Deposition of solids in drilling fluids on borehole walls

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Abstract
Suspended solid particles are introduced into well bores during various operations such as the use of drilling muds. These particles in drilling muds can build a filter cake on the wall of the bore and migrate to the porous formation immediately adjacent to the well bore. In either case, the entrainment and deposition of particles cause an observed decline in productivity of some wells or increase of injection pressures. It is the objective of this work to develop a practical mathematical approach to the formation of a filter cake at the face of the well bore. This is achieved first by defining and identifying relevant mechanisms which contribute to the cake formation and particle migration in porous media. Then, conservation principles expressed in terms of quantifications of these mechanisms lead to a system consisting of governing partial differential equations. These equations are averaged to obtain analytical expressions to predict the cake thickness as a function of solid concentration, injection rate, or filtrate rate, and time. The results are compared with experimental data obtained by some researchers. Excellent match is obtained between the theoretical and experimental results.

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