Pore-scale analysis of formation damage in Bentheimer sandstone with in-situ NMR and micro-computed tomography experiments

We investigated fines movement through sandstone in-situ at the micrometre pore scale and studied the associated pore-scale mechanisms leading to formation damage. We used two in-situ techniques to accomplish this, namely nuclear magnetic resonance T2 relaxation time (NMR) measurements (of pore size distributions) and high resolution x-ray micro-computed tomography (μCT; at high resolutions of (0.89 μm)3 and (3.4 μm)3). The μCT images showed the precise 3D location of the fines particles in the plug and demonstrated that initially pore throats are plugged, followed by filling of adjacent pore bodies by solid particles. These measurements in combination with traditionally used (indirect) permeability and production curve measurements and ex-situ SEM imaging enabled us to propose a new mechanistic pore-scale plugging model; furthermore we demonstrated that the amount of fines trapped decayed rapidly with core depth. We conclude that it is feasible to analyse formation damage in-situ by a combination of NMR and μCT measurements.