PREDICTION OF DIAGENESIS AND RESERVOIR QUALITY USING WIRELINE LOGS: EVIDENCE FROM THE UPPER TRIASSIC (RAETHIAN) FLUVIAL RESERVOIR TAGS - TOUAL FIELD, GASSI TOUIL AREA, SE ALGERIA (original) (raw)
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The Open Geology Journal, 2009
Well logs are essential in the study of geological formations, in terms of taking into account the nature and the structure of the formations, as well as the sedimentary processes. Qualitative and quantitative interpretations of well logs respond to a sedimentologic need as well as the establishment of lithological columns, according to the response to logging tools. In this study, electrofacies have been defined by manual well-log analysis of ten surveys of Triassic formations in the Hassi R'Mel area of Algeria. The data thus obtained were then matched with sedimentary facies defined by core analysis. The results obtained during the facies analysis made it possible to define ten electrofacies (sands, shale, dolomite, and evaporite, as well as the presence of andesite and clay). The model obtained by the Petrolog software was also developed and tested on other wells. A semi-automatic data processing was then carried out on seven other wells. Our aim is to highlight the added value of this integrated regional-scale to reservoir-scale approach in identifying nearfield exploration potential and additional recovery opportunities in producing reservoirs. Based on this aim, we emphasise the following points using our facies modelling: (1) improved definition of deposition within and between reservoirs, (2) development of regionally sedimentological models for reservoir intervals (the Hassi R'Mel Formations), and (3) recognition of paleosols from well log analysis and controls on reservoir architecture and their links to the Triassic Province of Algeria.
Marine and Petroleum Geology, 2002
The Triassic TAGI (Trias Argilo-Greseux Inferieur) fluvial sandstones are the main oil reservoirs in the Berkine Basin, Algeria. None theless, their provenance and diagenesis, and their impact on reservoir quality, are virtually unknown. Samples from the Ourhoud field, representing the Lower, Middle and Upper TAGI subunits, were studied using a combination of petrographic, mineralogical and geochemical techniques. The Lower TAGI sandstones have an average framework composition of Q98.3Fo.6Rl.l and 95% of the quartz grains are mono crystalline. By contrast, the Middle-Upper TAGl sandstones have an average framework composition of QSSJF98RI9 and 79.7% of the quartz grains are monocrystalline. The Lower TAGI quartz arenites derived from Paleozoic siliciclastic rocks, whereas the Middle-Upper TAGI subarkoses originated mainly from metamorphic terrains. This change in provenance is a potential criterion for correlation within the TAG!. Also, this change has contributed to the significantly different diagenetic paths followed by the Lower TAG! quartz arenites and the Middle Upper TAGI subarkoses. Grain-coating illitic clays are abundant in the Lower T AGl, where they exert a critical control on reservoir quality. These clays are interpreted as pedogenic and/or infiltrated in origin and to have had, in part, smectitic precursors. Shallow burial Fe-dolomite cementation was favored in the downthrown block of the field-bounding fault, where it contributed to the poor reservoir quality. Magnesite-siderite cements are multiphase. The earliest generation is composed of Fe-rich magnesite that precipitated during shallow burial from hypersaline fluids with high Mg/Ca ratios, probably refluxed residual brines associated with the Liassic evaporites. Later magnesite-siderite generations precipitated during deeper burial from waters with progressively higher FelMg ratios. Authigenic vermicular kaolin largely consists of dickite that replaced previously formed kaolinite. Dickitization was followed by late-stage illitization related to the dissolution of detrital and authigenic K-feldspar. Quartz, the most abundant cement, was mainly sourced by the pressure-or clay-induced dissolution of detrital quartz and is a critical factor controlling the reservoir quality. Overall, quartz cement is more abundant in the Lower TAGI than in the Middle Upper TAGI, and this increase correlates with a decrease in average porosity. Within the Lower TAGI, quartz cement abundance is stratigraphically very variable, which is in part related to facies controlled variations in grain-coating clay, resulting in major vertical variations in reservoir quality. Anhydrite and barite cements postdate quartz overgrowth. The sulfate necessary for their formation was likely sourced by deep subsurface dissolution of Late Triassic-Liassic evaporites.
The Triassic TAGI (Trias Argilo-Greséux Inférieur) fuvial sandstones are the main oil reservoirs in the Berkine Basin, Algeria. Nonetheless , their provenance and diagenesis, and their impact on reservoir quality, are virtually unknown. Samples from the Ourhoud Feld, representing the Lower, Middle and Upper TAGI subunits, were studied using a combination of petrographic, mineralogical and geochemical techniques. The Lower TAGI sandstones have an average framework composition of Q98.3 F0.6 R1.1 and 95% of the quartz grains are mono-crystalline. By contrast, the Middle-Upper TAGI sandstones have an average framework composition of Q88.3 F9.8 R1.9 and 79.7% of the quartz grains are monocrystalline. The Lower TAGI quartz arenites derived from Paleozoic siliciclastic rocks, whereas the Middle-Upper TAGI subarkoses originated mainly from metamorphic terrains. This change in provenance is a potential criterion for correlation within the TAGI. Also, this change has contributed to the significantly different diagenetic paths followed by the Lower TAGI quartz arenites and the Middle± Upper TAGI subarkoses. Grain-coating illitic clays are abundant in the Lower TAGI, where they exert a critical control on reservoir quality. These clays are interpreted as pedogenic and/or infiltrated in origin and to have had, in part, smectitic precursors. Shallow burial Fe-dolomite cementation was favored in the downthrown block of the feld-bounding fault, where it contributed to the poor reservoir quality. Magnesite-siderite cements are multiphase. The earliest generation is composed of Fe-rich magnesite that precipitated during shallow burial from hypersaline fuids with high Mg/Ca ratios, probably refuxed residual brines associated with the Liassic evaporites. Later magnesite±siderite generations precipitated during deeper burial from waters with progressively higher Fe/Mg ratios. Authigenic vermicular kaolin largely consists of dickite that replaced previously formed kaolinite. Dickitization was followed by late-stage illitization related to the dissolution of detrital and authigenic K-feldspar. Quartz, the most abundant cement, was mainly sourced by the pressure-or clay-induced dissolution of detrital quartz and is a critical factor controlling the reservoir quality. Overall, quartz cement is more abundant in the Lower TAGI than in the Middle-Upper TAGI, and this increase correlates with a decrease in average porosity. Within the Lower TAGI, quartz cement abundance is stratigraphically very variable, which is in part related to facies controlled variations in grain-coating clay, resulting in major vertical variations in reservoir quality. Anhydrite and barite cements postdate quartz overgrowth. The sulfate necessary for their formation was likely sourced by deep subsurface dissolution of Late Triassic-Liassic evaporites.
Marine and Petroleum Geology, 2021
The Triassic stratigraphy of the UK contains many major reservoir rock units, present in all major offshore and onshore basins, historically resource rich in oil, gas and water. The Ormskirk Sandstone Formation (Sherwood Sandstone Group) and Tarporley Siltstone Formation (Mercia Mudstone Group) represent the main reservoirs found in in one of the UK's earliest producing oilfields at an unusually shallow depth of 30 to 90 m. In this study, environments of deposition present, maximum burial depth, and reservoir quality are evaluated from well Formby-7 using modern analytical techniques. Wireline data and core analysis data were made available by Aurora Energy Resources for the purposes of this study. Formby-7 was continuously cored so that the whole section was logged for sedimentary structures and grain size. Optical analysis of thin sections was conducted, along with SEM-EDS, using thin sections from core plugs. The Ormskirk Sandstone Formation was deposited in a proximal setting by a braided, dryland river with aeolian influence; the Tarporley Siltstone Formation was deposited in a more distal setting on the margins of a playa environment. The study found that the reservoir quality is excellent in the deeper Ormskirk sediments, but relatively poor in the overlying Tarporley sediments. Good reservoir quality present in the Ormskirk Sandstone Formation is linked to early depositional textures, grain size (medium sand) and general lack of pore-filling cements. In the Tarporley, reservoir quality is poor due to the grain size (very fine sand) and the variable presence of pore-filling gypsum associated with playa deposits. Minor feldspar diagenesis (both dissolution and precipitation) occurred in both the Sherwood and Mercia sediments. The small degree of mechanical compaction and lack of any signs of mesodiagenesis suggest that the clastic sediments in the Formby-7 well have not been buried deeper than about 1,000 m. The findings reported here can be used to iii help the understanding of UK Triassic sedimentology and reservoir quality for oil and gas, geothermal energy, CCS (carbon capture storage) and water supply.
Tikrit Journal of Pure Science
Unit A of Kurra Chine Formation has been studied in the well Shaikan - 4 (SH-4) at Shaikan Oilfield in Northern Iraqi Kurdistan Region. The available conventional wireline log data and the existed core test values have been used to characterize the reservoir properties of the studied unit and to determine the flow efficiency of the reservoired fluids. The dolomite and anhydrite dominated lithology of the studied unit contains low percentages of shale except the upper most part of the unit in which shale content exceeds 30%. The porosity is less than 5% in most parts of the unit and secondary porosity comprises less than 4% of the total porosity in some horizons. The shale content consists primly of Illite and Chlorite and distributes in a dispersed pattern. Hydrocarbons are exist almost along the studied unit in saturations exceeding 70% at the middle and lower part of the unit. No effective permeable intervals observed at the upper part of the unit, whereas permeable zones of great...
Marine and Petroleum Geology, 2004
The Triassic Sherwood Sandstone in the Corrib Field, Slyne Basin west of Ireland on the European continental margin, is a dry gas reservoir with a Mercia mudstone top-seal. Petrographic analysis combined with X-ray diffraction, stable isotope, fluid inclusion and core analysis have been used to assess: timing of growth and origin of mineral cements, whether sandstone diagenesis involved mass flux, the controls on reservoir quality and how reservoir quality is likely to vary in more deeply buried sections. Depositional and early diagenetic characteristics of the Sherwood in Corrib are typical of a semi-arid fluvial environment, containing groundwater of meteoric origin. Early diagenesis included the development of copious dolomite cement, in the form of dolocrete, as well as the formation of abundant clay while less volumetrically important, grain-coating haematite and K-feldspar cement also grew. Burial diagenesis witnessed the initial growth of minor chlorite and albite. Quartz overgrowths and ankerite followed and are the most important burial cements growing over a temperature interval between 100 and 1165 8C. Albite commenced growth at about 90 8C, quartz cement at 100 8C and ankerite at 110 8C. These cements reached the zenith of their development at 105-110 8C for albite, 125-130 8C for quartz and 135-145 8C for ankerite. Siderite and anhydrite are relatively minor, late-stage cements. The formation water has been consistently highly saline during burial and, in terms of mineral cement-derived oxygen stable isotope values, is likely to be a diagenetically evolved version of the initial depositional water suggesting longterm stagnation of the pore-fluids. The diagenetic reactions that formed burial cements all seem to be essentially isochemical including the ankerite that has carbon isotope characteristics of the cannibalisation of dolocrete. Reservoir quality is mainly controlled by early diagenetic dolomite and clay although grain size is also important because only sandstones with .200 mm grain size have. 50 md permeability. Both shallower and deeper sections than Corrib may have similar porosity and permeability since temperature-dependent diagenetic controls on reservoir quality, e.g. quartz and illite cement, are peripheral.
Evaluation of the Quantitative Criteria of Triassic Carbonate Rocks Reservoirs
Journal of Geology & Geophysics, 2023
the technology of identifying reservoirs according to quantitative criteria that determine the "reservoir-non-reservoir" boundary at the static level is necessary to clarify the interpretation [9-12]. In order to determine the boundary values, correlation dependencies were constructed based on the parameters obtained from special laboratory core tests. Lithological and petrographic characteristics of Triassic carbonate reservoirs Lower Triassic deposits (T1): The carbonate-terrigenous sequence of the Lower Triassic (T1), which lies at the base of the oil and gas complex, is composed of rhythmically interbedded siltstones, sandstones, mudstones, and limestones. Due to numerous ammonite finds in the carbonate-terrigenous sequence, the age of the carbonate-terrigenous sequence has been determined to be late Olenekian [13-15]. The reservoirs (porous-fractured) are
Diagenesis and formation water chemistry of Triassic reservoir sandstones from southern Tunisia
Sedimentology, 1994
The fluvial Triassic reservoir snbarkoses and arkoses (2409.5-2519.45 m) of the El Borma oilfield, southern Tunisia, were subjected to cementation by haematite, anatase, infiltrated clays, kaolinite and K-feldspar at shallow burial depths from meteoric waters. Subsequently, basinal brines controlled the diagenetic evolution of the sandstones and resulted initially in the precipitation of quartz overgrowths, magnesian siderite, minor ferroan magnesite and anhydrite. The enrichment of siderite in "C isotope (613C,,B=-14.5 to-9%0) results from derivation of carbon from the thermal decarboxylation of organic matter. During further burial, the precipitation of dickite and pervasive transformation of kaolinite into dickite occurred, followed by the formation of microcrystalline K-feldspar and quartz, chlorite and illite, prior to the emplacement of oil. Present day formation waters are Na-Ca-C1 brines evolved by the evaporation of seawater and water/mineral interaction and are in equilibrium with the deep burial (13.1 km) minerals. These waters are suggested to be derived from the underlying Silurian and Devonian dolomitic mudstones.
Journal of African Earth Sciences, 2019
Understanding the variability in outcrop reservoir properties may give a guide for subsurface reservoir quality prediction, more significantly for the more stable and resistant reservoir rocks as sandstones, compared to the carbonates. This study was planned to investigate the outcrop lithofacies and reservoir properties of different sandstone lithofacies of the Late Triassic Minjur Formation outcrop, and attempted to develop a relationship between these aspects in outcrop and subsurface settings. Based on field and petrographic analyses, sandstone lithofacies of Minjur Formation were categorized into five types upon their textures. These lithofacies were intensively investigated for porosity and permeability. Variography analyses were applied on composite outcrop lithofacies, and also on porosity and permeability data. A good relationship was observed between porosity and permeability, which coincides with the univariate statistics of each and confirmed by variography analysis. Combination of outcrop and subsurface reservoir properties showed an acceptable correlation between outcrop reservoir properties and data from central Saudi Arabia and Rub' Al-Khali Basin in southern and southeastern Saudi Arabia. This
2019
The Upper Ordovician glaciogenic deposits are thought to have an important quantity of hydrocarbon across North Africa. Insight is provided about the IV-3 reservoir unit in the In-Adaoui-Ohanet field in the Illizi basin of south-east Algeria. The aim is to: 1) describe the lithofacies; 2) interpret the depositional environment; 3) describe the petrographic characteristics; 4) investigate the petrophysical properties; and 5) perform a biostratigraphic analysis of the unit IV-3 reservoir (Upper Ordovician) in the In-Adaoui-Ohanet field based on the core description and samples collected from the well IA-115. Lithofacies described in the study area are MT1, MT2, MT3, MT6, and MT9. Subglacial tillite is the depositional environment associated with lithofacies MT3, MT6, and MT9. These lithofacies are thought to be deposited medial to a distal fan, whereas lithofacies MT1 and MT2 are thought to be deposited in high-energy flows. Acritarch and Chitinozoan species are the most common biozones described in the study reservoir and they are thought to be affiliated with an Upper Ashgilian stage. Petrographic analysis shows that the study reservoir unit is formed by fine to coarse-grained sandstone. Quartz is considered to be the principal framework mineral (mean, 56.30%). Cementing minerals observed in this reservoir unit are quartz and carbonate. From a compositional point of view, the unit IV-3 reservoir in the In-Adaoui-Ohanet field is predominantly formed by quartz arenites, which are considered to be mature. Additionally, the tectonic setting of these arenites is most likely associated with a passive margin origin. The emphasis throughout this study is on the role of factors such as permeability, carbonate cement, and quartz overgrowth on the reservoir quality of unit IV-3 in the In-Adaoui- Ohanet field. The quality of this reservoir unit is highly influenced by the quartz overgrowth and pores that are plugged by carbonate cement, which dramatically reduces the pore network. An enhanced porosity was observed only in the MT3lithofacies (up to 22.3%). Additionally, from an economic point of view, the study reservoir unit is classified as a tight gas-bearing reservoir.