Sand Production Prediction in High Rate, Perforated and Open-hole Gas Wells

Abstract

Abstract This paper presents an analytical model for the prediction of the on-set of sand production or critical drawdown pressure (CDP) in high rate gas wells. The model describes the perforation and open-hole cavity stability incorporating both rock and fluid mechanics fundamentals. The pore pressure gradient is calculated using the non-Darcy gas flow equation and coupled with the stress-state for a perfectly Mohr-Coulomb material. Sand production is assumed to initiate when the drawdown pressure condition (i.e. at CDP) induces tensile stresses across the cavity face. Both spherical and cylindrical models are presented. The spherical model is suitable for cased and perforated applications while the cylindrical model is used for a horizontal open-hole completion. For input, the model requires cohesive strength and an internal friction angle that characterizes a Mohr-Coulomb material; preferably predicted using a log-based mechanical properties algorithm in order to generate a foot-by-foot profile of the maximum sand free drawdown for gas wells. The example GOM well illustrates a continuous profile of critical drawdown with depth, providing quick identification of potential sand producing zones. This allows a gravel pack decision to be made in the period between logging and completion. It also facilitates the design of selective perforation programs. The model demonstrates that non-Darcy flow has a considerable effect on the sanding tendency of weak but competent rock, and completion decisions in high gas-rate wells that neglect the influence of non-Darcy flow could be overly optimistic. It also shows that the CDP of a horizontal well with slotted liner is less than that of the corresponding cased and perforated completion.