Physical Properties of Carboniferous and Devonian Rocks Drilled in The
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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] Beratungsgesellschaft mbH Renate Pechnig (Geophysica Beratungsgesellschaft mbH, Lütticherstraße 32, 52064 Aachen, Germany ; e-mail: [email protected] Cuttings investigations in the RWTH-1 borehole Core-Log integration of physical properties 8 Log Log/Core Log Core Core Core We present the physical properties of the Carboniferous and The density varies from 2.64 g/cm³ and 2.84 g/cm³ with a mean of Cores samples were available for three sections (1392-1515 Caliper Resistivity VP Gamma Ray Density Vp Suszept. (in) (ohm-m) (km/s) (API) (g/cm³) (km/s) (SI) Devonian Rocks drilled in the 2500 m deep RWTH-1 borehole. The 2.78 g/cm³. The thermal conductivity (TC) varies between 2.2 m, 2128-2143 m, 2536-2544 m) covering a total length of 150 8910 100 1000 56 80 120 2.7 2.8 2.9 56 10 20 30 borehole is located in the center of Aachen, in only few meter W/m/K and 8.9 W/m/K (Fig. 3). The high values can be explained by m. On the cores, the following physical properties were 1390 distance to the University main building. The geological setting is in a high percentage of quartz. Quartz cemented clean sandstones measured by a multi-sensor core logger: gamma density, front of the Aachen Overthrust , the large southeast dipping fault are frequently observed in the deeper part of hole below 1895 m. magnetic susceptibility and p-wave velocity. 1400 belt, which separates the Eifel Mountain geology from the 6 northwestern foreland (Fig. 1). The well penetrates carboniferous Vp-data were used for comparing core with logging data.After 1410 and devonian formations, which are dominated by series of the correction of a 1.2 m depth shift (log deeper core) and the interlayered sandstones, siltstones and shales. Organic shales and use of a sliding window average on the core data, in-situ and 1420 laboratory data comes to an excellent fit (Fig. 4). The data fits thin coal layers were locally drilled in the upper 1016 m, as part of (W/m/K) the Lower Carboniferous deltaic cycles. Carbonates only occurred best in the carbonate bearing section down to 1440 m and in 1430 in the underlying Upper Devonian series between 1016 and 1440 Thermal Conductivity 4 the deepest part of core section 1. Between 1460 and 1490 m slight off-sets can be observed, which might be attributed to m. The deeper parts of the borehole are dominated by variegated 1440 shale and sandstone series, which are of Lower Devonian age bedding anisotropies. Effects of a Vp lowering by pressure relief are not observed for the RWTH-1 cores. (Ribbert 2006). 1450 In total 57 cutting samples were selected at a regular interval every Depth (m) 1460 50 box th ., resulting in a depth interval of 50 m. On the cuttings, 2 Core and log data were compared with the petrographic core matrix density and thermal conductivity were measured (Fig. 2). 2.65 2.7 2.75 2.8 2.85 descriptions (Österreich 2005). In some cases petrophysical Matrix Density 1470 Density was measured by a helium pycnometer; the thermal (g/m³) property variation follows the optical subdivision. This is valid conductivity was determined with a line source device on a for the carbonate bearing rocks and the thin sandstone cuttings-water mixture. Since the rock porosity is very low (< 0.1%), interlayers. The separation made petrographically for the 1480 the influence of the pore fluid on the effective thermal conductivity 12 shales and siltstone can not be constrained by the can be neglected. Fig. 1: Geological setting of the RWTH-1 borehole in front of the Aachen petrophysical data. This is, because petrographical 1490 Overthrust. separation is guided by optical markers, such as colour and bedding changes, attributes which can, but must not have a 1500 Matrix Density Thermal Conductivity 8 (g/cm³) (W/m/K) 1510 GR (GAPI) 0. 200. 2.64 2.68 2.72 2.76 2.8 2.84 2468 K1 (%) 0 1520 0. 15. Carbonatic Sandstone Frequency sand - clay Carbonatic Shale Shale Shaly Siltstone Sandy Siltstone Fig. 4: Petrophysical core and log data of the first core section 4 compared with the petrographic core description. Silty Shale Siltstone Sandstone Shale and Limestone 4500 Binnenwerke (mit 34 Flözen) Westfal A Breitgang-Schichten (mit 4 Flözen) 4000 500 Außenwerke (mit 5 Flözen) I 1 Continuous thermal property profiles of the formation 0 Krebs-Traufe-Schichten 3500 Oberkarbon 2.6 2.65 2.7 2.75 2.8 2.85 2.9 Gedauer Konglomerat Wilhelmine-Schichten Matrix Density (g/cm³) Namur Burgholz-Sandstein Walhorn-Schichten 10 The core measurements have a good fit with the associated 3000 Oberer Kohlenkalk 2 logging measurements of the borehole wall. Using the Visé Mittlerer Kohlenkalk 1000 nal Unter- karbon Tour- Unterer Kohlenkalk = Etroeungt-Schichten ? logging measurements, the borehole could be divided in 7 2500 3 zones. These zones correspond with the stratigraphic Condroz-Schichten 8 subdivision of the borehole (Fig. 2). Cheiloceras-Kalk II Famenne-Schiefer 2000 Oberdevon Frasnes-Schiefer mit Knollenkalken 4 Due to the paleoenvironment and post-sedimentary Oberer Massenkalk Fras- nes Famenne Grenzschiefer 6 processes, the relation between the natural gamma activity Unterer Massenkalk quadrigeminum-Schichten Givet 1500 and the relative clay volume differ between these zones. 1500 ? Friesenrath-Schichten Using the natural gamma-ray log for each different zone, it Frequency Mitteldevon Vichter Konglomerat was possible to calibrate the gamma-ray with the thermal 5 4 Ems Eifel conductivity measured on cores und cuttings. The zone 1000 Zweifall-Schichten identification made it possible to derive a continuous thermal “Siegener” Schichten Siegen conductivity profile over the entire borehole depth (Speer 2 500 Obere Arkose Unterdevon 2005). Bunte Schiefer mit Kalkknollen 2000 Bunte Schiefer III 6 Gedinne mit Konglomeraten Furthermore a continuous radiogenetic heat production 0 Silur Untere Arkose 0 profile was calculated over the borehole depth, derived from 0123456789 the spectral gamma log (Bücker & Rybach 1996). Thermal Conductivity (W/m/K) Fig. 2: Cuttings measurements of matrix density and thermal 7 Thethermal properties are used for a design calculation of conductivity compared to the borehole zonation (after logging Fig. 3: Cross-plot and histograms of density and thermal the (SuperC) borehole heat exchanger and for prognostic 3D data) and the standard stratigraphic profile known from the 2500 conductivity measured on cuttings of the RWTH-1 modelling of heat flow and temperature in a larger region. Eifel mountains (after Knapp 1980). borehole. References Fig.6: Displayed are continuous thermal properties curves, Bücker, C. & L. Rybach (1996): A simple method to determine heat production from gamma-ray logs. Österreich, B., (2005): Petrographische Beschreibung der RWTH-1 Kernsektionen. Interner Bericht, calulated from logging data. TC-Am: Arithmetic mean - thermal geologischer Dienst NRW, Krefeld. Marine and Petroleum Geology 13, 373-377 conductivity profile; TC-Gm: Geometric mean - thermal Knapp, G. (1980): Erläuterungen zur Geologischen Karte der nördlichen Eifel 1:10000. – 155 S., Speer, S., (2005): Design calculations for optimising a deep borehole heat exchanger, Diplomarbeit, conductivity profile; A: Heat production profile; VC: Volume of Geologischer Dienst Nordrhein-Westfalen, Krefeld. Angewandte Geophysik, RWTHAachen. clay - displayed is the clay content and the quartz/carbonate rock matrix. Ribbert, K.H. (2006): Die Bohrung RWTH-1- Regionalstratigraphische Einordnung und Deutung. Interner Bericht, Geologischer Dienst NRW, Krefeld..