Abstract

The Vaca Muerta shale is an emerging shale play within the Neuquén basin in Argentina. Like most unconventional shale plays, the formation exhibits geomechanical, acoustic and permeability anisotropy. Therefore, advanced logging tools as well as advanced techniques for core measurements and analysis are necessary to properly characterize the geomechanical behavior of the formation. The results of an integrated core and logging analysis of the geomechanical and acoustic properties of the Vaca Muerta formation is presented in this paper with the use of well-known techniques for formation characterization. The geomechanical and acoustic measurements of the core samples from a well in the base of the our study area in Vaca Muerta formation have been used to determine the dynamic and static elastic properties of the formation and how to relate the static properties to the dynamic data. In addition, cross-dipole logging data from the same well was utilized to compare the core data with the logs. The results of the core test were used to develop an anisotropic formation model for which the logs could be calibrated with. Thomsen coefficient epsilon was determined being not equal to gamma while relationships between the stiffness coefficients have been relatively consistent. This finding allowed us to develop an anisotropic model based on the vertical transverse isotropy (VTI) using the core data as an input for the model. The model was then utilized with the logging data to determine the anisotropic stiffness tensor as a function of depth. Based on the Thomsen coefficient gamma, the degree of both vertical and horizontal transverse isotropy has been determined. The results of this analysis indicate that the formation almost exclusively exhibits VTI behavior whether examined through the logs, core, drilling or microseismic data in our study area. The magnitude of the core acoustic measurements does not match well the logging measurements, and this is most likely due to preferential core sampling methods that intentionally exclude natural fractured sections in the cores. Microseismic analysis has shown potential fault reactivation near one of the wells in Loma Jarillosa Este block in addition to the conventional seismicity from the hydraulic fracturing operation that requires further attention in the future development well designs in the area.

The results of the model developed in this study can be applied to better geomechanical characterization of the Vaca Muerta formation that will help designing suitable completion techniques and hydraulic fracturing design in optimizing production and minimizing footprint in the basin. The accuracy of the model will be anticipated to be improved as additional core measurements are completed and more well data from other wells in the area become available.

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