Drilling Liner (9|-in. pipe)
Drilling liner is set between 10.500 ft and 14.000 ft with an overlap of 600 ft between 13| in casing and 9| in liner. The liner is cemented from the bottom to the top. Design loads for collapse and burst are calculated using the same assumptions as for the intermediate casing (refer to Fig. 3.8). The effect of biaxial load on collapse and design requirement for buckling are ignored.
Collapse pressure at 10,500 ft = external pressure — internal pressure
External pressure at 10,500 ft = Gpmi x 10.500 ft
= 12 x 0.052 x 10.500 = 6.552 ft
Internal pressure at 10,500 ft = Gpmix fluid column height (Fig. 3.8)
= 17.9 x 0.052 x (10.500 — 7,006)
= 3.252 psi
Collapse pressure at 10,500 ft = 6.552 — 3.252
= 3,300 psi
Collapse pressure at 14,000 ft = external pressure — internal pressure
External pressure at 14,000 ft = 12 x 0.052 x 14,000
= 8.736 psi
Internal pressure at 14,000 ft = 17.9 x 0.052 x 6.994
|
8.736 — 6.510 2.226 psi |
= 6.510 psi
Grade Weight Coupling Collapse resistance
(lb/ft) (psi]_______
SF =1 SF = 0.85
P-110 47 LTC 5,310 6,247
L-80 58.4 LTC 7,890 9,282
In Fig. 3.12 the collapse line is constructed between 3,300 psi at 10,500 ft and 2,226 psi at 14,000 ft. The collapse resistances of suitable steel grades from Table
3.3 are given in Table 3.22. Notice that both P-110 (47 lb/ft) and L-80 (58.4 lb/ft) grades satisfy the requirement for collapse load design.
Burst
rst pressure at 10,500 ft (Fig. 3.8)
= internal pressure — external pressure
nternal pressure at 10,500 ft = surface pressure + hydrostatic
pressure of drilling fluid column + hydrostatic pressure of the gas column
= 5.000 + 8.901.6 x 17.9 x 0.052 + (10.500 — 8,901.6) x 0.1 = 13,445 psi
|
External pressure at 10,500 ft = |
hydrostatic head of the salt water column
0. 465 x 10,500 4,882.5 psi
|
4,882.5 |
Burst pressure at 10,500 ft = 13,445.44
= 8.563 psi
Burst pressure at 14,000 ft = injection pressure at 14.000 ft
— saturated salt water column = 13,788.32 — 0.465 x 14,000 = 7.278 psi
In Fig. 3.12, the burst pressure line is constructed between 8,563 psi at 10,500 ft and 7,278 psi at 14,000 ft. The burst resistances of the suitable grades from Table 3.3 are shown in Table 3.23. The burst resistances of these grades are also plotted in Fig. 3-12 as vertical lines and those grades that satisfy both burst and
|
Grade |
Weight |
Coupling |
Burst resistance |
|
(lb/ft) |
(psi) |
||
|
SF = 1 SF = 1.1 |
|||
|
L-80 |
54.4 |
LTC |
8,650 7,864 |
|
P-110 |
47 |
LTC |
9,440 8,581 |
collapse design requirements are given in Table 3.24.
Suitability of the selected grade for tension is checked by considering cumulative buoyant weight, shock load, and pressure testing. The results are summarized in Table 3.25.
From Table 3.25 it follows that L-80 (58.4 lb/ft) and P-110 (47 lb/ft) satisfy the requirement for tension due to buoyant weight and shock load. Inasmuch as the safety factor is double the required margin, it is not necessary to check for pressure testing.