Formation susceptibility to wellbore instability and sand production in the Pannonian basin, Hungary

Wellbore instability and formation sand production pose potential risks for wellbore drilling, completion and production operations. In many sandstone reservoirs worldwide, sand production has been observed to accompany oil and gas production. In this study, we aim to estimate, predict and quantify wellbore instability and sand production potentials in the Hajdúszoboszló field, Pannonian Basin, Hungary, using the Mechanical Earth Model (MEM). Our study relies on petrophysical log data obtained from an onshore gas well within the field as input data. Our 1-D MEM utilizes a workflow that develops wellbore and sand failure mechanisms, first creating the mechanical stratigraphy of the reservoir rock; followed by estimating the pore pressure, overburden stress, rock strength, rock elastic properties, and horizontal stresses of the reservoir rock with reference to the depth of stratigraphic column, from compressional slowness, shear slowness, density, porosity and shale volume. Lastly, we conduct a wellbore stability and sand management analysis. Our results show the mechanical stratigraphy of unconsolidated sandstone and shale distribution in the reservoir, wellbore shear and tensile failures, wellbore breakout and breakdown pressures, wellbore sensitivity analysis, sanding interval analysis, critical drawdown pressure (CDDP) profile and sand failure zones. Based on careful observation of our results, we predict the wellbore intervals with high sand production potentials and wellbore instability within the reservoir formations. Therefore, we suggest significant wellbore failure during drilling process and also a high possibility of sand production into the wellbore during well completion at a formation interval of 550-937 m. Although there is need for data from additional wells in the field to be incorporated into our model prediction, we suggest that our preliminary model can be useful for critical decision making during drilling and completion operations across the Hajdúszoboszló field, Pannonian Basin, Hungary. In addition, our study provides a platform for further investigation into wellbore stability and sanding analysis in other parts of the Pannonian Basin where available well data can also be incorporated in our model.