4 Results
4.2 Petrophysical parameters
4.2.2 Density and porosity
Grain density
As described in section 3.2, the determination of water-loss and physical porosity requires density data. The measured grain and wet densities are presented in Tab. 4-6. The variation in grain densities is rather narrow, thus displaying a range from 2.66 – 2.84 g/cm3 for all but two samples. The sample from the Posidonienschiefer shows a lower grain density of 2.53 g/cm3 whereas the iron oxide-rich sample from the Wutach Formation oolith shows a high value of
2
Gravimetric wet water content Ciemat (%)
Gravimetric wet water content UBe (%) 1:1
SLA-816.73 SLA-765.31
SLA-860.77
Malm'Brauner Dogger'Opalinus ClayLias
0 1 2 3 4 5 6 7 8
2.94 g/cm3. The relative uncertainty of the grain density derived from standard deviation is below 1 % for most samples (highest value is 1.2 %). By comparison, the analytical uncertainty of the kerosene density method is estimated to be 1.3 %.
Bulk wet density
The bulk wet density data shows the same trend as that of the grain density, thus displaying a rather narrow range of 2.48 – 2.65 g/cm3 for all but the Posidonienschiefer sample with (2.32 g/cm3; Tab. 4-6). Note that this latter rock sample also has highest organic carbon content (Tab. 4-1). The relative uncertainty derived from standard deviation is somewhat larger than for the grain density (0.2 – 3.4 %, except for sample SLA 742.68 with 10.6 %). This is due on one hand to the lower number of subsamples and on the other hand to the larger methodological error compared to that of the grain density. The analytical error, which is determined by that of the paraffin density, is estimated to be 1.2 %.
Bulk dry density
Bulk dry density measurements also follow the same trend as grain density (Tab. 4-6). All measurements lie in the range of 2.29 – 2.54 g/cm3. The relative uncertainty derived from standard deviation is below 1 %. For consistency check, dry densities have been calculated from measured wet densities and water-loss measurements according to eq. 3-11. The resulting values are also presented in Tab. 4-6. The comparison with the measured bulk dry densities reveals good agreement, with a relative difference in the range of 0.1 – 2.9 %. It is noted, however, that most bulk dry density values calculated from measured wet densities are slightly below the measured bulk dry density values.
Water-loss porosity
The data for water-loss (WL) porosity calculated from gravimetric wet water content and grain density measurements (eq. 3-5) and their uncertainties based on standard deviation and eq. 3-6 are presented in Tab. 4-7. The porosities for the Effingen Member (Malm) samples are lower than those of the deeper samples. They are in the range of 6.8 – 8.2 vol.-%. The 'Brauner Dogger' samples show a rather broad range of 3.7 – 13.4 vol.-% (except for the Wutach Forma-tion sample which has a value of 17.3 vol.-%). As already highlighted in the gravimetric wet water content measurements, WL porosities in the 'Brauner Dogger' show an increasing trend with depth (Fig. 4-12a), which is largely explained by the increasing clay-mineral content.
Opalinus Clay samples show a narrower range of 8.8 – 11.6 vol.-% and no depth dependency.
The Lias samples display a WL porosity range of 9.7 – 12.3 vol.-% with an increasing trend with depth (Fig. 4-12a).
Physical porosity
Physical porosity was calculated from gravimetric dry water content, grain density and bulk wet density according to eqs. 3-11 and 3-14. Bulk wet density data rather than bulk dry density data (measured on dried samples) was selected because the former data is considered to be more accurate (Mazurek et al. 2012). The uncertainties of physical porosity data were derived from standard deviation data and linear error propagation (eq. 3-15). The calculated relative uncer-tainty is typically 5 – 10 % (range 1 – 28 %) for all but one sample from the Effingen Member (SLA 742.48 m depth) for which a very high uncertainty (> 100 %) resulted by this estimation method. Inspection of that data indicates that this high error, which is caused by the large standard deviation of the bulk wet density of the two measured subsamples, is not realistic. A smaller error is indicated from the small difference between measured bulk wet densities and those calculated from the measured bulk dry densities. Therefore for this sample, the error was
derived from the standard deviation of the two bulk wet density and the three bulk dry density measurements, which results in a relative error of 41.8 %. This is still probably too high, but deemed more reasonable.
The physical porosity shows the same trend as the WL porosity, but displays somewhat higher uncertainties due to higher uncertainty in bulk wet density measurements. As depicted in Fig. 4-13, the two porosities correlate well with each other (r2 = 0.76), but the physical porosity is slightly higher than WL porosity in most samples. This trend is also illustrated in the WL-porosity physical WL-porosity graph (Fig. 4-12b) which reveals that the data generally plot above the 1:1 line. In principle there are three possible reasons for a higher physical porosity compared to WL porosity (Waber ed. 2008): (i) not all water is removed at 105 C in clay-rich samples, (ii) presence of isolated pores (fluid inclusions), and (iii) the presence of gas-filled pores. The difference is believed to be mainly due to (i) and perhaps partly also to (iii). A relevant contribution of (ii) (fluid inclusions) is probably negligible in these types of sedimentary rocks (see section 4.11).
Tab. 4-6: Grain, wet and bulk dry density measurements analysed at Uni Bern.
* calculated from grain density and bulk wet density measurements
Sample ID Stratigraphy SLA 734.89 Effinger Schichten 2.767 0.024 2.605 0.006 2.525 0.003 2.523 SLA 742.48 Effinger Schichten 2.742 0.017 2.597 0.090 2.543 0.004 2.529 SLA 750.73 Effinger Schichten 2.769 0.020 2.571 0.024 2.533 0.011 2.490
SLA 758.79 Wutach-Fm. 2.944 0.006 2.651 0.007 2.498 0.024 2.475
SLA 765.31 Variansmergel-Fm. 2.764 0.027 2.582 0.018 2.521 0.006 2.512 SLA 768.62 Parkinsoni-Württembergica-Sch. 2.774 0.014 2.546 0.054 2.442 0.003 2.443 SLA 778.70 Parkinsoni-Württembergica-Sch. 2.769 0.022 2.553 0.000 2.474 0.014 2.459 SLA 779.27 Parkinsoni-Württembergica-Sch. 2.767 0.046 2.538 0.044
SLA 787.33 Parkinsoni-Württembergica-Sch. 2.692 0.012 2.496 0.013 2.422 0.010 2.376 SLA 795.27 Humphriesioolith-Fm. 2.748 0.053 2.654 0.029
SLA 800.01 Humphriesioolith-Fm. 2.768 0.000 2.529 0.002 2.408 0.010 2.409 SLA 812.11 Wedelsandstein-Fm. 2.734 0.001 2.507 0.000 2.407 0.009 2.377 SLA 816.73 Wedelsandstein-Fm. 2.723 0.014 2.486 0.002 2.391 0.013 2.344 SLA 823.53 Wedelsandstein-Fm. 2.741 0.021 2.482 0.008 2.397 0.006 2.350 SLA 825.42 Wedelsandstein-Fm. 2.779 0.020 2.491 0.000
SLA 833.08 Opalinuston 2.732 0.026 2.556 0.077 2.477 0.009 2.451
SLA 844.56 Opalinuston 2.658 0.003 2.531 0.008 2.404 0.000 2.413
SLA 852.06 Opalinuston 2.698 0.001 2.522 0.000 2.469 0.009 2.413
SLA 857.96 Opalinuston 2.715 0.000 2.517 0.047
SLA 860.77 Opalinuston 2.800 0.024 2.565 0.089 2.443 0.014 2.457
SLA 872.12 Opalinuston 2.705 0.029 2.552 0.017 2.491 0.007 2.464
SLA 880.30 Opalinuston 2.729 0.009 2.525 0.005 2.466 0.023 2.419
SLA 888.33 Opalinuston 2.735 0.029 2.517 0.031 2.440 0.005 2.412
SLA 898.31 Opalinuston 2.755 0.033 2.544 0.024 2.490 0.019 2.440
SLA 908.32 Opalinuston 2.788 0.012 2.509 0.032 2.473 0.016 2.402
SLA 915.67 Opalinuston 2.751 0.001 2.536 0.028 2.457 0.014 2.423
SLA 921.15 Opalinuston 2.751 0.015 2.540 0.041 2.475 0.010 2.436
SLA 929.40 Opalinuston 2.772 0.022 2.555 0.040 2.492 0.001 2.446
SLA 938.28 Opalinuston 2.744 0.037 2.532 0.012
SLA 939.48 Opalinuston 2.747 0.029 2.509 0.000 2.455 0.002 2.394
SLA 949.45 Opalinuston 2.745 0.019 2.547 0.000 2.487 0.002 2.452
SLA 960.38 Posidonienschiefer 2.532 0.019 2.325 0.032 2.286 0.001 2.227 SLA 971.89 Obtusus-Schichten 2.775 0.003 2.523 0.038 2.459 0.002 2.419 SLA 981.04 Obtusus-Schichten 2.836 0.012 2.521 0.045 2.465 0.015 2.408 SLA 987.61 Psiloceras-Schichten 2.815 0.011 2.536 0.034 2.461 0.010 2.419
Tab. 4-7: Calculated water-loss and physical porosity, and S/L ratio for Uni Bern samples.
* calculated by first order error propagation approximation as explained in text Sample ID Stratigraphy
SLA 734.89 Effinger Schichten 8.17 0.12 8.81 0.82
SLA 742.48 Effinger Schichten 6.79 0.27 7.76 3.25
SLA 750.73 Effinger Schichten 8.19 0.38 10.07 1.06
SLA 758.79 Wutach-Fm. 17.30 0.58 15.94 0.38
SLA 765.31 Variansmergel-Fm. 7.20 0.52 9.13 1.11
SLA 768.62 Parkinsoni-Württembergica-Sch. 10.41 1.28 11.93 1.97 SLA 778.70 Parkinsoni-Württembergica-Sch. 9.59 0.60 11.20 0.73 SLA 779.27 Parkinsoni-Württembergica-Sch. 12.86 0.62 12.93 2.10 SLA 787.33 Parkinsoni-Württembergica-Sch. 12.01 0.24 11.76 0.62
SLA 795.27 Humphriesioolith-Fm. 3.72 0.19 4.74 2.11
SLA 800.01 Humphriesioolith-Fm. 12.05 0.70 12.94 0.28
SLA 812.11 Wedelsandstein-Fm. 12.97 0.32 13.07 0.13
SLA 816.73 Wedelsandstein-Fm. 14.07 0.16 13.90 0.45
SLA 823.53 Wedelsandstein-Fm. 13.37 0.09 14.29 0.72
SLA 825.42 Wedelsandstein-Fm. 13.84 0.64 15.26 0.66
SLA 833.08 Opalinuston 10.52 0.76 10.29 2.86
SLA 844.56 Opalinuston 11.51 0.87 9.22 0.48
SLA 852.06 Opalinuston 10.84 0.16 10.56 0.08
SLA 857.96 Opalinuston 11.55 0.54 11.56 1.67
SLA 860.77 Opalinuston 10.99 0.97 12.25 3.14
SLA 872.12 Opalinuston 8.80 0.37 8.90 1.17
SLA 880.30 Opalinuston 10.64 0.13 11.36 0.34
SLA 888.33 Opalinuston 10.59 0.31 11.78 1.45
SLA 898.31 Opalinuston 10.50 0.42 11.44 1.36
SLA 908.32 Opalinuston 10.99 0.22 13.83 1.15
SLA 915.67 Opalinuston 11.32 0.16 11.91 0.96
SLA 921.15 Opalinuston 10.42 0.30 11.45 1.53
SLA 929.40 Opalinuston 11.00 0.43 11.77 1.57
SLA 938.28 Opalinuston 12.22 0.58 12.21 1.27
SLA 939.48 Opalinuston 11.63 0.17 12.87 0.94
SLA 949.45 Opalinuston 9.55 1.15 10.65 0.77
SLA 960.38 Posidonienschiefer 9.69 0.45 12.04 1.39
SLA 971.89 Obtusus-Schichten 10.78 0.10 12.82 1.32
SLA 981.04 Obtusus-Schichten 11.28 0.83 15.06 1.57
SLA 987.61 Psiloceras-Schichten 12.28 1.20 14.08 1.34
(a) (b)
Fig. 4-12: (a) Water-loss porosity vs. depth and (b) water-loss porosity (closed symbols) and physical porosity (open symbols) vs. depth.
Fig. 4-13: Water-loss (WL) porosity vs. physical porosity; 1:1 line shown as comparison.
Densities and porosity parameters obtained by Ciemat
A compilation of density data for Ciemat subsamples is listed in Tab. 4-8. The depth profiles of the density data are displayed in Fig. 4-14, together with those obtained at Uni Bern. Note that bulk dry densities (mass of dry rock per total volume) as obtained from a volume measurement in the wet state (see section 3.2.4) are shown; for the Uni Bern samples, these values were calculated from the bulk wet densities and the gravimetric water contents according to eq. 3-11.
There is a reasonable agreement between the bulk dry density data (with bulk volume obtained in wet state) obtained at the two laboratories, whereas the grain densities obtained at Ciemat are generally slightly smaller (on average by ~ 0.05 Mg m–3 or ~ 1.8 %) than those obtained at Uni Bern (Fig. 4-15). The slight differences may be related to differences in the preparation of the samples (drying at 110 °C for 24 h at Ciemat, drying at 105 °C to constant weight at Uni Bern) and the different fluids used for the pycnometry (He versus kerosen). The bulk dry densities in the dry state obtained from Hg porosimetry data match approximately with those obtained in the wet state by mercury displacement; no trend to larger values in the dry state is observed.
Porosities obtained for the Ciemat samples are displayed in Tab. 4-9 and in Fig. 4-16 as a func-tion of depth, together with those obtained at Uni Bern. There is a fair correspondence between the WL porosities and the physical porosities obtained at Ciemat, with the physical porosities tending to be slightly larger (Fig. 4-17). The trend is less pronounced as compared to that of the data obtained at Uni Bern. This results from the slight differences in the grain densities between the two laboratories. In general, there is a good agreement between the water-loss porosities obtained at the two laboratories, except for samples SLA 765.31 and SLA 816.73 from the 'Brauner Dogger', as in case of the gravimetric water contents. The physical porosities show larger uncertainties when compared with the gravimetric water contents and the water-loss porosities. A somewhat larger scatter around the 1:1 line is also observed for the physical poro-sities when comparing the results of the two laboratories (Fig. 4-18), with mainly the samples SLA 929.40 (Opalinus Clay), SLA 981.94 and SLA 987.61 (both Lias) showing somewhat larger deviations, in addition to the sample SLA 816.73 ('Brauner Dogger'). The different inter-lab correlation pattern for the physical porosities compared to the water contents and the WL porosities is of course affected by the slight differences of the obtained grain densities between the two laboratories, which tends to shift the points along the x-axis to the right in the plot.
Tab. 4-8: Grain, bulk dry and bulk wet density measurements for samples analysed at Ciemat.
Sample ID Stratigraphy Grain density SLA 816.73 Wedelsandstein Fm. 2.708 0.002 2.440 0.025 5 2.387 2.538 0.026 5 SLA 833.08 Opalinuston 2.682 0.002 2.356 0.024 2.371 2.457 0.025
1 volume obtained in wet state, from Hg pycnometry
2 volume obtained in dry state, from Hg injection
3 calculated from bulk dry density (in wet state) and gravimetric dry water content
4 based on first order error propagation
5 estimated based on average relative standard deviation (s.d.) of bulk dry density of other samples
Tab. 4-9: Calculated water-loss and physical porosity for samples analysed at Ciemat.
Sample ID Stratigraphy Water-loss
porosity Uncertainty SLA 780.35 Parkins.-Württemb. Beds 11.78 0.12 11.44 0.25 SLA 816.73 Wedelsandstein Fm. 9.83 0.31 2 9.90 0.91 2
SLA 833.08 Opalinuston 10.06 0.21 12.14 0.88
SLA 860.77 Opalinuston 12.18 0.86 13.41 0.14
SLA 880.30 Opalinuston 10.49 0.33 2 10.59 0.92 2
SLA 898.31 Opalinuston 10.07 0.58 10.77 1.84
SLA 915.67 Opalinuston 10.63 0.37 12.24 2.36
SLA 929.40 Opalinuston 11.30 0.20 9.31 0.90
SLA 939.48 Opalinuston 11.41 0.44 13.26 1.32
SLA 971.89 Obtusus Beds 11.09 0.12 10.79 0.26
SLA 987.61 Psiloceras Beds 11.85 0.19 11.06 0.13
1 based on first order error propagation
2 based on average relative standard deviation (s.d.) of bulk dry density and, in case of WL porosity, average relative s.d. of water content
Fig. 4-14: Comparison of depth profiles of bulk dry (in wet state) and grain densities obtained for subsamples analysed at Ciemat and at Uni Bern.
Malm'Brauner Dogger'Opalinus ClayLias
2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3.0
(a) (b)
Fig. 4-15: Correlations between the densities obtained at Ciemat and Uni Bern; (a) bulk dry density (left), (b) grain density.
(a) (b)
Fig. 4-16: Comparison of Ciemat and Uni Bern data; (a) WL porosity, (b) physical porosity.
Malm'Brauner Dogger'Opalinus ClayLias
6 8 10 12 14 16 18
700
750
800
850
900
950
1000
WL-porosity Ciemat WL porosity UBe
Porosity (vol%)
Depth (m)
SLA 816.73 SLA 765.31
Malm'Brauner Dogger'Opalinus ClayLias
6 8 10 12 14 16 18
700
750
800
850
900
950
1000
Phys. porosity Ciemat Phys. porosity UBe
Porosity (vol%)
Depth (m)
SLA 816.73
SLA 987.61
Fig. 4-17: Correlation between water-loss porosity and physical porosity of the Ciemat samples; the Uni Bern data are also shown.
(a) (b)
Fig. 4-18: Correlations between Ciemat and Uni Bern data; (a) WL porosity, (b) physical porosity.