Formation and preservation of deposits at great depths in the Tarim oil and gas basin

The authors of this article analyzed published research from recent years on the discoveries of deep and ultra-deep hydrocarbon accumulations in the Tarim oil and gas basin, including studies conducted prior to drilling ultra-deep wells. The classical understanding of hydrocarbon formation, accumulation, and preservation is described. The article presents data on the reservoirs and oil and gas source rocks associated with deposits in ultra-deep horizons. Selected results from ultra-deep well drilling where liquid hydrocarbons were encountered are presented. The results of geochemical studies conducted in the region are presented, along with the results on the main oil source strata. The results of reconstructing the subsidence model, paleoheat flow history, and heating of the Tabei uplift strata based on well RP7 data are presented. The geothermal regime of the basin is described as one of the most important factors in the formation of hydrocarbons of various phase compositions. The main conclusion from the analysis is that the sedimentary basin began intensive subsidence approximately 10 Ma, and only in the last 5 Ma the oil source rocks subsided more than 2 km and exited the oil window. Nowadays, temperatures at depths of approximately 10000 m do not exceed 190 °C, which contributes to the preservation of liquid hydrocarbons at extremely deep depths.

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