Abstract

Particulate damage is often cited as a cause of permeability impairment around boreholes, producing a decline in well performance. The mobility of particles within a formation, with respect to both damage and recovery mechanisms, is not easy to quantify

Removal of such damage from the formation has been attempted using water and a variety of low concentration drilling fluids. The results demonstrate that, in normal stable media, the fluids' formation sealing properties outwiegh any special viscosity and particle carrying abilities they may have compared to water, even at low concentrations. Only where the medium was fluidized did the polymers show any advantages over water.

Particulate movement and redistribution under borehole operating conditions has been assessed for a range of artificial and natural formations. It has been shown that movement is limited mainly to formations with a bimodal particle size distribution. In formations with a log-normal distribution, particle movement is restricted to all but the finest particles. The key factor governing particle mobility is therefore the structure of the porous medium.

Particulate damage, however caused, cannot always be effectively removed using normal development and rehabilitation techniques, and should therefore be avoided in the first place, by taking greater care during the drilling, sample collection and analysis, design, construction and development of a borehole.

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