Experimental Investigation of Proppant Flowback Phenomena Using a Large Scale Fracturing Simulator

Abstract

This paper evaluates the maximum flow rate before the sand production initiates while flowing back a reservoir after the hydraulic fracturing treatment. The experiments are performed in a high pressure slot which simulates a fracture. The slot is a parallel plate device, which is 7 ft high and 9 1/3 ft long with provisions for varying fracture gap width. The slot is filled with proppant to simulate a propped fracture, then, the closure pressure is applied with 12 actuators to simulate confining pressure on the proppant pack. Water is pumped into the slot to simulate flowing back of the fracturing fluid. The water flow rate is varied till the proppant pack destabilizes, and the sand production begins. The sand distribution is observed in the fracture with a vision system. The experimental results show that the critical water flowback rate decreases as the closure pressure increases, or when the fracture gap width increases. However, the sand-free maximum water flow rate increases as the sand size increases for a given fracture gap width. Lastly, the cumulative sand production decreases as the closure stress decreases at a particular flow rate. The visual observations of the proppant flowback phenomena show that the sand production initiates close to the perforation. After the initiation of the sand flow, continued pumping of the water results in sand production through a channel formed in the proppant pack.

Fracturing Fluid Characterization Facility

“…The FFCF study shows that there is a critical flow rate beyond which the sand will be produced from the propped fracture; below this rate, there is negligible sand production. 25 This result disproves Stein's 26 conclusion that the unconsolidated sand would flowback at any flow rate.…”

“…Previous numerical and experimental investigations of the flowback phenomena concluded that a proppant pack is stable when the range of the ratio of the fracture width to proppant diameter is between the values from three to six. [27][28][29] But these studies did not observe that these ratios are dependent on the cleanup flow rates; on the other hand, the FFCF results 25 show that the proppant flowback can occur within the recommended ratios, albeit at higher fluid rates as compared to the rates for the higher ratios.…”

DEM-CFD Modeling of Proppant Pillar Deformation and Stability during the Fracturing Fluid Flowback

“…The number of applied stress cycles and the initial RCP pack strength appear to be the dominant factors that govern proppant back-production. Goel and Shah [11] investigated proppant flowback phenomena using a large-scale fracturing simulator. Experimental results show that flowback initiates at lower cleanup rates when the closure stress increases or when the fracture width increases and flowback initiates at higher cleanup rates when the sand size increases.…”

Proppant Distribution and Flowback in Off-Balance Hydraulic Fractures

“…They observe that packs with width/grain diameter larger than 6 are inherently unstable. Goel et al's5 experimental results indicate that this ratio depends on closure stress, with higher values corresponding to lower closure stresses. All of the above analyses are based on simplified fracture models, where proppant beds are formed horizontally and gravity actually helps keep the proppant in place.Experimental results also show the presence of a critical flow rate through the pack above which the pack becomes unstable.…”