The unconventional play in the Neuquén Basin, Argentina - insights from the outcrop for the subsurface

The U. Jurassic - L. Cretaceous Vaca Muerta (VM) Formation in the Neuquén Basin, Argentina, has enormous unconventional resource potential. The excellent exposure of the formation offers the unique opportunity to address fundamental questions about the distribution of sedimentary facies, total organic carbon (TOC), geo- mechanical properties of the various facies, and the factors controlling these variables with detailed outcrop analysis.

The Neuquén Basin is filled by prograding clinoforms whose lower foresets and bottomsets are prone to be organic- rich. Synthetic seismic sections generated from facies and geometries observed in the Sierra de la Vaca Muerta (SdlVM) calibrate the seismic clinoforms. This calibration aids in placing the organic-rich intervals within clinoform geometries and in the sequence stratigraphic framework. The correlation of outcrop sections to core and well logs is achieved by adding spectral gamma ray, TOC and other geochemical properties with high resolution (0.5-1m spacing) to the lithology in each section. One-meter cores at key intervals provide ultra-high resolution data (0.5-5cm spacing) of elements and mineralogy measured with X-ray fluorescence (XRF), X-ray diffraction (XRD), Near-Infrared Spectroscopy (NIR), and Hyperspectral Core Scanning (HCI). In the Puerta Curaco area a composite section is constructed by splicing together the best-exposed parts of nine different sections. This reference section serves as an outcrop analog for the VM Formation in the hydrocarbon-producing basin center where outcrop and subsurface show a nearly uniform formation thickness. Key log-signature subdivisions from the subsurface correspond to sequence stratigraphic divisions identified in the Puerta Curaco outcrop. TOC, Spectral gamma ray, and isotope data can be placed in a sedimentologic and stratigraphic context and the comparison with sections measured in the Sierra de la Vaca Muerta documents facies and petrophysical changes from proximal to distal. The addition of subsurface data to our existing outcrop dataset confirms our previous finding that high TOC is not restricted to a unique stratigraphic level but is a recurring pattern within the prograding depositional system, resulting in multiple organic-rich zones in similar sequence stratigraphic positions in each sequence. This outcrop calibration provides invaluable insight into the evolution and distribution of the high TOC intervals in the Neuquén Basin that is not immediately apparent from the well data alone.