This paper describes the results of a research project about the extent of damage caused by clay based and clay free inhibitive fluids in two consolidated sandstones of permeability ranges 0.008-0.013 μm2(D) and 2.2-2.6 μm2(D) under simulated borehole conditions, using a closed loop circulating facility.

The fluids containing K+, Mg++ or Ca++ ions as well as clays, solid bridging materials and different polymers can be used either as drilling fluids or as workover, fracture and gravel pack fluids.

The damage was studied by two factors, viz, damage ratio DR (Percentage of original permeability lost after encountering the fluids) and sectional damage ratio SDR (Determined by cutting the damaged core into several segments and then determining the damage ratio of each segment relative to the original permeability of the core). The sectional damage ratio is used to determine the radius and extent of damage in the formation.

The dynamic filtration characteristics and the rheological properties of the used fluids were also evaluated.

The effects of increasing the temperature and differential pressure on formation damage and filtration characteristics of the used fluids were also investigated.

The effect of the presence of formation pore bridging materials (viz, chalk) in decreasing the extent of damage is also demonstrated here.

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