Expro’s StimTube recovers difficult well for Unocal
Posted: 25 July 2003
Oilfield services provider Expro International Group PLC recently
provided expertise in stimulation services on a successful job for
Unocal in the Gulf of Mexico.
Expro Group's StimTube process was utilised by Unocal to stimulate
a previously zero production gas well back to a stable production
level of 4 MMSCFD.
StimTube is an oxidiser-based tool for reservoir stimulation which,
when detonated, can generate large volumes of high-pressure gas
— as much as 20,000 psi at the reservoir face.
These high-pressure gas pulses are effective in perforation breakdown,
fracture initiation and elimination of near wellbore damage.
StimTube can be run through tubing or on slickline to stimulate
existing perforations and eliminate the need for additional stimulation
techniques, thus resulting in significant cost savings for clients.
It can break down scale in the wellbore and displace fines from
gravel pack screens. It is also an effective tool in breaking down
asphaltenes and other plugging agents in heavy oil wells.
Unocal¹s well, located in the Brazos A105 block, had been
initially completed with 300 feet of open perforations in the low
permeability Big Hum "D" formation.
Production rates and pressures had steadily decreased over time
and large diameter tubing hindered the well's natural lifting capabilities.
Over time, the well was unable to produce against a system pressure
of 500 psi.
A decision was made to isolate the bottom 138 feet of perforations
due to water and sand production and leave 162 feet of perforations
open to flow.
While this successfully eliminated water and sand production, stable
flow could not be initiated. Wellhead pressure would build readily
to 1500 psi. when shut-in, but when brought online would drop to
below line pressure in a matter of minutes.
It became clear to Unocal that stimulation was in order to re-establish
flow from this low perm interval. Expro was called upon by Unocal
to assist in the recovery of the well.
Expro came on location and ran a Gamma Ray/ Casing Collar Locator/
Pressure and Temperature gauge survey using their slickline depth
correlation system. Unocal selected the best zones to stimulate
based upon the original log data and simulation runs by Expro.
The decision was made to run three 15 feet assemblies of StimTube
and treat 75 feet of total interval.
Upon firing the first StimTube using the Expro Slickline Firing
Head System, an immediate pressure increase of 90 psi was observed
at the surface.
After the second firing, an additional increase of 20 psi was recorded.
This same effect was observed following the third StimTube firing,
with a total increase of 120 psi observed in surface pressures over
the three runs.
At this point, the well was successfully brought online and a stable
flow rate of 4 MMSCFD was established. Rates as high as 5 MMSCFD
have been observed
Murray E. Gardin, Unocal Operations Engineer, said of the job,
"StimTube definitely allowed us to re-establish flow from this
well. Its performance was beyond our expectations and I believe
the potential exists for this technology to benefit many other wells.
Payout of our entire project occurred in less than 10 days and I
could not be more pleased with the outcome."
Expro International Group PLC is a leading international oilfield
service provider of key products and services necessary to safely
complete and manage oil and gas wells.
These products and services are packaged into three distinct business
segments: Cased Hole Services, Subsurface Systems, and Surface and
Environmental Systems, giving clients the ability to maximise the
recovery of their reserves.
The Expro Group employs over 2,000 people worldwide and has become
an innovative leader in oilfield technology aligned with the needs
of its customers.
For more information see www.exprogroup.com.
Posted by Richard Price,
Editor Pipeline Magazine
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