Determination of safe mud weight window and optimal drilling path in the Gadwan formation using rock failure criteria in one of the hydrocarbon fields in southwest Iran

Today, the economies of Middle Eastern countries rely heavily on increasing their crude oil production and exploitation rates. With the understanding that the discovery of large hydrocarbon fields will become increasingly rare in the future, oil companies' planning focuses on optimal production from existing fields. The Gadwan formation is one of the important reservoirs in the Abadan Plain, composed of shale and sandstone sequences. Drilling production wells in this formation has always been a challenge due to the weak nature of the shale sequence. More than 90% of the well problems in the Gadwan formation are due to wellbore instability, including collapse, narrowing, and sticking of the drill bit, resulting in increased non-productive time (NPT) and drilling costs. The main objective of this study is to evaluate the stability of a well located in southwestern Iranian oilfields using a one-dimensional geomechanical model based on well log data. After constructing a one-dimensional geomechanical model, the Mohr-Coulomb and Mogi-Coulomb criteria were used to evaluate wellbore stability. The results showed that the Mohr-Coulomb criterion provides a better estimate of collapse pressure. Furthermore, the orientation of the identified collapses on the image log was northwest-southeast, indicating the direction of minimum horizontal stress. According to the sensitivity analysis results, the optimal drilling direction for the Gadwan formation is northwest-southeast, and for vertical drilling in this formation, the safe mud weight estimated according to the well's geomechanical model is 14.9 pounds per gallon (LB/G). The results of this study can be used as a reference for determining the optimal mud weight window in planning future wells in this field to deal with drilling stability problems.