Now, let's move on to kick capacity.
First of all, what is kick?
a "kick" refers to an influx of formation fluids (like oil, gas, or water) from the surrounding rock
formations into the wellbore during drilling operations.
As you can see in the table,
For the intermediate casing, the kick capacity is set at 25 barrels for the local requirement.
However, for UITM field development, the kick is up to 50 barrels. This is because it's a bigger
project with more complexities, demanding a higher level of kick tolerance. For the production
casing, both the local requirement and UITM field development are set at 25 barrels.
Next, let's see how we calculate kick tolerance at intermediate and production casing.
For the surface casing, kick tolerance is not calculated. Why? Because we've set it at a modest
2000 ft depth through the shallowest formation. At this level, the pressure is lower compared
to more profound formations. The surface casing, placed at this specific depth, only acts as a
shield, protecting freshwater zones, isolating shallow gas zones, and providing a robust
structural foundation for the well. In another word, the pressure conditions here are within a
manageable range.
Moving back to how we calculate kick tolerance. Basically, first, we need to insert the input
data required, such as hole size, depth, initial mud weight, and more. We must “fill in” all these
turquoise box to plot the influx.
Next is the graph. The kick line here is represented by the dotted red line. The kick line
represents the expected pressure exerted by the mud weight during drilling. To check that the
kick tolerance is at an acceptable range, the kick line needs to be in the safe zone on the
graph. We did change the depth of our intermediate casing four times to make sure that the
kick line was in between safety pore and fracture pressure. This is because the depth of the
casing influences the overall pressure conditions in the wellbore, which, in turn, affects the
kick tolerance line.
Moving on to the mud weight selection, firstly, we calculate the mud weight by adding the
overbalance pressure to the safety pore pressure in psi. Then we convert the mud pressure
to equivalent mud weight (EMW) in ppg. Hence, we get the EMW value for each of the casing
depths. For the conductor and surface casing,the calculated equivalent mud weight is 11.4.
For the surface casing, the mud weight is 12.1 ppg, and lastly, the mud weight obtained for
the production casing is 14.3 ppg. If we take a look at the graph, the mud weight is represented
by the mustard line colour. The mud weight line should be positioned between the safety pore
pressure and safety fracture pressure lines to ensure safe drilling operations. So, in the graph
itself, the mud line is positioned in the safety margins, indicating that the calculated mud weight
earlier is within an acceptable range.
Now let's go through the summary of our casing design.
Starting with the surface casing:
- Grade/WT: H-40/48 nominal weight
- Connection use: BTC
- Max Depth: 2000 ft
- Safety Factors Maintained: Above 1.0 for Collapse, 1.1 for Burst, 1.3 for Tension. This is
applied to all of the casing designs.
Moving on to the intermediate casing:
- Grade/WT: C-75/43.5 nominal weight
- Connection: Prem.
- and Max Depth is at 8600 ft
Lastly, the production casing:
- Grade/WT: C-75/29" nominal weight.
- Connection type is prem
- and Max Depth at 10500 ft
Next is drilling fluid summary.
We have decided to use 7% KCL/PHPA for both conductor and surface casing, which is a
water-based mud. This mud formulation contains 7% potassium chloride (KCL) and PHPA
(Partially Hydrolyzed Polyacrylamide) as a polymer additive. Potassium chloride is used to
help control the pressure of the formation. It is also commonly used to prevent shale from
swelling. Meanwhile, PHPA enhances the rheological properties of the fluid and helps reduce
fluid loss. Using 7% KCL/PHPA mud is appropriate as PHPA can provide shale inhibition,
which helps stabilize the wellbore in reactive clay formations also present at this depth.
On the other hand, KCL-Brine is used for intermediate and production casing. KCL-Brine mud
contains potassium chloride (KCL) mixed with water to create a brine-based drilling fluid. Brine
muds are commonly used in drilling when there is a need for a non-damaging fluid to control
formation pressures. A brine-based mud like KCL-Brine is often used to control high formation
pressures while minimizing formation damage. Switching to KCL-brine is common in deeper
sections where higher salt concentrations can provide better shale inhibition and stability.
