Determination of the critical drawdown pressure to predict potential risk of sand production of a gas well in Bangladesh

Abstract

Sub-surface formations are always in a stressed state, mostly due to overburden and tectonic stresses. When an oil or gas well is drilled into a formation, stressed solid material is removed. The fluid pressure of the borehole supports the borehole wall. As this fluid pressure generally does not match with the in situ formation stresses, there will be stress redistribution around the wellbore. The new stress may be greater than the stress that the formation can support and subsequently failure may occur. Knowledge of the stresses around a well is therefore imperative to determine the wellbore stability and subsequently any potential risk of sand production. Due to lack of proper knowledge for calculating Critical Drawdown Pressure and predicting sand production, some gas wells in Bangladesh have started producing sand. For the same reason, production rate from some gas wells have been kept limited assuming that sand production may trigger although the well formation has sufficient strength to prevent sand production. The main objective of this project is to determine the Critical Drawdown Pressure of a gas well which is the maximum difference between reservoir pressure and bottom-hole flowing pressure that the formation can withstand without sand being produced along with the formation fluid. Different existing Models have been used for this purpose and comparative analysis of those models have been performed. Based on this study, the Drucker-Prager model result meets and explain the current operating condition of the sample gas well. Hence with all its limitation, Drucker-Prager failure criterion has been considered a reliable criterion to predict sanding production when the well is in production.