Petroleum generation and expulsion characteristics of Lower and Middle Jurassic source rocks on the southern margin of Junggar Basin, northwest China: implications for unconventional gas potential

Abstract

Jurassic strata along the southern margin of Junggar Basin are important petroleum system elements for exploration in northwest China. The Lower and Middle Jurassic source rock effectiveness has been questioned as exploration progresses deeper into the basin. These source rocks are very thick and are distributed widely. They contain a high total organic carbon composed predominantly of Type III kerogen, with some Type II kerogen. Our evaluation of source rock petroleum generation characteristics and expulsion history, including one-dimensional basin modeling, indicates that Jurassic source rocks are gas prone at deeper depths. They reached peak oil generation during the Early Cretaceous and began to generate gas in the Late Cretaceous. Gas generation peaked in the Paleogene-Neogene. Source rock shales and coals reached petroleum expulsion thresholds at thermal maturities of 0.8% and 0.75% vitrinite reflectance, respectively, when the petroleum expulsion efficiency was ϳ40%. The petroleum generated and expelled from these source rocks are 3788.75 × 10 8 and 1507.55 × 10 8 t, respectively, with a residual 2281.20 × 10 8 t retained in the source rocks. In these tight reservoirs, a favorable stratigraphic relationship (where tight sandstone reservoirs directly overlie the source rocks) indicates short vertical and horizontal migration distances. This indicates the potential for a large, continuous, tight-sand gas resource in the Lower and Middle Jurassic strata. The in-place natural gas resources in the Jurassic reservoirs are up to 5.68 × 10 12 − 15.14 × 10 12 m 3 . Jurassic Badaowan and Xishanyao coals have geological characteristics that are favorable for coal-bed methane resources, which have an in-place resource potential between 3.60 × 10 12 and 11.67 × 10 12 m 3 . These Lower and Middle Jurassic strata have good shale gas potential compared with active US shale gas, and the inferred in-place shale gas resources in Junggar Basin are between 20.73 × 10 12 and 113.89 × 10 12 m 3 . This rich inferred conventional and unconventional petroleum resource in tight-sand, coal-bed, and shale gas reservoirs makes the deeper Jurassic strata along the southern margin of Junggar Basin a prospective target for future exploration.Résumé : Les strates jurassiques le long de la bordure sud du bassin de Junggar constituent des éléments importants d'un système pétrolier exploitable dans le nord-ouest de la Chine. L'efficacité de la roche source (Jurassique inférieur et moyen) a été mise en question à mesure que l'exploration progressait plus profondément dans le bassin. Ces roches sources sont très épaisses et couvent de grandes étendues. Leur teneur en carbone organique total est élevée et il est principalement composé de kérogène de type III avec un peu de kérogène de type II. Selon notre évaluation des caractéristiques de génération de pétrole à partir de roches souches et de l'historique d'expulsion, incluant une modélisation du bassin à une dimension, ces roches sources du Jurassique devraient contenir du gaz à de grandes pro...

Source rock characteristics and hydrocarbon expulsion potential of the Middle Eocene Wenchang formation in the Huizhou depression, Pearl River Mouth basin, south China sea

“…Hydrocarbon expulsion occurs when the hydrocarbon generation potential decreases (Fig. 3;Pang et al, 2005;Guo et al, 2014), and the corresponding geological condition is defined as the hydrocarbon expulsion threshold (Zhou and Pang, 2002;Pang et al, 2005). Before hydrocarbons begin to be expelled, the hydrocarbon generation potential index is called the original hydrocarbon generation potential index (GPI o ) (Fig.…”

“…where k is the restoration coefficient; 0.83 is the average carbon content in the hydrocarbons (Burnham, 1989;Guo et al, 2014); GPI r is the remaining hydrocarbon generation potential index (mg HC/g TOC); PGI o is the hydrocarbon generation potential index at the expulsion threshold (mg HC/g TOC).…”

Impact of Paleosalinity, Dilution, Redox, and Paleoproductivity on Organic Matter Enrichment in a Saline Lacustrine Rift Basin: A Case Study of Paleogene Organic-Rich Shale in Dongpu Depression, Bohai Bay Basin, Eastern China

“…The shale gas and oil revolution of North America changed the world energy structure and stimulated shale oil exploration and research in many other countries around the world. Precise prediction of “sweet spots” is one of the key musts for successful shale oil exploration. − Recent studies indicate that the organic matter content in a shale determines the hydrocarbon generation capacity of the shale, − affects the pore space development, ,− and strongly correlates to the residual hydrocarbon (adsorption) capacity. ,,,− Therefore, shale oil “sweet spots” and organic-rich intervals are closely related, − , and determination of the main factors controlling organic matter enrichment in shales is of great significance.…”

New insights on the petroleum migration and accumulation in the basal conglomerate reservoir of Cretaceous Qingshuihe Formation of Yongjin area, Central Junggar Basin

“…The C 27 ‐, C 28 ‐, and C 29 ‐regular steranes appear in an asymmetric ‘V’‐shaped distribution, suggesting the double contribution of lower organisms and higher plants, with the latter being the dominant of the two. The moderate abundance of C 21 pregnane (C 21 P) and C 22 homopregnane (C 22 HP) revealed a depositional environment with high salinity (Guo et al, 2014).…”

“…On the m/z 191 chromatograms, the crude oils featured a high abundance of C 20 , C 21 , and C 23 -tricyclic terpanes (C 20 , C 21 , and C 23 TTs, respectively) with C 21 TT as the peak compound, and high abundance of C 30 hopane (C 30 H; Figure 12). An abnormally high abundance of gammacerane (Ga) further supports the presence of a reducing depositional environment (Guo et al, 2014). The content of C 27 18α(H), 21β (H)-22, 29, 30-trisnorneohopane (Ts) is higher than that of C 27 17α (H), 21β(H)-22, 29, 30-trisnorhopane (Tm), showing a higher thermal maturity (Clayton, Yang, King, Lillis, & Warden, 1997) The factors that affect the composition of biomarkers are highly complex, and a single biomarker cannot work as an effective indicator of oil-source correlation (Xie, Qin, Zhang, & Li, 2013).…”