Browsing by Subject "Diagenesis"
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Item Analysis of the effects of carbonate mounds on associated stratal geometry and fracture development, Sacramento Mountains, New Mexico, USA(2016-12) Tinker, Nathan Scott; Janson, Xavier; Zahm, Christopher Kent; Kerans, Charles; Fisher, William LThe objective of this research is an integrated structural‐stratigraphic analysis of compaction‐related fracturing in carbonate mounds and associated cover strata. The influence of early-cemented carbonate mounds on subsequent sediment deposition (such as creation of hard substrates and topographic relief) is relatively well-understood. The effect of early-cemented carbonate mounds during burial, however, has not been studied in detail. Early marine cementation of mounds enhances mechanical rigidity, which reduces mound compaction during burial as compared to less-resistant sediments surrounding and overlying the mound. This rigidity difference facilitates differential compaction of sediments overlying the mound, which are warped over the inflection point created by the mound topography. This study hypothesizes that there is a measurable increase in fracture intensity associated with differential compaction above early-lithified carbonate mounds. Thus, this work analyzes and quantifies the effects of differential compaction on stratal geometry, mechanical stratigraphy, and fracture development in Mississippian strata overlying carbonate mounds which are well-exposed in the Sacramento Mountains in southeast New Mexico. Methods employed in this study are drawn from structural geology, sedimentology, petrography, and remote sensing in an effort to adequately determine facies, examine fracture characteristics (e.g. size, orientation, and intensity), and to better understand which process(es) most directly control those characteristics (e.g. host rock facies type, diagenesis, bed thickness, mound proximity, mound size). Innovative methods of outcrop characterization such as high-resolution gigapan photography and unmanned aerial vehicle (UAV) photography were combined with photogrammetric techniques to create photo-realistic 3D outcrop models. The resulting models enabled a cost-effective, more detailed, less-distorted, and more comprehensive interpretation compared to previous methods, and improved understanding of the relationship between stratigraphy, rock mechanical evolution, and structural deformation in carbonate mound systems. Field work documented facies, stratal geometries, folds, faults, and fracture sets which validated observations and characterizations made using high-resolution field photographs and 3D outcrop models. Results of this work show that paleotopographic relief which has been early lithified (in this instance, Mississippian carbonate mounds) directly controls fracture development and overlying stratal geometry, in that there is a significant increase in tension fracture (mode 1) intensity above pre-existing rigid structures and over-steepening of bed dips beyond an expected and reasonable angle of repose. Additionally, this work outlines a multi-stage tectonostratigraphic sequence of the development of the stratigraphically complex Teepee Mound assemblage based on field observations of facies, fractures, stratal geometries, and diagenetic effects (e.g. cementation, compaction, and chertification), which includes new evidence of late-Mississippian tectonic compression. This result emphasizes the importance of understanding both syndepositional and post-depositional processes in outcrop characterization. Specifically, syndepositional processes establish the original mechanical stratigraphy and control the formation and propagation of early mechanical discontinuities, which in turn set up the fabric of weaknesses preferentially utilized by later fracture development. Post-depositional mechanical and diagenetic processes alter mechanical stratigraphy and rock brittleness, and thus influence fracture propagation through time.Item Characterization and prediction of reservoir quality in chlorite-coated sandstones : evidence from the Late Cretaceous Lower Tuscaloosa Formation at Cranfield Field, Mississippi, U.S.A.(2013-05) Kordi, Masoumeh; Fisher, W. L. (William Lawrence), 1932-; Hovorka, Susan D. (Susan Davis)The effectiveness of CO₂ injection in the subsurface for storage and EOR are controlled by reservoir quality variation. This study determines the depositional processes and diagenetic alterations affecting reservoir quality of the Lower Tuscaloosa Formation at Cranfield Field. It also determines the origin, time and processes of the grain-coating chlorite and its impacts on reservoir quality. Moreover, by integrating depositional and diagenetic characteristics and by linking them to sequence stratigraphy, the distribution of reservoir quality, could be predicted within a sequence stratigraphic framework. The studied sandstones are composed of medium to coarse-grained, moderately sorted litharenite to sublitharenite with composition of Q76.1F0.4L23.5. Depositional environment of this formation in the Mississippi Interior Salt Basin is interpreted as incised-valley fluvial fill systems. The cross sections and maps at the field show trend of the sandy intervals within channels with a NW-SE paleocurrent direction. During burial of the sandstones, different digenetic alterations including compaction, dissolution, replacement and cementation by chlorite, quartz, carbonate, kaolinite, titanium oxides, pyrite and iron-oxide modified the porosity and permeability. Among these, formation of chlorite coats plays the most important role in reservoir quality. The well-formed, thick and continuous chlorite coatings in the coarser grain sandstones inhibited formation of quartz overgrowth, resulted in high porosity and permeability after deep burial; whereas the finer grain sandstones with the poorly-formed, thin and discontinuous chlorite coatings have been cemented by quartz. The optimum amount of chlorite to prevent formation of quartz overgrowths is 6% of rock volume. The chlorite coats are composed of two layers including the inner chlorite layer formed by transformation of the Fe-rich clay precursors (odinite) through mixed-layer clays (serpentine-chlorite) during early eodiagenesis and the outer layer formed by direct precipitation from pore waters through dissolution of ferromagnesian rock fragments during late eodiagenesis to early mesodiagenesis. In the context of the reservoir quality prediction within sequence stratigraphic framework, the late LST and early TST are suitable for deposition of chlorite precursor clays, which by progressive burial during diagenesis could be transformed to chlorite, and thus results in preserving original porosity and permeability in deep burial.Item Deposition and diagenesis of the Fort Terrett Formation, near Junction, Texas(Texas Tech University, 1984-12) Trabelsi, Ali M. S.Not availableItem Deposition, diagenesis and distribution of an "Upper Silurian" dolostone reservoir, RK Devonian Field(Texas Tech University, 1984-12) Young, Joe BrianThe RK Devonian Field was discovered in May 1975 with the completion of RK Petroleum Corporation's #1 G.T. Hall for an initial flowing potential of 455 BOPD on a 7/64" choke with a flowing tubing pressure of 1018#'s from five feet of perforations from 11,810-15' after treating with 250 gallons of acid. The well is located 660 feet from the north and west lines of Section 4, T&P RR. Co. Survey, Township 2-N, Block 37, Martin County, Texas. The field is situated in central Martin County (Fig. 1) approximately three miles north of the village of Tarzan and now includes all or parts of the following surveys and blocks: T&P RR. Survey, Township 2-N, Block 37, R.E. Montgomery Survey, Block A.Item Depositional and diagenetic history of the late Triassic Dockum Group, Young Ranch, Nolan County, Texas(Texas Tech University, 2002-05) Slayden, Jason PThe Late Triassic Dockum Group is a series of continental sediments comprised of lacustrine, deltaic, and fluvial deposits. Dockum sediments are found in Eastern New Mexico, Colorado, and West Texas, Oklahoma, and Kansas. The Santa Rosa and Trujillo Formations represent the Dockum Group on the Young Ranch, Nolan County, Texas. Santa Rosa and Trujillo Formations are fluvial deposits consisting of alternating layers of sandstone and conglomerate. These formations are found on the same topographic level on the ranch. Identification of the Santa Rosa and Trujillo formations can be made through petrographic and paleocurrent analysis. The Santa Rosa Formation tends to be more quartzose and arkosic, while the younger Trujillo Formation is more lithic, with an abundance of metamorphic rock fragments and rare volcanic rock fragments. The Santa Rosa Formation has a reported sediment provenance in the present day Wichita-Arbuckle Mountains. Santa Rosa paleocurrent direction on the Young Ranch trend toward the south. The Trujillo Formation has a reported provenance in the lower Ouachita Tectonic Belt. Trujillo paleocurrent directions on the Young Ranch trend toward the north. Therefore, the paleocurrent analysis on the Young Ranch supports the reported Santa Rosa and Trujillo sediment provenances. Lithofacies types and vertical sequences along with a muitistoried channel stacking architecture indicate a braided fluvial system for the deposition of the Santa Rosa Formation. The presence of the Trujillo Formation at the same topographic level on the ranch leads to the conclusion of deposition in two incised valleys. Diagenetic history of the Dockum Group is marked by a variety of cementation events. Kaolinite and iron oxide occurred as early, shallow burial cementation. Zoned dolomite cement was emplaced during burial. Quartz overgrowths and microcrystalline quartz cement formed during Early Cretaceous Edwards exposure due to pedogenic silerete formation in the overiying Lower Cretaceous Antlers Sandstone. Dedolomite/Poikilitopic calcite formed because of dissolution of the Kirsehberg Evaporite during Early Cretaceous Edwards exposure. Desiccation of recent freshwater springs precipitated gypsum as the final diagenetic event.Item Depositional environment, diagenesis and reservoir quality of the middle Bakken member in the Williston Basin, North Dakota(2016-08) Ayhan, Oguzhan; Fisher, W. L. (Williams Lawrence), 1932-; Hammes, Ursula; Kerans, CharlesThe Upper Devonian-Lower Mississippian Bakken Formation in the Williston Basin is an important source rock for oil production in North America. The Bakken Formation is comprised of three units: Upper and Lower Bakken black shales and Middle Bakken Member. Upper and Lower Bakken shales are high quality source rocks which source reservoirs in the Middle Bakken, Upper Three Forks and lower Lodgepole Formations. The Middle Bakken Member, consisting of predominantly gray, silty and sandy dolostone, is under investigation in this study. The goals of this study are to determine the regional distribution of lithofacies and depositional environments of the Middle Bakken Member and explain diagenetic sequence and reservoir quality parameters in the Williston Basin. The reservoir quality of the Middle Bakken Member is mainly influenced by mineralogical composition and cementation resulting in low porosity and permeability and linked to lithofacies distribution in the basin. Dolomitization is pervasive throughout the unit, and also occurs as dolomite cement. Moreover, cementation occurred including quartz overgrowths, K-felspar, clay cement and pyrite as both cement and nodules. Not only dolomitization but also pyrite cementation plays an important role in reducing pore space in the reservoir. The pore types that were identified are intergranular, intragranular, fracture and moldic pores. Secondary intragranular porosity generally resulted from dissolution of biogenic fragments and dissolution of other unstable minerals including feldspar and dolomite. In this study, five lithofacies and one sandy interval within lithofacies C were described throughout the North Dakota portion of the Williston basin. The sandy interval in Lithofacies C was interpreted as bars or channel fills, which differentiates this study from previous studies in terms of core description. N-S, W-E, NE-SW, NW-SE oriented cross-sections drawn via cores suggest that the lithofacies of the Middle Bakken Member pinch out towards the edges. However, the anticlines in the basin affect their thickness distributions. Sandy interval in Lithofacies C reaches its thickest succession in the center of the basin. Lithofacies C and D consist of up to 80% of dolomite although the other lithofacies consist of relatively lower dolomite (up to 65%). While well logs indicate 4-8% of porosity, point-counting results show up to 5% of porosity. The sequence of diagenetic events in the North Dakota portion of the Williston Basin is from youngest to oldest: micritization, mechanical and chemical compaction, calcite cementation, dolomitization, pyrite cementation, microcrystalline quartz cementation, syntaxial calcite overgrowth, quartz overgrowth, K-Feldspar overgrowth, dolomite dissolution, feldspar dissolution, dedolomitization, fracturing, anhydrite cementation and hydrocarbon migration.Item Diagenesis of Strawn Limestone, Lovington East Field, Lea County, New Mexico(Texas Tech University, 1973-12) Gray, Terry LeeOil producing Strawn bioherms in Lovington East Field represent mud mounds where lime mud was baffled by blastoids, crinoids, and cryptostome bryozoans. Abundant aragonitic molluscs, fusulines, and ostracods also inhabited the bioherm core. Bioherms were flanked by aprons of grainstone which consist predominantly of echinoderm components and siliceous sponge spicules with some ooids. Relatively soon after deposition unstable Strawn carbonates became subaerially exposed by an eustatic drop of sea level. Development and retention of effective porosity reflects interaction of lithofacies and biofacies with vadose-phreatic groundwater dynamics. All primary porosity of marginal grainstone lithofacies was rapidly occluded by precipitation of epitaxial cement on monocrystalline echinoderm components and wells drilled into bioherm flanks are nonproductive. Development of secondary porosity was initiated in bioherm cores by solution of aragonitic mollusk shells. Because lime mud matrix was incompletely lithified, molds of aragonitic fossils partially collapsed, forming crumbly fractures which became enlarged into solution channels. Interconnected vugs were formed along solution channels by solution "stoping." Owing to continuous flow of fresh ground water and greater efficiency of solution-precipitation reactions, the paleophreatic zone stabilized long before the superjacent vadose zone where diagenesis was related to rainfall and downward infiltration of water. As carbonate mineralogy of the paleovadose zone slowly stabilized by solution and solution-precipitation, Ca and C0^~ ions were transported down to the phreatic zone and precipitated in unfilled voids as coarsely crystalline ferroan calcite cement which occluded all effective porosity. Large voids within the vadose zone remained unfilled because, after stabilization, there was no superjacent unstable zone with which it could engage in a donor-receptor relationship as it had with the subjacent phreatic zone.Item Diagenesis of Strawn limestone, South Carlsbad Field, Eddy County, New Mexico(Texas Tech University, 1977-05) Maley, Elaine GailStrawn bioherms in South Carlsbad Field represent carbonate mud mounds formed by sediment trapping and baffling organisms, which colonized topographically higher areas of the sea floor. Communities of fenestellid and cyclostome bryozoa created wave-resistant shelters along the Early Strawn shelf margin, behind which dense populations of the phylloid algae Ivanovia thrived. Crinoids, blastoids and siliceous sponges inhabited slightly deeper regions along mound flanks. The mound core was the site of deposition for micrites abundant in aragonitic and calcitic skeletal grains. Skeletal grainstones were deposited along mound flanks and in intermound channels. Relatively soon after deposition biohermal carbonates were subaerially exposed during a eustatic lowering of sea level and were subjected to mineralogic stabilization in vadose and phreatic fresh water environments. Porosity development and preservation reflect interaction of mixed mineral assemblages with vadose-phreatic groundwater dynamics. Porosity within mound flank and intermound grainstones was rapidly occluded by epitaxial cement growth on monocrystalline echinoderm components. Development of secondary moldic and fracture porosity occurred during dissolution of skeletal aragonite. Distribution of remaining primary fossil and sheltered porosity and secondary moldic porosity resulted from differential cementation rates, which in turn reflects (1) characteristics of the substrate and (2) length of exposure to vadose and phreatic diagenetic environments. Stabilization reactions in the vadose zone released calcium carbonate, which migrated downward and enriched phreatic solutions. Accelerated rates of stabilization and porosity occlusion in phreatic zones forced the upward movement of the groundwater table, and phreatic diagenetic fabrics were superimposed on earlier vadose features. Diagenetic fabrics in Strawn carbonates record a slowly rising groundwater table, exhibiting numerous fluctuations due to humid climatic conditions. Sediments subjected to predominantly phreatic diagenesis have retained little or no porosity and permeability, and these intervals are generally non-productive. Throughout the zone of groundwater table fluctuation, porosity preservation is strongly influenced by nature of the substrate for cement precipitation. Upper intervals were subjected to prolonged vadose diagenesis, and porosity in these intervals was preserved because no overlying donor of calcium carbonate was available.Item Environments of deposition and diagenesis of the Upper Clear Fork Group, Yoakum County, Texas(Texas Tech University, 1987-08) Moore, Brian KeithThis project provides an Interpretation of the depositional environments, diagenesls, and resultant porosity relationships within the upper Clear Pork of Yoakum County, Texas. Of primary interest to this investigation Is the description of a small bryozoanalgal patch reef located at the base of the studied section. A discussion of the paleoecology, lateral variations, and community succession of the buildup also is given.Item Evaluating stable isotope proxies (δ¹³C, δ¹⁸O, and δ¹⁵N) for detecting photosymbiosis in fossil corals(2016-05) Tornabene, Chiara; Martindale, Rowan C.; Bell, Christopher J.; Breeker, Daniel O.; Shanahan, Timothy M.Photosymbiosis is a mutually beneficial relationship that many scleractinian corals have developed with dinoflagellates called zooxanthellae. Photosymbiosis is often considered the evolutionary innovation that allowed corals to become major reef-builders; nevertheless it is difficult to determine whether ancient reef-building corals harbored symbionts because zooxanthellae are not preserved in the fossil record. Two stable isotope measurements were previously proposed as proxies for ancient photosymbiosis: δ18O/δ13C and δ15N. Modern zooxanthellate (Z) and azooxanthellate (AZ) corals can be differentiated by skeletal δ18O and δ13C due to fractionation caused by zooxanthellae photosynthesis (Stanley and Swart, 1995) and by the δ15N of their skeletal organic matrix because nitrogen is influenced by trophic lifestyle (Muscatine et al., 2005). In this study, Modern, Holocene, Oligocene, and Triassic coral skeletons with varying morphologies (Z-like and AZ-like morphologies) were analyzed for δ18O/δ13C and δ15N to test whether these geochemical techniques are applicable to the fossil record. To avoid altered signals due to recrystallization, samples were visually tested for diagenetic alteration through petrography and scanning electron microscopy (SEM). The δ18O and δ13C data displayed enriched isotopic values for both C and O in fossil corals and higher variability in Triassic corals than previously reported suggesting that the proxy is not dependable when used on fossil corals. The δ15N analyses of fossil material failed to reproduce the significant Z vs. AZ offset originally identified by Muscatine et al. (2005). Although AZ-like specimens were specifically selected, all of the samples were collected from shallow-water platforms and it is possible that they were zooxanthellate despite their morphology. It is also possible that all corals shared the same nitrogen sources by living in the same environment thus leading to similar organic matrix δ15N values. Future research on this proxy should focus on understanding the influence of the nitrogen cycle on organic matrix δ15N and analyzing fossil deep-water corals to establish whether the δ15N of fossil coral organic matrix can serve as a reliable proxy for ancient photosymbiosis. The establishment of a successful proxy for photosymbiosis will allow scientists to define the evolutionary relationship between coral-zooxanthellae symbiosis and reef-building.Item A fluid inclusion and cathodoluminescence approach to reconstruct fracture growth in the Triassic-Jurassic La Boca Formation, Northeastern Mexico(2011-12) Kaylor, Autumn Leigh; Laubach, Stephen E. (Stephen Ernest), 1955-; Eichhubl, Peter; Catlos, Elizabeth; Ketcham, RichardOpening-mode fracture shapes are typically the result of brittle deformation and proportional growth in fracture height, length, and width. Based on the typical fracture shape, it is assumed that fracture tips are free to propagate in all directions. Some natural rock fractures have been shown to form as a result of slow non-elastic deformation processes. Such fractures may propagate to a finite length or height and accommodate further growth by aperture widening only. To determine the growth conditions of a fracture in the Triassic-Jurassic La Boca Formation of northeastern Mexico and to test fracture growth models, I combined fluid inclusion microthermometry and SEM-based cathodoluminescence cement texture analysis to determine the relative timing of fracture cement precipitation and related fracture opening for five samples collected along its trace. Fracture growth initiated at a minimum age of 70 Ma as two separate fractures with branching fracture tips that coalesced to a single continuous fracture under prograde burial conditions at a minimum age of 54 Ma. At this stage, fracture growth was accommodated by both propagation (i.e. increase in trace length) and by an increase in aperture during maximum burial and early exhumation. Samples collected at the fracture tips recorded temperatures reflecting fracture opening starting with maximum burial at a minimum age of 48 Ma at one tip and of 38 Ma at the other tip. Synkinematic fluid inclusions in crack-seal cement track continued fracture opening close to the fracture tips without a concurrent increase in trace length after 38 Ma until about 21 Ma. I attribute the observed change in fracture growth mechanism to a change in material response. The stage in aperture increase without propagation corresponds to an increase in elastic compliance or in non-elastic flow properties. Non-elastic flow can be attributed to solution-precipitation creep of the host rock. Dissolution of host quartz grains and subsequent quartz precipitation is consistent with the abundance of quartz fracture cement formed during exhumation. Cement textures from fractures in the La Boca Formation mimic those found in subsurface core, which allows application of the results to a variety of geologic environments.Item How diagenesis affects osteon counts on skeletal remains from Colha, Belize(2012-05) Giraldo, Sammy; Paine, Robert R.; Durband, Arthur C.This histological study of Maya skeletal remains from Colha, Belize looked at 16 burials that yielded a total of 56 thin sections for analysis. These 56 thin sections were further divided into 24 thin sections from rib samples and 32 thin sections from clavicle samples. The data analyzed here can offer significant insight into the possibilities that microscopic histological features can provide in terms of knowledge about the health of a population. Unfortunately, due to the deteriorated condition of the bone and diagenesis present, the results obtained in this research did not make any significant correlations between skeletal lesions and the histological features analyzed with the exception of EH and clavicle ISOD. The findings described in this thesis need to be looked at in more depth in future research endeavors which focus specifically on trying to correlate the effects that dietary health and skeletal lesions have on the histological features of bone in Maya skeletal remains. The skeletal material that was used was known to suffer from multiple diet related bone pathologies, but the analysis did not allow any direct correlation to be made between diet and bone histology. Specifically, it was not possible to determine if diet or nutrition had any effect on the HCA, CBA or ISOD.Item Lithologic heterogeneity of the Eagle Ford Formation, South Texas(2014-05) Ergene, Suzan Muge; Milliken, K. L.Grain assemblages in organic-rich mudrocks of the Eagle Ford Formation of South Texas are assessed to determine the relative contributions of intra- and extrabasinal sediment sources, with the ultimate goal of producing data of relevance to prediction of diagenetic pathways. Integrated light microscopy, BSE imaging, and X-ray mapping reveal a mixed grain assemblage of calcareous allochems, biosiliceous grains (radiolaria), quartz, feldspar, lithics, and clay minerals. Dominant fossils are pelagic and benthic foraminifers and thin-walled and prismatic mollusks; echinoderms, calcispheres, and oysters are present. Early-formed authigenic minerals, including calcite, kaolinite, dolomite, albite, pyrite, quartz, and Ca-phosphate, some reworked, add to the overall lithologic heterogeneity. Point counting of images produced using energy-dispersive X-ray mapping in the SEM provides observations at a scale appropriate to classifying the mudrocks based on the composition of the grain assemblage, although grains and other crystals of clay-size cannot be fully characterized even with the SEM. Each sample is plotted on a triangle, whose vertices correspond to terrigenous and volcanic grains (extrabasinal components), calcareous allochems, and biosiliceous grains. As a subequal mix of grains of intrabasinal and extrabasinal origins the detrital grain assemblage of the Eagle Ford, presents a formidable challenge to the task of lithologic classification of this unit, as neither conventional limestone nor sandstone classifications can be readily applied. The abundant marine skeletal debris in the Eagle Ford is accompanied by abundant calcite cementation and the dissolution and replacement of biosiliceous debris is accompanied by authigenic quartz, suggesting that mudrock grain classification has potential for yielding diagenetic predictions.Item Pore Characterization and Classification in Carbonate Reservoirs and the Influence of Diagenesis on the Pore System. Case Study: Thrombolite and Grainstone Units of the Upper Jurassic Smackover Formation, Gulf of Mexico(2014-07-10) Tonietto, SandraThe grainstone and the thrombolite units of the Smackover Formation at Little Cedar Creek Field, in Alabama, USA, were analyzed to determine their reservoir characteristics. The Smackover Formation reservoirs in this field have only minor dolomitization, and most of the depositional texture of the reservoirs is preserved, making Little Cedar Creek Field a unique location to study facies distribution and diagenetic alteration of these reservoirs. Depositional facies define good quality reservoirs of Smackover Formation, but diagenesis plays an important role on enhancing or reducing their porosity and permeability. Thrombolite and ooid-oncoid-peloid grainstone are the most prolific reservoir facies of the Smackover Formation, whereas dolomitization and dissolution are the main diagenetic processes improving porosity and permeability. A paragenetic sequence based on petrography, cathololuminescence, and minor and trace elements analysis was determined on both reservoirs types. Image analysis of scanned thin sections calculated the percentage of grains, pores and cements in the samples. Both reservoirs record distinct early diagenetic events, but similar late diagenetic evolution. The microbial thrombolite was exposed only to marine diagenesis, but the ooid-oncoid-peloid grainstone also was exposed to meteoric phreatic waters. Samples of the dolomitized Smackover Formation thrombolite unit from Appleton and Vocation fields were analyzed and compared to Little Cedar Creek Field thrombolite samples. Porosity, permeability and capillary pressure analysis was completed on thrombolite samples with no dolomitization and samples with distinct degrees of dolomitization. The dolomitization, associated with dissolution of calcite, created an intercrystalline pore network in the thrombolite, increasing porosity and pore connectivity (permeability), and usually reducing pore size. These processes also caused the high petrophysical heterogeneity of the thrombolite to decrease laterally and vertically, resulting in a more homogeneous pore system. In this study a new pore characterization applied to carbonate rocks was developed. It encompasses pore geometry, pore connectivity and the influence of diagenesis in the pore system by generating a quantitative result in order to identify and map reservoir flow units and diagenetic trends. This new pore characterization is based on features observed in thin sections, being a fast and less expensive method to evaluate porosity characteristics.Item Principles of cementation, environmental framework and diagenesis of the Grayburg and Queen formations, New Mexico and Texas(Texas Tech University, 1969-08) Williams, Karl W.This investigation consists of a detailed diagcnetic study of the Grayburg and Queen Formations conducted within the context of the depositional and post-depositional environmental fraraework. Paleogeography, paleoclimatology, and depositional dynamics of these formations are described, and analogous recent sedimentological and diagenetic models proposed. Data utilized in environmental reconstructions were collected from Grayburg and Queen outcrops as well as from subsurface core and core chip samples from 43 oil V7ells located throughout the Northwest Shelf and Central Basin Platform (Figure 3 and Plate 1). Types of evidence evaluated include stratigraphic relationships, primary sedimentary structures, genetic sequences, directional data, paleontologic, textural, mineralogical data, and core test data.Item The role of bacteria in the deposition and early diagenesis of the Posidonienschiefer, a Jurassic oil shale in southern Germany(1988-05) Hiebert, Franz Kunkel; Folk, Robert L.The Jurassic (Toarcian) Posidonienschiefer of southern Germany is famous for its well preserved vertebrate fossils and its high organic content. The majority of the Posidonienschiefer (10 meters thick in the study area) consists of the Bituminous Shale, a fossiliferous laminated illite claystone. Two thin (30-40 mm) clayey pyritic biomicrosparites, the Upper and Lower Schlacken, interrupt the Bituminous Shale. Geologists who have studied the Posidonienschiefer disagree about the exact nature of its depositional environment. The argument centers on the interpretation of an impoverished benthic fauna and whether or not the water column directly above the sediment-water interface was anoxic or normally oxygenated. Kauffman (1981) proposed that an algal/fungal mat located at or near the sediment/water interface marked the boundary between aerobic and anaerobic conditions during deposition. The purpose of my research was to investigate the geologic conditions during deposition and early diagenesis of the Bituminous Shale and the Schlacken and to search for evidence of microbial activity. A detailed petrologic investigation of these two lithologies found no evidence of an algal/fungal mat, but did reveal the important contribution of microbial activity in the formation of pyrite and calcite cement. The Bituminous Shale was deposited in a low-energy tropical seaway. The upper water-column supported a diverse marine fauna. The aerobic/anaerobic boundary in the water column may have been located several millimeters above the sediment/water interface. Pore waters of the ocean-floor mud were dysaerobic to anaerobic. Occasional oxygenation events allowed opportunistic benthic organisms to colonize the sea-floor. Compaction of the Bituminous Shale occured prior to cementation of original porosity. Framboidal pyrite was formed during sulfidic diagenesis under anaerobic, but open, sediment/pore water conditions. Euhedral pyrite formed later as communication between pores became restricted during sediment compaction. The skeletal grains of the Schlacken formed as a winnowed lag deposit of Bituminous Shale sediment. During the early stages of sulfidic diagenesis the winnowed beds were rapidly cemented in a concretion-like sheet. Early cementation preserved delicate algal spores and clay fabric. Fossil bacteria were discovered in the calcite cement of the Schlacken by modified petrographic techniques, and confirmed with the scanning electron microscope. Experiments in which live bacteria were gradually entrapped in halite produced a crystal fabric identical to that of the fossiliferous calcite cement of the Schlacken. The microbial production of bicarbonate and ammonia during sulfidic diagenesis played a significant role in altering local geochemical conditions in the Schlacken sediment and initiated the precipitation of calcite cements. Fossil bacteria in the cements of the Schlacken are direct evidence of the presence and entrapment of bacteria during cementation, but do not conclusively prove their active role in the formation of calcite.Item Stable isotope geochemistry of upper cretaceous and paleocene strata in Big Bend National Park, Texas(Texas Tech University, 2009-05) Schmidt, David R.; Lehman, Thomas; Karlsson, Hal; Barrick, Jim; Chatterjee, SankarFluvial deposits in the Javelina and Black Peaks Formations in Big Bend National Park provide a stratigraphic sequence spanning the Cretaceous-Tertiary (K-T) system boundary. The stable carbon and oxygen isotopic compositions of carbonate and organic matter from these deposits provide information on environmental change associated with the K-T boundary. Carbonate samples are analyzed in groups based on their morphology, crystal fabric, and facies association. The groups comprise pedogenic or ground-water carbonates, lacustrine or surface-water carbonates, early diagenetic carbonates, and late diagenetic carbonates. Although the isotopic compositions of all groups overlap to some degree, and indicate that isotopic exchange may have occurred, distinct isotopic compositions are recognized for each group. The pedogenic and lacustrine carbonates precipitated under similar conditions, and have δ18O values that span a range of about 5‰, suggesting precipitation from surface waters at varied temperature, or from waters concentrated to varied degree by evaporation. Stratigraphic excursions (± 2‰) in carbonate δ18O values could reflect dramatic but brief temperature change (“greenhouse†events) or periods of more or less intense evaporation. The pedogenic carbonates are slightly enriched isotopically relative to lacustrine carbonates and charophyte oogonia; and some contain inclusions of barite crystals, suggesting that soil waters were subject to evaporation. Stratigraphic variation in δ18O, and the more negative values of Paleocene pedogenic carbonates compared to Cretaceous, could also be due in part to the coastal effect on meteoric waters resulting from sea level change. Both pedogenic and lacustrine carbonates have δ13C values indicative of precipitation from solutions in equilibrium with CO2 derived from decomposition of terrestrial plant material. The diagenetic carbonates likely precipitated under early shallow burial conditions and later during deep burial methanogenesis or hydrothermal conditions. Particulate sedimentary organic carbon from alluvial mudstones and intact organic carbon extracted from fossil woods have isotopic compositions compatible with C3 vegetation. Carbon from alluvial mudstone and fossil wood differs in composition slightly, due perhaps to original differences between arborescent and understory vegetation, or varied contributions from different plant parts of local or allochthonous origin. Average δ13C values of conifer and angiosperm woods differ by 2‰, and Cretaceous woods as a group are isotopically heavier than Paleocene woods. No abrupt excursion in organic δ13C concides with the K-T boundary, but variation throughout the entire section could reflect temporal variation in vegetation type, source of organic matter, or atmospheric pCO2. Estimated atmospheric pCO2 levels for the Late Cretaceous (1520 ppmV) are five times that for the Paleocene (370 ppmV). Although this corresponds with cooler wetter conditions interpreted for the Paleocene on the basis of paleosols, the isotopic changes do not coincide with any change in alluvial sediment mineralogy, and it has not been possible to correlate isotopic excursions among the studied sections.Item Structural controls on CO₂ leakage and diagenesis in a natural long-term carbon sequestration analogue : Little Grand Wash fault, Utah(2011-08) Urquhart, Alexander Sebastian MacDonald; Meckel, Timothy Ashworth; Eichhubl, Peter; Laubach, Stephen E. (Stephen Ernest), 1955-; Flemings, Peter B; Hesse, Marc A; Tinker, Scott WThe Little Grand Wash normal fault near Green River, eastern Utah, hosts a series of naturally occurring CO₂ seeps in the form of active and extinct CO₂-charged springs distributed along the fault zone. I have studied the association of fault structure with CO₂-related alteration as an analogue for the long-term (1,000- to 10,000-year) effects of leakage through faults in CO₂ sequestration reservoirs. Structure and alteration in a portion of the Little Grand Wash fault zone were mapped at a 1:700 scale in order to determine the association of faulting with CO₂-related diagenesis. I combined structural and diagenetic mapping were combined with laboratory analyses of mineralogical, isotopic and textural changes in order to assess controls on the migration of CO₂ traveling up the fault and its effects on the fault itself. The fault zone is 200 m wide at its widest and contains 4-5 major subparallel fault segments that form multiple soft- and hard-linked relay ramps. The area includes a travertine deposit and related sandstone alteration: outcrop-visible coloration, porosity-occluding calcite cement and veins occasionally so abundant that they obliterate the rock fabric. Structural mapping shows that the travertine is located at an intersection of major fault segments constituting the hard link of a 450-meter-long relay ramp. Sandstone alteration is confirmed to be related to the CO₂ seep by mapping its distribution, which shows a decrease in concentration away from the travertine, and by the unique isotopic signature of calcite cement near the travertine. At distances greater than 25 m from the travertine intense alteration disappears, though scattered fault-subparallel veins and patchy, burial-related calcite cement remain. Intense alteration is limited to major fault overlaps and does not permeate the fault zone along its entire length, nor does it extend outside the zone. This indicates that rising CO₂-laden fluids do not flow uniformly through the entire fault zone, but that vertical flow is channeled at fault intersections. In thin section, porosity near the travertine has been extensively or completely occluded by calcite cement. Permeability in some conduit samples is less than 1 mD, three or four orders of magnitude lower than sandstone away from the travertine. In active CO₂ conduits, such reduction in porosity and permeability would occlude the preferred flow conduit and ultimately restrict upward flow of CO₂-charged water. X-ray diffraction detects small amounts of goethite and hematite and a decrease in chlorite-smectite in altered conduit sandstones. Calcite is abundant, but many authigenic minerals predicted by geochemical models of CO₂ influx into sandstone reservoirs are not observed, including kaolinite, aragonite, dolomite, siderite, ankerite or dawsonite. This difference between observed and predicted mineral occurrence likely results from differences in mineral kinetics between natural and laboratory systems. Prediction of leakage risk based on fault geometry improves the ability to assess the suitability of potential carbon sequestration reservoirs, many of which will be faulted. The point seep nature of leakage through a fault zone limits the amount of CO₂ that can escape over time and also enables targeted surface monitoring for CO₂ escape into the atmosphere--both critical for ensuring the effectiveness of injection projects and earning the trust necessary for carbon sequestration to gain public acceptance. The point seep nature of leakage also accelerates the rate at which conduits may seal through mineralization, since precipitation from a large volume of fluid is focused in a narrow conduit. The presence of multiple fossil and active seep locations along the Little Grand Wash fault, active at different times in the geologic past, indicates that cementation may be effective in sealing single conduits but that fault systems with complex geometry such as Little Grand Wash may continue to leak for a long period of time.Item Understanding fluid flow in rough-walled fractures using x-ray microtomography images(2015-08) Tokan-Lawal, Adenike O.; Eichhubl, Peter; Prodanović, Maša; Cardenas, M. Bayani; Fisher, William LNatural fractures provide fluid flow pathways in otherwise low permeability reservoirs. These fractures are usually lined or completely filled with mineral cements. The presence of these cements causes very rough fracture walls that can constrict flow and hinder the connectivity between the fracture and matrix/fracture pores thereby reducing porosity, permeability and matrix/fracture transfer. In order to accurately predict fluid transport in the unconventional reservoirs, I study the influence of diagenesis (cementation and compaction in particular) and fracture roughness on flow in artificial (fractured polyethylene) and naturally fractured carbonate (Niobrara formation outcrop) and tight gas sandstones (Torridonian outcrop and Travis Peak reservoir in particular). X-ray microtomography imaging provides information on fracture geometry. Image analysis and characterization of the connectivity and geometric tortuosity of the pore space and individual fluid phases at different saturations, is performed via ImageJ and 3DMA Rock software. I also use a combination of the level-set-method-based progressive-quasistatic algorithm (LSMPQS software), and lattice Boltzmann simulation (Palabos software) to characterize the capillary dominated displacement properties and the relative permeability of the naturally cemented fractures within. Finally, I numerically investigate the effect of (uniform) cementation on the fracture permeability as well as the tortuosity of the pore space and the capillary pressure-water saturation (Pc-Sw) relationship in the Niobrara. Permeability estimates in the different formations vary by several orders of magnitude with the different correlations that currently exist in the literature for all samples studied. The presence of cements increases the geometric tortuosity of the pore space and capillary pressure while reducing the permeability and porosity. Contrary to our expectation, the tortuosity of either wetting or non-wetting phase and their respective relative permeabilities show no clear correlation. Overall, pore scale methods provide an insight to flow characteristics in rough walled fractures at micron scale that are not well represented by existing correlations. The measured properties can be used as input in reservoir simulators.