scholarly journals Carbon and Hydrogen Isotopic Reversals in Highly Mature Coal-Derived Gases: A Case Study of Paleozoic Gases in the Southern Ordos Basin, China

Geofluids ◽  
2019 ◽  
Vol 2019 ◽  
pp. 1-23
Author(s):  
Dan Liu
Keyword(s):  
Source Rock ◽  
Vitrinite Reflectance ◽  
Ordos Basin ◽  
Isotopic Fractionation ◽  
Carbon Isotopic ◽  
Wet Gas ◽  
The Ordos Basin ◽  
Almost All ◽  
Mixing Of Gases

The compositional carbon isotopic seriesδ13C-CH4<δ13C-C2H6<δ13C-C3H8<δ13C-C4H10is common in thermogenic gases. With the exploration of deeper strata, however, isotopic reversals (δ13C-CH4>δ13C-C2H6>δ13C-C3H8) in overmature unconventional shale gases and conventional (coal-derived) gases have been identified. Paleozoic gases in the southern Ordos Basin, China, with partial or complete isotopic reversals, were studied as examples of isotopic fractionation in overmature coal-derived gases. Isotopic compositions of gases of different maturities from the Ordos Basin and shale gases from around the world were compared. Results indicate that carbon isotopic series are related to maturity. Complete isotopic reversal occurs mostly in regions with vitrinite reflectanceRo>2.4%. Where2.4%>Ro>2.0%, almost all gases display partial isotopic reversal, withδ13C-CH4>δ13C-C2H6orδ13C-C2H6>δ13C-C3H8. Carbon isotopic reversal in coal-derived gases is not caused by abiotic origin, the mixing of gases from different types of source rock, abiotic polymerization, wet gas cracking, and other mechanisms that contribute to reversal in shale gases. Based on the unique structure of coaly source rock and the geology of the Ordos Basin, closed-system aromatization-polycondensation reactions are considered the most likely cause of carbon isotopic reversal. During the reactions, isotopically light gases are generated by recombination of previously formed hydrocarbons and residual kerogen-coal. Hydrogen isotopic reversal in the southern Ordos Basin might also be caused by aromatization-polycondensation reactions.

Origin Type and Generating Mechanism of Coal Measure Limestone Gas: A Case Study of L1 Limestone Gas in the Taiyuan Formation of the Shenzhou Coal Mine, Eastern Edge of the Ordos Basin, China

2020 ◽  
Vol 34 (9) ◽  
pp. 10904-10914
Author(s):  
Longqing Shi ◽  
Tianhao Liu ◽  
Xiaoyang Zhang ◽  
Jiyun Huang ◽  
Wu Zhang ◽  
...  
Keyword(s):  
Coal Mine ◽  
Ordos Basin ◽  
Coal Measure ◽  
Taiyuan Formation ◽  
The Ordos Basin ◽  
Eastern Edge

A case study: evaluating low-porosity and ultra-low-permeability Triassic reservoir rocks in the Ordos Basin by the integration of logs and core

2017 ◽  
Vol 23 (4) ◽  
pp. 454-465 ◽  
Author(s):  
Fengqi Tan ◽  
Rui Zhao ◽  
Yangyang Zhao ◽  
Zhejun Pan ◽  
Hongqi Li
Keyword(s):  
Ordos Basin ◽  
Low Permeability ◽  
Reservoir Rocks ◽  
The Ordos Basin ◽  
Low Porosity

scholarly journals Geochemical characteristics and depositional environments of the Narimba Formation source rock, Bass Basin, Australia

2020 ◽  
Vol 10 (8) ◽  
pp. 3207-3225
Author(s):  
Mohamed Ragab Shalaby ◽  
Muhammad Izzat Izzuddin bin Haji Irwan ◽  
Liyana Nadiah Osli ◽  
Md Aminul Islam
Keyword(s):  
Source Rock ◽  
Vitrinite Reflectance ◽  
Depositional Environments ◽  
Geochemical Characteristics ◽  
Type Ii ◽  
Wet Gas ◽  
Kerogen Type ◽  
Rock Characterization ◽  
Rock Eval ◽  
Oil Gas

Abstract This research aims to conduct source rock characterization on the Narimba Formation in the Bass Basin, Australia, which is made of mostly sandstone, shale and coal. The geochemical characteristics and depositional environments have been investigated through a variety of data such as rock–eval pyrolysis, TOC, organic petrography and biomarkers. Total organic carbon (TOC) values indicated good to excellent organic richness with values ranging from 1.1 to 79.2%. Kerogen typing of the examined samples from the Narimba Formation indicates that the formation contains organic matter capable of generating kerogen Type-III, Type-II-III and Type-II which is gas prone, oil–gas prone and oil prone, respectively. Pyrolysis maturity parameters (Tmax, PI), in combination with vitrinite reflectance and some biomarkers, all confirm that all samples are at early mature to mature and are in the oil and wet gas windows. The biomarkers data (the isoprenoids (Pr/Ph), CPI, isoprenoids/n-alkanes distribution (Pr/nC17 and Ph/nC18), in addition to the regular sterane biomarkers (C27, C28 and C29) are mainly used to evaluate the paleodepositional environment, maturity and biodegradation. It has been interpreted that the Narimba Formation was found to be deposited in non-marine (oxygen-rich) depositional environment with a dominance of terrestrial plant sources. All the analyzed samples show clear indication to be considered at the early mature to mature oil window with some indication of biodegradation.

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