Formation Susceptibility to Wellbore Instability and Sand Production in the Hajdúszoboszló field, Pannonian Basin: Hungary

Abstract

<p>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.</p>

Modified approach for identifying weak zones for effective sand management

“…They concluded that the produced sand volume and sand mass rate increase with the drawdown pressure. Kolawole, Federer-Kovács and Szabó (2018) utilized a proprietary software to predict and quantify wellbore instability and sanding potentials in a Hungarian field. They were able to demarcate the formation into two separate intervals describing one zone as over-pressured, unconsolidated and highly stressed formation with a high tendency for wellbore failure during drilling process and with 90% possibility of wellbore instability.…”

Quantitative characterization of collapse and fracture pressure uncertainty based on Monte Carlo simulation

“…The rock mechanics parameters and in-situ stress input in the existing calculation model of formation collapse and fracture pressure are all treated according to the fixed value, and the prediction results of formation collapse and fracture pressure are all single value results. This method ignores the error between the prediction result and the actual result due to the uncertainty of the input parameters of the calculation model of collapse and fracture pressure (Guangfu et al 2019;Kolawole et al 2018;Moos and Peska 2003). The in-situ stress and rock mechanics parameters in the calculation model need to be calculated based on the indirect formula according to the seismic or logging data, and there is uncertainty (Mostafavi et al 2011;Zhide , 2004;Limin et al 2017).…”

Rock physics and geomechanical application in the interpretation of rock property trends for overpressure detection

“…A technique for predicting pore pressure and associated fracture gradient would be helpful in selecting adequate mud weight to ensure well and drilling safety, in preventing the use of excess mud weights leading to fracture or losses, in preventing hole collapses and to assist in correct designing of casing scheme to ensure optimum completion and maximum productivity (Basu et al 1994;Law and Spencer 1998;Babu and Sircar 2011). The geomechanical knowledge and pressure level would also afford the opportunity to pre-determine any sand production into a borehole, a problem which has been identified in drilling operations for long as it affects well productivity and the drilling equipment (Ispas et al 2012;Zhou et al 2016;Kolawole et al 2018).…”