Physical properties of Carboniferous and Devonian Rocks drilled in

Physical properties of Carboniferous and Devonian Rocks
drilled in the RWTH-1 borehole
Lydia Dijkshoorn (Applied Geophysics, RWTH Aachen, Lochnerstraße 4-20, 52064 Aachen, Germany; e-mail: [email protected]
Renate Pechnig (Geophysica Beratungsgesellschaft mbH, Lütticherstraße 32, 52064 Aachen, Germany ; e-mail: [email protected]
mbH
Cuttings investigations in the RWTH-1 borehole
We present the physical properties of the Carboniferous and
Devonian Rocks drilled in the 2500 m deep RWTH-1 borehole. The
borehole is located in the center of Aachen, in only few meter
distance to the University main building. The geological setting is in
front of the Aachen Overthrust , the large southeast dipping fault
belt, which separates the Eifel Mountain geology from the
northwestern foreland (Fig. 1). The well penetrates carboniferous
and devonian formations, which are dominated by series of
interlayered sandstones, siltstones and shales. Organic shales and
thin coal layers were locally drilled in the upper 1016 m, as part of
the Lower Carboniferous deltaic cycles. Carbonates only occurred
in the underlying Upper Devonian series between 1016 and 1440
m. The deeper parts of the borehole are dominated by variegated
shale and sandstone series, which are of Lower Devonian age
(Ribbert 2006).
Core-Log integration of physical properties
8
Thermal Conductivity
(W/m/K)
The density varies from 2.64 g/cm³ and 2.84 g/cm³ with a mean of
2.78 g/cm³. The thermal conductivity (TC) varies between 2.2
W/m/K and 8.9 W/m/K (Fig. 3). The high values can be explained by
a high percentage of quartz. Quartz cemented clean sandstones
are frequently observed in the deeper part of hole below 1895 m.
In total 57 cutting samples were selected at a regular interval every
50 box th ., resulting in a depth interval of 50 m. On the cuttings,
matrix density and thermal conductivity were measured (Fig. 2).
Density was measured by a helium pycnometer; the thermal
conductivity was determined with a line source device on a
cuttings-water mixture. Since the rock porosity is very low (< 0.1%),
the influence of the pore fluid on the effective thermal conductivity
can be neglected.
Cores samples were available for three sections (1392-1515
m, 2128-2143 m, 2536-2544 m) covering a total length of 150
m. On the cores, the following physical properties were
measured by a multi-sensor core logger: gamma density,
magnetic susceptibility and p-wave velocity.
6
4
2.65
2.7
2.75
2.8
Core and log data were compared with the petrographic core
descriptions (Österreich 2005). In some cases petrophysical
property variation follows the optical subdivision. This is valid
for the carbonate bearing rocks and the thin sandstone
interlayers. The separation made petrographically for the
shales and siltstone can not be constrained by the
petrophysical data. This is, because petrographical
separation is guided by optical markers, such as colour and
bedding changes, attributes which can, but must not have a
2.85
Matrix Density
(g/m³)
12
Fig. 1: Geological setting of the RWTH-1 borehole in front of the Aachen
Overthrust.
Thermal Conductivity
(W/m/K)
0.
GR (GAPI)
200.
K1 (%)
15.
2.64 2.68 2.72 2.76 2.8 2.84
2
4
6
0
Log
Resistivity
(ohm-m)
100
1000
Log/Core
Log
Core
VP
Gamma Ray Density
(km/s)
(API)
(g/cm³)
5
6
80 120
Core
Vp
(km/s)
2.7 2.8 2.9
1440
1450
1460
1470
1480
1490
1500
1520
Carbonatic Sandstone
Fig. 4: Petrophysical core and log data of the first core section
compared with the petrographic core description.
Shale
Shaly Siltstone
Sandy Siltstone
Silty Shale
Siltstone
Sandstone
Oberkarbon
Westfal A
2.6
0
Silur
2.65
2.7
Gedauer Konglomerat
Wilhelmine-Schichten
Mittlerer Kohlenkalk
Unterer Kohlenkalk = Etroeungt-Schichten
Friesenrath-Schichten
2.8
2.85
2.9
Matrix Density (g/cm³)
The core measurements have a good fit with the associated
logging measurements of the borehole wall. Using the
logging measurements, the borehole could be divided in 7
zones. These zones correspond with the stratigraphic
subdivision of the borehole (Fig. 2).
2
?
1000
3
Condroz-Schichten
Cheiloceras-Kalk
Famenne-Schiefer
Frasnes-Schiefer mit Knollenkalken
Oberer Massenkalk
Grenzschiefer
Unterer Massenkalk
quadrigeminum-Schichten
2.75
10
Oberer Kohlenkalk
II
8
Due to the paleoenvironment and post-sedimentary
processes, the relation between the natural gamma activity
and the relative clay volume differ between these zones.
Using the natural gamma-ray log for each different zone, it
was possible to calibrate the gamma-ray with the thermal
conductivity measured on cores und cuttings. The zone
identification made it possible to derive a continuous thermal
conductivity profile over the entire borehole depth (Speer
2005).
4
?
Frequency
Visé
Tournal
Famenne
Oberdevon
Frasnes
Givet
Gedinne
500
Eifel
Unterkarbon
1000
Mitteldevon
1500
Ems
2000
Siegen
2500
Continuous thermal property profiles of the formation
0
Burgholz-Sandstein
Walhorn-Schichten
Unterdevon
3000
500
1
Krebs-Traufe-Schichten
Namur
3500
Binnenwerke (mit 34 Flözen)
I
1500
Vichter Konglomerat
6
4
5
Zweifall-Schichten
“Siegener” Schichten
Obere Arkose
Bunte Schiefer
mit Kalkknollen
Bunte Schiefer
mit Konglomeraten
2
III
2000
6
Untere Arkose
0
0
Fig. 2: Cuttings measurements of matrix density and thermal
conductivity compared to the borehole zonation (after logging
data) and the standard stratigraphic profile known from the
Eifel mountains (after Knapp 1980).
2
3
4
5
6
7
8
9
Furthermore a continuous radiogenetic heat production
profile was calculated over the borehole depth, derived from
the spectral gamma log (Bücker & Rybach 1996).
Thermal Conductivity (W/m/K)
Fig. 3: Cross-plot and histograms of density and thermal
conductivity measured on cuttings of the RWTH-1
borehole.
References
Bücker, C. & L. Rybach (1996): A simple method to determine heat production from gamma-ray logs.
Marine and Petroleum Geology 13, 373-377
Österreich, B., (2005): Petrographische Beschreibung der RWTH-1 Kernsektionen.
geologischer Dienst NRW, Krefeld.
Knapp, G. (1980): Erläuterungen zur Geologischen Karte der nördlichen Eifel 1:10000. – 155 S.,
Geologischer Dienst Nordrhein-Westfalen, Krefeld.
Speer, S., (2005): Design calculations for optimising a deep borehole heat exchanger, Diplomarbeit,
Angewandte Geophysik, RWTH Aachen.
Ribbert, K.H. (2006): Die Bohrung RWTH-1- Regionalstratigraphische Einordnung und Deutung. Interner
Bericht, Geologischer Dienst NRW, Krefeld.
1
7
2500
Interner Bericht,
10 20 30
1430
4500
Außenwerke (mit 5 Flözen)
Core
Suszept.
(SI)
1510
4
Breitgang-Schichten (mit 4 Flözen)
6
1420
sand - clay
4000
5
1410
8
8
10
1400
Frequency
0.
9
1390
Vp-data were used for comparing core with logging data. After
the correction of a 1.2 m depth shift (log deeper core) and the
use of a sliding window average on the core data, in-situ and
laboratory data comes to an excellent fit (Fig. 4). The data fits
best in the carbonate bearing section down to 1440 m and in
the deepest part of core section 1. Between 1460 and 1490 m
slight off-sets can be observed, which might be attributed to
bedding anisotropies. Effects of a Vp lowering by pressure
relief are not observed for the RWTH-1 cores.
2
Matrix Density
(g/cm³)
Caliper
(in)
8
Depth (m)
Beratungsgesellschaft
The thermal properties are used for a design calculation of
the (SuperC) borehole heat exchanger and for prognostic 3D
modelling of heat flow and temperature in a larger region.
Fig.6: Displayed are continuous thermal properties curves,
calulated from logging data. TC-Am: Arithmetic mean - thermal
conductivity profile; TC-Gm: Geometric mean - thermal
conductivity profile; A: Heat production profile; VC: Volume of
clay - displayed is the clay content and the quartz/carbonate
rock matrix.
Carbonatic Shale
Shale and Limestone

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