A modified pressure-gradient-based (PGB) sand failure criterion for dynamically and preferentially characterizing wormhole growth and propagation during CHOPS processes

Abstract

In this paper, a recently developed pressure-gradient-based (PGB) sand failure criterion has been modified to improve its applicability for accurately quantifying the dynamic and preferential wormhole growth and propagation during cold heavy oil production with sand (CHOPS) processes. More specifically, the resistance of sand mobilization is analyzed and mechanical balance at pore-scale is established. The heterogeneous porosity distribution is newly integrated into the PGB sand failure criterion to identify the preferential directions of wormhole propagation. The sand failure is quantitatively examined by comparing the pressure gradients along with the potential directions at a threshold pressure gradient. Such an improved PGB sand failure criterion has been incorporated with a commercial reservoir simulator, in which three sets of relative permeability are utilized to represent the three physically distinct stages of the CHOPS processes. Subsequently, the newly modified PGB sand failure criterion is validated by laboratory sand production experiments and then extended to a field application. Good agreements between the simulated and measured data (i.e., production profiles and pressure) have been achieved from the laboratory experiments. As the preferential directions of the wormhole propagation can be dynamically determined through pressure gradient and porosity distribution, the simulated wormholes are much closer to the experimental observations than the previous work (Fan et al., 2019). The accuracy of the simulated production profiles has also been significantly improved by using three sets of permeability to separately represent the dominant impacts (i.e., sand failure, slurry flow, and boundary effect) on different stages of the CHOPS processes. In addition, good agreements between the simulated and measured data have been obtained from the field case by use of the improved PGB sand failure criterion, demonstrating its robustness and versatile applicability of predicting the dynamic and preferential wormhole network under various laboratory and field conditions.