Most oil reservoirs that were found in the Junggar Basin are located in the Mahu sag and neighboring areas.Oil sources and classifications remain unresolved in this region.Oil source assessment can be partially incons...Most oil reservoirs that were found in the Junggar Basin are located in the Mahu sag and neighboring areas.Oil sources and classifications remain unresolved in this region.Oil source assessment can be partially inconsistent on the basis of different molecular and isotopic parameters.In the present study,classifications for the 92 studied oils from the Mahu sag and neighboring areas were performed using chemometric analysis,e.g.,hierarchical cluster analysis(HCA)and principal component analysis(PCA)on the basis of integration of sixteen facies parameters.These parameters consist of isotope reversal index(RI),δ^(13)C of n-C_(25),Ph/n-C18,β-carotane/n-C21,six terpane ratios of Ts/C_(23) tricyclic terpanes,Ts/(C_(28)+C_(29) tricyclic terpanes),C_(29) Ts/C_(23) tricyclic terpanes,C_(29)Ts/(C_(28)+C_(29) tricyclic terpanes),C_(30) diahopane/C_(23) tricyclic terpane and C_(30) diahopane/(C_(28)+C_(29) tricyclic terpanes),and six ratios of polynuclear aromatic hydrocarbons(PAH)including trimethylnaphthalenes(TMNs)/(TMNs+phenanthrene(Phen)),tetramethylnaphthalenes(TeMNs)/(TeMNs+Phen),TMNs/(TMNs+methylphenanthrenes(MPs)),TeMNs/(TeMNs+MPs),TMNs/(TMNs+chrysene(Ch))and TeMNs/(TeMNs+Ch).These sixteen parameters are mainly influenced by source facies and less influenced by maturity as demonstrated in the crossplots of these sixteen parameters versus concentrations of C_(30) hopane.Oil classifications are more reliable and convenient using chemometric analysis(HCA and PCA)integrating the sixteen facies parameters,compared with using crossplots of two parameters or star charts of several parameters.The 92 oils are classified into three groups using HCA and PCA,i.e.,Group Ⅰ, Ⅱ and Ⅲ. Group Ⅰ and Ⅱ oils are derived from source rocks within the Lower Permian Fengcheng Formation(P_(1)f)and Middle Permian Lower Wuerhe Formation(P_(2)w),respectively.Group Ⅲ oils are mixtures of Group Ⅰ and Ⅱ oils. Group Ⅰ consists of fifty oils mainly located at the northeastern and central areas of the Mahu sag with only three oils at the southwestern area of the Mahu sag.Group Ⅱ consists of fourteen oils at the southwestern area of the Mahu sag.Group Ⅲ consists of twenty-eight oils located at the southwestern and central areas of the Mahu sag.Locations of Group Ⅰ, Ⅱ and Ⅲ oils reflect the distributions of effective source rocks containing oil-prone Type Ⅰ/Ⅱ kerogen within the Fengcheng(P_(1)f)and Lower Wuerhe formations(P_(2)w).展开更多
基金funded by the Strategic Priority Research Program of the Chinese Academy of Sciences(XDA14010104)the National S&T Major Project of China(Grant No.2017ZX05008-002-030)。
文摘Most oil reservoirs that were found in the Junggar Basin are located in the Mahu sag and neighboring areas.Oil sources and classifications remain unresolved in this region.Oil source assessment can be partially inconsistent on the basis of different molecular and isotopic parameters.In the present study,classifications for the 92 studied oils from the Mahu sag and neighboring areas were performed using chemometric analysis,e.g.,hierarchical cluster analysis(HCA)and principal component analysis(PCA)on the basis of integration of sixteen facies parameters.These parameters consist of isotope reversal index(RI),δ^(13)C of n-C_(25),Ph/n-C18,β-carotane/n-C21,six terpane ratios of Ts/C_(23) tricyclic terpanes,Ts/(C_(28)+C_(29) tricyclic terpanes),C_(29) Ts/C_(23) tricyclic terpanes,C_(29)Ts/(C_(28)+C_(29) tricyclic terpanes),C_(30) diahopane/C_(23) tricyclic terpane and C_(30) diahopane/(C_(28)+C_(29) tricyclic terpanes),and six ratios of polynuclear aromatic hydrocarbons(PAH)including trimethylnaphthalenes(TMNs)/(TMNs+phenanthrene(Phen)),tetramethylnaphthalenes(TeMNs)/(TeMNs+Phen),TMNs/(TMNs+methylphenanthrenes(MPs)),TeMNs/(TeMNs+MPs),TMNs/(TMNs+chrysene(Ch))and TeMNs/(TeMNs+Ch).These sixteen parameters are mainly influenced by source facies and less influenced by maturity as demonstrated in the crossplots of these sixteen parameters versus concentrations of C_(30) hopane.Oil classifications are more reliable and convenient using chemometric analysis(HCA and PCA)integrating the sixteen facies parameters,compared with using crossplots of two parameters or star charts of several parameters.The 92 oils are classified into three groups using HCA and PCA,i.e.,Group Ⅰ, Ⅱ and Ⅲ. Group Ⅰ and Ⅱ oils are derived from source rocks within the Lower Permian Fengcheng Formation(P_(1)f)and Middle Permian Lower Wuerhe Formation(P_(2)w),respectively.Group Ⅲ oils are mixtures of Group Ⅰ and Ⅱ oils. Group Ⅰ consists of fifty oils mainly located at the northeastern and central areas of the Mahu sag with only three oils at the southwestern area of the Mahu sag.Group Ⅱ consists of fourteen oils at the southwestern area of the Mahu sag.Group Ⅲ consists of twenty-eight oils located at the southwestern and central areas of the Mahu sag.Locations of Group Ⅰ, Ⅱ and Ⅲ oils reflect the distributions of effective source rocks containing oil-prone Type Ⅰ/Ⅱ kerogen within the Fengcheng(P_(1)f)and Lower Wuerhe formations(P_(2)w).
