From Semi-Circular Bending Test to Microseismic Maps: An Integrated Modeling Approach to Incorporate Natural Fracture Effects on Hydraulic Fracturing

Abstract

An integrated cohesive modeling is proposed to analyse hydraulic fracturing jobs in the presence of a natural fracture network. A propagating hydraulic fracture may arrest, cross, or divert into a pre-existing natural fracture depending on fracture properties of rock, magnitude and direction of principal rock stresses, and angle between fractures. Activation of natural fractures during fracturing treatment improves the effectiveness of the stimulation tremendously. Here, we present an integrated methodology initiated with lab scale fracturing properties using Semi-Circular Bending Test (SCBT ) to determine cohesive properties of rock and natural fractures. We used cohesive finite element models to reproduce laboratory results to verify the numerical model for the interaction of the hydraulic fracture and cemented natural fractures. Based on the initial results, distribution of pre-existing natural fractures could play a significant role in the final geometry of the induced fracture network; however in practice, there is not much information about the distribution of natural fractures in the subsurface due to the limited access. Hence, we also introduce a special optimization scheme to generate the geometry of the natural fracture network from the location of microseismic events. Accordingly, the criteria for evaluating the fitness of natural fracture realizations is defined as the total minimum distance squares of all microseismic events. Moreover, an additional constraint in this problem is that we need to set a minimum distance between fracture grids. Our results show a constructive approach to integrate microseismic maps with lab mechanical measurements and bottomhole pressure to estimate the geometry of induced fracture network in the subsurface which does not suffer from any limiting assumption about fracture geometries.