Page 328 - Hydrocarbon Exploration and Production Second Edition

Production Operations and Maintenance 315

gas lift gas
export gas

gas-liquid
gas lift gas separator (CAO monitored)
distribution
(CAO controlled) export liquids

production
manifold
(CAO monitored)

gas

test
(CAO monitored)
wells separator

liquid
Figure 12.2 Use of CAO in gas-lift optimisation.
producing GOR (using the test separator) provides a CAO system with the
information to calculate the optimum gas-lift gas required by each well, and then
distributes the available gas-lift gas (a limited resource) between the producing wells.
Testing of the production rate of each well on a routine basis can be performed at
the drilling platform or at the centralised production facility (Figure 12.3). Consider
an offshore development with four eight-well drilling platforms and one centralised
production platform. If the production from each drilling platform is manifolded
together for transfer to the production platform then the there are two principal
ways of testing the production from each well on a routine basis (required for
reservoir management described in Section 16.1, Chapter 16):

1. A test separator is provided on each drilling platform and is used to test the wells
sequentially. The capacity of the test separator would have to be equal to the
production from the highest rate well.
2. A test separator is provided on the production platform, and is large enough to
handle the production from any one of the drilling platforms. An individual well
would be tested by passing the production from its drilling platform through the
test separator and then shutting in the well under consideration and calculating its
production from the reduction in rate. This is referred to as ‘testing by difference’.