- Pau, France
Vincenzo De Gennaro
Schlumberger-Doll Research, PTS, Department Member
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The study of the mechanical behaviour of the soil-structure interfaces in the context of the theoretical framework of strain localization is presented in this paper. Classical conditions for localization of deformation are compared with... more
The study of the mechanical behaviour of the soil-structure interfaces in the context of the theoretical framework of strain localization is presented in this paper. Classical conditions for localization of deformation are compared with other existing criteria and applied, by means of deviatoric hardening constitutive model, to the analysis of the stability in interface tests performed in a purpose-built apparatus. The post-peak behaviour is described applying an homogenisation technique. Results are compared with the observed behaviour.
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This paper investigates development of a finite element model to analyse PiezoCone Penetration Test (PCPT) in unsaturated porous soil. The study is carried out due to presence of a type of marine soil which contains Gas Hydrate. This... more
This paper investigates development of a finite element model to analyse PiezoCone Penetration Test (PCPT) in unsaturated porous soil. The study is carried out due to presence of a type of marine soil which contains Gas Hydrate. This componenet which can be found in seabed sediments of the continental shelf, is stable under special conditions of temperature and pressure. By missing this required condition, the existing theories are unable to predict the soil behaviour, so a numerical code called θ-Stock (Gatmiri, 1997) developed to overcome this problem. The behaviour of soil is considered to be nonlinear elastic and the Piezocone penetration has been modeled in two steps. Interaction of different soil phases have been considered completely coupled. Also all mechanical and hydraulic properties of environment are supposed to be temperature dependent. The intial data of this modeling derived from some field observations in Guinea Golf. The results of this numerical model describe the dissipation and mechanical behavior of these gas hydrate bearing marine sediments with an acceptable accuracy and can be improved in the case of having access to sufficient field observations.
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The integration of data and discipline specific knowledge is a common challenge when attempting to optimize or accelerate an asset's recovery through hydraulic fracture stimulations. Any potential omission of data or understanding... more
The integration of data and discipline specific knowledge is a common challenge when attempting to optimize or accelerate an asset's recovery through hydraulic fracture stimulations. Any potential omission of data or understanding will increase uncertainty and a project's chance of failure. Therefore, when looking to optimize the production of a given asset, it is key to take a holistic approach that breaks down any technical and organisational barriers. This project couples the output of the different subsurface and stimulation disciplines to reduce the uncertainty associated with the production forecast of planned stimulation designs. The following paper presents the integrated approach for the Graben sector of UK's North Sea Clair oil field, largest oil field currently in Europe. Geophysicists, petrophysicists, and geologists generate a static model which is calibrated and validated by reservoir engineers through dynamic reservoir simulation. This model is used to ide...
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Emerging unconventional exploration targets in North Africa are gaining increasing attention. Experience gained over the past two decades on unconventional gas reservoirs (e.g., tight sands, gas shales) has demonstrated that viable... more
Emerging unconventional exploration targets in North Africa are gaining increasing attention. Experience gained over the past two decades on unconventional gas reservoirs (e.g., tight sands, gas shales) has demonstrated that viable economics for unconventional resource plays can only be met if reserves are proved (reservoir quality) and producible (completion quality). With the reservoir quality identified, improved productivity in ultra-low-permeability unconventional reservoirs requires extensive hydraulic fracturing treatment to maximize contact area and unlock resources. North Africa geological settings represent a challenging environment for effective hydraulic fracturing design. Deep reservoir targets, active tectonics and simultaneous occurrence of heterogeneous rock properties (including isotropic and anisotropic behavior) constitute a unique endeavor for a correct geomechanical modeling and a reliable assessment of closure pressures and fracture containment as input for hyd...
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The contributions assembled in the present volume proceed from the lectures of the 2009 ALERT Geomaterials School devoted to the Failure in the multiphase geomaterials. The multiphase behaviour of geomaterials used to be mainly considered... more
The contributions assembled in the present volume proceed from the lectures of the 2009 ALERT Geomaterials School devoted to the Failure in the multiphase geomaterials. The multiphase behaviour of geomaterials used to be mainly considered from the point of view of the serviceability of the structures, or in other terms, of deformation analysis (REGC, Vol. 9, 2005). On the other hand, our understanding of the failure mechanisms in geomaterials exposed to thermal, chemical, and atmospheric fields with all their multiphysical coupling has reached today a fairly mature stage. Just the variety of failure modes and variables involved has expanded significantly. The editors of this volume believe that focusing on failure of geomaterials in the presence of multiphysical phenomena will provide an excellent tool for discussion, learning and outlining future developments in this fascinating and critically important area. The discussed topics aim at providing theoretical, experimental and numer...
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# 202 Time dependent behaviour of fluids filled geomaterials: application to reservoir formations Authors:
این مقاله یک مدل اجزاء محدود را برای تحلیل آزمایش نفوذ پیزوکن (PCPT) در خاک متخلخل غیراشباع ارائه میدهد. لزوم بررسی این آزمایش بخاطر وجود نوعی از خاکهای غیراشباع میباشد که دارای ترکیب هیدرات گاز میباشند. این ترکیب در بستر اقیانوسها و... more
این مقاله یک مدل اجزاء محدود را برای تحلیل آزمایش نفوذ پیزوکن (PCPT) در خاک متخلخل غیراشباع ارائه میدهد. لزوم بررسی این آزمایش بخاطر وجود نوعی از خاکهای غیراشباع میباشد که دارای ترکیب هیدرات گاز میباشند. این ترکیب در بستر اقیانوسها و در قسمت فلات قارهای یافت میشود و تحت شرایط خاصی از فشار و دما پایدار میباشد. با توجه به اینکه پس از ناپایداری این ترکیب، نمیتوان با تئوریهای موجود برای خاک اشباع رفتار خاک را بدرستی مدلسازی کرد، از برنامه ?-Stock (گتمیری-1997) و با اعمال تغییراتی در این مدل، استفاده شدهاست. رفتار خاک الاستیک غیرخطی در نظر گرفته شده و عملیات نفوذ پیزوکن در دو مرحله انجام شدهاست. اندرکنش فازهای مختلف موجود در خاک غیراشباع در حضور تغییرات درجه حرارت بصورت کاملا کوپله در نظر گرفته شدهاست، بطوریکه کلیه خصوصیات مکانیکی و هیدرولیکی محیط وابسته به دما میباشد. اطلاعات اولیه این مدلسازی از آزمایشهای میدانی انجام شده در خلیج گینه بدست آمدهاست. نتایج این تحقیق حاکی از توانایی کیفی مدل عددی مذکور در پیشبینی رفتار رسوبات دریایی دارای هیدرات گاز میباشد و با داشتن د...
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The compaction of chalky reservoirs during oil extraction and other important problems like the "casing collapse" or the "chalk production" are related to the mechanical properties of chalk. Controlling compaction is... more
The compaction of chalky reservoirs during oil extraction and other important problems like the "casing collapse" or the "chalk production" are related to the mechanical properties of chalk. Controlling compaction is very important because reservoir deformations imply seabed subsidence that endangers the offshore stations. The first explanation of subsidence links the compaction to the pore pressure decrease in the reservoir. The solution was the injection of gas and water into the oilfield in order to repressurise the reservoir. But the waterflooding induced additional subsidence. Though many studies have been already performed on chalks, the basis mechanism of the water sensitivity was not defined. Obviously, no satisfactory constitutive law can be written without this deep insight of the phenomenon. This is the scope of the ongoing EC Research Program Pasachalk. The origin of the research is in the comparison of experimental results obtained on Lixhe chalk and...
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The paper presents a benchmarking study carried out within the ‘Mechanics of Unsaturated Soils for Engineering' (MUSE) network aimed at comparing different techniques for measurement and control of suction. Techniques tested by the... more
The paper presents a benchmarking study carried out within the ‘Mechanics of Unsaturated Soils for Engineering' (MUSE) network aimed at comparing different techniques for measurement and control of suction. Techniques tested by the eight ‘Mechanics of Unsaturated Soils for Engineering' research teams include axis-translation (pressure plate and suction-controlled oedometer), high-capacity tensiometer and osmotic technique. The soil used in the exercise was a mixture of uniform sand, sodium bentonite (active clay) and kaolinite (non-active clay), which were all commercially available. Samples were prepared by one team and distributed to all other teams. They were normally consolidated from slurry under one-dimensional conditions (consolidometer) to a given vertical stress. The water retention characteristics of the initially saturated specimens were investigated along the main drying path. Specimens were de-saturated by applying suction through the liquid phase when using an ...
Research Interests: Civil Engineering, Environmental Science, Geology, Numerical Modeling, Geotechnical Engineering, and 15 moreGenetic Algorithms, Soil Mechanics, Soil Dynamics, Earthquake Geotechnical Engineering, Optimization Methods, Soil Investigation and Testing, Soil Behavior, Bentonite, Geotechnique, Osmotic Suction, Excavations, Finite Element Simulations, Slurry, Soil Foundations, and Géotechnique
The contributions assembled in the present volume proceed from the lectures of the 2009 ALERT Geomaterials School devoted to the Failure in the multiphase geomaterials. The multiphase behaviour of geomaterials used to be mainly considered... more
The contributions assembled in the present volume proceed from the lectures of the 2009 ALERT Geomaterials School devoted to the Failure in the multiphase geomaterials. The multiphase behaviour of geomaterials used to be mainly considered from the point of view of the serviceability of the structures, or in other terms, of deformation analysis (REGC, vol. 9, 2005). On the other hand, our understanding of the failure mechanisms in geomaterials exposed to thermal, chemical, and atmospheric fields with all their multiphysical coupling has reached today a fairly mature stage. Just the variety of failure modes and variables involved has expanded significantly. The editors of this volume believe that focusing on failure of geomaterials in the presence of multiphysical phenomena will provide an excellent tool for discussion, learning and outlining future developments in this fascinating and critically important area.
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With growing worldwide activity in exploration and development of ultra-low permeability unconventional reservoirs the O&G industry has become increasingly dependent on efficient and effective horizontal wells drilling as well as... more
With growing worldwide activity in exploration and development of ultra-low permeability unconventional reservoirs the O&G industry has become increasingly dependent on efficient and effective horizontal wells drilling as well as hydraulic fracture completions to increase surface area and promote gas migration. Integrated geomechanical workflow allows encompassing rigorous 3D stress modelling provided by VISAGE* system, hydraulic fracture modelling by P3D model, near wellbore analyses and drillling optimization techniques. Solutions span from data screening, throughout data integration and analysis and finally to well design support covering various scales. They rely on a more accurate 3D stress field characterization, reflecting the structure, heterogeneity/anisotropy, pressure, temperature effects from well to reservoir scale.
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The contribution of geomechanics to provide a rigorous quantification of porosity changes and associated permeability changes is often neglected when considering hydrocarbon production. However, it often has significant effects on... more
The contribution of geomechanics to provide a rigorous quantification of porosity changes and associated permeability changes is often neglected when considering hydrocarbon production. However, it often has significant effects on production rates and ultimate recovery. For the cold heavy oil production with sand (CHOPS) technique, geomechanics is the key for reservoir simulations and promoting successful operations. In fact, the technique employed in CHOPS significantly affects the stress state within the reservoir by inducing “on-purpose” formation damage. It is not only vital to comprehend the behaviour of the reservoir during production, but it is crucial to identify how to harness that behaviour to improve productivity. In order to simulate the mechanical behaviour of unconsolidated sand material, an elastoplastic damage model was formulated. Fluid-flow-geomechanical modelling was then performed for predicting individual well behaviour and overall field performance. The combine...
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Une etude experimentale preliminaire a ete menee au CERMES au moyen d'essais oedometriques par paliers pour mettre en evidence le role joue par les fluides lors de la compaction des craies. Fondee sur une recherche precedente,... more
Une etude experimentale preliminaire a ete menee au CERMES au moyen d'essais oedometriques par paliers pour mettre en evidence le role joue par les fluides lors de la compaction des craies. Fondee sur une recherche precedente, l'analyse de la subsidence des reservoirs petroliers en Mer du Nord, l'adaptation de l'essai oedometrique aux craies multiphasiques (air/eau ou huile/eau) a necessite des precautions particulieres. La procedure a ete validee avec succes par les premiers resultats qui mettent en evidence un effet du fluide saturant sur le fluage unidimensionnel du materiau. En effet, le fluide selon sa mouillabilite diminue la resistance du materiau et amorce un comportement visqueux precoce. Dependant du rapport entre la contrainte appliquee et la limite elastique, le fluage est plus important quand l'echantillon est sature du fait de la diminution de la limite elastique qui en suit. La prise en compte de ces aspects du comportement mecanique des craies s&#...
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Due to seasonal environmental changes (i.e. water table, hygrometry) the pillars of mines in chalk are often submitted to variations of the degree of water saturation. These changes could affect the short and long term stability of... more
Due to seasonal environmental changes (i.e. water table, hygrometry) the pillars of mines in chalk are often submitted to variations of the degree of water saturation. These changes could affect the short and long term stability of pillars in the underground quarries. Experimental investigations have been conducted on saturated, partially saturated and dry chalk. In this context, the concepts and the methods of mechanics unsaturated soils have been applied to partially saturated chalks. Water retention properties and a series of high pressure controlled suction odometer compression tests were carried out on the samples of the chalk from the pillars of the abandoned Estreux mine (France). These results show that the yield stress of chalk increases when the water saturation decreases. They have been simulated by means of the Barcelona Basic Model - BBM (Alonso et al., 1990) allowing to account the swelling and collapse under wetting at constant vertical load
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Summary In this paper two rate dependent constitutive models for porous chalks are presented. The common background of both models formulation is the isotach approach, which is first introduced. The theoretical basis and the mathematical... more
Summary In this paper two rate dependent constitutive models for porous chalks are presented. The common background of both models formulation is the isotach approach, which is first introduced. The theoretical basis and the mathematical formulation of the models are then proposed. Finally, numerical predictions of both models are compared with experimental results and discussed. The two formulations include strain rate and creep effects. Suction dependency on creep is also discussed. Some perspectives about the constitutive modelling of time-dependent behaviour of partially saturated chalks are given with respect to the description of the coupled effect of suction and time.
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Dans les fondations profondes la caracterisation du contact entre le sol et l'element structural, le pieu, joue un role majeur dans la definition des conditions de stabilite de l'ouvrage. Nous presentons dans ce travail une... more
Dans les fondations profondes la caracterisation du contact entre le sol et l'element structural, le pieu, joue un role majeur dans la definition des conditions de stabilite de l'ouvrage. Nous presentons dans ce travail une analyse numerique par la methode des elements finis du comportement mecanique de fondations profondes isolees sous charge axiale. Une attention particuliere est consacree a la modelisation du contact sol granulire - pieu -interface), et a la definition d'elements de contact speciaux, capables de reproduire les traits essentiels du comportement d'interface. La formulation d'une loi de comportement elastoplastique d'interface appropriee (modele MEPI) est d'abord presentee. Sa validation est realisee sur des essais de cisaillement d'interface. Cette loi, integree dans le conde aux elements finis CESAR-LCPC, est utilisee ensuite pour la simulation des essais de chargement d'un pieu modele en chambre d'etalonnage. L'accord s...
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A 10 m seabed subsidence has developed in the last ten years in the Ekofisk oilfield in the North Sea, due to enhanced oil recovery by seawater injection (waterflooding). This subsidence imposed an important structural rehabilitation of... more
A 10 m seabed subsidence has developed in the last ten years in the Ekofisk oilfield in the North Sea, due to enhanced oil recovery by seawater injection (waterflooding). This subsidence imposed an important structural rehabilitation of the operating offshore platforms (Hermansen et al., 2000). Although it is now widely accepted that the main cause of the seabed settlement is the compaction of the layer of reservoir chalk (300 m thick at 3000 m, porosity n ~ 45-50%), the origin of the compaction is still an open issue. Due to the presence of two fluids in the chalk pores where oil and water interact each other and together with the chalk skeleton, attempts to apply standard saturated geomechanics approaches based on the effective stress principle revealed serious shortcomings. It was then proposed to adopt a coupled hydro-mechanical framework taken from the mechanics of unsaturated soils (containing water and air as a non wetting fluid) and to adapt it to reservoir chalks (containin...
When considering the interaction of two media in contact with highly-distinct deformability characteristics failure is often accompanied by the formation within the more deformable medium of a rather thin zone oriented in the direction of... more
When considering the interaction of two media in contact with highly-distinct deformability characteristics failure is often accompanied by the formation within the more deformable medium of a rather thin zone oriented in the direction of the contact surface. This zone, called the soil-structure interface, or simply interface, experiences intense strain localization and plays the role of a kinematic discontinuity characterized by extremely high strain gradients. Quite a large number of civil engineering structures lie in contact with soils. Such is the case, for example, in soil-retaining walls, soil-anchorage rods, soil-piles or micropiles, or soil-reinforcements (e.g. “terre armee”, nailed soils). Failure in these structures occurs mainly due to progressive shearing and is often observed at the interface, in the softer medium (i.e. the soil mass), where stresses and strains are transmitted. The description of the mechanical behaviour, mainly in terms of mobilized friction between ...
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ABSTRACT During exploration and exploitation in deep offshore areas (beyond 1000 metres depth) oil companies have recently been faced with geotechnical problems related to the presence of shallow gas in marine sediments leading to... more
ABSTRACT During exploration and exploitation in deep offshore areas (beyond 1000 metres depth) oil companies have recently been faced with geotechnical problems related to the presence of shallow gas in marine sediments leading to eruptions during drilling, difficulties in conductor installation and anomalous high pore pressures measurements during piezocone penetrometer testing (PCPT). Gassy soils can result from various factors, including hydrates dissociation. They represent a critical issue for the oil and gas industry, at least for two reasons: (i) the detection of gas is still not reliable, and (ii) the effect on the mechanical properties of the soil is still rather unclear. In this paper a preliminary numerical analysis of an ideal piezocone penetration in gassy sediment is presented. This study will serve as a basis in view of a possible interpretation of available in situ measurement of cone penetration resistance in gas-bearing sediments.