| Popis: |
Hydraulic fracturing of unconsolidated materials has been a long-recognized technique to control sand production. This work describes the results of an experimental investigation on the dominant parameters of hydraulic fracturing in unconsolidated sands. The variables in this study, each varied by several orders of magnitude, are sample permeability, fluid rheology, remote stresses, and fluid injection rate. We have quantified the results of these experiments in terms of injection pressuretime history, fracture aperture, and leakoff thickness. Directly measuring the magnitude of fracture aperture and leakoff thickness is significant in hydraulic fracturing of unconsolidated materials to constrain modeling this process.Laboratory observations presented here suggest that in our experiments, the leakoff process is primarily confined to the tip of the fracture and that leakoff precedes fracture propagation. This may be the first direct experimental observation of the dominance of the leakoff process in the tip region of a propagating fracture in cohesionless materials.Our experimental results also suggest that the primary factor affecting peak (initiation) pressure and fracture aperture is the magnitude of the confining stresses. However, the morphology of the fracture (and fluid leakoff zone) changes significantly not only with stresses, but also with other parameters such as flow rate, fluid rheology, and sample permeability. Typical features of the observed fractures are multiple offshoots, a blunt fracture tip, leakoff primarily confined to the fracture tip region, and material shear banding. Dimensional analysis of the recorded experimental data results in the power-law dependence of the peak injection pressures on the dominant experimental parameters.The results presented here quantify the effect of the experimental parameters on injection pressures, magnitude of leakoff, and fracture aperture. This is a significant development and our data set is consistent with available field observations, also discussed in this work. |
