Artificial Fracture Stimulation of Rock Subjected to Large Isotropic Confining Stresses in Saline Environments: Application in Deep-Sea Gas Hydrate Recovery

Abstract

The low permeability of gas hydrate deposits leads to poor extraction rates. Artificial fracture stimulation could significantly improve the recovery rate of an estimated 300 trillion m3 of this untapped future energy source, which form in seabed sedimentary deposits. Because conventional methods of rock fragmentation are inapplicable in such deposits due to sudden release of energy that may impose the risk of methane release to the atmosphere, alternative rock fragmentation technologies are necessary for artificial fracture stimulation of gas hydrate deposits. We checked the effectiveness of a new hydrophobic non-explosive demolition agent as a rock fracturing technique, which could potentially be used as a third-generation disruptive technology for mining (3G-DTM). Laboratory experiments performed by mimicking deep-sea environments suggest that the density of the gradually generated rock mass fractures increases with confining pressure and pore fluid salinity. Importantly, due to the fracturing nature of 3G-DTM, the fracture density can be significantly improved (by 116%) with increasing the confining pressure (from 70 kPa to 20 MPa). Increased salinity of the rock pore fluid also improved the fracture density by 38% at 20 MPa confining pressure when the salinity increased from 0% to 20%. Furthermore, the rock is subjected to a gradual fracturing process in the 3G-DTM fracturing (10–15 h in the laboratory experiments) allowing for a safer, more controlled fracture propagation, making 3G-DTM a substitute for conventional rock fragmentation in marine environments.