Geochemistry and possible origin of the hydrocarbons from Wells Zhongshen1 and Zhongshen1C, Tazhong Uplift

Abstract

In 2013, a great breakthrough of deep petroleum exploration was achieved in the Cambrian pre-salt intervals of Wells Zhongshen1 (ZS1) and Zhongshen1C (ZS1C), Tazhong Uplift. However, the hydrocarbon discovery in the Cambrian pre-salt intervals has triggered extensive controversy regarding the source of marine oils in the Tarim Basin. The geochemistry and origin of the Cambrian pre-salt hydrocarbons in Wells ZS1 and ZS1C were investigated using GC, GC-MS and stable carbon isotope technique. These hydrocarbons can be easily distinguished into two genetic families based on their geochemical and carbon isotopic compositions. The oil and natural gases from the Awatage Formation of Well ZS1 are derived from Middle-Upper Ordovician source rocks. In contrast, the condensate and gases from the Xiaoerbulake Formation of Wells ZS1 and ZS1C probably originate from Cambrian source rocks. The recent discovery of these hydrocarbons with two different sources in Wells ZS1 and ZS1C suggests that both Middle-Upper Ordovician-sourced hydrocarbons and Cambrian-sourced petroleums are accumulated in the Tazhong Uplift, presenting a great exploration potential.

Oil charging history and pathways of the Ordovician carbonate reservoir in the Tuoputai region, Tarim Basin, NW China

“…5, Table 1), indicating that they derived from a different oil family. Previous reports showed that oils in these wells derived from Cambrian-Lower Ordovician source rocks (e.g., Li et al 2010aLi et al , b, 2012Li et al , 2015Song et al 2016). …”

“…Two typical oil samples collected from Wells TD2 and T904 were also analyzed for comparison. Oils in these two wells are considered to be sourced from Cambrian-Lower Ordovician source rocks (Ma et al 2005;Zhang and Huang 2005;Li et al 2010aLi et al , b, 2012Li et al , 2015Song et al 2016). …”

The evolution characteristics of diamondoids in coal measures and their potential application in maturity evaluation

“…First, vitrinite reflectance cannot be detected to assess maturity, for vitrinite derived from higher plants is absent in marine sediments. Second, conventional molecular organic geochemical maturity parameters, such as biomarker parameters (Song et al, 2016;Song et al, 2017;Xu et al, 2021;Xu et al, 2022, etc), may be invalid at the high-to overmature stage.…”

Characteristics and controlling factors of the Upper Permian Dalong Formation in northwestern Sichuan Basin, China

“…Many factors control the formation of high-quality source rocks, including productivity, the effect of the depositional environment on the preservation of organic matter, and hydrothermal activity (Song et al, 2016;Song et al, 2019;Meng et al, 2022). We studied the sedimentary paleoenvironment and the hydrothermal activity associated with the Dalong Formation high-quality source rocks.…”