THE RELATIONSHIP BETWEEN THE DIAGENESIS OF UPPER PALAEOZOIC RESERVOIR SANDSTONES AND THE PRODUCTION CAPACITY IN DANIUDI GAS FIELD, THE ORDOS BASIN

Based on analysis of petrology,diagenesis,pore structure,microfracture and relationship with the gas yield of the Upper Palaeozonic reservoir sandstones in Daniudi Gas Field,Northern Ordos Basin,fine diagenetic difference exists on Upper Palaeozoic potential reservoir.The compaction is the main diagenesis resulting in pore and permeability lost,cementation greatly changes the pore structure and further reduces porosity and permeability although dissolution may improves the reservoir quality to some extent.The cementation type and strength exhibit difference with stronger quart and relatively less carbonates cementation in Carboniferous Taiyuan Formation(C₁t),and with less quart and relatively stronger carbonates cementation in Lower Shihezhi Formation(P₁x).Pore structure analysis shows that the Third and Second Member of Lower Shihezhi Formation(P₁x³ and P₁x²) with larger permeability than P₁x¹ and other reservoirs is related with the microfractures contributing to higher production capacity in P₁x³ and P₁x².