Clamp-on sonar well testing on a
mature gas condensate field
Customer's problem
Expro's solution
Marathon Oil UK owns a 38 percent interest in the East Brae Field, a
mature gas-condensate field in the Central North Sea. Marathon has
undertaken several projects in the East Brae Field to maximise
production from this field, balancing the need for periodic well
testing and the requirement to optimise production from the field's
low pressure wells.
Expro proposed that their sonar surveillance services could be used
in place of the test separator for well testing. This testing would
allow the well gas production rates to be accurately determined
without the trade-off of decreased production during well testing.
Marathon has modified its production facilities to enable the test
separator to be operated at a reduced pressure thereby allowing it
to act as a low pressure production separator to sustain or boost
production from the field's low pressure wells. With the test
separator operating in this mode, Marathon can maximise
production from its struggling well stock.
Although overall field production is increased, the conversion of the
test separator into a low pressure production separator precludes its
use for production surveillance. In order to measure the production
on a well by well basis, the low pressure separator has to be
temporarily reverted into a test separator, causing decreased
production of the low pressure wells during this period. This results
in deferred production during well testing. Ideally, Marathon seeks a
well testing solution that would allow it to continue to produce all
wells at the optimum production rates during well testing periods.
exprogroup.com
A trial of Expro's ActiveSONAR™ and PassiveSONAR™ meters has
been implemented on two separate occasions on the East Brae
Platform by Expro Meters' expert Surveillance Engineer to:
• Prove that the meters can be applied to East Brae wells to
determine well performance (accuracy +/- 10%)
• To prove the applicability of the flow meters over wells with a wide
range of gas/liquid ratios
• To evaluate the merits of both the ActiveSONAR and
PassiveSONAR flow meters
• Minimise the production losses associated with traditional well
testing
The meters were installed and supported by one engineer and
rigged up ready for operation in a matter of hours.
Clamp-on sonar well testing on a
mature gas condensate field
Results
Technologies used
Both the ActiveSONAR and the PassiveSONAR meters installed on
East Brae showed very close agreement with recent test separator
values for the predominant gas phase. If the gas trends for a well
are in line with expectations then the test can be used for allocation
purposes and well performance monitoring. If the test result is
outside of expectations then the well will be flagged for a full twophase well test in the test separator when an opportunity arises
Both ActiveSONAR and PassiveSONAR meters were successfully
trialled by Expro Meters for wellhead production surveillance.
The ActiveSONAR and PassiveSONAR meters took less than one
hour each to rig up. The kit is packaged appropriately for
convenient transport by helicopter. The clamp-on well testing can be
performed by one trained Expro Field Surveillance Engineer.
A sonar well test report was generated as part of the deliverable to
Marathon, using Expro Meters automated report generation tools
with base-engineering reviews to ensure accuracy and consistency.
Based on contracting with Expro to provide clamp-on well testing
services, Marathon has the potential to save over £150,000 for each
testing campaign.
exprogroup.com
PassiveSONAR is the technology that pioneered clamp-on Sonar
metering. It uses passive listening technology to determine
volumetric flow rate. PassiveSONAR is well-suited for high rates and
high liquid loadings.
The ActiveSONAR meter uses pulsed-array sensors to track the
speed of coherent flow structures. The technology offers enhanced
performance for surveillance applications where low flow rates and
thick walled pipes present measurement challenges for traditional
clamp-on meters.
Expro Meters automated well test reporting tools were used to
generate a clear, concise and accurate well test report for the
customer on a timely basis.