Permeability, porosity and surface characteristics of filter cakes from water-bentonite suspensions

摘要

Water - bentonite suspensions behave as non-Newtonian fluids with exceptional rheological and filtration characteristics at low temperatures which deteriorate at temperatures higher than 120°C. Additives restore these characteristics but many of them are thermally unstable at the temperatures encountered, for example in oil-well and geothermal drilling. Greek lignite has been proven to be an excellent additive for water-bentonite suspensions at temperatures up to 177°C. In this work we attempt to assess the reason for such good performance by studying the surface characteristics and the permeabilities of filter cakes of water - bentonite suspensions with and without the additive (various lignite types) after exposing the samples to thermal static aging at 177°C for 16 hours. The filter cakes are produced with an American Petroleum Institute filter press allowing filtration for sufficient time to produce a filter cake with adequate thickness. The surface morphology of the filter cakes has been assessed with a scanning electron microscope. The permeabilities of the filter cakes were determined with an in-house technique which creates a 'wet core' of the filter cake of sufficient thickness and the water permeability is measured in a Hassler type meter. The differences between the reference samples (cakes from bentonite suspensions at room temperature) with cake samples from thermally aged water-bentonite suspensions and water-bentonite-lignite suspensions both in surface characteristics and in cake permeability are noted and discussed.