Characterization of Sand Production for Clayey-Silt Sediments Conditioned to Hydraulic Slotting and Gravel Packing: Experimental Observations, Theoretical Formulations, and Modeling

Abstract

Summary In our previous work (Jin et al. 2021), an experimental effort has been made to microscopically observe sand failure, migration within a matrix, invasion toward gravel-packing zones, and production conditioned to the openhole gravel packing, while three sanding patterns (i.e., fractures, wormholes, and fluidized channels) have been identified. The first pattern is associated with an uneven strain-stress effect, while the last two patterns result from liquid seepage. To theoretically reproduce our previous experimental measurements, in this study, the experimental techniques have been further modified and improved to eliminate the associated uneven strain-stress effect by uniformly injecting water into a radial flow vessel. Experimentally, by generating slots near the gravel packing, sand failure dynamics, sand flow paths, and sand production for the clayey-silt sediments can be microscopically observed, geometrically depicted, and volumetrically quantified conditioned to different operational conditions (i.e., no hydraulic slot, single hydraulic slot without proppants, single hydraulic slot with different lengths, and double hydraulic slots with different intersection angles). Theoretically, a wormhole growth model has been proposed to reproduce the sand production for both hydrate-free and hydrate-bearing sandpacks by accounting for a sand failure criterion as well as the porosity and permeability alteration models. Good agreements between the measured and simulated data (i.e., pressure and temperature profiles, cumulative gas and water production, and produced sediment volumes) have been achieved. The experimental results show that hydraulic slotting can be used to not only effectively mitigate the skin effect near a wellbore but also decrease the pressure gradient near the wellbore. In this way, the possibility of sand failure is decreased if a predesigned hydraulic slotting after well completion is deployed. It is revealed that the operational conditions dictate the sand failure patterns, sand production volumes, and sizes of the produced particles. Similar to hydrate dissociation, sand production is also divided into three stages: before dissociation (transport of free particles or weakly consolidated particles), during hydrate dissociation (sand detachment because of the loss of hydrate cohesion and massive water production), and after hydrate dissociation (transport of fully unlocked particles). Furthermore, sensitivity analysis shows that cumulative sediment production and permeability increment are affected by the following strong-to-weak order: intrinsic failure resistance, tortuosity, Kozeny coefficient, and absolute permeability. Also, the breakdown pressure is dominated by absolute permeability, while pressure during the stable stage is mainly dictated by the intrinsic failure resistance, tortuosity, and Kozeny coefficient.