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
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November 30th, 2009 at 8:59 am
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?
December 3rd, 2009 at 3:25 am
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”.