Schlumberger

Performance Report: IWA Completes Multi-Phase Workover Off Germany

Challenge: The operator planned a major workover on the production well on its Mittelplate structure, which is Germany’s largest oil producing field. The complex, multi-phase operation consisted of sealing all perforations and killing the well, followed by extraction of the old production pump. After cleaning the wellbore and perforating areas, the operator was to install a new production pump. The operator required the operation be completed with minimal trips, no reservoir-damaging losses while working in an environment where the precise pressure regime was unknown. Furthermore, as the Mittelplate field is produced from an artificial island in the Wattenmeer National Park, there were to be zero environmental incidents.

Solution: For this complex operation, the operator selected the SPECIALIZED TOOLS and clean-up chemicals incorporated in the M-I SWACO comprehensive INTEGRATED WELLBORE ASSURANCE (IWA) package. The IWA approach would be used to extract the old pump, clean the well and perforations area and then install the replacement production pump. The package also included the WELL COMMANDER* tool, which was installed in the 9 5/8-in casing to provide an alternate circulation path if needed. M-I SWACO would have one individual project engineer on the rig who would be responsible for all operations.

Result: The wellbore clean-up was completed in one trip with zero losses, even though a heavier than expected fluid density had to be employed to address unexpectedly high reservoir pressure. The fluid loss control technology utilized optimum particle size distribution (PSD) to deliver exceptional bridging and further minimize filtrate invasion. Furthermore through the engineered displacement, the optimum combination of SPECIALIZED TOOLS and the SAFE chemical wash pill provided superior wellbore and perforation cleaning with less waste generated. The displacement was accomplished successfully with only 1.2 well volume circulated as opposed to the planned 1.5 volumes. As a result, about 30 m³ of brine was saved for future useand the costs for waste disposal of contaminated brines and crude oil were cut in half. In addition, the operation was completed with zero HSE incidents.

Owing to the estimated reservoir pressure, 9.8 lb/gal (1.18 sg) NaCl brine kill fluid initially was deemed sufficient for sealing the perforations and killing the well as it would deliver around 31-bar overbalance. However, after the sized salt pill was placed and the NaCl brine displaced, the well flowed with pressure increasing higher than estimated. Consequently, 11.2 lb/gal (1.35 sg) CaCl2 brine was ordered immediately and prepared at the onshore ENVIRO CENTER and shipped to location. An estimated 237 m3 was displaced in the well when the fluid loss control pill reached all the perforations as calculated. A flow check showed no losses or back flow.

Once the old production pump was pulled, the mechanical wellbore cleanout assembly including brushes, scrapers and magnets was delivered on schedule and the SAFE chemical wash surfactant clean-up pill was prepared and pumped downhole. Since the pump had a limited flow rate (1.500 l/min) and the maximum had been reached, there was no reason to open the ports in the WELL COMMANDER tool. Therefore, displacement continued with this lower pump rate through the entire string. Despite the lower than planned flow rate, acceptable hole cleaning was observed. The packer fluid was prepared during installation of the new pump and the displacement from brine to the packer fluid proceeded incident-free with no spacer required.


Download: IWA Completes Multi-Phase Workover Off Germany (0.49 MB PDF)

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"The entire clean-up, pump extraction and re-installation was completed successfully in one trip with zero losses or environmental incidents. In addition, thanks to superb communication between operator and M-I SWACO, when the reservoir pressure exceeded the initial estimate, the higher density kill brine was ordered quickly and delivered to location.”
Dr. Martin Karad
Project Engineer
M-I SWACO