Micro to Nano-Scale Characterization of the Late Jurassic-Early Cretaceous Vaca Muerta Formation, Neuquén Basin, Argentina

Abstract

This study comprises characterization of pore types and their distribution in the Vaca Muerta Formation, in the Neuquén Basin of Argentina. This mudrock formation is characterized by the distribution of nano- to micrometer scale pore sizes. Organic matter richness from source rock analysis data registered values up to 9.5 wt% TOC. Thermal maturity of the Vaca Muerta Formation is mainly associated with burial and it increases from east to west in the basin. In association with this concept, vitrinite reflectance values in the eastern portion of the basin, where our data were collected from, correspond to the early oil generation window. A scanning electron microscopy study was conducted to determine mineral compositions, grain assemblages, morphology, organic content, and distribution of porosity. Samples were argon ion-milled to obtain a flat surface for pore observations and to avoid misinterpretation of void spaces generated by plucked grains. Mineral composition and distribution maps from QEMSCAN observations provided spatial relationships of the mineralogy and porosity. Interparticle and intraparticle pores are ubiquitous throughout the samples. Interparticle pores are common around rigid detrital grains, such as quartz and feldspars. Porosity within authigenic clay cements is included as framework porosity, and samples may contain up to a maximum of 30% clay. Partial grain dissolution resulted in available intraparticle pore space. Organopores are the least abundant pore types in this setting. These intraparticle organic matter pores are directly related to thermal maturation of the Vaca Muerta Formation. A detailed characterization of the pore types and their distribution is key for understanding the pore distribution and impact of each pore type to the overall pore volume in the Vaca Muerta Formation.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016