Although clustered perforations have become a primary choice of completion for horizontal wells in the development of low-permeability reservoirs, downhole measurements and production logging often indicate nonuniform production from the perforation clusters, with some of them not stimulated or not contributing to the production. One of the mechanisms contributing to this is nonuniform/inefficient breakdown of the perforations. However, being able to assess the effectiveness of perforation breakdown because of lateral variation of the formation properties and stresses is challenging, not only because of the lack of the data, but also because of the lack of a practical engineering model to predict the fracture initiation and breakdown pressures for cased and perforated completions due to the complexity of well configuration and perforation geometry. In this paper, an analytical fracture initiation model is presented along with the comparison against 3D numerical simulations and published experimental data. The breakdown pressure data from a Marcellus shale horizontal test well in the US Department of Energy (DOE)–sponsored Marcellus Shale Energy and Environmental Laboratory consortium are analyzed and compared to the model prediction using the high-resolution 1D mechanical earth model derived from high-tier logs.