Carbonate Reservoir Characteristics Study Of Qom Formation, Central Iranian Basin

Qom Formation is a carbonate deposition of Neogene Period in a back-arcforeland basin,which is main exploration target stratum in Kashan area of CentralIran Basin. Qom formation is a characteristic diamicton of carbonate and someterrigenous clastics & volcanic clasts.On the basis of detailed observation of 1225pieces of thin-sections, combine with the drilling information,logging informationand physical testing information, lithology character,diagenesis,pore space andphysical property of Qom formation are sdudied.Qom formation is predominantly limestones:Bioclastic limestone, micrite etc.There are also some mudstone,sandstone and tuff.The diagenesis aresimple.Cementation,compaction, pressolution, packing action are the destructivediagenesis.And micrite envelope, chemical erosion, dolomitization,recrystallizationare constructive ones.There are multiform pores microscopically in Qom formation,which can bedivided into primary pores and secondary pores.Primary ones include biologicalantrum pore & residual intergranular pore.Secondary ones include intragranulardissolution pore,intergranular dissolution pore,mold pore,intercrystalline pore &vuggy pore etc.There are no pores observed in 580 pieces of thin-sections in all the 1225ones.The visual porosity of the rest predominantly≤2％,mainly 0.5％～1％.Combinewith the results of physical test of cores we can see that carbonate reservoir of Qomformation is a low-porosity low-permeability reservoir.And exist severeheterogeneity.By the explanation of logging information of Qom formation,we can see that theporosity of each member is very small. ClassⅠand classⅡreservoir are mainlyoccurred in boiclastic limestone and shoal microfacies.Comparisons between threewells show shat there are more reservoir in Am-1,then Am-2,and Fkh-1 is the worst.Diagenesis study shows that mixing-water dolomitization and associated erosionwere of great importance to the development of reservoir.