History matching and uncertainty quantification of facies models with multiple geological interpretations

Uncertainty quantification is currently one of the leading challenges in the geosciences, in particular in reservoir modeling. A wealth of subsurface data as well as expert knowledge are available to quantify uncertainty and state predictions on reservoir performance or reserves. The geosciences component within this larger modeling framework is partially an interpretive science. Geologists and geophysicists interpret data to postulate on the nature of the depositional environment, for example on the type of fracture system, the nature of faulting, and the type of rock physics model. Often, several alternative scenarios or interpretations are offered, including some associated belief quantified with probabilities. In the context of facies modeling, this could result in various interpretations of facies architecture, associations, geometries, and the way they are distributed in space. A quantitative approach to specify this uncertainty is to provide a set of alternative 3D training images from which several geostatistical models can be generated. In this paper, we consider quantifying uncertainty on facies models in the early development stage of a reservoir when there is still considerable uncertainty on the nature of the spatial distribution of the facies. At this stage, production data are available to further constrain uncertainty. We develop a workflow that consists of two steps: (1) determining which training images are no longer consistent with production data and should be rejected and (2) to history match with a given fixed training image. We illustrate our ideas and methodology on a test case derived from a real field case of predicting flow in a newly planned well in a turbidite reservoir off the African West coast.     

Nouvelles données sur le téphra de Sarliève et le téphra CF7, marqueurs chrono-stratigraphiques de Grande Limagne (Massif central,France)

A trachytic tephra, discovered in the ancient lake of Sarliève, ‘Grande Limagne’, has been dated using the thermoluminescence technique. The obtained age, 16±4 ka ($\text{2}\text{σ}$), is older than that of the trachytic volcanoes of the Cha??ne des Puys, the ashes of which have already been locally recognised in the region. Its analysis confirms its originality. In the course of the comparisons made to search for its spring, it appears that the wide-dispersion tephra CF7, beforehand correlated by hypothesis to the Puy de Clierzou, probably originates from the Kilian crater or the Puy de Vasset. To cite this article: D. Miallier et al., C. R. Geoscience 336 (2004).     

Coupes équilibrées à travers le massif subalpin de la Chartreuse

Résumé

Pour étudier la tectonique des chaînes subalpines du Nord, et proposer un modèle cinématique régional, nous avons utilisé les résultats d’une expérience géophysique réalisée en 1985, et les observations géologiques de surface publiées à ce jour. Ces données ont été analysées de manière à préciser le style tectonique, le positionnement des failles par rapport aux horizons stratigraphiques et le schéma de branchement des failles. La construction simultanée d’une coupe interprétative, d’une coupe restaurée et d’une carte de branchement des failles a permis d’estimer l’amplitude du raccourcissement par la méthode des coupes équilibrées. Au niveau du Nord de la Chartreuse, la valeur minimale du raccourcissement global est de 14 km, 4 km étant associés au système chevauchant du Jura et 10 km à celui du massif des Bornes et des Bauges. Compte tenu des imprécisions existant sur les données utilisées, trois modèles cinématiques, qui correspondent à une plage de raccourcissement comprise entre 14 et 25 km, sont proposés.     

Quantifying Asymmetric Parameter Interactions in Sensitivity Analysis: Application to Reservoir Modeling

In this paper, a new generalized sensitivity analysis is developed with a focus on parameter interaction. The proposed method is developed to apply to complex reservoir systems. Most critical in many engineering applications is to find which model parameters and parameter combinations have a significant impact on the decision variables. There are many types of parameters used in reservoir modeling, e.g., geophysical, geological and engineering. Some parameters are continuous, others discrete, and others have no numerical value and are scenario-based. The proposed generalized sensitivity analysis approach classifies the response/decision variables into a limited set of discrete classes. The analysis is based on the following principle: if the parameter frequency distribution is the same in each class, then the model response is insensitive to the parameter, while differences in the frequency distributions indicate that the model response is sensitive to the parameter. Based on this simple idea, a new general measure of sensitivity is developed. This sensitivity measure quantifies the sensitivity to parameter interactions, and incorporates the possibility that these interactions can be asymmetric for complex reservoir modeling. The approach is illustrated using a case study of a West Africa offshore oil reservoir.     

Apport de la cathodoluminescence à haute résolution à l'étude de la diagenèse météorique dans les formations sédimentaires carbonatées

Different diagenetic transformations and their relative chronological sequence are studied in the meteoric diagenetic zone from the Upper Oligocene limestone at the North of the Aquitaine Basin (France), by combining high-resolution cathodoluminescence spectroscopy and electron-microprobe analyses. More than 128 spot analyses by electron microprobe and 60 analyses by cathodoluminescence spectroscopy are done on different meteoric cements firstly identified by classic optical microscopy. Three cement types are identified according to the relative intensity of the bands of their respective cathodoluminescence spectra (350, 380, 430, 500, and 620 nm). From these investigations, we could identify for each meteoric cement different phases of crystalline growth and crystalline dissolution. As a result, a better and more realistic meteoric diagenetic model is proposed. It illustrates the cyclic transformations from vadose zone (unsaturated) to meteoric zone (saturated). To cite this article: R. Chapoulie et al., C. R. Geoscience 337 (2005).     

Mise au point d'un milieu de culture pour l'étude de l'altération de silicates en présence de Pseudomonas aeruginosa

The influence of microorganisms on mineral alteration is not easy to determine in environmental conditions, because of the difficulty to raise for comparison purposes an identical but abiotic system. Another problem in this context is the choice of reliable tracers to evaluate the alteration rate of materials during in vitro experiments. To face such difficulties, we elaborated a defined medium allowing both the growth of Pseudomonas aeruginosa and a precise measurement of the elements solubilized from the minerals. Thanks to this medium, we were able to quantitatively determine the amounts of major elements solubilized from the materials in the presence of bacterial growth, compared to a sterile system. Moreover, the analysis by ICP-MS of trace elements was possible after a chromatographic treatment, which selectively eliminated 99% of the sodium content of the medium. To cite this article: G. Aouad et al., C. R. Geoscience 337 (2005).     

Seismic sequence stratigraphy of Miocene deposits related to eustatic,tectonic and climatic events,Cap Bon Peninsula,northeastern Tunisia

The Cap Bon Peninsula, belonging to northeastern Tunisia, is located in the Maghrebian Alpine foreland and in the North of the Pelagian block. By its paleoposition, during the Cenozoic, in the edge of the southern Tethyan margin, this peninsula constitutes a geological entity that fossilized the eustatic, tectonic and climatic interactions. Surface and subsurface study carried out in the Cap Bon onshore area and surrounding offshore of Hammamet interests the Miocene deposits from the Langhian-to-Messinian interval time. Related to the basin and the platform positions, sequence and seismic stratigraphy studies have been conducted to identify seven third-order seismic sequences in subsurface (SM1-SM7), six depositional sequences on the Zinnia-1 petroleum well (SDM1-SDM6), and five depositional sequences on the El Oudiane section of the Jebel Abderrahmane (SDM1–SDM5). Each sequence shows a succession of high-frequency systems tract and parasequences. These sequences are separated by remarkable sequence boundaries and maximum flooding surfaces (SB and MFS) that have been correlated to the eustatic cycles and supercycles of the Global Sea Level Chart of Haq et al. (1987). The sequences have been also correlated with Sequence Chronostratigraphic Chart of Hardenbol et al. (1998), related to European basins, allows us to arise some major differences in number and in size. The major discontinuities, which limit the sequences resulted from the interplay between tectonic and climatic phenomena. It thus appears very judicious to bring back these chronological surfaces to eustatic and/or local tectonic activity and global eustatic and climatic controls.     

Crustal melting and recycling: geochronology and sources of Variscan syn-kinematic anatectic granitoids of the Tormes Dome (Central Iberian Zone). A U–Pb LA-ICP-MS study

International Journal of Earth Sciences - In this study, we report U–Pb Laser Ablation ICP-MS zircon and ID-TIMS monazite ages for peraluminous granitoid plutons...     

Variability of annual precipitation in Sweden

Summary Different measures of variability of precipitation are discussed and it is concluded that it is preferable to apply therelative intersequential variability in cases when overall trends are feared in the records. 127 stations in Sweden have been studied for the period 1901–1950 as to the relative interannual variability of precipitation. For a selection of these stations other measures have also been calculated and a comparison has been made between the coefficient of variation and the intersequential variability. As the relation between these measures varies with the existence of serial correlations in the records the serial correlation coefficient for a lag of one element has been calculated. The value of the coefficient has indicated the existence of trends in certain areas of Sweden generally in agreement with earlier investigations byÅngström.The geographical distribution of the relative interannual variability in Sweden is discussed and also the distribution of anomalies of relative variability compared with the world's normal curve completed byConrad. It is shown that the relationship between relative variability and precipitation amount for Swedish stations can be expressed by a hyperbolic function deviating fromConrad's world normal curve only by an additive constant.

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Zusammenfassung Der Verfasser erörtert verschiedene Maße für die Variabilität des Niederschlages und kommt zu der Feststellung, daß in den Fällen, in denen eine einseitige Tendenz in den Beobachtungsreihen zu befürchten ist, die Verwendung derrelativen reiheninternen Variabilität am geeignetsten ist. 127 Stationen in Schweden sind für die Periode 1901–1950 im Hinblick auf die relative interannuelle Variabilität des Niederschlags untersucht worden. Für eine Auswahl dieser Stationen wurden auch andere Maße berechnet und der Schwankungskoeffizient mit der reiheninternen Variabilität verglichen. Da die Beziehung zwischen diesen Maßen mit dem Auftreten von Serienkorrelationen in der Beobachtungsreihe variiert, wurde der Serienkorrelationskoeffizient für eine Verschiebung eines Elements berechnet. Die erhaltenen Werte des Koeffizienten deuten auf das Vorhandensein gesetzmäßiger Tendenzen in gewissen Gebieten Schwedens hin und stehen im allgemeinen in guter Übereinstimmung mit älteren Untersuchungen vonÅngström.Die geographische Verteilung der relativen interannuellen Variabilität in Schweden sowie die Verteilung der Anomalien der relativen Variabilität, verglichen mit der vonConrad aufgestellten Weltnormalkurve, werden erörtert. Schlie\lich wird gezeigt, daß es möglich ist, den Zusammenhang zwischen relativer Variabilität und Niederschlagsmenge für schwedische Stationen durch eine hyperbolische Funktion zu beschreiben, die vonConrads Weltnormalkurve nur durch eine additive Konstante abweicht.

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Résumé L'auteur mentionne différentes mesures de la variabilité des précipitations et conclut qu'il est préférable d'appliquer la variabilité relative interséquentielle lorsqu'une tendance unilatérale des séries d'observations est à craindre. Il a étudié la variabilité relative interannuelle des précipitations pour 127 stations suédoises (1901/50) ainsi que d'autres mesures de variabilité pour un choix restreint de stations et il a comparé le coefficient de variation à la variabilité relative interséquentielle. Comme la relation entre ces mesures varie avec l'existence de corrélations de série dans les séries d'observations, le coefficient de corrélation de série a été calculé pour un déplacement d'un terme; la valeur de ce coefficient indique l'existence de tendances générales dans certaines régions de Suède, ce qui confirme les résultats anciens deÅngström.La distribution géographique de la variabilité relative interannuelle en Suède ainsi que celle des anomalies de la variation relative comparée à la courbe normale mondiale dressée parConrad fait l'objet d'un examen. Enfin on montre qu'il est possible d'exprimer la relation entre la variabilité relative et la quantité de précipitations en Suède par une fonction hyperbolique qui ne diffère de la courbe normale deConrad que par une constante additive.

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With 5 Figures

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Dedicated to Dr.Anders K. Ångström on the occasion of his 70th birthday.