Guidelines to define the critical injection flow rate to avoid formation damage during slurry injection into high permeability sandstone

摘要

In a slurry injection application, the goal is to inject high solid content fluids (up to 25%). To accomplish this without plugging the near-wellbore pore space, the fracture is created using a pad of clean fluid. Once the fracture is open, the slurry is introduced to the formation. In some cases, where the formation has a high permeability-thickness product (k?×?H), a high injection flow rate is needed to open up the fracture with clean fluids. Most disposal wells do not have large enough pumps to provide high enough flow rates in these circumstances.A combination of a lack of geomechanical understanding combined with poor injection or facility design leads some operators to create high formation damage around the wellbores in slurry injection applications by injecting slurry at flow rates which are insufficient to open fractures. When solids-laden fluid slurries are injected under a matrix flow regime, suspended solids will plug the near-wellbore pore throats and will form a filter cake layer at the formation face, causing the injection pressure to gradually increase. At the point where the injection pressure exceeds the formation fracture pressure, the formation will finally fracture. However, the near-wellbore filter cake remains a factor in future injection and leakoff characteristics. Moreover, the damage causes injection pressure to build up rapidly, facilitating the creation of short fractures which tend to cause near-wellbore stresses to increase more rapidly for a given amount of solid deposition than is the case with longer fractures.Case studies have been presented in this paper which evaluates such slurry injection wells. Based on the data analyzed in this study, inducing the fracture with solids-laden slurry rather than with clean fluid by causes the injection pressure to continuously increase, ultimately leading to significantly reduced formation capacity. Recommendations are presented as well for how to avoid this condition even if the pumps do not have the capacity to provide the required injection flow rate using clean fluid. One such solution is to add a viscosifier to the clean pad fluid to raise the fluid viscosity which enables the creation of a hydraulic fracture at lower flow rate.