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Abstract:
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During waterflooding , or chemical EOR processes with polymers , fractures are frequently generated in injectors . This can have a profound impact on the process performance and reservoir management . A fracture growth model was developed and linked to a reservoir simulator that incorporates the effect of (i ) particle plugging due to filtration of solids and oil droplets in the injected fluids ; (ii ) non -Newtonian polymer rheology (shear -thinning and -thickening ) for polymer injection ; and (iii ) thermal stresses induced by cold water injection . Dynamic fracture growth , which results from the pore pressure increase due to particle plugging or complex polymer rheology , affects the well injectivity and reservoir sweep significantly . With the fracture growth model , simulations can be made not only to make more accurate reservoir sweep and oil recovery predictions , but also to help identify well patterns that may improve reservoir performance .
In homogeneous reservoirs , the injectivity is significantly affected by the propagation of an injection induced fracture ; but the ultimate oil recovery and reservoir sweep are relatively unaffected . In multi -layered reservoirs , however , reservoir sweep and oil recovery are impacted significantly by the fracture growth . The oil recovery results from our fracture growth model differ substantially from those obtained based on the assumption of no fracture generation or a static fracture . For polymer injection processes , the shear rate dependence of the polymer viscosity is critical in determining the injectivity , fracture growth , and oil recovery .
In addition to vertical injection well fractures , horizontal injection well fractures have been simulated by using the fracture growth model . The reservoir stress distribution determines the fracture orientation near a horizontal well . When the minimum horizontal stress orientation is perpendicular to the horizontal injector , a longitudinal fracture is generated , while with the minimum horizontal stress orientation parallel to the injector , a transverse fracture is developed . The impact of static and dynamic transverse /longitudinal fractures on well injectivity and reservoir sweep has been investigated . The impacts of (i ) lengths of horizontal injector and producer ; (ii ) location of water oil contact ; (iii ) sizes of transverse and longitudinal fractures ; (iv ) particle concentration in the water , were further investigated .
The well injectivity model was validated successfully by history matching injection of water (with particles ) and shear rate dependent polymer injection . The history match was performed by adjusting the effective particle concentration in the injected water or the shear rate dependent polymer rheology . Based on history matching the long -term injection rates and pressures , estimates of the fracture length were made . These fracture dimensions could not be independently measured and verified . Based on the simulation results recommendations were made for strategies for drilling well patterns , water quality and injection rates that will lead to better oil recovery . |