Kelly Pipe Calculator

Calculate total hook load by defining the components of your drill string.

Drill String Weight Calculator

Weight Component Breakdown

Component	Length (ft)	Weight per Foot (lbs/ft)	Total Component Weight (lbs)	% of Total Weight
Kelly Pipe	40	151	6,040	5.8%
Drill Pipe	5,000	19.5	97,500	94.2%
Total	5,040	–	103,540	100%

Summary of drill string components and their respective contributions to the total hook load.

What is a Kelly Pipe Calculator?

A kelly pipe calculator is a specialized tool used in the oil and gas drilling industry to determine the weight of the drill string. The Kelly is a heavy-duty pipe with a square or hexagonal cross-section that is used to transmit rotary motion from the rotary table or top drive to the drill string. Calculating the weight of the Kelly and the attached drill pipes is fundamental to understanding the total hook load—the total weight hanging from the rig’s hoisting system. An accurate kelly pipe calculator is essential for drillers and engineers to ensure safe operating parameters, prevent equipment overload, and manage the forces applied during drilling. This tool simplifies what can be a complex manual calculation, providing quick and reliable weight estimations which are critical for operational efficiency and safety on the rig.

This type of calculator is primarily used by drilling supervisors, rig managers, and drilling engineers. Miscalculating the string weight can lead to catastrophic failures, including dropped strings or derrick collapse. A common misconception is that the Kelly itself provides the majority of the weight; however, as our kelly pipe calculator demonstrates, the thousands of feet of drill pipe typically make up the bulk of the hook load.

Kelly Pipe Calculator Formula and Mathematical Explanation

The calculation performed by the kelly pipe calculator is based on fundamental principles of weight and mass. It computes the total weight of the drill string (in air) by summing the individual weights of its main components: the Kelly pipe and the drill pipes. The formula is broken down into steps:

1. Calculate Total Kelly Weight: This is found by multiplying the length of the Kelly pipe by its nominal weight per unit length.
2. Calculate Total Drill Pipe Weight: Similarly, the total length of all drill pipes is multiplied by the nominal weight per unit length of the pipe.
3. Calculate Total Hook Load: The final step is to add the total Kelly weight and the total drill pipe weight together.

The general formula is:
Hook Load = (L_k × W_k) + (L_dp × W_dp)

It is important to use a reliable kelly pipe calculator like this one to ensure these values are computed accurately for a safe Drill String Weight Calculation.

Variables in the Hook Load Calculation

Variable	Meaning	Unit	Typical Range
Lk	Length of the Kelly Pipe	Feet (ft)	40 – 54
Wk	Weight per foot of the Kelly	Pounds per foot (lb/ft)	80 – 180
Ldp	Total Length of Drill Pipe	Feet (ft)	1,000 – 30,000+
Wdp	Weight per foot of the Drill Pipe	Pounds per foot (lb/ft)	15 – 25

Practical Examples (Real-World Use Cases)

Using a kelly pipe calculator is a daily task in drilling operations. Here are two practical examples:

Example 1: Shallow Onshore Well

An engineer is planning a shallow vertical well. The plan requires a 40-foot Kelly and 3,500 feet of drill pipe.

• Inputs:
  • Kelly Length: 40 ft
  • Kelly Weight: 147 lb/ft
  • Drill Pipe Length: 3,500 ft
  • Drill Pipe Weight: 19.5 lb/ft
• Calculator Output:
  • Kelly Weight: 40 × 147 = 5,880 lbs
  • Drill Pipe Weight: 3,500 × 19.5 = 68,250 lbs
  • Total Hook Load: 74,130 lbs
• Interpretation: The drilling supervisor knows the hoisting system must safely support over 74,000 lbs. This value is also crucial for determining the available weight on bit (WOB). The kelly pipe calculator gives a baseline for the Hook Load Formula before accounting for buoyancy.

Example 2: Deep Offshore Well

A deepwater project involves drilling to a total depth of 18,000 feet with a more robust drill string. A 54-foot Kelly is used.

• Inputs:
  • Kelly Length: 54 ft
  • Kelly Weight: 178 lb/ft
  • Drill Pipe Length: 18,000 ft
  • Drill Pipe Weight: 21.9 lb/ft
• Calculator Output:
  • Kelly Weight: 54 × 178 = 9,612 lbs
  • Drill Pipe Weight: 18,000 × 21.9 = 394,200 lbs
  • Total Hook Load: 403,812 lbs
• Interpretation: The immense hook load of over 400,000 lbs highlights the importance of precise calculations. A simple mistake could exceed the derrick’s capacity. The kelly pipe calculator provides the data needed to select appropriate equipment and drilling parameters.

How to Use This Kelly Pipe Calculator

This kelly pipe calculator is designed for simplicity and accuracy. Follow these steps to get your results:

1. Enter Kelly Length: Input the length of your Kelly pipe in feet in the first field.
2. Enter Kelly Weight: Input the linear weight of the Kelly in pounds per foot (lb/ft). You can find this in the manufacturer’s specifications.
3. Enter Drill Pipe Length: Input the total combined length of the drill pipe sections in the string.
4. Enter Drill Pipe Weight: Input the linear weight of your drill pipe in pounds per foot (lb/ft).
5. Review Results: The calculator will instantly update the Total Hook Load, along with the individual weights of the Kelly and drill pipe. The chart and table will also adjust to provide a clear visual breakdown. These results are essential for understanding your setup, and our kelly pipe calculator makes the process effortless. You can learn more about Drilling Engineering Basics on our blog.
6. Reset or Copy: Use the ‘Reset’ button to return to the default values or ‘Copy Results’ to save the output for your reports.

Key Factors That Affect Kelly Pipe Calculator Results

While this kelly pipe calculator provides the weight in air, several factors affect the actual hook load during operations:

• Drilling Fluid (Mud) Weight: Drilling fluid exerts a buoyant force on the drill string, reducing the effective weight (hook load). Our calculator provides the air weight, which is the maximum possible load. A higher mud weight results in a greater buoyant force and a lower hook load.
• Pipe Dimensions: The outer diameter (OD) and wall thickness determine the pipe’s weight per foot. Using the correct weight value from specifications is critical. Even a small error can be magnified over thousands of feet.
• Component Wear: Over time, drill pipes can lose wall thickness due to abrasion and corrosion, slightly reducing their weight. Regular inspections are necessary to update these parameters for an accurate kelly pipe calculator.
• Additional Components (BHA): The Bottom Hole Assembly (BHA), which includes drill collars, stabilizers, and the bit, is not included in this calculator but adds significant weight. It must be calculated separately and added to the string weight. We have a separate Top Drive vs Kelly analysis tool for that.
• Hole Drag and Friction: In deviated or horizontal wells, friction between the drill string and the wellbore can add significant tension (drag), increasing the hook load when pulling out of the hole.
• Temperature Effects: Thermal expansion of the steel pipe in a hot wellbore can slightly alter its length and properties, though this is often a secondary effect compared to buoyancy and friction. Using a kelly pipe calculator is the first step in a comprehensive analysis.

Frequently Asked Questions (FAQ)

1. What is the difference between a Kelly and a top drive system?

A Kelly system uses a rotary table on the rig floor to turn the Kelly, which in turn rotates the entire drill string. A top drive system is a motor that hangs from the derrick and rotates the string directly from the top. Top drives are more modern and efficient, but Kelly systems are still in use. This kelly pipe calculator is relevant for rigs using a Kelly and rotary table.

2. Why isn’t buoyancy included in this calculator?

This tool is designed to calculate the static weight of the drill string in air, which represents the maximum load on the derrick. Buoyancy depends on the drilling fluid’s density, which can change. Calculating the air weight is a crucial first step before applying a buoyancy factor.

3. How do I find the weight per foot of my pipes?

The weight per foot (or nominal weight) is a standard specification provided by the pipe manufacturer. It can be found in API specification sheets or pipe data tables. Using the correct value is essential for an accurate kelly pipe calculator result.

4. Does this calculator work for heavyweight drill pipe (HWDP)?

You can use this calculator for HWDP by adding its weight and length to the “Drill Pipe” fields. For a more precise calculation involving multiple string components, you should calculate each section’s weight separately and sum them up.

5. What is hook load?

Hook load is the total force pulling down on the hook of the traveling block in a drilling rig. It includes the weight of the drill string, Kelly, BHA, and any other attached equipment, minus the buoyant effect of the drilling fluid. Our kelly pipe calculator helps determine the largest component of this load.

6. Is this calculator suitable for casing strings?

Yes, you can adapt it. Simply enter the total casing length in the “Drill Pipe Length” field and the casing’s weight per foot in the “Drill Pipe Weight” field. Set the Kelly inputs to zero.

7. What happens if the actual hook load exceeds the calculated value?

If the measured hook load (from the weight indicator) is significantly higher than the value from a kelly pipe calculator, it could indicate a problem, such as borehole friction (drag) or sticking. If it’s lower, it might point to an issue with the weight indicator itself.

8. Where does the Bottom Hole Assembly (BHA) fit in?

The BHA is the lowest part of the drill string. Its weight should be calculated separately and added to the total from this kelly pipe calculator to get the complete string weight. Drill collars in the BHA are very heavy and are the primary source of weight on bit (WOB).