**Radius of Curvature Method **is the most famous method for directional survey calculation. You can calculate North, East and TVD between directional surveys based on the Radius of Curvature Method as per formula below:

Where;

MD = measured depth between surveys 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

**Calculation example for Radius of Curvature Method**

**Survey 1**

Depth = 7500 ft

Inclination = 45 degree (I1)

Azimuth = 130degree (A1)

**Survey 2**

Depth = 7595 ft

Inclination = 52 degree (I2)

Azimuth = 139 degree (A2)

MD = 7595 – 7500 = 95 ft

As per the calculation above,

North = -49.97 ft

East = 50.66 ft

TVD = 62.91 ft

**Please find the Excel sheet used for directional survey calculation with Radius of Curvature Method.**

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