International EAGE Workshop on Geomechanics and Energy

The candidate host rocks for a deep geological repository in Switzerland are analyzed in terms of correlations between petrophysical and geomechanical properties such as clay content, porosity, permeability and effective stress. The analysis leads to a workflow for estimating formation hydraulic properties for the different host rocks and at different depths based on geophysical log data. Consequently, common empirical relationships for permeability are tested for their ability to predict matrix permeability of the candidate formations. The coupled hydro-mechanical observations are additionally verified with micro-structural investigations of the pore space using nanotomography. The derived physical properties are finally compared to analyses of packer tests, evaluating the predictive ability of the proposed approach for the different host rock formations, and conclusively ranking them according to the predictability of the barrier function of the host rock.

There is an international consensus on the advisability of storing high-level nuclear waste in the deep geological repository with low permeability. Boom Clay which is characterized by low hydraulic conductivity and the self-sealing capacity is known as one of the potential host rock for this geological disposal process. The excavation process in deep geological host rocks is expected to create a perturbed zone around the underground structures in rock masses in which the significant irreversible deformations and significant properties changes can be occurred. Modelling of the fracturing system and extension of the so-called Excavation Damaged Zone EDZ as an essential issue is focused in this study using the strain localization approach as a classical mode of failure of geo-materials. Numerical modelling of strain localization needs a specific approach to overcome the practical problem of mesh size dependency within the framework of classical finite elements. The second gradient method is used in this study in order to overcome this problem. Coupled numerical modelling of a gallery excavation in in Boom Clay host rock is performed. The simulation provides information about the strain localization in shear bands mode accomplished by the evolution of EDZ during the gallery excavation.

Understanding gas transport processes is one of the key issues in the assessment of radioactive waste repository performance. The actual gas migration mechanisms may entail standard two-phase flow or more complex mechanisms involving coupled two-phase geomechanical and possibly geochemical phenomena. Laboratory tests on OPA cores from a shallow borehole in the Mont Terri Underground Research Laboratory (URL) and from a deep borehole in northern Switzerland were performed by two different laboratories, which include retention behavior and geomechanical tests, as well as specific water and air injection tests to determine single-phase liquid and two-phase properties. For the investigation of the laboratory measurements, numerical models were developed implementing the geometry of the rock core and the boundary conditions on the injection and outflow sides. The specific information from the laboratory experiments in terms of the stress dependence of void ratios and changes in permeability and capillary pressure were implemented in the numerical model, which reproduced well the measured injection pressure and outflow responses of both air injection tests parallel and normal to bedding.

Heating and cooling of the buildings represent an important area of energy consumption in the developed countries. Furthermore, a large part of this demand is still satisfied with fossil resources such as oil or gas. Therefore, developing alternative and renewable heat sources for buildings is a major challenge for future energy policies. But because of the congestion of the urban underground, conventional ground source heat pump systems need new heat exchangers with the ground. Therefore, embedding absorber pipes within foundation and underground structures represent a great opportunity while it saves the cost of dedicated drillings for boreholes. Shallow tunnels are numerous in large cities for roadways and metro lines. Therefore, using them as heat exchanger with the ground could provide an efficient heat source for the overlying buildings. Different solutions were identified and among them, heat exchanger anchors are the less investigated because of the emerging technology. The present paper investigates the potential of using tunnel anchors as heat exchangers for ground source heat pumps. The study is based on thermo-hydro-mechanical finite element analyses of a cut and cover tunnel and a bored tunnel. Different conditions are tested as well as the efficiency of seasonal heat storage and its mechanical implications.

This paper presents a three-dimensional model that couples both soil mass and storage system behaviour. The proposed model is applied to consider a field application case study, with particular focus on the correct representation of the surface flux and its impact on ground energy storage. It is shown that the correct assessment of the nature of the heat transfer process occurring on the surface of the soil is important for the estimation of the amount of energy stored in the ground.

Rock mechanical properties including wave velocities, Poisson’s ratio, Young’s, shear and bulk modulus have important applications in geomechanical analysis of petroleum reservoirs. Direct measurement of these parameters is usually not viable due to the high cost of testing or a lack of available data, particularly in old wells. Therefore, indirect methods are often used to predict these parameters from available data. The simplest, and still extremely common, method is empirical equations. However, these relationships are highly sensitive to different types of fluids or lithologies and are often not relevant for local geology. In recent years, intelligent systems have been used in different branches of sciences and technologies and have often been demonstrated to be useful in prediction and optimization problems. Herein, we attempt to predict a range of geomechanical parameters for different rock types using intelligent systems. For this purpose, wave velocities and rock mechanical properties of different lithologies were predicted from conventional petrophysical data that are available in most of petroleum wells. The results showed that the used methodologies are fast and reliable (around 95% accuracy) in estimation of geomechanical properties in our case studies and can be used in geomechanical/petrophysical modelling of coal seam gas and petroleum reservoirs.

A LOT is essentially a measurement of the formation strength and it strongly depends on the lithology of the formation being analyzed. The aims of this work is to analyze several LOT's and XLOT responses carried out in the Maracaibo Basin at different type of formations: level of grain cohesion (consolidated and unconsolidated) and lithologies (sand and clay contents), and study the effect of those parameters on LOT response. The methodology comprised five (5) steps: 1. Gather LOTs and XLOT carried out in the Western area of Venezuela, 2. Characterize the lithology of the formation being tested, 3. Analyze and interpret the test responses, 4. Find a relationship between the lithology and test response and 5. Identify the relationship between the clay minerals and shale plasticity behaviour. It was found that LOT performed on high shale content lithologies (80%) and unconsolidated formations exhibited plasticity behaviour; in contrast, well consolidated formations with high shale content showed elasto-plastic behaviour and, also, a non-consolidated formation with high sand content (80%) behaved as a elastoplastic material. Finally, in unconsolidated formations plastic or elastic behavior is governed by the lithology, in contrast, a consolidated formation will behave as elasto-plastic regardless of the shale content.

Optimal exploitation of conventional and unconventional hydrocarbon reservoirs requires detailed knowledge on the specific in situ stress field including all perturbations in stress magnitude and orientations due to faults and contrasts in rock mechanical properties. A geomechanical model comprising the detailed reservoir geometry and a mechanical stratigraphy is successfully built for a case study gas field in the North German Basin. The model is calibrated against well data and reveals in detail the local distribution of the in situ stresses. This validated model can now be used for stress predictions in the inter-well space and undrilled parts of the reservoir. In addition, the tendency of the existing fault network to slip or dilate in the present-day stress regime can be addressed. This is also possible for paleo-stress states, however, uncertainties especially regarding the paleo-stress field description and the paleo-properties of rocks and faults have to be kept in mind. The workflow outlined above can be used to build 3D geomechanical FE models for various types of reservoirs and ranging from field-scale models to smaller, highly detailed submodels of specific fault blocks.

The experimental methods of drained triaxial compression test for artificial CO2-hydrate-bearing sediment sample is given and its triaxial compressive property is discussed. The applicability of a constitutive equation which was proposed for CH4-hydrate-bearing sediment sample is discussed. The constitutive equation can almost express the relationship between deviator stress and axial strain of CO2-hydrate-bearing sediment sample.

Large amounts of CO2 and other waste fluids are being injected into reservoirs all around the world. Preventing leakage of the fluids into sensitive ground water reservoirs and to the surface and assuring safe long terms storage are essential requirements in these operations. One example is the injection of about one million tons of CO2 per year since 1996 into the Utsira formation at Sleipner in the Norwegian North Sea. Conventional reservoir simulations fail to the formation of flow chanels or chimneys, and the fast spreading underneath the caprock. We developed a new numerical code that predicts the formation of chimneys as a consequence of coupled deformation-fluid flow, without prescribing pre-exiting fractures. Our 3D model includs full mechanics and visco-elastic deformation, allowing for simulation of injection into a pre-stressed reservoir. Observations that are used to evaluate our simulation results against resevoir data include pressure at the wellhead, CO2 filled porosity, CO2 flux over time, distribution of CO2 in the reservoir, spreading of CO2 underneath the caprock and pattern (chimney) fomation. Our model helps to understand and explain under which conditions localization of fluid will occure and is also applicable to the injection of other fluids (e.g. waste water).