StimWell Completes Wintershall’s K-18 Five-zone Schlochtern Frac Campaign in Record Time



After drilling an appraisal well in 2006, Wintershall Noordzee B.V. subsequently drilled a near-horizontal open-hole side track into the Schloctern sandstone. The well was completed using a 4-1/2” StageFrac lower completion consisting of 5 Packer-Plus ball- actuated sliding sleeves with tandem open-hole packers. The completion program called for each zone to be fracced with 500,000 lb of coated 12/18 ceramic using an aggressive tip-screen-out, maximising net-pressure build-up, fracture width and fracture conductivity. Each fracced zone was to be isolated by dropping a large diameter metal ball in the displacement stage, pumping it to the ‘next seat up the completion’ and then hydraulically opening the sleeve to provide access to the next zone to be fracced. In landing on the seat, the ball isolated the previously fracced zone from the next operation.

Distance between zones was very small, and to ensure maximum net-pressure build-up, the ball was dropped without rate-change at the tail-end of the final proppant stage, effectively seating at the point the treatment was displaced to a small pre- calculated under-displacement. This was a difficult and untried proposition.

After completing a suite of quay-side full-scale ball-drop/sleeve tests, StimWell’s Island Patriot vessel was called upon to perform the 5 treatments.

Entering service in 2010, the Island Patriot is the newest and largest stimulation vessel available in the North Sea, designed with the capacity to carry out multiple-stage treatments such as Wintershall’s in a single mobilisation.

The vessel left port in early September 2011, loaded with 2,500,000 lbs of coated ceramic, all chemicals required and 430,000 gallons of KCl brine on- board. There was no intention of going back into port to re-load, and any additional KCl brine required was to be provided by supply-vessel in-field.

Using Stimwell’s HPG fresh- water borate cross-linked gel, Stimbor-H45F for the 270 deg F bottom-hole temperature, all 5 treatments were pumped without incident. All fracs achieved in the region of 1,000 psi net pressure increase and all were regarded as a complete success.

The campaign took just 19 days from start to finish, 10 of which were spent waiting on weather. It is a tribute to the pre-planning, quay-side testing, completion type, and not least the performance of the Island Patriot and StimWell crew that Wintershall now regard 10 days as their new benchmark for a 5 frac campaign in contrast to their historical norm of 40 days. Production from the well exceeded all expectations.

Campaign highlights include the first sub-sea multi-frac horizontal well to be completed in the North Sea. The largest single mobilization load-out achieved for a stimulation vessel, and the first use of ball-actuated sliding- sleeves for propped fracturing in the North Sea.

StimWell Services look forward to such ground-breaking treatments becoming routine in the North Sea and across the globe.

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