Critical Drawdown Pressure of Depleted Reservoir

Abstract

For long time production, most oilfields have entered the later development stage, and the pore pressure is seriously depleted. The pressure depletion will affect in situ stress, and change the stress state around the borehole, and then the affect the critical drawdown pressure to cause sand production. The theoretical formula of two horizontal in situ stress changes with pore pressure is obtained based on generalized Hoek’s law, and then the stress distribution formula around the borehole in pressure depleted reservoir is established. The calculation model of sand production critical bottom hole flowing pressure in depleted reservoir is established using the Mohr–Coulomb criterion, Drucker–Prager criterion and Mogi–Coulomb criterion, respectively. The influence of pressure depletion on critical drawdown pressure is analyzed. The results show that: with the pore pressure decreasing, the horizontal in situ stress and critical drawdown pressure become smaller; the error of prediction model based on Mogi–Coulomb criterion is the minimum, and it is more in line with the actual field data; the prediction model based on Mohr–Coulomb criterion is conservative but most safe. The establishment of prediction model provides a guidance for actual production decisions in pressure depleted reservoir.