Thermal impact of igneous sill-complexes on organic-rich formations and implications for petroleum systems: A case study in the northern Neuquen Basin, Argentina

Numerous sedimentary basins in the world host voluminous igneous sill-complexes, i.e. stacking of sills that are emplaced in different levels of the sedimentary sequence. When sills are emplaced in organic-rich sedimentary formations, they can considerably affect the thermal and maturation history of the hydrocarbon source rock and can be highly relevant elements of the petroleum system. Most models of the thermal impacts of igneous sills on source rock consider one or few intrusions. However, the parameters that govern host rock maturation related to full sill-complexes remain unclear. In this contribution, we integrate borehole data and thermal 2D-modelling to quantify the temperature and maturation effects of a sill-complex in a 2D section on the sedimentary formations of the Neuquen basin, Argentina. In this basin, extensive magmatic activity took place during Oligocene-Miocene and upper Miocene age. There are numerous magmatic intrusions, dominantly sills, emplaced in organic-rich shale formations in the study area. Our modelling results show that (1) the source rock maturation in the study area was dominantly triggered by the sills, so that the area would be immature without the sills, (2) multiple sills have more pronounced thermal impact than a single, thick sill, (3) volumes of host rock between intrusions can have different degree of maturation depending on intrusion spacing, and (4) the temperature of the host rock at the time of sill emplacement controls to a great extent the thermal and maturation impact of the sills. Our work provides valuable insights into how the sills affected hydrocarbon generation during Oligocene-Miocene and Upper Miocene magmatic activity in the Neuquen basin. In addition, our study suggests that most of the kerogen has been transformed to hydrocarbon in areas where the sills are located.