Empirical relations of rock properties of outcrop and core samples from the Northwest German Basin for geothermal drilling

Abstract

Abstract. Information about geomechanical and physical rock properties, particularly uniaxial compressive strength (UCS), are needed for geomechanical model development and updating with logging-while-drilling methods to minimise costs and risks of the drilling process. The following parameters with importance at different stages of geothermal exploitation and drilling are presented for typical sedimentary and volcanic rocks of the Northwest German Basin (NWGB): physical (P wave velocities, porosity, and bulk and grain density) and geomechanical parameters (UCS, static Young's modulus, destruction work and indirect tensile strength both perpendicular and parallel to bedding) for 35 rock samples from quarries and 14 core samples of sandstones and carbonate rocks.With regression analyses (linear-and non-linear) empirical relations are developed to predict UCS values from all other parameters. Analyses focus on sedimentary rocks and were repeated separately for clastic rock samples or carbonate rock samples as well as for outcrop samples or core samples. Empirical relations have high statistical significance for Young's modulus, tensile strength and destruction work; for physical properties, there is a wider scatter of data and prediction of UCS is less precise. For most relations, properties of core samples plot within the scatter of outcrop samples and lie within the 90 % prediction bands of developed regression functions. The results indicate the applicability of empirical relations that are based on outcrop data on questions related to drilling operations when the database contains a sufficient number of samples with varying rock properties. The presented equations may help to predict UCS values for sedimentary rocks at depth, and thus develop suitable geomechanical models for the adaptation of the drilling strategy on rock mechanical conditions in the NWGB.

Evaluation of Interactions Between Oilfield Chemicals and Reservoir Rocks

“…Despite the limited data points (n = 4) in this study, the UCS-porosity relationship from the current work is consistent with that for sandstone and carbonates with wide range of petrophysical properties, mineralogy and heterogeneity as shown in Fig. 8 (Palchik 1999;Palchik and Hatzor 2004;Chang et al 2006;Sabatakakis et al 2008;Reyer and Philipp 2014). However, a cautious approach is suggested when utilizing such empirical relationships to estimate UCS which has also been noted by Chang et al (2006) where they indicated that porosity alone is not a good indicator of UCS in low porosity (< 5%) sandstone and carbonates.…”

Characterizing the physical properties of rocks from the Paleozoic to Permo-Triassic transition in the Upper Rhine Graben

“…8a; e.g. Reyer and Philipp (2014); Adelinet et al (2010); Mielke et al (2017)). In this study, the sedimentary rocks have, for the most part, lower density and P-wave velocity than the basement rocks, though there is significant variability in the P-wave velocity of the sedimentary rocks (Fig.…”

“…However, particular barriers to the development of deep geothermal resources in sedimentary basins are the risks of wellbore instabilities (Dusseault 2011;Zeynali 2012) and the high costs associated with deep drilling exploration (York et al 2009;Proehl 2002;Li et al 2012). Thus, the physico-chemical characterisation of regional rocks analogous to lithologies that may be in proximity to reservoirs informs the analysis and interpretation of non-invasive geophysical exploration techniques and regional modelling (Reyer and Philipp 2014) and can help mitigate these risks (Khaksar et al 2009).…”

The 3D stress state from geomechanical–numerical modelling and its uncertainties: a case study in the Bavarian Molasse Basin

“…An increase in model uncertainties may be observed if variability in material properties as well as lateral or vertical inhomogeneities within the same unit, that may affect all modelled stress magnitudes, are regarded. Available studies from other areas indicate large standard deviations in material properties (Reyer and Philipp 2014). In particular, this is significant for the locations of the calibration data points.…”