Productivity Impairment From Kaolinitemobilization: Laboratory And Fieldrnexperience, Oseberg Sor

摘要

The Oseberg Sφr field, operated by Hydro Oil & Energy, is situated 130 km west of the Norwegian coast on the eastern flank of the Viking Graben structure. It consists of fault-bounded structural units of varying geological complexity. Within these units, the reservoir intervals are of moderate to poor quality and can exhibit strong contrasts in permeability and formation-water composition. Reservoir-pressure support is provided by combined injection of gas and Utsira aquifer-produced water. The wells are a combination of platform and subsea and include extended-reach horizontals with complex geometry and lesser numbers of vertical wells.rnCoreflooding was undertaken with material from the major producing intervals (Ness, Middle and Upper Tarbet, and Upper Jurassic). This coreflooding has been used to assess potential formation damage resulting from application of oil-based mud (OBM) or scale-inhibitor squeeze treatment. In all instances, the major cause of formation damage was the mobilization of kaolinite that can form up to 20 wt% of the bulk rock and that occurs in all producing intervals. Coreflooding demonstrated that even at low flow rates (30 mL/h), permeability was reduced by up to 99% during initial plug saturation and before the onset of treatment. Modification of the coreholder allowed multiport permeability measurements to be made; these measurements gave an indication of the depth of damage.rnField evidence gives only an indirect indication of the effect of kaolinite mobilization on well productivity. For example, a gradual reduction in well productivity was reversed after squeeze treatment. This gradual decline is possibly a result of the migration of kaolinite during well inflow, the consequence of which is a reduction in permeability. Squeezing could have caused the dispersion of kaolinite away from the near wellbore with an increase in well productivity.rnGiven the adverse results obtained from coreflooding caused by kaolinite mobilization, significant effort has been directed toward identifying methods by which to reduce its impact, including through incorporation of clay stabilizers in scale-inhibitor squeeze treatments and remedial treatments with mud-acid stimulation. Laboratory results of these evaluations will be presented.rnAlthough the occurrence of kaolinite on Oseberg Sφr has potentially reduced well inflow performance, it has had a positive influence on scale-inhibitor squeeze lifetimes. A field example will be given to show this.