Abstract
The objective of this study is the geomechanical characterization of the VacaMuerta formation, in the Parva Negra Oeste block. Therefore, the existing information was analyzed and two pilot wells were drilled, whose data serves as the basis for characterizing the geomechanics of the area.
Overpressure has been detected as the main risk during drilling, not only in the Vaca Muerta formation but also in overlying formations. For this reason, two pilot wells were drilled using the MPD (Managed Pressure Drilling) system to keep the well under control. While drilling, this system allows Build Up Tests and LOT to be performed dynamically to adjust the operating mud window and provide data for future wells. At the same time, a core of the formation and a complete set of borehole logs were obtained, which includes crossed dipole acoustics, NMR and borehole image logs.
The pore pressure model is calibrated based on the Build UpTests performed while drilling. On the core a scatch test was carried out, which is used to calibrate themechanical strength of the rock, with high vertical resolution. Additionally, the borehole image logs turn out to be essential to evaluate the continuity of the carbonate layers, which are usually seen byconventional logs as barriers to the propagation of hydraulic fractures, being in some cases true tabular layers and other cases concretions. In the latter case, they will not constitute barriers to the propagation of hydraulic fractures. All this allowed to generate an adjusted VTI geomechanical model.
The MPD turns out to be useful for geomechanics, not only achieving quality LOT, but also multiple build up tests, which were used to calibrate the operating window (pore and fracture pressure). The geometry of the calcareous layers can be characterized by the borehole image logs, allowing to distinguish between tabular layers, which have lateral continuity, from calcareus concretions with lenticular geometry, which will not significantly limit the growth of hydraulicfractures. This feature cannot be discriminated with conventional logs.
