Thesis (M.S.)--University of Wisconsin--Madison. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 137-142).

Thesis (Ph. D.)--Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution, 1986. / Includes bibliographical references (p. 193-207).

This thesis investigates the impacts of diagenesis on the Late-Cretaceous Eagle Ford Formation (Fmn) in south-west Texas. This was achieved utilising many techniques such as of outcrop and core analysis, standard petrographic techniques (including cathodoluminescence [CL] and scanning electron microscopy [SEM]), and geochemical analysis (x-ray diffraction [XRD], stable isotope analysis of C and O within inorganic minerals and Rock Eval pyrolysis). The bulk of diagenetic products and textures were identified via petrographic techniques, with geochemical analysis confirming interpretations based on visual observations. This thesis shows the Eagle Ford Fmn is a calcareous, organic-rich mudstone containing eight distinct lithofacies, which have all been directly impacted by burial diagenesis. The Lower Eagle Ford Fmn mainly comprises of dark organic and clay-rich lithofacies which represent a classic source rock with interbedded carbonate rich lithofacies. The Upper Eagle Ford Fmn is organic and clay-poor, with the bulk of lithofacies carbonate dominated and heavily cemented. An initial anoxic, open marine depositional environment which transitions into an oxic deepening environment is inferred during deposition of the Eagle Ford Fmn. Early, microbial derived redox reactions have precipitated authigenic calcite and pyrite within the Eagle Ford Fmn. Authigenic calcite infills and preserves biogenic debris (mainly planktonic and benthic foraminifera), with pyrite framboids post-dating the carbonate cements. Kaolinite infilling biogenic debris is also a common occurrence indicating it is also an early diagenetic product. Smectite is converted to mixed layer I/Sand illite during deep burial processes at similar depths and temperatures to hydrocarbon generation and expulsion. Authigenic quartz cements precipitate within primary porosity and on top of carbonate cements. Chlorite is observed as the last mineral precipitated in the Eagle Ford Fmn, often pseudomorphed from kaolinite within the micritic matrix. Diagenesis has had the greatest impact on porosity distribution in the Eagle Ford Fmn. The organic, clay-rich lithofacies contain little intra/inter-crystalline porosity with the bulk observed as clay-held or organic porosity. Meanwhile the carbonate-rich lithofacies contain mainly intra-crystalline porosity. Concretions are a common feature observed in the Lower Eagle Ford Fmn outcrops. Four concretion types were identified and studied using a variety of petrological and geochemical techniques. Diagenesis plays a major role in all concretions types. However, primary factors such as sea level fluctuation, sediment input and tectonic activity also have key impacts on the formation of concretions.

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Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 217-260).

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Most of the hydrocarbon reservoirs in the world are carbonates, and most of these carbonate reservoirs are fractured. Fractures can form due to tectonic activity, mainly associated with fold and faults, and as a result of diagenesis. In many cases, the fractures in carbonates are cemented due to fluid flow, where these fluids precipitate cements. The presence of fractures can enhance reservoir fluid flow if the fractures were open and connected. This thesis focuses on carbonate reservoir fractures, and understanding the evolution of fluids from the cements that have precipitated within them. This thesis relates regional tectonic events to the formation of fractures, and of the environment and temperature of the fluids of precipitation in cement fractures the Early Cretaceous Thamama Group, in the United Arab Emirates (UAE). First, samples were studied from the subsurface in a highly faulted oil Field (A) located in South East Abu Dhabi. Core samples were taken from wells close to major faults in the field in both oil and water legs. Second, fractures in outcrop in Wadi Rahaba, Ras Al Khaima (RAK) in the Northern Emirates were studied where the Upper Thamama Group is exposed. The field study in the outcrop included the fracture orientation and cement types. The fractures in the outcrop were divided into two main generations, F1, (en-echelon) and F2 and they were both fully or partially cemented. The main tectonic events that affected the fracture formation in the Thamama Group are foreland autochthon in the Precambrian to Lower Cretaceous, a frontal triangle zone in Neogene and Dibba zone which consists of Hawasina units (Triassic to Cretaceous), and the Sumeini units (Lower to Middle Cretaceous). F1 is related to the NS orientation fracture system consistent to the Arabian Trend sets caused by Cenozoic compression. F2 is related to the EW orientation fracture system matching Tethyan extensional trend sets. Petrographic analysis of the subsurface thin sections revealed the presence of three main sets of fractures. Fracture Set 1 (cemented), Fracture Set 2 (open) and Fracture Set 3 (cemented, only in Lower Thamama). The fracture cement included equant and blocky calcite as well as saddle dolomite. Cathodoluminescence (CL) analysis assigned the number of cement zones in each cement type in the fractures, and revealed more cement zones in the Lower Thamama reservoirs than the Upper. The most important diagenetic events were cementation and dissolution, which took place towards the end of the paragenetic sequence. The reservoirs contained significant amounts of stylolites, dissolution seams and bitumen, which were associated with most of the dissolution events. mMg/mCa obtained from in situ elemental analysis showed variation through the calcite and dolomite cement zones in the different reservoirs of the Thamama Group. This was inferred to be due to temperature changes. The Upper Thamama Reservoirs (A, B, and C) show lower mMg/mCa (0.072-0.48) than the Lower Thamama reservoirs (F,G) (0,4-1.3), meaning that the Upper Thamama fracture calcite cements were precipitated at higher overall temperatures than the Lower Thamama reservoirs. Mn-Fe analysis allowed an understanding of the redox index through the different cement zones, in both Fracture Set 1 and Fracture Set 3. Analysis of Sr showed the absence of exotic fluids role in the diagenetic system. In-situ (SIMS) δ18OVPDB values were obtained for the calcite cementation history of the two fracture sets in the five reservoirs of the Thamama Group. The δ18OVPDB analysis indicated that Fracture Set 1 has a longer cementation history than Fracture Set 3, and has wider range of temperatures (58-128°C). A comparison of the outcrop analysis results and the subsurface reservoir was established at the end to distinguish the similarities and differences between the subsurface and outcrop in fracture types, fracture cement types and characteristics of the elemental analysis curve behaviours. The fracture cement in both subsurface and outcrop seemed to be precipitated at deep burial environment.

A detailed laboratory study of sandstone samples from outcrops and conventional core samples from the Maastrichtian-Paleocene Scollard-age fluvial strata in the Western Canada foredeep was undertaken to investigate the reservoir characteristics, burial depth history, and sandstone diagenesis. The sandstones are predominantly litharenites and sublitharenites, which accumulated in a variety of fluvial environments. The porosity of the sandstones is both syn-depositional and diagenetic in origin. The potential of a sandstone to serve as a reservoir for producible hydrocarbons is strongly related to the sandstones diagenetic history. Detailed study of the distribution of authigenic minerals of the Scollard sequence suggests that the diversities in the pattern distribution of authigenic clay minerals in the regions are not random but they coincide with the burial depth of these strata and has a well-defined relation to the sequence stratigraphic framework The general absence of dickite, coupled with limited conversion of smectite into illite in the Scollard sandstones, suggests crystallization at a depth less than 1.5 km. In contrast, the occurrence of blocky dickite, fibrous illite and chlorite in the Coalspur and Willow Creek sandstones, coupled with albitized feldspars and quartz cement, suggests that sandstones there underwent a maximum burial depth greater than 3 km. It has been observed that kaolin mineral content increases in sandstones lying below subaerial unconformities, which mark the most significant stratigraphic hiatuses and hence the sequence boundaries in fully fluvial successions. This study demonstrates the effects of burial depth and paleoclimate on pore-water chemistry, which in turn, influenced the mineralogy and the distributions of authigenic minerals in the sandstones. The 13C and 18O compositions of pedogenic carbonate nodules from the Willow Creek Formation associated with the red shale host sediments have been used as a paleoclimate and paleoenvironmental proxy. The isotopic composition of nodules suggests that these formed during drier conditions when C3 vegetation prevailed at the site. The predominance of smectite and illite in fines and the poor floral content point to a low seasonal rainfall in a semi-arid climatic environment.

Thesis (Ph. D.)--University of Texas at Austin, 1999. / Vita. Includes bibliographical references (leaves 343-385). Available also in a digital version from Dissertation Abstracts.

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