Engineering Calculators & Drilling Tools
Dogleg Severity (DLS) Calculator
This calculator determines the Dogleg Severity (DLS), a critical measure of borehole curvature in directional drilling. By inputting survey data from two points, you can accurately quantify the change in trajectory, which helps in managing torque, drag, and casing wear. This tool is essential to calculate dog leg using any TVD-correlated survey data.
Select the unit for Measured Depth.
Survey Station 1 (Upper)
MD at the upper survey station.
Angle from vertical in degrees.
Directional angle from North in degrees.
Survey Station 2 (Lower)
MD at the lower survey station.
Angle from vertical in degrees.
Directional angle from North in degrees.
Dogleg Severity (DLS)
2.60 °/100ft
Intermediate Values
2.60°
100.00 ft
2204.05 ft
Survey Angles Comparison
What is Dogleg Severity?
Dogleg Severity (DLS) is a fundamental concept in directional drilling that quantifies the total curvature of a wellbore over a specific length. It combines the change in both inclination (the vertical angle) and azimuth (the horizontal direction) to provide a single rate of change, typically expressed in degrees per 100 feet or degrees per 30 meters. Drilling engineers, directional drillers, and geologists use DLS to assess wellbore tortuosity. High dogleg severity can lead to significant operational problems such as increased torque and drag, drill pipe fatigue, casing wear, and difficulties running logging tools or completing the well. Therefore, to accurately calculate dog leg severity using any TVD-correlated survey data is crucial for planning a smooth well path and preventing costly issues.
Dogleg Severity Formula and Explanation
The most widely accepted method for calculating DLS is the Minimum Curvature method. It models the wellbore path between two survey stations as a smooth circular arc. The dogleg angle (β), representing the total angle change, is calculated first.
The formula for the Dogleg Angle (β) in degrees is:
β = arccos(cos(Inc₂ - Inc₁) - sin(Inc₁) * sin(Inc₂) * (1 - cos(Azi₂ - Azi₁)))
Once the dogleg angle (β) is found, the Dogleg Severity (DLS) is calculated by normalizing this angle over a standard course length (e.g., 100 ft or 30 m).
DLS = β * (Standard Length / Course Length)
| Variable | Meaning | Unit (Auto-Inferred) | Typical Range |
|---|---|---|---|
| Inc₁, Inc₂ | Inclination at survey stations 1 and 2 | Degrees | 0 – 90 |
| Azi₁, Azi₂ | Azimuth at survey stations 1 and 2 | Degrees | 0 – 360 |
| MD₁, MD₂ | Measured Depth at survey stations 1 and 2 | feet or meters | 0 – 30,000+ |
| β | Dogleg Angle (Total 3D angle change) | Degrees | 0 – 20+ |
| DLS | Dogleg Severity | °/100ft or °/30m | 0 – 15+ |
Practical Examples
Example 1: Gentle Turn
A drilling team needs to confirm the DLS while building angle slowly in a conventional well.
- Inputs: MD1 = 8000 ft, Inc1 = 15°, Azi1 = 120°; MD2 = 8100 ft, Inc2 = 16.5°, Azi2 = 122°
- Units: Imperial (feet)
- Results: The calculated dogleg angle is approximately 1.58°. This results in a Dogleg Severity of 1.58 °/100ft, which is well within acceptable limits for most drilling operations.
Example 2: Aggressive Turn in a Horizontal Well
In the curve section of a horizontal well, a more rapid change is planned. The driller needs to verify the achieved DLS.
- Inputs: MD1 = 2500 m, Inc1 = 40°, Azi1 = 270°; MD2 = 2530 m, Inc2 = 48°, Azi2 = 275°
- Units: Metric (meters)
- Results: The calculated dogleg angle is approximately 8.64°. Over a 30-meter course length, this yields a Dogleg Severity of 8.64 °/30m. This is a high DLS, typical for building the curve in unconventional wells, and highlights the importance of using a robust drilling engineering formulas calculator.
How to Use This Dogleg Severity Calculator
Using this tool to calculate dogleg severity is straightforward and provides instant, reliable results.
- Select Units: Start by choosing your measurement system, either ‘Imperial (feet)’ or ‘Metric (meters)’, from the dropdown menu. The normalization length will adjust automatically.
- Enter Survey Station 1 Data: Input the Measured Depth (MD), Inclination (Inc), and Azimuth (Azi) for the upper survey point.
- Enter Survey Station 2 Data: Input the corresponding data for the lower, more recent survey point.
- Interpret Results: The calculator will instantly update. The primary result is the Dogleg Severity (DLS) in the standard units (°/100ft or °/30m). You can also view intermediate values like the total Dogleg Angle and the Radius of Curvature.
- Analyze Chart: The bar chart provides a quick visual comparison of the changes in inclination and azimuth between the two survey stations.
Key Factors That Affect Dogleg Severity
Several factors during the drilling process directly influence the resulting DLS. Understanding these is key to managing wellbore trajectory effectively.
- Bottom Hole Assembly (BHA) Design: The type of BHA (e.g., packed-hole, building, or dropping assembly) is the primary driver of trajectory change. The placement of stabilizers and the type of motor or RSS used dictates the build or drop rate.
- Weight on Bit (WOB): For certain BHA configurations, increasing WOB can increase the build rate and thus the dogleg.
- Formation Characteristics: Drilling from a soft formation into a hard one (or vice-versa) can cause the bit to deflect, leading to an unplanned change in trajectory. Anisotropic formations can also cause “formation walk.”
- Drilling Fluid Properties: Hydraulic forces from the bit jets can influence the trajectory, especially in softer formations. Proper mud properties are also essential for hole cleaning, which affects BHA performance.
- Rotary Speed (RPM): The speed of drill string rotation can affect how the BHA interacts with the wellbore, influencing the final dogleg.
- Toolface Orientation: In directional drilling with a mud motor, the orientation of the motor’s bent housing (the toolface) directly controls the direction of the curve and is a primary input for any wellbore trajectory calculation.
Frequently Asked Questions (FAQ)
For vertical sections, DLS is ideally kept below 1-2°/100ft. In planned curve sections, it can range from 3°/100ft (medium radius) to over 15°/100ft (short radius wells). There is no single “good” value; it depends entirely on the well plan and equipment limitations.
While DLS is calculated along the Measured Depth (MD), or the actual path of the well, its consequences are often evaluated in the context of TVD. For instance, high DLS in a shallow section (low TVD) puts more stress on surface equipment and shallow casing strings. The prompt to “calculate dog leg using any tvd” refers to using survey data that is ultimately used to calculate the well’s TVD.
Yes, you can calculate the DLS between any two survey stations. However, the industry standard is to calculate it between consecutive surveys to monitor the well path in real-time.
The Radius of Curvature gives a physical sense of how sharp the bend is. A smaller radius means a sharper turn and a higher DLS. This is critical for ensuring that stiff casing strings or BHA components can pass through the section without getting stuck.
Excessive DLS can cause keyseating (where the drill pipe wears a groove into the wellbore), stuck pipe, casing wear, and difficulties with artificial lift equipment later in the well’s life. It creates a point of high friction and stress.
No. As the formula shows, the effect of an azimuth change is multiplied by the sine of the inclinations. At very low inclinations (near vertical), even a large change in azimuth results in a very small dogleg severity. The effect becomes much more pronounced at higher inclinations.
Simply select “Imperial” or “Metric” from the dropdown. The calculator automatically uses the correct normalization factor (100 for feet, 30 for meters) to ensure the DLS output is in the standard format for your chosen system.
Tortuosity is a qualitative term for how crooked or winding a wellbore is. Dogleg severity is the quantitative measure of tortuosity. Understanding the what is tortuosity helps in planning smoother well paths.