2. Basic Calculations
Table of Content
- Volumes and Strokes
- Slug Calculations
- Accumulator Capacity — Usable Volume Per Bottle
- Bulk Density of Cuttings (Using Mud Balance)
- Drill String Design (Limitations)
- Ton-Mile (TM) Calculations
- Cementing Calculations
- Weighted Cement Calculations
- Calculations for the Number of Sacks of Cement Required
- Calculations for the Number of Feet to Be Cemented
- Setting a Balanced Cement Plug
- Differential Hydrostatic Pressure Between Cement in the Annulus and Mud Inside the Casing
- Hydraulicing Casing
- Depth of a Washout
- Lost Returns — Loss of Overbalance
- Stuck Pipe Calculations
- Calculations Required for Spotting Pills
- Pressure Required to Break Circulation
2.15 Lost Returns — Loss of Overbalance
Number of feet of water in annulus
Feet = water added, bbl ÷ annular capacity, bbl/ft
Bottomhole (BHP) pressure reduction
BHP decrease, psi = (mud wt, ppg − wt of water, ppg) × 0.052 × (ft of water added)
Equivalent mud weight at TD
EMW, ppg = mud wt, ppg − (BHP decrease, psi ÷ 0.052 ÷ TVD, ft)
Example:
Mud weight = 12.5 ppg
Water added = 150 bbl required to fill annulus
Weight of water = 8.33 ppg
Annular capacity = 0.1279 bbl/ft (12-1/4 x 5.0 in.)
TVD = 10,000 ft
Number of feet of water in annulus
Feet = 150 bbl ÷ 0.1279 bbl/ft
Feet = 1173 ft
Bottomhole pressure decrease
BHP decrease, psi = (12.5 ppg − 8.33 ppg) × 0.052 ×
1173 ft
BHP decrease = 254 psi
Equivalent mud weight at TD
EMW, ppg = 12.5 ppg − (254 psi ÷ 0.052 ÷ 10,000
ft)
EMW = 12.0 ppg