Details

Autor(en) / Beteiligte

• Burton, Zachary Florentino Murguia

Titel

Characterizing Oil, Gas Hydrate, and Sedimentary Systems Via Geochemistry, Computational Modeling, and Global Synthesis

Ort / Verlag

ProQuest Dissertations & Theses

Erscheinungsjahr

2020

Quelle

ProQuest Dissertations & Theses A&I

Beschreibungen/Notizen

• At the highest level, this dissertation investigates marine systems from a geochemical and sedimentological perspective through the undertaking of six distinct and only somewhat tenuously interrelated contributions. Nonetheless, the work detailed herein might be thought of as fitting, very broadly speaking, under two central themes, being (i) investigations into the formation, evolution, and destruction of hydrocarbon systems and (ii) advancement and refinement of the understanding of global controls on deep-sea clastic depositional systems. These investigations have important bearing on the interplay of climate, tectonics, and paleoceanography and attendant modulation of deep-marine depositional systems and the oceanic carbon cycle at local, regional, and global scales, and throughout Earth history.Chapter 1 of this dissertation presents an organic geochemical assessment of petroleum quality using petroleum seep samples from frontier exploration regions along the east coast of New Zealand’s North Island and northern South Island. We analyze biomarker compounds to assess the degree of biodegradation to which these samples have been subjected, and use biomarker and diamondoid analysis to estimate the thermal maturity of these oils and to identify petroleum mixing that may have occurred during migration and accumulation of these oils. Assessment of biodegradation based upon distributions of nalkane, isoprenoid, sterane, and terpane compounds indicates negligible biodegradation of oils from the northern portion of our study area and low to moderate biodegradation in southern oils, with measurement of 25-norhopane further suggesting that biodegradation in southern oils may be solely aerobic. Taken together, these findings suggest fresh, active seepage (and thus, petroleum systems) in the north, and suggest that the quality of potential subsurface accumulations throughout the studied regions is potentially unaffected by biodegradation. Assessment of thermal maturity, oil-to-gas conversion, and hydrocarbon mixing using sterane, terpane, and diamondoid compounds reveals three distinct petroleum mixtures among the seeps, including components generated throughout the oil window as well as intensely cracked condensate-wet gas components. Identification of black oil components might indicate the presence of actively producing source rock in all regions represented by these seeps, while the intensely cracked components indicate petroleum mixing via thermogenic gas infiltration, and thus suggest an impact on oil quality.Chapter 1 has been published in Energy & Fuels (2018, vol. 32, p. 1287–1296) with coauthors Mike Moldowan, Richard Sykes, and Steve Graham, all of whom provided input and discussion important to the scope, design, and implications of the study. Mike Moldowan provided me the training and laboratory space necessary to the execution of the experimental portion of this work, and was particularly helpful in guiding and informing my interpretations of the results described herein. Richard Sykes provided me with the samples analyzed herein, courtesy of longtime Stanford geosciences collaborator GNS Science in New Zealand, and also provided key contextual information and public data on petroleum geochemistry of New Zealand oil and gas samples. Steve Graham was the one who, alongside Jared Gooley, first suggested I consider undertaking investigation of the frontier basins off New Zealand’s east coast of New Zealand, supported my early forays into petroleum geochemistry, and provided financial support for this study.Chapter 2 presents a geochemical assessment of petroleum source rock depositional environments and age based upon expanded analysis of the set of New Zealand oil seep samples investigated in Chapter 1. We use biomarker distributions, stable carbon isotope distributions, and sulfur concentrations of these oil seep samples to interpret source rock characteristics including type of organic matter input, redox conditions, sedimentary facies, and age. Results show that samples generally cluster into two groups on the basis of these characteristics. These groups correlate with geographic location of seeps—namely, a distinct northern group and southern group emerge. While source rocks associated with all seep samples are interpreted to be marine, results suggest northern samples had more terrigenous organic matter input to their source rock(s), while southern samples had more marine input. Results suggest northern sample source rock(s) had more oxic depositional environments, whereas southern sample source rock(s) had more reducing environments. A shale source rock sedimentary facies was indicated for all samples. These observations suggest that southern samples may be derived from slightly higher quality source rocks (i.e., higher hydrogen index, deposited in more reducing conditions), although source rocks in both regions are oil prone. Biomarker age parameters suggest that the northern oil samples are from a younger (Cenozoic) source rock, whereas the southern oil samples are from an older (Cretaceous) source rock. Taken together, source rock characteristics (depositional environment and age) examined herein indicate the presence of at least two different source rocks—and, advance our understanding of paleodepositional environments and prospective petroleum systems in this underexplored frontier setting.Chapter 2 has been published in International Journal of Earth Sciences (2019, vol. 108, p. 1079–1091) with coauthors Mike Moldowan, Les Magoon, Richard Sykes, and Steve Graham. Coauthor contributions to this study are as detailed for Chapter 1, above, with additional key contributions by Les Magoon, who provided useful discussion, framing, and input—particularly with regard to assessment of oil seeps and correlative source rocks from a holistic petroleum systems perspective.Chapter 3 presents findings from an integrated computational modeling (i.e., basin and petroleum system modeling) study of the impact of tectonic uplift on the stability of submarine gas hydrate systems. We use two-dimensional modeling of a structurally restored transect from the Hikurangi margin of New Zealand (a region with confirmed presence of subsea gas hydrates) to investigate the potential for tectonic shortening and uplift to drive changes in the thickness and extent of the gas hydrate stability zone. We predict evolution of the gas hydrate stability zone from the late Oligocene to present, and demonstrate substantial (~70%) decreases in the extent of the gas hydrate stability zone over this period of tectonic uplift and attendant decreases in water depth along the modeled transect. These results provide modeling-based validation that tectonic uplift can destabilize subsea gas hydrate, with important implications for ocean chemistry and the carbon cycle, particularly during periods of increased plate convergence.Chapter 3 has been published in Geophysical Research Letters (2020, vol. 47) with coauthors Karsten Kroeger, Allegra Hosford Scheirer, Yongkoo Seol, Blair Burgreen- Chan, and Steve Graham, all of whom contributed to discussion of and publication of this work. Karsten Kroeger provided key discussion of gas hydrate systems and input to the overall framing of this study, with particularly helpful input regarding the modeling of gas hydrates, gas hydrate and sedimentary depositional systems of New Zealand, and interpretation of the gas hydrate stability zone from seismic datasets of offshore New Zealand. Allegra Hosford Scheirer suggested the idea of using Blair Burgreen-Chan’s Hikurangi margin basin model to explore model capabilities with regard to characterization of gas hydrate systems, and alongside other instructors in our group, was instrumental to my training in the use of basin and petroleum system modeling software. Yongkoo Seol provided insight into gas hydrate system dynamics (especially gas hydrate stability) and has provided financial support of my gas hydrate research efforts since late 2016. Blair Burgreen-Chan achieved the tremendous task of constructing the two-dimensional model (and performing the painstakingly detailed structural restorations incorporated into this model) that was adapted in this study for investigation of gas hydrate systems. Steve Graham provided unwavering encouragement of my pursuit of this novel approach to investigating gas hydrate stability from the time I first embarked on this work in early 2018, and also provided financial support.Chapter 4 presents a global compilation of sediment organic properties at marine biogenic gas hydrate localities to shed light on the minimum organic carbon and hydrogen contents required for the formation of gas hydrate—given that organic matter in shallow sediments is requisite as the feedstock for microbial metabolism and resultant generation of methane. We undertake a comprehensive synthesis of published total organic carbon (TOC) and hydrogen index (HI) values from analysis by previous workers of shallow (up to ~2 km subseafloor) sediment at marine gas hydrate localities. We compile data from 43 known gas hydrate sites along five continents, which include average site-by-site TOC values ranging from 0.3–3+ wt. % (compatible with previous studies suggesting a minimum TOC of 0.3–0.5 wt. % needed for gas hydrate formation) and an average TOC for all sites of 1.2 wt. % (n = 2000+ total analyses). HI values range from 50–400+ mg hydrocarbon/g TOC, suggesting an HI of 50 may result in gas hydrate formation. Average HI for all sites is 170 (n = 500+ total analyses). This compilation provides both understanding of average organic properties of gas hydrate-associated sediment as well as possible empirical evidence of the minimum TOC and HI necessary for the formation of gas hydrate.Chapter 4 is in preparation for submission to Marine and Petroleum Geology with coauthors Allegra Hosford Scheirer and Ken Peters, both of whom have provided helpful revisions of