Expro International Group has provided expertise in stimulation services on a job for Unocal in the Gulf of Mexico. Unocal used Expro Group's StimTube process to stimulate a zero production gas well back to a stable production level of 4 MMcf/d.
StimTube is an oxidizer-based tool for reservoir stimulation that 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.
According to Expro, StimTube can be run through tubing or on slickline to stimulate existing perforations and eliminate the need for additional stimulation techniques, resulting in cost savings for clients. The company says it can break down scale in the wellbore and displace fines from gravel pack screens and is an effective tool in breaking down asphaltenes and other plugging agents in heavy-oil wells.
Unocal's well in the Brazos A105 block had been completed with 300 ft of open perforations in the low permeability Big Hum D formation. Production rates and pressures had decreased, 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 ft of perforations due to water and sand production and leave 162 ft of perforations open to flow. While this eliminated water and sand production, stable flow could not be initiated. Wellhead pressure built to 1,500 psi when shut-in, but when brought online would drop to below line pressure. It became clear to Unocal that stimulation was in order to re-establish flow from this low-perm interval. Unocal called upon Expro to assist in the recovery of the well.
Expro 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 on the original log data and simulation runs by Expro. The decision was made to run three 15-ft assemblies of StimTube and treat 75 ft of total interval.
Upon firing the first StimTube using the Expro Slickline Firing Head system, Expro observed an immediate pressure increase of 90 psi at the surface. After the second firing, the company recorded an additional increase of 20 psi. Expro observed this same effect following the third StimTube firing, with a total increase of 120 psi observed in surface pressures over the three runs. At this point, Expro brought the well online and established a stable flow rate of 4 MMcf/d. Rates as high as 5 MMcf/d have been observed.