Project Management in the Oil and Gas Industry

 
T
T
T
T
a
o
m
p
4
6
,
 
(3.1)
where T
a
is average time, T
o
is optimistic time, T
p
is pessimistic time, and 
T
m
is most likely time.

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Pitfalls in Time Schedule Planning 103
3.5.7.2 Example
For the previous example of constructing the concrete foundation, there 
are three values for time for each activity, as shown in the following table.
After defining the critical path from the previous example, calculate the 
expected time at each activity as shown in Equation 3.1.
Calculate the standard deviation using the following equation:
 
s
T
T
P
o
6
 
(3.2)
Variance, V, is S
2
.
From Table 3.5 calculate the Ta, which is the average time and the stan-
dard deviation based on Equations 3.1 and 3.2, respectively. The variance 
Table 3.4 PERT example.
To
Tm
Tp Activity
Item
1
3
5 Mobilization
1
6
8
11 Excavation
2
8
16
25 (Pouring concrete foundation and piping support)
3
3
4
5 Install the piping
4
1
1
2 Install the mechanical package
5
1
1
3 Put the grouting 
6
2
5
7 Connect the piping
7
1
1
2 Commissioning and start up
8
T
o
T
p
T
m
T
a
Frequency
Time
Figure 3.10 Probability distribution for every distribution.

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104 
Project Management in the Oil and Gas Industry
is calculated as it is only possible to sum the variance. You cannot perform 
summation for the standard deviation.
The minimum time to finish the project is eighteen days and the maximum 
time to finish is 39 days. The average time period to finish the project is in 
23.31 days.
What is the probability if you increase the project time over 25 days? 
This value can be calculated from the following equation:
V = 0.44 + 0.694 + 1.36 + 0.028 + 0.11 + 0.11 = 2.74 days.
Standard deviation (S) is 1.66 days.
z
26 23 31
1 66
1 62
.
.
.
From the probability distribution tables, the probability that the project 
completion period is more than 26 days is five percent. The probability 
that the execution time for the project is equal to or less than 26 days is 
95 percent, as shown in Figure 3.11.
3.5.7.3 Time schedule control
For real projects, four legs platforms in a water depth around 80 m, the 
percentage of hours of different disciplines will be as follows in Table (3.6) 
as a guideline:
The approximate man hours for structure engineering activities is about 
5600–6300 man hours, whereas the total project man hour is about 38000