The Upper Devonian,Middle Famennian Dankovo-Lebedyansky sediments in Southeast Tatarstan territory are a carbonate sequence composed of limestone and dolomite,which is important hydrocarbon reservoir units,therefore,i...The Upper Devonian,Middle Famennian Dankovo-Lebedyansky sediments in Southeast Tatarstan territory are a carbonate sequence composed of limestone and dolomite,which is important hydrocarbon reservoir units,therefore,it is necessary to conduct in-depth study on its microfacies and depositional environment.In this study,a multidisciplinary approach that combines core observation with thin section examination is used.The limestone contains abundant skeletal grains(echinoderms,foraminifera,algae,gastropods,and calcispheres),as well as non-skeletal grains(intraclasts and peloids).On the basis of detailed petrographic investigations,six sedimentary microfacies can be identified,including(i)peloidal grainstone(MF 1),(ii)cemented bioclastic peloidal grainstone(MF 2),(iii)echinodermconcentrated packstone(MF 3),(iv)algae packstone(MF 4),(v)bioclastic wackestone(MF 5),(vi)whole-fossil wackestone(MF 6),as well as dolomite or dolostone as diagenetic facies(MF 7).Based on microfacies analysis,the Dankovo-Lebedyansky sediments were deposited in three distinct sedimentary facies belts(shoal,lagoon and open marine environment).In order to reflect dispositional energy condition,the microfacies were grouped into facies associations:(i)low-energy microfacies associations including MF 5 and MF 6,(ii)moderate energy microfacies associations including MF 1,MF 2,MF 3,and MF 4.The dolomite,or diagenetic facies(MF 7),is the result of slightly to extensively dolomitization of limestone in the Dankovo-Lebedyansky sediments.Most of frequent dolostone types are euhedral planar-e and subhedral planar-s.According to petrographic characteristic of the dolostone,a seepage reflux model can be used to explain the dolomitization process of Dankovo-Lebedyansky sediments.展开更多
The results of integrated sedimentology,petrography,and petrophysical study of the Upper Devonian(Middle Famennian)Dankovo-Lebedyansky carbonates from Southeast Tatarstan of the Volga-Ural Basin revealed a variety of ...The results of integrated sedimentology,petrography,and petrophysical study of the Upper Devonian(Middle Famennian)Dankovo-Lebedyansky carbonates from Southeast Tatarstan of the Volga-Ural Basin revealed a variety of microfacies and diagenetic events that impacted the reservoir quality.Although our earlier study documented microfacies analysis and depositional environments,none of the studies focused on diagenesis,microfacies interaction,and their controls on the studied sediment's reservoir quality.Based on petrographic and microfacies analyses,the seven identified microfacies types are peloidal grainstone MF 1,cemented bioclastic peloidal grainstone MF 2,echinoderm-concentrated packstone MF 3,algae packstone MF 4,bioclastic wackestone MF 5,whole-fossil wackestone MF 6,and dolomite MF 7.For the investigated sediments,a gently deepening carbonate ramp depositional model with an inner,middle,and outer ramp setting is proposed.The observed diagenetic events in this study include micritization,calcite cementation(six cement types),dolomitization(six dolomite types),dissolution(fabric and non-fabric-selective dissolution),compaction,and microfracturing.The identified microfacies were classified into three distinct classes based on their petrophysical characteristics.MF 1 and MF 7 are microfacies types with the best reservoir quality.MF 3 and MF 4 are microfacies types of moderate reservoir quality.MF 2,MF 5,and MF 6 are microfacies types with poor or non-reservoir quality.Calcite cementation,micritization,and compaction are the primary diagenetic modifications responsible for porosity reduction.Moldic pores created by dissolution are a significant porosityimproving process.Porosity is locally enhanced by stylolite and microfractures.Dolomitization improved reservoir quality by creating intercrystalline and vuggy porosity.Understanding the impact of microfacies and diagenesis on reservoir quality is crucial for understanding reservoir properties in nearby fields with similar settings.展开更多
基金supported by the Ministry of Science and Higher Education of the Russian Federation under agreement No.075-15-2022-299 within the framework of the development program for a world-class Research Center“Efficient development of the global liquid hydrocarbon reserves”.
文摘The Upper Devonian,Middle Famennian Dankovo-Lebedyansky sediments in Southeast Tatarstan territory are a carbonate sequence composed of limestone and dolomite,which is important hydrocarbon reservoir units,therefore,it is necessary to conduct in-depth study on its microfacies and depositional environment.In this study,a multidisciplinary approach that combines core observation with thin section examination is used.The limestone contains abundant skeletal grains(echinoderms,foraminifera,algae,gastropods,and calcispheres),as well as non-skeletal grains(intraclasts and peloids).On the basis of detailed petrographic investigations,six sedimentary microfacies can be identified,including(i)peloidal grainstone(MF 1),(ii)cemented bioclastic peloidal grainstone(MF 2),(iii)echinodermconcentrated packstone(MF 3),(iv)algae packstone(MF 4),(v)bioclastic wackestone(MF 5),(vi)whole-fossil wackestone(MF 6),as well as dolomite or dolostone as diagenetic facies(MF 7).Based on microfacies analysis,the Dankovo-Lebedyansky sediments were deposited in three distinct sedimentary facies belts(shoal,lagoon and open marine environment).In order to reflect dispositional energy condition,the microfacies were grouped into facies associations:(i)low-energy microfacies associations including MF 5 and MF 6,(ii)moderate energy microfacies associations including MF 1,MF 2,MF 3,and MF 4.The dolomite,or diagenetic facies(MF 7),is the result of slightly to extensively dolomitization of limestone in the Dankovo-Lebedyansky sediments.Most of frequent dolostone types are euhedral planar-e and subhedral planar-s.According to petrographic characteristic of the dolostone,a seepage reflux model can be used to explain the dolomitization process of Dankovo-Lebedyansky sediments.
基金supported by the Ministry of Science and Higher Education of the Russian Federation under agreement No.075-15-2022-299 within the framework of the development program for a world-class Research Center“Efficient development of the global liquid hydrocarbon reserves”.
文摘The results of integrated sedimentology,petrography,and petrophysical study of the Upper Devonian(Middle Famennian)Dankovo-Lebedyansky carbonates from Southeast Tatarstan of the Volga-Ural Basin revealed a variety of microfacies and diagenetic events that impacted the reservoir quality.Although our earlier study documented microfacies analysis and depositional environments,none of the studies focused on diagenesis,microfacies interaction,and their controls on the studied sediment's reservoir quality.Based on petrographic and microfacies analyses,the seven identified microfacies types are peloidal grainstone MF 1,cemented bioclastic peloidal grainstone MF 2,echinoderm-concentrated packstone MF 3,algae packstone MF 4,bioclastic wackestone MF 5,whole-fossil wackestone MF 6,and dolomite MF 7.For the investigated sediments,a gently deepening carbonate ramp depositional model with an inner,middle,and outer ramp setting is proposed.The observed diagenetic events in this study include micritization,calcite cementation(six cement types),dolomitization(six dolomite types),dissolution(fabric and non-fabric-selective dissolution),compaction,and microfracturing.The identified microfacies were classified into three distinct classes based on their petrophysical characteristics.MF 1 and MF 7 are microfacies types with the best reservoir quality.MF 3 and MF 4 are microfacies types of moderate reservoir quality.MF 2,MF 5,and MF 6 are microfacies types with poor or non-reservoir quality.Calcite cementation,micritization,and compaction are the primary diagenetic modifications responsible for porosity reduction.Moldic pores created by dissolution are a significant porosityimproving process.Porosity is locally enhanced by stylolite and microfractures.Dolomitization improved reservoir quality by creating intercrystalline and vuggy porosity.Understanding the impact of microfacies and diagenesis on reservoir quality is crucial for understanding reservoir properties in nearby fields with similar settings.
