LaminaecombinationandshaleoilenrichmentpatternsofChang73sub-memberorganic-richshalesintheTriassicYanchangFormation,OrdosBasin,NWChina<spanid="corr-video"class="type"style="display:none">附视频</span>

The Chang 73 sub-member of Triassic Yanchang Formation in the Ordos Basin was taken as an example and the lamina types and combinations, reservoir space features and shale oil enrichment patterns in organic-rich shale strata were investigated using core observation, thin section analysis, XRF element measurement, XRD analysis, SEM, high solution laser Raman spectroscopy analysis, and micro-FTIR spectroscopy analysis, etc. According to the mineral composition and thickness of the laminae, the Chang 73 organic-rich shales have four major types of laminae, tuff-rich lamina, organic-rich lamina, silt-grade feldspar-quartz lamina and clay lamina. They have two kinds of shale oil-bearing layers, "organic-rich lamina + silt-grade feldspar-quartz lamina" and "organic-rich lamina + tuff-rich lamina" layers. In the "organic-rich + silt-grade feldspar-quartz" laminae combination shale strata, oil was characterized by relative high maturation, and always filled in K-feldspar dissolution pores in the silt-grade feldspar-quartz laminae, forming oil generation, migration and accumulation process between laminae inside the organic shales. In the "organic-rich + tuff-rich lamina" binary laminae combination shale strata, however, the reservoir properties were poor in organic-rich shales, the oil maturation was relatively lower, and mainly accumulated in the intergranular pores of interbedded thin-layered sandstones. The oil generation, migration and accumulation mainly occurred between organic-rich shales and interbedded thin-layered sandstones.