Abstract
This paper shows how a geomechanical model helped to reduce risks and non-productive time experienced in the past in a field in the Neuquén Basin (Argentina) operated by Petrobras Energia S.A. (PESA). Tight hole and stuck pipe were common problems in spite of the tight and strong formations in the field. Gas inflows were also experienced when drilling through the overpressured formations. All these events made the decision of building a geomechanical model for the field in order to optimize the drilling time.
Pore pressure, stresses and mechanical rock properties were constrained based on good quality data set from eight wells. After that, the geomechanical model was validated using the caliper data and drilling experience. A key part of the model building was the estimation of pore pressure using wireline logs, gas inflows during the drilling, production data and minifrac tests. Overpressured zones were identified improving the design of the casing depths for new wells, minimizing the risks of kicks while maintaining the wellbore stability. Based on the remaining uncertainties of the model, an update phase was recommended to be done after the collection of new data such as image logs in the well to be drilled.
After drilling the new well using the recommendations of the geomechanical model, the drilling experience showed that the well was drilled almost without non-productive time (NPT) through the same formations where in the past tight holes and stuck pipes were experienced. A good image data collected in the drilled well showed that the breakouts stayed below the catastrophic limit, confirming that the mud weight was correctly recommended in the phase 1, maintaining the wellbore stability without reducing the ROP. Also, the observed breakout orientation and width confirmed the orientation and magnitude of the maximum horizontal stress constrained in the phase 1.
