Oladoyin Kolawole

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 estimate, predict and quantify wellbore instability and sand production potentials in the Hajdúszoboszló field, Pannonian Basin, Hungary, using the Mechanical Earth Model (MEM). Our model relies on petrophysical log data obtained from an onshore gas well within the field as input data. Our model develops rock and sand failure mechanisms by estimating the rock elastic and strength properties, in-situ stresses and pore pressure of the reservoir rock with reference to the depth of stratigraphic column, from compressional slowness, shear slowness, density, porosity and shale volume. We adopted the 1-D MEM for our wellbore stability and sand production study of the Hajdúszoboszló field, because the model considered all available data to develop the rock mechanical properties, and also provide real-time numerical representation of the geomechanical state of the Hajdúszoboszló field in the Pannonian Basin. The 1-D MEM utilizes a workflow that involves, first, the creation of the mechanical stratigraphy of the reservoir rocks; second, the estimation of pore pressure, rock strength, rock elastic properties, and the horizontal stresses; third, wellbore stability analysis, where we developed mud weight profiles, wellbore shear failure and borehole breakdown; followed by sanding interval analysis for perforation completions. We further established the critical drawdown (CDDP) and critical reservoir pressure profiles for the suspected wellbore depth interval. 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.