To address the discrepancies between well and seismic data in stratigraphic correlation of the Triassic Yanchang Formation in the Ordos Basin,NW China,traditional stratigraphic classification schemes,the latest 3D sei...To address the discrepancies between well and seismic data in stratigraphic correlation of the Triassic Yanchang Formation in the Ordos Basin,NW China,traditional stratigraphic classification schemes,the latest 3D seismic and drilling data,and reservoir sections are thoroughly investigated.Guided by the theory of sequence stratigraphy,the progradational sequence stratigraphic framework of the Yanchang Formation is systematically constructed to elucidate new deposition mechanisms in the depressed lacustrine basin,and it has been successfully applied to the exploration and development practices in the Qingcheng Oilfield.Key findings are obtained in three aspects.First,the seismic progradational reflections,marker tuff beds,and condensed sections of flooding surfaces in the Yanchang Formation are consistent and isochronous.Using flooding surface markers as a reference,a progradational sequence stratigraphic architecture is reconstructed for the middle-upper part of Yanchang Formation,and divided into seven clinoform units(CF1-CF7).Second,progradation predominantly occurs in semi-deep to deep lake environments,with the depositional center not always coinciding with the thickest strata.The lacustrine basin underwent an evolution of“oscillatory regression-progradational infilling-multi-phase superimposition”.Third,the case study of Qingcheng Oilfield reveals that the major pay zones consist of“isochronous but heterochronous”gravity-flow sandstone complexes.Guided by the progradational sequence stratigraphic architecture,horizontal well oil-layer penetration rates remain above 82%.The progradational sequence stratigraphic architecture and associated geological insights are more consistent with the sedimentary infilling mechanisms of large-scale continental depressed lacustrine basins and actual drilling results.The research results provide crucial theoretical and technical support for subsequent refined exploration and development of the Yanchang Formation,and are expected to offer a reference for research and production practice in similar continental lacustrine basins.展开更多
Recent advances in the understanding of deltaic deposits provide new tools for the study and analysis of deltaic deposits in shallow epicontinental seas.After the introduction of sequence stratigraphic concepts,meter-...Recent advances in the understanding of deltaic deposits provide new tools for the study and analysis of deltaic deposits in shallow epicontinental seas.After the introduction of sequence stratigraphic concepts,meter-scale coarsening and thickening upward successions have been considered as“parasequences”originated by high-frequency sea-level changes.Nevertheless,recent studies enhanced the importance of wave-aided low-dense hyperpycnal flows in transporting fine-grained sediments in shallow shelfal areas.These poorly-known(and at the same time very common)types of delta,known as hyperpycnal littoral deltas(HLD),develop very low gradient progradational units,controlled by changes in the sediment supply instead of sea level changes.These small-scale progradational units are very common in shallow epicontinental seas like the Lower Cretaceous Agrio Formation in the Neuquén Basin.This study provides a first detailed analysis of hyperpycnal littoral deltas from the Agua de la Mula Member(upper Hauterivian-lower Barremian)of the Agrio Formation.This unit has been studied in three locations near Bajada del Agrio locality in the central part of the Neuquén Basin,Argentina.Six sandy facies,three heterolithic facies,three muddy facies and four calcareous facies were recognized.From facies analysis,three facies associations could be determined,corresponding to offshore/prodelta,distal ramp delta and proximal ramp delta.The three stratigraphic sections discussed in this study are internally composed of several small-scale sequences showing a coarsening and thickening upward pattern,transitionally going from muddy to sandy wave-dominated facies,and ending with calcareous bioclastics levels on top.These small-scale sequences are interpreted as delta front deposits of wave-influenced hyperpycnal littoral deltas,punctuated by calcareous intervals accumulated during periods of low sediment supply.It is interpreted that the development of hyperpycnal littoral deltas could have been facilitated by a decrease in sea water salinity related to an increasing runoff.展开更多
基金Supported by the National Science and Technology Major Project(2017ZX05001)CNPC Technology Project(2023YQX20111).
文摘To address the discrepancies between well and seismic data in stratigraphic correlation of the Triassic Yanchang Formation in the Ordos Basin,NW China,traditional stratigraphic classification schemes,the latest 3D seismic and drilling data,and reservoir sections are thoroughly investigated.Guided by the theory of sequence stratigraphy,the progradational sequence stratigraphic framework of the Yanchang Formation is systematically constructed to elucidate new deposition mechanisms in the depressed lacustrine basin,and it has been successfully applied to the exploration and development practices in the Qingcheng Oilfield.Key findings are obtained in three aspects.First,the seismic progradational reflections,marker tuff beds,and condensed sections of flooding surfaces in the Yanchang Formation are consistent and isochronous.Using flooding surface markers as a reference,a progradational sequence stratigraphic architecture is reconstructed for the middle-upper part of Yanchang Formation,and divided into seven clinoform units(CF1-CF7).Second,progradation predominantly occurs in semi-deep to deep lake environments,with the depositional center not always coinciding with the thickest strata.The lacustrine basin underwent an evolution of“oscillatory regression-progradational infilling-multi-phase superimposition”.Third,the case study of Qingcheng Oilfield reveals that the major pay zones consist of“isochronous but heterochronous”gravity-flow sandstone complexes.Guided by the progradational sequence stratigraphic architecture,horizontal well oil-layer penetration rates remain above 82%.The progradational sequence stratigraphic architecture and associated geological insights are more consistent with the sedimentary infilling mechanisms of large-scale continental depressed lacustrine basins and actual drilling results.The research results provide crucial theoretical and technical support for subsequent refined exploration and development of the Yanchang Formation,and are expected to offer a reference for research and production practice in similar continental lacustrine basins.
基金financed by CONICET PUE0047COANPCyT 0419 projects。
文摘Recent advances in the understanding of deltaic deposits provide new tools for the study and analysis of deltaic deposits in shallow epicontinental seas.After the introduction of sequence stratigraphic concepts,meter-scale coarsening and thickening upward successions have been considered as“parasequences”originated by high-frequency sea-level changes.Nevertheless,recent studies enhanced the importance of wave-aided low-dense hyperpycnal flows in transporting fine-grained sediments in shallow shelfal areas.These poorly-known(and at the same time very common)types of delta,known as hyperpycnal littoral deltas(HLD),develop very low gradient progradational units,controlled by changes in the sediment supply instead of sea level changes.These small-scale progradational units are very common in shallow epicontinental seas like the Lower Cretaceous Agrio Formation in the Neuquén Basin.This study provides a first detailed analysis of hyperpycnal littoral deltas from the Agua de la Mula Member(upper Hauterivian-lower Barremian)of the Agrio Formation.This unit has been studied in three locations near Bajada del Agrio locality in the central part of the Neuquén Basin,Argentina.Six sandy facies,three heterolithic facies,three muddy facies and four calcareous facies were recognized.From facies analysis,three facies associations could be determined,corresponding to offshore/prodelta,distal ramp delta and proximal ramp delta.The three stratigraphic sections discussed in this study are internally composed of several small-scale sequences showing a coarsening and thickening upward pattern,transitionally going from muddy to sandy wave-dominated facies,and ending with calcareous bioclastics levels on top.These small-scale sequences are interpreted as delta front deposits of wave-influenced hyperpycnal littoral deltas,punctuated by calcareous intervals accumulated during periods of low sediment supply.It is interpreted that the development of hyperpycnal littoral deltas could have been facilitated by a decrease in sea water salinity related to an increasing runoff.
