Integration of an optical FBG sensor into a nuclear magnetic resonance core flooding system

Abstract

A new platen was designed and developed for Nuclear Magnetic Resonance (NMR) core flooding cell to integrate Fibre Bragg Grating (FBG) strain sensors. The platen is made from carbon fibre material with a special channel to insert FBG inside the cell, and it is compatible with NMR overburden system (i.e., no metal, and it’s resistant to pressure, temperature and reactive chemicals) to allow advanced chemical experiments and the like. This development has allowed us to acquire both fluid dynamics behaviour, from NMR, and deformation/elastic properties, from FBG sensors, during NMR core flooding experiments for advanced hydro-mechanical-chemical coupling characterisation. Generally, pore fluid redistribution occurs while changing the surrounding stress and/or temperature conditions of the tested material, will generate elastic and geomechanical responses. The impact of rock-fluid interactions during NMR core flooding has not been evaluated until now, mainly due to technical limitations. Fortunately, FBG sensing technique is a localised/discreet micro-strain gauges (a 8 mm long and 125 micro thick), and it is applicable to monitor pseudo-tomography during core flooding experiments. We recently managed to attached 8 FBG sensors on a carbonate rock plug to monitor strain alteration during brine imbibition under 800 psi confining pressure. Results validates the capacity of FBG sensors to track mechanical strength alteration due to pore pressure changes and also detect waterfront velocity during injection. The integrated FBG sensors into NMR core flooding has added a new capability to NMR overburden system to simultaneously monitor material deformation with FBG sensors during pressure/temperature alterations as a first basic application.