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Application of Simultaneous Inversion and Gemechanical Facies in the Characterization of an Unconventional Play: An Example From the Vaca Muerta Formation in Argentina



The Vaca Muerta formation, covering approximately 30,000 square kilometers in Argentina's Neuquén Basin is a developing unconventional resource play. The giant Vaca Muerta shale oil and gas field has an estimated resource potential of 600+ billion barrels of oil and 1,000+ TCF of natural gas. Like other unconventional shale plays, horizontal drilling and hydraulic fracture stimulation are essential for economic viability. Main factors that can strongly influence the effectiveness of hydraulic stimulation are the distribution and values of horizontal stresses, elastic moduli and rock strength properties.

This paper describe a workflow used to estimate elastic moduli, geomechanical facies and stresses in a 3D volume based on geological concepts, well-based 1D petrophysical and geomechanical models and pre-stack seismic inversion to estimate the lateral variation of elastic properties away from well control.

The stress regime in the study area has two distinct environments, the normal pore pressure interval, covering all the Previous HitoverburdenNext Hit and the over-pressurized region, rich in hydrocarbons where the unconventional reservoir is allocated. The limit between these two distinct regions is a stratigraphical surface regionally continuous that delimits two sedimentary cycles deposited in different basin conditions (Figure 1). The workflow uses conventional, velocity based, pore pressure prediction Previous HitestimationNext Hit together with an isotropic assumptions for the Previous HitestimationNext Hit of the elastic properties from density, shear and compressional velocities. Horizontal stresses has been calculated at well locations assuming stress anisotropy and using elastic properties, pressure and tectonic strains following Cipolla et al 1994 approach and calibrating estimated curves with several mini-frac tests. The same set of assumptions used for the 1D Previous HitModelNext Hit at well locations is used for the Previous HitestimationNext Hit away of well control based on P and S wave velocities derived from pre-stack inversion and used as soft constrain in the static Previous HitmodelNext Hit. The Previous HitmodelTop is being used to select both the location of appraisal wells and the horizontal interval to be navigated based on stresses and brittleness variations