Hamdalla Abdel-Gawad Abdel-Aziz Wanas

@kau.edu.sa

Department of petroleum Geology and Sedimentology, Faculty of Earth Sciences, King AbdulAziz University
King AbdulAziz university, Menofiya university



              

https://researchid.co/hwanaskau.edu.sa

EDUCATION

Geology

RESEARCH INTERESTS

Sedimentology and Sequence Stratigraphy

49

Scopus Publications

Scopus Publications



  • Depositional architecture and sequence stratigraphic framework of the fluvio-lacustrine Ash Shumaysi Formation, Jeddah-Makkah Region, Saudi Arabia: Implications for climatic and tectonic changes in a local-scale sub-basin
    Faisal A. Alqahtani, Murad R. Abdulfarraj, and Hamdalla A. Wanas
    Wiley
    AbstractThis study aims to interpret and document the depositional architecture styles and sequence stratigraphic framework of the Ash Shumaysi Formation in the Jeddah‐Makkah region, the west‐central part of Saudi Arabia, and presents an example of rarely discussed, local‐scale sub‐basins (half grabens). It also shows the relationships between synchronous sedimentary processes and pre, syn and post‐rift conditions. The described lithofacies and their facies associations indicate the presence of seven architectural depositional styles: proximal‐distal braided fluvial, meandering fluvial (point bar), crevasse splay, floodplain, estuarine and lacustrine. A proposed depositional model for the Ash Shumaysi Formation is drawn. The Ash Shumaysi Formation forms a second order depositional sequence, which is organised into two third order depositional sequences (sequences I and II) bounded by three sequence boundaries. Each third‐order sequence encloses the low accommodation systems tract and high accommodation systems tract. The low accommodation systems tract represents the coarse‐grained, braided‐distal fluvial facies developed during low accommodation space associated with high sediment supply (high discharge). The high accommodation systems tract encloses the fine‐grained deposits of point bar, estuarine and lacustrine facies that reflect the creation of significant accommodation space and low sediment supply (low discharge). Vertical and lateral variations of the inferred depositional architectural styles, sequences and systems tracts reflect that tectonic forces and climate are the main controlling factors during deposition of the Ash Shumaysi Formation, although base‐level changes in response to sea‐level changes cannot be ruled out.


  • Geoheritage meaning of past humidity in the central Western Desert of Egypt
    Fatma A. Mousa, Mohamed M. Abu El-Hassan, Hamdalla A. Wanas, Emad S. Sallam, Vladimir A. Ermolaev, and Dmitry A. Ruban
    Elsevier BV







  • Well log-aided source rock potential, basin modeling, and seismic attributes: Petroleum geology case study of Pliocene discovery at South Mansoura Area (Nile Delta)
    Ahmed M. Elatrash, Mohammad A. Abdelwahhab, Hamdalla A. Wanas, Samir I. El-Naggar, and Hasan M. Elshayeb
    Springer Science and Business Media LLC
    Confirming hydrocarbon charge in reservoir assessment is crucial for exploration and appraisal phases of oil and gas business. This paper addresses the source rock assessment and basin modeling, as well as seismic attributes, of Miocene-Pliocene sequences, shedding light on petroleum potential at South Mansoura Area. South Mansoura-1 well was chosen in performing the required investigation. It contains complete set of logs, enclosing gamma ray, resistivity, neutron, density, and sonic logs. Passey formula was used in calculating the TOC (total organic carbon) within the source rock intervals, employing resistivity and porosity logs. 1-D basin model was established to retrieve the burial history and maturation levels within the area. Various seismic attributes have been extracted for the Pliocene target, to confirm the hydrocarbon accumulation within the reservoir intervals. The results show a rather significant source-prone interval for Middle-Late Miocene Sidi Salem and a predominant source potential for Pliocene Kafr El Sheikh shales, capable of feeding reservoir intervals of Messinian Qawasim, Abu Madi, and Pliocene Kafr El Sheikh formations, due to the adequate generation level featuring the penetrated rocks. The shales of the penetrated units are in the main generation window for expelling hydrocarbons. Moreover, direct hydrocarbon indicator and seismic attribute analyses of Pliocene and Miocene Kafr El Sheikh and Abu Madi formations, respectively, confirm the hydrocarbon charging within the reservoir intervals. Accordingly, it is recommended to expand the investigations to reveal out the structural configuration controlling the area, and migration pathways revealed applying 2-D basin modeling approaches, so as to mark the best locations for drilling new development wells. Furthermore, the established 1-D basin model, performed in this study, could be effectively used as a baseline for future plays at the Nile Delta basin.

  • Multi-disciplinary approach to sedimentary facies analysis of Messinian Salinity Crisis tectono-sequences (South-Mansoura Area, Nile Delta): Incised-valley fill geological model reconstruction and petroleum geology–reservoir element delineation
    Ahmed M. Elatrash, M. A. Abdelwahhab, H. Wanas, Samir I. El-Naggar and Hasan M. Elshayeb

    The quality of a hydrocarbon reservoir is strongly controlled by the depositional and diagenetic facies nature of the given rock. Therefore, building a precise geological/depositional model of the reservoir rock is critical to reducing risks while exploring for petroleum. Ultimate reservoir characterization for constructing an adequate geological model is still challenging due to the in general insufficiency of data; particularly integrating them through combined approaches. In this paper, we integrated seismic geomorphology, sequence stratigraphy, and sedimentology, to efficiently characterize the Upper Miocene, incised-valley fill, Abu Madi Formation at South Mansoura Area (Onshore Nile Delta, Egypt). Abu Madi Formation, in the study area, is a SW-NE trending reservoir fairway consisting of alternative sequences of shales and channel-fill sandstones, of the Messinian age, that were built as a result of the River Nile sediment supply upon the Messinian Salinity Crisis. Hence, it comprises a range of continental to coastal depositional facies. We utilized dataset including seismic data, complete set of well logs, and core samples. We performed seismic attribute analysis, particularly spectral decomposition, over stratal slices to outline the geometry of the incised-valley fill. Moreover, well log analysis was done to distinguish different facies and lithofacies associations, and define their paleo-depositional environments; a preceding further look was given to the well log-based sequence stratigraphic setting as well. Furthermore, mineralogical composition and post-depositional diagenesis were identified performing petrographical analysis of some thin sections adopted from the core samples. A linkage between such approaches, performed in this study, and their impact on reservoir quality determination was aimed to shed light on a successful integrated reservoir characterization, capable of giving a robust insight into the depositional facies, and the associated petroleum potential. The results show that MSC Abu Madi Formation constitutes a third-order depositional sequence of fluvial to estuarine units, infilling the Eonile-canyon, with five sedimentary facies associations; overbank mud, fluvial channel complex, estuarine mud, tidal channels, and tidal bars; trending SW-NE with a Y-shape channel geometry. The fluvial facies association (zone 1 and 3) enriches coarse-grained sandstones, deposited in subaerial setting, with significantly higher reservoir quality, acting as the best reservoir facies of the area. Although the dissolution of detrital components, mainly feldspars, enhanced a secondary porosity, improving reservoir quality of MSC Abu Madi sediments, continental fluvial channel facies represent the main fluid flow conduits, where marine influence is limited.

  • Provenance, tectonic setting and source area-paleoweathering of sandstones of the Bahariya Formation in the Bahariya Oasis, Egypt: An implication to paleoclimate and paleogeography of the southern Neo-Tethys region during Early Cenomanian
    Hamdalla A. Wanas and Ehab M. Assal
    Elsevier BV
    Abstract The Lower Cenomanian Bahariya Formation forms the most prolific hydrocarbon reservoir in the Western Desert of Egypt, and represents a good example to illustrate the paleogeographical evolution of the southern Neo-Tethys region during the Early Cenomanian. It is also particularly important for its diverse vertebrate fauna including dipnoans, chelonians, crocodyliforms, squamates, plesiosaurs, decapod crustaceans and dinosaurs, which reflect sustained regional biostratigraphical and paleoenvironmental significance. It consists of fluvio-marine siliciclastic rocks (sandstones and mudrocks). A multidisciplinary approach of fieldwork, petrography and bulk-rock geochemistry of the sandstones of the Bahariya Formation was used to constrain their provenance, tectonic setting, source area-paleoweathering and paleoclimatic conditions within the Neo-Tethyan realm. Petrographically, the studied sandstones are mainly of quartz-arenite type with subordinate sub-arkose and sublithic ones. Quartz types, trace and rare earth element concentrations and ratios indicate the sandstones were sourced from felsic granitic rocks with a rare contribution of felsic gneisses. The modal analysis reflects that the sandstones are mainly of cratonic interior and quartzose recycled tectonic provenance. The chondrite-normalized REE distribution pattern of the Bahariya sandstones are characterized by enriched LREE and flat HREE similar to those of UCC with negative Eu/Eu* anomalies. Major and trace elements of the sandstones suggest their deposition on a Neo-Tethys passive continental margin related to the Early Cretaceous rifting. The weathering indices (CIA, CIW, PIA and ICV) and the Al2O3-(CaO+Na2O)-K2O diagram suggest moderate to severe chemical weathering in the source area under semi-humid to humid climatic conditions. In conclusions, the Bahariya sandstones could be sourced by a fluvial reworking of moderately- to intensively-weathered Precambrian granites and gneisses of the surrounding Gebel Uweinat Massive (at the southwest of the study area), and were deposited in a low-lying basin (Bahariya area) of a Neo-Tethys passive continental margin. In a broad interest, results of this study play an important role in reconstructing the paleoclimatic conditions and paleogeographical evolution of the southern Neo-Tethys region during the Early Cenomanian.

  • Were springline carbonates in the kurkur–dungul area (Southern Egypt) deposited during glacial periods?
    Sándor Kele, Emad S. Sallam, Enrico Capezzuoli, Mike Rogerson, Hamdalla Wanas, Chuan-Chou Shen, Mahjoor Ahmad Lone, Tsai-Luen Yu, Andrew Schauer, and Katharine W. Huntington
    Geological Society of London
    The tufa deposits in the Kurkur–Dungul area, southern Egypt, date from marine isotope stage (MIS) 11 to MIS 1. Springs across the region were active during glacial periods (with sea-level below –50 m), reflecting changed atmospheric circulation over the Indian Ocean, as well as peak interglacial periods. During times of low sea-level, reduced Indonesian throughflow promoted formation of an Indian Ocean Warm Pool, and anomalous rainfall on its western margin. We suggest that Egypt lies at the intersection of westerly (‘maghrebian’) and easterly (‘mashriqian’) rainfall provinces, which show different timing with relation to orbital forcing and different source water regions. Tufa-growth periods are therefore not mechanistically linked to ‘humid periods’ or ‘sapropel events’ identified elsewhere. Stable isotope and T(Δ47) data are also inconsistent with these spring systems being part of a larger system spanning northern Africa, and lack a clear interaction between northern hemisphere heating and mid-latitude rainfall. We also follow previous researchers in concluding that formation of springline deposit formation was probably delayed compared with rainfall, owing to aquifer flow distances. This delay is unlikely to be sufficient to explain why rainfall is out of phase with movements of the monsoon belts, but may complicate interpretation of these records.Supplementary material: A lithofacies description and supplementary figures and tables are available at https://doi.org/10.6084/m9.figshare.c.5246661

  • Depositional model and sequence stratigraphy of the Paleocene-Lower Eocene succession in the Farafra Oasis, Western Desert, Egypt
    H.A. Wanas, A.M. Abu Shama, and S.A. El-Nahrawy
    Elsevier BV
    Abstract This work is to reconstruct a depositional model and establish a sequence stratigraphic framework for the exposed Paleocene-Lower Eocene succession in the Farafra Oasis, Western Desert, Egypt. This has been performed by an integration of the microfacies analysis with aid of the nannofossils and P/B foraminiferal ratio in the studied rocks. The identified microfacies and their related palaeoenvironments suggest a deposition in a carbonate shelf (inner, middle and outer shelf) environment. The Paleocene deposits (Dakhla, Tarawan and lower part of Esna formations) were laid down in a mid-to outer-shelf setting, whereas the deposits of Early Eocene age (Farafra Formation and upper part of Esna Formation) were deposited in an inner shelf setting. An integration of the resultant microfacies, nannofossils and P/B foramineferal ratio in the studied four stratigraphic sections led to record five 3rd order depositional sequences (SQs) separated by six sequence boundaries (SBs). Each sequence consists of transgressive (TST) and highstand (HST) systems tracts. The TST consists of a retrogradational package of facies (planktonic foraminiferal wackstones/packstones, as well as shales and marls rich in planktonic foraminifera) ended by marine flooding surface (MFS). The HST is made up of aggradational package of facies (nummulitic bioclastic packstone, algal alveoline packstone, alveoline-miliolid packstone and shale with a relatively low P/B foraminiferal ratio) topped by sequence boundary (SB). The sequence boundaries are distinguished by lithologic and paleontologic criteria. The recognized lithologic criteria comprise calcretes, iron-stained surface, extensive bioturbation and erosional irregular surfaces. The paleontologic criteria are evidenced by the time gaps (hiatus). The maximum flooding surfaces are recognized where there are a relatively high P/B foraminiferal ratio in the studied facies. The integrated results suggest that sedimentation regime of the studied Paleocene-Lower Eocene rocks was mainly controlled by tectonic activities and subsequent sea-level changes that were a result of a reactivation of the Syrian Arc System during Early Paleogene time.

  • 3D geological modeling of the Upper Cretaceous reservoirs in GPT oil field, Abu Sennan area, Western Desert, Egypt
    Mohamed F. Abu-Hashish, Hamdalla A. Wanas, and Emad Madian
    Springer Science and Business Media LLC
    Abstract This study aims to construct 3D geological model using the integration of seismic data with well log data for reservoir characterization and development of the hydrocarbon potentialities of the Upper Cretaceous reservoirs of GPT oil field. 2D seismic data were used to construct the input interpreted horizon grids and fault polygons. The horizon which cut across the wells was used to perform a comprehensive petrophysical analysis. Structural and property modeling was distributed within the constructed 3D grid using different algorithms. The workflow of the 3D geological model comprises mainly the structural and property modeling. The structural model includes fault framework, pillar girding, skeleton girding, horizon modeling and zonation and layering modeling processes. It shows system of different oriented major and minor faults trending in NE–SW direction. The property modeling process was performed to populate the reservoir facies and petrophysical properties (volume of shale (Vsh), fluid saturations (Sw and Sh), total and effective porosities (Φt and Φe), net to gross thickness and permeability) as extracted from the available petrophysical analysis of wells inside the structural model. The model represents a detailed zonation and layering configuration for the Khoman, Abu Roash and Bahariya formations. The 3D geological model helps in the field development and evaluates the hydrocarbon potentialities and optimizes production of the study area. It can be also used to predict reservoir shape and size, lateral continuity and degree of interconnectivity of the reservoir, as well as its internal heterogeneity.

  • Petrography and geochemistry of the Jurassic siliciclastic rocks in the Khashm El-Galala area (NW Gulf of Suez, Egypt): Implication for provenance, tectonic setting and source area paleoweathering
    E.S. Sallam and H.A. Wanas
    Elsevier BV
    Abstract The petrography and geochemistry (major and trace elements) of the Jurassic sandstones from the Khashm El-Galala area (NW Gulf of Suez, Egypt) have been investigated to infer their provenance, tectonic setting, and degree of source rocks paleoweathering. The studied sedimentary succession is made up of two rock units, namely the Rieina Formation (Bajocian) and the Ras El-Abd Formation (Bathonian–Oxfordian). These formations consist mainly of sandstones, siltstones and claystones, with local interbeds of limestones. Petrographic, modal, and major elemental analyses demonstrate that the studied sandstones are texturally-matured quartz-arenites. The sediments were primarily derived from plutonic felsic igneous (granitic) rocks and recycled older quartzose sedimentary rocks, with a rare contribution from a metamorphic source. The detrital modes of sandstones suggest cratonic provenance. As indicated by Chemical Index of Alteration and Chemical Index of Weathering (averages values are 76.73 and 79.45, respectively), the source area of the studied sandstones was affected by a relatively high degree of chemical weathering and alteration under warm humid conditions. The trace element concentrations and their ratios (La/Th, Cr/Th, Th/Sc, Cr/V, and Y/Ni) suggest the predominant felsic character of source lithologies. Regarding the regional tectonic setting, discrimination diagrams based on major and trace elements indicate that the studied sandstones were deposited in a passive continental margin. In terms of palaeogeography, it can be suggested that the studied Jurassic sandstones were deposited on the margin of one of the rift basins existed in the northwestern part of the Arabo-Nubian Shield.

  • Microbially-induced fluvial tufa in Gunna hills, Farafra Oasis, Egypt: Facies analysis and stable isotopes
    H.A. Wanas and I. Armenteros
    Elsevier BV
    Abstract This work addresses the characteristic sedimentary facies and stable isotopic (δ13C and δ18O) signature of the tufa unit that occurs in the uppermost part of the stratigraphic succession at North and South Gunna hills in the Farafra Depression (Western Desert, Egypt). This has been done to reconstruct the depositional setting and genesis of the tufa unit. The tufa unit occurs as chaotic dark fallen blocks and pile-like carbonate mound covering the slope of a marine Paleocene-Eocene substrate. In outcrop and at close-up view, the tufa unit displays three main lithofacies: laminated, massive and granular tufa, which can be interpreted as deposited in a fluvial setting. The microfacies analysis reveals the dominance of a variety of micro-textures including: a) crystalline laminated texture showing different shapes (bacterial-shrubs, crystal shrubs, and recrystallized robust palisades of leaf-like crystals), b) clotted-peloidal texture and c) clotted-oncoidal texture, all of them reflecting an influence of biotic processes (likely cyanobacterial activity) during tufa deposition. The moderate covariance (r = 0.53) between δ18O and δ13C suggests some evaporation effect during the tufa precipitation. Low δ13C values (−11.27‰ to −7.64‰ V-PDB) values indicate that soil CO2 is principally derived from C3 plants, pointing to flowing waters with low residence time. The recorded low δ18O values (−10.82‰ to −8.50‰ V-PDB) are also consistent with carbonates precipitating from meteoric waters related with pluvial episodes impoverished in 18O by continental effects. The pluvial period from which the tufa was formed could be related to air masses that crossed from the Atlantic-Mediterranean Sea during interglacial time period, bringing rain to the Sahara at least as far back as 450 000 yr (Late Pleistocene) before present.

  • Middle–Late Jurassic sedimentation and sea-level changes on the northeast African margin: A case study in the Khashm El-Galala area, NE Egypt
    Dmitry A. Ruban, Emad S. Sallam, and Hamdalla A. Wanas
    Elsevier BV
    Abstract The northeast African margin looks like a natural laboratory for studying mid-Jurassic sedimentation and sea-level changes on the southern periphery of the Tethyan oceans. A new, detailed investigation of two representative sections of the Bajocian–Oxfordian (Middle–Late Jurassic) strata has been undertaken in the Khashm El-Galala area in the Gulf of Suez region of Egypt. Facies and sequence stratigraphic architecture have been examined. 12 microfacies have been identified and grouped into 4 facies associations. The latter permit to establish fluvial, peritidal flat, restricted lagoonal/subtidal, and barrier shoal depositional environments. The fluvial, chiefly siliciclastic sedimentation took place in the Bajocian, and the marine, chiefly carbonate sedimentation took place in the Bathonian–Oxfordian. The stacking patterns of the recognized facies associations permit to classify the Bajocian–Oxfordian stratigraphical succession into the Bajocian lowstand systems tract, the Bathonian–early Callovian transgressive systems tract, and the late Callovian–Oxfordian highstand systems tract. This helps us to reconstruct the relative sea-level changes throughout the Bajocian–Oxfordian, in which the Bajocian lowstand was followed by the transgression that peaked in the early Callovian. Then, the sea level stabilized and started to fall gradually. This cycle corresponds well to the global long-term eustatic changes. If so, the eustatic control on the regional shoreline shifts was more important than the factors of local tectonic activity and sediment supply. Generally, the results of this study prove the importance of the northeast African margin for further justification of the Jurassic eustatic curve.

  • Calcareous Nannofossil Biostratigraphy of the Paleocene-Lower Eocene Successions in the Farafra Oasis, Western Desert, Egypt
    A.M. Abu Shama, H.A. Wanas, and S.A. El-Nahrawy
    Elsevier BV
    Abstract This work deals with a high-resolution analysis of calcareous nannofossil in four exposed Paleocene-Lower Eocene successions in the Farafra Oasis, Western Desert, Egypt in order to detect the different types of stage boundaries and hiatuses. The studied four sections were collected from five localities (Gebel North Gunna, Gebel South Gunna, Ain Ramla, El-Quss Abu Said and Bir Karawin). In the study area, the Paleocene-Lower Eocene succession is made up of four formations, namely Dakhla (at base), Tarawan, Esna and Farafra (at top) that unconformably overlie the Maastrichtian Khoman Formation. The oldest Paleocene calcareous nannofossil Zone (NP 4) is recorded in the Dakhla Formation. It unconformably overlies the latest Maastrichtian Micula prinsii (CC 26b) subzone that is recognized in the uppermost part of the Khoman Formation at North Gunna section. Although Zone NP 4 is successively overlain by the Paleocene-Lower Eocene calcareous nannofossil zones NP 5, NP 6, NP 7/8, NP 9a, NP 9b, NP 10a. These zones are not sequentially recorded in all the studied sections. The Danian/Selandian boundary is traced in the uppermost part of Zone NP 4 at North Gunna and South Gunna sections. At this boundary, a minor hiatus is observed. This is in consistence with the global drop in relative sea level during the Late Danian. A pronounced hiatus is founded slightly after the base of Selandian to the base of the Thanetian at North Gunna and South Gunna sections. In contrast, in the western part of the studied area at Ain Ramla-ElQuss Abu Said section, a conformable relation is recorded at the Selandian/Thanetian boundary where the uppermost part of Zone NP 4 is directly followed by Zones NP 5, NP 6 and NP 7/8. A hiatus between the Paleocene and the Eocene (Thanetian/Ypresian boundary) is observed in the lower part of the Esna Formation at North Gunna section. The nature of the Paleocene/Eocene boundary is not recognized in Ain Ramla-ElQuss Abu Said and South Gunna sections because they are described as composite sections. However, the Ypresian NP 9b subzone is recorded at the base of South Gunna section. Subzone NP 10a is recorded in all the studied sections, which may a response to a relative sea level rise during the Early Eocene time.


  • Carbonate diagenesis in the Barremian-Aptian Tirgan Formation (Kopet-Dagh Basin, NE Iran): Petrographic, geochemical and reservoir quality constraints
    M. Javanbakht, H.A. Wanas, A. Jafarian, N. Shahsavan, and M. Sahraeyan
    Elsevier BV
    Abstract This study aims to establish the diagenetic evolution of carbonate rocks of the Barremian-Aptian Tirgan Formation (Kopet-Dagh Basin, NE Iran), with special emphasis in their impact on reservoir quality to be used as analog for their equivalent carbonate reservoirs. To achieve this target, basic petrography complemented by elemental and stable isotopic (δ 18 O and δ 13 C) analyses of the studied carbonate rocks was used. In addition, the visible porosity was detected. The recognized carbonate diagenetic processes include micritization, cementation, dolomitization, compaction, dissolution, stylolitization, fracturing, silicification and neomorphism. These diagenetic processes took place in four diagenetic environments: marine-phreatic, meteoric-phreatic, meteoric-vadose and burial. Early dolomitization of lime muds, micritization of skeletal allochems and cementation by isopachous equant calcite represent marine-phreatic diagenesis. The meteoric-phreatic diagenesis was accompanied with the development of granular non-ferroan calcite cement, neomorphosed carbonate matrix and recrystallized bioclasts. The meteoric-vadose diagenesis led to prevalence of dissolution process and sparry calcite infilling the fractures. Late dolomitization, ferroan blocky and poikilotopic calcite cement, stylolitization and silicification processes were developed during burial diagenesis. An integration of the petrographic study with the geochemical analysis confirms that the studied carbonate rocks were originally composed of aragonite, which was eventually recrystallized to calcite and replaced by dolomite during diagenesis. In terms of reservoir quality, the recognized diagenetic alterations and visible porosities show that the diagenetic processes have a direct effect on modification of both inter- and intra-granular/crystalline porosity. In this manner, it is found that the calcite cementation, micritization and compaction decline the pore spaces, whereas the dolomitization, dissolution, formation of moldic pores and fracturing increase the pore volumes. Consequently, prevalence of dolomitization, dissolution, occurrence of moldic pores and fracturing in the Tirgan carbonate rocks gives the Tirgan Formation and its equivalent rocks a good opportunity to be an excellent reservoirs.

  • Facies analysis, diagenesis and sequence stratigraphy of the carbonate-evaporite succession of the Upper Jurassic Surmeh Formation: Impacts on reservoir quality (Salman Oil Field, Persian Gulf, Iran)
    Maryam Beigi, Arman Jafarian, Mohammad Javanbakht, H.A. Wanas, Frank Mattern, and Amin Tabatabaei
    Elsevier BV
    This study aims to determine the depositional facies, diagenetic processes and sequence stratigraphic elements of the subsurface carbonate-evaporite succession of the Upper Jurassic (Kimmeridgian-Tithonian) Surmeh Formation of the Salman Oil Field (the Persian Gulf, Iran), in an attempt to explore their impacts on reservoir quality. The Surmeh Formation consists mainly of carbonate rocks, intercalated with evaporite layers. Petrographically, the Surmeh Formation consists of nine microfacies (MF1-MF9). These microfacies are grouped into three facies associations related to three depositional environments (peritidal flat, lagoon and high-energy shoal) sited on the inner part of a homoclinal carbonate ramp. The recorded diagenetic processes include dolomitization, anhydritization, compaction, micritization, neomorphism, dissolution and cementation. Vertical stacking patterns of the studied facies reveal the presence of three third-order depositional sequences, each of which consists of transgressive systems tract (TST) and highstand systems tract (HST). The TSTs comprise intertidal and lagoon facies whereas the HSTs include supratidal and shoal facies. In terms of their impacts on reservoir quality, the shoal facies represent the best reservoir quality, whereas the peritidal and lagoonal facies exhibit moderate to lowest reservoir quality. Also, poikilotopic anhydrite cement played the most significant role in declining the reservoir quality, whereas the widespread dissolution of labile grains and formation of moldic and vuggy pores contributed in enhancing the reservoir quality. In addition, the HSTs have a better reservoir quality than the TSTs. This study represents an approach to use the depositional facies, diagenetic alterations and sequence stratigraphic framework of carbonate –evaporite succession for a more successful reservoir characterization.

  • Abiotically-formed, primary dolomite in the mid-Eocene lacustrine succession at Gebel El-Goza El-Hamra, NE Egypt: An approach to the role of smectitic clays
    H.A. Wanas and E. Sallam
    Elsevier BV
    Abstract This study discusses the role of smectitic clays in the formation of an abiotic (physio-chemical) primary dolomite within an evaporative alkaline-saline marginal lake system, in the absence of carbonate precursor and microbes. The present work has been achieved in terms of textural, mineralogical, and geochemical characteristics of dolostones in the Mid-Eocene (Bartonian) lacustrine succession cropping out at Gebel El-Goza El-Hamra (Shabrawet area, NE Egypt). This lacustrine succession is 15–16 m thick, and made up of alternating horizontal beds of dolostone, marlstone and mudrock that show some pedogenic and subaerial exposure features. The dolostones are composed mainly of dolomite (60–90%), smectite (20–30%) and quartz grains (5–10%). The dolomite comprises fine-crystalline rhombs to micro-spherical crystals with no obvious relics of microbial activity and/or carbonate precursor. It is, ordered, nearly stoichiometric (with 46–50% mole of MgCO 3 ) and has δ 18 O and δ 13 C values ranging from + 0.44 to + 2.96 VPDB ‰, and 0.93 to − 8.95 VPDB ‰, respectively. The smectite occurs as thin mats that are commonly intergrown and associated with dolomite. Mineralogical, textural and stable isotopic results of the dolomite indicated that the dolomite was formed as an abiotic primary precipitate in alkaline saline lacustrine systems. In this respect, the gel-like highly viscous smectitic medium plus progressive CO 2 degassing, elevated evaporation, low sedimentation rate, low sulphates level and alkaline soil solution lowered the kinetic barriers of dolomite precipitation from solution and promoted the incorporation of Mg 2 + in the structure of dolomite. Consequently, the presence of smectitic clays in evaporative saline lakes is significant for dolomite formation because they can generate a gel-like highly viscous medium and provide Mg 2 + that can facilitate the physcio-chemical precipitation of primary dolomite from solution at ambient temperatures. However, more work is needed to better characterize the role of clays during dolomite formation in alkaline lacustrine environments at ambient temperatures.