Comprehensive analyses were performed on thin-section

carbon

oxygen and strontium isotopes and fluid inclusions of reservoirs in the Feixianguan Formation of northeastern Sichuan Basin.In the northeastern part of Kaijiang-Liangping shelf

intercrystalline pores resulting from dolomitization of calcite are absent in the high-quality reservoirs.In contrast

dolomite intergranular dissolution pores or intergranular enlarged dissolution pores are well developed in these reservoirs.Both two kinds of dissolution pores may coexist closely with calcites of light carbon isotope and occur in space between solid bitumen and dolomite crystals

thus they should have been produced by dolomite dissolution after solid bitumen precipitation.In the southern part of Kaijiang-Liangping shelf

dolostones are absent

thus pores of similar origin are also not developed.Under acidic conditions

dolomite may react with anhydrite or celestite

to produce MgSO

4

in the northeastern part of Kaijiang-Liangping shelf.As the MgSO

4

can be easily reduced by hydrocarbons to produce H

2

S

further promoting the dissolution of dolomite

anhydrite and celestite

the precipitation of giant crystal/poikilitic calcite

and the enlarging of secondary pores in local areas.This genetic mechanism can clearly explain the differences of reservoir physical properties between the northeastern and northwestern areas.The MgSO

4

is likely to be the primary intermediate reactants of TSR.