Page 409 - Hydrocarbon Exploration and Production Second Edition

396 Managing the Surface Facilities

gas
terminal
export
pipeline
pump
separator
water
50 Mb/d 48 Mb/d 45 Mb/d 55 Mb/d 60 Mb/d

maximum capacity of items
(under current conditions)

Figure 16.9 Surface production systems.

on each other. For example, the operating pressure and temperature of the
separators will determine the inlet conditions for the export pump. System modelling
may be performed to determine the impact of a change of conditions in one part of
the process to the overall system performance. This involves linking together the
mathematical simulation of the components, for example the reservoir simulation,
tubing performance, process simulation and pipeline behaviour programmes. In this
way the dependencies can be modelled, and sensitivities can be performed as
calculations prior to implementation.
De-bottlenecking is particularly important when the producing field is on
plateau production, because it provides a means of earlier recovery or acceleration of
hydrocarbons, which improves the project cashflow and NPV.
Figure 16.9 may be characterised by an alternative diagram, called a choke model
in which equipment items are represented as chokes in the system. Again a system
model can be built around this to identify the current constraints and hence
opportunities for increasing throughput or availability.

16.2.2. Availability constraints

Availability refers to fraction of time which the facilities are able to produce at full
capacity. Figure 16.10 shows the main sources of non-availability of an equipment item.
An equipment item is designed to certain operating standards and conditions,
beyond which it should not be operated. To ensure that the equipment is capable
of performing safely at the design limit conditions, it must be periodically inspected
and/or tested. For example, a water deluge system for fire-fighting would be
periodically tested to ensure that it starts when given the appropriate signal, and
delivers water at the designed rate. If equipment items have to be shutdown to test or
inspect them, for example inspecting for corrosion on the inside of a pressure vessel,
this will make the equipment temporarily unavailable. If the equipment item is a
main process system item, such as one of those shown in Figure 16.9,thenthe
complete production train would be shutdown. This would also be the case in testing