Characterization of the northeastern region of the Neuquén Basin basement, Argentina, from 3D magnetotelluric inversion

Abstract

An electrical resistivity profile of the basement of the northeastern region of the Neuquén Basin and overlying units based on magnetotelluric data is presented. The data were obtained from the area where the basalts of the Payenia magmatic province cover the surface of the Eastern Platform near the basin edge. The exploration of the hydrocarbon potential in the Neuquén Basin has led to extensive investigations to identify structures that could act as traps and reservoirs. However, due to primary commercial objectives, most of these studies remain unpublished. While seismic methods are widely employed in geophysical surveys, their effectiveness is reduced in regions where shallow basalts are present. Additionally, in the study area, also the basement is shallow, restricting the depth of characterization to the first few hundred meters. Under such conditions, the resolution limitation and economic infeasibility of seismic methods make electromagnetic methods more suitable for subsurface prospecting. Thus, with the aim of determining the structures in the subsurface, 50 magnetotelluric sites were acquired. The three-dimensional inversion of the data revealed stepped changes in the resistivity units correlated with the basement and the layer above it. These resistivity steps could be associated with normal faults that accommodate hemigrabens parallel to the basin edge, in the NW-SE direction, mainly affecting the Choiyoi Group and Precuyo Group units. This result is consistent with the orientation of the fault system established in the southeastern sector of the study region. In the depocenters, a maximum sedimentary depth of 1 km was estimated. Finally, shallow regions with higher resistivity than their surroundings were also identified. These regions could be associated with hydrocarbon migration or even accumulation towards the basin edge.