Abstract
Recent studies of core extracted adjacent to fractured wells show evidence of multi-stranded fractures as opposed to the conventional expectation of a single fracture per cluster. The cores show that fractures propagate as tightly spaced network of parallel strands and their number exceeded the number of perorations/clusters by a large amount. Previously (Sesetty and Ghassemi, 2019), we examined the conditions for the formation of multiple fractures from a perforation by focusing on the near wellbore region. In this work, we study hydraulic fracture segmentation and its impact on the net pressure. Furthermore, an advanced, rigorous P3D model is used to simulate multi-cluster multi-stage field scale planar hydraulic fracture propagation. In our modeling, we use the displacement discontinuity method (DD) to incorporate stress shadow between the parallel fracture strands. Depending on the regime of fracture propagation viscous/leak-off/toughness tip solutions are employed. A number of numerical simulations are considered for each stimulation concept, under varying field conditions with emphasis on the resultant treatment pressures and fracture conductivities. Results indicate that traditional modelling approach even when accounting for natural fractures cannot explain very high ISIP's (>1000 psi) that are often observed in field. On the other hand, simulations of multi-stranded hydraulic fractures considered under different geometric configurations can explain tight fracture spacing and high ISIP's. Also, formation of multi-clusters or stranded fractures adversely impact fracture apertures (especially the inner fractures) due to high stress shadow effect between the fractures, which poses a challenge to effective proppant placement. The fracture segment or strand height is the controlling parameter that dictates the minimum spacing allowed between the parallel strands for them to propagate simultaneously to very large distances from wellbore. Results show that accounting for the effects of multi-stranded fractures in numerical models can capture the field observed phenomena of high net pressures, multiple hydraulic fractures, and less than optimum proppant placement without resorting to ad hoc variation of natural fracture and rock properties. The novel numerical models used in this study have a computation time comparable to the conventional single fracture models, while handling a large number of interacting fractures.
