Callovian-Oxfordian sedimentary microfacies in the middle of Block B on the right bank of the Amu Darya Basin,Turkmenistan

The right bank of the Amu Darya Basin enjoys abundant natural gas resources,on which the Callovian-Oxfordian strata in the middle of Block B serve as the major horizons for natural gas production.However,the characteristics and distribution patterns of the sedimentary microfacies in these strata are yet to be further explored.Based on the analysis of data on drilling,logging,cores,and thin sections from 29 typical wells,as well as the regional sedimentary background,this study inferred that the middle of Block B evolved from the Callovian ramp platform into the Oxfordian rimmed platform.Moreover,this study determined that the inner-ramp intertidal-subtidal shallow-water subfacies mainly developed during the Callovian and transitioned into the shallow shelf subfacies during the Oxfordian.This study identified eight sedimentary microfacies,namely reef knoll,reef-shoal complex,bioclastic shoal,psammitic shoal,bioherm,lime mud mound,intershoal(intermound),and static-water mud.Based on research into the high-precision sequence-sedimentary microfacies framework,this study built a geological model for the development of sedimentary microfacies in the study area.According to this geological model,the sedimentary microfacies in the study area are characterized by vertical alternation of reef-shoal complex,bioclastic(psammitic)shoal,bioherm,and intershoal microfacies.Moreover,they show the development of reef knoll,reef-shoal complex,bioclastic(psammitic)shoal,and bioherm(or lime mud mound)laterally from west to east,with the physical properties of the reservoirs deteriorating from west to east accordingly.The microfacies of reef-shoal complex and the bioclastic(psammitic)shoal predominate in the study area,and their deposition and development are controlled by sequence boundaries and are also affected by paleo-landforms.The Oxfordian reef-shoal complexes were largely inherited from the Callovian uplifts and show lateral seaward progradation.

Microfacies types and distribution of epicontinental shale: A case study of the Wufeng–Longmaxi shale in southern Sichuan Basin, China

For black shales,laminae and bedding are hard to identify,grain size is difficult to measure,and trace fossils do not exist.Taking the Ordovician Wufeng–Silurian Longmaxi shale in southern Sichuan Basin,China,as an example,the types,characteristics and models of microfacies in epicontinental shale are analyzed by means of full-scale observation of large thin sections,argon-ion polishing field emission-scanning electron microscopy(FE-SEM),and kerogen microscopy.The epicontinental sea develops delta,tidal flat and shelf facies,with black shale found in microfacies such as the underwater distributary channel and interdistributary bay under delta front facies,the calcareous and clayey flats under intertidal flat facies,the calcareous and clayey shelfs under shallow shelf facies,the deep slope,deep plain and deep depression under deep shelf facies,and the overflow under gravity flow facies.Basinward,silty lamina decreases and clayey lamina increases,the grain size changes from coarse silt to fine mud,the silica content increases from about 20%to above 55%,the carbonate and clay minerals content decreases from above 40%to around 10%,and the kerogen type changes from type II2 to type II1 and type I.Provenance and topography dominate the types and distribution of shale microfacies.The underwater distributary channel,interdistributary bay,clayey flat,clayey shelf,and overflow microfacies are developed in areas with sufficient sediment supply.The calcareous flat and calcareous shelf are developed in areas with insufficient sediment supply.The deep shelf shale area is divided into deep slope,deep plain,and deep depression microfacies as a result of three breaks.The formation of epicontinental shale with different microfacies is closely related to the tectonic setting,paleoclimate,and sea level rise.The relatively active tectonic setting increases the supply of terrigenous clasts,forming muddy water fine-grained sediment.The warm and humid paleoclimate is conducive to the enrichment of organic matter.The rapid sea level rise is helpful to the widespread black shale.

Prediction of Sedimentary Microfacies Distribution by Coupling Stochastic Modeling Method in Oil and Gas Energy Resource Exploitation

In view of the problem that a single modeling method cannot predict the distribution of microfacies, a new idea of coupling modeling method to comprehensively predict the distribution of sedimentary microfacies was proposed, breaking the tradition that different sedimentary microfacies used the same modeling method in the past. Because different sedimentary microfacies have different distribution characteristics and geometric shapes, it is more accurate to select different simulation methods for prediction. In this paper, the coupling modeling method was to establish the distribution of sedimentary microfacies with simple geometry through the point indicating process simulation, and then predict the microfacies with complex spatial distribution through the sequential indicator simulation method. Taking the DC block of Bohai basin as an example, a high-precision reservoir sedimentary microfacies model was established by the above coupling modeling method, and the model verification results showed that the sedimentary microfacies model had a high consistency with the underground. The coupling microfacies modeling method had higher accuracy and reliability than the traditional modeling method, which provided a new idea for the prediction of sedimentary microfacies.

Microfacies of Deep-water Deposits and Forming Models of the Chinese Continental Scientific Drilling-SKII

Extensive transgression of lake water occurred during the Cretaceous Qingshankou Stage and the Nengjiang Stage in the Songliao basin, forming widespread deep-water deposits. Eleven types of microfacies of deep-water deposits have been recognized in the continuous core rocks from the SKII, including mudstone of still water, marlite, dolostone, off shale, volcanic ashes, turbidite, slump sediment, tempestite, seismite, ostracoda limestone and sparry carbonate, which are divided into two types： microfacies generated due to gradually changing environments （Ⅰ） and microfacies generated due to geological events （Ⅱ）. Type Ⅰ is composed of some special fine grain sediments such as marlite, dolomite stone and oil shale as well as mudstone and Type Ⅱ is composed of some sediments related to geological events, such as volcanic ashes, turbiditie, slump sediment, tempestite, seismite, ostracoda limestone. The formation of sparry carbonate may be controlled by factors related to both environments and events. Generally, mudstone sediments of still water can be regarded as background sediments, and the rest sediments are all event sediments, which have unique forming models, which may reflect controlling effects of climatics and tectonics.

Microfacies and Depositional Environments of Miocene Isolated Carbonate Platforms from Central Luconia, Offshore Sarawak, Malaysia

The Luconia Province-offshore Sarawak-is a key geological unit for understanding the distribution of hydrocarbon resources in Malaysia. Nevertheless, little effort has been made to address the palaeoenvironmental characteristics of the Tertiary carbonates in the key sector of Central Luconia.We study the sedimentology and petrography of core samples from a well in Central Luconia, for which thirteen microfacies have been identified reflecting different depositional settings. This is the first microfacies scheme elaborated for Luconian carbonates. Lithofacies and microfacies distribution are compatible with deposition in a reef complex, originating around a framework reef, within the euphotic zone. Sediments were deposited in environments of backreef, reef crest, and forereef. The fair weather wave base is marked by the presence of coralline red algae, foraminifera, decreasing degree of bioclast fragmentation and other microfacies features. As a result, a depositional-environmental model is constructed, depicting a reef complex built around a framework reef developed on the margin of an isolated platform. In addition, an innovative, preliminary time series analysis of facies, microfacies and depositional environment data reveal the existence of seasonal cycles in the stacking patterns of facies and microfacies.

New Insights into the Depositional Environments of Ordovician Carbonate Formations in the Yubei Area of Tarim Basin Based on Standard Microfacies Types

Objective The Yubei area is located in the mid-east Maigaiti slope of southwestern Tarim Basin, China, with an exploration history of several years. Recent exploration has preliminarily indicated that the Ordovician carbonate formations in this area have some oil and gas potential. Carbonate microfacies provides material basis for reservoir development, seal formation and hydrocarbon generation. Therefore, this work utilized the standard microfacies （SMF） types to study the microfacies of the Ordovician formations in the Yubei area in order to provide theoretical basis for the next exploration.

Microbiostratigraphy, microfacies and sequence stratigraphy of upper cretaceous and paleogene sediments, Hendijan oilfield, Northwest of Persian Gulf, Iran

Hendijan oilfield is located on Northwest of Pesian Gulf offshore of Iran and geologically in the Dezful embayment. In this study, the paleosedimentary depositional environment of the Early Cenomanian to Late Eocene deposits of the Sarvak, Ilam, Gurpi, Pabdeh and JahrumPabdeh Formations was evaluated using microbiostratigraphy, microfacies and D-INPEFA curves which are an accurate method in sequence stratigraphy in terms of regression and transgression of the sea. Also, we used limited elemental geochemical data of oxygen and carbon isotopes in compare with palaeontological data to infer the upper part, 10 m, of the Sarvak Formation. Statistical correlation analyses of geochemical data from upper part of the Sarvak Formation enable inference of differences in paleoconditions at this part and Sarvak Formation, and another Formation, Ilam, was distinguished. Palaentilogical analysis using planktonic foraminifera and calcareous nannofossils enables inference about time scale of each Formation. Petrographic data and different sediment textures support those inferences resulted from Gamma ray logs as D-INPEFA curves about different paleo-conditions that occurred during the development of the studied Formations. Synthesis of the analyses leads to the final interpretation that upper Cretaceous, Sarvak, Ilam and Gurpi Formations, at the Hendijan oil field were formed in a carbonate ramp that was likely closed to the open sea, where Gurpi Formation was deposited, by a shallow barrier that allowed seawater recharge into the basin and deep marine basin where Paleogene sediments, Pabdeh and Jahrum-Pabdeh, were deposited.

Microfacies Patterns and Depositional Environments of the Sarvak Formation in the Abadan Plain, Southwest of Zagros, Iran

The Sarvak Formation is the second major oil-bearing reservoir in the south and south west of Iran. The Middle Cretaceous Sarvak formation in the Zagros Mountains (Zagros Basin) is mainly composed of carbonate sequences. Based on facies studied, thirteen microfacies were recognized in the studied area, which were categorized in the three facies groups: including inner ramp, mid ramp and outer ramp. Evidences such as the gradual changes in the facies (basin slope), the absence of extensive uninterrupted barrier reef, the lack of calciturbidite and gravity sediments as well as the high proportion of grain-supported indicated that the Sarvak Formation was deposited in the ramp like depositional system, particularly on an inner ramp setting. Inner ramp facies group is the principal setting and subdivided to tidal flat, restricted and unrestricted lagoon as well as shoal sub-environments.

Biostratigraphy,Microfacies and Depositional Environment of the Sarvak Formation at the Pyun Anticline(Zagros Basin,Southwest of Iran)

The Sarvak Formation is a carbonate sequence of Late Albian–Early Turonian age in Zagros Basin in Iran.In this investigation,the Sarvak Formation at the Pyun Anticline section(Izeh Zone)has been studied.It consists of 797 m thick limestone which overlies the Kazhdumi Formation conformably and underlies the Gurpi Formation unconformably at the Pyun Anticline.A very rich fossil association(85 genera and 132 species)characterizes the Pyun section.Based on the stratigraphic distribution of diagnosed foraminifera,five biozones are established:1,Muricohedbergella-Globigerinelloides sp.assemblage zone(Late Albian);2,Praealveolina iberica-Chrysalidina gradata interval zone(Early Cenomanian);3,Chrysalidina gradata-Cisalveolina fraasi(fallax)and C.lehneri interval zone(Middle Cenomanian);4,C.fraasi(fallax)and C.lehneri-Praetaberina bingistani assemblage zone(Late Cenomanian);5,Nezzazatinella picardi-MangashtiaDicyclina assemblage zone(Early Turonian).Based on the petrographic and sedimentological analyses,some 13 carbonate microfacies were identified.The investigated microfacies confirm a ramp-type paleoenvironment.These microfacies,from distal to proximal environments,consist of:MF1:planktonic foraminifera wackestone-packstone;MF2:Oligostegina planktonic foraminifera wackestone to packstone;MF3:planktonic-benthic foraminifers sponge spicules wackestonepackstone;MF4:rudist floatstone;MF5:rudist rudstone;MF6:bioclast intraclast grainstone;MF7:peloid intraclast grainstone;MF8:benthic foraminifers rudist grainstone-packstone;MF9:peloid bioclast grainstone-packstone;MF10:bioclast(benthic foraminifers)wackestone-packstone;MF11:peloid bioclast packstone;MF12:dacycladacea benthic foraminifera packstone-wackestone;MF13:miliolids wackestone-packstone.

Microfacies Analysis and Paleoecology of the Oligocene Succession in a Central Tethyan Carbonate Platform,Zagros Basin,SW Iran

Two stratigraphic sections(Arjooieh and Firoozabad)of the Mymand anticline,located in the Interior Fars subbasin of the Zagros Mountains,were measured and sampled,in order to document sedimentological characteristics,microfacies types and paleo-seagrasses indicators of the Oligocene succession(Asmari Fm.).Planktonic and benthic foraminifera and coralline red algae are the principal fossils from these strata.Foraminifera are represented by the following families:Soritidae,Peneroplidae,Austrotrillinidae,Alveolinidae,Planorbulinidae,Discorbidae,Lepidocyclinidae,Amphisteginidae,Rotaliidae,Nummulitidae and Globigerinidae.Nine microfacies types were recognized,namely planktonic foraminifera-peloidal packstone(MF1),bioclast nummulitid/Nerorotalia/Amphistegina packstone-grainstonerudstone-floatstone(MF2),Neorotalia-echinoid coralline red algae packstone-grainstone(MF3),coral boundstone(MF4),coral/coralline red algae rudstone-floatstone-packstone-grainstone(MF5),diverse imperforate foraminifera bioclast packstone-grainstone(MF6),peloid wackestone-packstone-grainstone(MF7),fenestrated mudstone and microbial mats(MF8)and anhydrite(MF9).MF1 indicates an outer ramp,MFs 2-4 represent a mid-ramp and MFs 5-9 are interpreted as inner ramp environment.Paleo-seagrass indicators consisting of foraminifera,hooked and tabular forms of coralline red algae and corals.They were identified in MFs 5 and 6,reflecting the presence of vegetated environments within the mid/inner ramp setting.The Mymand anticline was dominated by the outer ramp environment at the start of the Rupelian.Mid to inner ramp environments prevailed during the Rupelian.The Chattian corresponds to the spread of the inner ramp setting over the Mymand anticline.

Characteristics and impacts on favorable reservoirs of carbonate ramp microfacies: A case study of the Middle-Lower Ordovician in Gucheng area,Tarim Basin,NW China

Based on the latest drilling core, thin section, 3D seismic, well logging data as well as exploration results, the sequence stratigraphy and sedimentary microfacies of the Middle-Lower Ordovician carbonates in Gucheng area, and their controlling effects on the development of reservoir were examined by the theories and methods of fine carbonate sedimentology.The results show that the Middle-Lower Ordovician in Gucheng area is a set of typical carbonate ramp deposits, which can be divided into 10 microfacies in 4 subfacies as follows: back ramp, inner shallow ramp, outer shallow ramp, and deep ramp. The back ramp subfacies consists of muddy-dolomitic flat and dolomitic lagoon microfacies;it is dominated by lamellar micrite dolomite tight in lithology. The inner shallow ramp subfacies includes dolomitic shoal and dolomitic flat in shoal top and dolomitic flat between shoals microfacies;it is mainly composed of crystal dolomite with metasomatic residual structure, as well as abundant karst vugs and intercrystalline pores. The crystal dolomite has an average porosity of 4.36%. The outer ramp subfacies includes medium-high and low energy grain shoal and inter-shoal microfacies;it is dominated by sandy limestone,oolitic limestone, and micrite limestone with few pores. The deep ramp subfacies is dominated by low-energy argillaceous deposits, with local presences of storm shoal microfacies. The Lower-Middle Ordovician has six third-order sequences from bottom to top, among which sequence(SQ3) represents the third member of Yingying Formation. The main reservoir has three fourth-order high-frequency sequences. Apparently, the favorable reservoir in the study area is jointly controlled by sedimentary microfacies and high frequency sequence in the carbonate ramp. The former controls the primary pore structure, and the latter controls the intensities of karstification exposure and dolomitization in the penecontemporaneous period. The dolomitic shoals and top dolomitic flats of different stages, superimposed and connected into favorable reservoirs of considerable scale like "platform margin", are favorable exploration facies in the carbonate ramp.

Microfacies and Sedimentary Environments of the Fahliyan Formation from the Southwest of Iran (Shiraz, Zagros)

The Fahliyan Formation is a carbonate sequence of Lower Cretaceous (Berriasian-Hauterivian) in age and was deposited in the Zagros sedimentary basin. This formation is a part of Khami Group and is a reservoir rock in Zagros Basin. This formation was investigated by a detailed petrographic analysis in order to clarify the depositional facies and sedimentary environment in the Kuh-e-Gadvan in Fars Province. Petrographic studies led to the recognition of nine microfacies that were deposited in four facies belts: tidal flat, lagoon, and barrier and shallow open-marine. An absence of turbidite deposits, reefal facies, and gradual facies changes indicate that the Fahliyan Formation was deposited on a carbonate ramp.

Microfacies and diagenetic alteration in a semi-deep to deep lacustrine shale: The Yanchang Formation in the Ordos Basin, China

The mineralogical development and diagenetic sequence of lacustrine shales in the Chang 7 Member of the Yanchang Formation in the Ordos Basin are detailed studied.A model of their depositional system and a diagenetic diagram are proposed in this study.Through detailed petrographic,mineralogical,and elemental analyses,four distinct shale types are identified:argillaceous shale,siliceous shale,calcareous shale,and carbonate,clay,and silt-bearing shale.The main diagenetic process in argillaceous shale is the transformation of illite to smectite,negatively impacting shale porosity.Siliceous shale undergoes carbonate cementation and quartz dissolution,contributing to increased porosity,particularly in mesopores.Calcareous shale experiences diagenesis characterised by carbonate formation and dissolution,with a prevalence of siderite.In carbonate,clay,and silt-bearing shale,the dissolution of K-feldspar contributes to illitization of kaolinite.Argillaceous shale,characterised by more clay minerals and lower mesopore volume,is identified as a potential hydrocarbon seal.Siliceous shale,with the highest pore volume and abundant inter-mineral pores,emerges as a promising shale oil reservoir.These findings contribute to a comprehensive understanding of shale properties,aiding in the prediction of shale oil exploration potential in the studied area.

Carbonate Ontology and Its Application for Integrating Microfacies Data

Carbonate rocks record essential information on changes in paleoclimate and paleoceanography. Abundant geological and geochemical data of carbonate rocks have been accumulated over the past decades;however, most of the data are stored in the published literature with highly unstructured forms, and are thus difficult to reuse. The ontology is a standard knowledge model for data integration, which can promote data storage and reutilization. This study proposes a carbonate ontology that represents the concepts in carbonate microfacies. The carbonate ontology constructed by the top-down process contains 215 terms of classifications and petrographic descriptions of carbonate rocks. Furthermore, carbonate microfacies of the Cretaceous(Aptian) carbonate platform in the Betic Cordillera and Jurassic carbonate platform in Tibet provide the data from case studies for the testing and initial validation of the proposed ontology. The carbonate ontology is under continuous expansion following the bottom-up approach and open access on the website of the deep-time digital Earth(DDE) program.

Microfacies and paleoenvironment of microbialites of the Cambrian(Stage 4)Qingxudong Formation in the Huayuan area,northwestern Hunan Province,southern China

After the extinction of Archaeocyatha(sponges),microbial bioherms were well developed in the lower Cambrian of the Yangtze cratonic basin,especially in the Qingxudong Formation(Cambrian(Stage 4))of the Huayuan area,northwestern Hunan Province,southern China.Herein,four sections from this area were chosen for investigating and analyzing their microfacies and depositional environment.Twelve microfacies types were recognized through petrographic analysis of textural attributes and calcimicrobes(including Epiphyton,Renalcis,Girvanella and Kenella),respectively as:laminated calcareous mudstone(MF1),algal wackestone(MF2),intraclastic grainstone(MF3),algal intrasparrudite(MF4),oolitic algal intrasparrudite(MF5),sparry oolitic grainstone(MF6),Epiphyton framestone(MF7),Renalcis bafflestone(MF8),Kenella bafflestone(MF9),Girvanella boundstone(MF10),thrombolitic boundstone(MF11),and dolomite(MF12).These microfacies represent four major depositional environments:carbonate ramp,carbonate platform,slope and tidal flat.Calcimicrobes played an important role in the transition from carbonate ramp to platform,while the evolution from ramp to tidal flat must be ascribed to sea-level fall during the Cambrian Age 4.

A knowledge graph for standard carbonate microfacies and its application in the automatical reconstruction of the relative sea-level curve

The reconstruction of high-resolution sea-level variation curves in deep time based on the standard car-bonate microfacies knowledge graph(SMFKG)is of great scientific significance for exploring the Earth system evolution and predicting future sea-level and climate changes.In this study,the concepts,attri-butes,and relationships among standard carbonate microfacies(SMF)are comprehensively analyzed;an ontology layer is established and its data layer is constructed using thin-section descriptions;and finally,the SMFKG is established.Additionally,based on the knowledge graph,an application for automatically identifying SMF using identification markers and reconstructing the high-resolution relative sea-level variation curve using the SMF and facies zones is compiled.Then,all thin sections of the late Ediacaran Dengying Formation in the western margin of the Yangtze Platform are observed and described in detail,the SMF and facies zones are identified automatically,and the relative sea-level curve is recon-structed automatically using the SMFKG.The reconstruction results show that the Yangtze Platform experienced four sea-level rise and fall cycles in the late Ediacaran,of which two intense regressions led to subaerial-exposed unconformities in the interior and top of the Dengying Formation,which is highly consistent with previous research results.This shows that the high-resolution relative sea-level variation curve in deep time can be reconstructed efficiently and intelligently using the SMFKG.Additionally,in the near future,the combination of an automatic digital slide-scanning system,machine-learning techniques,and the SMFKG can achieve one-stop fully automatic SMF recognition and reconstruction of high-resolution relative sea-level variation curves in deep time,which has a high application value.

Microfacies analysis and depositional environment of the Upper Devonian Dankovo-Lebedyansky sediments,Tatarstan,Volga-Ural Basin,Russia

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.

Impact of microfacies and diagenesis on the reservoir quality of Upper Devonian carbonates in Southeast Tatarstan,Volga-Ural Basin,Russia

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.

Evaluation of Chang 2 Reservoir in Zichang Area, Ordos Basin

In this paper, the Chang 2 reservoir in Zichang Area of Ordos Basin, the second largest sedimentary basin in China, is classified and evaluated by using logging and core data, thin section identification and electron microscopy. The main sedimentary microfacies of Chang 213 is braided river delta sedimentary system in geological history, and there are three main sedimentary microfacies types: swamp microfacies, distributary channel microfacies and natural embankment microfacies on land. The heterogeneity in the study area is as follows: Chang 212 formation has the strongest heterogeneity, followed by Chang 211 formation with strong heterogeneity, and finally Chang 213 formation with medium heterogeneity. The reservoirs of Chang 2 member in the study area are dominated by IIIa, IIb and IIIb, and the reservoirs are mainly composed of ultra-low porosity and low permeability reservoirs and low porosity and low permeability reservoirs.