Reservoir geomechanics is a production induced phenomena that is experienced in large number of fields around the world. Hydrocarbon production changes the pore pressure which in turn alters the in-situ stress state. For reservoirs that are either stress sensitive or where rock is soft and unconsolidated, stresses have appreciable effect on rock properties like porosity and permeability. Anisotropic and isotropic permeability changes affect flow direction and movement of flood front thereby influencing well performance and reservoir productivity. Coupling of geomechanical calculation with multi-phase flow calculation is needed to make prudent predictions about the reservoir production and recovery. The post processing tools provided with the simulators cannot monitor flood front movement and fail to capture important information like flow directionality and dominant phase in a flow. Geomechanical simulation is combined with streamline tracing to aid in better understanding of the reservoir dynamics through visualization of flow patterns in the reservoir. Streamline tracing is a proved reservoir engineering tool that is widely used by industry experts to capture information on flood movement, injector-producer relations and swept area. In the present research, we have incorporated total velocity streamlines and phase streamlines for coupled geomechanical simulation and compared the results with streamline tracing for conventional reservoir simulator to explain geomechanics behavior on reservoir flow processes in a more detailed and appealing manner. Industry standard simulators are used for coupled geomechanical simulation and conventional simulation and streamline tracing has been done through in-house tracing code. The research demonstrates the benefits and power of streamline tracing in visualizing flow patterns through work on two cases; first, a synthetic case for studying water injection in a five spot pattern and second, a SPE 9th comparative study. The research gives encouraging results by showing how geomechanics influences reservoir flow paths and reservoir dynamics through visualization of flow. The streamlines captures flow directionality, information regarding appearance and disappearance of gas phase and the connectivity between injector and producer.

Philosophiae Doctor - PhD / Geomechanical analysis and integrity assessment of hydrocarbon reservoirs upon depletion and injection are crucial to ensure that CO2 storage projects can be safely implemented. The Bredasdorp Basin in South Africa has great potential for CO2 storage, given its hugely available exploration data. However, there has not been any geomechanical characterization carried out on this basin to determine its integrity issues. This study aims to investigate the feasibility of a carbon storage project in the E-M depleted gas field. The preliminary geological assessment demonstrates that Zone 2 and Zone 3 display acceptable injectivity for CO2 injection of the E-M gas field. Seismic lines display faults that could affect the caprock's integrity during depletion and carbon storage. Geomechanical characterization provides a guideline as to how geomechanical analysis of depleted fields can be done for a safe CO2 sequestration practice. The geomechanical model constructed at a depth of 2570 m indicated that the magnitudes of the principal vertical, minimum, and maximum horizontal stresses in the field are respectively 57 MPa, 41 MPa, and 42-46 MPa. Fault and fracture stabilities were examined before and after depletion. It was found that faults and fractures in compartments C1 and C2 of the reservoir are stable before and after depletion, while normal faults (FNS8 and FNS9) in compartment C3 dipping SW were critically stressed. The minimum sustainable pressure of the reservoir determined by simulating depletion is 6 MPa. Below that, pressure depletion causes normal faulting in reservoir compartments C1 and C2. The maximum sustainable pressure, on the other hand, was found to be 25 MPa. The geomechanical studies also reveal that it is possible that the reservoir experienced compaction of 8 cm during depletion and will experience an uplift of 3.2 cm during 71 years of injection. The economic model of a CO2-enhanced gas recovery project in E-M gas field, the annual expenses (Aexp) of carbon capture and storage range between Zar20 3.31 × 109 and Zar20 4.10 × 109. The annual revenues (RA) were estimated to be Zar20 1.42 × 1010. The cash flow analysis derived from Aexp and RA confirms that enhanced gas recovery could partially offset the cost of CO2 storage if a minimum of 5 % of CO2 fraction is allowed in the natural gas recovered. Geological and geomechanical studies have demonstrated that carbon storage is physically feasible in the E-M gas field. However, the project's completion lies in the among the gas recovered to balance the cost of CO2. http://

Complex deformation processes observed in massive slow-moving, active, landslides are contributed to by topography, non-uniform shear surfaces, heterogeneous rockmass and shear zone strength characteristics, composite failure mechanisms and hydrogeology. This thesis provides a systematic means to account for geology, geomorphology and geomechanics when interpreting slope deformation processes. Significant contributions to the field of landslide geomechanics have been made by analyzing how spatially discriminated slope deformations are influenced by spatial variation of geological and geotechnical factors and temporal changes in piezometric levels. The Downie and Beauregard landslides are massive instabilities that have extensive histories of slope monitoring and observational assessment, and where detailed site investigations have been completed. A methodology has been developed for the interpretation of 3-dimensional shear zone geometries using spatial prediction algorithms complemented by sound engineering judgment. The applicability of this process to other spatial data, such as displacement or piezometric records and measurements of material properties is demonstrated. Composite landslide deformations have been analyzed for both Downie and Beauregard to characterize global slope behaviour and identify localized events. Furthermore, a new interpretation of landslide morphological regions at Downie is provided. The research presented in this thesis demonstrates the importance and value of 3-dimensional numerical modelling. A rigorous procedure to numerically simulate large landslides has been developed. This sophisticated method accounts for complex geometries, heterogeneous shear zone strength parameters, internal shears, interaction between discrete landslide zones and piezometric fluctuations. This advance in state-of-the-art landslide modelling provides an important tool for investigating dynamic landslide systems. Based on Downie and Beauregard field data numerical models have been calibrated to reproduce observed slope behaviour. The calibration process has provided insight on key factors controlling massive slope mechanics. Calibrated models are used to investigate how trigger scenarios may accelerate deformations at Downie and the effectiveness of a proposed slope drainage system at Beauregard. The ability to reproduce observed behaviour and forward test hypothesized changes to boundary conditions has valuable application in landslide hazard management. The capacity of decision makers to interpret large amounts of data, respond to rapid changes in a system and understand complex slope dynamics has been enhanced. / Thesis (Ph.D, Geological Sciences & Geological Engineering) -- Queen's University, 2010-09-24 14:13:43.605

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In recent years, hydraulic fracturing has led to a dramatic increase in the worldwide production of natural gas. In a typical hydraulic fracturing treatment, millions of gallons of water, sand and chemicals are injected into a reservoir to generate fractures in the reservoir that serve as pathways for fluid flow. Recent research has shown that both the effectiveness of fracturing treatments and the productivity of fractured reservoirs can be heavily influenced by the presence of pre-existing natural fracture networks. This work presents a fully implicit hydro-mechanical algorithm for modeling hydraulic fracturing in complex fracture networks using the two-dimensional discontinuous deformation analysis (DDA). Building upon previous studies coupling the DDA to fracture network flow, this work emphasizes various improvements made to stabilize the existing algorithms and facilitate their convergence. Additional emphasis is placed on validation of the model and on extending the model to the stochastic characterization of hydraulic fracturing in naturally fractured systems. To validate the coupled algorithm, the model was tested against two analytical solutions for hydraulic fracturing, one for the growth of a fixed-length fracture subject to constant fluid pressure, and the other for the growth of a viscosity-storage dominated fracture subject to a constant rate of fluid injection. Additionally, the model was used to reproduce the results of a hydraulic fracturing experiment performed using high-viscosity fracturing fluid in a homogeneous medium. Very good agreement was displayed in all cases, suggesting that the algorithm is suitable for simulating hydraulic fracturing in homogeneous media. Next, this work explores the relationship between the maximum tensile stress and Mohr-Coulomb fracture criteria used in the DDA and the critical stress intensity factor criteria from linear elastic fracture mechanics (LEFM). The relationship between the criteria is derived, and the ability of the model to capture the relationship is examined for both Mode I and Mode II fracturing. The model was then used to simulate the LEFM solution for a toughness-storage dominated bi-wing hydraulic fracture. Good agreement was found between the numerical and theoretical results, suggesting that the simpler maximum tensile stress criteria can serve as an acceptable substitute for the more rigorous LEFM criteria in studies of hydraulic fracturing. Finally, this work presents a method for modeling hydraulic fracturing in reservoirs characterized by pre-existing fracture networks. The ability of the algorithm to correctly model the interaction mechanism of intersecting fractures is demonstrated through comparison with experimental results, and the method is extended to the stochastic analysis of hydraulic fracturing in probabilistically characterized reservoirs. Ultimately, the method is applied to a case study of hydraulic fracturing in the Marcellus Shale, and the sensitivity of fracture propagation to variations in rock and fluid parameters is analyzed.

El texto completo de este trabajo no está disponible en el Repositorio Académico UPC por restricciones de la casa editorial donde ha sido publicado. / The application of conventional techniques, such as kriging, to model rock mass is limited because rock mass spatial variability and heterogeneity are not considered in such techniques. In this context, as an alternative solution, the application of the Gaussian simulation technique to simulate rock mass spatial heterogeneity based on the rock mass rating (RMR) classification is proposed. This research proposes a methodology that includes a variographic analysis of the RMR in different directions to determine its anisotropic behavior. In the case study of an underground deposit in Peru, the geomechanical record data compiled in the field were used. A total of 10 simulations were conducted, with approximately 6 million values for each simulation. These were calculated, verified, and an absolute mean error of only 3.82% was estimated. It is acceptable when compared with the value of 22.15% obtained with kriging.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第17875号 / 工博第3784号 / 新制||工||1579(附属図書館) / 30695 / 京都大学大学院工学研究科都市社会工学専攻 / (主査)教授 松岡 俊文, 教授 大津 宏康, 准教授 村田 澄彦 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Au cours de la production d'hydrocarbures, l'extraction de fluides fait décroître la pression de pore dans les réservoirs (« depletion »). Ceci induit un changement du champ de contraintes qui résulte en une augmentation des contraintes effectives appliquées sur le réservoir. Les mesures in situ montrent que les variations de contraintes peuvent être décrites par un paramètre appelé chemin de chargement (stress path), défini comme le rapport entre la variation de contrainte effective horizontale et la variation de contrainte effective verticale par rapport aux conditions initiales dans le réservoir. La compaction induite par la production d'hydrocarbures peut avoir de graves conséquences dans le cas de roches faiblement consolidées car elle induit des variations des propriétés pétrophysiques des roches in situ, notamment de la perméabilité, un des paramètres les plus importants pour estimer la performance d'un réservoir mais aussi un des plus difficiles à mesurer. Pour compliquer encore les choses, la perméabilité est souvent anisotrope dans les réservoirs avec de forts contrastes entre la perméabilité horizontale kh et la perméabilité verticale kv.L'objectif de cette étude est de comprendre l'influence des chemins de chargement sur le comportement mécanique et les évolutions couplées de perméabilité pour un sable quartzeux (Sable de la Durance, DS) et un grès faiblement consolidé (grès d'Otter Sherwood, OSS, qui constitue la roche réservoir du champ pétrolier de Wytch Farm en Angleterre). Nos résultats montrent que le grès peu consolidé présente un comportement mécanique similaire à celui de roches consolidées. Au contraire, le sable présente un comportement différent, avec une transition plus graduelle entre les régimes de déformation qui nécessite d'utiliser un critère basé sur l'évolution du rayon de courbure des courbes contraintes-déformations pour déterminer les contraintes limites : cette méthode a été validée par une étude d'analyse des émissions acoustiques pour caractériser l'endommagement. Les domaines de déformation élastique et plastique ont été bien définis et les contraintes limites ont été comparées aux prédictions du modèle Cam-Clay modifié et du modèle d'enveloppe limite normalisée. Les perméabilités horizontale et verticale ont été mesurées sous contraintes. Pour analyser l'influence des effets de bord dans les essais mécaniques, les perméabilités mesurées soit classiquement sur toute la longueur de l'échantillon, soit entre deux points intermédiaires ont été comparées. Pour l'écoulement horizontal, les facteurs géométriques et facteurs d'anisotropie ont été déterminés par des simulations numériques en éléments finis afin de pouvoir déterminer les vraies valeurs de perméabilité horizontale. L'évolution de la perméabilité suit l'évolution de la déformation des matériaux et est contrôlée aussi bien par la déformation volumique que par la déformation en cisaillement. A partir de nos mesures il est possible de séparer l'effet de la pression moyenne de l'effet de la contrainte déviatorique sur l'évolution de la perméabilité en construisant des cartes d'isoperméabilités dans l'espace des contraintes. Enfin une modélisation élasto-plastique a été réalisée pour prédire le comportement hydro-mécanique du grès faiblement consolidé. L'approche utilisée permet de prédire de manière satisfaisante l'évolution de la perméabilité avec les contraintes, à partir d'une loi exponentielle fonction de la déformation effective. Au contraire, pour le sable de la Durance le lien entre l'évolution de la perméabilité et la déformation est loin d'être évidente, notamment aux faibles contraintes où la réduction de perméabilité est très rapide. Pour mieux comprendre ces évolutions de perméabilité, une analyse de l'endommagement a été réalisée par des mesures sur échantillons et en utilisant des techniques d'imagerie à plusieurs échelles. / During hydrocarbon production, the extraction of fluid induces a decrease of pore pressure called depletion. This depletion causes a change in the stress field that results in an increased stress on the rock by enhancement of the effective stress in the reservoir. In situ measurements show that the stress variations can be described by the so-called stress path parameter, defined as the ratio of the change in effective horizontal stress by the change in effective overburden stress from initial reservoir conditions. This production induced compaction can have severe consequences in the case of poorly consolidated reservoirs. Compaction induces variations of petrophysical properties of in situ rocks and particularly permeability variations, one of the most important parameters controlling reservoir performance. Yet it is one of the most difficult property to measure. To complicate matters further, permeability anisotropy is often found in reservoirs. Therefore the horizontal permeability kh, may be different from the vertical permeability kv.The aim of this study is to understand the influence of stress paths on the mechanical behavior and coupled permeability evolutions of a Quartz sand (Durance Sand, DS) and a weakly consolidated sandstone (Otter Sherwood Sandtone, OSS which is the reservoir rock of the Wytch Farm oil field, UK). We found that the weakly consolidated rock presents a mechanical behavior similar to that of consolidated rocks. However, the sand shows a different behavior, with a gradual transition regime which requires the use of a curvature criterion to peak yield stresses on the stress-strain evolution plot; this criterion has been validated on the basis of Acoustic Emission analysis. The elastic and plastic deformation regimes are well identified and the determined yield stresses are fitted using the modified Cam-Clay and Elliptic Cap models for all observed onsets of plastic yielding. Both vertical and horizontal permeability have been measured during loading. To analyze the influence of end effects during loading in the triaxial cell, permeabilities measured over the mid-section and over the total core length were compared. For the horizontal flow, the geometrical and anisotropy factors were determined using Finite Element simulations in order to calculate the correct horizontal permeability. Permeability evolution follows closely the material deformation and is controlled by both volumetric and shear strains. It is possible to infer the effect of the mean pressure and/or the deviatoric stress on the permeability evolution by building isopermeability maps in the stress space. Finally, an application of elasto-plastic modeling to predict the hydromechanical behavior of the weakly consolidated rock is presented. This approach allows a satisfying prediction of the permeability evolution with stresses, using an exponential function of an effective strain. Reversely for DS, the link between strain and permeability is not obvious as permeability reduction is pronounced at early stage of loading. To understand these permeability evolutions, a damage analysis has been performed using core analysis measurements and multi-scale imaging.

[pt] Os reservatórios de hidrocarbonetos em rochas carbonáticas representam aproximadamente 50 por cento da produção mundial de petróleo e tem por característica marcante sua complexidade, uma vez que são bastante heterogêneos. No Brasil, as rochas carbonáticas ganharam uma grande importância com a descoberta dos reservatórios carbonáticos do pré-sal. Entender e caracterizar estes reservatórios, que apresentam baixas taxas de penetração, exigirá grandes esforços em pesquisa e desenvolvimento. Uma pequena contribuição neste sentido é proporcionada nesta dissertação, onde três distintas rochas carbonáticas, o travertino romano, o travertino turco e o travertino de Itaboraí, foram caracterizadas geológica e geomecanicamente. O programa experimental consistiu na caracterização mineralógica, química, textural e diagenética, bem como na realização de ensaios de resistência e de porosidade. De posse dos resultados do programa experimental buscou-se correlações entre os índices/propriedades/parâmetros determinados. Verificou-se que a resistência à compressão simples dos materiais é diretamente proporcional, a sua densidade, a sua velocidade de propagação de ondas e ao índice esclerométrico; e inversamente proporcional a sua porosidade. Constatou-se ainda que a velocidade de propagação de ondas dos materiais é diretamente proporcional a sua densidade e inversamente proporcional a sua porosidade. / [en] Hydrocarbon reservoirs in carbonate rocks represent circa 50 percent of all oil produced worldwide. Those reservoirs are very complex since they are quite heteregeneous. In Brazil, carbonate rocks gained a great importance with the discovery of the pre-salt reservoirs. Understand and characterize these reservoirs, that present low penetration rates, will require major efforts in research and development. A small contribution in this regard is provided in this dissertation, where three travertines (i.e., Roman, Turkish and Itaboraí) were geologically and geomechanically characterized. The experimental program consisted in the chemical, mineralogical, textural and diagenetic characterization, as well as strength and porosity tests. A comprehensive analysis of test results from the experimental program was carried out in order to seek correlations between the indexes/properties/parameters determined. It was found that the unconfined compression strength of materials is directly proportional to its density, its velocity of ultrasonic wave propagation and to Schmidt test hammer index; and inversely proportional to its porosity. It was also found that the velocity of ultrasonic wave propagation of materials is directly proportional to its density and inversely proportional to its porosity.

Coalbeds are an extremely complicated porous medium with characteristics of heterogeneity, dual porosity and stress sensitivity. In the past decades great achievements have been made to the simulation models of pressure depletion coalbed methane (CBM) recovery process and CO2 sequestration and enhanced coalbed methane (ECBM) recovery process. However, some important mechanisms are still not or not properly included. Among them, the influence of geomechanics is probably the most important one. Because of its influence coalbed permeability, the key parameter for the success of recovery processes, changes drastically with alterations of in situ stresses and strains during these processes. In present reservoir simulators, the change of coalbed permeability is estimated with analytical models. Due to the assumptions and over simplifications analytical models have limitations or problems in application. In this research to properly estimate the changes of permeability and porosity in the simulation of CO2 sequestration and ECBM recovery process, comprehensive permeability and porosity models have been developed with minimum assumptions and simulation methods established. Firstly, a set of continuum medium porosity and permeability coupling models is built up and a simulation procedure to apply these models in reservoir and geomechanical coupled simulations proposed. Using the models and simulation procedure a sensitivity study, mainly on the parameters related to coalbed permeability change and deformation, has been made for the CBM recovery process. Then based on the understanding, a set of discontinuum medium porosity and permeability coupling models is developed and a procedure to apply these models in reservoir and geomechanical coupled simulations presented. The new models are more comprehensive and adaptable, and can accommodate a wide range of coalbeds and in situ conditions. The proposed equivalent continuum deformation model for coal mass is validated by simulating a set of lab tests including a uniaxial compression test in vacuum and a CO2 swelling test under axial constraint in the longitudinal (vertical) direction. At last the discontinuum medium porosity and permeability coupling models and the simulation procedure are successfully applied to simulate part of a series of micro-pilot tests of ECBM and CO2 sequestration at Fenn Big Valley of Alberta, Canada. / Geotechnical Eengineering