TADPRO - Torque and Drag Model

• TADPRO: Torque and Drag Model (English)
• TADPRO: Modelo de par y arrastre (Española)
• TADPRO: 摩阻和扭矩模型 (中文)

• Torque and Drag: Concepts that Every Drilling and Completion Engineer Should Know

Q1. How are friction factors (FFs) defined in TADPRO?
FFs are defined in Wellbore Interval table. Cased hole friction factors (CHFFs) and open hole friction factors (OHFFs) are defined separately. These are user defined values, though recommended values are accessible using the quick help feature next to the FF portion of the table (the question mark button).
For sections of the string that have tools or centralizers, the friction factor might be reduced or changed. This can be accounted for at the bottom of the detailed table for each component by using a percent friction reduction.
If the tools/centralizers are free to rotate relative to the string, the rotational FF is used to calculate torque instead of the values listed in the wellbore intervals table.

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Q2. What is the calculation interval option?
It defines the locations of string bottom where the torque and drag profile is calculated. The smaller the calculation interval, the longer the calculation time.
The calculation interval simply determines how often points are calculated/placed in the history graphs. History graphs are hook load and surface torque, as well as stretch and twist graphs. The default interval is 100 ft, though smaller intervals can be chosen to increase the accuracy or smoothness of the history graphs. Since a full set of profile tables/graphs (side force/axial force/torque) are needed for each point placed in a history graph, choosing a small calculation interval can increase the required calculation time.

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Q3. What is the “Calculation on survey points” option?
T&D software calculates in small segments and cumulatively sums the results, beginning at the bottom of the string and working up to the surface. Choosing the ‘calculate on survey points’ option will set the segment length to the distance between survey points, as reflected in the survey. Surveys with a 100 ft interval for a 15,000 ft well would result in 150 separate sections over which torsional and axial forces are determined.
For each string bottom location, in order to calculate torque and drag, the pipe is divided into many elements. Each component should have the same mud weight, wellbore size, pipe geometry and dogleg. Calculation on survey points ensures the same dogleg in each component.

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Q4. What does the “Calculate torque and drag without FF reduction” option do?
This will run an automated comparison between the T&D model as set up and the T&D model without friction reduction applied. The without friction reduction T&D model affects the pipe tab only by setting the ‘FF reduction’ to zero and the tool/centralizer ‘free to rotate’ box to unchecked for all pipe components.

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Q5. What is the side force normalization length, and how does it affect side force?
Side force is calculated as a force per distance (i.e. lb/ft). The normalization length simply multiplies the force per unit distance by a length. The normalization length does not affect the calculations, but rather the numbers displayed in the side force graph. At 100 lb/ft, a normalization length of 31 ft would show 3,100 lbs in the graph vs. a normalization length of 40 ft resulting in 4,000 lbs on that same graph.
When the side force is set to ‘per joint’, the normalization length will default to the joint length for each pipe component. It is therefore possible to have the side force normalized for different length components in the same graph, such as 31 ft for drill pipe and 40 ft for casing/liner.

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