Impairment by Suspended Solids Invasion: Testing and Prediction

Summary A new model was developed to predict wellbore impairment by internal filter-cake formation during water injection. In the model, formation damage is approached semiempirically; no assumptions were made with respect to the specific mechanism underlying impairment. Model constants, derived from linear core-flow experiments, were used to calculate radial flow damage. Radial coreflow experiments subsequently were carried out to validate the proposed model. Theory and experiment were in good agreement. This paper shows that the model can obtain realistic performance and half-life estimates for water injectors. During the experiments, a pronounced velocity effect on impairment rate was found. The extent of impairment increased by several orders of magnitude when injection dropped below a critical inflow velocity of 2 cm/min. The generally accepted : "⅓: 17 rule" (the particle/pore ratio for internal cake formation) is confirmed for inflow velocities exceeding 10 cm/min. At low injection velocities (2 cm/min), even smaller particles were found to cause increased damage: a "⅓: 114 rule" may be more applicable for such low inflow velocities.