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North Sea: Selective matrix stimulation with continuous streaming of real-time reservoir data

Tool in operation:

This operation has been Target Interventions first field application of the 3.75” electric straddle tool. A major operator in the Norwegian sector of the North Sea wanted to trial the new technology to selectively isolate and acid stimulate multiple perforation intervals. Conventional straddle applications had historically resulted in unreliable performance, mainly due to lack of downhole information during the stimulation.

The operation utilised conventional 2.375” Coiled Tubing (CT) surface equipment and a CT internal cable, resistant to acid and non-intrusive to standard CT operating procedures. Target Intervention supplied the complete bottom hole assembly (BHA) including standard functions like end-connector and release tool, as well as advanced features like the tension-compression sub and casing-collar-perforations-locator (CCPL) for accurate depth correlation.

One of the fundamental challenges was to be able to pass through a 3.80” restriction in the completion, while still offering a mechanical packer solution capable of setting inside the horizontal 5.5” liner.

All functions of the electric straddle tool are electrically controlled from surface. Setting the packers, as well as opening and closing of valves within the BHA can be performed without relying on pumping through the CT or CT force manipulation from surface. Hence no disturbance of the downhole pressure occurs due to pumping operations and forces acting on the BHA in a horizontal well are easier to control. Packers were set independently of each other, which allowed identification of zonal isolation behind the casing in real-time. Pressure sensors are installed above and below the packers of the electric straddle tool, as well as in between. Once the packers were set, downhole diagnostics were performed prior to starting to pump through the CT, supporting the selection of the most promising perforation interval to be stimulated.

A total of 4 perforation zones were straddled but based on feedback from the downhole diagnostics only two of them were stimulated. Altogether over 300 bbl of hydrochloric acid were injected into the 2 intervals at a maximum pump rate of 5.0 barrels/min and differential pressures in between the packers ranging from 3000-5000 psi. Due to the electrical activation method, the packers stay set also when pumping is stopped, which allows the observation of the stimulation pressures falling off after the treatment. A comparison of the perforation zone’s pressure response before and after can therefore be obtained, before electrically un-setting the packers.