Page 336 - Hydrocarbon Exploration and Production Second Edition

Production Operations and Maintenance 323

equipment item Type A Type B

capex ($) $A $B

operating and
maintenance strategy 1 2 3 1 2 3

opex ($) $A1 $A2 $A3 $B1 $B2 $B3

Full Life Cycle Cost

Figure 12.7 Full life cycle costing.

A suitable maintenance strategy should be developed for equipment by
considering the criticality and failure mode, and then applying a mixture of the
forms of maintenance described above. In particular, the long-term cost of
maintenance of an item of equipment should be estimated over the whole life of the
project and combined with its capital cost to select both the type of equipment and
form of maintenance which gives the best full life cycle cost (on a discounted basis),
whilst meeting the technical, safety and environmental specifications (Figure 12.7).
Although Figure 12.7 indicates a linear step-wise procedure for selecting the
equipment type and the operating and maintenance strategies, the actual procedure
will involve a number of loops to select the best option. This procedure will
require input from the process engineers, facilities engineers, production operators
and the maintenance engineers, and demonstrates the integrated approach to field
development planning.
When estimating the operating and maintenance costs for various options, it is
recommended that the actual activities which are anticipated are specified and
costed. This will run into the detail of frequency and duration of maintenance
activities such as inspection, overhaul, painting, etc. This technique allows a much
more realistic estimate of OPEX to be made, rather than relying on the traditional
method of estimating OPEX based on a percentage of CAPEX. The benefits of this
activity-based costing are further discussed in Chapters 14 and 16.
By diligent operations and maintenance activity, operators are able to achieve
overall uptimes on plants of around 95%, excluding planned shutdowns. This is
critical in meeting production targets which will have factored in the anticipated
uptime during the forecasting exercise. Uptime refers to the fraction of time the
plant is available.