Page 278 - Hydrocarbon Exploration and Production Second Edition

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Surface Facilities

Introduction and Commercial Application: This section covers the processes applied to
fluids produced at the wellhead in preparation for transportation or storage. Oil and
gas are rarely produced from a reservoir already at an export quality. More
commonly, the process engineer is faced with a mixture of oil, gas and water, as
well as small volumes of undesirable substances, which have to be separated and
treated for export or disposal. Oil and gas processing facilities also have to be
designed to cope with produced volumes which change quite considerably over the
field lifetime, whilst the specifications for the end product, for example export
crude, generally remain constant. The consequences of a badly designed process can
be, for example, reduced throughput or expensive plant modifications after
production start-up (i.e. costs in terms of capital spending and loss of income).
However, building in overcapacity or unnecessary process flexibility can also be very
costly.
Though the type of processing required is largely dependent upon fluid
composition at the wellhead, the equipment employed is significantly influenced by
location, whether, for example, the facilities are based on land or offshore, in
tropical or arctic environments. Sometimes conditions are such that a process which
is difficult or expensive to perform offshore can be ‘exported’ to the coast and
handled much more easily on land.
As well as meeting transport or storage specifications, consideration must also be
given to legislation covering levels of emission to the environment. Standards in
most countries are becoming increasingly rigorous and upgrading in order to
reduce emissions can be much more costly once production has started.
Engineering skills should be focused on adding greatest value to the product at
least cost, whilst working within a consistent set of health, safety and environmental
policies.
Most projects can be sub-divided into four parts: wells, gathering system,
processing plant and export facilities. Some or all of these components need to be
supported on a platform, which can be a land site, the seabed, a fixed steel jacket or
a floating structure. Though projects are often characterised by platform type, the
design of a project usually starts by consideration of the process required to handle
the reservoir fluids. The selection of a platform type can come quite late in the
project design and will generally be influenced mainly by the physical environment
in which the process plant has to be located. The following sections are laid out
with this logic in mind. Process facilities will be discussed first, followed by a
description of platform type and selection.

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