Origin and depositional model of deep-water lacustrine sandstone deposits in the 7th and 6th members of the Yanchang Formation (Late Triassic), Binchang area, Ordos Basin, China

Abstract

Sandstones attributed to different lacustrine sediment gravity flows are present in the 7th and 6th members of the Yanchang Formation in the Ordos Basin, China. These differences in their origins led to different sandstone distributions which control the scale and connectivity of oil and gas reservoirs. Numerous cores and outcrops were analysed to understand the origins of these sandstones. The main origin of these sandstones was analysed by statistical methods, and well logging data were used to study their vertical and horizontal distributions. Results show that the sandstones in the study area accumulated via sandy debris flows, turbidity currents and slumping, and sandy debris flows predominate. The sandstone associated with a single event is characteristically small in scale and exhibits poor lateral continuity. However, as a result of multiple events that stacked gravity flow-related sandstones atop one another, sandstones are extensive overall, as illustrated in the cross section and isopach maps. Finally, a depositional model was developed in which sandy debris flows predominated and various other types of small-scale gravity flows occurred frequently, resulting in extensive deposition of sand bodies across a large area.

Multiple-stacked Hybrid Plays of lacustrine source rock intervals: Case studies from lacustrine basins in China

“…5a). The heterogeneous organic-rich shale source rock is usually interbedded with fine-grained, massive sandy debrite, fine-grained siltstone to sandstone turbidites, and sandy slumps (Zou et al 2012(Zou et al , 2015Liu et al 2017; Fig. 5b, c), indicating that tight oil and shale oil potentials coexist in the Chang7 source rock interval.…”

Reservoir Quality Under the Control of Gravity Flows in the C7 Member of Yanchang Formation in the Jinghe Oilfield, Ordos Basin, China

“…Despite, from for being reservoirs with inadequate physical properties, precisely they have also stacked facies systems and a strong level of diagenetic processes, and mineral cement constitutions that play a considerable impact on reservoir quality [24,40]. In addition, the gravity flows present high particle combinations, which contributes to support in rock heterogeneities and alter the pore space of reservoir rock [22].…”

Depositional Models of Deep-Water Gravity-Flow in Lacustrine Basin and Its Petroleum Geological Significance—A Case Study of Chang 6 Oil Group in Heshui Area, Ordos Basin, China

“…Extensive studies have been conducted on the provenance, paleontology, and geochemical characteristics of gravity-flow deposits in Chang 7 and Chang 6 (Luo et al, 2007;Yang and Deng., 2013;Yao et al, 2013;Zhang et al, 2014;Yuan et al, 2015;Fu et al, 2018). However, no universal cognition on the depositional models of gravity-flow has been made, with a single sedimentary model being used in the previous research to explain these deposits in this area (Yang et al, 2014;Zhang et al, 2016;Liu et al, 2017). Most works studied the characteristics of gravity-flow deposits by taking slide-slump, sandy debris flow, and turbidity current as research objects without considering the macroscopic depositional context or depositional patterns (Fu et al, 2008;Li et al, 2011;Zou et al, 2012;Ran and Zhou., 2019).…”