Geomecon GmbH

Potsdam, Germany

Geomecon GmbH

Potsdam, Germany

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Backers T.,Geomecon GmbH | Gruehser C.,Geomecon GmbH | Meier T.,Helmholtz Center Potsdam | Dresen G.,Helmholtz Center Potsdam
74th European Association of Geoscientists and Engineers Conference and Exhibition 2012 Incorporating SPE EUROPEC 2012: Responsibly Securing Natural Resources | Year: 2012

In this numerical study the influence of different fracture propagation criteria on the evolution of breakouts around an isostatically loaded borehole is discussed. The material properties are reflecting those of a shale material. The simulation results are compared to fracture patterns as generated in laboratory experiments on borehole breakout formation in Posidonia shale (Meier et al., 2012). Comparing the fracture patterns as observed in the laboratory experiments of borehole failure in Posidonia shale to the numerical simulation results shows general similarities of fracture pattern attributes in case of fracture propagation based on the maximum shear stress criterion. This criterion assumes the fractures to grow in the direction of local maximum shear stress. In contrast, the simulations based on a tangential stress criterion, which assumes extension fracture propagation, shows borehole parallel fracture growth; this is not observed in the shale material. From these observations it may be concluded that the fracture growth in the laboratory experiments in shales is shear dominated; this was also concluded from microstructural observations by Meier et al. (2012).


Rinne M.,Fracom Ltd. | Shen B.,CSIRO | Backers T.,Geomecon GmbH
Journal of Rock Mechanics and Geotechnical Engineering | Year: 2013

The Äspö Pillar Stability Experiment (APSE) was conducted to study the rock mass response in a heated rock pillar between two large boreholes. This paper summarizes the back calculations of the APSE using a two-dimensional (2D) fracture propagation code FRACOD. To be able to model all the loading phases of the APSE, including the thermal loading, the code was improved in several ways. A sequential excavation function was developed to model promptly the stepwise changing loading geometry. Prior to the modelling, short-term compressive strength test models were set up aiming to reproduce the stress-strain behaviour observed for the Äspö diorite in laboratory. These models simulate both the axial and lateral strains of radial-controlled laboratory tests. The volumetric strain was calculated from the simulations and compared with the laboratory results. The pillar models include vertical and horizontal 2D models from where the stress in the pillar wall was investigated. The vertical model assesses the stability of the experimental rock volume and suggests the resultant stress below the tunnel floor in the pillar area. The horizontal model considers cross-sections of the pillar between the two large boreholes. The horizontal model is used to simulate the evolution of the stress in the rock mass during the excavation of the boreholes and during and the heating phase to give an estimation of the spalling strength. The modelling results suggest that the excavation-induced stresses will cause slight fracturing in the pillar walls, if the strength of the APSE pillar is set to about 123. MPa. Fracture propagation driven by thermal loading leads to minor spalling. The thermal evolution, elastic behaviour and brittle failure observed in the experiment are well reflected by the models. © 2013.


Rybacki E.,German Research Center for Geosciences | Meier T.,Geomecon GmbH | Dresen G.,German Research Center for Geosciences
Journal of Petroleum Science and Engineering | Year: 2016

Successful stimulation of shale gas reservoirs by hydraulic fracturing operations requires prospective rocks characterized by high brittleness to prevent fast healing of natural and hydraulically induced fractures and to decrease the breakdown pressure required to (re-) initiate a fracture. We briefly reviewed existing brittleness indices (B) and applied several, partly redefined, definitions relying on composition and deformation behavior on various, mainly European black shales with different mineralogical composition, porosity and maturity. Samples were experimentally deformed at ambient and elevated pressures (P) and temperatures (T), revealing a transition from brittle to semibrittle deformation behavior with increasing pressure and temperature. At given composition and deformation conditions, B values obtained from different definitions vary considerably. The change of B with applied deformation conditions are reasonably well captured by most definitions based on the stress-strain behavior, which do not correlate with the fraction of individual phases, e.g., clay content. However, at given deformation conditions, most composition-based indices show similar variations with bulk composition as those derived from stress-strain behavior. At low P-T conditions (≲4 km depth), where samples showed pronounced post-failure weakening, B values determined from composition correlate with those calculated from pre-failure stress-strain behavior and both correlate with the static Young's modulus. In this regime, the brittleness concept can help to constrain successful hydraulic fracturing campaigns and brittleness maybe estimated from core or sonic logs at shallow depth. However, long term creep experiments are required to estimate in-situ stress anisotropy and the healing behavior of hydraulically induced fractures. © 2016 Elsevier B.V.


Backers T.,Geomecon GmbH
76th European Association of Geoscientists and Engineers Conference and Exhibition 2014: Experience the Energy - Incorporating SPE EUROPEC 2014 | Year: 2014

When stimulating a reservoir at depth, the existing fractures are propagated and coalesce. Whilst at low stresses Mode I (tensile) fracturing is mostly dominating, at large overburden stresses Mode II (shear) becomes the dominant mechanism for fracture extension. The contribution analyses the influence of fracture orientation and stress path during a stimulation at depth and discusses the implications for the fracture extension. It is shown that Mode II becomes the dominant mode during hydraulic stimulation at depth >3km.


Meier T.,Helmholtz Center Potsdam | Meier T.,Geomecon GmbH | Rybacki E.,Helmholtz Center Potsdam | Backers T.,Geomecon GmbH | Dresen G.,Helmholtz Center Potsdam
Rock Mechanics and Rock Engineering | Year: 2015

The stability of wells drilled into bedded formations, e.g., shales, depends on the orientation between the bedding and the borehole axis. If the borehole is drilled sub-parallel to bedding, the risk of borehole instabilities increases significantly. In this study, we examined the formation of stress-induced borehole breakouts in Posidonia shale by performing a series of thick-walled hollow cylinder experiments with varying orientations of the bedding plane with respect to the borehole axis. The thick-walled hollow cylinders (40 mm in diameter and 80 mm in length containing an 8 mm diameter borehole) were loaded isostatically until formation of breakouts. The onset of borehole breakout development was determined by means of acoustic emission activity, strain measurements, ultrasonic velocities and amplitudes. The critical pressure for breakout initiation decreased from 151 MPa by approximately 65 % as the bedding plane inclination changed from normal to parallel to the borehole axis. The finely bedded structure in the shale resulted in an anisotropy in elasticity and strength from which the variation in strength dominated the integrity of the thick-walled hollow cylinders. © 2014, Springer-Verlag Wien.


Moeck I.,German Research Center for Geosciences | Backers T.,Geomecon GmbH
First Break | Year: 2011

Hydraulic stimulation is frequently used to enhance reservoir productivity. The aim of hydraulic stimulation is to increase the formation pressure by fluid injection to create artificial fractures that act as additional fluid pathways. But large-scale fluid injection as applied in hydrocarbon and geothermal reservoirs can also induce seismicity and fault reactivation depending on the reservoir geomechanics and stress regime. Recent case studies in stimulation of geothermal reservoirs have shown induced seismicity as an undesirable side effect which needs to be understood prior to massive fluid injection. Slip tendency analysis has been successfully used to characterize fault slip likelihood and fault slip directions in any stress regime. In our study, we applied slip tendency analysis to assess the reactivation potential of shear and dilational fractures in a deep geothermal reservoir in the North-East German Basin, based on the notion that slip on faults is controlled by the ratio of shear to normal effective stress acting on the plane of weakness. The results from slip tendency analysis are supported by the spatial distribution of recorded microseismicity, which indicates slip rather than extension along a presumed NE-striking failure plane. © 2011 EAGE.


Backers T.,Geomecon GmbH | Stephansson O.,Geomecon GmbH | Stephansson O.,Helmholtz Center Potsdam
Rock Mechanics and Rock Engineering | Year: 2012

The suggested method for the determination of Mode II fracture toughness is reviewed. This so-called Mode II loading in fracture mechanics, the crack faces slide relative to each other and displacements of the crack surfaces are in the crack plane and perpendicular to the crack front. For any specimen preparation treatment appropriate high precision tools should be used. The specimens should be right circular cylinders having a height L to diameter D ratio of 1:1 and a diameter D equal to 50 mm. The minimum information on each specimen shall include dimensions, specimen preparation routines, special observations made during specimen preparation, moisture content, and macroscopic description of the surface. The report of each experiment should include source of specimen as precisely as possible; location and orientation. The shear stress at failure is reported to increase with confining pressure for various rock types.


Shen B.,CSIRO | Kim H.-M.,Korea Institute of Geoscience and Mineral Resources | Park E.-S.,Korea Institute of Geoscience and Mineral Resources | Kim T.-K.,SK Engineering and Construction SKEC | And 4 more authors.
Rock Mechanics and Rock Engineering | Year: 2013

This paper describes a boundary element code development on coupled thermal-mechanical processes of rock fracture propagation. The code development was based on the fracture mechanics code FRACOD that has previously been developed by Shen and Stephansson (Int J Eng Fracture Mech 47:177-189, 1993) and FRACOM (A fracture propagation code - FRACOD, User's manual. FRACOM Ltd. 2002) and simulates complex fracture propagation in rocks governed by both tensile and shear mechanisms. For the coupled thermal-fracturing analysis, an indirect boundary element method, namely the fictitious heat source method, was implemented in FRACOD to simulate the temperature change and thermal stresses in rocks. This indirect method is particularly suitable for the thermal-fracturing coupling in FRACOD where the displacement discontinuity method is used for mechanical simulation. The coupled code was also extended to simulate multiple region problems in which rock mass, concrete linings and insulation layers with different thermal and mechanical properties were present. Both verification and application cases were presented where a point heat source in a 2D infinite medium and a pilot LNG underground cavern were solved and studied using the coupled code. Good agreement was observed between the simulation results, analytical solutions and in situ measurements which validates an applicability of the developed coupled code. © 2012 Springer-Verlag.


Grant
Agency: European Commission | Branch: H2020 | Program: RIA | Phase: LCE-16-2014 | Award Amount: 3.40M | Year: 2015

Securing abundant, affordable, and clean energy remains a critical scientific challenge. Fortuitously, large shale formations occur within Europe. As the conventional gas production in Europe peaked in 2004, European shale gas could become a practical necessity for the next 50 years. However, the exploitation of shale gas remains challenging. Further, its environmental footprint is at present poorly quantified. Great care is needed to assess and pursue this energy resource in the safest possible way for the long-term future of Europe whilst protecting the European diverse natural environment. With this in mind, ShaleXenvironmenT assembled a multi-disciplinary academic team, with strong industrial connections. A comprehensive approach is proposed towards ensuring that the future development of shale gas in Europe will safeguard the public with the best environmental data suitable for governmental appraisal, and ultimately for encouraging industrial best practice. The primary objective is to assess the environmental footprint of shale gas exploitation in Europe in terms of water usage and contamination, induced seismicity, and fugitive emissions. Using synergistically experiments and modeling activities, ShaleXenvironmenT will achieve its objective via a fundamental understanding of rock-fluid interactions, fluid transport, and fracture initiation and propagation, via technological innovations obtained in collaboration with industry, and via improvements on characterization tools. ShaleXenvironmenT will maintain a transparent discussion with all stakeholders, including the public, and will suggest ideas for approaches on managing shale gas exploitation, impacts and risks in Europe, and eventually worldwide. The proposed research will bring economical benefits for consultancy companies, service industry, and oil and gas conglomerates. The realization of shale gas potential in Europe is expected to contribute clean energy for, e.g., the renaissance of the manufacturing industry.

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