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Salt Dome Drilling

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Salt Dome Drilling

Directional drilling programs are sometimes used to overcome the
problems of drilling near salt domes. Instead of drilling through the salt,
the well is drilled at one side of the dome and is then deviated around and
underneath the overhanging cap.

Use Of Torque & Drag Programs For BHA Weight Evaluation

Use Of Torque & Drag Programs For BHA Weight Evaluation

These programs have a wide range of applications, but have mainly been
used to evaluate drillstring design integrity and alternative well plans for
horizontal wells or complex, unusual directional wells. However, the
program can be used to check BHA weight calculations for normal
directional wells. The program will calculate axial drag for a non-rotated
assembly and also calculates the position of the neutral point in the
drillstring. In addition, the program calculates the forces on the drill pipe
and will “flag” any values of compressive load which exceed the critical
buckling force for the drill pipe.

Typical Drillstring - Wellbore Friction Factors

The E*C TRAK Torque and Drag Module

The E*C TRAK Torque and Drag Module
This program, developed at the Drilling Research Center in Celle,
Germany, is used to calculate torque and drag when a friction factor
(coefficient of sliding friction) is known or estimated. It will calculate the
friction factor when either torque or hookload is known.
Software accuracy has been verified against actual field data, with inputs
and outputs handled in user selected units.
General Uses
The program may be used to:
• Optimize well path design for minimum torque and drag
• Analyze problems either current or post-well
• Determine drillstring design limitations
• Determine rig size requirements
Inputs Required
• Drillstring component data (OD, ID, tool joint, and material
composition)
• Survey data (actual or planned)
• Friction factor(s) or actual hookload or torque values (for friction
factor calculation)
Outputs
Information concerning loads, torques and stresses are calculated for
discrete points in the drillstring from rotary table to the bit. These values
are output in both tabular (summary or detailed) and graphical formats:
• Drag load (pick-up or slack-off)
• Pick up load
• Slackoff load
• Rotating off bottom load
• Drilling load
• Rotating off bottom torque
• Rotary torque (drilling and off-bottom)
• Maximum allowable hook load (at minimum yield)
• Drillstring weight (in air)
• Bit to neutral point distance drillstring twist
• Drillstring twist
• Axial stress
• Torsional stress
• Bending stress
• Total equivalent stress

Computer Models of Drillstring Friction

Computer Models of Drillstring Friction

Proper evaluation of drillstring friction requires the use of a computer
program. These programs analyze drillstring friction for rotary drilling as
well as drilling with no drillstring rotation.
These mathematical models make a number of simplifying assumptions
and consider the drillstring as composed of discrete elements. Using these
models, it is possible to solve equations for the normal force of drillstring/
well bore contact at the bottom drillstring element, the friction force
deriving from that normal contact force, and the load condition at the upper
end of the drillstring element. Such methods, repeated for each drillstring
element over the length of the drillstring, yield the following information:
• Surface hookload and rotary torque
• Normal forces of drillstring/well bore contact at each drillstring
element
• Average torsional and tensile load acting upon each drillstring
element

Along Hole Components of Force

Along Hole Components of Force

Consider a short element of a BHA which has a weight W.
Effective weight in drilling mud = W(BF)
Component of weight acting along borehole = W(BF)cosq
If the BHA is not rotated, the force of friction, FFR acting up the borehole
on the BHA element is given by:
FFR = mN
...where m is the coefficient of friction,
N is the normal reaction force between the BHA element and the borehole
wall. If this normal reaction is due only to the weight of the BHA element
itself, then:
N = W(BF)sinq and hence
FFR = mW(BF)sinq
The net contribution to the WOB from this BHA element is therefore
WBIT = W (BF) (cosq - msinq)

Along Hole Components of Force

Torque & Drag

Torque & Drag

Several factors affect hole drag, including hole inclination, dogleg severity,
hole condition, mud properties, hole size, and drillstring component types,
sizes and placement. However, as mentioned earlier, in drilling situations
where the drillstring is not rotated (as when a steerable system is used in
the oriented mode) axial drag can become very significant and should be
evaluated using a Torque and Drag computer program. Torque and Drag
programs can be found in EC*Track and DrillByte.

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Pages

Salt Dome Drilling

Use Of Torque & Drag Programs For BHA Weight Evaluation

Typical Drillstring - Wellbore Friction Factors

The E*C TRAK Torque and Drag Module

Computer Models of Drillstring Friction

Along Hole Components of Force

Along Hole Components of Force

Torque & Drag

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