In this study, data from seven wells were used to investigate and model the stability of the deviated well wall in the drilling of the Shili Formation, one of the largest oil fields in southwestern Iran. The problems of well wall instability have caused excessive costs and delays in advancing the field development program. Therefore, in order to build the geomechanical model, a well with complete information on petrophysical diagrams, longitudinal and shear wave transit times was selected. Appropriate relationships are presented to estimate the static geomechanical data of the studied field, which have been validated using laboratory data (core). Formation pore pressure is one of the main input parameters for building the mechanical model, and the estimated relationship was validated using real data from the RDT diagram. In order to calculate the values ​​of the principal stresses and determine the stress regime of the area, the minimum and maximum horizontal stresses were validated using the formation leakage test (LOT) data and the well wall collapse locations in the visual diagram, respectively. By examining the visual charts and analyzing 89 cases of well wall collapse and induced failure, the horizontal stress directions have been determined with high accuracy. Then, using numerical and analytical analysis of well wall stability, the minimum mud weight required in azimuth and different angles of the deviated well was calculated using the Mohr-Colomb failure criterion. The predicted mud weight was validated by actual drilling data of four adjacent wells in the field. In the quantitative risk analysis stage, the goal is to investigate the effect of the uncertainty of the main parameters (input variables of the relationship for determining the minimum mud weight required based on the Mohr-Colomb failure criterion) and their sensitivity in increasing the success rate and reducing failure. In the quantitative risk analysis method, the Monte Carlo simulation method has been used and the results are displayed in the Tornado diagram.