PETE Well Completion Design

Transcription

1 PETE 71 Well Completion Design Casing Design Casing Design Why Run Casing? Types of Casing Strings Classification of Casing Wellheads Burst, Collapse and Tension Example Effect of Axial Tension on Collapse Strength Example 1

2 Casing Design Why run casing? To prevent the hole from collapsing. Onshore - to prevent contamination of fresh water sands To prevent water migration to producing formation To confine production to the wellbore To control pressures during drilling To provide an acceptable environment for subsurface equipment in producing wells 3 Casing Design To confine production to the wellbore. To control pressures during drilling. To provide an acceptable environment for subsurface equipment in producing wells. You need 14 ppg to control a lower zone, but an upper zone will fracture at 1 ppg. What do you do? 4

3 Types of Casing Strings Depth BML (ft) Diameter Range Example Drive pipe or structural pile (Gulf coast and offshore only) " 60" 30" Conductor casing " 48" 0" Surface casing /8" 0" 13-3/8" Intermediate casing As needed 7-5/8" 13-3/8" 9-5/8" 5 Types of Strings of Casing Depth BML (ft) Diameter Range Example Production casing As needed 4-1/" 9-5/8" 7" Liner(s) As needed 4-1/" 9-5/8" Tubing string(s) As needed Up to 4" 6 3

4 Example Hole and Casing Sizes Hole Size 36" 6" 17-1/" 1-1/4" 8-3/4" Structural casing Conductor casing Surface casing Intermediate casing Production liner Pipe Size 30" 0" 13-3/8" 9-5/8" 7" 7 Example Hole and String Sizes (in) Structural casing Conductor casing 50' 1,000' 4,000' Surface casing Intermediate casing Production Liner 8 4

5 Classification of Casing Outside diameter of pipe (e.g. 9 5/8 ) Wall thickness (e.g. 1/ ) Grade of material (e.g. N-80) Type to threads and couplings (e.g. API LCSG) Length of each joint (RANGE) (e.g. Range 3) Nominal weight per foot (e.g. 47 lb/ft) 9 Casing Grades and Properties Most Common Grades H-40 J-55 Minimum Yield Strength (psi) 40,000 55,000 Ultimate Tensile Strength (psi) 60,000 75,000 σ σ u K-55 C-75 L-80 55,000 75,000 80,000 95,000 95,000 95,000 σ y N-80 C-90 80,000 90, , ,000 ε C-95 95, ,000 P ,000 15,000 V , ,

6 Length of Casing Joints RANGE ft RANGE 5-34 ft RANGE 3 34 ft. 11 Casing Threads and Couplings API round threads (short) API round threads (long) Buttress Extreme line CSG LCSG BCSG XCSG 1 6

7 Typical API Design Factors Required 10,000 psi 100,000 lbf 10,000 psi Collapse 1.15 Tension 1.8 Burst 1.1 Design 11,50 psi 180,000 lbf 11,000 psi 13 Pore Pressure Conductor Pipe Abnormal Surface Casing Production Casing Production Tubing Liner Normal Pore Pressure psi/ft Abnormal Pore Pressure > psi/ft 14 7

8 15 Design Louisiana from State bottom University Wellhead Assembly 16 8

9 Wellhead Assembly 17 Casing Design Tension Depth Tension Burst Collapse Collapse Burst: Collapse: Tension: 18 STRESS Assume full reservoir pressure all along the wellbore. Hydrostatic pressure increases with depth Tensile stress due to weight of string is highest at top 9

10 Casing Design Tension 19 Casing Design Collapse (from external pressure) Yield Strength Collapse Plastic Collapse Transition Collapse Elastic Collapse Collapse pressure is affected by axial stress 0 10

11 Casing Design Collapse 1 Casing Design Burst Internal yield pressure for pipe Internal yield pressure for couplings Internal pressure leak resistance P P 11

12 Casing Design Example Burst Design a 7 casing string to 10,000 ft. Pore pressure gradient = 0.5 psi/ft Design factor, N i =1.1 Design for burst only. 3 Burst Example Calculate probable reservoir pressure. psi p res = 0.5 = ft ( 10,000 ft ) 5,000 psi Calculate required pipe internal yield pressure rating ( 5,000)( 1.1) 5,500 psi pi = pres Ni = = 4 1

13 Example Select the appropriate casing grade and weight from tables: Burst pressure required = 5,500 psi 7", J-55, 6 lb/ft has BURST Rating of 4,980 psi 7", N-80, 3 lb/ft has BURST Rating of 6,340 psi 7", N-80, 6 lb/ft has BURST Rating of 7,40 psi Use N-80 casing, 3 lb/ft 5 Collapse Pressure The following factors are important: The collapse pressure resistance of a pipe depends on the axial stress There are different types of collapse failure Yield strength collapse Plastic collapse Transition collapse Elastic collapse 6 13

14 Casing Design Collapse pressure correction for axial stress (Neglects internal pressure) P C P CR σ A σ y σa P C = PCR σy σ σ A Y = Adjusted collapse rating = Collapse rating for zero axial stress = Axial stress in pipe (psi) = Pipe material minimum yield strength (psi) 7 Casing Design Collapse Calculate D/t to determine the proper equation to use for calculating the collapse rating Yield strength collapse P yp ( D/t) 1 ( ) D/ t = σy Plastic collapse P p F1 = σy F F3 D/ t 8 14

15 Casing Design Collapse Transition collapse: P t F4 = σy F5 D/t Elastic Collapse: P e = D D 1 t t 9 Casing Design Collapse If axial tension is zero: Grade Yield Plastic Transition Elastic J N P D/ t 30 15

16 Example Determine the collapse rack rating of 5 1/" (J- 55, 14 lb/ft) casing under zero axial load. Calculate D/t: D t = ( ) = Example Check the mode of collapse Table 7.4 on p. 309 of Bourgoyne et al. shows that, for J-55 pipe with < D/t < 5.01, the mode of failure is plastic collapse. The plastic collapse is calculated from: A Pp = Yp B C D/ t = ( 55,000 ) 3, psi

17 Example 3 Determine the collapse rating for a 5 1/" (J-55, 14 lb/ft) casing under axial load of 100,000 lbf The axial tension will reduce the collapse pressure as follows: P CC = P CR σ σ z y 1 σ σ z y 33 σ Tension = Area π 4 100,000 = = z ( ) 480 psi Example 3 (cont.) The axial tension will reduce the yield stress to an apparent value: σ y,e 480 ( ) = = 38,16 psi Here the axial load decreased the J-55 rating to an apparent J-38. rating 34 17

18 Example 3 (cont.) P p = σ y,e F1 F D / t F.945 = ( 38,16) 4.557x10.54,550 psi compared to 3,117 psi with no axial stress! 18