Profitable Diagenetic Path and Reservoir Formation Efficiency of the Sinian-Lower Cambrian Dolostone:Origins of deep dolomites and differential reservoir formation
[Objective]Deep-ultra-deep carbonate rocks have great potential in oil and gas exploration,and their reservoirs are characterized by strong heterogeneity and difficult prediction,which is closely related to their complex diagenetic alterations.Therefore,clarifying the beneficial diagenetic processes in reservoir development,that is,profitable diagenetic path and reservoir formation efficiency,is the key to revealing the genesis of deep carbonate reservoirs.[Methods]We have systematically compared the geochemical parameters,porosity,and permeability of the Sinian to lower Cambrian dolostone from the Sichuan Basin and Tarim Basin(including a small amount of data from the Oman Basin and Siberian Platform),including carbon and oxygen isotopes(n=617),strontium isotope(n=189),rare earth elements(n=106),fluid inclusion homogenization temperature(n=161),cluster isotope tempera-ture(n=117),and porosity and permeability(n=1 557).The geochemical feature templates of dolomite and late calcite of different origins in the two reservoirs were established.[Results]The results show that the geochemical characteristics of diagenetic minerals in the two reservoirs are similar,and both have undergone constructive diagenetic alterations such as dolomitization,meteoric water,fracturing,and hydrothermal fluids.Compared with the lower Cambrian dolostone reservoirs,the highest-quality reservoirs in the area(Dengying Formation)have experi-enced stronger seepage-reflux dolomitization,particularly the more intense hydrothermal alternations,suggesting that differential effective diagenetic alterations are the key to good carbonate reservoir formation.[Conclusions]Based on the above characteristics,the development of Sinian-Cambrian high-quality dolostone reservoirs in the Sichuan Basin and Tarim Basin is jointly controlled by the development of evaporite facies in the depositional period and the develop-ment of late structural hydrothermal fluids.The above findings can be used to predict deep-ultra-deep carbonate reser-voirs,and have enlightenment significance for deep-ultra-deep oil and gas exploration.
deep-ultra-deep oil and gas explorationcarbonatesdolomitizationdiagenesisporosity evolutionreservoir formation efficiency
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