Analysis of Interference between Sequential Fractures in Multistage and Multipad Hydraulic Fracturing

Abstract

AbstractReservoir pressure and stress behaviors are simulated during elapsed time between sequential fractures in multistage and multipad hydraulic fracturing scenarios to analyze interference between fractures and to manage potential fracture given interactions. Commonly current implemented completion techniques such as conventional sequential fracturing (CSF) and modified zipper fracturing (MZF) are investigated. Finite element analysis is implemented to simulate time dependent post-fracture behavior of formation pore pressure distribution and stress magnitude in multistage and multipad fracturing jobs in horizontal wellbores. A coupled stress-displacement to hydraulic diffusivity modeling technique was implemented to estimate formation pore pressure distribution and to account for the effective in-situ stresses in the near fracture region. Governing equations, methodology, and boundary conditions are provided in detail to allow readers to implement of this technique.Completion techniques rely on the principle of elapsed time between consecutive fractures as a mean to minimize interference between fractures optimizing resources at the same time. Post-fracture reservoir pressure and stress time-dependent behaviors within the stress shadow area are discussed. These parameters are computed at several observation points inside the reservoir such as at the tip of the fracture, away of the fracture, and at the parent horizontal wellbore. This analysis provides unique insight of scenarios occurring during sequential fracturing jobs. Permeability of rock matrix is a controlling factor of the diffusion processes occurring post-fracture. It was found that unconventional shales exhibiting extremely low permeability values show low diffusion of hydraulic fracturing fluids from the induced fracture to the formation. For this reason, disappearance of stress shadow effects in the near induced fractures region are not being allowed during elapsed times between sequential stages executed in the named completion techniques. These findings are relevant because inadequate management of elapsed time does not favor the subsequent induced fractures to grow parallel to the previous one due to changes of direction of stresses. When interference becomes critical, the phenomenon identified as "Frac-Hits" can also be predicted; therefore, managed using this tool.