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6.3. Results and discussion 85intensity [a.u.]40003500300025002000150010005000S w= 1 (step 1)S w= S wi(step 2)S w= 1 -S or(step 3)S w= S wi(step 4)0.01 0.1 1T 2[s]Fig. 6.5: Transverse relaxation time spectra of 2 H content in middle slice of the core in experimentA03.6.3.2 NMR relaxation times of fluids in sandstoneThe transverse relaxation behavior of D 2 O in the Bentheim rock at room temperatureand at full water saturation was measured in each experiment after the initial saturationcycle (step 1). The spin echo trains were inverted with the CONTIN procedure, alreadydescribed in Chapter 2, to obtain the T 2 spectra. In Figure 6.5 the T 2 spectrum is shownfor the middle slice of the core in experiment A03. A main broad peak is found with itsmaximum at T 2 = 0.247 s. A smaller peak is found near 0.037 s. In terms of the areaunder the peaks the smaller peak contributes only to 6% of the total area. The weightedmean T 2,AV , defined as∫T2 P (T 2 )dT 2T 2,AV = ∫ , (6.1)P (T2 )dT 2where P (T 2 ) is the distribution function of T 2 , is equal to 0.246 s, which indicates thatthe smaller peak contributes only slightly to the overall relaxation rate. Similar spectrawere acquired for all other slices and all other cores. The average contribution of themain peak was 95 ± 1%. The average of the T 2 values derived from the maximum of themain peak was 0.25 ± 0.01 s. The average of the T 2 values derived from the maximumof the secondary peak was 0.025 ± 0.006 s. Drainage of the core through the injectionof oil (step 2) results in lower signal intensities for 2 H. The magnitude (or area) of themain peak is reduced by 79%. The secondary peak is broadened, which is attributed toa reduced signal-to-noise ratio, but the area is unchanged. The weighted mean T 2,AV isreduced to 0.192 s. Secondary imbibition (step 3) leads to an increase of the magnitudeof the main peak to 71% of the original magnitude (step 1), and T 2,AV increases to 0.226s. Finally, secondary drainage results in a reduction of the magnitude of the main peak to19% of the original magnitude, and T 2,AV decreases to 0.170 s. Throughout each cycle the