Internal Magnetic Field Gradients in Paramagnetic Shale Pores

MARTÍN C.A.; RAMIA M.E.

Otro; Applied Magnetic Resonance; 2016

Thepresent work involves a comprehensive study to provide a theoretical model ofthe internal magnetic field gradients, present in paramagnetic shale pores, inorder to explain the main relaxation features observed by Nuclear MagneticResonance transversal relaxation measurements. In the systematic analysisprocess of relaxation data it is necessary to know up to what extent themagnetic field gradients are generated by the logging tool and/or ariseinternally in the rock due to their paramagnetic impurities content. Thephysical model to explain the relaxation features is based in the calculationof field gradients in a planar pore with and without relaxatives walls. Theresults reproduce the features of the relaxation parameters in pores due to paramagneticand tortuous walls. The mechanism that drives the relaxation process isgoverned by anomalous diffusion within micro-pores. These relaxation processes arisefrom the interactions between the protons, belonging to the liquid moleculesand the pore walls, whose structure is characterized by both large tortuosityand abundance of paramagnetic impurities, giving rise to local strong timedependent magnetic field gradients. The theoretical results are compared withthose obtained experimentally in order to validate the relaxation model. The experimentaldata were gathered from a sample belonging to the ?Vaca Muerta? formation ofthe Neuquén basin, Argentina.