There are a lot of sandy laminations in the Triassic Yanchang Formation shale in the central and southern Ordos Basin

but their influence on hydrocarbon accumulation is not clear.In order to reveal the geological characteristics of sandy lamination and explore its favorable effect on hydrocarbon accumulation

we have studied its lithologic and porosity-permeability characteristics

fracture development as well as oil and gas accumulation

through integration of methods such as core observation

microscopic identification

and organic geochemical analysis.The result shows that

the lithology of sandy lamination is mostly siltstone

argillaceous siltstone

and silty shale; the lamination mainly appears in the form of thin lamina

thin band

and thin interbed.And the existing sandy laminations have changed the way of lithological contact:denser development of the sandy lamination promotes more intense alternation of rock lithology

which is usually more favorable for hydrocarbon expulsion from source rocks.Besides

the sandy lamination favors pore size growth

so improving the physical property of the reservoir in turn.It changes the mechanical property of rocks

resulting in the change of distribution patterns of fractures.It also provides larger reservoir space for liquid hydrocarbon

dissolved gas

and free gas.Shale with highly developed sandy lamination in the Ordos Basin is the main target for present exploration and development

whereas thick deep-lacustrine shale

which is abundant in hydrocarbon

but due to limitations of present developing techniques

may only be producible in the future.