Shale and Carbonate Wellbore Stability Charts for Drilling Operations

Abstract

AbstractThe oil industry suffered a great deal of time and financial damage because of wellbore instability problems reflected by well collapsing. This suggests that more meticulous well drilling planning are required to avoid such rock failure. Shale has been a difficulty for many drilling operators, and shale instability difficulties are to blame for 90% of borehole collapse problems. Additionally, compared to shale or sandstone, carbonate rocks are believed to be more capable and to face less instability problems. However, carbonate-based reservoirs make up the majority of the world's hydrocarbon reserves. As a result, a sizable number of wells are drilled in carbonate deposits every year. Due to this, there are now more wellbore instability problems being experienced while drilling carbonate formations globally.Rock failure will occur if the field's rock mass is subjected to a huge stress beyond what it can withstand. Construction of models that can foresee the conditions in which a rock can fail will greatly aid in preventing serious problems like borehole collapse and solids generation. Therefore, by accurate geomechanical modeling, the most suitable mud density and borehole trajectory should be understood in advance before drilling. The Mogi-Coulomb failure criterion and a linear elastic stress model for the field are utilized in this study as a geomechanical stability model. The effects of all the major stresses in the fields are reflected and depicted in this three-dimensional stability model. For the benefit of all drilling engineers and operators in Oman, various charts are produced using the stability model.Wellbore stability study is generally a difficult task that may need for a highly specialist consultation and is a time-consuming procedure. An important requirement that is overlooked in the oil and gas sector is the need to simplify the wellbore stability analysis in a way that makes it simple and ready for direct use by drilling engineers. The stability charts give the minimum allowable mud density for shale and carbonate rocks to prevent borehole collapse for all drill trajectories. Due to the emphasis on Oman's shale and carbonate formations and the most common possibilities, the created charts are limited for ranges of rock geomechanical characteristics. According to the input parameters, the produced stability charts are divided into several groups. The effect of each geomechanical property is studied to understand the relationships among them. The produced charts for shale and carbonate deposits in Oman and elsewhere are used in actual field case studies. Some of these field applications have already been carried out, while others are still in the works and will likely be discussed in a future project.