A review of alkane gas geochemistry in the Xujiaweizi fault-depression, Songliao Basin

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

“…(4) Abiotic Polymerization. Under conditions of ultrahigh temperatures and pressures, similar to those at which inorganic gases are generated, polymerization processes could alter carbon isotope distributions to be similar to those of inorganic gases [45]. If abiotic polymerization occurred, carbon isotopic separation of 1000ln(σ C2-C1 ) would be expected to decrease as thermal stress increased.…”

“…Taking 1000ln(σ C2-C1 ) as an indicator of thermal stress, the dryness indicator C 1 /(C 2 +C 3 ) should decrease with decreasing 1000ln(σ C2-C1 ) if the gases were generated by polymerization. Zeng et al [45] suggested that gases from the Songliao field with isotopic reversals were generated by abiotic polymerization, and the trend for their data is plotted in Figure 9 for comparison. As shown in Figure 9, there is an initial increase and then decrease of C 1 /(C 2 +C 3 ) ratios with increasing 1000ln(σ C2-C1 ) values for the Songliao gases.…”

Isotopic Composition of Abiogenic Gas Produced in Closed-System Fischer-Tropsch Synthesis: Implications for the Origins of the Deep Songliao Basin Gases in China

“…The Xujiaweizi fault depression is located in the north part of the Songliao Basin (Figure 1(a)). From younger to older, the deep strata of the Xujiaweizi fault depression comprise the Denglouku Formation, Yingcheng Formation, Shahezi Formation, and Huoshiling Formation (Figure 1(b)) [36]. Among these, the deposition periods of the Huoshiling and Yingcheng formations were the main developing times for volcanic rocks in fault depression, the deposition period of Shahezi Formation was the main developing period for hydrocarbon source rocks in the fault depressions, and the Denglouku Formation was the regional cap rock of the natural gas in the deep fault depression [41].…”

“…The simple rules of FTS indicate that more olefins and carbon dioxide are formed on iron catalysts, whereas more alkanes and water are produced on nickel and cobalt catalysts [53]. In hydrothermal systems, carbon dioxide is the most likely reactant, 2 Geofluids Figure 1: Location of the Xujiaweizi Fault Depression (modified from [41]) and the stratigraphic column for the deep strata of Xujiaweizi fault depression (modified from [36]). 4 Geofluids and many laboratory experiments [57][58][59][60][61][62][63] have shown that saturated hydrocarbons and other organic compounds can be generated by FTS reactions with carbon dioxide as an indirect carbon source.…”

“…It has previously been observed that some abiogenic CO 2 and biogenic hydrocarbon gas reservoirs have been found successively in the Xujiaweizi fault depression of the Songliao Basin [34,35]. Most of these gases are produced by Ro > 2 0% source rocks and have carbon isotopic reversals (δ 13 [36]. Their genetic origin has been debated for a long time (e.g., Guo et al 1997; [37][38][39][40][41]), mainly because of their common carbon isotopic reversals.…”