Geological parameters controlling the bedding-parallel vein distribution in Vaca Muerta Formation core data, Neuque=n Basin, Argentina

It is important to understand the occurrence of bedding-parallel veins in the Vaca Muerta Formation because this helps to predict their presence away from well controls so that they can ultimately be incorporated in reservoir simulators and hydraulic fracturing modelers. Given that their occurrence has a significant impact on the propagation of hydraulic fractures, their spatial distribution will help to select sweet spots for unconventional resource development. In this study, we try to identify the key parameters that control bedding-parallel veins. Therefore, detailed sedimentological core descriptions were performed on 10 different wells, including total organic carbon measurements at a spacing of 0.5 cm and several degrees of maturity ranging from 0.7% to 1.8% vitrinite reflectance. Through a comparison between bedding-parallel vein localization and sedimentological descriptions, we built a statistical method to identify key parameters controlling the localization of such veins within the Vaca Muerta Formation. We show that bedding-parallel veins are primarily located at facies boundaries (70%) rather than in homogeneous facies (30%). The major rheological discontinuities, such as ashbeds and calcitic concretion boundaries, as well as organic-rich facies have a significant impact on the localization of both bedding-parallel veins. The total organic carbon seems to influence the generation of bedding-parallel veins by locating these fractures in organic-rich areas with more than 2 wt. % in total organic carbon. We also found a correlation between the degree of maturity of the source rock within a same sequence stratigraphy and the (1) number of bedding-parallel veins and (2) thickness of the bedding-parallel vein, suggesting a strong link between the generation of hydrocarbons during the burial of the rock with the generation and distribution of bedding-parallel veins.

Automated summary

Research indicates that bedding-parallel veins in the Vaca Muerta Formation primarily occur at facies boundaries and are influenced by major rheological discontinuities such as ashbeds, calcitic concretion boundaries, and organic-rich facies. Total organic carbon content also plays a role in the generation of these veins. Source rock maturity is correlated with the number and thickness of bedding-parallel veins, suggesting a link between hydrocarbon generation and the formation of these veins.