Sand production instability is considered as the result of wellbore fluid pressure reduction (drawdown) below some critical level. A continuum model for massive continued sand production is developed by considering coupling of fluid flow with the flow of the granular matrix. The model provides a physical mechanism describing propagation of a yielding front away from the wellbore as sand production continues. Solid flow proceeds by "unravelling of fabric" because yield front motion is opposite to the direction of solids mass transport. Short-term enhancement of fluid production because of simultaneous sand production turns out to be dependent not only on instantaneous sand flux, but also on the current radius of the yielded zone around wellbore, that is, the history of sand production for the well. Long-term enhancement is stipulated mainly by growth of a yielded, highly permeable zone around the wellbore.

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