PETE 7212 Completion Design - UiS

1 1 pete 7212 Completion DesignCASING Design EXAMPLE2 Louisiana State UniversityCollege of EngineeringLouisiana State UniversityCollege of EngineeringCasing Design Example Example Problem API Design Factors Worst Possible Conditions Effect of Axial Tension on Collapse Strength Design for Burst, Collapse and Tension23 Louisiana State UniversityCollege of EngineeringLouisiana State UniversityCollege of EngineeringCasing Design Example Design a 9 5/8", 8000-ft combination casing string. Completion fluid is ppg drilling mud. Formation pore pressure is expected to be 6,000 psi. Use API Design factors. Design for worst possible State UniversityCollege of EngineeringLouisiana State UniversityCollege of EngineeringCasing Design Solution Before solving this problem is it necessary to understand what we mean by Design Factors and worst possible conditions.

2 API Design FactorsDesign factors are essentially safety factors that allow us todesign safe, reliable casing strings. Each operator may have his own set of Design factors, based on his experience, and the condition of the State UniversityCollege of EngineeringLouisiana State UniversityCollege of EngineeringCasing Design We will use the Design factors recommended by the API unless otherwise specified. These are the API Design Factors: Tension and joint strength:FT= Collapse (from external pressure):FC= Burst (from internal pressure):FB= State UniversityCollege of EngineeringLouisiana State UniversityCollege of EngineeringCasing Design What this means is that, for example, if we need to Design a string where the maximum tensile force is expected to be 100,000 lbf, we select pipe that can handle 100,000 = 180,000 lbf in tension.

3 Note that the tables provided by Bourgoyneet al. list actual pipe strength (without safety factors)47 Louisiana State UniversityCollege of EngineeringLouisiana State UniversityCollege of EngineeringCasing Design Unless otherwise specified in a particular scenario, we shall also assume the following: Worst possible conditionslFor collapse Design , assume that the casing is empty on the inside (Pi= 0)lFor burst Design , assume no backup fluid on the outside of the casing (Pe= 0)lFor tension Design , assume no buoyancy effectlFor collapse Design , assume no buoyancy effect8 Louisiana State UniversityCollege of EngineeringLouisiana State UniversityCollege of EngineeringCasing Design The casing string must be designed to stand up to the expected conditions in burst, collapse and conditions are quite conservative.

4 They are also simplified for easier understanding of the basic State UniversityCollege of EngineeringLouisiana State UniversityCollege of EngineeringCasing Design Solution Burst requirements (based on the expected pore pressure) The entire casing string must be able to withstand 6,600 psi without failing in burst. When would it ever fail in burst?psi 600, 000,6 Factor Designpressure porePB= = =DPDesignPorePressure6,0006,600 Pbr10 Louisiana State UniversityCollege of EngineeringLouisiana State UniversityCollege of EngineeringCasing Design Solution Collapse Requirements For collapse Design , we start at the bottom of the string and work our way up. Our Design criteria will be based on hydrostatic pressure resulting from the ppg mud that will be in the hole when the casing string is run, prior to State UniversityCollege of EngineeringLouisiana State UniversityCollege of EngineeringCasing Design Review Design of a combination casing string requires an iterative the depth capability without axial the axial stress in the casing at this collapse resistance corresponding to axial stress the depth where this pressure with previous depth estimate.

5 Repeat steps 2-4 if not converged. Accept answer if depths that the selected casing will meet tension requirements at the wellhead. Typically between 2-4 iterations are required. Agreement to within 30 ft (one casing joint) is State UniversityCollege of EngineeringLouisiana State UniversityCollege of EngineeringCasing Design SolutionCollapse Requirements, cont d()()()()psi 850, , =Due to lower pressures and higher tension,Collapse requirements are less severefurther up the ,2005,850Pc713 Louisiana State UniversityCollege of EngineeringLouisiana State UniversityCollege of Engineering6,6204,7603,8103,090 Collapse Rating (psi)Fails Burst and Area (in2)6, ,87047N-807, ,75040N-80 Burst Rating (psi)Weight (lb/ft)GradeCasing Design Solution We can make the following preliminary selections for the bottom section of casing : Burst: 6,600 psiCollapse.

6 5,850 psi6,6204,7603,8103,090 Collapse Rating (psi) Area (in2)6, ,87047N-807, ,75040N-80 Burst Rating (psi)Weight (lb/ft)Grade6,6204,7603,8103,090 Collapse Rating (psi)Fails Burst and CollapseFails Burst and Area (in2)6, ,87047N-807, ,75040N-80 Burst Rating (psi)Weight (lb/ft)Grade6,6204,7603,8103,090 Collapse Rating (psi)Fails CollapseFails Burst and CollapseFails Burst and Area (in2)6, ,87047N-807, ,75040N-80 Burst Rating (psi)Weight (lb/ft)Grade6,6204,7603,8103,090 Collapse Rating (psi)Meets Burst and CollapseFails CollapseFails Burst and CollapseFails Burst and Area (in2)6, ,87047N-807, ,75040N-80 Burst Rating (psi)Weight (lb/ft)Grade14 Louisiana State UniversityCollege of EngineeringLouisiana State UniversityCollege of EngineeringCasing Design Solution Note that two of the weights of N-80 casing meet the burst requirements, but only the lb/ft pipe can handle the collapse requirement at the bottom of the hole.

7 The lb/ft pipe could probably run all the way to the surface (we would still have to check tension), but there may be a lower cost State UniversityCollege of EngineeringLouisiana State UniversityCollege of EngineeringCasing Design Solution How deep can we safely run N-80, 47 lb/ft? The maximum annular pressure that this pipe may be exposed to is: This corresponds to a depth of The casing will certainly collapse if we run it this deep. WHY?psi 231, ,4factor designpipe ofating r CollapsePc===()()ft509, State UniversityCollege of EngineeringLouisiana State UniversityCollege of EngineeringCasing Design Solution 6,495 ft is the depth to which the pipe could be run if there were no axial stress in the pipe. But at 6,495 we have 1,505 of lb/ft pipe below us.

8 The weight of this pipe will reduce the collapse resistance of the upper 47 lb/ft string. The weight of 1,491 ft of lb/ft casing is This weight results in an axial stress of:8,000 6,509 ()()lbf769, 877,5in 769,79areaweight21=== 917 Louisiana State UniversityCollege of EngineeringLouisiana State UniversityCollege of EngineeringCasing Design Solution The above stress will reduce the collapse pressure from 4,760 psi to Note use of the Design factor of psi067, =18 Louisiana State UniversityCollege of EngineeringLouisiana State UniversityCollege of EngineeringCasing Design Solution This pressure (4,067 psi) occurs at a depth of This depth does not agree with the initial depth of 6,509 ft. We need to do another iteration.()()ft 256, ,4h2==1019 Louisiana State UniversityCollege of EngineeringLouisiana State UniversityCollege of EngineeringCasing Design Solution Second Iteration Consider running the 47 lb/ft pipe to the new depth of 6,257 ft.

9 ()psi871, 251, )257,6000,8(W22== = =20 Louisiana State UniversityCollege of EngineeringLouisiana State UniversityCollege of EngineeringCasing Design Solution This pressure occurs at a depth of This is within 45 ft of the assumed value of 6,257 ft. We should do one more iteration:()()ft212, , =1121 Louisiana State UniversityCollege of EngineeringLouisiana State UniversityCollege of EngineeringCasing Design Solution Iteration #3 Run 47 lb/ft casing to 6,212 ft. This value is within 10 ft of the assumed value of 6,212 ft. Just for fun, let s do another iteration.()ft202,6hpsi 031,4 Ppsi429, , )212,6000,8(Wft212,6h33c332==== = ==22 Louisiana State UniversityCollege of EngineeringLouisiana State UniversityCollege of EngineeringCasing Design Solution Iteration #4 Run 47 lb/ft casing to 6,202 ft.

10 This value is within 2 ft of the assumed value of 6,202 ft. It s time to stop!()ft200,6hpsi 030,4 Ppsi119, , )202,6000,8(Wft212,6h44c443==== = ==1223 Louisiana State UniversityCollege of EngineeringLouisiana State UniversityCollege of EngineeringCasing Design Solution This is the answer we are looking for, , we can run 47 lb/ft N-80 pipe to a depth of 6,200 ft, and lb/ft pipe between 6,200 and 8,000 ft. Perhaps this string will run all the way to the surface (check tension), or perhaps an even more economical string would include some lb/ft pipe?24 Louisiana State UniversityCollege of EngineeringLouisiana State UniversityCollege of EngineeringCasing Design Solution At some depth the lb/ft pipe would be able to handle the collapse requirements. We have already determined that it will not meet burst requirements.