78 research outputs found
Impact des hétérogénéités sédimentaires sur le stockage géologique du CO2
No full textLa démarche d’intégration des hétérogénéités dans les modèles réservoirs en est à ses prémices dans le domaine du stockage géologique de CO2. C’est dans ce contexte que s’inscrivent ces travaux de thèse. Un protocole d’analyse depuis l’étude de terrain jusqu’aux simulations réservoirs a été établi. La caractérisation du Minjur Sandstone (formation Triasique d’Arabie Centrale) met en avant le caractère crucial de la connectivité des corps dans l’architecture du réservoir, notamment en liant génétiquement leur nature, leur connectivité et leur position dans la séquence de dépôt. S’appuyant sur la connaissance de cette formation, un modèle conceptuel est construit, puis reproduit stochastiquement par un algorithme permettant l’élaboration de modèles conditionnés par une histoire sédimentaire. Le protocole prévoit la création de 50 scénarios illustrant divers degrés de connectivité ; chaque scénario étant composé de deux modèles de même architecture mais à remplissage sédimentaire différent. Cette approche permet d’appréhender (a) l’impact de la connectivité et (b) des hétérogénéités sédimentaires sur les performances réservoirs. L’estimation de capacité par l’approche statique des volumes disponibles estime une capacité moyenne d’environ 13Mt (aquifère semi-infini de 25 km par 25 km et 60m d’épaisseur à 1000 m de profondeur). Les hétérogénéités internes (sédiments argileux appelés oxbow lakes) entraînent une différence de capacité de 30%. Les simulations dynamiques confirment ces résultats et révèle une variabilité de capacité de 23% liée la connectivité des corps. De plus les hétérogénéités réduisent la migration verticale du gaz ce qui peut augmenter l’intégrité du stockage.In the CO2 storage context, heterogeneity has only been rarely considered in reservoir models to date. To address this key issue, the project aims at developing a workflow that manages the heterogeneity from the field observations up to the reservoir simulation. The characterisation of the Minjur Sandstone (a Triassic formation from Central Saudi Arabia) shows the crucial role of connectivity in the reservoir architecture, and the genetic link between the nature, location and connectivity of the sedimentary bodies in the sequence. Stemming from this study, a conceptual model was established and stochastically reproduced through an algorithm simulating models conditioned to a sedimentary history. Fifty scenarios were simulated, representing various connectivity degrees. Each of these scenarios is composed of two models, identical by their architecture but different in their internal sedimentary fill. This approach allows the study of the impact of the (a) reservoir bodies’ connectivity and (b) their internal sedimentary heterogeneity on the reservoir’s performances. The capacity estimates using a static calculation based on the available pore volumes reveals a mean capacity of 13 Mt (for a 25 x 25 km x 60 m semi finite aquifer at 1000m deep). The sedimentary heterogeneity (shaly deposits called oxbow lakes) is responsible for a 30% difference of capacity. The flow simulations confirm these results and show that the connectivity of the reservoir bodies creates a 23% capacity variation. Moreover, the heterogeneities tend to reduce the amount of CO2 able to reach the uppermost reservoir which may enhance the storage integrity
Impact des hétérogénéités fluviatiles sur les performances réservoirs
No full textL'intégration des hétérogénéités fluviatiles dans les modèles statiques et dynamiques permet d'améliorer la compréhension et la gestion de ces réservoirs (entre autre Labourdette, 2007 ; Larue et Hovadik, 2006, 2008). Ces derniers sont des systèmes complexes formés de nombreux corps réservoirs très hétérogènes dont la connectivité est variable et dépend en grande partie de l'histoire sédimentologique du système. La caractérisation réservoir permet de déterminer (a) la nature et dimension des corps sédimentaires, ainsi que (b) les mécanismes de contrôle de la connectivité ainsi que son évolution verticale et horizontale. Cette étude porte sur l'intégration des hétérogénéités sédimentaires dans les modèles réservoirs etleur impact sur les écoulements multiphasiques (application au CO2). Dans un premier temps un travail de terrain a été réalisé sur la formation du Minjur Sandstone (Trias, Arabie Saoudite). Douze environnements de dépôts et corps sédimentaires associés y ont été identifiés et leur répartition a été analysée au travers d'une étude séquentielle. Il a été démontré l'impact de la tectonique, des variations du niveau marin relatif et du couple espace disponible/volume sédimentaire sur l'architecture du système (Issautier et al., 2012a,b). Cette compréhension génétique a ensuite été formalisée dans un modèle conceptuel liant la nature des corps sédimentaires et leur connectivité. Dans un deuxième temps, un algorithme stochastique a été élaboré afin de reproduire numériquement ce concept, tout en intégrant une variation de la connectivité des corps représentative de la variabilité d'un système fluviatile. Cinquante réalisations ont été générés, toutes conditionnées au mêmes données (Strategy driven model ; Perrin et al., 2005). Chacun de ces scénarios est composé d'une paire de modèles dont l'architecture est identique mais avec un remplissage sédimentaire différent : dans un cas le remplissage interne des corps sableux est homogène (modèles B), dans l'autre cas sont considérés des oxbow lakes (Modèles A). Cette approche permet de comparer : (a) l'impact de la connectivité des corps sableux (hétérogénéité 1er ordre) sur les écoulements et (b) l'impact du remplissage interne (hétérogénéité 2nd ordre) sur les écoulements. Les modélisations dynamiques d'injection de CO2 dans ces réservoirs ont mis en avant le très fort impact des hétérogénéités internes sur les performances de stockage avec une capacité moyenne de 27 Millions de tonnes (Modèles A) contre 37 Millions de tonnes (modèles B). Cette différence représente une " perte de capacité " d'environ 37% directement imputable à la compartimentalisation induite par la présence des oxbow lakes. La migration du CO2 est également fortement impactée avec une réduction notable du déplacement du panache de CO2 vers le toit du réservoir augmentant ainsi l'intégrité du stockage
Impacts of fluvial sedimentary heterogeneities on CO2 storage performance
No full textSession H24B. Heterogeneity and Geologic Storage of CO2 IIThe heterogeneity of fluvial systems is a key parameter in sedimentology due to the associated impacts on flow performance. In a broader context, fluvial reservoirs are now targets for CO2 storage projects in several sedimentary basins (Paris Basin, North German Basin), thus calling for detailed characterization of reservoir behaviour and capacity. Fluvial reservoirs are a complex layout of highly heterogeneous sedimentary bodies with varying connectivity, depending on the sedimentary history of the system. Reservoir characterization must determine (a) the nature and dimension of the sedimentary bodies, and (b) the connectivity drivers and their evolution throughout the stratigraphic succession. Based on reservoir characterization, geological modelling must account for this information and can be used as a predictive tool for capacity estimation. Flow simulation, however, describes the reservoir behaviour with respect to CO2 injection. The present work focuses on fluvial reservoir performance and was carried out as part of a PhD (2008-2011) dedicated to the impact of sedimentary heterogeneity on CO2 storage performance. The work comprises three steps: ● Reservoir characterization based on detailed fieldwork (sedimentology and sequence stratigraphy) carried out in Central Arabia on the Minjur Sandstone. Twelve depositional environments and their associated heterogeneity are identified, and their layout is presented in a high-resolution sequence stratigraphy analysis. This step is summed up in a 3D geological model. ● Conceptual modelling based on this field data, using gOcad software and an in-house python code. The purpose was to study, for a given architecture, the impact of sedimentary heterogeneity on storage capacity estimations using two models: one with heterogeneity within the sedimentary fill (model A); the other without heterogeneity within the sedimentary fill (model B). A workflow was designed to estimate and compare the storage capacities for a series of some 50 scenarios. The results show that a strong compartmentalization, due to a shaly barrier, may decrease storage capacity by 11 to 25 percent. ● Flow-simulation of an 8-scenario sample extracted from the 50 possible scenarios. In contrast to the static modelling estimated capacities, the preliminary flow-simulation results indicate that capacity remains similar whichever model is applied (A or B). This is because the scale of the heterogeneity is similar to the extent of the CO2 plume, meaning that heterogeneity does not affect the amount of injected CO2 that can be stored in the sedimentary body. Nevertheless, connectivity strongly influences storage capacity, as determined by the 8 scenarios (model A) in which the total amount of CO2 injected ranges between 7 and 12 Mt over a 50-year period. Moreover, heterogeneity significantly increases pressure build-up, and may strongly disrupt the hydrodynamics in the aquifer
Anisotropy of Alfvénic Turbulence in the Solar Wind and Numerical Simulations
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Impacts of fluvial reservoir heterogeneity on connectivity: Implications in estimating geological storage capacity for CO2
No full textInternational audienceOur awareness of global warming and increasing greenhouse gas emissions emphasises the need to develop counteractive technologies. One promising tool in this respect would appear to be the geological storage of CO2, but there still remain uncertainties regarding the geological complexity of the subsurface. As in the oil and gas context, determining the scale of the heterogeneities that impact the reservoir storage capacity and fluid flow efficiency is crucial. In this paper, we propose to study the impact of two fluvial heterogeneity scales: (1) the architectural scale (megascopic scale) which consists in the connectivity between the main channel belts and (2) the scale of the channel belt (macroscopic scale) which considers the internal sedimentary fill, mainly composed of silty-sandy abandoned channel. To assert geological consistency, this study relies on a conceptual geological model discussed here and based on fieldwork in Saudi Arabia. This model incorporates sedimentary bodies ranging from fluvial braided to high- and low-wandering meandering type. Following the established concept, the largest reservoir bodies are found at the base and top of the system. A workflow is then proposed to statistically analyse the impact of the two considered heterogeneity scales onto CO2 storage characteristics. A code has been implemented to stochastically generate two series of 3D numerical models that account for the conceptual geological model. Each pair of models from the two series share the same architectural structure and only differ in their internal channel body infill. These two series of homologous 3D models support a statistical analysis of the impact of the heterogeneity representation on reservoir capacity. For a 25 km by 25 km by 60 m thick 3D model with a net to gross of 15%, the results show that estimated storage capacities can reach 5.7 Mt and 7.5 Mt respectively for the uppermost and the basal bodies. The presence of oxbow lakes, however, can lead to an estimated loss of capacity of about 11% (∼0.9 Mt) in the basal volumes and 20% (1.3 Mt) in the uppermost volumes
Large-scale Impact of CO2 Storage Operations: Dealing with Computationally Intensive Simulations for Global Sensitivity Analysis
No full textAbstractAssessing the potential impacts associated with CO2 storage operations implies using large-scale models characterized by a very large number of grid cells (>500,000) and high computation time cost (> several hours). Yet, investigating the influence of the input parameters on the model results requires multiple simulations (>1,000), which might become impracticable due to the computation burden. A meta-modelling strategy is then proposed, basically consisting in approximating the long running model by a costless-to-evaluate model, for instance a Gaussian Process, based on a very limited number of simulations (e.g., 50). This strategy is tested to investigate the sensitivity of the overpressure induced by an industrial-scale CO2 injection into a fluvial heterogeneous reservoir, to the properties of the shale formation using a 3-dimensional long running multiphase flow model (with CPU time > 5 days)
Impact des hétérogénéités sédimentaires sur le stockage géologique du CO2
No full textLa démarche d intégration des hétérogénéités dans les modèles réservoirs en est à ses prémices dans le domaine du stockage géologique de CO2. C est dans ce contexte que s inscrivent ces travaux de thèse. Un protocole d analyse depuis l étude de terrain jusqu aux simulations réservoirs a été établi. La caractérisation du Minjur Sandstone (formation Triasique d Arabie Centrale) met en avant le caractère crucial de la connectivité des corps dans l architecture du réservoir, notamment en liant génétiquement leur nature, leur connectivité et leur position dans la séquence de dépôt. S appuyant sur la connaissance de cette formation, un modèle conceptuel est construit, puis reproduit stochastiquement par un algorithme permettant l élaboration de modèles conditionnés par une histoire sédimentaire. Le protocole prévoit la création de 50 scénarios illustrant divers degrés de connectivité ; chaque scénario étant composé de deux modèles de même architecture mais à remplissage sédimentaire différent. Cette approche permet d appréhender (a) l impact de la connectivité et (b) des hétérogénéités sédimentaires sur les performances réservoirs. L estimation de capacité par l approche statique des volumes disponibles estime une capacité moyenne d environ 13Mt (aquifère semi-infini de 25 km par 25 km et 60m d épaisseur à 1000 m de profondeur). Les hétérogénéités internes (sédiments argileux appelés oxbow lakes) entraînent une différence de capacité de 30%. Les simulations dynamiques confirment ces résultats et révèle une variabilité de capacité de 23% liée la connectivité des corps. De plus les hétérogénéités réduisent la migration verticale du gaz ce qui peut augmenter l intégrité du stockage.In the CO2 storage context, heterogeneity has only been rarely considered in reservoir models to date. To address this key issue, the project aims at developing a workflow that manages the heterogeneity from the field observations up to the reservoir simulation. The characterisation of the Minjur Sandstone (a Triassic formation from Central Saudi Arabia) shows the crucial role of connectivity in the reservoir architecture, and the genetic link between the nature, location and connectivity of the sedimentary bodies in the sequence. Stemming from this study, a conceptual model was established and stochastically reproduced through an algorithm simulating models conditioned to a sedimentary history. Fifty scenarios were simulated, representing various connectivity degrees. Each of these scenarios is composed of two models, identical by their architecture but different in their internal sedimentary fill. This approach allows the study of the impact of the (a) reservoir bodies connectivity and (b) their internal sedimentary heterogeneity on the reservoir s performances. The capacity estimates using a static calculation based on the available pore volumes reveals a mean capacity of 13 Mt (for a 25 x 25 km x 60 m semi finite aquifer at 1000m deep). The sedimentary heterogeneity (shaly deposits called oxbow lakes) is responsible for a 30% difference of capacity. The flow simulations confirm these results and show that the connectivity of the reservoir bodies creates a 23% capacity variation. Moreover, the heterogeneities tend to reduce the amount of CO2 able to reach the uppermost reservoir which may enhance the storage integrity.AIX-MARSEILLE1-BU Sci.St Charles (130552104) / SudocSudocFranceF
Structural architecture and metamorphism of the Mayombe Chain and Niari Basin (West Congo Belt) in Congo Brazzaville
No full textInternational audienceGeological mapping of the Mayombe Chain and Niari Basin of Congo Brazzaville allows for the first time defining the structural architecture and metamorphism of the West Congo Belt. Four different tectono-metamorphic domains, separated by crustal-scale shear zones, are now distinguished (Niari Basin (NB), Eastern (EMC), Central (CMC) and Western (WMC) Mayombe Chain).The NB is marked by only weak regional deformation under middle to upper diagenetic conditions. It is delimited in the west from the EMC by the Mount Belo Shear Zone forming the terminal thrust system of the West Congo orogen.The tectonic style in the EMC is characterized by discrete, widely-spaced low-angle thrusts, reverse faults and strike-slip faults resulting in the formation of duplex and/or positive flower structures. Off these high-strain zones, the rocks are folded into gentle syn- and anticlines. Penetrative schistosity starts in shales in the western part. The metamorphism increases from eastern anchizonal conditions to lower greenschist facies in the west. The EMC is juxtaposed along the Moukondo thrust/back-thrust system with the CMC.The CMC is typified by open to closed upright to NE-verging folds, S1 schistosity with moderate to steep SW dips, onset of regional crenulation cleavage (S2), frequent reverse thrusts and numerous faults. Metamorphic conditions remain in the greenschist facies. The Loukenéné-Mandji Thrust marks the CMC-WMC contact and coincides with a jump in metamorphic grade marked by biotite-in.The WMC consists of Palaeoproterozoic basement stacked with Neoproterozoic rocks. Autochthonous Palaeoproterozoic gneiss and schist record Late Eburnean sedimentation, magmatism and metamorphism between 2110 and 1970 Ma, which are compared with the Eburnean history in Gabon and the Transamazonian orogeny in Brazil. The allochthonous Bikossi Group was thrust during the Pan-African event from the west over Tonian metavolcaniclastic and plutonic rocks before further folding and stacking of both units. The intensity of Pan-African deformation increases from open to closed folds with spaced cleavage in the southeast of the WMC to thrust-dominated tectonics in the northwest, where the Palaeo- and Neoproterozoic rocks are transposed into parallelism with the pronounced schistosity.Geochronology of illite and muscovite documents two Pan-African events at 590-570 Ma (M1) and at 520-500 Ma (M2) that are related to the main collisional and late thermal events in the Araçuai-Ribeira Belt in Brazil. Metamorphic isogrades shifted from M1 to M2 for more than 30 km to the west. Detrital mica and metamorphic illite of the Mpioka Group record M1 and M2, respectively constraining sedimentary deposition between 570 and520 Ma, which implies the interpretation of the group as molasse of the West Congo Belt
Review of Iberia-Eurasia plate-boundary basins: Role of sedimentary burial and salt tectonics during rifting and continental breakup
Get PDFInternational audienceWe document the role of sedimentary burial and salt tectonics in controlling the deformation style of continental crust during hyperextension. The Iberian-European boundary records a complex history of Cretaceous continental extension, which has led to the development of so-called smooth-slope type basins. Based on the review of the available geological constraints (crustal-balanced cross sections, sedimentary profile evolution, RSCM thermometer, low-temperature thermochronology) and geophysical data (Bouguer anomaly, Moho depth, seismic reflection profiles, and Vp/Vs velocity models) on the Tartas, Arzacq, Cameros, Parentis, Columbrets, Mauléon, Basque-Cantabrian and Internal Metamorphic Zone basins, we shed light on the main characteristics of this type of basin. This synthesis indicates that crustal thinning was influenced by two decoupling horizons: the middle crust and Triassic pre-rift salt, initially located between the basement and pre-rift sedimentary cover. These two horizons remained active throughout basin formation and were responsible for depth-dependent thinning of the crust and syn-rift salt tectonics. We therefore identify several successive deformation phases involving (1) pure shear dominated thinning, (2) simple shear dominated thinning and (3) continental breakup. In the first phase, distributed deformation resulted in the development of a symmetric basin. Field observations indicate that the middle and lower crust were under dominantly ductile conditions at this stage. In the second phase, deformation was localized along a crustal detachment rooted between the crust and the mantle and connecting upwards with Triassic pre-rift salt. During continental breakup, basin shoulders recorded the occurrence of brittle deformation while the hyperextended domain remained under predominantly ductile thinning. The formation of smooth-slope type extensional basins was intrinsically linked to the combined deposition of thick syn-rift and breakup sequences, and regional salt tectonics. They induced significant burial and allowed the continental crust and the pre-rift sequence to deform under high temperature conditions from the rifting to continental breakup stages
Large-scale vertical movements in Cenomanian to Santonian carbonate platform in Iberia: indicators of a Coniacian pre-orogenic compressive stress
No full textThe Cenomanian to early Santonian interval is usually considered a time of postrifting tectonic quiescence around the northern margins of Iberia that preceded the onset of the Pyrenean convergence by crustal thrusting in the latest Santonian. However, plate kinematic models of the Mesozoic evolution of Iberia poorly constrain the Turonian-Santonian position of Iberia relative to Eurasia. This study reconstructs changes in the sedimentary facies and architecture of the Iberian carbonate platform throughout the Late Cretaceous and sheds new light on the geodynamic evolution of the Iberia-Eurasia relationship at that time. Sixteen outcrop sections were described and 24 sedimentary facies identified that define 5 depositional environments ranging from the deep marine basin to the continental setting. From these and previously published field data we reconstruct the evolution of the Pyrenean carbonate platform, on an east-west transect nearly 400 km long, on the basis of 11 short-term depositional sequences and 5 long-term hemicycles. In our interpretation, the Cenomanian and Turonian correspond to a postrift stage during which the European and Iberian margins, together with the deep basin between them, subside gently, as shown by accommodation rates varying from ∼15 to 30 m/My in the margins and ∼100 to 150 m/My in the basin. The Coniacian and early Santonian are characterized by a large-scale flexural response consisting of (1) uplift of the southern Iberian margin, with negative accommodation rates, karstified surfaces and paleosols, and (2) increasing subsidence rates in the basin and its edges (the northern Iberian margin and eastern Aquitaine platform), with accommodation rates several times greater than during the Turonian. We propose that far-field stress possibly related to the northeastward motion of Africa, and/or onset of shortening at the Iberia-Europe boundary in the central and eastern Pyrenees led to the incipient large-scale flexural deformation in the Pyrenean domain. The late Santonian and Campanian are an early orogenic stage marked by rapid subsidence throughout the Pyrenean domain, except at its western end. We evidence for the first time a pre-orogenic flexure at the Iberia-Europe plate boundary induced by regional plate reorganisation between Africa and Europe during the Coniacian and the early Santonian
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