Project Management in the Oil and Gas Industry

3.5.2 Arrow Diagram Method (ADM)
This diagram depends on the definition of each activity by an arrow, as 
shown in Figure 3.4, and the point of connecting arrows called nodes, which 
are drawn as circles. This method is also called Activity on Arrow (AOA).
In Figure 3.5, activity A depends on activity B. However, activity C 
depends on B and D, but there is no activity line between D and C. So, put 
in a dummy arrow (with dashed line) with time zero to solve this situation. 
Dummy activities for large activities can present a problem, so the use of a 
precedence diagram is preferred.
Activity 1
Activity 2
Activity 3
Jan.
Feb.
Mar.
Apr.
May
Figure 3.4 Example for a Gantt chart.

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Project Management in the Oil and Gas Industry
3.5.3 Precedence Diagram Method (PDM)
This method is the most common one. In this method, every activity is 
presented by a box or a rectangle, as shown in Figure 3.5, and the detail of 
the rectangle is shown in Figure 3.6. The rectangles are connected by the 
arrows which represent the dependencies between the activities. From this 
figure, it is clear that activity C starts after activities D and B.
Figure 3.6 presents the inside of a rectangle, which will note the dura-
tion, early start time (ES), early finish (EF) time, and also the latest start 
(LS) and latest finish (LF) time.
3.5.4 Critical Path Method (CPM)
The essential technique for using CPM is to establish a model of the project 
that includes a list of all activities required to complete the project, the time 
duration that each activity will take to completion, and the dependencies 
between the activities. 
By using these values, CPM calculates the longest path of planned activ-
ities to the end of the project and the earliest and latest time that each 
activity can start and finish without making the project take a longer time.
This process determines which activities are “critical,” which are the 
activities on the longest path, and which have “total float,” as these activi-
ties can be delayed without making the project longer.
Any delay of an activity on the critical path directly impacts the planned 
project completion date (i.e. there is no float on the critical path). A project 
can have several critical paths. An additional parallel path through the