Jiyoung Choi

Marine silicate weathering in the anoxic sediment of the Ulleung Basin: Evidence and consequences

Marine silicate weathering (MSiW) in anoxic sediments has been recently shown to be a significant sink for CO2 generated by methanogenesis. Independently, the roles of clay dehydration (illitization) in producing water and driving upward fluid advection have been well established in deep marine sediments, but to date the K+ source required for the reaction has not been established. Here we present chemical and strontium isotope properties of pore fluids from seven cores in the Ulleung Basin, which show radiogenic 87Sr/86Sr values (up to ∼0.71045), very high alkalinity values (maximum ∼130 mM), and enrichment in H4SiO4, Na+, K+, and Mg2+, consistent with MSiW. This reaction consumes CO2, generates alkalinity, and acts as a K+ source for illitization; water released from MSiW-supported illitization drives upward fluid flow. Our results highlight the importance of MSiW along continental margins and its underappreciated role in carbon cycling, silicate diagenesis, and hydrogeology of marine systems.

Inorganic and Organic Geochemical Characteristics of Devonian Bitumen Carbonate in Alberta, Canada

Inorganic and organic geochemical characteristics of Devonian bitumen carbonates in Alberta were studied using two drilling cores, Saleski 03-34-88-20w4 and Saleski 08-01-88-20w4, taken from the Core Research Center of Canada. The results of elements analyses showed high Total Inorganic Carbon, low Total Nitrogen and Total Sulfur, and Rock-Eval pyrolysis showed double peaks in the oxidation part. These mean that the Devonian bitumen carbonates are mainly composed of dolomite formed by diagenesis, and its crystal texture is dominantly subhedral to anhedral but often euhedral. Bitumen contents were 3.6~19.0% in Saleski 3-34-88-20w4 and 5.0~16.4% in Saleski 08-01-88-20w4, respectively. As samples color become dark, bitumen and Total Organic Carbon contents are generally increasing in two cores. The results of biomarker analyses showed that the contents of resins and asphaltenes were 5~28% higher than those of saturated hydrocarbon, interring that the bitumen has been heavily biodegradated. According to the results of carbon isotope analyses in each component of bitumen, asphaltenes had highest values and the others had constant values. However, their values were varied in the range of normal crude oil (-18~-30‰).

Geochemical analyses on bituminous carbonate reservoir in Alberta, Canada: focusing on the GC/GC-MS results of bitumen

The geochemical study on bituminous carbonate reservoir in Alberta has been performed to document the organic geochemical characteristics of the Grosmont Formation using two drilling cores (SAL 03-34 and SAL 08-01), especially focusing on the GC and GC-MS analyses. The results of GC and GC-MS analyses for the extracted organic matter (EOM) showed that all samples have been severely undergone a biodegradation process. However, the GC-MS data have displayed a little variation among the samples, which may be due to degree/type of biodegradation and the type of microbial activity. Triterpane biomarkers are present in low amounts, and steranes in even lesser amounts. Source and maturity assessments from both biomarkers are limited due to the lack of peaks by advanced biodegradation. The demethylated hopanes, which are typical of biodegraded oils, are not seen in these samples but they are apparently not unusual for the Athabasca tar sands, probably due to the specific type of post-emplacement microbial activity. Triterpanes biomarkers illustrate that a highly anoxic hypersaline source environment has contributed to the original oils, at the same time having anoxic marine carbonate/marl character. There is also tenuous evidence for a post-Triassic source according to the tricyclic terpane ratios. The steranes similarly indicate a marine, possibly carbonate-influenced source. Some of the aromatic compounds could also indicate a marine and anoxic hypersaline sourcing. The available peak ratios and patterns of EOM by GC-MS suggest high maturity, and aromatic parameters infer condensate window level with a vitrinite reflectance equivalent range of ∼0.9–1.2%. This could explain the remaining relatively light n-alkanes in the saturated GC chromatograms.

Performance analysis of a counter-rotating tubular type micro-turbine by experiment and CFD

Micro hydraulic turbines have a growing interest because of its small and simple structure, as well as a high possibility of using in micro and small hydropower applications. The differential pressure existing in city water pipelines can be used efficiently to generate electricity in a way similar to that of energy being generated through gravitational potential energy in dams. The pressure energy in the city pipelines is often wasted by using pressure reducing valves at the inlet of water cleaning centers. Instead of using the pressure reducing valves, a micro counter-rotating hydraulic turbine can be used to make use of the pressure energy. In the present paper, a counter-rotating tubular type micro-turbine is studied, with the front runner connected to the generator stator and the rear runner connected to the generator rotor. The performance of the turbine is investigated experimentally and numerically. A commercial ANSYS CFD code was used for numerical analysis.

Biological early diagenesis and insolation-paced paleoproductivity signified in deep core sediment organic matter

The dynamics of a large stock of organic matter contained in deep sediments of marginal seas plays pivotal role in global carbon cycle, yet it is poorly constrained. Here, dissolved organic matter (DOM) in sediments was investigated for core sediment up to ~240 meters deep in the East/Japan Sea. The upper downcore profile (≤118 mbsf, or meters below seafloor) at a non-chimney site (U1) featured the exponential production of dissolved organic carbon (DOC) and optically active DOM with time in the pore water above sulfate-methane-transition-zone (SMTZ), concurrent with the increases of nutrients and alkalinity, and the reduction of sulfate. Such depth profiles signify a biological pathway of the DOM production during the early diagenesis of particulate organic matter presumably dominated by sulfate reduction. Below the SMTZ, an insolation-paced oscillation of DOM in a ~405-Kyr cycle of orbital eccentricity was observed at site U1, implying astronomically paced paleoproductivity stimulated by light availability. Furthermore, DOM dynamics of the deep sediments were likely governed by intensive humification as revealed by the less pronounced protein-like fluorescence and the lower H/C and O/C ratios below SMTZ among 15,281 formulas identified. Our findings here provide novel insights into organic matter dynamics in deep sediments.

Geochemical Characteristics of Devonian Bitumen Carbonates in Alberta, Canada

The objective of this study is to investigate inorganic characteristics of Devonian bitumen carbonates in Alberta using two drilling cores, Saleski 03-34-88-20w4 and Saleski 08-01-88-20w4, taken from the Core Research Center (CRC) of Canada. The bitumen carbonates are mainly composed of less than 0.2 mm dolomites and some carbonate includes small amount of quartz and calcite. The bitumen carbonates from two cores are interpreted to have formed in similar sedimentary environments and dolomitization processes. Carbonates from Saleski 03-34-88-20w4 core were formed under higher inflow of clastic sediment than those from Saleski 08-01-88-20w4 core. Range of crystallization temperature of dolomites in the both bitumen carbonate cores is about 40~. Dolomitizing fluid of the bitumen carbonates would be Devonian seawater. Bitumen carbonates from Cairn Formation, compared with the CRC cores, have experienced a similar crystallization temperature, but dolmititizing fluid of the bitumen carbonates from Cairn Formation have been modified from the isotopic exchange with continental crust.

Biodegradation characteristics of bitumen from the Upper Devonian carbonates (Grosmont and Nisku formations) in Alberta, Canada

In this study, we investigated the biodegradation processes of bitumen from the Upper Devonian carbonates (Grosmont and Nisku formations) in Alberta using GC and GC-MS analyses of four drilling cores. The analyzed samples contain notable rich extracted bitumen, which is predominantly composed of NSO and asphaltene compounds and has lesser amounts of saturated and aromatic hydrocarbons (HCs). The GC and GC-MS results for both saturated and aromatic HCs indicate that there are considerable variations among the samples, which are primarily attributed to the differences in the degree of biodegradation involving microbial activity. The sulfur content and its isotope values for the samples also support biodegradation. Three groups can be classified based on the biomarker distributions as follows: (1) in Group 1, C19-C25 tricyclic terpanes are most abundant, particularly the C23 compounds; (2) Group 2 has no C30-C35 αβ hopanes and more abundant 25-norhopanes than the other two groups; and (3) Group 3 is similar to Group 1, but generally has less abundant C19-C25 tricyclic terpanes than Group 1. The reservoir alteration processes have notably influenced the biomarker properties of the samples. The most pronounced effects are the reduction of the amounts of C30+ hopanes and increasing demethylated hopanes, particularly in Groups 1 and 2, but not in Group 3. For Group 3, unlike Group 1, the degradation of hopanes apparently does not result in demethylated hopanes, indicating that there is another pathway to produce hopanes and/or destroy demethylated hopanes. These findings indicate that the biodegradation processes that occurred in the Grosmont and Nisku formations have been spatially and vertically varied due to the different environmental conditions and microbial processes.