Characteristic And Formation Mechanism Of Carboniferous Carbonate Reservoirs In The Middle Caspain Sea Basin

The southeastern margin of the Caspian Sea Basin has always been a favorable pointing area for oil and gas,with rich oil and gas resources and superior reservoir formation conditions.It development multiple reservoir-forming combinations,in which Carboniferous carbonate rocks have been the main target layer for exploration.After fully reviewing previous research literature,with the use of rock flakes and cast flakes picture?logging data?Carbon-oxygen stable isotope?Electronic probe trace elements to make investigate of Characteristic and formation mechanism.Carboniferous carbonate rocks are mainly composed of spangled grain limestone(53.13%),followed by microcrystalline grain limestone(29.75%)and dolomite(10.36%).The types of reservoir rocks in the upper and lower reservoir sections are different.The main types of reservoir rocks in the KT-I section are spangled grain limestone(33.61%),microcrystalline grain limestone(33.74%)and powdermicrocrystalline dolomite(20.99%),while the KT-II section of bright crystallized limestone(69.79%)occupies a high proportion.The development of the reservoir space is related to the type of rock.The KT-I section is developed due to the development of bright crystal oolitic and gravel sandstone limestone,so the intragranular dissolution pores and mold pores(27.75%)are more developed.A large number of plaster mold pores and paste dissolution pores(19.14%)and dissolution pores(18.18%)are storage spaces.The KT-II section mainly develops bright crystal raw debris limestone,which is more likely to form intergranular pores and intergranular dissolution pores(60.91%).Furthermore,the Carboniferous carbonate reservoirs in the study area are divided into oolitic beaches,gravel-sand shoal facies limestone reservoirs,and bioclastic shoal facies limestone reservoirs through the combined relationship between the type of reservoir rock and the type of storage space.,Microcrystalline limestone reservoir,powder-microcrystalline dolomite reservoir,powder-fine crystal dolomite reservoir,medium-coarse crystal dolomite reservoir.Among them,bioclastic shoal limestone reservoirs are the most developed,followed by oolitic shoal and gravel shoal shoal facies reservoirs,and powder-microcrystalline dolomite reservoirs are only developed in the KT-I section,while other types of reservoirs are less developed.The formation of the Carboniferous carbonate reservoirs in the study area was affected by various diagenesis.Among them,dolomitization,dissolution and karstification played a key role in the formation of the reservoir.Based on previous studies,this article further clarifies the dolomite petrochemical model and defines the identification marks for each stage of dissolution and karstification.Based on the analysis of diagenesis,the diagenetic evolution sequence of the study area is established to explore the formation mechanism of different types of reservoirs.Through the study of the basic characteristics of the reservoir and the mechanism of formation,combined with a large number of statistical data,finally find out the main controlling factors of reservoir formation.The development of Carboniferous carbonate reservoirs in the study area is closely related to the types of reservoir rocks.The formation of reservoirs is affected by high-energy depositional environments,dolomiteization,and dissolution.The distribution of reservoirs is affected by sequence sea level changes,high-energy,and A combination of factors such as the high-growth beach body,the restricted relationship between the high-salinity dolomite and unconformity on the platform,and the topography of the Carboniferous karst valley.