A reliable estimation of in situ stress orientation and magnitude is necessary for determining wellbore stability in the oil and gas industry, or assessing excavation stability for mining and civil engineering projects. Methods of stress estimation in deep borehole investigations are generally limited to the use of hydraulic methods or borehole imaging techniques, which identify borehole breakouts and/or borehole deformation. However, the collection of data in a thrust regime, or in horizontally laminated ground, can be difficult and lead to unreliable results. Moreover, the back analysis of stress magnitude from both hydraulic methods and borehole imaging methods are sensitive to estimates of strength and elastic properties around the borehole. This research has shown that the magnitude of the axial stress relative to the stresses normal to the borehole axis contributes to the magnitude and distribution of maximum deviatoric stress experienced around an advancing borehole. Furthermore, an analysis of the stress path incorporating the complete stress tensor shows that the maximum deviatoric stress does not always correlate with the typical solutions for induced stresses around a circular excavation. As a result of the limitations and uncertainties associated with traditional stress estimation methods, an integrated approach to determining the stress conditions at a given site using numerical models to simulate the loading history has been evaluated. A 2-dimensional finite element model of the Paleozoic sedimentary sequence of the eastern edge of the Michigan basin has shown that a systematic incorporation of the geological and stress history can approximate a given stress profile. Numerical models are also applied for estimating the magnitude of glacially induced stress change in the upper crust for the purpose of estimating long-term stress evolution. The framework and methodology used for numerical stress reconstruction and evolution can be included at the site characterization and engineering design stages for various types of projects, including deep geologic repositories, where estimates of in situ stress and future stress change are important. / Thesis (Master, Geological Sciences & Geological Engineering) -- Queen's University, 2013-04-29 13:26:53.082

Scenarios developed by the National Energy Board of Canada predict that Canadian unconventional gas production, including coalbed methane (CBM), may be required to meet Canadian energy demands by the year 2008, and could constitute up to 65% of supply by 2025. Although there has been considerable CBM exploration and development in Alberta in recent years, there has been relatively limited activity in Saskatchewan.<p>The in-situ stress regime can have a strong influence on coal bed methane (CBM) production, coal permeability, hydraulic fracturing pressure, and borehole stability while drilling horizontal wells. A limited number of stress regime analyses have been conducted previously on a regional scale, for the entire Western Canada Sedimentary Basin (WCSB), but none has been conducted with a focus on Saskatchewan. The primary objective of this study was to investigate in-situ stress magnitudes and orientations in southwestern Saskatchewan. The secondary objective was to quantify the influence of in-situ stresses on operational practices that would be used to exploit CBM targets.<p>Analysis of vertical stress magnitudes and gradients were conducted using bulk density data compiled for 257 wells in southwest Saskatchewan. Vertical stress magnitudes calculated at the base of the Belly River Formation in the region where its CBM potential is greatest were found to be in the 6 to 12 MPa range. Vertical stress magnitudes at the top of the Mannville Group in the region where its CBM potential is greatest were found to be in the 12 to 18 MPa range. Data available for interpretation of minimum horizontal stress magnitudes were considerably more limited. A technique was developed to estimate these magnitudes using fracture stimulation data, which were available for the Viking Formation and Mannville Groups. Using this technique, minimum horizontal stress magnitudes at the top of the Mannville Group in the region of greatest interest were estimated to be 10 to 14 MPa. The results of these analyses suggest that depth is a dominant controlling factor for minimum horizontal stress magnitude, but that pore pressures (sub-normal pressures cause lower stresses) and lithology (shaley rocks, and perhaps coals, have higher stresses) also have notable effects. Insufficient data were obtained for direct estimation of minimum horizontal stresses in the Belly River Formation. Minimum horizontal stress magnitudes in this formation might be quite close to vertical stress magnitudes.<p>Borehole breakouts were analyzed to interpret the orientation of maximum horizontal stress (¥òHmax) in the study area. The mean orientation of the mean borehole breakouts gives a 137¨¬ with a circular standard deviation of 12¨¬, which parallels the minimum horizontal stress in the study area with a notable inflection overlying the Swift Current platform. The data is portrayed in a trajectory map. The trajectories indicated on the map can be used for predicting the orientation of induced hydraulic fractures, and the likely orientation of face cleats in coals. Knowledge of the orientations of these features is essential to effective development of CBM resources.<p>Based on the stress and pore pressure data presented in this thesis, it is anticipated that minimum effective stresses in the Belly River coals will typically be a few MPa, and up to 10 MPa in the Mannville coals. A very rough estimate of permeabilities based on the data compiled for various Canadian coals suggests that permeabilities could be in the 0.01 to 10 millidarcy range for the former, and 0.01 to 1 millidarcy range for the latter. <p>Borehole stability analyses were conducted for both the Belly River Formation and the Mannville Group. The results suggest that horizontal drilling of the Mannville coals should be feasible, without the need for high-density drilling muds. Given that the Belly River coals occur in numerous thin seams, they are most likely to be developed using vertical wells. Borehole instability is not likely to be a major problem in these vertical wells.<p>Recommendations are provided for laboratory investigation of coal permeabilities and mechanical properties, field testing for minimum horizontal stress magnitudes in coal seams and adjacent strata, and additional analysis of existing fracture stimulation, log and core data for strata not analyzed in this project.

Scenarios developed by the National Energy Board of Canada predict that Canadian unconventional gas production, including coalbed methane (CBM), may be required to meet Canadian energy demands by the year 2008, and could constitute up to 65% of supply by 2025. Although there has been considerable CBM exploration and development in Alberta in recent years, there has been relatively limited activity in Saskatchewan.<p>The in-situ stress regime can have a strong influence on coal bed methane (CBM) production, coal permeability, hydraulic fracturing pressure, and borehole stability while drilling horizontal wells. A limited number of stress regime analyses have been conducted previously on a regional scale, for the entire Western Canada Sedimentary Basin (WCSB), but none has been conducted with a focus on Saskatchewan. The primary objective of this study was to investigate in-situ stress magnitudes and orientations in southwestern Saskatchewan. The secondary objective was to quantify the influence of in-situ stresses on operational practices that would be used to exploit CBM targets.<p>Analysis of vertical stress magnitudes and gradients were conducted using bulk density data compiled for 257 wells in southwest Saskatchewan. Vertical stress magnitudes calculated at the base of the Belly River Formation in the region where its CBM potential is greatest were found to be in the 6 to 12 MPa range. Vertical stress magnitudes at the top of the Mannville Group in the region where its CBM potential is greatest were found to be in the 12 to 18 MPa range. Data available for interpretation of minimum horizontal stress magnitudes were considerably more limited. A technique was developed to estimate these magnitudes using fracture stimulation data, which were available for the Viking Formation and Mannville Groups. Using this technique, minimum horizontal stress magnitudes at the top of the Mannville Group in the region of greatest interest were estimated to be 10 to 14 MPa. The results of these analyses suggest that depth is a dominant controlling factor for minimum horizontal stress magnitude, but that pore pressures (sub-normal pressures cause lower stresses) and lithology (shaley rocks, and perhaps coals, have higher stresses) also have notable effects. Insufficient data were obtained for direct estimation of minimum horizontal stresses in the Belly River Formation. Minimum horizontal stress magnitudes in this formation might be quite close to vertical stress magnitudes.<p>Borehole breakouts were analyzed to interpret the orientation of maximum horizontal stress (¥òHmax) in the study area. The mean orientation of the mean borehole breakouts gives a 137¨¬ with a circular standard deviation of 12¨¬, which parallels the minimum horizontal stress in the study area with a notable inflection overlying the Swift Current platform. The data is portrayed in a trajectory map. The trajectories indicated on the map can be used for predicting the orientation of induced hydraulic fractures, and the likely orientation of face cleats in coals. Knowledge of the orientations of these features is essential to effective development of CBM resources.<p>Based on the stress and pore pressure data presented in this thesis, it is anticipated that minimum effective stresses in the Belly River coals will typically be a few MPa, and up to 10 MPa in the Mannville coals. A very rough estimate of permeabilities based on the data compiled for various Canadian coals suggests that permeabilities could be in the 0.01 to 10 millidarcy range for the former, and 0.01 to 1 millidarcy range for the latter. <p>Borehole stability analyses were conducted for both the Belly River Formation and the Mannville Group. The results suggest that horizontal drilling of the Mannville coals should be feasible, without the need for high-density drilling muds. Given that the Belly River coals occur in numerous thin seams, they are most likely to be developed using vertical wells. Borehole instability is not likely to be a major problem in these vertical wells.<p>Recommendations are provided for laboratory investigation of coal permeabilities and mechanical properties, field testing for minimum horizontal stress magnitudes in coal seams and adjacent strata, and additional analysis of existing fracture stimulation, log and core data for strata not analyzed in this project.

No description available.

Reliable and inexpensive methods of in-situ stress measurement have been sought for more than 40 years. A number of non-destructive core-based methods of in-situ stress determination are currently available, among which Deformation Rate Analysis ' DRA ' and Acoustic Emissions ' AE ' method have the most promising potential due to their ability to measure stress as opposed to strain, which is measured by strain recovery techniques. The DRA and AE method are similar in their utilisation of a phenomenon termed Kaiser effect in the case of AE and deformation memory effect in the case of DRA. The KE/DME is defined as a recollection of a maximum stress a rock core had been subjected prior to its retrieval from the in-situ environment. The physical nature of this phenomenon has not however been universally established. In this study, interaction of microcracks as the most probable cause of the KE/DME, was investigated. To reproduce the damage that occurs to rock at the micro level, a discrete element modelling code was required, which enabled dynamic failure propagation to be modelled. Commercially available code PFC [ superscript 2D ] was found to be suitable for this purpose due to its ability to explicitly model mechanical damage in rocks. The numerical model was based on a real prototype - a sandstone rock core, which had also been previously subjected to the DRA. Although the bulk of the numerical tests were conducted on intact rock models, it was found that changes in the lithology and introduction of discontinuities did not have significant effect on the DME. Influence of the confining stress on the DME was confirmed. It was assumed that only the highest historical stress could be determined reliably using the DRA technique. The ability of the numerical model to reproduce the DME was validated. The link between the DME and development of microcracks was established. The results of the study encourage further use of the code for understanding the micromechanical behaviour of rocks under loading. / Thesis (M.Eng.Sc.)--Australian School of Petroleum, 2004.

Geothermal energy is being explored as a supplement to traditional fossil fuel resources to meet growing energy demand and reduce carbon emissions. Geothermal energy plants harvest heat stored in the Earth’s subsurface by bringing high temperature fluids to the surface and generating steam to produce electricity. Development of geothermal resources is often inhibited by large upfront risk and expense. Successful mitigation of those costs and risks begins with efficient characterization of the resource before development. A typically successful geothermal reservoir consists of a fractured reservoir that conducts hydrothermal fluids and a cap rock seal to limit convective heat loss through fluid leakage. The controls on the system include the density and orientation of fractures, mechanical rock properties, and the local stress field acting on those rocks. The research presented in this dissertation utilizes diverse data sets to characterize core, wireline borehole logs, and laboratory data to describe the distribution of fractures, rock properties, and the orientation and magnitude of stresses acting on the borehole. The research demonstrates there is a potential resource in the region and describes the controls on the vertical extent of the hydrothermal fluids. The distribution of fractures is controlled by the distribution of elastic rock properties and rock strength. A cap rock seal is present that limits hydrothermal fluid loss from a fractured artesian reservoir at 1,745 m (5,726 ft). In addition to characterization of the resource, this research demonstrates that an equivalent characterization can be used in future exploration wells without the expense and risk of collecting core. It also demonstrates that multiple methods of analysis can be utilized simultaneously when some data are not available. Data collection from deep wellbores involves risk and data loss or tool failure is a possibility. In these cases, our methods show that successful characterization is still possible, saving time and money, and minimizing the financial risk of exploration

abstract: This research focuses on the stress and structure evolution observed in-situ during the earliest stages of thin film growth in Cu on Au(111)-reconstruction. For the research, an ultra high vacuum-scanning tunneling microscopy (UHV-STM) system was modified to have the additional capabilities of in-situ deposition and in-situ stress evolution monitoring. The design and fabrication processes for the modifications are explained in detail. The deposition source enabled imaging during the deposition of Cu thin films, while also being columnar enough to avoid negatively impacting the function of the microscope. It was found that the stress-induced changes in piezo voltage occurred over a substantially longer time scale and larger piezo scale than used during imaging, allowing for the deconvolution of the two sources of piezo voltage change. The intrinsic stress evolution observed at the onset of Cu growth was tensile in character and reached a maximum of 0.19 N/m at approximately 0.8ML, with an average tensile slope of 1.0GPa. As the film thickness increased beyond 0.8 ML, the stress became less tensile as the observation of disordered stripe and trigon patterns of misfit dislocations began to appear. The transport of atoms from the surface of enlarged Cu islands into the strained layer played an important role in this stage, because they effectively reduce the activation barrier for the formation of the observed surface structures. A rich array of structures were observed in the work presented here including stripe, disordered stripe and trigon patterns co-existing in a single Cu layer. Heteroepitaxial systems in existing literature showed a uniform structure in the single layer. The non-uniform structures in the single layer of this work may be attributed to the room temperature Cu growth, which can kinetically limit uniform pattern formation. The development of the UHV-STM system with additional capabilities for this work is expected to contribute to research for the stress and structure relationships of many other heteroepitaxial systems. / Dissertation/Thesis / Ph.D. Materials Science and Engineering 2012

An imperative task for successful underground mining is to ensure the stability of underground structures, since it influences the safety, and in turn, the production capacity and economic performance of the mine. This is more so for deep excavations in soft rock which may be under significantly high stresses. In this thesis, stability studies on two tunnels, a horseshoe-shaped and an inverted arch-shaped tunnel, have been presented. The tunnels, running at a depth of 1325 m, are part of the Xiezhuang Coal Mine, in the Xinwen mining area, in China. Using the available information on stratigraphy, geological structures, in-situ stress measurements and geo-mechanical properties of intact rock and discontinuity interfaces, a three-dimensional numerical model has been built using the 3DEC 3-Dimensional Distinct Element Code to simulate the stress conditions around the tunnels. Based on available discontinuity geometry constraints, the rock mass has been modelled as a mixture of a discontinuum medium close to the tunnels and as an equivalent-continuum in the far field. Due to the unavailability of field measurements for rock mass mechanical parameters, the parameters have been estimated by incorporating the available intact rock mechanical properties and field deformation monitoring data into a strength reduction model calibration procedure. This back-analysis (calibration) has been carried out through a pseudo-time dependent support installation routine which incorporates the effect of time through a stress-relaxation mechanism. The results from the back-analysis indicate that the rock mass cohesion, tensile strength, uniaxial compressive strength, and elastic modulus values are about 35-45 % of the corresponding intact rock property values. Additionally, the importance of incorporating stress relaxation before support installation in numerical modeling has been illustrated, for the first time in literature, through the increased support factors of safety and reduced grout failures. The calibrated models have been analyzed for different supported and unsupported cases in an attempt to quantify the effect of supports in stabilizing the tunnels and to estimate the adequacy of the existing supports being used in the mine. A direct outcome is that the findings indicate that longer supports may be better suited for the existing geo-mining conditions around the tunnels since they have fractured zones that are larger than the supports currently in use at the mine. The effects of supports have been demonstrated using changes in deformations and yield zones around the tunnels, and changes in the average factors of safety and grout failures of the supports. The use of longer supports and floor bolting has provided greater stability for the rock masses around the tunnels. A comparison between the closure strains in the two differently shaped tunnels indicates that the inverted arch tunnel may be more efficient in reducing roof sag and floor heave for the existing geo-mining conditions. Additional analyses focusing on parametric sensitivity studies on the rock and joint mechanical properties show that the tunnel stability is highly sensitive to changes in cohesion and internal friction angle of the intact rock, and changes in joint basic friction angle. Tunnel stability is seen to not be very sensitive to changes in intact rock tensile strength and joint shear stiffness for the tunnels being studied. Finally, support optimization studies conducted by studying the effect of changing cable diameters and grout uniaxial compressive strengths on support factors of safety and grout failures show the trade-off that is necessary in selecting cable strength vis-à-vis grout strength. The results indicate that simply increasing either one of cable or grout strength parameters without considering their interactions and compatibilities could be detrimental to the stability of the support system.

A case study is considered in which data produced by different techniques have been gathered in various locations within a rock mass in which topography effects are most likely significant. Measurements were performed for the design of a re-powering scheme that includes a new hydraulic conduit and an underground cavern that will primarily be excavated in granite. An integrated approach for extrapolating the results from the various in situ tests to the rock mass volume of interest for the hydroelectric power scheme is presented. This approach includes the development of an equivalent continuum mechanics model. The integration of in situ tests and numerical modelling enables to determine the stress spatial variation which helps ascertain the loading mechanism at the origin of the measured stress field as well as the long-term rheological behavior of the equivalent geomaterial under consideration.

Considérons un cas d’étude dans lequel les données produites par différentes techniques ont été obtenues en divers points d’une masse rocheuse où les effets topographiques sont très probablement significatifs. Les mesures ont été effectuées pour la conception du réseau hydroélectrique. Le réseau comprend une conduite hydraulique ainsi qu’une nouvelle centrale souterraine placée à mi-parcours de la conduite et sera principalement creusé dans le granite. Les diverses données ont été intégrées à un modèle continu équivalent afin d’évaluer le champ de contrainte régional et ainsi d’extrapoler les résultats des divers tests au volume de masse rocheuse concerné par le plan hydroélectrique. L'intégration des essais in situ et du modèle permet de déterminer les variations spatiales du champ de contrainte. Il est ainsi possible d’identifier le mécanisme de chargement à l’origine du champ de contrainte mesuré ainsi que le comportement rhéologique à long terme du géomatériel équivalent considéré. / A case study is considered in which data produced by different techniques have been gathered in various locations within a rock mass in which topography effects are most likely significant. Measurements were performed for the design of a re-powering scheme that includes a new hydraulic conduit and an underground cavern that will primarily be excavated in granite. An integrated approach for extrapolating the results from the various in situ tests to the rock mass volume of interest for the hydroelectric power scheme is presented. This approach includes the development of an equivalent continuum mechanics model. The integration of in situ tests and numerical modelling enables to determine the stress spatial variation which helps ascertain the loading mechanism at the origin of the measured stress field as well as the long-term rheological behavior of the equivalent geomaterial under consideration.