From the previous post, I posted about how to calculate dogleg severity based on Radius of Curvature Method. What’s more, there is another way to calculate dogleg severity based on the concept of Tangential Method.

The following formula provides dogleg severity in degrees/100 ft and is based on the Tangential Method:

**Dogleg severity (DLS) = 100 ÷ {MD x [(sin I1 x sin I2) x (sin Az1 x sin Az2 + cos Az1 x cos Az2) + (cos I1 x cos I2)]} **

where

DLS = dogleg severity in degrees/l00 ft

MD = measured depth between survey points, ft

I1 = inclination (angle) at upper survey in degrees

I2 = inclination (angle) at lower in degrees

Az1= Azimuth direction at upper survey

Az2 = Azimuth direction at lower survey

Calculation example for dogleg severity based on Tangential Method

**Survey 1**

Depth = 7500 ft

Inclination = 45 degree (I1)

Azimuth = 130 degree (Az1)

**Survey 2**

Depth = 7595 ft

Inclination = 52 degree (I2)

Azimuth = 139 degree (Az2)

Dogleg severity (DLS) = 100 ÷ {95 x [(sin 45 x sin 52) x (sin 130 x sin 139 + cos 130 x cos 139) + (cos 45 x cos 52)]}

Dogleg severity (DLS) = 1.07 degree/100 ft

**Please find the Excel sheet for calculating dogleg severity with the concept of Tangential Method**

**Ref book: ** **Formulas and Calculations for Drilling, Production and Workover, Second Edition**

The calculations for DLS via the two methods give very different answers for the example data.

Which one is correct, or does the result have to state the method to be meaningful?

Looking at the assumption of both methods, the minimum curvature is more accurate and most of operators and directional drilling services recommend to use “minimum curvature method”.

I appreciate the DLS learning for a DD starter.