--> Acoustic Facies Characterization, Vaca Muerta Formation, Argentina

AAPG ACE 2018

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Acoustic Facies Characterization, Vaca Muerta Formation, Argentina

Abstract

Unconventional resource plays rely primarily on recognizing target intervals suitable for hydraulic fracturing on seismic data. Successful exploitation of such plays requires reservoir zones to be brittle, porous, and rich in hydrocarbons. These properties are largely dependent on the composition of the background rock, and TOC and carbonate content. In addition, these properties have to be identifiable from seismic signature. Some efforts have been made to calibrate different seismic and acoustic impedance facies in the Vaca Muerta with core data, but few laboratory calibrations have been published. Here we present laboratory measurements of horizontal and vertical acoustic velocities that aid assessing the mechanical properties of different facies within the Vaca Muerta Formation.

To obtain usable acoustic measurements, unaltered plug samples (little to no surface exposure) of representative facies and rock types within the Vaca Muerta Formation we drilled several short core drilling campaigns in different outcrop locations and recovered over 100 m of short core (3” diameter). Over 40 m of recovered core, strategically distributed throughout the Puerta Curaco reference section, allow us to sample all dominant facies of the Vaca Muerta Formation.

Acoustic velocities from over 150 plug samples from both short core and sub-surface and porosity were measured for all plug samples under a variety pressure conditions and saturation states. Porosity which between 1-29%, while compressional velocities vary between 3 and 5.5 km/sec and their poisson’s-ratio ranges from 0.19 to 0.33. Carbonate content is between 1% and 89%, while Total Organic Carbon (TOC) content measured on an Elemental Analyzer varies between 1-10%. The measured acoustic data is compared to data from mudstones of different ages and locations. The Vaca Muerta mudstones show both substantially lower compressional and shear velocities than most other datasets. In addition, Vaca Muerta mudstones display a very high degree of anisotropy (VTI) with an average e of 0.06, ranging from 1-15%.

Well documented acoustic properties of the different facies in the Vaca Muerta Formation will not only improve well log interpretation, but enhance the understanding and ability to interpret seismic data and its attributes. Successful determination of transverse anisotropy parameters will aid and improve seismic processing and result in better imaging.