L'étude a pour but de caractériser les facteurs de contrôles de la distribution des propriétés pétrophysiques et mécaniques dans les réservoirs carbonatés. Pour y répondre, il a été entrepris une démarche intégrant des analyses sédimento-diagénétiques (sédimentologiques, pétrographiques, géochimiques…) et de la fracturation (stratigraphie mécanique et stratigraphie de fracture, hiérarchisation, chronologie…). L'acquisition des données a été réalisée sur un analogue de terrain d'un réservoir carbonaté fracturé : la Formation Madison, d'âge Carbonifère inférieur (357-340 Ma), affleurant dans le Bassin de Bighorn (Wyoming, USA) et qui est aussi un réservoir exploité en subsurface. Cette acquisition a été réalisée dans cinq sites : Wind River Canyon, Shell Canyon, Sheep Mountain, Shoshone Canyon, et Clark's Fork Canyon (selon une polarité paléogéographique proximale - distale).Dans le Wyoming (USA), la Formation Madison est une série carbonatée, atteignant une épaisseur de 340 m, formée de sept séquences de dépôt basse fréquence (SBF). Les deux premières (SBF1 et 2) se sont formées sur une rampe qui, en conséquence de progradations extensives, s'est aplanie progressivement pour former une plate-forme sur laquelle se sont déposées les cinq autres séquences (SBF3 à 7). SBF1 à 3, d'âge Kinderhookien à Osagéen inférieur, se sont formées sous climat aride à la faveur d'une subsidence tectonique générale compensant les chutes eustatiques épisodiques. Les cortèges de rétrogradation se caractérisent par le développement étendu des milieux inter- à supratidaux et des processus de précipitation d'évaporites et dolomitisation. / The purpose of this study is to characterize factors controlling the distribution of the petrophysical and mechanical properties in carbonate reservoirs. To do so, a pluridisciplinary approach integrating sedimento-diagenetic and fracturing analyses on a carbonate reservoir analogue: he Madison Formation, (Lower Carboniferous, 357-340 My), outcropping in the Bighorn Basin (Wyoming, USA) and that is also a subsurface reservoir.The Madison Formation is a 340 m thick carbonate series composed of seven low frequency depositional sequences (LFS). The first two (LFS 1 and 2) formed on a prograding ramp passing upward into a vast platform on which the other five LFS deposited (LFS3 à 7). LFS 1 to 3 (Kinderhookian to lower Osagean) deposited under arid conditions during general subsidence that balanced eustatic falls. Retrograding system tracts are characterized by the development of supratidal to intertidal environment dominated by evaporite precipitations and carbonate dolomitization. Prograding system tracts are mainly mainly by early-lithified grainstones. LFS 4 to 7 (Osagean) deposited under humid conditions (glacial conditions in high-latitudes) that contributed to a decrease in evaporite precipitations and carbonate dolomitization but that involved karstifications on tops of LFS 4 to 7 during uplift episodes and eustatic falls.

Les objectifs de cette thèse sont (1) de définir les facteurs contrôlant le développement à grande échelle des plateformes carbonatées intracratoniques et (2) de relier la diagenèse précoce des discontinuités avec les paléoenvironnements et les modèles de stratigraphie séquentielle. L’évolution de la plateforme carbonatée de l’ouest de la France a été reconstituée de l’Aalénien à l’Oxfordien (17 millions d’années). La topographie du socle contrôle la répartition latérale des bathymétries jusqu’au Bathonien moyen. La tectonique régionale favorise ou empêche localement la production carbonatée. À l’échelle des bassins ouest-téthysiens, des phases généralisées de disparition et de croissance des plateformes carbonatées sont contrôlées par les variations du climat d’une période de 9 millions d’années. La production carbonatée est faible pendant les périodes humides et importante au cours des périodes sèches perturbées par de courtes moussons. Des analyses isotopiques (δ18O et δ13C) à haute résolution ont été réalisées sur des ciments précoces variés localisés sous des discontinuités, permettant de reconstituer l’histoire paléoenvironnementale aboutissant à leur formation. Les ciments en dents de chien ainsi que les ménisques et enveloppes micritiques analysées ont précipité directement en calcite faiblement magnésienne dans l’eau de mer. Un nouveau modèle reliant architecture, stratigraphie séquentielle, faciès et diagenèse précoce est proposé pour une bordure de plateforme oolithique. Sur la plateforme interne, les discontinuités passent latéralement de surfaces subaériennes à des hardgrounds marins, dont l’érosion aboutit au dépôt de niveaux à intraclastes sur la bordure de plateforme. La cimentation précoce est uniquement localisée sous les discontinuités et est absente dans la bordure de plateforme où la sédimentation est continue. / The objectives of this thesis are (1) to characterize the factors controlling the large-scale development of intracratonic carbonate platforms and (2) to link early diagenesis of discontinuities with palaeoenvironments and sequence stratigraphy models. The evolution of the western France carbonate platform is reconstructed from the Aalenian to the Oxfordian (17 million years). The basement topography controls bathymetries until the mid-Bathonian. Regional tectonics promotes or prevents locally carbonate production. General stages of carbonate platform growth and demise in western Tethyan basins are controlled by 9 million years’ climatic variations. Carbonate production is low during humid intervals and high during dry intervals disturbed by short periods of intensive rainfall. High resolution isotopic analyses(δ18O and δ13C) were performed on various early cements located below discontinuities to reconstruct the palaeoenvironmental conditions leading to their formation. Dogtooth cements, micritic meniscus and envelopes precipitated in low-magnesium calcite directly in seawater. A new model, linking architecture, facies, sequence stratigraphy and early diagenesis is proposed for an oolitic platform wedge. On the inner platform, discontinuities change laterally from subaerial surfaces to marine hardgrounds, whose erosion leads to the deposit of an intraclasts level on the platform wedge. Early cements are only located under discontinuities and are absent in the platform wedge because of a continuous sedimentation rate.

Low pH zones in portions of the overburden at the Dave Johnston Coal Field, Converse County, Wyoming are the subject of this study. The low pH zones are restricted to limonite stained sandstones which grade downdip into normal pH gray sandstones. Changes in color, clay mineralogy, cementation and feldspar surface textures are noted between the two sandstone units. These changes appear to be the result of post depositional alteration that was responsible for oxidation of pyrite and chlorite, dissoluion of calcite, and the etching of feldspar grains. The parameters for the diagenesis fit those of uranium roll front models proposed for the Powder River Basin. The alteration appears responsible for the low pH values reported in the yellow sandstone. Research by the North Dakota Geological Survey on similar problems associated with lignite mines in North Dakota suggests reclamation procedures for dealing with these potentially hazardous overburden spoils.

No description available.

No description available.

Prompted by increased interest in understanding microporosity, recent efforts at describing and classifying pore types in mudstones have focused primarily on siliceous, gas producing unconventional reservoirs with little attention being paid to carbonate, mixed oil-and-gas producers. The Niobrara Formation in the Denver-Julesburg Basin is a self-sourced resource play producing oil and natural gas from low permeability chalks. Key reservoir lithologies consist of chalk, chalky marl and marl. These lithologies contain flattened chalk fecal pellets which play a significant role in providing porosity. Integration of depositional fabric with pore-type distribution emphasizes the unique textural and depositional nature of chalk and provides a starting point for evaluation of diagenetic porosity modification. Chalk depositional textures comprise two main subdivisions. The first, called rainstone, includes chalks that form largely from settling of planktonic skeletal remains and fecal pellets as marine snow. New terms related to pelagic chalk textures are pelagic mudstone, pelagic wackestone, and pelagic packstone. The second, called allochthonous chalk, consists of chalks formed from syndepositional tectonic disruption of the seafloor, resulting in mass-movement and redeposition of chalk as turbidites and slide sheets. New terms related to allochthonous chalk textures are allomudstone, allofloatstone, and allorudstone. A chalk porosity classification consisting of four major pore types is presented that can be used to quantify Niobrara chalk pores and relate them to depositional texture, porosity networks, diagenetic history, and pore distributions. Interparticle porosity occurs largely between coccoliths and coccolith fragments, and decreases with burial ranging from 27-38% to 5-17%. Intraparticle porosity occurs within chalk pellets, coccospheres, coccolith plates and foraminifera tests, and also decreases with burial. Organic matter pores are intraparticle pores located within organic matter and are related to hydrocarbon generation. Channel pores, where present, can have significant influence on hydrocarbon storage and permeability networks. In the Niobrara, burial diagenesis in the form of mechanical compaction, chemical compaction, and syntaxial cement overgrowths, modifies pore shape and abundance. Porosity distribution is controlled by the abundance of chalk pellets and the mineralogy of the matrix. Permeability is a function of matrix lithology (micrite-rich vs. silt- and clay-rich). Understanding chalk depositional and diagenetic processes, and how they relate to porosity formation and pore evolution provide a foundation for more accurately predicting the occurrence and distribution of hydrocarbon source and reservoir rocks within the Niobrara.

No description available.

This thesis demonstrates that geological setting, depositional facies, open system flux of hot basinal brines and descending of shallow waters have a strong impact on the distribution of the diagenetic alterations within continental and paralic/shallow marine sandstones which in turn control the quality and heterogeneities of the reservoirs. Geological setting controls the mineralogical and textural maturity of sandstone, whereas depositional facies control the pore water chemistry (marine, brackish or meteoric), sedimentary texture and sand body geometry. Eogenetic alterations in the fluvial deposits are dominated by precipitation of infiltrated clays, kaolinitization of detrital silicates, whereas the shallow marine deposits are dominated by precipitation of early calcite and kaolinite. Conversely mesogenetic alterations are dominated by clay minerals transformation, quartz overgrowths and Ferroan- carbonates, barite and anhydrite. Flux of hot basinal brines is evidenced by precipitation of mesogenetic minerals that lack of internal sources (e.g. barite, anhydrite and ferroan carbonate cements), which is evidenced by: (1) restricted occurrence of these minerals in downthrown blocks. (2) The high fluid inclusion homogenization temperatures (Th) of quartz overgrowths (Th &gt; 110-139°C), and carbonate cements (T &gt; 80-140°C), which also have light δ18OV-PDB(-17.6‰ to -6.7‰). Flux of hot basinal brines is further evidenced by occurrence of saddle Fe-dolomite along stylolites. Fluid inclusion microthermometry further revealed a dramatic shift in pore- water chemistry from NaCl dominated brines during precipitation of quartz overgrowths to NaCl-CaCl2 dominated brines during cementation by Fe-dolomite. Presence of mixed brine (NaCl+CaCl2) systems in the fluid inclusions suggests flux of descending waters, which have circulated in the overlying carbonate-evaporite successions. The restricted occurrence of oil- filled inclusion to quartz overgrowths and methane to Fe-carbonate cements suggest migration of oil during precipitation by quartz and migration of methane during precipitation by Fe- carbonate cements. The extensive mesogenetic cements in the down thrown blocks is attributed to flux of basinal brines along deep seated faults, i.e. open system diagenesis. Integration of fluid inclusion microthermometry, isotopes, Raman spectrometry and thermal tectonic evolution of basins are essential techniques for unraveling the evolution of basinal fluids, cementation conditions and relative timing of hydrocarbons migration. / <p>Errata: Felaktigt disputationsdatum på spikbladet.</p>

Thesis (MSc)--Stellenbosch University, 2013. / This study presents a facies outcrop characterization and petrographical analysis of Unit B of the Permian Laingsburg Formation. Unit B is interpreted as a base-ofslope system, which represents a strikingly sand-rich succession. The base-of-slope system is defined by a channel-levee complex. The study provides systematically a clear understanding and description on reservoir heterogeneities, in terms of facies distribution, physical processes and architectural elements. The dataset included detailed sedimentary logs, photomosaic interpretations, supplemented by a petrographical study to determine the textural and compositional attributes of the studied sandstones. Seven lithofacies was recognised within Unit B, based on detail observation and description on grain size and sedimentary structures. They mainly consist of 1) thick to massive bedded ‘structureless’ sandstone, 2) horizontal and ripple cross-laminated thin-medium bedded sandstone, 3) silty sandstone, 4) structureless siltstone, 5) hemipelagic mudstone, 6) muddy slump, and 7) sandy slump. Palaeocurrent analysis indicates that the mean sediment transport direction of Unit B was to the E and NE. Lithofacies 1 comprises thickly to massive bedded, frequently amalgamated, mostly very-fined grained sand, mixed grading, irregular to sharp upper contacts, structured upper bedding planes, large floating mudstone clasts and granules, rare groove and flute casts. Also, scour and fill features have been documented. Lithofacies 1 has been interpreted to result from channelized sandy debris flow currents. Lithofacies 2 composes of thin-medium bedded, very fine-grained sand, ungraded, sharp upper contacts, discrete units with traction bed forms, horizontal and cross-lamination, mud-draped ripples, internal erosional surfaces and preserved crests. Lithofacies 2 shows diagnostic sedimentary features for a deep-water bottom reworking current. Lithofacies 5 composes of very fine–grained mud, ‘structureless’ to finely horizontally laminated, fissile mudstone. Deposition resulted from suspension settling of mud fractions out of a low-energy buoyant plume. Lithofacies 6 composes of contorted and convoluted bedding, steeply dipping layers and irregular upper contacts. Deposition occurred via slumping on an unstable slope. Lithofacies 7 composes of fine–grained ‘structureless’ sandstone, amalgamated units, with dark floating mudstone granules. Lithofacies 7 has been interpreted to form from channelized flows evolving into slump deposition on an unstable slope. The petrographic data reveals that the reservoir quality of the sandstones is strongly controlled by depositional processes and diagenetic products. The sediments of the Karoo Basin appear to be diagenetically controlled as a function of burial depth. The major diagenetic products controlling the reservoir quality of the sandstones, includes compaction (mechanical and chemical), and authigenic porefilling constituents (quartz cement, feldspar dissolution and partial to complete replacement, calcite cement, chlorite and illite). Compaction played a major role in the evolution of the sediment, as compared to the effect of quartz cementation, and is considered here to have caused irreversible destruction of depositional porosity and permeability. The sediment has undergone intense mechanical compaction during early-stage diagenesis, low temperature and shallow depth of burial (probably the first 2 km). The high burial palaeotemperature (250 ± 500C) or more specifically the high geothermal gradient of the Karoo Basin consequently increased the number of diagenetic reactions. The high burial temperatures may have increased pressure dissolution and quartz cementation. With compaction been limited, quartz cementation and the authigenesis of chlorite and illite at deeper depths may have had a profound effect on the permeability distribution of the studied sandstones. After the completion of diagenesis, the pore systems of these sandstones were completely destroyed by low-grade regional burial metamorphism.

No description available.