Rock salt stimulation feasibility for well abandonment

Publieke samenvatting / Public summary

The abandonment of thousands of wells in NL in the near future requires cost-efficient and reliable solutions. Reducing P&A costs and increasing long term safety could be achieved by developing new methods for well plugging and annular zonal isolation based on the use of natural sealing formations. Rocksalt is particularly attractive because of its ductility, ability to creep and self-healing/sealing behavior. The advantage of restoring the original caprock is its very low permeability, proven long-term sealing capacity and chemical stability. Many evaporites, even when ductile and principally suited for natural formation sealing might creep (causing wellbore convergence and closure) too slow for the application within P&A operations, particularly at shallow depths above 2000 m.

The aim of the project is to investigate the potential options for Zechstein rocksalt stimulation, through experimental verification, and to provide a concept design for a pilot test in order to enable implementation of the most promising technique. The project is aimed at oil, gas, geothermal wells and salt producers in the Netherlands that are faced with decommissioning wells that transect, or operate in, Zechstein rocksalt formations. Zechstein rocksalt overlies a high proportion of Dutch gasfields, many of which will be decommissioned in the coming decades, both on- and off-shore. Moreover, the Dutch salt mining industry is one of the largest in the EU, with many wells to be decommissioned or re-used for energy storage in solution-mined caverns, which will likely be needed even more in the near future.

Korte omschrijving
The project is split in two phases. The aim of Phase 1 is to make an inventory of options for Zechstein rocksalt stimulation and select the most promising stimulation technique(s) that can be tested experimentally in Phase 2. Selection will be based on the literature review operator experience and industry expertise (e.g. AkzoNobel). At the end of Phase 1, a go/no-go decision by project partners (unanimous) is foreseen to initiate the next phase. In Phase 2, a limited series of dedicated laboratory experiments will be designed and performed to test the most promising stimulation options. Tests will be performed on Zechstein rocksalt specimens at the HPT Laboratory at Utrecht University. Experiments could include testing wellbore convergence and healing/sealing of well plugs in an open wellbore versus a wellbore filled with granular/graded salt, with and without additives for enhancement of rocksalt ductility and sealing/healing behavior.

The project will provide quantification of the effects of the most promising salt stimulation technique on rocksalt ductility and sealing/healing behavior. In case of positive outcome from experiments, the operational feasibility of well plug placement will be assessed and a field test will be designed. The results of the project will deliver the basis for the development of such a field test (not part of this project).