DEVELOPMENT OF FIBROUS CALCITE VEINS RELATED TO HYDROCARBON GENERATION AND OVERPRESSURING IN ORGANIC-RICH SHALE SOURCE ROCKS: THE VACA MUERTA FORMATION, NEUQUÉN BASIN, ARGENTINA

SPACAPAN JUAN; COMERIO M.; RUIZ REMIGIO; ROCHA EMILIO

JOURNAL OF PETROLEUM GEOLOGY

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2022

0141-6421

Fibrous calcite bed-parallel veins (BPVs) are a typical feature of the Upper Jurassic ? LowerCretaceous Vaca Muerta Formation in the subsurface of the Neuquén Basin (Argentina).The formation is considered to be the main source rock in the basin as well as an importantunconventional play. This study examines the growth of BPVs through an analysis of core fromthree wells located along a transect extending for some 150 km from the NE Platform nearthe basin margin in the east to the Agrio fold-and-thrust belt at the Andean deformation frontin the west. The main objective is to integrate fluid inclusion data with the palaeothermaland palaeopresure evolution obtained from a regional-scale 2D basin and petroleum systemsmodel to examine the timing of fracture development and its relationship with hydrocarbongeneration in the Vaca Muerta Formation through time. The apertures of BPVs were measured in more than 360 m of core from three wells (wells A, D and E). This data was combined with optical petrography to investigate the number of calcite cementation events, and the temperature of cement precipitation based on fluid inclusion data. The organic geochemical and mineralogical characteristics of the Vaca Muerta source rock were also analysed. The integrated results were incorporated into a poro-elastic basin model to investigate the impact of horizontal shortening due to Andean compression on pore pressure development and fracturing in the Vaca Muerta Formation.This framework allowed the timing of BPV formation to be determined together with possiblemechanisms governing overpressure conditions through time.Near the Andean deformation front in the west of the modelled section where the VacaMuerta Formation is in the wet gas window (well D) and dry gas window (well A), BPVsare characterized by two or more generations of calcite fibres indicating multiple growthphases. Calcite which precipitated during cementation event 1 (E1) in the internal zones ofBPVs consists of crystals oriented perpendicular to fracture walls, indicating perpendicularvein opening. Calcite precipitated during cementation event 2 (E2) in the outer zones ofBPVs includes curved and oblique crystals