# Drilling Formulas

Norton J. Lapeyrouse

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Formulas and Calculations

CONTENTS

Chapter 1

1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19.

Basic Formulas

P. 3

Pressure Gradient Hydrostatic Pressure Converting Pressure into Mud Weight Specific Gravity Equivalent Circulating Density Maximum Allowable Mud Weight Pump Output Annular Velocity Capacity Formula Control Drilling Buoyancy Factor 12. Hydrostatic Pressure Decrease POOH Loss of Overbalance Due to Falling Mud Level Formation Temperature Hydraulic Horsepower Drill Pipe/Drill Collar Calculations Pump Pressure/ Pump Stroke Relationship Cost Per Foot Temperature Conversion Formulas

Chapter 2

1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18.

Basic Calculations

P. 25

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

Chapter 3

1. 2. 3. 4. 5. 6. 7. 8. 9. 10.

Drilling Fluids

Increase Mud Weight Dilution Mixing Fluids of Different Densities Oil Based Mud Calculations Solids Analysis Solids Fractions Dilution of Mud System Displacement - Barrels of Water/Slurry Required Evaluation of Hydrocyclone Evaluation of Centrifuge

P. 63

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Formulas and Calculations

Chapter 4

1. 2. 3. 4. 5. 6. 7.

Pressure Control

Kill Sheets & Related Calculations Pre-recorded Information Kick Analysis Pressure Analysis Stripping/Snubbing Calculations Sub-sea Considerations Work-over Operations

P. 81

Chapter 5

1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11.

Engineering Calculations

Bit Nozzle selection - Optimised Hydraulics Hydraulics Analysis Critical Annular Velocity & Critical Flow Rate “D” Exponent Cuttings Slip Velocity Surge & Swab Pressures Equivalent Circulating Density Fracture Gradient Determination - Surface Application Fracture Gradient Determination - Sub-sea Application Directional Drilling Calculations Miscellaneous Equations & Calculations

P. 124

Appendix A Appendix B Index

P. 157 P. 164 P. 167

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Formulas and Calculations

CHAPTER ONE BASIC FORMULAS

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Formulas and Calculations

1.

Pressure Gradient

Example: 12.0 ppg fluid

Pressure gradient, psi/ft, using mud weight, ppg

psi/ft = mud weight, ppg x 0.052 psi/ft = 12.0 ppg x 0.052 psi/ft = 0.624

Pressure gradient, psi/ft, using mud weight, lb/ft3

psi/ft = mud weight, lb/ft3 x 0.006944 psi/ft = 100 lb/ft3 x 0.006944 psi/ft = 0.6944 OR psi/ft = mud weight, lb/ft3 ÷ 144 psi/ft = 100 lb/ft3 ÷ 144 psi/ft = 0.6944 Example: 100 lb/ft3 fluid Example: 100 lb/ft3 fluid

Pressure gradient, psi/ft, using mud weight, specific gravity (SG) psi/ft = mud weight, SG x 0.433 psi/ft = 1.0 SG x 0.433 psi/ft = 0.433 Example: 1.0 SG fluid

Convert pressure gradient, psi/ft, to mud weight, ppg

ppg = pressure gradient, psi/ft ÷ 0.052 ppg = 0.4992 psi/ft : 0.052 ppg = 9.6 Example: 0.4992 psi/ft

Convert pressure gradient, psi/ft, to mud weight, lb/ft3

lb/ft3 = pressure gradient, psi/ft ÷ 0.006944 lb/ft3 = 0.6944 psi/ft ÷ 0.006944 lb/ft3 = 100 Example: 0.6944 psi/ft

Convert pressure gradient, psi/ft, to mud weight, SG

SG = pressure gradient, psi/ft 0.433 SG 0.433 psi/ft ÷ 0.433 SG = 1.0 Example: 0.433 psi/ft

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Formulas and Calculations

2.

Hydrostatic Pressure (HP)

Hydrostatic pressure using ppg and feet as the units of measure HP = mud weight, ppg x 0.052 x true vertical depth (TVD),...

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