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161277235.xls.ms_office MITCHELL ENGINEERING PROGRAMS

COPYRIGHT 1990 MITCHELL ENGINEERING, PO BOX 1492. GOLDEN, CO, 80402, USA (303) 273 3744

Buckling & Wellhead Load After Cementing

CASING PROPERTIES

CASING OD (IN.) 7 EXTERNAL END AREA (SQ.IN.) 38.48

CASING ID (IN.) 6.276 INTERNAL END AREA (SQ.IN.) 30.94

CASING WT./FT 26 STEEL END AREA (SQ.IN.) 7.55

CASING LENGTH (FT 10,000

Wellhead Loads after Cementing

INITIAL CONDITIONS (While cement sets)Wellhead Load (=Tension at surface)

T; Mlbs

Mud wt. inside (MWi) 9 ppg +wt. of pipe +wpf*L/1000 260

Mud wt outside (MWo) 12 ppg +wt mud inside +0.052MWi Ai L/1000 145

Pressure inside (Pi) 1,500 psi -wt cement -0.052MWc Ao(L-TOC)/1000 -64

Pressure outside (Po) 1,000 psi -wt. mud outside -0.052MWo Ao TOC/1000 -192

Avg cement dens (MWc) 16 ppg + pressure-area + (PiAi - PoAo)/1000 8

Top of cement (TOC) 8,000 ft + Pickup + Pickup 18

Pickup is + 18 Mlb (Slackoff is -)

Initial Wellhead Load 175

FINAL CONDITIONS

Mud wt inside 13 ppg

Mud wt outside 8 ppg

Pressure inside 2,000 psiPressure outside 3,000 psi

Changes (final - initial) Formulae for dT dT; Mlbs

dMWi 4 ppg + (0.052dMWi)Ai(TOC)/1000 15

dMWo -4 ppg - (0.052dMWo)Ao(TOC)/1000 19

dPi 500 psi +2 dPi Ai/1000 9

dPo 2,000 psi -2 dPo Ao/1000 -46

dTemp 34 F -AE(dTemp)/1000 -53Total dT -55

Final Wellhead Load 119

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161277235.xls.ms_office MITCHELL ENGINEERING PROGRAMS

Buckling of Casing after Cementing

INITIAL CONDITIONS (While cement sets)Initial Effective tension at TOC Teff;Mlbs

Mud wt. inside (MWi) 9 ppg +pipe below TOC +wpf(L-TOC)/1000 52

Mud wt outside (MWo) 12 ppg +wt mud inside +0.052MWi Ai(L-TOC)/1000 29

Pressure inside (Pi) 1,500 psi -wt cement -0.052MWc Ao(L-TOC)/1000 -64

Pressure outside (Po) 1,000 psi +Pickup +Pickup 18Avg. cement dens (MWc) 16 ppg

Top of cement (TOC) 8,000 ft Initial Teff at TOC 35

Pickup 18 Mlb (Slackoff is -)

FINAL CONDITIONSMud wt inside 13 ppg

Mud wt outside 8 ppg

Pressure inside 2,000 psi

Pressure outside 3,000 psi

Changes (final - initial) Formula for d dTeff;Mlbs

dMWi 4 ppg -(1-)(0.052dMWi)Ai(TOC)/1000 -36

dMWo -4 ppg +(1-)(0.052dMWo)Ao(TOC)/1000 -45

dPi 500 psi -(1-2)dPi Ai/1000 -6dPo 2,000 psi +(1-2)dPo Ao/1000 31

dTemp 34 F -AE(dTemp)/1000 -53

If Teff < 0, assume casing is buckled. Total dTeff -109

Final Teff at TOC -74

Buckled? Yes

TEMPERATURE CALCULATIONS

(For drilling strings )Static Temperatures

Surface (Ts) 60 F y = TOC/TVD 0.57

Bottom hole (Tb) 355 F k = 0.4+0.306y+0.029y 2-0.125y 3 0.561

TVD next hole section 14,000 ft Init. avg temp: Ts + (Tb-Ts)y/2 144Final avg temp;F: Ts+(Tb-Ts)k 225

Must be entered above;F: dTemp 81

(For completion strings )

Surface Injection (Tsi) 32 F y = TOC/TVD 0.89

At perforations (Tp) 123 F For big jobs f = 3 Little jobs f = 2 3

TVD Perforations 9000 ft Final avg temp; F: Tsi+(Tp-Tsi)y/f 59Must be entered above; F: dTemp -85

30,000,000 psi; Poisson's ratio = 0.3; Coefficient of thermal expansion = 6.9E-6 /F

PROGRAM DOS NAME: CAS_BUCK.XLS

PURPOSE: Computes stresses, loads, and buckling in casing after cementing

COMPUTATIONS:

1. Buckling in intermediate and completion casings

2. Wellhead loads in intermediate and completion casings

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