Abstract

Los Cavaos (Neuquén Basin, Argentina) is a large oil field in a fold-and-thrust belt setting, where voluminous igneous sill complexes are emplaced in different levels of the sedimentary sequence. In this field, the sills (horizontal igneous intrusions) are predominantly hosted in organic-rich units such as the Vaca Muerta and Agrio formations. The sills can be highly relevant elements of the petroleum system because they affect the thermal and maturation history of the hydrocarbon source rocks, and they also act as fractured reservoirs. In this chapter, we integrate new borehole data, core descriptions, petrophysical tests, and organic geochemistry to perform a two-dimensional (2-D) modeling of Los Cavaos oil field, a world-class case study of an igneous petroleum system in a fold-and-thrust belt. Especially, we focus on quantifying the implications of the sill complex on the hydrocarbon generation, migration, and accumulation. Our data and new modeling results show that (1) intrusions are the main reservoirs in the study area, with the highest amount of oil accumulation and reaching levels of oil saturation between 90% and 100%; (2) the reservoir quality of igneous intrusions is dominated by the combination of matrix and fracture framework properties; (3) zeolites are the most common type of cement in igneous reservoirs, and they have a relevant impact on reservoir quality as they preserve porosity; (4) intrusions released heat and modified the background geothermal gradient, promoting source rock maturation, especially during Miocene when most intrusions were emplaced; and (5) close to the sills, large hydrocarbon masses are generated and expelled in a short time (∼300 years), whereas in areas without sills, the hydrocarbon generation and expulsion is gradual and occurs over a longer time (thousands of years). In Los Cavaos, oil production happens only from the sills emplaced in the Vaca Muerta Formation. The cumulative oil production of some sills in the Vaca Muerta Formation reached peaks of 1886 bbl/d during the first 10 years. This study concludes that sill complexes may be highly relevant components of petroleum systems, as they promote source rock maturation and act as fractured reservoirs. Our conclusions can thus have major implications on hydrocarbon exploration in other volcanic basins worldwide.