Abstract: Offshore reservoirs are generally exploited without energy supplement, and reservoir pressure depletion will cause rock stress changes which results in an increasing likelihood of serious sand production in the unconsolidated sandstone reservoir. This paper aims at offshore unconsolidated sandstone gas reservoirs, analyzes rock stresses of the borehole wall with impact of reservoir pressure depletion on in-situ stresses. Combining with fully-polyaxial rock failure criterion Mogi-Coulomb, a new sanding Critical Drawdown Pressure (CDP) calculating model. Furthermore, an applicable sanding prediction method for pressure depleted gas reservoir in well whole life cycle is proposed. The model was applied in F gas reservoir, the chart of sanding CDP for Well F-1 in the whole production life cycle is plotted. The research results indicate:initially, the sanding CDP is relatively large; with formation pressure depletion, CDP is reduced step by step until depleted to the critical reservoir pressure, and sand will be produced no matter how small the drawdown is. The research outcomes are consistent with actual oilfield production situation, which can provide some theoretical supports for sand production gas wells.

Key words: unconsolidated sandstone, reservoir pressure depletion, failure criterion of rock, sand production, critical drawdown pressure