Reservoirs Characteristics and Evaluation of Yanchang Formation in Zhidan Area, Ordos Basin

In this paper,we analyze the data of drilling cores and cast thin sections,study the petrologic characteristics,characteristics of pore and permeability,and the porosity types,and discuss the effect of such factors on oil-bearing layers of Chang-2,Chang-3,Chang-4+5,and Chang-6 in ZHidan area. The resultindicates that the Yanchang reservoir is characterized by low mineral maturity and highst ructure maturity,of which Chang-2,Chang-3,and Chang-4+5 are better than Chang-6 in mineral maturity. The physical property shows that Chang-2 is characterized by middle-sized pores and low permeability while Chang-3,Chang-4+5,and Chang-6 are very low in permeability. Reservoirs are divided in to four types by several parameters,withChang-2 oil-bearing layer containing reservoir type and Chang-6 oil-bearing layers mostly containing reservoir type-Ⅲ.