typically higher due to the cost of steel casing, welding, and installation time required to obtain the desired depth.
Reverse Circulation is a method of drilling which uses a dual wall drill rod that consists of an outer and inner tube. The inner tube allows the drill cuttings to be transported back to the surface in a continuous flow. The method requires a pneumatic hammer or tri-cone bit which provides a very representative sample. The method has high penetration rates. Reverse Circulation is often preferred for large diameter casing because it yields a high-quality borehole at very deep depths.
In sum, rotary drilling provides both power and versatility within substrates that can be tricky for other drilling technologies. Still, the use of a specific rotary methodology will depend heavily on the parameters of your projects.
A Real-world Example of the Power of Rotary Drilling
Cascade utilized rotary drilling for one Arizona client to safely recover well pumps and piping that had fallen over 700 feet below the surface to the bottom of two production wells.
The client had three specific goals in place: avoid the complete loss of two already-damaged production wells, recover the fallen equipment, and complete the project without injury or further damage.
The well pump and the drop pipe in two production wells presented some specific challenges, namely the depth and weight. One well was 735 feet deep, another was 835 feet deep, and the client estimated the weight of the column pipe, line shaft, and pump in excess of 50,000 pounds.
The site geology was comprised of sands, gravels, clays, volcanic rocks, and various bedrock. This geology, coupled with the particular on-site challenges required an innovative approach. With over a decade of experience under his belt, our Lead Driller was confident that a combination of air and mud rotary drilling technologies, along with the custom safety engineering controls, would provide the necessary power and versatility to complete the project.
The extensive weight of the equipment and well depth required a minimum pull back capacity on the drill rig of 100,000 pounds. To meet safety requirements, the drill rig and support equipment would require additional retrofits including handrails, lockout devices, and crown out devices. Lastly, all equipment had to pass a thorough safety inspection from the client and a third-party engineer.
The dual combo of air and mud rotary drilling was chosen because there is no other drilling technology capable of safely reaching the extreme depth and diameter required for this project. This particular rig is also capable performing a wide range of drilling tasks with little reconfiguration including air rotary casing hammer, down-hole hammer, direct air rotary and mud rotary. This range of function was quite useful in reducing down-time thanks to the near seamless transition between project phases.
All the damaged equipment was safely recovered on the first attempt in the first production well. The client was able to altogether avoid the cost of closing the well and installing a new one. This success was the result of the unique combination of Cascade’s expert crews, properly selected and effectively utilized drilling technology, and fishing equipment. The recovery project is still underway for the second well. Learn more about this project here.
It can be impossible to know if rotary drilling is right for your project without the help of a dedicated expert. This project is indicative of the level of experience and expertise Cascade crew members bring to complex on-site problems. The job sites and the problems are often unique, but at Cascade, we pride ourselves on finding the right solution.