scholarly journals Study on the Mechanism of Organic Matter Enrichment in Early Cambrian Marine Shales in the Lower Yangtze Area, South China: An Example Using Well JXY1

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
Sihong Cheng ◽  
Bin Li ◽  
Kun Zhang ◽  
Weiwei Liu ◽  
Jun Peng ◽  
...  
Keyword(s):  
Organic Matter ◽  
Oxygen Isotope ◽  
Water Body ◽  
Organic Carbon Content ◽  
Hydrocarbon Generation ◽  
Early Cambrian ◽  
Biological Productivity ◽  
Carbon And Oxygen Isotope ◽  
Lower Yangtze ◽  
Hydrothermal Activities

The abundance of organic matter in shales, which has a direct effect on the hydrocarbon generation potential of shales, is an important organic geochemical parameter for evaluating shale gas reservoirs. The total organic carbon content (TOC content) in shale is controlled by the abundance of original sedimentary organic matter. Therefore, it is very important to study the mechanism of organic matter enrichment in shale. In this paper, the Lower Cambrian marine shales from the Lower Yangtze region are selected as the research subject, most of which originate from a typical area well called Well JXY1. The degree of pyritization (DOP) is used to characterize the redox environment of the water body, while the P/Al ratio is used to analyze the biological productivity of paleoseawater. The paleosalinity of seawater is calculated via carbon and oxygen isotope analysis. In addition, the early Cambrian hydrothermal activities were studied by using core description; Si, Al, Fe, and Mn elemental analysis; and oxygen isotope calculations. The results show that during the early Cambrian Wangyinpu sedimentary period, the seawater was an anaerobic water body with H2S, and the oxygen concentration was approximately 0 mL/L. In the middle stages of the Wangyinpu sedimentary period, the water body had the strongest reducibility and the highest biological productivity. Moreover, the paleoocean in this period between the Yangtze plate and the Cathaysian plate was greatly affected by hydrothermal activities, with temperatures ranging from 90°C to 120°C. Active hydrothermal activities promoted high biological productivity and an anaerobic environment, both of which were conducive to the preservation and enrichment of organic matter, resulting in extremely high TOC content in the Wangyinpu shales (from 6.5% to approximately 16%).

scholarly journals Characterization of organic matter from a stratigraphic sequence intercepted by the Nemo-1X well, Mozambique: Potential for hydrocarbon generation

2018 ◽  
Vol 36 (5) ◽  
pp. 1157-1171
Author(s):  
Agostinho Mussa ◽  
Deolinda Flores ◽  
Joana Ribeiro ◽  
Ana MP Mizusaki ◽  
Mónica Chamussa ◽  
...  
Keyword(s):  
Organic Matter ◽  
Organic Carbon ◽  
Total Organic Carbon ◽  
Hydrocarbon Exploration ◽  
Published Data ◽  
Organic Carbon Content ◽  
Hydrocarbon Generation ◽  
Offshore Area ◽  
Type Iii ◽  
Kerogen Type

The Mozambique Basin, which occurs onshore and offshore in the central and southern parts of Mozambique, contains a thick sequence of volcanic and sedimentary rocks that range in age from the Jurassic to Cenozoic. This basin, along with the Rovuma basin to the north, has been the main target for hydrocarbon exploration; however, published data on hydrocarbon occurrences do not exist. In this context, the present study aims to contribute to the understanding of the nature of the organic matter of a sedimentary sequence intercepted by the Nemo-1X exploration well located in the offshore area of the Mozambique Basin. The well reached a depth of 4127 m, and 33 samples were collected from a depth of 2219–3676 m ranging in age from early to Late Cretaceous. In this study, petrographic and geochemical analytical methods were applied to assess the level of vitrinite reflectance and the organic matter type as well as the total organic carbon, total sulfur, and CaCO3 contents. The results show that the total organic carbon content ranges from 0.41 to 1.34 wt%, with the highest values determined in the samples from the Lower Domo Shale and Sena Formations, which may be related to the presence of the solid bitumens that occur in the carbonate fraction of those samples. The vitrinite random reflectances range from 0.65 to 0.86%Rrandom, suggesting that the organic matter in all of the samples is in the peak phase of the “oil generation window” (0.65–0.9%Rrandom). The organic matter is mainly composed of vitrinite and inertinite macerals, with a minor contribution of sporinite from the liptinite group, which is typical of kerogen type III. Although all of the samples have vitrinite reflectances corresponding to the oil window, the formation of liquid hydrocarbons is rather limited because the organic matter is dominated by gas-prone kerogen type III.

scholarly journals The Role of Deep Geofluids in the Enrichment of Sedimentary Organic Matter: A Case Study of the Late Ordovician-Early Silurian in the Upper Yangtze Region and Early Cambrian in the Lower Yangtze Region, South China

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-12
Author(s):  
Kun Zhang ◽  
Jun Peng ◽  
Weiwei Liu ◽  
Bin Li ◽  
Qingsong Xia ◽  
...  
Keyword(s):  
Organic Matter ◽  
Water Surface ◽  
Sedimentary Organic Matter ◽  
Biological Productivity ◽  
Upper Ordovician ◽  
Longmaxi Formation ◽  
Lower Silurian ◽  
Lower Yangtze Region ◽  
Lower Yangtze ◽  
Volcanic Activities

Organic matter is the material basis for shales to generate hydrocarbon, as well as the main reservoir space and seepage channel for shale gas. When the thermal evolution degree is consistent, the organic carbon content in present shales is subject to the abundance of primitive sedimentary organic matter. Deep geofluids significantly influence the sedimentary organic matter’s enrichment, but the mechanism remains unclear. This paper is aimed at determining how hydrothermal and volcanic activities affected the enrichment of sedimentary organic matter by studying lower Cambrian shales in the lower Yangtze region and upper Ordovician-lower Silurian shales. Oxidation-reduction and biological productivity are used as indicators in the study. The result shows that hydrothermal or volcanic activities affected the enrichment of sedimentary organic matter by influencing climate changes and the nutrients’ sources on the waterbody’s surface and reducing water at the bottom. In the lower Cambrian shales of the Wangyinpu Formation in the lower Yangtze region, hydrothermal origin caused excess silicon. During the sedimentary period of the lower and middle-upper Wangyinpu Formation, vigorous hydrothermal activities increased the biological productivity on the waterbody’s surface and intensified the reducibility at the bottom of the waterbody, which enabled the rich sedimentary organic matter to be well preserved. During the sedimentary period of the lower upper Ordovician Wufeng Formation and the lower Silurian Longmaxi Formation in the upper Yangtze region, frequent volcanic activities caused high biological productivity on the waterbody surface and strong reducibility at the bottom of the waterbody. As a result, the abundant organic matter deposited from the water surface can be well preserved. During the sedimentary period of the upper Longmaxi Formation, volcanic activities died down gradually then disappeared, causing the biological productivity on the water surface to decrease. Besides, the small amount of organic matter deposited from the water surface was destroyed due to oxidation.

scholarly journals The calcareous concretions (cementsten) in the Fur Formation (Paleogene, Denmark): isotopic evidence of early diagenetic growth

1996 ◽  
Vol 43 ◽  
pp. 78-86
Author(s):  
Gunver Krarup Pedersen ◽  
Bjørn Buchardt
Keyword(s):  
Organic Matter ◽  
Oxygen Isotope ◽  
Volcanic Ash ◽  
Pore Space ◽  
Sulphate Reduction ◽  
Isotopic Evidence ◽  
Carbon And Oxygen Isotope ◽  
Marine Shell

The Paleogene Fur Formation in northwestem Denmark is a c. 60 m thick clayey diatomite that comprises calcite concretions, the so-called cementsten. The diatomite is interbedded with 179 isochronous and recognizable layers of volcanic ash, which demonstrate that the concretions occur at six stratigraphic levels throughout the Fur Formation. The concretions formed through precipitation of calcite in the pore space within the diatomite or the ash layers. Carbon and oxygen isotope compositions were determined on the concretionary calcite. 613C values around -20%0 to -16%0 indicate that most (bi)carbonate was of bacterial ongin, formed through metabolization of organic matter by sulphate reduction. 6180 values of -1%0 to -3%0 indicate that calcite precipitated at temperatures corresponding to those measured in contemporaneous marine shell materiai. It is speculated that rare blooms of phytoplankton made the six stratigraphic levels the preferred sites of nucleation of the concretions.

Organic matter removal for the analysis of carbon and oxygen isotope compositions of siderite

2014 ◽  
Vol 372 ◽  
pp. 54-61 ◽  
Author(s):  
Oanez Lebeau ◽  
Vincent Busigny ◽  
Carine Chaduteau ◽  
Magali Ader
Keyword(s):  
Organic Matter ◽  
Oxygen Isotope ◽  
Organic Matter Removal ◽  
Carbon And Oxygen Isotope

scholarly journals Depositional conditions and petroleum potential of the Middle Triassic Passhatten Member (Bravaisberget Formation), Spitsbergen

2014 ◽  
Vol 35 (1) ◽  
pp. 41-71
Author(s):  
Przemysław Karcz
Keyword(s):  
Organic Matter ◽  
Organic Carbon ◽  
Middle Triassic ◽  
Oxygen Deficiency ◽  
Intermediate Stage ◽  
Black Shales ◽  
Water Dynamics ◽  
Maximum Temperature ◽  
Organic Carbon Content ◽  
Biological Productivity

Abstract The Passhatten Member (Anisian-Ladinian) is the most westward exposure of the Middle Triassic sedimentary sequence of Spitsbergen. The member has an average organic carbon of 2.21 wt %. The sediments were deposited in a shallow shelf environment under conditions of high biological productivity stimulated by a well−developed upwelling system and an enhanced nutrient supply from land areas. The high biological productivity caused a high supply of organic particles to the shelf bottom. Decomposition of organic matter initiated oxygen deficiency in the bottom waters; however, bottom water dynamics on the shallow shelf temporarily replenished the oxygen. Consequently, the Passhatten Mb section is bioturbated, even in thick black shale horizons and consists of alternately spaced lithological layers with variable organic carbon content. The organic matter is dominated by type II kerogen with a mixture of strongly altered marine and/or land derived organic matter. Calculated initial hydrogen index values suggest oil−prone organic matter similar to kerogen I and II types. The organic matter is in the upper intermediate stage of thermo−cata− lytic alteration, close to the cata- and metagenetic boundary. Maturity indicators including Rock−Eval, Maximum Temperature, Organic Matter Transformation Ratio, Residual Car− bon content, as well as the volume of methane generated suggest mature to overmature organic matter. Methane potential retained in the black shales sequence is significant. Unexpelled gas is estimated at 395 mcf/ac−ft for the examined section.

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