CHARACTERIZATION OF THE RESERVOIR ROCK SATURATING FLUIDS BY THE NMR PERFIDI SEQUENCE

The possibility to characterize and measure the saturating reservoirs fluids is a well-known key factor to optimize production. To this purpose, Nuclear Magnetic Resonance Relaxation (MRR) and Magnetic Resonance Imaging (MRI) techniques have since long played a central role. MRR and MRI measurements are commonly used in the oil Industry, in the form of both laboratory (bench top) and field (logging) applications. MRR and MRI are non-destructive and non-invasive techniques, and can provide a huge amount of information concerning both petrophysical properties of reservoir rocks and saturating fluids. As for water-wet rocks containing brine and light oil, the MRR distribution of longitudinal relaxation times (T1) typically exhibit two distinct peaks, permitting the study of the two saturating phases. If paramagnetic minerals are present, as in most of the rocks, the MRR distribution of transverse relaxation times (T2) of oil and brine merge and become indistinct. Therefore, unless gradient techniques are applied (with the disadvantage to increase both the complexity of the experiments and the procedures of data inversion and interpretation), for laboratory investigation of brine and oil saturations in preserved core the T1 measurements are preferable. In this work, the innovative Parametrically Enabled Relaxation Filters with Double and multiple Inversion (PERFIDI) sequences that implement T1 filters are illustrated and used in MRI on reservoir rock samples saturated with light oil and water. PERFIDI filter sequences, using preambles of inversion pulses prepended to the standard MRR or MRI sequences, similarly to the electronic filters, provide an effective attenuation of the signal in a selected range of T1 values, while the remaining signal undergoes a computable attenuation. Therefore, the PERFIDI filter sequences act differently than the other MRR/MRI techniques dedicated to the signal selection found in literature, whose effects, in general, are to filter the signal for a discrete number of T1 values. PERFIDI method seems a valid tool to evaluate oil saturation inside a core. In particular, the use of PERFIDI method with MRI, allows to obtain the spatial distribution of the oil phase.