The transition from meandering river delta to braided river delta: Depositional characteristics and controlling factors from the second member of Shanxi Formation to the eighth member of Lower Shihezi Formation in Southeastern Ordos Basin

Abstract

The Ordos Basin, as one of the most petroliferous basins in China, hosts 12.9 billion tons of oil reserves and 15.2 trillion cubic meters of natural gas reserves. The extensive hydrocarbon exploration and production shows that the southeastern Ordos Basin contains considerable potential in the Shanxi Formation and Lower Shihezi Formation. In this study, cores, wireline logs, thin sections, and heavy minerals are employed to carry out research on classification of sequence stratigraphy, identification of sedimentary facies, reconstruction of palaeo‐geomorphology, analysis of sediment supply, palaeo‐climate, and accommodation space changes. The results indicate that palaeo‐geomorphology gradient tends to be steep, which results in increasing hydrodynamics and turns to be wide and flat which results in decreasing accommodation space. In addition, heavy mineral distribution reveals the direction of sediment supply which indicates provenance changes. The palaeo‐climate changes commonly cause differences in lithology associations, monsoon and vegetation properties. The differences in temperature and humidity result in different colours of lithology associations which indicate various sedimentary environments. The prevalence of monsoon assists in the preservation of fluvial delta by controlling lateral migration of rivers through affecting vegetation and lithology associations. The accommodation space variations control the development of fluvial delta and result in various depositional characteristics of fluvial delta. All these factors trigger the transition from meandering river delta to braided river delta. The reconstruction of the transition and analysis of controlling factors play an important role on understanding the sedimentary evolution of analogous reservoir successions.

The sandstone reservoir characteristics and controlling factors of Shanxi Formation and Lower Shihezi Formation in Southeastern Ordos Basin

“…The heavy minerals from 32 wells were collected from Xinjiang Oilfield Company, including 15 samples from Shanxi Formation and 17 samples from Lower Shihezi Formation (Min et al, 2020). As a sensitive provenance indicator, heavy mineral associations can be used to reveal provenance information.…”

“…The total thickness of Shanxi Formation ranges from 40 to 120 m, in which the thickness of the second member ranges from 20 to 60 m. The Lower Shihezi Formation is a little thicker than that of Shanxi Formation ranging from 120 to 170 m. The thickness in Shanxi Formation and Lower Shihezi Formation both increases towards the north of study area (Min et al, 2020).…”

“…The Shanxi Formation overlies Taiyuan Formation with regional scoured surface (Min et al, 2020; Zhao, Yu, Fu, Han, & Du, 2019). The bottom of the Shanxi Formation develops ‘Beichagou’ sandstone which is mainly characterized by greyish‐white medium‐ to coarse‐grained quartz sandstone and lithic quartz sandstone.…”

“…The Ordos Basin, as a petroliferous basin in China, contains significant hydrocarbon reserves during its long‐term basin evolution (Chen, Li, Zhang, Cheng, & Cheng, 2011; Cui, 2019; Darby & Ritts, 2002; Mattauer et al, 1985; Min, Deng, Xia, & Ye, 2020; Zou et al, 2013; Yu et al, 2017). The Upper Palaeozoic (Shanxi Formation and Lower Shihezi Formation), as a potential exploration interval in southeastern Ordos Basin, has provided numerous considerable resources (Chen et al, 2011; Cui, 2019; Li et al, 2017; Liu, Zhang, & Li, 2018; Shao et al, 2014; Tian et al, 2011; Wang, 2014).…”

“…In the last few decades, the studies have mainly focused on tectonic evolution, sequence stratigraphy, depositional systems, and reservoir mechanism in northern and eastern Ordos Basin (Li, Chen, Hou, Xiang, & Chen, 2008; Wang, 2014; Wang, Tian, Chen, Li, & Xiao, 2009; Yang, 2002; Zheng, Hu, Chen, Liu, & Jia, 2015). By comparison, scholars began recently to conduct research including tectonic and sedimentological issues of the Upper Palaeozoic in southeastern Ordos Basin (Li et al, 2017; Liu et al, 2018; Min et al, 2020; Qu, Ma, Gao, Mei, & Miao, 2011a, 2011b; Shan et al, 2018; Wang, Chen, Wang, & Guo, 2007; Wang, Ji, Men, & Ai, 2013; Wang et al, 2018; Yu et al, 2017; Zhou et al, 2014). However, it can be seen from sparse public reports that few studies pertain to reservoir characteristics and associated controlling factors (Wang et al, 2018; Zhao, Wang, Gao, & Yin, 2015; Zhou et al, 2014).…”