The Ordovician oil reservoirs in Tarim Basin are highly heterogeneous with a complex distribution pattern of fluids.Drilling data

mud logging and well logging data were integrated to analyze the lithology and thickness of high-resistivity layers in the Yingshan Formation.Well tie profiles of each wellblock and inner-outer zones based on single well histograms were generated and the distribution patterns of these high-resistivity carbonates were mapped.The lithology of high resistivity layers in the Yingshan Formation is mainly micritic limestone.They occur as layered bright yellow on imaging logs and show spatial distribution featuring in "lateral unstableness and vertical superimposition".Examination of rock mineral cast thin sections of high resistivity layers indicates that the high resistivity layers were formed mainly by mechanical-chemical filling and selective dissolution by atmospheric water.In addition

the thickness of high resistivity layer correlate well with properties of oil in the underlying reservoir

daily oil/gas production and gas/oil ratio.With increasing thickness of high resistivity layer

daily oil/gas production and gas/oil ratio increase

while density and viscosity of oil decrease

suggesting that high resistivity layers could have a certain control on underlying oil and gas distribution.The high resistivity layers in the Yingshan Formation could act as a set or multiple sets of subtle local seals for the underlying reservoir.