Abstract

Ingress of sand usually occurs in wells abstracting from sandstone aquifers that are poorly cemented. Impacts can be serious and may add significantly to production costs. They include loss of yield and continuity of supply, a reduction in the efficiency and operational life of wells and pumps, more frequent maintenance of wells and ultimately well replacement. The design of high-capacity sand-free wells in sandstone aquifers is often problematical. This is partly because a substantial proportion of the flow is through fractures, which means that well design criteria of screen slot size and artificial pack grain size and grading that have been developed for unconsolidated granular aquifers are not generally applicable. Also, many sandstone aquifers are multi-layered. Interbedded fine-grained and friable sandstone layers or loose sands are often responsible for sand entering a well. Excluding them is often difficult in practice without blocking productive fracture zones, and, therefore, risking a reduction of well yield. Well design alone is not always capable of controlling sand pumping. Pumping at a lower discharge rate, regulating flow at start-up, and the use of sand traps at the ground surface or inside wells are other measures that can assist in alleviating the problem.

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