Production
Measurement Management
Production
measurement process is the entire chain from data collection in the
field up to the final production reporting, comment Lex (A.M.) Scheers
and Chris (C.J.M.) Wolff
The
production measure ment process is more than just measurement hardware
in the field but is the entire chain from data collection in the field
up to the final production reporting. It includes all intermediate steps
such as measurement and sampling guidelines, operational procedures,
data processing (pVT), data transmission and reconciliation/allocation
procedures. The customers of this measurement process are generally
spread over several disciplines in the oil and gas companies and their
partners or government bodies. Each of these customers has their own
requirements regarding the measurement process.
Production
measurements have a vital economic impact on the business; it not only
costs money, but also delivers data that is used in decision-making
processes such as production optimisation or reservoir modelling and
in measuring the economic returns. Economics then not only set the uncertainty
requirements for the production measurement process but often also indicate
the most critical measurements. This could be oil flow rate, gas flow
rate, watercut, GOR, gas volume fraction or even water flow rate in
water-constrained facilities.
As
every field development has its own specific requirements for the production
measurement process it will be demonstrated that a design phase and
operations phase should be established. In the design phase the requirements
from the customers are investigated and then compiled into a measurement
philosophy and subsequently this results in detailed design and description
of the system. Once production has started the measurement process should
be managed through proper custodianship. The latter should be transparent
and auditable and some organisational issues will be further discussed.
In
addition, with the more advanced measurement technology being installed
in the field, such as multi-phase flow meters or modelling techniques,
it becomes clear that proper management of this technology is essential
in order to meet the customer’s expectations.
Introduction
A
significant amount of publications have been issued over the last decade
on the new metering concepts, like Coriolis meters for mass flow rate
and net-oil measurement, Ultrasonic gas flow meters, Multiphase Flow
Meters and Wet Gas Meters. However, most of these publications, if not
all, are discussing the pure technical measurement issues, e.g. meter
performance, test loop evaluations, accuracies and the various operational
applications. With the introduction of all this more advanced measurement
equipment in the upstream area of the oil and gas business one should
ask the question whether we can still manage the production measurement
chain with the resources we were using in the old days of orifice plates
and turbine meters. The introduction of more advanced electronics, sophisticated
fluid flow models, wet gas over-reading correlations, the number of
additional fluid parameters required to properly run the modern measurement
equipment also makes it necessary to adapt the skills of the staff in
the field. Moreover the organi-sation should be tuned such that proper
management (custodianship) of this production measurement chain can
be done with the appropriate tools.
In
addition to the more advanced technology, the industry has changed over
the last decade in how they develop their infrastructure. Productions
facilities of different oil companies have been linked together, hydrocarbon
production is crossing concession boundaries, oil and gas is treated
in facilities owned by other oil companies and pipelines are used to
transport commingled production. One thing remains unchanged, as soon
as money is involved we all want to have our fair share of the money
pot and measurements are the basis for this.
Costs
vs Accuracy
The
value of any well flow rate production measurement, whether it is a
regular well test with a fully equipped three-phase test separator or
a relatively simple differential pressure measurement over the choke
of a wellhead, should be evaluated in order to justify the measurement.
It should not only be evaluated at design stage but also during the
operation phase. Who will use the data and for what purpose? What should
be the accuracy? What are the costs (both capital investments and operational
expenses)? In general there are three main purposes why we need production
measurements in the upstream area of the oil and gas industry.
- Surface
control
Information
allows the operators to monitor and optimise well production and manage
facility throughput, e.g. well performance-monitoring, optimisation
of production with artificial lift, planning, programming and forecasting.
- Sub-surface
control
Information
used by reservoir engineering, petroleum engineering to optimise the
sub-surface part of the production process, e.g. work over wells,
open/close zones, adjust artificial lift, manage reservoirs, etc.
- Fiscal
or allocation measurement
This
is a sales or allocation measurement that directly influences the
cash flow of the company. With proper single phase fluids the uncertainties
attached to these measurements are generally random and it may be
a loss or a gain with an average of zero. However, with allocation
measurements moving further upstream and dealing with non-ideal single-phase
fluids and more complex metering equipment, systematic errors might
be introduced with the consequence of a permanent gain or loss.
For
measurements that fall into the first two categories, in the past often
an uncertainty of 10% for each individual oil, water and gas stream
was quoted. However, a sound justification for ....
....contd
