Dogleg severity (DLS) is a normalized estimation, normally described in degrees per 100 feet or degree per 30 meters, of the overall well bore curvature between two consecutive directional surveys. Regarding a planned well path, dogleg severity may be synonymous about build and/or turn. The following formula provides dogleg severity in degrees/100 ft based on the Radius of Curvature Method.

**Dogleg severity (DLS) = {cos ^{-1} [(cos I1 x cos I2) + (sin I1 x sin I2) x cos (Az2 – Az1)]} x (100 ÷ MD)**

Where;

DLS = dogleg severity in degrees/l00 ft

MD = Measured Depth between survey points in 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

**Example for dogleg severity based on Radius of Curvature Method**

**Survey 1**

Depth = 7500 ft

Inclination = 45 degree (I1)

Azimuth = 130degree (Az1)

**Survey 2**

Depth = 7595 ft

Inclination = 52 degree (I2)

Azimuth = 139 degree (Az2)

**Dogleg severity (DLS) = {cos ^{-1} [(cos 45 x cos 52) + (sin 45 x sin 52) x cos (139 – 130)]} x (100 ÷ 95)**

**Dogleg severity (DLS) = 10.22 degree/100 ft**

**Please find the Excel sheet used to calculate dogleg severity based on Radius of Curvature Method.**

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

** Directional Drilling Books**

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and this is the same tangential method. Well this is the correct Tangential Method. It just a matter of simplified Trigonometric Law. cos (B-A) = sinA*sinB + cosA*cosB.

Radius Curvature Method is a way complicated than showed above.