Combined Spatially Resolved and Non-resolved 1H-NMR Relaxation Analysis to Assess and Monitor Wettability Reversal in Carbonate Rocks

Wettability is a petrophysical property that directly affects oil recovery by controlling the location, flow and distribution of fluids inside the reservoir. In this study it has been verified that a polar interaction mechanism to change wettability of a carbonate rock from water-wet to oil-wet by acid adsorption onto the rock surface can be obtained by injecting adequate chemicals, and in particular oleic acid dissolved in non-polar oil, like Soltrol® 170 used for laboratory experiments. The paper deals with the assessment and monitoring of wettability reversal of carbonate rocks used in laboratory studies to evaluate the efficiency of chemical EOR methods, and in particular alkali flooding. The study is performed by combining spatially resolved and spatially non-resolved 1H-NMR information obtained on full-size cores (up to 7cm in diameter). In particular, spatially resolved quantitative NMR imaging maps (or Quantitative Relaxation Tomography, QRT) and spatially-non resolved (or Magnetic Resonance Relaxometry, MRR) analyses have been performed on full-size cores to track the process and to assess the quality of wettability reversal. Changes of relaxation time distributions and of T1 maps obtained in the experiments seem correlated with changes in wettability resulting from the chemical treatment, i.e., the contamination with oleic acid. Although further investigations are needed, MRR and QRT are promising techniques to correlate the wettability index with local values of T1 in internal sections of a rock sample.