Geomechanical Modeling Helps Designing the Wells in the Neuquén Basin, Argentina

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 EnergÍa 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. Introduction The Neuquén Basin is an important province for gas exploitation in Argentina (Figure 1) where Petrobras EnergÍa S.A. (PESA) has been operating a field in which most of wells drilled in the past experienced considerable non-productive time (NPT) due to tight holes and stuck pipe problems in spite of the strong formations in the lithological column. Gas inflows were also detected indicating an overpressured zone that should be well identified in order to reduce the risks of kicks and well control problems. Because of that drilling experience, PESA made the decision of building a geomechanical model for the field to optimize the drilling time, by obtaining a good rate of penetration (ROP) while maintaining the wellbore stability, and reducing the risk of kicks. In order to build the geomechanical model, a data audit was carried out over eight wells covering a representative area of the field. The data used included: regular wireline logs (gamma ray, density, resistivity, sonic, caliper), daily drilling reports, image data, production data, pore pressure measurements and also minifracs. By using all the available data and applying the best geomechanical modeling techniques the stress field, pore pressure and rock properties were constrained. In addition, in order to reduce the remaining uncertainties, a specific data acquisition was recommended for the designed well. In the wellbore stability analysis the potential risks of kicks and instability problems were evaluated in order to optimize the casing depths and keep a good ROP. The designed well showed a significant improvement in the reduction of the NPT related to wellbore instability problems, while the ROP was maintained at very good levels. Following the recommendations for data acquisition a good set of image data was obtained in the well, which confirmed the direction and magnitude of the maximum horizontal stress and also that the mud weight was effectively designed as the average breakout width stayed below the catastrophic limit.

Modelo Geomecânico Aplicado À Análise De Estabilidade De Poços Com Ênfase Em Folhelhos

“…Araujo et al, (2009) Na Figura 2.16 a validação de um peso de fluido de perfuração para um novo poço do campo foi feita com o fim de reproduzir os problemas experimentados nas mesmas profundidades e litologias nos poços perfurados (Araujo et al, 2009). …”