Shale hydration damage captured by nuclear magnetic resonance

Wellbore instability could restrict the efficient development of unconventional petroleum resources in shales as drilling fluids may influence the integrity of shales by causing hydration damage. In this work we study the impact of hydration on shale samples from Xi Feng formations using Nuclear Magnetic Resonance. Samples were saturated in distilled water for different durations and then samples’ T₂ relaxation time and the spectrum area were analyzed using NMR. Damage variable, which can not only interpret the hydration damage in shales quantitatively but has also a key importance to build the damage theory, was defined with NMR T₂ spectrum area, according to a relationship between the T₂ relaxation time and the size of damage. Accuracy of the defined damage variable was verified by NMR images.GRAPHICAL ABSTRACT (Figure presented.).