SUMMARYA sand production model was developed for volumetric sand production predictions that take into account the e!ects of the external stresses and #uid #ow rate. The model couples the poro-mechanical behaviour of the solid}#uid system with the erosion behaviour of the solids due to #uid #ow. It predicts reasonably experimental volumetric sand production data from a hollow cylinder test on a weak sandstone. The test results show that in weak and compactive sandstones, sand production is associated with decohesioning and plastici"cation of a zone around the inner hole which can then be mobilized by the hydrodynamic forces of the #uid #ow. The sand production rate increases both with external applied stress and #uid #ow rate but it is constant with time under constant external stress and #uid #ow rate. In both cases a critical lower limit has to be exceeded for sand production initiation.

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TX 75083-3836, U.S.A" fax 01·972·952·9435. AbstractThis study is focusing on sand production processes in weak sandstone formations with a uniaxial compressive strength in the range of 0 -10 MPa, with special emphasis on the ultraweak facies where uniaxial compression tests hardly can be conducted. The relative influence of rock mechanical properties on rock failure and sand production modes is addressed to understand sand production data from wells in a weakly consolidated basin, Results of physical model experiments of sand production from boreholes and perforation cavities as well as numerical simulations have been used along with the field data to evaluate different criteria for the onset of sand production in ultra-weak formations. It is shown how in particular the shallow and weakest strata deviates from the classical behavior of more competent formations, and a simple empirical criterion for estimation of the conditions for onset of sand production is proposed, Finally, alternatives to classical sand control strategies are discussed, which directly take into account the nature of weak sandstone,