Mechanical alteration of the organic matters contained in shales through thermal treatment for an improved fracturing job: A molecular – Level investigation

The injection of a fluid into a reservoir at a lower temperature than the reservoir has been recently used to induce the initiation and propagation of hydraulic fractures. Rock matrix, initially under reservoir conditions, is subjected to a decrease in temperature by the injected fluid, altering its stress state. A positive impact on the productivity of reservoirs, subjected to such treatment, has been reported, including the unconventional ones such as shale formations. The mechanisms by which cold injection enhance fracture stimulation remain uncertain. The organic matter known as kerogen, composed of aromatic and aliphatic chains of carbons, is characteristically different from other inorganic minerals. Kerogens are scattered uniformly within shale matrix. They are anticipated to exhibit a behavior similar to that of polymer, being capable of absorbing stresses during fracturing without failure. Cold fluid injection could potentially alter the elasticity of kerogens, favoring fracture initiation. The objective of this work is to study the impact of cold fluid injection on the mechanical behavior of kerogen. The created kerogen structure is subjected to a series of mechanical property assessments, including assessments of its elastic constants, such as the Young's, bulk, and shear moduli, as function of decreasing temperature. Kerogen at lower temperatures shows earlier signs of failure under applied stress. The ductility indicator decreases from 6.6 to 3.0; this is consistent with changes in Poisson's ratio. This work provides a novel methodology to investigate thermal alteration of kerogen as a means to degrade its mechanical integrity to enhance hydraulic fracturing jobs.