--> Fully Coupled Geomechanics-Basin Modelling and the Link Between Tectonics and Natural Hydraulic Fracturing: Application to the Neuquen Basin

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Fully Coupled Geomechanics-Basin Modelling and the Link Between Tectonics and Natural Hydraulic Fracturing: Application to the Neuquen Basin

Abstract

The Neuquen basin is located in the Central part of the Andes, between 32°S and 40°S. It is made up of several thrust belts from north to south resulting from a polyphased tectonic history from Palaeozoic to present. The last widely reported major shortening episode within the Andean belt is the Neogene Quechua phase, observed along the entire Cordillera, from Colombia to Patagonia. Shortening is still active. The Neuquen Basin is an historic prolific petroleum province for conventional hydrocarbon. Lately, it has also become a major play for unconventional oil and gas shale, with the exploration of the Vaca Muerta shale formation. The source rock formation has also been found with exceptionally high overpressure despite the latest erosional history that comes with the uplift associated to latest Quechua compressive event. Modelling of the petroleum system is dedicated to the simulation of the thermal and pressure history of the basin, with specific focus on source rock maturity, fluid expulsion and migration. The main routing mechanisms for overpressure are the compaction disequilibrium (porous volume reduction) and the HC generation (fluid volume expansion). In the particular case of the Neuquen Basin, the overpressure and their impact on the natural hydraulic fracturing are hardly simulated without involving the tectonic history of the basin, and specifically the recent compressional phase. Modelling tectonic forces imply the integration of a the geomechanics in the simulation, and an appropriate formulation of the poroplasticity to describe efficiently both compaction and rock failure through the whole basin history. Coupling strategies between petroleum system modelling and mechanical simulator are applied to the Neuquen basin to address the issue of the overpressure generation and its impact on the fracturing recent history. The results of the coupled simulation illustrate the impact of the compression on the excess of pressure rise. Former classical approach could only reproduce the pressure intensity with anomalously low shale permeability. Thanks to the full coupling approach, observed and measured shale permeability from Vaca Muerta samples could be introduced in the model. Thus, the fluid history could be properly linked to both burial and tectonic compression. The rise of the pressure leads to very low effective stress, which combined to the compressive state of stress leads to fracturing, both in tension and shear through the basin.