Detection of magnetic nanoparticles against proppant and shale reservoir rocks.

With the expansion in the production of shale oil and gas, there is a desire to obtain detailed information of the downhole environment resulting from hydraulic fracturing (fracking). Nanomagnetite (nMag) has been proposed as a suitable contrast agent for magnetic imaging. In order to determine its suitability, 15 nm oleic acid-stabilised magnetite nanoparticles were synthesised and the magnetic susceptibility was measured and compared against two types of proppant. Although frac sand is diamagnetic (−0.20 × 10−5SI), ceramic proppant is paramagnetic (25.7 × 10−5SI) due to the presence of Fe2O3. The quantity of the nanoparticles that would be required for differentiation against the background levels in the proppant pack was calculated to be 0.269 g/L for sand and 1.01 g/L for ceramic, which correlates to a minimum of 15,000 kg and 56,000 kg per well, respectively. In order to determine the contrast with the reservoir rock itself, the magnetic susceptibility was mapped for cores from two typical shale gas reservoirs (Harrison and Rackley, Arkansas), which show a general low level of paramagnetism (ca. 45 × 10−5SI). However, regions are observed with higher susceptibility (>200 × 10−5SI) necessitating the use of 242,000 kg nMag per well in order to provide contrast with the reservoir. [ABSTRACT FROM PUBLISHER]