Production Casing Design 

Considerations

Presented by Brad Hansen

Devon Energy Corporation
NYSE: DVN www.devonenergy.com page 2

Agenda

• Introduction

• Casing Design Factors

• Casing Design Loads

• Pipe Performance

• Materials Selection

• Casing Connections

• Stimulation
Introduction
NYSE: DVN www.devonenergy.com page 4

Three Major Responsibilities when 

Performing Casing and Tubing Design:

• Ensure the well’s mechanical integrity.

• Optimize well costs.

• Provide operations personnel with maximum allowable loads. 
NYSE: DVN www.devonenergy.com page 5

Info Needed for Casing Design

• Mud weights

• Formation pressures

• Frack gradients

• Casing seats

• Casing sizes

• Directional plans

• Cement program

• Temperature profiles

• Base frack fluid, proppant type, and max proppant concentration

• Max anticipated frack surface pressure

• Produced fluid composition
Casing Design Factors
NYSE: DVN www.devonenergy.com page 7

Load Cases

• Dividing the pipe rating by a corresponding load results in a design 

factor. If the design factor is greater than the minimum 

acceptable design factor, then the pipe is acceptable for use with 

that load.

DFmin planned load

pipe rating DF
NYSE: DVN www.devonenergy.com page 8

Devon Minimum Casing Design 

Factors 

• Internal Yield (Burst) 1.25 (1.1 if SICP < 5,000 psi)

• Collapse 1.1

• Tension 1.4 Based on yield strength

• Compression 1.2

• Von Mises Triaxial 1.25
NYSE: DVN www.devonenergy.com page 9

Yield Strength vs Ultimate 

Strength

.002

0.2%

.005 

0.5%
Casing Design Loads
NYSE: DVN www.devonenergy.com page 11

Tubing Leak 

• This load case represents a high surface pressure on top of the 

completion fluid created by a tubing leak near the surface. 

Surface pressure is based on a gas gradient extending upward from 

the reservoir. Tubing leaks are evaluated with both static and 

flowing temperature profiles.

Internal Casing Pressure

Produced fluid 

(gas) gradient

Completion 

fluid gradient

Reservoir pressure
NYSE: DVN www.devonenergy.com page 12

Injection Down Casing

• This load case applies to wells that experience high pressure 

injection operations such as a fracing down casing. The load case 

models a surface pressure applied to a static fluid column. This is 

analogous to a screen-out during a frac job.

Internal Casing Pressure

Applied surface 

pressure

Fluid gradient
NYSE: DVN www.devonenergy.com page 13

External Pressure Profile for 

Burst Cases

•The external pressure profile used 

for the standard burst load cases:

•Full mud gradient or deteriorated 

mud from the surface to the TOC.

•Cement mix-water gradient from the 

TOC to the outer casing shoe 

(typically 8.3 to 8.6 ppg).

•Pore pressure profile from the outer 

casing shoe to the base of the 

production casing.

External Casing Pressure

Mud gradient

Mix water 

gradient

Pore 

pressure 

profile
NYSE: DVN www.devonenergy.com page 14

Production Casing Collapse Loads 

• Full Evacuation

– This load case applies to severely depleted reservoirs or a large 

drawdown due to low permeability or plugged perforations. 

– It assumes zero pressure on the inside of the pipe (such as fill 

over perfs and the well pressure blown down).

– The external pressure used is the mud gradient from surface to 

the casing bottom.
Pipe Performance
NYSE: DVN www.devonenergy.com page 16

Internal Yield Strength

• Internal yield pressure is calculated from the Barlow Equation per API 

Bulletin 5C3

• P = 0.875 * [2*Yp*T]/D

• P= Internal yield pressure (psi)

• Yp = Yield strength of the pipe (example P110 is 110,000 psi)

• T = nominal wall thickness (inches)

• D = nominal OD of pipe (inches)

• Per API the calculated number is rounded to the nearest 10 psi.

• The 0.875 factor represents the allowable manufacturer’s tolerance of 

minus 12.5% on wall thickness per API specifications.
NYSE: DVN www.devonenergy.com page 17

Internal Yield Strength

Example Calculation

• 5.5” 23# P110 pipe has an ID of 4.67” 

• wall thickness = [5.500 - 4.670] / 2 = 0.415 inches

• P = 0.875 * [2*Yp*T]/D

• P = 0.875 * [2 * 110,000 * 0.415] / 5.5 = 14,525 ~ 14,520 psi

• Internal yield strength per cement manual = 14,520 psi
NYSE: DVN www.devonenergy.com page 18

Collapse Pressure Calculation

• Is based on four different equations based on the D/t ratio and the 

yield strength of the pipe

• Plastic collapse is based on a statistical regression analysis on 

empirical data from 2488 tests

• More information is in API Bulletin 5C3
NYSE: DVN www.devonenergy.com page 19

Axial Strength (Pipe Body)

• Axial strength of pipe body is calculated from the formula below:

• Fy = (π/4) * (D2– d

2

) Yp

• Fy = Tension strength (lbs. rounded to the nearest 1,000)

• Yp = Yield strength of pipe ( psi)

• D = OD of pipe (inches)

• d = ID of pipe (inches)
NYSE: DVN www.devonenergy.com page 20

Joint Strength of Connection

• Calculations for joint strength of different API connections is found 

in API Bulletin 5C3.

• Joint strength of API connections is based on the ultimate strength 

and not the yield strength.

• Most (but not all) premium or proprietary connections are based on 

the yield strength of the connection.
Materials Selection
NYSE: DVN www.devonenergy.com page 22

API Spec 5CT
NYSE: DVN www.devonenergy.com page 23

Mechanical Properties
NYSE: DVN www.devonenergy.com page 24

Chemical Requirements 
NYSE: DVN www.devonenergy.com page 25

Definition of Sour Service per 

NACE MR0175 / ISO 15156

• H2S exceeds 0.05 psia partial pressure

• Partial pressure = (ppm H2S)*(well pressure)/1,000,000

• Total pressure exceeds 65 psia for a gas well or 265 psi for an oil 

well 
NYSE: DVN www.devonenergy.com page 26

Selecting Tubulars for Sour 

Service (per NACE MR0175)
Casing Connections
NYSE: DVN www.devonenergy.com page 28

Connections

• Connections represent less than 3% of the pipe length

• More than 90% of pipe failures occur in the connection

• Connections represent 10%-50% of the total tubular costs
NYSE: DVN www.devonenergy.com page 29

API Connections

• STC 

– 8 threads per inch

– Threads have rounded crests and roots

• LTC –

– 8 threads per inch 

– Threads have rounded crests and roots 

– Thread section is longer so has better sealability and tensile 

strength than STC
NYSE: DVN www.devonenergy.com page 30

API Connections

• Buttress 

– 5 threads per inch

– Not symmetric for the load and stab flanks
NYSE: DVN www.devonenergy.com page 31

Metal-to-Metal Seal

Thread and Coupled (MTC)

• Generally have burst, collapse, and tension ratings equal to the 

pipe body
NYSE: DVN www.devonenergy.com page 32

Integral Joint Connection (IJ)

• Half the leak paths of thread and coupled connections

• Connection OD significantly smaller than coupled connections

• 70 to 80% of pipe body strength in tension
NYSE: DVN www.devonenergy.com page 33

Flush Joint Connection (FJ)

• Connection OD is same (within 2%) as pipe body

• 45 to 60% of pipe body strength in tension
NYSE: DVN www.devonenergy.com page 34

Tensile Strength of Connections

• Joint strength of API connections is based on ultimate strength

• Most (but not all) premium connections are based on yield strength
Stimulation
NYSE: DVN www.devonenergy.com page 36

Stimulation Considerations

• Design for screen out conditions at maximum sand concentration

– (max pressure at max sand concentration)

• Cooling affects tension 

• Ballooning from internal frack pressure affects tension
Thank You.