Daniudi gas field is located in the northeastern part of Yishan slope in Ordos Basin.One of the major reservoirs is the braided channel sandstone in Member Ⅰ of the Lower Permian Xiashihezi Formation.The sandstones consists mainly of lithic sandstones and lithic quartz sandstones with medium compositional and structural maturity.The sandstone reservoir is of strong heterogeneity.The porosity and permeability of the reservoirs are 4-14% and (0.05-2)×10

-3

μm

2

respectively

which repsent the typical characteristics of low porosity and permeability reservoirs or even tight reservoirs.The reservoir is at A

2

-B substage of the late diagenetic stage.Mechanical compaction

quartz overgrowth and calcite cementation are the main diagenesis for decreasing porosity of sandstone.Intergranular dissolution pore is the major pore type.Sedimentary microfacies

lithology and diagenesis are the main factors influencing reservoir properties.Using grey relational analysis(GRA)method

this paper divides the reservoirs in Member I of Xiashihezi Formation into three types based on multiple parameters such as sedimentary microfacies

reservoir macro-and micro-charac teristics.Type Ⅰ reservoirs have relatively high porosity and permeability

while type Ⅱ has relatively moderate porosity and permeability.The distributions of three different types of reservoirs are predicted and the evaluation criteria of the reservoirs in Member I of Xiashihezi Formation are also established.