Natural hydraulic fracturing in organic rich source rocks: field observations and physical modelling
Alain Zanella, lecturer at Université du Maine, will present his work on "Natural hydraulic fracturing in organic rich source rocks: field observations and physical modelling".
Top: Natural hydraulic fractures (beef) in the Vaca Muerta Formation, Neuquén Basin, Argentina. Bottom: Natural hydraulic fractures in physical model.
As a result of an increasing emphasis on unconventional resources, new data are becoming available for source rocks. Abnormally high values of pore fluid pressure and natural hydraulic fractures are very widespread worldwide in sedimentary basins, especially within formations of low permeability as source rocks for hydrocarbons. Geological evidences for natural hydraulic fractures in these formations are 'beef' (bedding-parallel calcite veins), but also bitumen veins. These structures are in particular well exposed in the Neuquén Basin (Argentina), but also in the Magallanes Basin (Chile-Argentina) or in the Wessex Basin (England). Several mechanisms have been evocated to be responsible for fluid overpressure and hydraulic fracturing, as mechanical or chemical compactions or diagenetic reactions. To investigate some of those processes, as chemical compaction, overpressure development and hydraulic fracturing, we have developed new techniques of physical modelling in a closed system. Models consisted of horizontal layers of two materials: (1) a mixture of equal initial volumes of silica powder and beeswax micro-spheres, representing source rock, and (2) pure silica powder, representing overburden. By heating, we surpassed the melting point of beeswax (~62°C) and generated a fluid from solid particles, as during the maturation of hydrocarbons.