In-situ nuclear magnetic resonance detection and visualisation of hydraulic fracture: A proof of concept

A novel approach to study hydraulic fracture initiation and propagation inside Nuclear Magnetic Resonance core flooding system (NMR) was examined on 38 mm diameter (1.5") outcrop sandstone rock plugs. A 3.4 mm diameter and about 35 mm long borehole (two-third of the plug's length) was drilled at the center of the plugs, and then a 3.17 mm diameter (1/8") PEEK tube was carefully inserted and glued. Dry plugs were assembled and loaded into the NMR confining system, and then hydrostatically pressurised to 500 psi (~3.5 MPa). Potassium iodide brine was slowly injected into the borehole, while the increasing injection pressure was monitored throughout the experiment using an independent pressure sensor positioned near the borehole's inlet face. NMR-T2 relaxation and saturation profile measurements were conducted at different pore pressure stages to locate and quantify any pore size changes. Both X-ray CT images and NMR spatial T2 measurements were only acquired before and after hydraulic fracture was created to support its location, aperture closure and growth. The results proved that NMR core flooding system is sensitive to any porosity or pressure changes induced by hydraulic fracture development.