Design Calculations Combination Strings Calculate the lower section, collapse Example TD 4000 ft, MW 10 #, 8 5/8” casing Assume empty pipe, the maximum condition Using a SF of 1.2 BHP 2496 psi K55 24# PC 1370 psi K55 32# PC 2530 psi Lower section is 32# next section 24# Depth of Bottom 24# section = 1370/.054 x MW x 1.2 = 2196 ft Length of 32# section 1804 ft, weight of section 57,744 # Stress 8327# se 50362 psi F1 = 2.978 F2 = .052 F3 = 1066.7 F4 = 2.00 F5 = .0348 Gives Elastic Lower 38.7 Plastic Upper 25.6 d/t 32.7 so transition mode

Design Calculations PcT = 1335 psi Sub this pressure back in, new Depth 2139 ft, Length 1861 ft weight 59,538 # stress 8585 psi se 50,202 New Pc = 1333 psi close enough Check joint strength 24# 263,000# SF 1.8 138,421#

Design Calculations Surface Casing Cement is circulated, so design for running. Mainly joint strength Intermediate String If cement is circulated, design for running. Check collapse for conditions while cementing. If not circulated, design must also take into account drilling conditions, at the TOC. Mud in the annulus and the possibility of empty casing. Burst pressure below the BOP.

Design Calculations So take the 8 5/8” casing example, The total weight of the string of 32 and 24# would be 113,120# JS of the 24# with SF 1.9 is 138,000# so that would hold. For circulated cement, assume the cement will weight 14.5 #/gal the plug displaced with water, 8.33 #/gal or a difference of 6.7 #/gal in the annulus or a gradient of .33 psi/ft. For a TOP, example 200’ of cement, start the calculations at that point. The burst for the top section is 2950 psi, suitable for 2500 psi wellhead

Design Calculations Production String Rarely circulated Design for drilling, completion and production. Collapse is designed using empty casing, possible during production if pumped with a rod pump, gas production without a packer Burst for completions work, frac job down casing top section is the weakest for burst Joint strength for running the casing