Multiphase
Flow Metering per Well,
Can it be justified?
Worldwide,
the application of MPFM’s is growing and some companies have adopted
the philosophy that MPFM’s are the first choice for new developments,
elaborate Lex (A.M.) Scheers, Khamis Busaidi, Mike Harper, Martin Halvorsen
and Tor Wideroe.
Currently
Multi-Phase Flow Meters (MPFM’s) are developing from a nursing technology
to mature technology and an increasing number of meters are being installed
worldwide. However, the majority of the MPFM installations are still
shared by a number of wells, i.e. replacement of the conventional test
separator and only a few applications have MPFM’s installed per individual
well. In the decision whether to implement a shared MPFM or single-well
MPFM, various aspects need to be taken into account, e.g. the uncertainty
in MPFM flow rate measurements, value of the MPFM information and the
various hardware and operating costs related to MPFM’s. With respect
to the later, MPFM’s are often considered too expensive to be included
by default on a per well basis.
Over
the last year Shell has spent a significant effort in evaluating MPFM’s,
which are low cost, relatively compact in size and do not use radioactive
sources (these sources call for additional licensees, procedures, staff,
costs, etc.). In addition, multiphase metering concepts that have the
potential to be further developed for the use in downhole applications
also have gained a lot of interest. A new and relatively low cost and
compact MPFM concept, manufactured by FlowSys has the potential to be
used on a per well basis. The meter has been extensively evaluated at
a production station in Gabon (May/Jul 2001) and in a test facility,
using live crude oil and natural gas, in China (Sep/Oct 2001 and Aug
2002). The FlowSys concept does not require a radioactive source but
instead uses advanced electric permittivity and conductivity measurements
combined with a conventional Venturi for both composition and gas/liquid
velocity measurement. The test results revealed that, within the operating
envelope of the meter, relative errors in the order of 10% for liquid
and gas and absolute errors of 5% in watercut are achievable.
Introduction
In
the area of production measurement, three major hardware developments
have taken place during the last decade; the introduction of Coriolis
meters for single-phase liquid, the large scale implementation of Ultrasonic
flow meters for single-phase gas flow rate measurement and the development
and implementation of the first series of flow meters for multi-phase
and wet gas flow regimes. Initial developments for the two single-phase
flow meter concepts started in the early 80’s and the instruments have
been applied in the field since the early 90’s. It has taken about 10
years from the initial development to reach the stage of fully accepted
field use. The advantages of these two meters over conventional flow
measurement equipment (orifice plate, venturi or turbine meters) have
been demonstrated in a large number of publications. Although their
applications are still more complex than conventional flow metering
devices, the Coriolis meter and the Ultrasonic flow meters have now
gained an appropriate place in the oil and gas industry and are being
applied on a large scale, both in new projects and in revamping existing
facilities. Internationally accepted standards for these meters have
been developed or are under development. However, with the introduction
of these two meters, the oil and gas industry has not made a drastic
simplification in the infrastructure and process facilities. Layout
and configuration of production facilities have remained the same over
the years; in fact one single-phase metering concept was replaced with
another single-phase metering concept.
During
the late 80’s the oil and gas industry started to realise that the availability
of MPFM’s could have an even much larger economic impact on the infrastructure
of oil and gas developments, e.g. replacement of test separators, removal
of sub-sea test lines and manifolds. In particular for sub-sea applications
these cost benefits are huge. This was the reason why the development
of MPFM’s, in contrast with the above-mentioned single-phase flow meters,
was primarily driven by the oil industry (see figure 1). The late 80’s
and the early 90’s saw various research programs being initiated, both
in-house with the oil companies and through Joint Industry Programs
(JIP’s). At present, we see MPFM’s being installed in the field but
it is still too early to conclude that they have been fully utilised
and accepted in the field. For sure, the developments have not been
completed. In comparison with the earlier mentioned Coriolis and Ultrasonic
flow meters, the MPFM is far more complex, both in terms of hardware
and in terms of fluid flow dynamics. There is still a long way to go
before the industry reaches the stage of routine field acceptance and
more effort is required. This, in particular, is the case with MPFM’s
used for fiscal or allocation purposes and for MPFM’s for sub-surface
applications.
Worldwide,
the application of MPFM’s is growing. Some companies have adopted the
philosophy that MPFM’s are the first choice for new developments and
only if the application of the MPFM is not suitable, the fall back application
of a test separator is used.
The
ultimate vision is to have a low-cost plug & play MPFM on every
single wellhead or downhole MPFM’s in multi-lateral wells. Although
not yet feasible, there are indications that within the next couple
of years a significant step in that direction will be made. Also in
the near future, translating the surface MPFM technology into concepts
that are suitable for the downhole applications is the obvious next
step. Downhole multiphase flow conditions are generally more favourable
for MPFM’s applications than surface conditions, this is because downhole
measurement is often done under much lower Gas Volume Fractions (GVF’s).
The challenges, however, are in the designs for high temperature and
high pressure, the reliability of the equipment and in particular, the
size of the equipment.
Impact
of MPFM’s on Production Facilities
The
conventional way of developing smaller fields, in the vicinity of an
existing production facility, is through the use of a test separator
on the existing facilities. This can either be an existing test separator
or a new test separator that is fully dedicated for the satellite production.
In this way, the satellite platform is kept as simple as possible with
only wellheads and a test and bulk header required to direct the production
streams to the test or bulk separator on the existing platform.
...contd.
