StimTube is an oxidizer-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.
Unocal's 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 wellıs 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."
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