Abstract:

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 Mg²⁺,the increase of Ca²⁺,the thermal maturation of organic matter and hydrocarbon migration and accumulation.The dedolomitization is charactorized by rich Mg,Fe,Mn,Sr and low δ ¹⁸O,δ ¹³C,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.