Modeling petroleum generation, retention, and expulsion from the Vaca Muerta Formation, Neuquen Basin, Argentina: Part I. integrating compositional kinetics and basin modeling

摘要

Improved understanding and prediction of petroleum expulsion, retention, and producibility from source rocks (SR) are achieved by integrating 3D basin modeling with customized compositional kinetics and retention model for the lower Vaca Muerta Formation (LVM), Neuqu ' en Basin, Argentina. Modeling results indicate basin-wide expulsion from LVM started in the late Cretaceous when petroleum generation exceeded the SR retention capacity at thermal maturity of 0.9-1.0% R-o, associated with increasing pore pressure (P-p), increasing then maintained porosity (phi), permeability (k), and free petroleum retained in the SR (free petroleum). Expulsion ceased around the middle Eocene when kerogen, polar components, and medium aromatics were totally cracked at about 1.1-1.3% Ro. In the late Eocene, a different type of expulsion occurred in deeply buried areas at > 1.3% R-o due to continued cracking of the remaining larger hydrocarbons to form smaller hydrocarbons. The petroleum cracking created volume expansion, which in turn induced rock fracturing, which then reduced P-p, phi, k, and free petroleum. Then, continuous thermal cracking increased P-p and maintained phi, k, and free petroleum. In the mid-Miocene, tectonic uplift stopped the thermal stress and secondary cracking, and decreased pressure and temperature. Modeled petroleum compositions and properties such as gas wetness, oil degrees API gravity, gas/oil ratio are calibrated to Vaca Muerta (VM) core extracts, produced oils, and mud gases at wells with maturities ranging from oil window to dry gas. Our study indicates larger and polar components are preferentially sorbed within the source rock and cracked through thermal maturation by 1.3%R-o. Genetic saturates/aromatics ratio (S/A) equals about one at <0.8% R-o, and gradually increases in all retained fluids due to preferential generation of saturates and preferential thermal cracking of aromatics, which are mostly consumed by 1.65%R-o. The preferential sorption of aromatics causes a higher S/A in the free oil. The method and the insights of this study improve the fundamental understanding of petroleum expulsion and retention and can be applied to global plays.