Characterization of a structural trap associated with an intrusive complex: the El Trapial oilfield, Neuquén Basin, Argentina

Abstract

Volcanic plumbing systems emplaced in sedimentary basins may exert significant mechanical and thermal effects on petroleum systems. The last decade of research has evidenced that igneous intrusions may enhance thermal maturation of organic matter in source rocks and lead to both small- and large-scale structures that can deeply impact fluid migration or trapping. This contribution describes how the emplacement of a whole intrusive complex generated a dome structure of the overburden, which is the main trapping structure of a large producing oil field. Our case study is the lower Miocene Cerro Bayo de la Sierra Negra intrusive complex, Neuquén Basin, Argentina, associated with the El Trapial oil field where the main trapping structure is a large domal antiform centered on the Cerro Bayo de la Sierra Negra complex. This study integrates the large subsurface data set produced during the development of the El Trapial oil field. More than 1,200 vertical wells (producers and injectors) have been drilled in the flanks of Cerro Bayo de la Sierra Negra complex. Additionally, five 3D seismic cubes have been acquired over the years, which have been merged and re-processed in a single volume. Such data set allows a detailed characterization of both the structure affecting the Mesozoic strata, and geometry of the intrusive complex. Igneous rocks have been recognized along the entire stratigraphical section. Sill intrusions appear to concentrate in the shale units and the stacking of them has a direct impact on the doming structure generation. Our study allowed us to establish a direct correlation between the distribution of the intrusions and the extent, amplitude, and style of doming, showing that the dome structure results from the emplacement of the intrusive complex. We also show that part of doming is related to intrusions emplaced in the Mesozoic formations of the Neuquén Basin, whereas the other part of the doming is related to deeper structures not imaged on the geophysical data. We estimate the amplitude of the doming to reach up to ~500 m. The voluminous subsurface data, combined with exposed outcrops, makes Cerro Bayo de la Sierra Negra a world-class case study for showing how the shallow plumbing system of a volcanic complex may control the growth of large-scale trapping structures for various fluids, such as drinkable water, geothermal fluids and hydrocarbons.