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![Internal Use Only
Casing Classification
API also defines the following casing properties:
ID The specified Internal Diameter
Drift Diameter
The minimum allowable internal
diameter of the casing
Collapse Resistance
Strength to resist outside pressure
crushing the casing [psi].
Burst Resistance
Strength to resist internal pressure
bursting the casing [psi].
Body Yield Strength
Tensile strength to resist permanent
deformation due to stretching [lbs]
or [1000-lbs]](https://image.slidesharecdn.com/casing-250824194820-ad2c6370/75/ndbiibdybeksmaobdisnzianwusnzudnxfbcnxxisisisisisisis-6-2048.jpg)
![Internal Use Only
s
e
Yp Up
σ = stress [force/area] ε = strain [unitless]
Yp = Yield Point [force/area] Up = Ultimate Strength [force/area]](https://image.slidesharecdn.com/casing-250824194820-ad2c6370/75/ndbiibdybeksmaobdisnzianwusnzudnxfbcnxxisisisisisisis-11-2048.jpg)
ndbiibdybeksmaobdisnzianwusnzudnxfbcnxxisisisisisisis
- 1. Internal Use Only CasingDesign and Considerations Technical Training Program 2012
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- 4. Internal Use Only CasingDefinition Casing is a length of large diameter pipe run down a wellbore and typically held in place by oilwell cement. The API metrics for casing are in the publication API Specification 5CT We will limit our focus to standard API steel casing.
- 5. Internal Use Only CasingClassification The API has three primary casing descriptions: Size (OD) Outer Diameter Grade Refers to strength requirement, corrosion resistance, steel composition Weight Mass per unit length of casing string, expressed in units of lb/ft (US units) Each of these is independent of the other two
- 6. Internal Use Only CasingClassification API also defines the following casing properties: ID The specified Internal Diameter Drift Diameter The minimum allowable internal diameter of the casing Collapse Resistance Strength to resist outside pressure crushing the casing [psi]. Burst Resistance Strength to resist internal pressure bursting the casing [psi]. Body Yield Strength Tensile strength to resist permanent deformation due to stretching [lbs] or [1000-lbs]
- 7. Internal Use Only CasingWeight and Buoyancy The weight of the casing string exerted on the rig (hookload) is affected by the buoyant forces resulting from submerging the casing in well fluid. The resulting weight of the casing is given by: ) ( sin sin BF Factor Buoyancy g ca fluid g ca casing Buoyant SG SG SG Weight Weight
- 8. Internal Use Only ExampleProblem: Buoyancy Effects A 1500’ string of 5-1/2”, 23.0 lb/ft casing is submerged in water (ρ = 8.33). Calculate the following: • The weight of the casing in air. • The weight of the casing submerged.
- 9. Internal Use Only CasingGrade The API grade of casing (designated by a letter and number combination, i.e. C-75) denotes the minimum acceptable properties of the steel used. The number corresponds to the minimum yield strength of the steel in thousands of pounds-force. This number is used as a factor in determining the Burst Resistance, Collapse Resistance, and Body Yield Strength of the casing The letter is an API designation of minimum tensile strength. API defines this term as the amount stress required to produce 0.5% deformation per unit length of the material.
- 10. Internal Use Only FromAPI Specification 5CT
- 11. Internal Use Only s e YpUp σ = stress [force/area] ε = strain [unitless] Yp = Yield Point [force/area] Up = Ultimate Strength [force/area]
- 12. Internal Use Only CasingBurst Resistance The maximum internal pressure the casing can withstand before failing
- 13. Internal Use Only CasingBurst Resistance The Burst rating for casing can be calculated from: OD t Y P p burst 2 875 . 0 Yp = Yield stress (from Casing Grade) t = Wall Thickness OD = Outside Diameter of the Casing
- 14. Internal Use Only ExampleProblem: Casing Burst An 18,000’ string of 5-1/2”, J-55 (ID = 4.802”) casing is cemented in place with 15.0 lb/gal cement to surface. The job was displaced with fresh water. • How much pressure will be required to land the plug? Assume no shoe joint • What is the calculated burst rating of the casing? • Will the casing rupture?
- 15. Internal Use Only CasingCollapse Resistance The maximum external pressure the casing can withstand before failing Collapse Resistance cannot be easily calculated. No single mathematical formula exists that accurately estimates this property. API compiles statistical data on thousands of tests to determine the published quantity.
- 16. Internal Use Only ExampleProblem: Casing Collapse A 15,000’ string of 5-1/2”, J-55, 14 lb/ft casing is cemented in place with 13.5 lb/gal cement to surface. The job was displaced with fresh water • Refer to the tables in the RedBook, what is the Collapse Resistance of the casing? • Will the casing fail at the end of the job? Assume no shoe joint
- 17. Internal Use Only CasingBody Yield Strength Tensile load rating of the casing body, without regard to connections, that will not result in permanent deformation of the pipe. This rating is a product of the minimum yield strength times the cross sectional area of the pipe 2 2 4 ID OD Y Body p yield
- 18. Internal Use Only CasingCouplings The casing couplings have several different typed of threads. The RedBook™ lists details for the most commonly found examples: • API 8-round (short) • API 8-round (long) • Buttress • Extremeline The tensile (body yield) strength of the joints will be different from that of the casing body.
- 19. Internal Use Only CasingProperties – Safety Factors Safety Factors are used to ‘de-rate’ the calculated and/or listed strength values of casing. Reasons for this include: • Customer Specifications • Unknown age of pipe • Unknown condition of pipe • Effects of temperature, torsion, tensile load, etc.
- 20. Internal Use Only CasingProperties – Safety Factors Property Safety Factor Multiply value by: Collapse Resistance 1.25 80% of listed value Burst Resistance 1.25 80% of listed Value Body Yield Strength 1.8 56% of listed value Always consult with the customer when selecting Safety Factors for casing properties The values presented here are guidelines from Halliburton’s Best Practices
- 21. Internal Use Only TheFour Primary Strings of Casing • Conductor • Surface • Intermediate • Production
- 22. Internal Use Only ConductorCasing • Prevent washing out under rig • Confines circulating fluids • Provide elevation for the flow line • Provide support for part of the wellhead • BOPs are usually not attached to conductor casings • Usually big casing OD: 16 to 30 in diameter • Set from 20 to 1,500 ft • Casing can be pumped out easily and is usually tied down
- 23. Internal Use Only SurfaceCasing • Protect fresh water zones • Control gas & fluid flow • Case off unconsolidated formations and lost circulation zones • Must support the weight of BOP, other surface equipment • Must support any additional strings of casing
- 24. Internal Use Only IntermediateCasing • Seal off large amounts of open hole • Protect the open hole from increased mud weight • Case off gas, water, salt, shale and lost circulation zones • Protect formations from high or low pressure caused by drilling or cementing operations • Control high pressure zones • Can be used as production casing (upper zones) • Provide a place to hang a production liner
- 25. Internal Use Only ProductionCasing • Case off gas, water, salt and shale zones • Provide control of the well at the wellhead (production & pressure control) • Protect pay zones from unwanted fluids • Provide a place to change out drill fluids to completion fluids which are compatible with the formations
Editor's Notes
- #1 Casing is used as a means of isolating the formations downhole. This is done to protect the environment, isloate weak formation and high pressure formations.
- #2 Casing being transported to location. Joints of casing are typically 30 to 40 feet in length (9 to 12 meters).
- #3 A view of the casing crew making up joints, or screwing them together, to run in the hole. The equipment used while running casing is similar to the equipment used in drilling except normally it is bigger to handle the larger sizes of casing. Casing crews are different than normal roughnecks. The crews travel from rig to rig running casing.
- #4 While steel is the most common material seen in casing manufacture, casing can be made from a wide variety of materials including aluminum, titanium, stainless steel, and various polymers.
- #5 API defines 15 standard casing sizes from 4-1/2” (114 mm) to 20” (508 mm). Throughout the industry, there are many more sizes of casing manufactured. The OD is used as both a major descriptor of casing and to determine the annular volume. When asked what type of casing is going to be run, a customer will often respond simply by giving you the OD. If the both the hole size and casing OD is known, then it is possible to determine the annular volume. Section 122 of the Redbook lists volumes between tubing and hole, casing and hole and drillpipe and hole. Regardless of the type of Tubular (casing / drillpipe / tubing,) the method of determining the annular volume is the same. On Page 10 of Section 240, the equations are listed that are used to determine these factors.
- #6 The Drift Diameter defines the maximum allowable size (or OD) of tools that may be run inside the casing string. The API specification of casing dictates that the maximum allowable variation in wall thickness is 12.5%. The Internal Diameter (ID) is the measure used to determine internal casing volume and volume per unit length of the casing string. The units of measure for Body Yield Strength are sometimes written as “kips” or “klb”. This term comes from ‘kilo’ (meaning 1000) and pounds force.
- #7 Steel has an average Specific Gravity (SG) of 7.86, which equates to a density of 65.595 lb/gal (7860 kg/m3) The second term in the equation is commonly referred to as the Buoyancy Factor (BF). Alternatively, you could use the density of the fluid and the density of the casing material instead of the SG of each. This equation is only valid if the casing is submerged in a single well fluid, both inside and outside the casing.
- #10 Data compiled from API Spec 5CT. Here, “Tensile Strength” is a quantity of stress that will impart no more than 0.5% deformation in length for a 2-in sample.
- #11 On a stress vs. strain diagram, there are two regions of importance. The first is the linear position between the origin and the yield point. From our university materials classes, we remember that this is the elastic region of a material. In this region, a material will deform and return linearly, to its undeformed state. The point of deflection, listed as the yield point is the MINIMUM YIELD STRENGTH of our casing. Between the yield point and the ultimate tensile strength, the material will deform and not return to it’s original shape. In this region the material will not fail. Once past the ultimate tensile strength, the material will fail. Note that while we take the Minimum yield strength into consideration for all of our calculations, the material will not fail until the ultimate yield stress has been exceeded. However once the materials has been yielded the overall strength of the material has also changed. Basically the more the material has been yielded the more likely a failure will occur with continued loading. On a similar note, as the casing grade increases, the difference between the two points decreases.
- #13 This equation is commonly known as the Barlow Equation. The factor of 0.875 appearing in the equation represents the allowable manufacturing tolerance of -12.5% on wall thickness specified in API Specification 5CT. This equation neglects detrimental effects of temperature, tensile stress, torsion, age, corrosion, etc. Age and previous stresses have a large impact on the Burst Resistance of the casing.