The dedolomitization of Lower Ordovician carbonate reservoirs in Ordos Basin could be divided into five types.Dedolonitization related to unconformity is characterized by producing lots of corrosion fabrics

small amounts of dedolomitized calcite with low contents of Sr

Fe

Mn and low homogenization temperature inclusions.Burial environment dedolomitization related to suture lines

gypsum nodules

burial dissolution caves and cracks

structure fissures are mainly resulted from the loss of Mg

2+

the increase of Ca

2+

the thermal maturation of organic matter and hydrocarbon migration and accumulation.The dedolomitization is charactorized by rich Mg

Fe

Mn

Sr and low δ

18

O

δ

13

C

high homogenization temperature inclusions

thus forming large amounts of dedolamitized calcite.The porosity of the dedolomitized dolomite is clearly higher than that of other dolomites and limestones.This could not only improve reservoir permeability

but also change nonpermeable beds into permeable ones.