# Production Casing Design Considerations Presented by Brad Hansen Devon Energy CorporationNYSE: DVN www.devonenergy.com page 2 

# Agenda • Introduction

• Casing Design Factors • Casing Design Loads • Pipe Performance • Materials Selection • Casing Connections • Stimulation

# IntroductionNYSE: 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 FactorsNYSE: 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.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 1.25NYSE: DVN www.devonenergy.com page 9 

# Yield Strength vs Ultimate Strength

.002 0.2% .005 0.5%

# Casing Design LoadsNYSE: 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.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.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.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 PerformanceNYSE: 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 psiNYSE: 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 5C3NYSE: 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 – d2) 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 SelectionNYSE: DVN www.devonenergy.com page 22 

# API Spec 5CTNYSE: DVN www.devonenergy.com page 23 

# Mechanical PropertiesNYSE: DVN www.devonenergy.com page 24 

# Chemical RequirementsNYSE: 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 wellNYSE: DVN www.devonenergy.com page 26 

# Selecting Tubulars for Sour Service (per NACE MR0175)

# Casing ConnectionsNYSE: 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 costsNYSE: 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 STCNYSE: DVN www.devonenergy.com page 30 

# API Connections • Buttress
– 5 threads per inch
– Not symmetric for the load and stab flanksNYSE: 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 bodyNYSE: 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 tensionNYSE: 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 tensionNYSE: 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

# StimulationNYSE: 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.