Project Management in the Oil and Gas Industry

Table 3.3 Float time calculation.
No. Activity
D Earliest
Latest
Float
Critical
ES EF LS LF TF FF
100 Mobilization
3
0
3
0
3
0
0
*
200 Excavation
8
3
11
3
11
0
0
*
300 Pouring concrete foundation 
and piping support
10 11
21
11
21
0
0
*
400 Install piping
4
3
7
14
18
11
0
500 Install the mechanical 
package
1
21
22
21
22
0
0
*
600 Put the grouting 
1
22
23
22
23
0
0
*
700 Connect the piping
5
7
12
18
23
11
11
800 Commissioning and start up
2
23
25
23
25
0
0
*

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102 
Project Management in the Oil and Gas Industry
3.5.7 Application of the PERT Method
We previously reported that the implementation of the activity takes time 
and needs resources. The PERT team may face a problem of how to esti-
mate the time of each activity, as they see that reliance on a single esti-
mate time is a weak assumption and is incompatible with the conditions 
of uncertainty, even under the best circumstances. The external environ-
mental factors surrounding the project may cause a deviation in the times 
of the activities planned.
Accordingly, the PERT method has been found to overcome the time 
uncertainty. By estimating the time of each activity with three estimated 
time values they will be gathered together with knowing the activity esti-
mate and time probability distribution curve to reach a statistical prob-
ability to estimate the time of the project’s completion. This method will 
apply as follows.
Optimistic time estimates the minimum possible time in which to do 
the activity, considering that all the factors affecting this activity are going 
smoothly. This time is usually low because all the circumstances must be 
good at the same time.
Pessimistic time estimates the maximum possible time in which to 
implement the activity. It considers the worst cases that happen to delay this 
activity. This usually provides a higher time period with low probability.
The “most likely time” presents the time period in which to perform this 
activity under normal conditions for all the factors affecting this activity. 
This value has the most probability of occurring.
The PERT method correlates the relation between the above three times 
by using a beta distribution as in Figure 3.10. The optimistic and pessimis-
tic value precincts the limits of the distribution, but the most likely value 
present is the frequencies of the event occurring.
To define the activity time period, the activity mean time needs to be cal-
culated, and this is done using the below equation. The summation of all the 
time periods on the critical path presents the mean time period for the project.
3.5.7.1 Statistics Calculation for Activity Time
From the beta distribution, the expected or average time for each activity is 
calculated according to the following equation: