Hem Bahadur Motra
@uni-kiel.de
Lecturer, Geosceinces
University of Kiel
I currently work as a academic staff at the institute of geoscience Kiel University, Germany. My research is mainly driven by my curiosity about the reliable engineering computing, structural reliability, risk and hazard analysis, quality evaluation of models, geostatistics, probabilistic methods, physical processes control rock material behaviour in the subsurface, along with the direct relevance of this field to socially relevant issues, such as mining, nuclear disposal, geotechnical engineering, geo-energy and oil production .
EDUCATION
PhD in Geotechnical Engineering
RESEARCH INTERESTS
Structural Reliability, Risk and Hazard Analysis
Uncertainty modeling in Structural and Geotechnical Engineering
Experimental/numerical soil and rock mechanics (porous media)
Damage and failure in rock and geo-materials (experimental and modeling)
Environmental geotechnics
Quality evaluation of numerical, mathematical, and experimental models
Geostatistics
Thermo-hydro-mechanical processes in porous media
Rock physics
Geothermal energy
Scopus Publications
Scholar Citations
Scholar h-index
Scholar i10-index
Scopus Publications
Chinmay Sethi, Bodhisatwa Hazra, Mehdi Ostadhassan, Hem Bahadur Motra, Arpan Dutta, J.K. Pandey, and Santosh Kumar
Elsevier BV
Chao Wang, Bo Liu, Mohammad-Reza Mohammadi, Li Fu, Elham Fattahi, Hem Bahadur Motra, Bodhisatwa Hazra, Abdolhossein Hemmati-Sarapardeh, and Mehdi Ostadhassan
Elsevier BV
Bo Liu, Mohammad-Reza Mohammadi, Zhongliang Ma, Longhui Bai, Liu Wang, Zhigang Wen, Yan Liu, Hem Bahadur Morta, Abdolhossein Hemmati-Sarapardeh, and Mehdi Ostadhassan
Elsevier BV
Kouqi Liu, Sirous Hosseinzadeh, Majid Safaei-Farouji, Bo Liu, Hem B. Morta, and Mehdi Ostadhassan
Elsevier BV
Kouqi Liu, Majid Safaei-Farouji, Yifei Gao, Thomas Gentzis, Bo Liu, Hem B. Morta, and Mehdi Ostadhassan
Elsevier BV
Mohammad Hosein Khosravi, Mahdi Kheirollahi, Bo Liu, Thomas Gentzis, Kouqi Liu, Hem B. Morta, and Mehdi Ostadhassan
Elsevier BV
Henok Hailemariam, Nils Blume, Hem B. Motra, and Frank Wuttke
Informa UK Limited
Mohsen Bazargan, Bjarne S. G. Almqvist, Hem Bahadur Motra, Pooyan Broumand, Tobias Schmiedel, and Christoph F. Hieronymus
MDPI AG
Laboratory-based elastic wave measurements are commonly used to quantify the seismic properties of Earth’s crust and upper mantle. Different types of laboratory apparatuses are available for such measurements, simulating seismic properties at different pressure and temperature. To complement such laboratory measurements, we present a numerical toolbox to investigate the seismic properties of rock samples. The numerical model is benchmarked against experimental results from a multi-anvil apparatus, using measurements of a stainless steel calibration standard. Measured values of the mean compressional- and shear-wave velocities at room conditions of the steel block were 6.03 km/s and 3.26 km/s, respectively. Calculated numerical results predicted 6.12 km/s and 3.30 km/s for compressional and shear-wave velocities. Subsequently, we measured Vp and Vs up to 600 MPa hydrostatic confining pressure and 600 °C. These measurements, at pressure and temperature, were then used as the basis to predict numerical wave speeds. There is, in general, good agreement between measurement and predicted numerical results. The numerical method presented in this study serves as a flexible toolbox, allowing for the easy setup of different model geometries and composite materials.
Sascha Zertani, Jan Pleuger, Hem B. Motra, and Timm John
Elsevier BV
Mohsen Bazargan, Hem Bahadur Motra, Bjarne Almqvist, Sandra Piazolo, and Christoph Hieronymus
Elsevier BV
Kim S. Mews, Mustafa M. Alhubail, Luka Hansen, Hem B. Motra, Frank Wuttke, Qiang Ye, Anil Misra, and Reza Barati Ghahfarokhi
American Society of Mechanical Engineers
Abstract The assessment of geomechanical properties of unconventional reservoirs is significant as they assist in placement as well as understanding of the geometry and properties of multi-stage hydraulic fractures in horizontal wells. Severe heterogeneities at micro-scale in addition to possibility of having non-intact samples provide opportunities for using micro-mechanics techniques on drill cutting size samples. This will lead to not only have a continuous log of geomechanical properties on heterogeneous formations but also be able to measure the mechanical properties of non-intact samples accurately. This study presents a multi-scale comparison of the elastic properties such as Young’s modulus and Poisson’s ratio on the Eagle Ford Formation. Peak Force Quantitative Nano-mechanical (PF-QNM) AFM-based technique has been performed and compared with true triaxial testing. A new model for AFM evaluation that corrects Young’s modulus in dependency of Poisson’s ratio has been developed. The results indicate that the distribution of Young’s modulus is separated into two regions, one dominated by brittle minerals indicating higher values and one dominated by ductile rock components resulting in lower values. The findings are significant as PF-QNM testing can be performed where only drill cutting-size samples are available, as it shows strong agreement with the triaxial testing result.
Sascha Zertani, Timm John, Frederik Tilmann, Hem B. Motra, Ruth Keppler, Torgeir B. Andersen, and Loic Labrousse
American Geophysical Union (AGU)
Subduction zone processes and the resulting geometries at depth are widely studied by large‐scale geophysical imaging techniques. The subsequent interpretations are dependent on information from surface exposures of fossil subduction and collision zones, which help to discern probable lithologies and their structural relationships at depth. For this purpose, we collected samples from Holsnøy in the Bergen Arcs of western Norway, which constitutes a well‐preserved slice of continental crust, deeply buried and partially eclogitized during Caledonian collision. We derived seismic properties of both the lower crustal granulite‐facies protolith and the eclogite‐facies shear zones by performing laboratory measurements on cube‐shaped samples. P and S wave velocities were measured in three perpendicular directions, along the principal fabric directions of the rock. Resulting velocities agree with seismic velocities calculated using thermodynamic modeling and confirm that eclogitization causes a significant increase of the seismic velocity. Further, eclogitization results in decreased VP/VS ratios and, when associated with deformation, an increase of the seismic anisotropy due to the crystallographic preferred orientation of omphacite that were obtained from neutron diffraction measurements. The structural framework of this exposed complex combined with the characteristic variations of seismic properties from the lower crustal protolith to the high‐pressure assemblage provides the possibility to detect comparable structures at depth in currently active settings using seismological methods such as the receiver function method.
W. Rabbel, S. Buske, T. Jusri, D. Köhn, J. Lehr, H.B. Motra, L. Schreiter, M. Thorwart, and
European Association of Geoscientists & Engineers
Mahmoud Khalifeh, Arild Saasen, Helge Hodne, and Hem Bahadur Motra
Elsevier BV
Abstract In this work, we have studied selected rheological properties and mechanical properties of rock-based geopolymers. The geopolymers are suggested for zonal isolation and permanent abandonment of hydrocarbon wells. Our viscosity measurements of the geopolymeric slurries shows a very small yield stress and a nearly constant additional viscosity. To find the effect of mechanical vibration, a rotational viscometer was modified by being equipped with a mechanical vibrator. Consistency of the geopolymeric slurry was measured by utilization of atmospheric and pressurized consistometers to find the impact of pressure and temperature on pumpability. The downhole temperature uncertainty was also studied by using atmospheric consistometers. Static-fluid-loss is an issue, which causes loss of hydrostatic pressure. Therefore, static-fluid-loss test was carried out. Strength development of the geopolymeric slurry was measured directly and indirectly by utilization of uniaxial compressive strength and Ultrasonic Cement Analyzers, respectively. As the pre-defined algorithm could not convert the sonic velocity to sonic strength, a custom algorithm was generated. The elastic shear wave and compressional wave velocities and velocity anisotropies of the samples were tried to be determined experimentally. The measurements were conducted on cube-shaped specimens in a triaxial multi-anvil press using the ultrasonic pulse-transmission technique. As it is necessary to study the bond strength between the geopolymers and pipe, steel pipe was used. The shear bond strength between pipe and the rock-based geopolymer was measured.
A. S. Sattari, H. B. Motra, Z. H. Rizvi, and F. Wuttke
Springer International Publishing
In order to determine the change of thermal conductivity of rock solids under coupled thermo-mechanical processes and developed microstructure fractures, an application of a new lattice element method (LEM) with additional interface elements representing the bond between the particles is investigated. The thermo-mechanical loadings in many engineering applications, such as deep geothermal systems, can result in a change of mechanical and thermal properties of rock solids. In the proposed model, the change of thermal conductivity under mechanical loading, thermal expansion and developed fractures due to coupled thermo-mechanical processes are considered. The main advantage of the new model is that it considers the thermal expansion while increasing the compression stresses in particles contact zone, which captures the true stress-strain behavior of the rock sample under coupled processes. The numerical results are eventually compared to the experimental results obtained from multi-anvil apparatus in Laboratory of CAU Kiel. It is shown that the new model is able to estimate the change of thermal conductivity under coupled thermo-mechanical loadings and developed microcracks.
H.B. Motra, J. Mager, A. Ismail, F. Wuttke, W. Rabbel, D. Köhn, M. Thorwart, C. Simonetta, and N. Costantino
Elsevier BV
Abstract Measuring rock elastic constants and anisotropy parameters and understanding their changes in response to changes in pressure and temperature is crucial for modeling and interpreting seismic measurements. The rapid advance in seismic exploration and characterization of conventional and unconventional reservoirs requires a thorough understanding of variations in seismic velocities in response to variations of the rock elastic constants and anisotropy parameters. In attempt to develop this understanding, we measured variations in the elastic constants of three rock samples in the lab as a function of temperature (up to 600 ∘C) and pressure (up to 150 MPa) to simulate the in-situ conditions using a triaxial ultrasonic pulse transmission method. The rock samples used in this study came from a metamorphic rock core sample collected from a geothermal reservoir at the Larderello Geothermal Field in Italy. The rock samples have different chemical and structural composition and inherently contain both vertical transverse isotropy (VTI) and orthorhombic isotropy. We used two different methods to calculate the elastic stiffness constants and corresponding anisotropic parameters including VTI and orthorhombic isotropy. Our results showed that increasing the pressure leads to an increase in the orthorhombic constants while increasing the temperature leads to a decrease in these constants. The lagging decrease of the elastic constants with respect to the decrease in the pressure is explained by the hysteresis phenomenon. These observations and results will promote a better understanding and interpretation of reservoirs within the seismic domain.
Hem Bahadur Motra and Hans Henning Stutz
Springer Science and Business Media LLC
It is important and meaningful for understanding the geomechanical properties of rock and providing guidance on analyzing and simulating the formation processes of engineering, geophysical, geothermal, civil and underground engineering projects. Variation in geomechanical properties of metamorphic rock, such as, seismic velocities (P-and S-wave) density deformation, is observed with the increase in pressure and temperature, Poisson’s ratio, elastic modulus, bulk modulus and shear modulus, are analyzed herein. A simple laboratory method, which measure seismic velocities has increasingly been conducted to determine the geomechanical properties of rock materials. Three metamorphic rock samples were selected for laboratory testing. Laboratory testing were done on cube samples of dry rocks in a true triaxial apparatus. First, P and S wave velocities were measured at 12–100 MPa pressure and at 20–600 °C temperature. Measurement showed that P and S wave velocities increase with increasing pressure and decrease with increasing temperature. Second, the wave velocities are used to calculate the geomechanical properties at lower to higher pressure and temperature. Furthermore, it was found that pressure and temperature have a significant effect on the change of geomechanical properties of rocks. These results contribute to a reliable estimate of geomechanical properties of rocks.
D. Köhn, T. Jusri, W. Rabbel, H.B. Motra, L. Schreiter, M. Thorwart, D. De Nil, F. Wuttke, and S. Buske
European Association of Geoscientists & Engineers
The characterization of geothermal reservoirs is primarily based on seismic imaging techniques. In most cases the underlying physics of seismic wave propagation relies on an isotropic acoustic or elastic approximation. In this study we investigate the effect of elastic anisotropy on the depth estimation of geothermal target horizons in seismic images. Realistic values for Tilted Transverse Isotropy (TTI) anisotropic elastic models are estimated from in-situ HP/HT laboratory ultrasonic measurements of rock samples from a geothermal reservoir in southern Tuscany (Italy). Seismic imaging by anisotropic Reverse Time Migration of numerical scattering experiments and reflection seismic data from the study area reveal a vertical displacement of up to 500 m for geothermal target layers compared to the isotropic elastic case.
Shaocheng Ji, Le Li, Hem Bahadur Motra, Frank Wuttke, Shengsi Sun, Katsuyoshi Michibayashi, and Matthew H. Salisbury
American Geophysical Union (AGU)
Hem Bahadur Motra and Sascha Zertani
Elsevier BV
Abstract Increased knowledge of the elastic and geomechnical properties of rocks is important for numerous engineering and geoscience applications (e.g. petroleum geoscience, underground waste repositories, geothermal energy, earthquake studies, and hydrocarbon exploration). To assess the effect of pressure and temperature on seismic velocities and their anisotropy, laboratory experiments were conducted on metamorphic rocks. P- (Vp) and S-wave (Vs) velocities were determined on cubic samples of granulites and eclogites with an edge length of 43 mm in a triaxial multianvil apparatus using the ultrasonic pulse emission technique in dependence of changes in pressure and temperature. At successive isotropic pressure states up to 600 MPa and temperatures up to 600 °C, measurements were performed related to the sample coordinates given by the three principal fabric directions (x, y, z) representing the foliation (xy-plane), the normal to the foliation (z-direction), and the lineation direction (x-direction). Progressive volumetric strain was logged by the discrete piston displacements. Cumulative errors in Vp and Vs are estimated to be
Mahmoud Khalifeh, Hem Bahadur Motra, Arild Saasen, and Helge Hodne
American Society of Mechanical Engineers
In this work, we have studied rheological behavior and mechanical properties of selected modified rock-based geopolymer, which are suggested for zonal isolation and permanent abandonment of hydrocarbon wells. Our rheological measurements of the geopolymeric slurries shows a very small Yield Stress and a constant plastic viscosity. Even though the yield stress is small, a non-Newtonian flow behavior is distinguished. Mechanical vibration measurements showed that vibrations have surprisingly little effect on the shear stress changes. Consistency of the geopolymeric slurry was measured by utilization of atmospheric and pressurized consistometers to find the impact of pressure and temperature on pumpability. A temperature decrease of 10°C postponed the geopolymerization by 4 hours and a temperature increase by 10°C accelerated the geopolymerization by 30 minutes. Static-fluid-loss test showed only 1.6 (ml) of fluid loss after 30 minutes which is another advantage of the geopolymeric slurry. The elastic shear wave and compressional wave velocities and velocity anisotropies of the samples were tried to be determined experimentally. However, our efforts showed that geopolymeric structure of the samples requires different frequencies as it damps the high frequency signal.
A. S. Sattari, Z. H. Rizvi, H. B. Motra, and F. Wuttke
Springer Science and Business Media LLC
The simulation of heat transport in a heterogeneous cemented geomaterial using lattice element method is the focus of this paper. The proposed method represents a heterogeneous cemented medium with the inter-connected Euler–Bernoulli beam elements for transmitting heat and mechanical loads. The mechanical equilibrium is assessed with minimizing the potential energy and in a meanwhile the conducted heat between solids is calculated based on modified thermal discrete element method. A validation study for heat transfer is carried out with the existing finite element method. In order to generate the heterogeneity, the random distribution or image processing techniques are implemented and subsequently the effective thermal conductivity (ETC) is determined. The effect of controlling parameters, such as mesh size, randomness factor, voids, heterogeneity and applied external mechanical loads, on calculated ETC is studied. Finally, with application of the proposed coupled thermo-mechanical lattice element, the ETC of three rock samples is determined and compared to the experimental data. The proposed method is able to model the heat transport in a heterogeneous cemented geomaterial and predict the ETC, which matches the experimental results.
Wolfgang Rabbel, Tomi Jusri, Daniel Köhn, Hem Bahadur Motra, Jan Niederau, Lena Schreiter, Martin Thorwart, and Frank Wuttke
Elsevier BV
Abstract Geothermal exploration relies in large parts on subsurface models derived from seismic reflection profiling. Based on a case study of the Larderello area we discuss the influence of seismic velocity uncertainties in geothermal prospecting and highlight the role of unrecognized seismic anisotropy. For the field study we investigated the anisotropy of typical rock samples under simulated in-situ HP/HT conditions. It turns out that the target horizons may be found up to 300 m shallower and 200 m horizontally displaced compared to the isotropic case due to anisotropic bias. Correspondingly, the uncertainty of temperature extrapolation may increase from 10 to 20%.
F. Wuttke, A. S. Sattari, Z. H. Rizvi, and H. B. Motra
Springer International Publishing
The effects of coupled thermo-mechanical processes under consideration of micro-fracturing of the solid geomaterial on mechanical and thermal properties of geomaterials are investigated and subsequently simulated using advance Lattice Element Method (LEM). As a result of that extension, the alteration of effective parameter due to structural changes become numerically understandable. Hence, the simulation of the coupled processes on the meso-scale helps to develop and validate reliable identification method for real cases. The obtained results make it obvious that LEM has a large potential for fracture problems in geomaterials.