A modified numerical model has been used in optimizing the drilling performance and field integrity in Vaca Muerta Formation of the Neuquén Basin of Argentina. In-situ stress analysis provided a steadily oriented stress tensor and principal stress magnitudes consistent with the normal fault stress regime that was confirmed with drilling and well log data. An integrated wellbore-integrity study was conducted to solve instabilities including stuck pipe and tight holes encountered during drilling operations at the offset wells, to optimize future drilling procedures, to maximize the drilling margin for the prospective wells, and to reduce drilling risks. The geomechanical model was coupled with in-situ stress and formation property anisotropies, temperature alteration, shale-fluid physico-chemical interactions, and the flow-induced stress using Mohr-Coulomb and Mogi-Coulomb failure criteria. The well trajectory, drilling-fluid density and types of water-based muds were confirmed to have a dominant impact on the occurrence of instabilities experienced while drilling and completion. Core data, imaging and sonic scanner logs along with conventional log data were utilized to obtain in-situ stress magnitudes, orientations and formation properties. The stochastic risk and sensitivity analysis were performed using thirteen well data to evaluate the sensitivity of the input data on the study outcome. Results show that higher mud weight is expected to minimize wellbore instabilities. Results of the wellbore integrity analysis presented in this study will benefit the remediation and/or prevention of wellbore instabilities for improving economic viability and sustainability of the field development in Vaca Muerta Formation.
The Vaca Muerta Formation is lithologically associated with the Late Jurassic calcareous and silicoclastic mixed shale that was deposited along the northwestern part of the Argentinean Patagonia in the Neuquén Basin (Fig. 1). It is a lithostratigraphic unit that can be easily recognized in outcrops as organic-rich marls (Fig. 2). The composing sedimentary architecture corresponds to a distal facies of a mixed carbonate sequence developed between the Jurassic Tithonian and Valanginian ages. This highly prolific source rock was deposited during the Tithonian (Late Jurassic) transgression that took place in the Neuquén Basin that rapidly flooded the underlying Eolian and fluvial units of the Tordillo Formation (Kimmeridgian). This transgression marks the maximum basin expansion of the marine environment that extended for about 30,000 km2.