Changes in Specific Surface as observed by NMR, caused by saturation of Chalk with porewater bearing divalent Ions

Nuclear Magnetic Resonance (NMR) spectrometry has proved to be a good technique for determining the petrophysical properties of reservoir rocks; such as porosity and pore size distribution. We investigated how pore water rich in divalent ions affect the NMR signal from chalk with two different depositional textures.

We compared two cases. The first experiments on outcrop chalk with high salinity brines showed that saturation with divalent ions (Mg2+,Ca2+and SO42-) cause major shifts in the T2 distribution curve, probably due to precipitation in the pore space. In a second set of experiments, fluid samples where precipitation takes place were found to show shifts in the T2 relaxation curve due to the creation of crystals.

We were able to identify how differences in the rock texture and precipitants within the pore space may affect the transverse relaxation time by altering the surface-to-volume ratio of the pore space. The results of this work could benefit the ongoing study on the optimization of the water composition for Enhanced Oil Recovery (EOR) methods and shed light on how it can affect the mechanical and physical properties of the rock.