Hydraulic fracturing involves the initiation and propagation of fractures in rock formations by the injection of pressurized fluid to enhance oil and gas production or for mineral extraction. Tiltmeters are often used in the process to monitor the generated fracture geometry by remotely measuring the fracture induced deformations. Asymmetric fracture growth wjth respect to the borehole when not accounted for in the design of the hydraulic fractures can result in a section of rock mass being not effectively stimulated or preconditioned, depending on the purpose of the fracture treatment. The ability to predict asymmetric growth in hydraulic fracturing is therefore important. This paper focuses on a method to infer the existence of asymmetric fracture geometry from tiltmeter measurements. The forward model used in the analysis is based on the displacement discontinuity method and the Bayesian inversion procedure is employed [l]. The forward model is developed from the analytical expression for computing the displacements and tilts due to a point source in an elastic half-space developed by Okada [2]. The displacements and tilts due to a given fracture geometry are then obtained by numerical integration of this solution, by considering the point sources to be located at the quadrature points. To validate the method, mapping of asymmetric fractures having polygon and elliptical geometries is carried out using synthetic data sets. Finally, the effect of the fracture asymmetry on the inverted results is also analysed. Real data from a field site [3] where asymmetry was measured from intersections of the hydraulic fracture with offset boreholes has been analysed. Preliminary results show that the procedure is able to satisfactorily predict fracture asymmetry from measured data when the fracture is relatively close to the tiltmeter array.
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