Mudstone Microfacies Research Articles

Tracking Depositional Architecture and Diagenetic Evolution in the Jurassic Carbonates, Trans Indus Ranges, NW Himalayas

The evolution of Jurassic carbonates is globally significant for understanding the depositional framework, diagenetic phases and sedimentary characteristics of shallow marine shelf deposits. For this purpose, two outcrop sections of the Jurassic carbonates with a road distance of 121 km in the Trans Indus Ranges, NW Himalayas, were included in this study. Geological fieldwork was conducted for sedimentological data, and representative samples were collected for microfacies analysis and diagenetic evolution complemented by carbon and oxygen isotope analysis. Results show that eight microfacies were identified in both sections where mudstone microfacies was only present in the Chichali section, whereas wackestone and packstone facies widely existed in both sections. The diagenetic evolution interpreted that dolomitization and stylolization were pronounced in the Paniala section, while micritization and calcite cementation were prevalent in the Chichali section. The interpreted depositional setting implies the wide range from supratidal to outer ramp shallow marine for the Chichali section, suggesting a wide range and relatively deeper environment, alongside merely intertidal to middle ramp settings for Paniala section. Diagenetic evolution suggests marine to meteoric influence in the Chichali section, while burial and uplift phases were dominant in the Paniala section. The diagenetic events were also validated by the isotopic analysis, where most of the samples with values up to −4‰ VPDB δ18O, corresponding to a carbon isotope range of up to +4‰, were interpreted as the burial phase of diagenesis; meanwhile, a few samples with −2 δ13C and −7‰ VPDB δ18O isotope signatures were marked as meteoric influx in the Paniala section. This study indicates the diversity of the depositional environment and diagenetic heterogeneity by integration of thin sections using isotope data, which are quite applicable to shallow marine carbonates.

Micro-facies characterization of the Cane Creek Shale, Paradox Basin, Utah: implications of diagenetic controls on reservoir quality

The fine-grained Pennsylvanian Cane Creek Shale of the Paradox Formation, Paradox Basin, Utah exhibits relatively thin cyclic interbeds of contrasting lithologies including fine sandstone to siltstone, organic-rich carbonate and dolomitic mudstone, and evaporites. As such, it provides a unique opportunity to evaluate micro-facies and the fluid storage capacity potential of mixed fine-grained systems. Micro-facies descriptions were performed using core and petrographic analyses, including scanning electron microscopy with energy dispersive spectroscopy. The study leverages core-based porosity and permeability data, as well as previous core description. These data are used together to explore mineralogical depositional and diagenetic controls on porosity and permeability. Twelve micro-facies were described based on sedimentological textures, grain size, lithology, and mineralogy categorized into three groups: 1) sandstone to siltstone, 2) mudstone, and 3) evaporitic micro-facies. Sandstone to siltstone micro-facies exhibit variable porosity and permeability. Porosity connectivity is dependent on the degree of authigenic cementation and compaction that negatively impacts porosity. Mudstone micro-facies show less variability in porosity and permeability; and are characterized by carbonate content, organic-matter, and clay nanopores. The development of early carbonate grains maintains porosity in mudstone and dolomitic siltstone micro-facies. Evaporitic micro-facies represented by evaporitic sabkha-like conditions are characterized by pore-reducing anhydrite and halite cement. A diagenetic paragenetic sequence was developed to assess the timing and impact of mineralogy on reservoir quality. Early (eogenetic), Middle (mesogenetic), and Late (telogenetic) stages correspond with diagenetic stages and known tectonic basin events. Syndepositional dolomite and diagenetic illite/smectite authigenic cements are the main controls on reservoir quality and have opposing effects related to porosity and permeability by preserving early pore space or reducing porosity and permeability.

Stratigraphy, Microfacies, Paleoenvironments and Paleoecology of Asmari Formation (Oligocene - Miocene), Zagros Basin, Western Iran

The present work involves the study of the Asmari Formation from the viewpoint of the stratigraphy, microfacies, and depositional environment. The Khorramabad area, Zagros basin, west Iran, has been investigated for the first time. For this purpose, seventy-three samples were taken from the Shurab section. Eight microfacies have been identified in the Asmari Formation: Sandy wackestone (MF1), Peloidal Mudstone (MF2), Bioclastic milina Wackestone-Packstone (MF3), Bioclastic imperforate foraminifera Wackestone-Packstone (MF4), Coral boundstone (MF5), Bioclastic packstone - grainstone (MF6), Bioclastic imperforate foraminifera grainstone (MF7), Mudstone microfacies (MF8). Two benthic foraminiferal biozones were recognized, which are Archaias asparagus- Archaias Henson Assemblage Zone, which is restricted to Chattian, and the Eulepidina- Miogypsina Assemblage Zone, which is restricted to Aquitanian. The biostratigraphic correlation with other studies in and outside Iran, executed across the studied section, enveloping the Chattian to Aquitanian, divulges a progression in the biozone thickness, indicating a migration of the depositional center towards the northwest of the basin. The Asmari Formation is deposited from an outer ramp and open shelf lagoon and is defined as a tropical environment.

Microfacies and Sedimentary Environments of Nfayil Formation (Middle Miocene) in Karbala Using Stable Isotope

A surface section of the Nfayil Formation (Middle Miocene) was studied approximately 80 km from the holy city of Karbala. The study area includes the Malutiyat area's Nyfail Formation (Middle Miocene age). The Nfayil Formation contains marls interbedded with limestones, as well as marly limestone. Fieldwork and petrographic analysis are being conducted on Miocene sediments from the Karbala region. Details obtained from textural and faunal properties aided in the designation of microfacies zones, which led to environmental subdivisions as a ramp. The carbonate lithic arenite sandstone has a significant amount of carbonate fragments. Microfacies characteristics of the whole successions showed skeletal and non-skeletal grains. The oysters, an index fossil of the Nfayil Formation are found in the lower part of the Nfayil Formation. The stable isotopes 18O/16O and 13C/12C in carbonates are analyzed to define the depositional characters and the basin paleo depth. The studied samples have negative δ18O isotope values (average -11.79 %). The carbon isotope composition is of positive values (average 2.16‰), The Z values, higher than 120, reflect the marine sediments of the formation. Four facies were identified, (Lime mudstone Microfacies, Sandy Lime mudstone Microfacies, Peloidal Bioclastic Packstone-Wackestone Microfacies, Bioclastic Wackestone Microfacies) and based on them, the formation environment was determined (restricted marine, and shallow open marine environments).

Petrography and Geochemistry of Limestone Upper Cretaceous Kometan Formation (Azmir Anticline): A Preliminary Assessment for Cement Production Suitability in the Kurdistan Region Northeast Iraq

A succession of slightly siliceous limestone of the Kometan Formation is studied geochemically and strati graphically. The studied area is located on the SW limb of the Azmir anticline at the northeastern of Sulaimaniyah city. The studied section is situated at longitudes 45°38'310"E and latitudes 35°36'129''N inside the Folded Zone, Kurdistan Region, northeastern Iraq. The exposed section is sampled for lab studies, and inspected by eyes and hand lenses in the field. In this study, petrographic and geochemical analyses of 17 limestone samples were carried out. This study aims to investigate the major oxides of the limestone samples, using the X-Ray Fluorescence (XRF), for preliminary assessment for possible cement production. A petrographic study was also carried out, in order. Depending on the petrographic study, three major microfacies were recognized: lime mudstone microfacies, lime wackestone microfacies, and lime packstone microfacies, which subdivided into four submicrofacies are planktonic foraminifera lime mudstone submicrofacies, planktonic foraminifera lime wackestone submicrofacies, and planktonic foraminifera lime packstone submicrofacies and heterohelix lime packstone submicrofacies. The geochemical analysis shows that a range of variations in constituents: LOI (35.90% to 42,72%), SiO2 (3.77% to 14.66%), CaO (42.59% to 49.95%), Al2O3 (0.44% to 2.22%), Fe2O3 (0.02% to 0.78%) and MgO (1.50% to 2.26%); K2O and Na2O are present in traces. The high CaO (49.95%) indicates that calcite is the primary carbonate mineral. Due to mineralogical considerations, CaO with LOI shows a positive correlation, whereas CaO with SiO2 shows a negative correlation. The low MgO contents in calcitic limestone and calcitic limestone with chert nodules recommend a lack of dolomitization process. The silica modulus and lime saturation factor from geochemical data indicated that the siliceous limestone samples from the Kometan Formation and Azmir Anticline can be used in the cement-making process provided they are processed for silica removal treatment to reduce its percentage to less than 8%, as required level, where the CaO can be automatically enriched. Depending on field observation, petrography, and geochemistry analysis, we conclude that the source of the chert or silica minerals is diagenetic processes and depositional environment origin.

Microfacies analysis and depositional environment of Shiranish Formation in Selected Sections, Kurdistan Region, NE Iraq

Shiranish Formation in both Smaquli and Rawanduz sections is composed of an alternation of marly limestones, limestone and marl beds with fissile shale beds. Depend on color, lithology and other sedimentological criteria during field observations of the studied sections, the Shiranish Formation is divided lithologically into lower, middle and upper units. Planktonic Foraminiferal Lime Mudstone Microfacies (Shf1), Lime Wackestone (Shf2) and Planktonic Foraminiferal Lime Packstone Microfacies (Shf3) have been defined as three distinct microfacies with four submicrofacies ((Keeled Planktonic Foraminiferal Lime Wackestone submicrofacies (Shf2b), Globular Chamber Planktonic Foraminiferal Lime Wackestone submicrofacies (Shf2a), Bioclastic Lime Wackestone submicrofacies (Shf2c), Planktonic Foraminiferal Lime Wackestone submicrofacies (Shf2d)). The major microfacies in both sections was lime wackestone which is dominated in middle and upper units in both sections. Sedimentological and paleontological evidences suggest that the Formation was deposited in the outer shelf setting and progressed to the upper bathyal setting, in addition to that the microfacies changed from packstone to mudstone meaning deeping upward sequence.

The transition from normal marine to evaporitic conditions recorded in a cold seep environment: The Messinian succession of Northern Italy

Messinian pre-evaporitic seep carbonates outcropping in the Tuscan-Romagna area share a common upward stratigraphic trend: massive seep carbonates rich in large lucinids, modiolids and planktonic foraminifera pass upward to horizontally laminated carbonates free of macrofauna and foraminifera. A transitional macrofauna-free facies marks the passage in some sections, sometimes with faint lamination. Thin section petrography, SEM-EDS analyses, and X-ray diffraction revealed a high textural and mineralogical variability between the studied sections and facies. In general, the upward facies transition is associated with a switch from massive packstone/grainstone with complex carbonate mineralogy to laminated mudstone microfacies with monomineralic, mostly dolomitic, carbonate composition. The δ13C values of all facies indicate domination of methane-derived carbon, thus demonstrating a methane-charged sedimentary setting with precipitation of authigenic carbonates induced by anaerobic oxidation of methane. The transitional and laminated facies contain several structures typical of microbial sediments, such as peloids, filamentous features, clotted micrite, fibrous cement, and frequent fenestrae; web-like structures are remnants of cyanobacterial mats and resemble Entophysalidaceae thriving at the bottom of the Messinian sea. The distinctive depositional and biotic switch (abrupt disappearance of macrofauna and planktonic foraminifera, predominance of dolomite over calcite, absence of aragonite, presence of horizontal lamination) reflects important environmental changes taking place in the basin. The rise of δ18O from the massive, through transitional, to the laminated facies suggests either a drop of bottom-water temperature or an increase of salinity. Nevertheless, other paleoenvironmental changes must have co-occurred in order to account for the dramatic facies shift observed. We hypothesize that this change could reflect the development of water-column stratification with respect to both salinity and oxygen concentration shortly before the Messinian Salinity Crisis.

Carbonate Ramp Facies and Porosity Recognition: Case Study of the Late Albian-Early Cenomanian Mauddud Formation in Ratawi Oilfield, Southern Iraq

The carbonate ramp facies of the Late Albian-Early Cenomanian Mauddud Formation were studied in the Ratawi Oilfield, Basra Governorate, south of Iraq using integrated borehole data set that included, core and cutting samples in three drilled wells to analyze the petrography of the Mauddud Formation, two hundred and eighty-one (281) thin sections were prepared and examined for the three selected wells. The results show that the formation is composed of light grey dolomitized limestone and pseudo-oolitic creamy limestone with green to bluish shale. The petrographic observations results show four facies’ associations in the Mauddud Formation. These include: Mid–Ramp environment which is represented by Argillaceous mudstone microfacies, Argillaceous wackestone microfacies and orbitolinid wackestone microfacies; the shallow open marine environment which is assimilated by foraminiferal wackestone microfacies and foraminiferal packstone microfacies; a restricted marine environment that represented by bioclastic fossiliferous wackestone microfacies and miliolid wackestone microfacies and Shoal environment is represented by bioclastic packstone microfacies, bioclastic grainstone microfacies, peloidal foraminiferal pack-grainstone microfacies, and peloidal packstone-grainstone microfacies with diverse skeletal grains. The porosity includes Vuggy, Interparticle, Intraparticle and Fracture porosity.

Microfacies Analysis and Diagenetic Effects of Middle Jurassic Succession in Rania and Sargelu Sections, Northern Iraq

The studied area covers two outcrops they are located within Sulaimaniya, northeastern of Iraq (Rania and Sargelu sections). Sargelu Sections are located in Sargelu village within Unstable Shelf, High Folded Zone, including Surdash anticline, while Rania Sectionis are located in Rania city near Hanjira village within the Unstable Shelf, High Folded Zone, including Shaweri anticline. The carbonates represent the major microfacies and constitute of lime mudstone microfacies, lime wackestone microfacies, Calcisphere-Posidonia lime wackestone submicrofacies, posidonia lime wackestone submicrofacies, lime packstone microfacies, Posidonia lime packstone submicrofacies, Posidonia-Ostacoda lime packstone submicrofacies, lime Crystalline Microfacies. The observations of the studied area show that the basin of the Sargelu Formation represents a deep part of a ramp system.These microfacies are variably affected by several diagenetic processes including mechanical and chemical compaction, cementation, recrystallization and dolomitization. The chert shows a high degree of quartz crystallinity which indicates a diagenetically product from the amorphous silica of the many radiolarians, remnant of which is preserved in several units of the Sargelu Formation

Facies Architectuer and Stratigraphic Evolution of Campanian Succession in Balad, East Baghdad and Kifl Oil Fields

The sediments of the Hartha Formation were deposited during the Upper Campanian- Maastrichtian cycle. Due to the importance of this sequence in terms of stratification and economics in the oil industry, it has been focused on in this study. The present study includes three oil fields in central of Iraq within the Mesopotaminan Zone, East Baghdad, Balad and Kifl oil fields. This study was accomplished by describing 190 thin sections and interpreting the response of the available well logging data. Seven major microfacies were diagnosed in the Hartha succession at studied oil fields, they are; Orbitoidal wackestone - packstone, Orbitoidal and miliolids wackestone, Rotaliidae and Siderolites with echinodermata wackestone - packstone, Peloidal - echinoderm packstone - grainestone, Pellets - echinodermata packstone - grainestone, Planktonic foraminifera wackstone - packstone and Evaporitic mudstone microfacies. These microfacies were deposited in lagoon, restricted, shallow open marine, shoal, mid ramp and outer ramp. The Hartha Formation in the studied oil fields represents one cycle third order with three cycles fourth order (A1, A2 and A3). These cycles are asymmetrical and starts with cycle A where the open marine facies in the Lower Hartha represents the TST underly the HST, which bounded below by a TS which coinside with the unconformable surface (SB1) with the underlying Sadi Formation. The highstand systems tract of cycle A1 is reflected by the open marine facies of the Hartha Formation, A2 is reflected by the open marine and mid ramp facies represent thick TST and then appear the HST which reflected by the open marine facies bounded by a transgressive surface (TS) reflected mid ramp and outer rampfacies in the TST which represents A3. The second cycle A2 is disappeared in Kifl Oil Field with appeared evaporitic lagoon facies.

Integrated geophysical, petrophysical and petrographical characterization of the carbonate and clastic reservoirs of the Waihapa Field, Taranaki Basin, New Zealand

Despite the economic importance of the Waihapa Field in Taranaki Basin in New Zealand, the structural setting, petrographic and petrophysical properties of its Cenozoic reservoirs are still poorly understood. This research integrates a 3D seismic survey with core and well logs data, as well as petrographic description in order to discuss the structural setting and the reservoir characterization of the Cenozoic reservoirs along the Waihapa Field, Taranaki Basin, New Zealand. A major thrust fault was interpreted dissecting both the Kapuni (Paleocene- Eocene) and Ngatoro (Oligocene- Early Miocene) groups and another opposite thrust fault affecting the Ngatoro Group and the Waihapa anticline. These compressional structures were resulted from the regional compression which affected the Taranaki Basin during the Miocene. Wai-iti Group (Miocene) is dissected by a set of NE-SW normal faults. These normal faults remark the end of the compressional phase and the beginning of a new extensional phase along the Taranaki Basin.The petrographic data of the studied reservoirs indicate that the Late Miocene Mount Messenger Formation is composed of feldspathic wacke, micaceous feldspathic quartz arenite and mudstone microfacies, whereas the Oligocene Tikorangi Formation is composed of five microfacies (bioclastic grainstone, bioclastic packstone, sandy wackestone, highly fractured silty mudstone and sandy glauconitic packstone microfacies). Downward, the Upper Eocene Mangahewa Formation is composed of ferruginated quartz arenite, micaceous quartz arenite, and ferruginated calcareous quartz arenite microfacies. Cementation and compaction are mostly affected the Mangahewa Formation while fracturing and dissolution are primarily affected the Tikorangi and the Mount Messenger formations respectively. The studied core data was discriminated into four petrophysical static rock types (PSRTs). The PSRT1, representing the Mount Messenger reservoir, has the best reservoir quality (av. porosity = 23.3%, av. permeability = 45.0 md, and meso pores, 2.60 μm) while the PSRT4 of Tikorangi Formation has the lowest reservoir quality (av. porosity = 5.5%, av. permeability = 0.01 md, and nano pores, 0.07 μm). The PSRT2 (av. porosity = 4.17%, av. permeability = 0.26 md, and micro pores, 0.59 μm) and PSRT3 (av. porosity = 5.93%, av. permeability = 0.08 md, and micro pores, 0.22 μm) are petrophysically considered transitional rock types between the PSRT1 and the PSRT4.However, Tikorangi reservoir is already producing oil from the borehole scale fractures. This work represents the workflow applied during integrating seismic, petrographical and petrophysical data in order to characterize carbonate and clastic reservoirs for any further hydrocarbon development plans along the field.

Microfacies and depositional environment of Bajawan and Baba Formations in Kirkuk Oil fields north Iraq

The study of six selected wells from Kirkuk oil field petrographic and physical properties ; investigation while leads to interpret the microfacies and environment for Bajawan and Baba Formations. Five carbonate microfacies distingished from Bajawan Formation ( Lime Mudstone Microfacies, Fossiliferous Lime Wackstone Microfacies, Miliolid Packstone Microfacies, Miliolid Grainstone Microfacies and Coral, Boundstone microfacies ), while Two microfacies described from Baba Formation (Limestone bearing Larger foraminifera (Lepidocylina- Nummulites) packstone-wackstone microfacies and Fossiliferous Floatstone bearing Larger Foraminifera microfacies ).
 According to different types of microfacies that described from Bajwan and Baba Formations , the depositional environment of Bajawan Formation is backreef/reef or restricted lagoon (inner ramp), but for Baba Formation is shallow water forereef (middle ramp). The facies model were constructed on basis of stratigraphy, lateral and vertical facies change and depositional environment of Oligocene succession.

Microfacies and depositional environment of Shiranish Formation in kirkuk Oil fields north Iraq

This study is reveal the characteristics of Shiranish Formation to elucidate the sedimentological properties of Kirkuk Oil fields north of Iraq from wells k-331, k-334, k-411. The studied rocks are consist of limestone, shaley limestone, marly limestone and thin bedded of marl. Facies analysis showed that the exact composition of Shiranish sequences composed of three facies succession of President rich Balmikarait and shells Alforamenavera floating. These facies and depending on popularity are Lime Wackestone Microfacies and Lime Mudstone Microfacies, these facies are divided in turn into secondary facies which Planktonic Foraminiferal Lime Wackestone Submicrofacies (W1), and Bioclastic Lime Wackestone Submicrofacies (W4). Depending on Facies and environmental analysis shows that the composition of sequences have deposited within the basin foreland achieved on the inactive edge Arabian plate and deposited in deep bathyal and out shelf environment

Microfacies and Sedimentary environment of Aliji Formation in selected wells from Kirkuk oil fields north Iraq

The study carried out of Aliji Formation (Late Paleocene) for selected wells in three oil fields Kirkuk, Bai Hassan and Jambur The thickness of formations in the studied wells area (K-229) 172m, (BH-96) 57m,and (JM-55) 52m.
 Lithological, Aliji Formation composed of limestone, marly limestone and shally limeston brown light –dark colour.
 The recognized microfacies where division to three main microfacies, Planktonic foraminiferal Lime Mudstone microfacies, Planktonic Foraminiferal Lime Wackstone microfacies and Planktonic Foraminiferal Lime Packstone microfacies.
 The Formation deposited in deep bathyal environment at (FZ1, FZ2, FZ3) (Toe of slope, Deep shelf, Deep sea) as indicated on the constract sedimentary model.

Eocene nannofossils and paleoenvironmental reconstruction of the Kuldana Formation in Yadgar area, Muzaffarabad, northern Pakistan

The Early Eocene Kuldana Formation (KF) consists of variegated color shales, mudstone, and sandstone with limestone interbeds/lenses in the Yadgar area, Muzaffarabad, of Sub-Himalayan foreland basin. We report, for the first time, 20 nannofossil species of 9 genera, discovered from carbonate units of KF. Based on this calcareous nannofossil assemblage, an Early Eocene Ypresian age (NP10) is determined. The presence of Coccolithus, Fasciculithus, Rhomboaster, Tribrachiatus and Sphenolithus indicates dominantly warm water and oligotrophic conditions during deposition of the carbonate units, while the presence of Zeugrhabdotus and Neococcolithes suggests minor cool-water, eutrophic to mesotrophic conditions. Five microfacies were identified based on the field and petrographic investigations of the study section, namely, Nummulitic wacke-packstone microfacies (KMF-1), Assilina wacke-packstone microfacies (KMF-2), Molluscan microfacies (KMF-3), Lime mudstone microfacies (KMF-4), and Ostracode wackestone microfacies (KMF-5), suggesting that the deposition occurred in inner to middle shelf, shallow marine environment.

Depositional Environment of Middle Jurassic Sargelu Formation Based on Petrographical Study in selected wells at Balad, Ajil, and Baiji Oilfields, Central Iraq

This work were carried out on 193 thin sections from Middle Jurassic Sargelu Formation. These samples are from three wells (Ajil-8, Balad-1 and Baiji-1). Petrographically, the Sargelu Formation composed of skeletal component (radiolaria, pelecypods, calcispheres, planktonic, benthonic foraminifera and ostracods), in addition non-skeletal such as pellets, groundmass of micrite and recrystallized microspars. Many diagenetic processes affected this formation the main which have been recognized are: compaction, micritization, cementation, neomorphism, dissolution, fractures and veins, silicifaction and dedolomitization in addition authigenic minerals (pyrite). Depending on the petrographic studies the following microfacies have been recognized: Lime Mudstone Microfacies which was divided into three submicrofacies (Pelecypodal Lime Mudstone, Radiolarian Lime Mudstone and Planktonic Foraminiferal Lime Mudstone), Wackestone Microfacies which was divided into four submicrofacies (Radiolarian Lime Wackestone, Halobia Wackestone, Calcispheres Wackestone and Planktonic Foraminiferal Wackestone) and Packstone Microfacies (Halobia Lime Packstone and Peloidal Lime Packstone). The overall characters of these microfacies indicate that the formation was deposited in two different environments: (1) upper Bathyal environment at the lower part (2) Outer shelf environment at the upper part.

Sedimentology and Diagenesis of the Early–Middle Eocene Carbonate Deposits of the Ceno-Tethys Ocean

An integrated study based on field observation, petrography, and scanning electron microscopy (SEM) on the Early–Middle Eocene carbonate rocks has been carried out, which were deposited in the Ceno-Tethys Ocean. The study area of the Yadgaar Section lies on the eastern margin of the Upper Indus Basin, Pakistan. The Early–Middle Eocene Margalla Hill Limestone and Chorgali Formation act as reservoir rocks in other parts of the basin and are also present in the Yadgaar Section. The lack of comprehensive study in this area makes these reservoir rocks highly attractive for sedimentological evaluations and future exploration of hydrocarbons. The Early–Middle Eocene carbonate rocks are divided into nine microfacies: dolomicritic foraminiferal mudstone–wackestone microfacies (EMI); green algae dominated, mixed foraminiferal wackestone–packstone microfacies (EMII); ostracod, green algae and gypsum dominating mudstone–wackestone microfacies (EMIII); algae and mixed foraminiferal wackestone–packstone microfacies (EMIV); Nummulites dominating mudstone–wackestone microfacies (EMV); algal limestone mudstone microfacies (EMVI); Assilina bed wackestone–packstone microfacies (EMVII); micritized larger benthic foraminiferal wackestone–packstone microfacies (EMVIII); and algal limestone, mudstone microfacies (EMIX). The transgressive-regressive environment in the Ceno-Tethys Ocean leads to the deposition of these microfacies in the platform interior, open marine platform, platform edge, platform margin reef, toe of the slope apron, arid–humid platform interior, platform edge, open marine platform interior, and restricted marine platform interior, respectively. Initial post-depositional diagenetic stages are identified from the base to the top of the strata by their respective cement types, i.e., the base–lower middle part of the strata demonstrates an eogenetic sub-stage with the appearance of drusy cement, the middle section indicates a mesogenetic sub-stage by the appearance of blocky cement, while the top portion again reveals an eogenetic sub-stage of diagenesis by the presence of drusy and blocky types of cement. The ascending–descending hierarchy of cement generations is directly proportional to the grade of diagenesis from the base to the top of the carbonate strata. Variable diagenetic effects on the various microfacies also increase the secondary porosity range and enhance the reservoir characteristics of the Formations. The presence of foraminifera microfossils determined that these carbonate formations date from the Early–Middle Eocene.

Microfacies Analysis and Stratigraphic Framework of Yamama Formation in Sindbad, Halfaya and Ad'daimah Oil Fields, Southern Iraq

The Yamama Formation represents a part of the Late Berriasian-Aptian sequence, deposited during the Early Cretaceous period within the main shallow marine depositional environment. The studied area covers three oil fields; Sindbad oil field, Halfaya and Ad'daimah oil field, located in southeastern Iraq. Six major microfacies were recognized in the succession of the studied area represented by the Yamama Formation to determine and recognize depositional paleoenvironments. These microfacies are; Peloidal Packstone, Algal Wackestone to Packstone, Bioclastic Wackestone – Packstone, Foraminiferal Bioclastic Wackstone, Packstone, Peloidal – Oolitic Grainstone and Mudstone Microfacies. These microfacies are classified into three standard microfacies and three Facies Zones MFS-18/FZ- 8, SMF 15/FZ-6 and SMF-10/FZ-7, representing the restricted marine, shoal and shallow open marine associations facies, respectively. The Yamama succession in the studied area is divided into three cycles representing three depositional stages of highstand system tracts. These three cycles are characterized by shallowing upward depositional mode where they are deposited in the shallow open marine shoal with semi-restricted associations facies for each cycle. To the northeast of the study area near Halfya-5 well, the shoal association appeared in the lower and middle part of the Yamama succession, and in Da-1 and Sn-2 were three cycles. This case suggests that the paleo high was developed north of the study area, while the open marine was extended to the southern part. The presence of shallow open marine association facies between the Sulaiy and Yamama successions refers to continuous deposition during the same depositional stage in all studied wells. It may mark the end of the Sulaiy succession with the maximum flooding surface (MFS). This first depositional stage is started with the shallow open marine association facies underlain by shoal facies association and then semi-restricted association. The repetition of this cycle in the studied sections symmetrically indicates the harmonic oscillation in sea level during the second and third depositional stages of this sequence. The Halfaya oil field within the Mesopotamian Block and Ad'daimah and Sindbad oil fields within the Basra Blok explain the significant variation in the thickness for this succession between the Halfaya oil field and the other oil fields. This may suggest the occurrence of high depositional subsidence in Basra Blok and uplifting during the Yamama depositional stages. The fact that the studied sections are distinguished by the same cycles, albeit roughly, indicates that the lifting and sit-down processes synchronized sedimentation.

Microfacies and Sequence Stratigraphy of the Saadi Formation within the sequences of the (Torunian - Santonian) cycle in Balad and Tikrit / Salah al-Din Governorate / Iraq

The current study included a study of the microfacies and sequence stratigraphy of Saadi Formation in two subsurface sections within the Balad and Tikrit oilfields, the first represented (Ba-5) with a thickness of (120) m, and the second section (TK-6) the thickness of this formation (270))m. The formation under study consisted of chalk limestone sequences with the layers of marley limestone, the study showed that the lower bounder is compatible with the of Tanuma Formation in both sections, while the upper bounder is conformable with the Mashura Formation within well (Ba-5) and is unconformable with the Hartha Formation in a well (TK-6).Petrographic study showed the presence of many microfacies at divided into five main microfacies and six submicrofacies Lime mudstone microfacies, Lime wackstone microfacies divided to (Calcispheres lime wackestone and Rotalid lime wackestone submicrofacies), Lime packestone microfacies divided to (keeled planktonic foraminiferal lime packstone, Hedbergella lime packstone, Calcispheres lime packstone and Rotalid lime packstone submicrofacies), lime grainstone microfacies and crystalline microfacies. Depending on microfacise the paleoenvironment of formation extended from slope, open marina, deep shelf and deep sea.The sequence stratigraphy defined of study divide to the sequences into sets, and each sets represents a sedimentary cycle that event a rise and fall in sea level during a certain period of time, the formation in well (Ba-5) compound one sequence and well (TK-6) consist three sequence, the sequence begins with the sequence boundary of (Type-2) and after the transgression system tract (TST) it deposit by Retrogadation and the upper surface of this tract represented by the Maximum Flood Surface (MFS), followed high stand system tract (HST) deposited in progradation pattern, which is characterized by a gradual decrease in sea level and a shallowing sedimentary environment. The presence of three sequence cycles through the Tk-6 well is due to the fact that the Tikrit field is shallower than the Balad field of sedimentation and is located at the edges of the deeper part of the sedimentary basin and the beginning of the shallowing, which is affected more The processes of marine Transgression, where the final report of the well (Tk-6) showed that the succession of shallow sedimentary facies with deep facies as shown, indicating the instability of the substratum and its significant impact on tectonic movements.

Reservoir Characterization of Lower Qamchuqa (Shu'aiba) Formation from the Well BH-86, Bai- Hassan Oil field, Northern Iraq

The reservoir characterization of Lower Qamchuqa (Shu'aiba) Formation (Aptian) is studied at the well BH-86 of Bai- Hassan Oilfield in Kirkuk area, Northern Iraq. The lithological study (of 91 thin sections) revealed that the formation consists of shaly limestone, a thin bed of marl within the limestone, and dolomitic limestone. Four petrographic microfacies were noticed Lime mudstone microfacies, Dolomudstone microfacies, Lime wackestone microfacies, subdivided into benthonic foraminifera lime wackestone submicrofacies and bioclasts lime wackestone submicrofacies, and the last microfacies is the Lime packstone microfacies, which is subdivided into pelloidal lime packstone submicrofacies and Orbitolina lime packstone microfacies. Shale content is calculated from the gamma-ry log, showing that the formation is mainly of low shale content (less than 35%). The porosity determined from sonic, density, and neutron logs reflect that the range between <1 and 15% and in some intervals about 6% is secondary porosity type. The estimated permeability ranges between <0.01 and 2.0mD, reflecting low permeability. The formation is subdivided into six reservoir units according to the shale content, average porosity, and permeability. The unit RU-5 has the best reservoir properties among the identified units with an average shale content of about 3.15%, about 6.2% porosity, and about 1.75mD average permeability. On the other hand, the least reservoir property is noticed in the unit RU-1 with average 9.48% shale content, 3.64% porosity, and 0.5mD average permeability. The research indicates that the fractures contribute to the flow within the Lower Qamchuqa Formation. Fluids flow through the formation in four unique Hydraulic Flow Units (HFU). Only about 8% of the gross 146m of the formation is expected to have the required reservoir properties for oil production and about 68% for gas production. The actual productive thickness for oil is only about 2.8% of the gross thickness of the studied section, and it’s more than 50% of the gross thickness for gas.