Abstract：Evaporation tidal flat facies are developed in the mid gas field of Ordos Basin. They can be subdivided into 7 microfacies, including mud-dolostone flat of the supralittoral zone, gypseous depression of the supralittoral zone, gypseous dolostone flat of the supralittoral zone, algae-dolostone flat of the intertidal zone, mud-dolostone flat of the intertidal zone, grain bank of the intertidal zone and limestone flat of the subtidal zone. Core observation and thin section analysis indicate that the diagenesis of reservoirs in the syngenesis diagenetic environment, freshwater diagenetic environment and buried diagenetic environment include dolomitization, dissolution, filling cohesion, fracture, replacement, compaction-pressure solution, recrystallization, breccia, etc. Based on the analyses of sedimentary facies and the effect of diagenesis on porosity and permeability characteristics of reservoirs, the sedimentary-diagenetic evolutions of carbonate reservoirs are divided into 4 periods, namely sediment-syngenesis diagenesis period, embedding diagenesis period, near floor, uplift-weathering period and late embedding diagenesis period. This unique evolution pattern constitutes vertical 5-layer reservoir architecture, including 2 high porous layers and 3 low porous layers, alternatively distributed. M51 1~M53 1 and M54 1a high porous layers are under the control of the paleokarst in sediment-syngenesis diagenesis period, uplift-weathering period and the microfacies of gypseous dolostone flat, M53 2~M53 3, M54 1b~M54 3b and M55 low porous layers are under the control of mud-dolostone flat, gypseous depression and limestone flat.
2010, Vol. 28 
