Drill String Design and Optimization

Course objectives:

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 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. 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.

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 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. 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.