12,25 UR 12,25 12,25 UR 12,5 12,25 UR 12,75
12,25 UR 13 12,25 UR 13,25 12,25 UR 13,5
12,25 UR 13,75 12,25 UR 14 12,25 UR 14,25
12,25 UR 14,5 12,25 UR 14,75 12,25 UR 15
Torque limit 13⅝” casing shoe
177
Figure 94: Surface torque 12¼” x 13½” hole. A zoom of Figure 93 showing the measured depth interval from 15.000 ft. to section TD.
15000
16000
17000
18000
19000
20000
17000 18000 19000 20000 21000 22000 23000
Measured depth (ft)
Torque (ft-lbf)
Depth vs. torque
12,25 UR 12,25 12,25 UR 12,5 12,25 UR 12,75 12,25 UR 13 12,25 UR 13,25 12,25 UR 13,5 12,25 UR 13,75 12,25 UR 14 12,25 UR 14,25 12,25 UR 14,5 12,25 UR 14,75 12,25 UR 15 Torque limit 13⅝” casing shoe
178 6.1.3 Hook load
These plots show the tensile and compressive yield limits at each of the string depths analyzed [WellPlan user manual]. From Figure 95 and Figure 96, you can tell the load that will fail the drillstring, but you will not be able to determine exactly where the failure occurred (then you have to run a different simulation analyzing the forces acting on each individual component in the string at the specific depth).
The simulation also displays two curves indicating the maximum weight to yield the string while POOH (pull out of hole), and the minimum weight to helically buckle the string while RIH (run in hole). The rig capacity limit of 2200 kip (kilo pound) is also plotted in the graph.
The first hook load values in the simulation are taken at the 13⅝” casing shoe, at depth 6693 ft. MD. Figure 95 shows that the values for RIH, ROB (rotate off bottom) and POOH all increase linearly until about 11.200 ft. MD. In the interval between 10.700 and 11.470 ft. MD the wellbore inclination increases from 59.98°-70.8° resulting in high frictional forces
working against pipe movement (and a reduced gravity component); seen from the following observations:
• The RIH values decrease
• The ROB values are more or less constant
• The POOH values increase slightly
As expected, the hook load generally increases with depth; with increasing depth (and in other words increasing weight of drillstring in order to reach further towards TD) comes increased hook load. Figure 96 shows that the biggest hole sizes have the biggest hook load values, and the smallest hole sizes have the smallest values in all three scenarios for this specific case studied giving the following relationships:
Hook loadRIH 12¼” < Hook loadRIH 13½” < Hook loadRIH 15”
Hook loadROB 12¼” < Hook loadROB 13½” < Hook loadROB 15”
Hook loadPOOH 12¼” < Hook loadPOOH 13½” < Hook loadPOOH 15”
179
According to theory presented in section 2.3.8.1, the friction works upwards when the
drillstring is RIH and downwards when the drillstring is POOH. The friction during POOH is higher compared to RIH. In section 2.3.6 the following two general equations (6) and (7) were given:
Hook loadRIH
1. Hook loadRIH = weight – friction
This implies that the less friction, the higher hook loads. If we have less friction with increasing hole sizes, the hook load should increase with increasing holes size.
- The simulation shows that the biggest hole sizes have the biggest hook load values, and the smallest hole sizes have the smallest values. This implies that with increasing annular clearance comes increased hook load during RIH.
Hook loadPOOH (the worst case with regards to tensile limit)
2. Hook loadPOOH = weight + friction
This implies that the less friction, the lower hook loads. If we have less friction with increasing holes sizes, the hook load should decrease with increasing holes size.
- The simulation on HLPOOH shows the opposite results; the hook load has a small increase with increasing hole size, i.e. that the 15” hole have higher HL values than the 12¼” for this specific case. In section 6.2.3 when running the liner, the 12¼” hole has higher HL values than the 15” as expected. This is most likely a result of the different operational parameters used on these two different scenarios.
180
A drilling operation and a casing/liner-run are two distinct different operations with different conditions like: running speed, pump rate, applied surface torque, and string conditions (size, stiffness and yield strength).
Running casing/liner to target depth is one of the biggest challenges in ERD wells, due to the well path, section length and well friction factor. An explanation for the results of the
simulation is that the friction may be more dominating in this particular operation compared to during drilling.
The hook load simulation for the drilling operation was also run with an increased section depth of 30.000 ft. MD. These observations indicate that the hook load weights for RIH and ROB decrease as a result of that the well takes more and more friction due to the well
geometry. Eventually there will not be enough weight at surface to move the string. The string may have to be either pushed or floated into the well; may get stuck and may not be able to pull the string out of the hole. The most common POOH limitations are usually the yield strength of the pipe and the rigs pull capacity at surface.
The jack-up West Linus is a modern and powerful rig (delivered in 2014), with large storage area and high deck load, designed to operate in harsh environments. The rig capacity is, as mentioned above, 2200 kip and the rig has a drilling depth capacity of up to 40.000 ft. (12.192 m). Older platform rigs may only have capacities of up to 750 kip. This implies that ERD operations may be way more challenging and that these rigs may not be suited for such challenging operations; at least seen from a load capacity perspective.
181
Min. weight buckle (RIH) ROB 12,25 POOH 13,5
RIH 12,25 ROB 13,5 POOH 15
RIH 13,5 ROB 15 Max. weight yield (POOH)
RIH 15 POOH 12,25 Rig capacity