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About this Training Course
The drillstring is often considered to be one of the most simple pieces of equipment in use on a drilling rig. Ninety-nine percent of the drillstring comprises plain tubes that are just screwed together. However, the Bottom Hole Assembly can go to the other extreme; including directional and lithological data and directional drilling equipment.
The principle tasks of the drillstring are also deceptively simple:
- To convey each drilling bit to the bottom of the hole and then retrieve it when worn;
- To act as a conduit to convey drilling fluid at high pressure down the hole to the bit; and
- To transmit torque from the surface to the bit.
A secondary task of the drillstring is to run and cement liners and act as the landing string for casings run and hung off in sub-sea wellheads. Indeed, deepwater landing strings are currently pushing the limits of conventional drillstring design. In performing these roles, the drillstring is exposed to a complex combinations of loads downhole including tension, compression, torque, bending, burst and collapse pressures, axial, lateral and torsional vibration, all under extreme temperatures. It also has to be able to resist corrosion and abrasion.
Drillstring failures can result in significant lost time and in some instances, significant well control problems or even the loss of the well.
- At best, a washout will require a round trip to locate and replace the leak. However, in Managed Pressure Drilling where the well is statically underbalanced, a shallow washout can lead to a severe well control challenge.
- Loss of the ability to circulate can lead to pack off in the annulus and stuck pipe.
- A twist off in open hole can prove difficult or even impossible to recover leading to significant financial impact of the loss of expensive MWD/LWD and/or directional tools and requiring a lengthy sidetrack. If it happens close to the previous casing shoe, it could lead to loss of the hole section and a change in the casing design for the well. It may result in not being able to reach TD with the required hole size.
Historically, drillstring design has been a very simplistic uni-axial engineering process. The industry has relied on very conservative design factors to avoid drillstring failures. However, as wells become deeper, hotter and with challenging directional demands, the drillstring has to be subjected to the same (if not more) rigorous engineering design as Casing and Tubing.
This 5-day course will address all elements of drillstring selection and design, integrating drilling optimisation with drillstring failure prevention. Participants will learn about the mechanical properties of all drillstring components, including their connections, both as individual pieces and when made up into a drillstring. Participants will also develop skills in the process of designing a drillstring using manual uniaxial and triaxial design techniques as well as spreadsheets and commercial tubular design software. Particular focus will be given to the impact and prevention of downhole drillstring vibration and failure. Equally, there is emphasis on how a comprehensive drillstring inspection process can minimise the risk of drillstring failures downhole.
