All types of ton-mile service should be calculated and recorded in order to obtain a true picture of the total service received from the rotary drilling line. There are several types of ton miles as follows;

1. Round trip ton-miles

2. Drilling or “connection” ton-miles

3. Coring ton-miles

4. Ton-miles setting casing

5. Short-trip ton-miles

For this time, I will show how to calculate round trip ton-mile.

**Round Trip Ton-Miles Calculation**

The formula for round trip ton-miles is listed below;

**RTTM = (Wp x D x (Lp + D) + (2 x D) x (2 x Wb + Wc)) ÷ (5280 x 2000)**

where

RTTM = Round Trip Ton-Miles

Wp = buoyed weight of drill pipe in lb/ft

D = hole measured depth in ft

Lp = Average length per stand of drill pipe in ft

Wb = weight of travelling block in lb

Wc = buoyed weight of BHA (drill collar + heavy weight drill pipe + BHA) in mud minus the buoyed weight of the same length of drill pipe in lb

** If you have BHA (mud motor, MWD, etc) and HWDP, you must add those weight into calculation as well not just only drill collar weight. **

2000 = number of pounds in one ton

5280 = number of feet in one mile

**Note: **One ton-mile equals 10,560,000 foot- pounds, and is equivalent to lifting 2,000 pounds a distance of 5,280 feet

Example: Round trip ton-miles

Mud weight = 10.0 ppg

Average length per stand = 94 ft

Drill pipe weight = 13.3 lb/ft

Hole measure depth = 5500 ft

Drill collar length = 120 ft

Drill collar weight = 85 lb/ft

HWDP length = 49 lb/ft

HWDP weight = 450 ft

BHA weight from directional driller = 8,300 lb

BHA length = 94 ft

Travelling block assembly = 95,000 lb

Solution:

**a) Buoyancy factor:**

BF = (65.5 – 10.0) ÷ 65.5

BF = 0.847

**b) Buoyed weight of drill pipe in mud, lb/ft (Wp):**

Wp = 13.3 lb/ft x 0.847

Wp = 11.27 lb/ft

**c) buoyed weight of BHA (drill collar + heavy weight drill pipe + BHA) in mud minus the buoyed weight of the same length of drill pipe in lb (Wc):**

Wc = {[(120×85) + (49×450) + (8300)] x 0.847} – [(120+450+94) x13.3x 0.847]

Wc = 26,866 lb

Round trip ton-miles = [(11.27 x 5500 x (94+ 5500)) + (2 x 5500) x (2 x 95000 + 26,866)] ÷ (5280 x 2000)

RTTM = 258.75 ton-mile

**Please find the excel sheet for round trip ton-miles calculation via click this link.**

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