For coring operation, the ton-miles calculation is also expressed in terms of work in round trip ton-miles. In order to determine the coring ton-miles, you need to figure out ton-miles for one round trip at the depth where coring stopped minus ton-miles for one round trip at the depth where coring began and the multiplied that value by 2.
The formula for calculating ton-mile for coring operation is shown below;
Tc = 2 x (T4 – T3)
Where;
Tc = ton-miles for coring operation
T4 = ton-miles for one round trip at depth where coring operation stopped before coming out of hole
T3 = ton-miles for one round trip at depth where coring get started
Example – Please determine coring ton-mils from 8000 ft to 8050 ft.
Ton-miles @ 8050 ft (end of coring operation) = 200
Ton-miles for trip @ 8000 ft (start of coring operation) = 190
Tc = 2 x (T4 – T3)
Tc = 2 x (200 – 190)
Tc = 20 ton-miles
Ton-Mile (TM) for Coring Operation Calculation Sheet
Ref book: 
Formulas and Calculations for Drilling, Production and Workover, Second Edition
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