Microfacies Types Research Articles

Sedimentary Reservoir Characteristics of Fuyu Oil Formation in the Middle of Fuxin Uplift, Southern Songliao Basin

Currently, the Fuyu reservoir in the middle of the Fuxin uplift, located in the southern Songliao Basin, is in a high water cut development stage. The understanding of this reservoir is limited, and the distribution of favorable reservoirs remains unclear, necessitating detailed reservoir characterization. This study employs a combination of well and seismic technologies to accurately depict the sedimentary and reservoir characteristics of the Fuyu oil reservoir. By conducting detailed correlations of oil zones, a regional high-resolution isochronous stratigraphic framework is established. The division of sedimentary microfacies enables fine characterization of single sand bodies, identifying channel boundaries, clarifying lateral connectivity, and detailing the vertical contact relationships of sand bodies across different deposition periods. The results demonstrate that root-mean-square amplitude and total energy metrics effectively correspond to sand bodies in the study area and can be used to analyze sand body distribution. Provenance is primarily from the southwest to the northeast, with shallow deltas predominantly developed. Delta plain subfacies are found in zones 4-12, while delta front subfacies are in zones 1-3. Microfacies types mainly include the main distributary channel, distributary channel sides, crevasse splay, overbank sand, and underwater distributary channels. The main distributary channel reservoirs exhibit the best physical properties, with porosity ranging from 20-25%, while sand bodies at the sides of distributary channels reach 15-20%. Predicted favorable areas are mainly located at the intersections of distributary channels and structural highs, where drilling is likely to yield high oil flow.

Microfacies and species richness analysis of upper Bartonian and Priabonian carbonate shelf deposits from the Thrace Basin (Tethyan Ocean, Greece): Paleoenvironmental evolution and species-richness hotspot revealed

Sediment, thin section, microfacies and foraminiferal analyses were conducted on middle-upper Eocene carbonate deposits to shed new light on the paleoenvironmental evolution and species richness of the Thrace Basin (Tethyan Ocean, Greece). Material from a total of 7 new sites, covering localities on the mainland and the north-eastern Aegean islands of Samothraki and Lemnos, was examined in order to analyze the general conditions and environmental evolution of the basin over as large a geographical area as possible. Analysis of the sedimentological and paleontological data allowed the identification of 5 microfacies types. These can be assigned to a sequence of interior to outer shelf environments and speak in favor of a model of a rimmed carbonate shelf with isolated platforms. Both open and restricted water circulation patterns have prevailed on and between the platforms. Triggered and driven by dynamic syn-rifting, topographic highs have developed in this area on which productive and species-rich reef structures could thrive. In the late Eocene carbonate deposits we found the highest documented species richness of larger symbiont-bearing foraminifers (LBF) to date, characterizing the Thrace Basin not only as a particularly species-rich and diverse area, but also as a LBF hotspot of diversity.

Millennial-scale sedimentary evolution of carbonate platforms during the Permian–Triassic boundary hyperthermal event

The millennial-scale response of shallow-water carbonate platforms to the climatic upheaval at the Permian–Triassic boundary (PTB) remains unclear. This study presents three carbonate platform sections across the Permian–Triassic (P–T) boundary in South China and the Lhasa terrane. A total of 14 types of carbonate microfacies were identified, which show that the Liangfengya and Taiping sections in South China were deposited in an inner ramp, and the Wenbudangsang section on the Lhasa terrane was deposited in an outer ramp. Bulk carbonate carbon isotope patterns through the sections are generally characterized by negative excursions (−2.2 to −3.5‰) during the PTB hyperthermal event. These excursions can be divided into four phases (NC1 to NC4), with NC1 before the negative carbon isotope excursion (NCIE) event, NC2 during the initiation phase of the NCIE, NC3 during the body of the NCIE, and the NC4 marking the recovery stage of the NCIE. The pattern of sedimentary changes in each section through the PTB hyperthermal event, and the relationship between these changes and the carbon isotope stages, was established. In the studied sections, the onset of the NCIEs (NC2 stage) preceded evidence for a carbonate production crisis, with the occurrence of anachronistic facies developed after this crisis but prior to the NC3 stage. In detail, our data show that the carbonate production crisis occurred 11 kyr after the onset of the NCIE, and 47 kyr before the first Permian–Triassic mass extinction (PTME), and that the carbonate production crisis may have been closely related to the environmental stresses associated with greenhouse gas emission from the Siberian Traps Large Igneous Province (STLIP).

PENNSYLVANIAN CONODONTS AND MICROFACIES FROM NORTHEASTERN MEXICO (TAMATÁN GROUP, CIUDAD VICTORIA BLOCK)

The biostratigraphic analysis of the Paleozoic sedimentary successions in Mexico is crucial for understanding their age, depositional setting, and paleogeographic implications. This study examined conodonts and microfacies of calcareous strata within the Del Monte Formation of the Tamatán Group in northeastern Mexico. Field observations have led to the identification of three units within the Del Monte Formation: Unit 1, characterized by calcareous sandstone, bioclastic limestone, shale, occasional conglomerate, and dolomitized beds; Unit 2, consisting of conglomerate and/or breccia associated with debris flows; and Unit 3 including turbiditic sandstone and shale. Conodonts were only recognized in Unit 1, with such genera as Idiognathoides, Neognathodus, Idiognathodus and less frequently, Streptognathodus, Adetognathus, and Diplognathodus. The faunal associations include Idiognathoides cf. Id. corrugatus Harris & Hollingsworth, 1933, Idiognathoides sulcatus sulcatus Higgins & Bouckaert, 1968, Idiognathoides convexus (Ellison & Graves, 1941), Idiognathoides asiaticus Nigmadganov & Nemyrovskaya, 1992, Neognathodus cf. N. atokaensis Grayson, 1984, Neognathodus aff. bothrops Merrill, 1972, Neognathodus nataliae Alekseev & Gerelzezeg, 2001 (in Alekseev & Goreva 2001), Streptognathodus parvus Dunn, 1966, Idiognathodus incurvus Dunn, 1966, and Idiognathodus aff. delicatus Gunnell, 1931, suggesting Morrowan and Atokan (Pennsylvanian) ages for the dolomitic limestone and grainstone beds. Five types of microfacies (MF) and several marine facies zone (FZ) have been detected: MF1-bioclastic grainstone and MF2-wackestone deposited at the platform margin (FZ 6 and FZ 7), MF3-dolomitized wackestone representing an inner restricted platform (FZ 8), MF4-mudstone from a deeper water zone (FZ 4), and MF5-siliciclastic beds with bioclasts indicating a high-energy barrier associated with a platform margin (FZ 6). The findings confirm a shallow to deep platform and imply a connection among Mexican peri-Gondwanan basins, including the Tamatán Basin, indicating similarities in sedimentary facies and/or depositional environments linked to the Rheic Ocean during the Early to Middle Pennsylvanian.

Depositional environments and carbon isotope excursions of the Middle Oxfordian (Transversarium Zone) sediments in the Central Saharan Atlas, Southwestern margin of the Tethys

This study examines the Middle Oxfordian sediments of the Theniet Et-Temar Formation in the Central Saharan Atlas (NW Algeria), which was located in the southwestern part of the Tethys Ocean during the Late Jurassic. Using microfacies analysis and δ13Ccarb isotopes, this research aims to elucidate the sedimentological and isotopic signatures of these sediments.Ten microfacies types were identified and grouped into four facies associations: nearshore (FA1), inner lagoon (FA2), shoal bar (FA3), and outer lagoon (FA4). Sequence stratigraphy, employing the T-R sequence concept, delineates the evolutionary stages of the studied succession into prograding deltaic front facies (LST1), retrogradational open marine facies (TST2), and deltaic plain facies within the highstand systems tract (HST2).Stable carbon isotopes from three sections namely, El Bayadh, Ghassoul, and Sidi Tifour of the Middle Oxfordian (Transversarium Zone) provide insights into carbon cycle perturbations and paleoenvironmental conditions. There are two δ13Ccarb excursions in the studied sections. A major positive excursion in the El Bayadh, Ghassoul and Sidi Tifour sections shows similar records in both southern (Saudi Arabia, Iraq) and northern Tethys regions (France, Poland, Scotland, Spain, Switzerland, and Uzbekistan). The negative δ13Ccarb shifts with values of −2.77‰ at the top of the Ghassoul section and −2.28‰ in the middle member of the Sidi Tifour section are coupled with more negative δ18Ocarb values suggesting alteration of isotopic values due to meteoric diagenesis.The variations in carbon isotopes suggest synchronous changes in the global marine dissolved inorganic carbon pool, potentially influenced by sea level fluctuations, climatic changes, and/or Jurassic dysoxic to anoxic events.

Biostratigraphy and facies around the D/C boundary interval of the Tuye-Darvar section, Eastern Alborz Range, NE Iran

The 1st order mass extinction at the Devonian/Carboniferous transition, known as the Hangenberg Crisis, is characterized by major transgressive/regressive cycles which led to widespread ocean anoxia during the Hangenberg Black Shale Event, as well as to a global major sea-level fall and the worldwide deposition of regressive Hangenberg Sandstone equivalents. The Devonian/Carboniferous transition at the Tuye-Darvar section in the eastern Alborz Range is studied in terms of conodont biostratigraphy, litho-, microfacies and sequence stratigraphy. In order to examine the biostratigraphical framework, forty conodont samples were systematically taken from the studied interval. Thirty-two conodont species belonging to ten genera led to the discrimination of twelve conodont zones, ranging from the Pseudopolygnathus granulosus Zone to the Scaliognathus anchoralis-Doliognathus latus Zone. Due to facies, the conodont record also exhibits some hiatuses. Field observations and sedimentological and microfacies studies led to the identification of thirteen facies types from sub-tidal environments to the fully marine environments, including seven microfacies types. The sediments deposited in a mixed carbonate-siliciclastic platform, revealed four third-order sequences. The Hangenberg Black Shale is not recorded in the Tuye-Darvar section as a result of depositional facies. In comparison with other studied Devonian/Carboniferous Boundary (DCB) sections of the central and northern Iran, the Tuye-Davar section suggests a tectonic position, which is most likely placed on a separate tectonic block.

Microfacies Analysis of the Mishrif Formation (Mid-Cretaceous) at the Tuba and Zubair Oilfields, Southern Iraq

The Cenomanian-Early Turonian Mishrif Formation, which has been studied in selected Oilfields of Tuba Well (TU-5, TU-24, TU-40) and Zubair Well (ZB-41, ZB-42, and ZB-46), which are located in the Mesopotamian basin, southern Iraq, and considered major carbonate reservoir in Iraq and the Arabian Gulf. Seven microfacies types are identified showing that Mishrif formation deposited in five sedimentary facies: 1. Basin Facies Associations; 2. Deep Marine Facies Associations: Bioclast pelagic foram mudstone-wackestone; 3. Shallow Open Marine Facies Associations: Foraminiferal bioclastic wackestone-packstones; 4. Rudisted Reef Facies Associations; 5. Shoal Facies Associations: Peloidal packstone-grainstone; 6.aBack-shoal Facies Association: a. Foraminiferal-bioclastic wackestone-packstone, b. Rudisted-foraminiferal wackestone-packstone; 7. Lagoon Facies Associations: a. Fossiliferous mudstone-wackestone, b. Bioclast foraminiferal wackestone, c. Benthic foraminiferal wackestone.

Integrated stratigraphical, hydrogeochemical, and geophysical studies to characterize the shallow groundwater aquifers in Wadi Araba area, western Gulf of Suez, Egypt

The construction of the New Galala City besides great mining (e.g., konoozmisr) and Seawater Reverse Osmosis Desalination Plant projects in the semiarid Gulf of Suez region of Egypt increases the demand for groundwater resources. So, the current research provides integrated stratigraphical, hydrogeochemical, and geophysical studies to investigate the shallow groundwater aquifers in Wadi Araba area on the western side of the Gulf of Suez. The stratigraphic column starts with pre-Cambrian basement rocks which are non-conformably overlain by sedimentary succession of Phanerozoic Erathem. A detailed land magnetic profile has been conducted and processed to estimate the aquifer’s geometrical parameters. This includes the subsurface spatial extension and thickness to delineate the prevailed subsurface structures in the study area. Lithostratigraphically, these aquifers are represented by the Paleozoic- lower Cretaceous siliciclastic-dominated sediments of the Nubia Group and fractured carbonate-dominated facies of the upper Cretaceous Galala Formation. Lithological characters, sedimentary facies (fluvial to shallow and open marine), microfacies types, and diagenesis processes (e.g., compaction, cementation, dissolution, and fracturing) are the main factors that affect the quality of the shallow aquifers in the study area. The main microfacies of the studied aquifers are quartz arenite, subarkose, sublitharenite, mudstone/wackestone, and packstone/grainstone. These facies are characterized by different primary and secondary porosities. According to the water sampling standard methods, nineteen groundwater samples were collected from the available hand-dug wells and springs from the Nubian sandstone aquifer and the Upper Cretaceous aquifer, respectively. Inductively coupled plasma–mass spectrometry (ICP–MS), titration, spectrophotometer and a flame photometer were used to obtain a complete chemical analysis. The results of hydrochemical analyses indicated that total dissolved solids (TDS) and concentrations of major ions as well in the lower Cretaceous aquifer increase toward the Gulf of Suez and in general higher than that of springs of the Upper Cretaceous Aquifer. The predominant factors influencing groundwater chemistry include seawater intrusion, evaporation, mineral alteration, dissolution of fossils, and ion exchange. Groundwater in the study area is unsuitable for drinking except in one sample and moderately suitable for irrigation with caution for higher salinity in samples located near the Gulf of Suez.

Sedimentary microfacies of Member 5 of Xujiahe Formation in the Dongfengchang area, Sichuan Basin

Member 5 of the Upper Triassic Xujiahe Formation (T3X5) in central Sichuan Basin has made a breakthrough in exploration recently. However, this new stratum has not been investigated sufficiently with respect to basic geology, making its types and distribution of sedimentary facies unclear, which severely restricts its subsequent exploration evaluation. In this study, types of sedimentary microfacies in the first sand group of T3X5 (T3X51) are clarified through core observation and logging interpretation using core, log and seismic data, and then distribution of sedimentary microfacies in T3X51 is determined according to seismic waveform features and seismic prediction. The results show that T3X51 in the Dongfengchang area is mainly composed of deltaic deposits of several microfacies, such as delta front underwater distributary channel, sheet sand, and interdistributary bay. On seismic sections, different microfacies are significantly different in waveform features, the underwater distributary channel is characterized by one trough between two peaks, while diversion bay exhibits chaotic reflections between T6 and T51. The sedimentary microfacies varied greatly during the depositional period of T3X51 in the Dongfengchang area, this is because that the sediment supply was mainly controlled by the southwest and southeast provenance regions. Three superimposed underwater distributary channels are developed in the Dongfengchang area. The phase-1 superimposed underwater distributary channel in the northwest transition to sheet sand in the northeast, the phase-2 superimposed underwater distributary channel in the south extends shortly, the phase-3 superimposed underwater distributary channel in the northeast has a large development scale. These research findings are helpful to guide the subsequent exploration of T3X5 gas reservoir and also theoretically significant for investigating the depositional evolution of the Xujiahe Formation in central Sichuan Basin.

Longshore changes in the microfacies and distribution of clastic barrier coastal sandbodies: a case from the Benxi formation in the Ordos Basin, China

AbstractThe Benxi Formation in the Ordos Basin is an important gas-producing layer in the Yanchang gas field. There are critical changes in the microfacies type and extension trend of sandbodies, which affects the understanding of reservoir formation and the deployment of development wells. Based on many core and thin section observations, as well as statistical analyzes of sandstone thickness and percentage of sandstone content from 1446 wells, we analyzed the coastal changes and control factors of the microfacies type, planar morphology and distribution of the Benxi Fm sandbodies in the field. The results indicate that the Benxi Fm of the Yanchang gas field is generally composed of terrigenous coastal clastic barrier deposits in a medium to small tidal range environment, but the wave action in the southern region is weak, forming typical barrier sandbars and backbarrier deposits. The wave actions in the north change more strongly, forming three major microfacies sandbodies: reworked barriers, shoals and incised valley filled tidal channels. The barrier sandbodies are arranged in a belt or bead-like pattern parallel to the shoreline and are distributed longshore near the provenance. The oval-shaped shoal sandbodies are dispersed further from the shoreline, and the filling of tidal channel sandbodies is controlled by ancient geomorphic grooves. This research has important guiding significance for the identification and evaluation of reservoirs in the Yanchang gas field and similar geological settings.

Magnetic micro-archaeology: a method for conducting rock magnetic microfacies analysis on archaeological soil micromorphology samples, with a case study from El Salt, Alcoy, Spain

For geoarchaeologists the use of multiproxy and multimethod integrative approaches has become common for studying the sedimentary context of archaeological materials. In this paper, we introduce a novel approach that combines rock magnetic analysis with micromorphological analysis. We first conduct a brief examination of the magnetic properties of organic resins used in micromorphology to understand the potential impact of the resin and manufacturing process on the magnetic signature. It is crucial to understand the original production of the samples to ensure that endothermic reactions do not compromise the magnetic data. We illustrate the advantages of this approach through a case study of a pit hearth from the Neanderthal archaeological site of El Salt in Alcoi, Spain. This study utilises archived micromorphological samples of a pit hearth (combustion structure H77) initially described by Leierer et al. (J Archaeol Sci 123:105237, 2020). Rock magnetic analysis of multiple magnetic parameters—including magnetic susceptibility, natural remanent magnetization, and progressive isothermal remanent magnetization—reveals that each microfacies type exhibits a unique magnetic pattern, even if there is overlapping in signatures across some magnetic parameters. The interpretation of the magnetic data aligns with the results and microfacies descriptions previously provided by Leierer et al. (J Archaeol Sci 123:105237, 2020), further supporting the interpretation of the combustion feature as being in situ with a history of repeated use. The approach presented here offers an enhanced tool for micromorphologists to better understand the magnetic characteristics of microfacies units in higher resolution and establish direct connections to the micromorphological results.

Microfacies Analysis and Paleoenvironment of Baba Formation, Anah Area Westren Iraq

Microfacies analysis and Paleoenvironment of Baba Formation were investigated in Anah area, Anbar Governorate, Western Iraq. Baba Formation was cropped out in Wadi Al-Khazgah section with 9 meters thick, consisting of white to creamy, chalky, coralline, high fracture Limestone. Five Microfacies types were recognized Coral Lime Boundstone, Lepidocyclina Lime Packstone, Nummulitids Lime Packstone, Miliolids Lime Packstone - Grainstone, and Coraline Algae Lime Wackestone described in 10 samples collected from one section (Wadi Al-Khazgah Al-Gharbi section). These Microfacies described on the basis of the presence of the Benthic Large Foraminifera (BLF) as Miliolids, Lepidocyclinide, Rotalide and skeletal fragments of brachiopod, coral, and algae shell. The paleoenvironment of Baba Formation was determined fore-Reef and Reef environments.

The geological controlling factors of the heterogeneity of a bioclastic limestone reservoir—a case study of the Cretaceous Kh2 layer in A oilfield, Iraq

Reservoir heterogeneity is one of the key factors affecting the exploration and development of oil and gas reservoirs. The Kh2 layer in the A field of Central Iraq is a major pay zone with strong longitudinal and lateral heterogeneity. The heterogeneity, controlled by geological factors, has not yet been confirmed, which seriously restricts the development of this pay zone. This study aims to establish a geological pattern for the reservoir heterogeneity of bioclastic limestone, providing a geological basis for heterogeneity evaluation. Based on the core observation, thin-section identification, and physical property analysis, the microfacies are classified, and the diagenetic sequences and the pore structure of the Kh2 layer are analyzed. Seven types of microfacies are developed in the Kh2 layer, namely, planktic foraminiferal wackestone (MFT1), lamellar bioclastic wackestone (MFT2), intraclastic–bioclastic packstone (MFT3), green algal packstone (MFT4), green alga–pelletoid packstone (MFT5), bioclastic–intraclastic packstone (MFT6), and intraclastic grainstone (MFT7). The heterogeneity of the different microfacies and heterogeneity within the same microfacies were evaluated using the variation coefficient of permeability tested from cores collected from wells and calculated by well-logging at different intervals. The highest heterogeneity was observed in the lamellar bioclastic wackestone (MFT2), with an average variation coefficient of 0.72. The lowest heterogeneity was observed in the green algal packstone (MFT4), with an average variation coefficient of 0.11. The vertical heterogeneity of the permeability is mainly controlled by sedimentation, while the lateral heterogeneity is mainly influenced by cementation, bioturbation, and the distribution of green algae. Finally, a micro-scale geological pattern for determining the reservoir heterogeneity of bioclastic limestone reservoirs is established. This study can guide the current injection development and remaining oil prediction in oilfields with similar backgrounds.

The Middle Miocene Microfacies, Cyclicity, and Depositional History: Implications on the Marmarica Formation at the Siwa Oasis, Western Desert (Egypt)

Microfacies studies were carried out on the Middle Miocene Marmarica Formation exposed at the Gabal Western Bahi El-Din and Gabal El-Najdeen, the Siwa Oasis, northwestern Desert (Egypt). It was distinguished into the lower, middle, and upper members. Eleven microfacies types were recognized, which include skeletal lime-mudstone, dolomitic lime-mudstone, intraclastic wackestone, bryozoan wackestone, foraminiferal wackestone, foraminiferal bryozoan packstone, glauconitic molluscan packstone, molluscan intraclastic packstone, pelletal peloidal skeletal packstone, dolostones, and claystone microfacies. This formation includes several types of emergence- meter-scale cycles (shallowing-upward). Field observations and petrographic analyses revealed that these cycles consist of pure carbonates and mixed siliciclastic carbonates. These cycles consist of four types of gradual cycles and six types of non-gradual cycles. The gradual emergence cycles indicate a balance between the rate of subsidence, sea level oscillations, and sedimentation rate. The non-gradual cycles indicate an irregular balance between sedimentation rate and subsidence rate. The non-gradual cycles denote high-frequency sea level variation and/or short-term sea level oscillations, which are associated with high carbonate formation. The depositional environments of the Marmarica Formation are restricted to lagoonal at the base, followed upward to open marine conditions. Both environments most probably characterize the platform setting.

Sedimentary: Carbonate microfacies and mineralogy of the southern Benue Trough and eastern Dahomey basin, Nigeria

This study presents a detailed investigation into the microfacies, geochemistry, and depositional environments of carbonate rocks from the southern Benue Trough and eastern Dahomey Basin. This analysis involved a combination of techniques, including X-ray diffraction, X-ray fluorescence, scanning electron microscopy with energy-dispersive X-ray spectroscopy and thin-section petrographic examination. Samples from the Igumale Formation of the southern Benue Trough and samples from Ewekoro Formation of the eastern Dahomey Basin were analyzed, offering insights into their mineral compositions, elemental distributions, and depositional environments. In each basin, two carbonate microfacies were identified. The two microfacies found in the Igumale Formation were recognized as micritic bioclastic packstone and sandy bioclastic wackestone. In the Ewekoro Formation, the two microfacies recognized were bioclastic packstone and sparitic peloidal wackestone. The X-ray diffraction analysis of samples from both basins revealed a dominance of calcite. X-ray fluorescence analysis showcased calcium oxide and calcium as the predominant oxide and elements in both basins with varying concentrations. Scanning electron microscopy-energy-dispersive X-ray spectroscopy results unveiled the elemental composition with calcium and silicon emerging as major constituents. The photomicrographs suggest distinct depositional conditions for both samples with those from the Igumale Formation showing evidence of shallow marine and that of the Ewekoro Formation suggesting calm marine environments comprised of fined grained carbonate rocks containing fossils. This study has provided detailed understanding on the nature, microfacies types, mineralogical composition, depositional environment and diagenetic processes of Cretaceous-Paleocene carbonate rocks within the studied basins.

Deciphering the implication of microfacies types and diagenesis on the reservoir quality of the Cambrian sequence in Hassi Messaoud Field, Algeria

The Cambrian Hassi Messaoud sequence is considered a main reservoir in East Algeria and North Africa. It is well represented in the Hassi Messaoud Basin by four units, from base to top they are R3, R2, R1 (Ra and RI units), and alteration zone. Among these, the Ra is the most important unit due to its reservoir potentiality; it is classified from base to top into D4, D3, D2, ID, and D1 reservoirs, while the RI zone is called D5. Due to their importance as oil-producing reservoirs, this study deals with the implementation of the microfacies type and pore architecture on the quality of these reservoirs. A detailed petrographical study and SEM imaging are applied to reveal the pore and grain fabrics, and decipher the dominant clay types and distribution. Also, a detailed study on the flow and storage capacities of 5108 plugs selected from the six Cambrian units, where porosity and permeability are measured and the reservoir quality parameters are also estimated including the flow zone indicator (FZI), the reservoir quality index (RQI), discrete rock type (DRT), and the effective pore radius (R35). Considering these parameters, the studied plugs are summed up into six petrophysical static rock types (PSRT). The PSRT1 has the best reservoir quality values due to its high porosity, permeability, DRT, R35, RQI, and FZI. This PSRT is primarily composed of siliceous quartz arenite microfacies and is highly affected by the dissolution and fracturing as a reservoir quality-supporting diagenetic features. On the other side, the PSRT6 is composed of micaceous and argillaceous subarkose microfacies and is controlled by tight compaction, cementation, and authigenic clay content as reservoir quality-deteriorating diagenetic features. It has the lowest porosity, permeability, DRT, R35, RQI, and FZI values. The PSRT2-5 samples are composed of four microfacies types: 1) siliceous quartz arenite, 2) kaolinitic and siliceous quartz arenite, 3) micaceous, kaolinitic, and siliceous quartz arenite, and 4) micaceous and argillaceous subarkose microfacies. They are affected by various diagenetic features including compaction, cementation, authigenic clay content, fracturing, and dissolution. In general, the whole PSRTs samples are characterized by high heterogeneity in both the mineral composition and the pore architecture. This study is recommended to be followed for delineating the main factors controlling the reservoir quality in various basins, so it may be extendible to the equivalent Cambrian sequences elsewhere.

Facies Association and Depositional Environment of the Sarmord Formation (Valanginian-Aptian), Kurdistan Region, Northeastern Iraq

The facies analysis, mineralogy and depositional environment of the Cretaceous Sarmord Formation are studied in two outcrops in the Imbrication and High Folded Zones of Northeastern Kurdistan region of Iraq. The formation comprises of rhythmic alternation of medium to thick-bedded marly limestone with marls. Petrographic investigation of marly limestones is on 60 thin sections and showed a variety of pelagic (open sea) faunas such as; ammonites, planktonic forams (Globigerina), radiolarians, calcispheres, ostracods, bioclasts, echinoderm plates and rare calpionellids. Peloids are the only non-skeletal grains components. Depending on detailed microfacies analysis of limestones, three main microfacies types and nine sub-microfacies are identified in the studied sections of the Sarmord Formation, these facies were incorporated into one facies association type relating to their environmental interpretation, that is basinal facies association. X-ray diffraction analysis of selected marl samples, displayed that the main clay minerals in the Sarmord Formation are illite, kaolinite, chlorite and mixed-layers of illite – chlorite. The high abundance of illite indicates that hot-arid climatic conditions prevailed during the deposition of the Sarmord Formation in the study area. From all of the petrographic, facies, textural and mineralogical analyses, it is concluded that the Sarmord Formation in the northeastern Iraq, was deposited in deep water, basinal (outer ramp) environment.

THE DEPOSITIONAL SETTINGS AND THE HYDROCARBON POTENTIAL OF THE NEOTETHYS PASSIVE CONTINENTAL MARGIN

The study area is associated with the outer passive wing of the foreland trough that was formed due to collisional-orogenic deformations of the Neotethys Arabian Plate. The sedimentological and paleoenvironmental features of the Cenomanian formation indicate that the carbonate sediments were deposited in a homoclinal ramp depositional settings. The depositional area comprises different bathymetric settings from the intertidal littoral and coastal shallow water to the open and relatively deep sublittoral. Microfacies analysis was performed based on the cores and thin sections observations to investigate the sedimentary and diagenesis evolution. Ten microfacies types are identified showing that carbonates deposited in three major sedimentary facies belts: outer ramp, middle ramp and inner ramp. In response to the relative sea level changes during sedimentation the section comprises of several sedimentary sequences. The sequences mainly reflect the prevailing of twocomponent depositional pattern, i.e., middle ramp and outer ramp, which is a result of low fluctuation of the relative sea level. The complete three-component sequences are associated with predominantly shallow areas that favorable for progradation event even under the low fluctuations of the relative sea level.The highest sedimentation rate is confined to the proximal shallow part of the middle ramp and to the distal part of the inner ramp with favorable conditions for the development of benthic organics due to abundant sunlight and nutrition supply. The best reservoir rocks with intergranular voids, composed of algal oolitic and bioclast grainstones of high dynamic shoal zone.This study provides an insight into reservoir quality prediction and prospect area evaluation of the oil bearing formation in the southern part of stable shelf which is controlled by spatial extension of grain supported deposits of inner ramp and transverse faults.

Oligocene biostratigraphy, depositional patterns, and stable isotope values in the eastern Zagros basin: Novel insight into the signature of regional and global events

Biostratigraphy, depositional environment, sequence stratigraphy, and paleoclimate iterpretation of the Asmari carbonate reservoir are the subject of the current study. Two, earlier uninvestigated stratigraphic sections are studied and correlated over the eastern Zagros basin. The vertical distribution of foraminifera (benthic and planktic) reveals that the Asmari Formation deposited during the Rupelian-Chattian. Three shallow benthic foraminifera biozones are established, namely the Globigerina-Turborotalia cerroazulensis-Hantkenina Assemblage Zone, the Nummulites vascus-Nummulites fichteli Assemblage Zone, and the Archaias asmaricus- Archaias hensoni-Miogypsinoides complanatus Assemblage Zone. Ten microfacies types associated with the inner, middle and outer ramp of a carbonate platform are identified. Three depositional sequences are recognized in the eastern Zagros basin. The oldest sequence is Rupelian in age, and two others are of Rupelian-Chattian and Chattian in age. Two maximum flooding surfaces occur in the eastern Zagros basin. The isotope startigraphical data show that the more positive values of the δ18O and δ13C coincide with the maximum flooding surfaces, while these values show depletion over the sequence boundaries. The exception is observed at the upper boundary of the succession where the hypersalinity conditions affected the trend. The stable isotope values obtained from bulk samples enable to identify the Oligocene glacial events such as Oi2 and, Oi2a (Rupelian) and Oi2b (Chattian). The examination of the grain associations of the MF3 and MF5 prove these cooling events. We suggest the middle ramp microfacies and MFS2 of Sq.2 as signatures for tracing these cooling events throughout the eastern Zagros basin.

Petrophysical rock typing based on the digenetic effect of the different microfacies types of Abu Madi clastic reservoir in Faraskur Gas Field, onshore Nile Delta, Egypt

The sandstone of Abu Madi clastic reservoir constitutes the prime gas-producing reservoir in the Nile Delta region. So, the present research aims to delineate its microfacies and dominant diagenetic features and their effect on the petrophysical characteristics of the Abu Madi reservoir in the Faraskur Gas Field. This could be achieved by integrating the petrographical studies and the conventional data to divide the reservoir into some reservoir rock types (RRTs) to delineate the impact of the mineral composition and diagenetic features on their reservoir quality and hydraulic flow zones. Petrographically, most samples are immature and described as angular to subrounded, poorly sorted, and slightly cemented. Five clastic microfacies types are recorded in the Abu Madi Formation: (1) quartz arenite, (2) feldspathic quartz arenite, (3) sub-feldspathic quartz arenite, (4) quartz wacke, and (5) sub-feldspathic quartz wacke. The most important post-depositional processes affecting the reservoir quality are the precipitation of pyrite and microsparite, as well as the feldspars alteration into authigenic dispersed clays represented by kaolinite and smectite/illite mixed layers. The dominant pore types are the primary intergranular, with some subsidiary fractures and dissolution pores. To check the reservoir quality of the Abu Madi clastics, the NPI (normalized porosity index), FZI (flow zone indicator), RQI (reservoir quality index), and λk (permeability anisotropy) were estimated. Petrophysically, the studied samples are summed up into four RRTs, with the RRT4 group has the lowest ∅ and k values (av. ∅ = 16.2%, av. kH = 6.87 md) and the lowest reservoir quality parameters (av. FZI = 0.89 μm, av. DRT = 10.4, av. RQI = 0.18 μm, av. R35 = 1.26 μm). On the contrary, the RRT1 group has the best petrophysical and reservoir parameters (av. ∅ = 25.9%, av. kH = 2695 md, av. DRT = 14.9, av. RQI = 3.12 μm, av. FZI = 8.85 μm, av. R35 = 32.7 μm). The permeability anisotropy of the RRT2 and RRT3 is the highest in Faraskur Field (av. λk = 2.4 and 2.62, respectively). This study is applicable to other extensions of the Abu Madi reservoirs in the Nile Delta basin to help in predicting their reservoir quality, petrophysical properties, and their hydrocarbon potentiality.