Comparison on Rare Gas Geochemical Characteristics and Gas Originations of Kuche and Southwestern Depressions in Tarim Basin, China

Abstract

The Kuche Depression is considered as the most important gas resource potential and gas exploring area with great gas resource potential and prospect in the Tarim Basin. Based on geochemical experimental analyses and comprehensive geological studies, the general geochemical characteristics of molecular and isotope compositions of rare gases as well as hydrocarbon gases and nonhydrocarbon gases are comparatively studied in the Kuche and Southwestern Depressions. Then, their genetic types are separately identified and gas originations are comprehensively discussed. The main results are as follows. (1) Gas fields in the Kuche Depression have a higher methane abundance, accompanied with low N2and CO2abundances, but the Akemomu gas field in the Southwestern Depression has a relatively lower average methane abundance, accompanied with high average N2and CO2abundances. The helium abundance of natural gases in gas fields from the Kuche Depression general has 1 order of magnitude higher than the air value. Comparatively, it has more than 2 orders of magnitude higher than the atmospheric value in the Akemomu gas field from the Southwestern Depression. The neon, argon, krypton, and xenon abundances in both Kuche and Southwestern Depressions are lower than the corresponding air values. (2) Natural gases from gas fields in the Kuche Depression and the Southwestern Depressions are generally typical coal-formed gases. The rare gases in the Kuche Depression have typical crustal genesis, mainly deriving from the radioactive decay of elements in the crust, while in the Akemomu gas field from the Southwestern Depression, the rare gases have main crustal genesis with a proportion of 92.5%, probably accompanied with a little mantled genetic contribution. (3) Natural gases in the Kuche Depression are generally derived from coal measure source rocks of Jurassic and Triassic, which principally originated from Jurassic in strata period and coals in source rock types. The Jurassic source rocks account for 55%-75% and the Triassic source rocks account for 25%-45% approximately, while coals occupy 68% and mudstones occupy 32% separately. Natural gases from the Akemomu gas field in the Southwestern Depression mainly originated from humic mudstones of marine and continental transitional source rocks of Carboniferous to Permian.

Shale Gas Resource Potential and Accumulation Model of the Middle Jurassic Yangye Formation in the Piedmont Zone of the Southwestern Margin of the Tarim Basin, Northwest China

“…The Southwestern Tarim Depression has been in uenced by the tectonic evolution of the West Kunlun-Pamir orogenic belt since the Late Palaeozoic and has experienced large changes in tectonic and sedimentary patterns and multiphase land-sea transitions. The study area has experienced four main stages of tectonic evolution [19,20]: (1) a transgressive-regression cycle during the Carboniferous-Early Permian and the developmental of continental basins in the Late Permian; (2) the overall uplift of the southwestern part of the Tarim Basin in the Triassic; (3) during the Jurassic, the inland basin in the Southwestern Tarim area evolved, and the sedimentary strata were mainly distributed in some isolated faulted depressions and sags in the piedmonts of the Kunlun Mountains and the South Tianshan Mountains; and (4) during the Cretaceous-Palaeogene, the Southwestern Tarim Depression was generally in a stretching environment, consisting of a set of thick layers of gypsum, ne clastic rocks, gypsum mudstone, and bioclastic limestone deposits [21,22].…”

Petrophysical and Geochemical Investigation-Based Methodology for Analysis of the Multilithology of the Permian Longtan Formation in Southeastern Sichuan Basin, SW China

“…Understanding the characteristics and extraction methods associated with these resources is crucial for maximizing their utilization and contributing to the diversification of the global energy mix [4]. The hydrocarbon source rock matrix contained in the coal measures is the main source for generating these natural gases [5].…”