The phenomenon of precipitation of the insoluble salts particularly calcium carbonate and calcium sulfate, deposited from cement filtrate into a rock pore space as a potential source of formation permeability damage, was studied.

The series of flow tests were run in laboratory on sandstone rock samples using cement slurry filtrate containing various additives such as extenders, dispersants, retarders and fluid loss control additives.

The impact of precipitation of insoluble salts on rock permeability reduction has been evaluated on the basis of experimental results applying different analytical methods: chemical and SEM/EDAX analysis, permeability change measurement, as well as X-ray computerized tomography (CT) imaging technique.

All of the three types of cement filtrates, obtained from API class G cement used in experiments, caused sandstone permeability reduction, mainly due to deposition of coprecipitated insoluble CaCO3 and CaSO4 salt crystals in the pore space. The use of cellulose derivative, as fluid loss control additive caused the most severe formation damage. Lignin derivative as retarder and synthetic polymer as dispersant, if used in cement slurry composition caused less damaging effects than in case of cement slurry filtrate without additives.

The permeability damage due to precipitation of CaCO3 and CaSO4 from cement slurry filtrate could be partially recovered flushing the rock with brine.

You can access this article if you purchase or spend a download.