Sedimentary and Stratigraphic Characterization of the Cretaceous Agrio Formation as an Unconventional Target: Neuquén Basin Argentina

OCHO, R.I.; BIRGENHEIER, L.; SCHWARZ, E.

Congreso; SEG/AAPG IMAGE 2021; 2021

SEG/AAPG

The Neuquén Basin of Argentina hosts one of the most prolific hydrocarbon systems in South America. It consists of multiple organic--rich marine source rocks, including the Lower Cretaceous rich marine source rocks, including the Lower Cretaceous Agrio, the youngest of the three. The Agrio Formation is characterized as a proximal-to-shoreline siliciclastic shoreline siliciclastic- rich mudstone in the south transitioning to a distal, rich mudstone in the south transitioning to a distal, basinal marine, carbonate- dominated mudstone facies in the north. Detailed outcrop investigations of the dominated mudstone facies in the north. Detailed outcrop investigations of the Agrio Formation have recently been published, but the formation?s variability in subsurface datasets is relatively unexplored. A critical knowledge gap in understanding its potential as a regional unconventional target and how the mixed environment correlates to the downdip carbonate--dominated environment remains. Sedimentological and geochemical outcrop investigations from the most northern dominated environment remains. Sedimentological and geochemical outcrop investigations from the most northern extent of the basinal marine setting are used in this study to correlate vertical and lateral heterogeneity into the subsurface marine setting are used in this study to correlate vertical and lateral heterogeneity into the subsurface across the central to northern part of the basin in order to fill the knowledge gap. Mineralogy from X--ray diffraction analysis ray diffraction analysis and Total Organic Carbon (TOC) from programmed pyrolysis identify compositional and hydrocarbon potential differences from two Mendoza Province outcrop field locations. Recently acquired outcrop data, this study, along with previously acquired data to the south, are used for sedimentological facies analysis, TOC, and stratigraphic thickness validation to correlate into the subsurface. Using subsurface well logs, a published petrophysical model approach for a mixed system analog was used in reservoir property prediction. Cuttings to log calibration were used for TOC prediction for the proximal to distal mudstone facies. One main technical challenge is to quantitatively distinguish the log signature of a carbonate mudstone (i.e., chalk) from a clay--rich calcareous mudstone (i.e., rich calcareous mudstone (i.e., marl) from a siliciclastic--rich rich heterolithic mudstone (i.e., interlaminated sandstone, siltstone, and claystone). The mudstone (i.e., interlaminated sandstone, siltstone, and claystone). The calibrated to cuttings petrophysical model produces mineral constituents pseudominerals defined as quartz, carbonate, clays, and heavies. defined as quartz, carbonate, clays, and heavies. The model is calibrated to programmed pyrolysis cuttings data, XRD, and electrical porosity logs. Predicted TOC from the mineral constituent?s model was found to be a better fit to measured TOC when compared to a first--order approach using the order approach using the log R Passey methodology. Passey TOC was not well correlated to measured data and was found to produce inconsistent TOC values. The novel petrophysical model employed here provides a means for distinguishing mudstone mineralogy composition in a mixed siliciclastic--carbonate system and allows for the further exploration of the lateral extent of high TOC stratigraphic carbonate system and allows for the further exploration of the lateral extent of high TOC stratigraphic zones.