casing design section
DESCRIPTION
Information about casingTRANSCRIPT
Gas Blowout &
Casing Design
• Eng: Tawfik A. Tawfik
•In drilling a high pressure gas bearing zone which was
encountered at depth 12,000 ft. Where a kick occurred, a part of
drilling fluid was blown-out of the well. The blown out fluid was
occupied a portion of the casing string 3000 ft long. The reservoir
pressure of gas bearing zone was 10,000 psi and the density of
drilling fluid was 80 lb/cu.ft.
* Calculate: -
•The pressure held on the BOP.
•The min. length of intermediate casing shoe which is necessary
to prevent subsurface blowout, (assume formation fracture
gradient was 0.875 psi/ft)
•Pressure just below casing shoe.
TVD = h 12,000 ft
hc ?
he 3000 ft
Ph
Pit gain
PCB psiP
ftG
hPhc
hcGfr
hehcP
hchPP
psi
hehPPPP
CB
rf
f
BOP
fCB
fhfBOP
9310)1043012000(*69.10*052.010000
1043069.10*052.0875.0
12000*69.10*052.010000
*052.0
**052.0
*
)(**052.0
)(**052.0
5000)300012000(*69.10*052.010000
)(**052.0
Casing String Design
Eng: Tawfik A. Tawfik
Surface
Conductor casing
Surface casing
Immediate casing
Production casing
Production liner
Stove casing
Conductor casing
Surface casing
Intermediate casing
Production Liner
Hole Size
30”
20”
13 3/8
9 5/8
7
5
Casing Size
36”
26”
17 1/2
12 1/4
8 ½
6
API Casing Specifications
1. Length of joint: average 22 – 31 – 42 ft
2. Outside diameter: OD 36” – 4.5” tubing less than 4.5”
3. Nominal Weight per foot & wall thickness & inside diameter
& drift diameter: 53.5 lbs./ft
4. Grade of steel, e.g. L-80: yield, collapse and burst
5. Thread connection: Round, Buttress, ..
• Short thread connection (STC) • Long thread connection (LTC) • Buttress thread connection (BTC) • Extreme line (EL) - Hydril – VAM – new VAM
Casing Loads
External
Internal
Tension
Designing A Combination Casing Strings
Design a 7" combination string to be run to the depth
of 3500 m.
•External pressure is created by a mud with the
density 1.25 g/cc;
•Internal pressure corresponding to the hydrostatic
head of the mud;
•The casing is empty;
•The design factor are :
fc = 1.125 (for collapse)
ft = 1.80 (for joint strength)
fi = 1.10 (for burst)
•The buoyancy is neglected;
•The effect of tensile load on collapse resistance is
neglected ;
•The string should not contain more than 4 different
grades.
Grade N.W kg/m Collapse Resisitance, kg/cm2
Joint Strength, Kg
Internal Pressure, kg/cm2
C-75,32 47.6 505 Pc1 288000 -
C-75,29 43.2 430 Pc2 255000 -
C-75,26 38.7 351 Pc3 222000 -
C-75,23 34.2 275 Pc4 189000 420
1- Collapse Design Pc min = 0.1 H fc = 0.1 * 1.25 * 3500 * 1.125 = 492 kg/cm2
So the first grade will be C-75,32 with length of L1
Pc2 = 0.1 (H – L1) fc
L1 = H - ---------------- = 440 m
L2 = H - L1 - ---------------- = 560 m L3 = 545 m
L4 = H – L1 – L2 – L3 = 1955 m
Pc2
0.1 fc Pc3
0.1 fc
2- Check for tensile
sec
length, m
N.wt, kg/m wt, kg cum wt
Joint strength ft
L1 440 47.6 20944 20944 288000 13.8 OK
L2 560 43.2 24192 45136 255000 5.6 OK
L3 545 38.7 21092 66228 222000 3.4 OK
L4 1955 34.2 66861 133089 189000 1.4 No
L4’ 1133 34.2 38749 104977 189000 1.8 OK
L5 822 38.7 31812 136790 222000 1.6 No
L5' 472 38.7 18344 123321 222000 1.8 OK
L6 348 43.2 15034 138355 255000 1.8 OK
'445
4
)332211(4'4
LLL
ftw
ftLwLwLwPjL
3 – Check for bursting For the weakest section of casing grades
Fi = --------------------------- > 1.1 safe
Internal pressure
0.1 Hi
Hi
Interval m
Grade
0-348 C-75,29
348-822 C-75,26
822-1955 C-75,23
1955-2500 C-75,26
2500-3060 C-75,29
3060-3500 C-75,32
Grade Effective Collapse Resistance, psi Joint
strength, lb
T.L, lb 0
T.L, lb 100,000
T.L, lb 200,000
T.L, lb 300,000
N-80, 32 lb 7400 6880 6280 5600 505,000
N-80, 26 lb 5620 4850 4290 3600 402,000
N-80, 23 lb 4300 3850 3310 2690 350,000
J-55, 23 lb 3290 2850 2250 1500 300,000
J-55, 20 lb 2500 2100 1550 980 254,000
H-40, 20 lb 1900 1490 960 ------ 191,000
•Design 7" graduated production casing string to be set at
depth of 10,000 ft in a hole full of 90 lb/cu.ft mud, using
conventional safety factor. The effective collapse resistance at
different tensile loads (T.L) is given in the following table for
different casing grades:
Collapse resistance
Ten
sile
str
ess
1- Collapse Design
32
))1(211(2
1
211
1
PcL
LHnwLnwBFW
L
PcHnwBW
BFs
m
Pc min = 0.1 H fc
sec
depth, ft
length, ft
N.wt, lb/ft wt, lb cum wt
B * cum wt
Joint strength ft
1 2735 32 87520 87520 71460 505,000 7.067
2 1901 26 49426 136946 111816 402,000 3.595
3 1631 23 37513 174459 142446 350,000 2.457
4 1218 23 28014 202473 165319 300,000 1.815
5 990 20 19800 222273 181486 254,000 1.400
6 1525 20 30500 252773 206389 191,000 0.925
4' 1289 23 29647 204106 166652 300,000 1.800
5 2444 23 56212 260318 212550 350,000 1.647
5' 1479 23 34017 238123 194427 350,000 1.800
6 965 26 25090 263213 214913 402,000 1.871
2- Check for tensile
Drill String Design
Eng: Tawfik A. Tawfik
•Derive an equation for determining the length of drill
collar required during drilling a well. If weight on bit
50,000 lb, total well depth to be drilled is 10,000 ft, mud
density 12 ppg.
Calculate lengths of D/C and D/P to be used.
Steel density = 489.5 lb/ft3
D/P (19.5 lb/ft) 5 in O.D. 4.276 in I.D.
D/C (150 lb/ft) 8in O.D. 2.812 in I.D.
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