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Multi-Sensor-Core-Logger (MSCL)

von Amalia Aventurin (Autor)

Praktikumsbericht / -arbeit 2013 19 Seiten

Geowissenschaften / Geographie - Sonstiges

Leseprobe

Table Of Contents

I. Introduction: MSCL Principle

II. Experimental measurements and Results

III. Calculation
II.1. Sample G1
II.2. Sample G2

IV. Error calculation

V. Interpretation and Conclusion

VI. References

I. Introduction: MSCL Principle

The MSCL-experiment encloses the stepwise measurement of three different parameters: Gamma density, P-wave-velocity (compressional wave travel time) and magnetic susceptibility. Each is measured by different sensors. A photo of the apparatus is shown in figure 1.

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Fig. 1: Used MSCL apparatus with description where the sensors lie.

The four core samples G1, a black stone, coarse-grained and compacted with small mica particles and bigger white quartz inclusions, could be a gabbro and G2 a greenish sandstone with small particles and lesser compaction, each unsaturated and saturated with water are halved and “transported on a stepper motor-driven tracking system” to the sensors. If the rock sample is heterogeneous and the halves don’t accord in their mineral composition, you will have now a potential error source. The samples are laid on the tracking system. A motor pushes them first to a laser, where the length is measured, than to the gamma source and then to the P-wave-velocity-sensor. Here you have a second potential error source: When the P-wave-velocity-sensor presses the samples down for measuring, they were lift on the other side. To avoid the lifting the rock samples have to be pressed and so the measurements are not really accurate. At least the samples were driven to the sensor, which measures the magnetic susceptibility. Due to the fact that the samples are a little bit short, we need to put dummies between the samples, which are not measured.

The measurement of the magnetic susceptibility is used to determine the degree of magnetization. The magnetization only depends on the composition of the rock and matrix properties. It is independent from any fluid, which may fill the pore spaces.

The measurement for gamma density bases on caesium137 compton-scattering: The denser a sample, the lesser electrons go through the sample. With the electron-intensity, the computer determines at the end the density of the rock sample. The P-wave-velocity bases nearly on the same principle, but here you have a sound-wave (P-wave), which goes through the sample.

Before the measurement can start the apparatus has to be calibrated. Those calibrations have to be done to determine the errors depending on ray energy reduction in consequence of the interaction of the rays with oxygen atoms and on the size of the sample.

The first calibration we have done is the P-wave velocity (Vp). For this we have four reference blocks with a defined thickness, which are placed one after another under the sensor. The values for the reference blocks are shown in table 1. The plotted values are shown in figure 2a. The values for the gate are given for each reference block and where entered manually in the computer.

What has to be considered in this case is that the porosity value for saturated material will be overrated by about 11%, so it has to be corrected by the following equation:

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Tab. 1: Values for the four reference blocks. Just the values for P-wave Travel time were measured by the sensor.

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Fig. 2a: Plotted values of tab. 1 in a diagram.

Out of these results a regression line was calculated by an excel sheet:

The number 14.585 gives us now the runtime, which is needed for the measurement.

Each measurement step was done every centimeter for 10 seconds for gamma-ray and density and 1 second for magnetic susceptibility.

The next calibration is now done for the gamma-ray density. This is done by 14 aluminum discs which are measured every time for 60 seconds. For this measurement the discs are laid one upon the other to increase mass, but the first measurement is done without any disc – to get a raw value. The results are shown in table 2 and figure 2b.

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Tab. 2a: Results for Gamma-ray-density intensity calibration

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Fig. 2b: Plotted results for Gamma-ray density (Ln [cps]). On the x-axes are the average density∙thickness plotted.

The regression line for this polynomial is

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and is now used for the calibration. The magnetic doesn’t need a calibration, so the sample measurements can start.

[...]

Details

Seiten
19
Jahr
2013
ISBN (eBook)
9783656644842
ISBN (Buch)
9783656644859
Dateigröße
1.1 MB
Sprache
Englisch
Katalognummer
v272605
Institution / Hochschule
Rheinisch-Westfälische Technische Hochschule Aachen – Lehrstuhl für Geologie, Geochemie und Lagerstätten des Erdöls und der Kohle
Note
2,3
Schlagworte
multi-sensor-core-logger mscl

Autor

  • Amalia Aventurin (Autor)

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Titel: Multi-Sensor-Core-Logger (MSCL)