Multiphase
Metering System for
Incentive Oil Metering
During
installation and commissioning, very good support from the vendor is
necessary, in order to execute a successful project, highlight Ivan
Susanto & Jerry Gani
Introduction
PT.
Caltex Pacific Indonesia (CPI), an Indonesia Business Unit of ChevronTexaco,
is the largest oil company in Indonesia. CPI operates several Secondary/
Enhanced Oil recovery (EOR) projects using water flood or steam flood
to maintain or increase oil production. One such project is in the Antara
field. Since the Antara Water Flood is a new EOR project, PT. CPI received
an incentive from the Government of Indonesia (GOI) for the incremental
oil production resulting from the additional capital investment in the
EOR project.
The
Antara Field is located in the Riau Province of Central Sumatra, an
area which contains numerous CPI operated oil fields, including the
massive Duri and Minas fields. Antara is a significantly smaller oilfield
located at the northern end of CPIs operated assets. It is located approximately
4 kilometers north of the larger Balam South Field as shown in Figure
1. The field was discovered in July 1978, and placed on production in
August 1979. The Antara Water Flood Project was generated in anticipation
of having excessive water production from the neighbouring Balam South
water flood project. The capital investment for injecting water into
the Antara reservoirs for pressure maintenance and improved sweep efficiency
was relatively inexpensive due to close proximity to the existing Balam
South water flood facilities.
The
project team created several different options for metering Antara oil
production. Theses options ranged from building Conventional Well Test
installation to Automatic Well Test (AWT).
From
the considered options, it was decided that a new AWT station using
multiphase metering system would be constructed to measure oil and water
production from each producer. The new test station was designed to
accommodate 16 production wells. It was located in the middle of Antara
field and equipped with instrumentation capable of communicating remotely
with the SCADA System at Balam South Gathering Station (GS) operator
room.
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Where:
A:
Balam South Total Fluid Production
B:
Antara Production Well (15 wells) that are not under testing
C:
Antara Production Well (1 well) that is under testing
D:
Antara Well Test Result (BOPD), the results are recorded and summed
for Antara total oil production ( S Well Test Result # 1,2,…16)
with Allocation Factor (AF) = 1 (see Fig.3 - Total Antara Oil
Production with AF = 1)
E:
Total fluid production from Balam South Field and Antara Field
F:
Total oil production from Balam South Field and Antara Field is
measured using Balam South Oil Meter
G:
Total Oil production from Balam South Field and Antara Field is
sent to shipping port for sale
(Balam
S. Oil production = Total oil production from Balam S. & Antara
Field - S Antara Well Test Result # 1,2…16 X Antara AF)
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The
decision to utilize an AWT was not easy. There were several accuracy
issues in the existing well test facility. Previously a well test facility
had never been used for incentive oil metering for an EOR project. Usually
a separate and dedicated GS with a single-phase oil meter is used for
measuring incentive oil production and consequently there was a risk
of project delay if the AWT facility failed to meet government regulation
and approval. However, the AWT system was chosen because a thorough
analysis & study revealed that the multiphase metering system could
meet GOI regulation, deliver superior economic, operational and maintenance
advantages.
After
several tests (Factory and Site Acceptance Test), the Antara AWT system
received GOI certification and is now in operation as an incentive oil
meter for the Antara field.
Project
Overview
The
production fluids from Antara wells and Balam South Wells were sent
to Balam South GS. At the Balam GS, a first stage of separation is made
to separate gas and liquid. The liquid was then further separated into
oil and water. The oil was sent to a shipping tank and then transferred
to a shipping port for sale. Formerly, the water component was treated
and then disposed off in an environmentally appropriate manner. Produced
liquids from Antara wells were periodically tested by well test facility
for well management.
With
the start of water flooding, the water was no longer disposed off, but
treated in Balam South Water Treating Plant (WTP) and sent to Antara
injection wells using injection pumps to be re-injected into Antara
oil reservoir to increase production of oil.
Incentive
oil was usually measured at a dedicated GS equipped with a dedicated
oil meter. For the Antara project, the project team used AWT to measure
incentive oil from each well and used existing Balam South GS to process
the produced fluids (see fig.2 – Block Diagram for Antara Oil Incentive
Meter).
Selecting
the Right Alternative: Why the Project Team Decided to Use an AWT for
Incentive Oil Metering?
Initially,
the project team came up with four options for treating fluid and shipping
oil (see table-1)
From
the four options reviewed, the project team selected option-3, which
had the lowest Capital Cost (US$ 3,810,000.00). As part of option-3,
the project team would build a dedicated Antara GS with a gas boot to
separate Antara production liquid from gas. The liquid would be separated
into oil and water in an Antara Wash tank. The oil would be sent to
a shipping tank and the water would be sent to water storage tank. The
oil from shipping tank would be send thru shipping line to a dedicated
incentive oil meter at Balam GS.
After
a further review and economic analysis of Option-3, the project team
developed an idea to use an Automatic Well Test (AWT) for oil metering
instead of building a dedicated Antara GS and use the existing Balam
South GS capacity for treating and shipping. The project team reviewed
capital cost for using AWT option as per table-2.
With
this significant capital cost saving it was decided to propose the AWT
option to the GOI. This option had mutual benefit for both CPI and GOI
in term of improving the project economics and significantly reducing
the capital expenditure for GOI, which has the major equity share.
Considerations
for AWT Design Criteria and Appropriate Technology
Since
there was no prior experience in using an AWT for fiscal oil metering
within CPI and the GOI, there were some concern over the accuracy and
reliability of such a system. Consequently, the project team had to
develop some design criteria parameters for the facility.
...contd.
