NMR logging method using superparamagnetic iron oxide nanoparticles

A method for NMR logging of a geological formation, comprising

• injecting or otherwise incorporating hydrophilic hydrophilic-Fe3O4 superparamagnetic iron oxide nanoparticles (hydrophilic hydrophilic-Fe3O4 SPIONs) into the geological formation,
• generating a magnetic field and detecting a magnetic signal,
• wherein the hydrophilic hydrophilic-Fe3O4 SPIONs are made by a process comprising:
• mixing an iron-containing precursor with a hydrophilic ligand or capping agent to form a homogeneous suspension;
• heating the homogenous suspension to a temperature sufficient to bind the hydrophilic ligand to the iron-containing precursor,
• cooling the resulting homogenous suspension,
• adding a solvent to the cooled homogeneous suspension to precipitate the hydrophilic-Fe3O4 SPIONs into a slurry,
• separating the precipitated hydrophilic-Fe3O4 SPIONs from the slurry, and
• washing the hydrophilic-Fe3O4 SPIONs to remove unbound hydrophilic ligands or capping agent, thereby making the hydrophilic hydrophilic-Fe3O4 SPIONs,
• wherein the iron-containing precursor is iron(III) acetylacetonate, the hydrophilic ligand or capping agent is polyethylene glycol 400 (PEG-400), the heating is at a pressure of about 15 to about 45 psi and at a temperature ranging from 175 to 185° C. for at least 12 to 36 hours, the solvent is a mixture of absolute ethanol and diethylether, and the hydrophilic-Fe3O4 SPIONs are washed in ethanol.