The dead line for oil and gas and implication for fossil resource prediction

Abstract

Abstract. Fossil fuel resources are invaluable to economic growth and social development. Understanding the formation and distribution of fossil fuel resources is critical for the search and exploration of them. Until now, the vertical distribution depth of fossil fuel resources has not been confirmed due to different understandings of their origins and the substantial variation in reservoir depths from basin to basin. Geological and geochemical data of 13 634 source rock samples from 1286 exploration wells in six representative petroliferous basins were examined to identify the maximum burial depth of active source rocks in each basin, which is referred to in this study as the active source rock depth limit (ASDL). Beyond the ASDL, source rocks no longer generate or expel hydrocarbons and become inactive. Therefore, the ASDL also sets the maximum depth for fossil fuel resources. The ASDLs of basins around the world are found to range from 3000 to 16 000 m, while the thermal maturities (Ro) of source rocks at the ASDLs are almost the same, with Ro ≈3.5±0.5 %. The Ro of 3.5 % can be regarded as a general criterion to identify ASDLs. High heat flow and more oil-prone kerogen are associated with shallow ASDLs. In addition, tectonic uplift of source rocks can significantly affect ASDLs; 21.6 billion tons of reserves in six representative basins in China and 52 926 documented oil and gas reservoirs in 1186 basins around the world are all located above ASDLs, demonstrating the universal presence of ASDLs in petroliferous basins and their control on the vertical distribution of fossil fuel resources. The data used in this study are deposited in the repository of the PANGAEA database at: https://doi.org/10.1594/PANGAEA.900865 (Pang et al., 2019).

Geologic controls on the genesis of the Arctic permafrost and sub-permafrost methane hydrate-bearing system in the Beaufort–Mackenzie Delta

“…According to the active source rock depth limit (Pang et al, 2020), the basin's heat flow generally controls the maximum burial depth for source rocks to generate and expel hydrocarbons produced by thermal cracking of kerogen (Behar et al, 1997). Since 1.6 MaBP, the Beaufort MD Basin exhibits an approximate heat flow of 55 mW m -2 (Figure 5B) in agreement with the moderate-heat-flow (40-60 mW m -2 ) basin suggested by Pang et al (2020).…”

“…According to the active source rock depth limit (Pang et al, 2020), the basin's heat flow generally controls the maximum burial depth for source rocks to generate and expel hydrocarbons produced by thermal cracking of kerogen (Behar et al, 1997). Since 1.6 MaBP, the Beaufort MD Basin exhibits an approximate heat flow of 55 mW m -2 (Figure 5B) in agreement with the moderate-heat-flow (40-60 mW m -2 ) basin suggested by Pang et al (2020). It implies that the upper limit of hydrocarbon generation, migration and accumulation is below 2,500 mbgl, conforming to the assumption that the GH-forming thermogenic gases originated from the Taglu Sequence (Figure 2B).…”

Carbon Isotope Stratigraphy of the Cambrian System in the Eastern Tarim Basin, China

“…During deep burial, δ 13 C org values of kerogen may increase by up to +1‰ due to generation of 13 C-depleted oil and gas (Clayton, 1991). The present kerogen maturity (R o ) of the lower Cambrian black shales from the Tadong2 Well is about 2.7% (Zhang et al, 2004), higher than the 'oil window' (R o : 0.7-1.3%), but still in the 'gas window' (R o : <3.5%) (Pang et al, 2020). As such, the present δ 13 C org values should be slightly heavier than those of the primary δ 13 C org values.…”

Evaluation and re-understanding of the global natural gas hydrate resources

“…The Mallik NGH accumulation occurs below thick permafrost and overlays directly on a free gas field sourced from deep thermal genetic gas of the basin. A basin wide study in the Beaufort-Mackenzie Basin (BMB) based on petrophysical logs from 251 oil and gas exploration wells showed that, although the NGH occurs in 122 wells (50%), only 7 contain net thickness greater than 5 meters, accounting for < 3% of the total wells studied (Osadetz and Chen 2010).…”