Shale Interbeds Research Articles

Geological setting of the Moorowie Formation, lower Cambrian Hawker Group, Mt Chambers Gorge, eastern Flinders Ranges, South Australia

Geological mapping in 1970 of lower Cambrian outcrop in the eastern Flinders Ranges of South Australia included the description and naming of the Moorowie Formation, representing the uppermost Hawker Group. The mapping is supported by 885 m of measured sections. An early Cambrian regressive-marine shelf-margin succession is described, from the massive Wilkawillina Limestone (base), the grey laminated limestones, syndepositional slump-induced intraformational folds and breccias, collapse talus, and graded sediment gravity flow deposits of the Mernmerna Formation, terrace-edge attrition megabreccias and reefs of the Moorowie Formation, passing up to the red beds of the Billy Creek Formation (top). Rapid changes in sedimentary facies are attributed to basement block movements and diapiric influence on sedimentation with abrupt vertical relief and paleoslope indicated by syndepositional slumping and platform margin collapse. Tuffs in the Mernmerna Formation record contemporaneous volcanism. Massive archaeocyathan limestones, ooid grainstones, peloid limestones, reef-sourced megabreccias and red shales define five members in the overlying Moorowie Formation, signalling shallow-marine regressive conditions and the development of a biologically diverse carbonate platform seaward of evaporitic lagoons and supratidal sabkhas. The megabreccias of the Moorowie Formation formed as thin semi-autochthonous debris aprons or shallow tidal-channel infills resulting from gradual and persistent wave attrition and repeated collapse of a carbonate terrace that was vigorously reworked by tidal currents. Shale interbeds within the Moorowie Formation represent lightly channelised shallow-marine ramp deposits, with adjacent mud flats, as easterly equivalents of the Oraparinna Shale, the earliest of which formed the substrate to the attrition megabreccias. Emergent evaporite diapirs near Mt John and Mt Frome are the probable sources of coarse siliciclastics within the carbonates. Some of the siliciclastics were likely transported onto the carbonate platform by sandstorms or migrating dunes. Late in the Cambro-Ordovician Delamerian Orogeny, earlier salt diapirs at depth were compressed and reactivated as highly mobile evaporite-rubble breccias and intruded as small plugs and dykes into fissures in a lithified and folded cover.The intrusive breccias include metasediment and metabasic xenoclasts attributable to the Callanna Group, while diapir-related faults also host minor copper, lead and barite mineralisation. Documentation of this unique record contributes to wider investigations of the Ediacaran-to-early-Cambrian succession of the Flinders Ranges sector of the Arrowie Basin, adding to its global heritage values, effective management and appreciation by the wider community.

Reservoir Rock Genetic Types Using Log Curve Shapes: Abu- Madi Formation, Offshore Nile Delta - Baltim Gas Field, Egypt

Recognizing of detail rock genetic types in Abu-Madi Formation using log curve shapes techniques is the main object of this research work. Abu-Madi Formation has been drilled in The Baltim gas field, offshore Nile Delta, and is deposited in a fluvio-marine environment which exhibits complex lithofacies. It is composed mainly of sandstone intercalated with siltstone and shale interbeds. The Abu Madi Formation is considered as the main gas producing reservoir rock in the Baltim gas field. Facies analysis and reconstruction of facies patterns for Abu-Madi Formation were performed using Log curve shapes interpretation. The constructed vertical profiles of three borehole logs data against lithologic intervals of the Abu-Madi Formation define the depositional history and the prevailing different rock genetic types. Two main rock genetic types were recognized indicating deltaic sedimentation. They are: 1. Distributary channel and 2. Stream Mouth bar deposits. They are exhibited either by a single unit of distributary channel or a complex superimposed on a stream mouth bar unit. Generally, they are representing lower deltaic plains and deltaic fringes sediments respectively. These rock genetic types are considered as the main gas producing zones in the Baltim field.

Estruturas locais condicionantes das características geométricas e hidráulicas do sistema Aquífero Guarani (SAG): alto estrutural da fazenda Santa Helena, município de Boa Esperança do Sul (SP)

Denominou-se Alto Estrutural da Fazenda Santa Helena (AEFSH) à subestrutura identificada em subsuperfície por perfurações de poços para captação de água subterrânea no Sistema Aquífero Guarani (SAG), alojada no Alto do Jacaré-Guaçu na região das bacias hidrográficas dos rios Jacaré-Guaçu e Jacaré-Pepira, Município de Boa Esperança do Sul (SP). Ainda com extensão não delimitada, o AEFSH representa estrutura de pequeno porte que condiciona as características geométricas e hidráulicas do SAG. Dados de poços profundos e de perfilagem geofísica mostraram que o SAG está representado, na área, por arenitos finos a muito finos, argilosos, intercalados por frequentes camadas de argilito. Essa sucessão, pertencente à porção basal da Formação Piramboia, assenta-se sobre siltitos e argilitos da Formação Corumbataí. A espessura reduzida, da ordem de 80 m, e as características litológicas locais do SAG afetam negativamente a transmissividade do aquífero, resultando em poços com baixa produtividade. O presente trabalho dá conhecimento da existência dessa subestrutura que exerce influência no armazenamento hídrico e nas potencialidades locais do SAG, e chama a atenção para a possibilidade de haver inúmeras outras em contexto geológico similar ou ocultas sob a cobertura basáltica da Formação Serra Geral e sedimentar do Grupo Bauru.

Extreme enrichment of arsenic and rare earth elements in acid mine drainage: Case study of Wiśniówka mining area (south-central Poland)

The Wiśniówka rock strip mining area (south-central Poland) with quartzite quarries, acid water bodies and tailings piles is one of the most unique acid mine drainage (AMD) sites throughout the world. This is due to the occurrence of enormous amounts of pyrite unknown in sedimentary formations worldwide. Of the two mineralization zones, one that is the most abundant in arsenical pyrite occurs in the lowermost Upper Cambrian formation of the Podwiśniówka quarry. The As-rich pyritiferous clastic rocks are exposed as a result of deep quartzite extraction during 2013–2014. In addition, the clayey-silty shale interbeds are enriched in rare earth element (REE) minerals. The mining operation left an acidic lake with a pH of about 2.4–2.6 and increased contents of sulfates, metal(loid)s and REE. The Podwiśniówka pyrite-rich waste material was stacked up in many places of the mining area giving rise to strongly acidic spills that jeopardized the neighboring environment. One of these unexplored tailings piles was a source of extremely sulfate- and metal(loid)-rich pools with unusual enrichments in As (up to 1548 mg L−1) and REE (up to 24.84 mg L−1). These distinctly exceeded those previously reported in the Wiśniówka area. A broad scope of geochemical, mineralogical and petrographic methods was used to document these specific textural and mineralogical properties of pyrite facilitating its rapid oxidation. The pyrite oxidation products reacted with REE-bearing minerals releasing these elements into acid water bodies. Statistical methods were employed to connect the obtained tailings pool hydrogeochemical data with those derived from this and the previous studies of the Podwiśniówka and Wiśniówka Duża acid pit lakes. In contrast to metal(loid) profiles, the characteristic shale-normalized REE concentration patterns turned out to be more suitable for solving different AMD issues including provenance of mine waste material in the tailings pile examined.

Trilobite biostratigraphy of the Cambrian 5 and Drumian stages, Series 3 (Laurentian Delamaran, Topazan, and Marjuman stages, Lincolnian Series) of the lower Emigrant Formation at Clayton Ridge, Esmeralda County, Nevada

AbstractThe Emigrant Formation at Clayton Ridge, Nevada, consists of 420 m of variably interbedded shale, siltstone, and limestone representing an outer shelf environment. It ranges in age from the youngest portion of the Dyeran Stage (Laurentian Waucoban Series; Cambrian Stage 4, Series 2) to Skullrockian Stage (Ibexian Series; Tremadocian Stage, Lower Ordovician). Consequently, it is condensed compared to other localities. For example, the age-equivalent succession in the House Range and the Wendover Range of Utah and Nevada, respectively, is seven times thicker.The 100 m thick lower limestone and siltstone member of the Emigrant Formation at Clayton Ridge ranges in age from theBolbolenellus euryparia/Nephrolenellus multinodusZone (Laurentian Dyeran Stage) to theCedaria brevifronsZone (Laurentian Marjuman Stage; Drumian Stage; this study). The 40 trilobites described herein from two closely spaced sections of the lower member belong to theGlossopleura walcotti/Ptychagnostus praecurrensZone (Laurentian Delamaran Stage; Stage 5),EhmaniellaZone (Laurentian Topazan Stage; Stage 5), andCedaria selwynitoC.brevifronszones (Laurentian Marjuman Stage; Drumian Stage) zones. The lower Emigrant Formation is <10% as thick as age-equivalent age strata elsewhere in Nevada, California, and Utah. This condensed nature of the lower Emigrant Formation began with the flooding event at the beginning of theOryctocephalus indicusbiochron and the subsequent build-ups of the thick carbonate platforms to the south and northeast.New species arePagetia aspinosa,P.claytonensis, andSyspacephalus mccollumorum.

EVALUATION OF HYDROCARBON POTENTIALS OF CAMPANIAN SOURCE ROCKS OF NKPORO SHALE (MGBOM SECTION), AFIKPO BASIN, SOUTH EASTERN NIGERIA

This work evaluated the hydrocarbon potential of Campanian source rocks of Nkporo Shale (Mgbom section) using parameters like Soluble Organic Matter (SOM), Total Organic Carbon (TOC) and Organic Matter Quality (OM) on samples taken from the section. The Nkporo Shale is dark grey in color and is highly fissile with interbeds of sandy shale, siltstone and mudstone. The investigated section exposed at Mgbom, Ebonyi State consisted of the Nkporo Shale, a formation in the Lower Benue Trough. The rocks are fairly to moderately rich in organic matter and can therefore be considered as potential source rocks. TOC analysis on sample revealed from the Mgbom Section in the range of 0.51w%-1.02wt% which exceeds the minimal amount needed for a potential source rock. The SOM ranges from 67mg/kg – 165mg/kg and the OM ranges from 77.40% – 89.30% indicating that the source rock is fairly rich in hydrocarbon content.

Microfacies analysis and diagenetic fabric of the Lockhart Limestone exposed near Taxila, Margalla Hill Range, Punjab, Pakistan

The microfacies analysis and diagenetic fabric of the Lockhart Limestone are studied in an outcrop section exposed in the Margalla Hill ranges. The Lockhart Limestone is predominantly composed of medium to thick bedded, nodular and occasionally brecciated, highly fossiliferous limestone with thin interbeds of marl and shale. On the basis of detailed petrographic investigations, four microfacies have been identified including bioclastic packstone, wackestone (siliciclastic bioclastic rich sub-microfacies), wackestone-packstone, and mud-wackestone. Based on the microfacies analysis, the Lockhart Limestone is interpreted to have been deposited in the fore-shoal mid-ramp, mid-ramp, and outer ramp depositional environments. The Paleocene age has been assigned to the Lockhart Limestone based on age diagnostic foraminifera, i.e., Miscellanea, Lockhartia, and Ranikothalia. The diagenetic fabric of the Lockhart Limestone is characterized by several diagenetic features such as micritization, neomorphism (aragonite to calcite transformation and development of microspar), compaction, pressure dissolution (microstylolites), and cementation (calcite-filled microfractures). Such diagenetic features are developed in marine, meteoric, and burial diagenetic settings. The Paleocene Lockhart Limestone of Pakistan shows analogous features to that of the Paleocene Zongpu Formation (Member-3) of the Gamba-Tingri Basin of southern Tibet based on the outcrop features, microscopic fabric, and depositional environment.

Diagenetic Features of Jurassic Fort Member Sandstone, Jaisalmer Formation, Western Rajasthan

ABSTRACT Jaisalmer Formation consists of 360m thick succession of medium to coarse grained sandstones with interbeds of shale, claystone and occasional lignite that rest over Lathi Formation, is the basal part of the Jaisalmer basin. The rocks are exposed amidst desert, low mounds and shallow stone quarries. Sandstones were deposited in shallow marine to deltaic environments. The studied sandstones consist of abundant quartz followed by feldspar, mica, chert, rock fragments and heavy minerals. The study mainly deals with identification of various diagenetic features such as compaction, cementation and porosity evolution. During mechanical compaction rearrangement of grains took place and point, long and suture contacts were formed. The sandstones are cemented by iron oxide, silica overgrowth, carbonate and clay. Porosity has developed due to dissolution of iron, carbonate cement and feldspar grains. Dissolution and alteration of feldspar, lithic fragments and pressure solution were the main source of quartz cements. The sandstones show good amount of existing optical porosity with an average of 7.19%. Porosity reduction is mainly due to early stage of mechanical compaction and subsequent pervasive calcite and iron oxide cementation. Further, porosity reduced due to deposition of clay cement.

Geostatistical lithofacies modeling of the upper sandstone member/Zubair formation in south Rumaila oil field, Iraq

Geological facies modeling is a crucial problem for reservoir characterization as it affects the reservoir heterogeneities and fluid flow performance prediction. The main purpose of this research is to adopt a stochastic simulation to construct 3D lithofacies models of the tidal/estuarine depositional environment of the upper sandstone member in south Rumaila oil field, located in Iraq. Based on core measurements, the upper sandstone member has three main lithofacies: sand, shaly sand, and shale. Literature review indicates that the formation is encompassed of mainly sandstone with some inter-bedded shale zones. To reconstruct the 3D lithofacies model, the sequential indicator simulation (SISIM) was adopted to build the categorical image, pixel by pixel, considering the nonparametric condition distribution. Specifically, SISIM depends on the variogram to address and model the variation between any two spatial points from the available data. Therefore, 12 different variograms were constructed given the three lithofacies in four different azimuth directions: 0°, 45°, 90°, and 135°.The resulting lithofacies models in the four selected azimuth directions have shown frequent tidal lithofacies channeling and indicate an approximate matching with the original description of the formation depositional environment of the tidal-dominated and sand-rich environment. The generated lithofacies model in 135° direction has sand channels prevailing towards the southeast shoreline of the reservoir. The created lithofacies model also preserves the reservoir complexity and heterogeneity because it was created using a high-resolution gridding system with approximately two million grids. Additionally, the resulting tidal lithofacies model ensures reservoir heterogeneity as the petrophysical properties are then distributed given each lithofacies with distinct indicator variograms.

Shear fracture direction and mechanical characteristics of the middle Yanchang Formation, southern Ordos Basin, China

Field observations, fractures identified from micro-resistivity logging images from six wells, and seismic anisotropy analysis all show that six sets of vertical shear fractures are developed in the middle Yanchang Formation in the southern Ordos Basin, comprising three orthogonal fracture systems. Of these, System I fracture sets predominate, trending approximately 75° and 150°, the result of NWW-SEE directed maximum compressive stress. System II fracture sets trend approximately 60° and 120°, the result of E-W directed maximum compressive stress, while System III fracture sets trend approximately 30° and 90°, the result of NEE-SWW directed maximum compressive tress. Fractures with a strike of 75° are most common in the middle Yanchang Formation because of rock heterogeneity, while three reservoir sets are present, comprising fluvial medium-to-fine grained blocky sandstones and thin interbeds of sandstone and shale from lacustrine-delta facies.

Rock-Eval pyrolysis and organic petrographic analysis of the Maastrichtian coals and shales at Gombe, Gongola Basin, Northeastern Nigeria

The Gongola Basin forms one of the inland Cretaceous to tertiary sedimentary basins in Nigeria with relatively unknown petroleum system. In this study, the investigated source rock intervals of the Maastrichtian Gombe Formation are located at the Maiganga coal mine, near Gombe, Gongola Basin, Nigeria. The exposed part of the mine consists of about 35-m thick coarsening upward section with the basal part made up of coal and shale interbeds while the upper part consists of siltstone and sandstone and probably deposited in fluvio-deltaic environment. The coal and interbedded shale appear most prospective source rock facies in the formation and were evaluated with respect to their hydrocarbon source rock potential. The organic geochemical results showed high TOC for the coals (37.71–65.29 wt%) and moderate organic carbon concentration (1.19–4.81 wt%) for the shales. S2 values ranges from 57.96 to 103.21 mgHC/g rock and 0.51–6.22 mgHC/g rock for the coal and shales, respectively. The HI is less than 200 mgHC/gTOC in all the coal and shale samples suggesting Type III kerogen and predominant plant contributions from terrestrial sources. Consequently, gaseous hydrocarbon potential is exhibited in the source beds. The organic petrography shows vitrinite as dominant maceral followed by inertinites and liptinites with inorganic minerals like pyrite and kaolinite. The Tmax is less than 435 °C in all the samples indicating pre-oil window stage; this is corroborated by the Romax value ranging from 0.45 to 0.55 %. Plot of PI against Tmax indicates low level organic matter conversion while the vitrinite reflectance values suggest a sub-bituminous coal. The study suggests that the investigated coal and shale samples constitute good source rock and have potential for gas. The generally low HI in the coals and the associated shales indicate more allochthonous and hydrogen poor organic matters in the source beds. Maceral composition of the coals suggests wet swamp environment and predominance of arborescent vegetation type. At present level, the organic matters are immature to marginally mature deeper level equivalents might have generated gas.

Nubian Sandstone reservoir characteristics: sedimentological and petrophysical evaluation in the Southern Gulf of Suez, Egypt

The Nubian Sandstone is a thick sequence of clastic and thin carbonate sediments in the Jebel El Zeit section of eastern Egypt. The sequence is composed mainly of sandstone with shale and minor carbonate interbeds and was deposited in continental and fluviomarine to marine settings. Petrographically, quartz arenite and quartz wacke are the main facies of Nubian Sandstone. They have different secondary components, cement and matrix types, reflecting their different depositional environments and diagenetic histories. The Nubian Sandstone is one of the most prolific hydrocarbon reservoirs in the Gulf of Suez oil province.The Nubian Sandstone has good reservoir quality with porosity varying from 10% to 29%, and permeability of up to 5000 millidarcies. The quality of the reservoir depends on its proportions of shale, diagenetic history and the depth of burial (compaction). X-ray diffraction and scanning electron microscope analyses indicate that kaolinite is the main clay mineral and is derived from the alteration of potash feldspar. Enhancement of oil recovery from the reservoirs of the Nubian Sandstone can be achieved by alkaline injection to dissolve the kaolinite.

Stratigraphy, petrography, and depositional history of the Ignacio Quartzite and McCracken Sandstone Member of the Elbert Formation, southwestern Colorado, U.S.A.

The Ignacio Quartzite—exposed in the San Juan Mountains of southwestern Colorado—is composed of red and brown arkose and subarkose sandstones and minor interbedded shales. The formation is newly divided here into the Tamarron Member (0–24 m) and the overlying Spud Hill Member (0–21 m). The Spud Hill Member has a greater abundance of sandstones with shale clasts, weakly fissile shale beds, and trace fossils than the Tamarron Member. The McCracken Sandstone Member of the Elbert Formation, which overlies the Ignacio, is chiefly white and off-white quartz-cemented quartzarenites. The McCracken is divided for the first time into the Mill Creek facies (0–12 m) to the south of Coal Bank Pass and the Sultan Creek facies (0–36 m) to the north of the pass. The Sultan Creek facies contains dolostone-sandstone parasequence tidal-flat cycles up to 70 cm thick with a composite thickness of 14 m. Eastward transgression across the western edge of the Transcontinental Arch permitted the accumulation of fluvial deposits of the lower Tamarron Member in the deepest channels incised into the craton. As sea level continued to rise, fluvial channels evolved into estuaries dominated by sandy tidal flats (upper Tamarron Member, Mill Creek facies, and Sultan Creek facies) and mixed sand and mud tidal flats (Spud Hill Member). Sandstone composition and ages of detrital zircons indicate that sand grains were derived from a complex terrain that included granitoid plutonic rocks (∼0.46 to >2.4 Ga), metamorphic rocks, and well-rounded quartz sand from eolian ergs. The area between the present Coal Bank and Molas passes was a boundary between a northern fluvial source with an abundance of superbly rounded quartz grains of eolian erg origin from a southern fluvial source with few such grains, but large amounts of K-feldspar. The Ignacio and McCracken units are, at least in part, coeval and of Late Devonian age as shown by the stratigraphic distribution of rocks resting on the basement, the presence of an Ordovician zircon in the Ignacio, and the presence in the same Ignacio sample of oboloid brachiopods of questionably late Cambrian age with well-dated Late Devonian placoderm fish plates.

Pennsylvanian Stratigraphy of Douglas County, Kansas: Glacioeustatically Modulated Cyclic Deposition on a Remarkably Smooth Shelf

The Middle and Late Pennsylvanian succession of Kansas consists of two types of cyclothems, lithologic successions that consist of several members that repeat in a particular order. Cyclothems are a few meters to a few tens of meters thick. One type of cyclothem, the Kansas cyclothem, or here the limestone-rich cyclothem, consists of interbeds of limestone and shale, where the amounts of limestone are approximately equal to the amount of shale or dominate the succession. This trip will study one such cyclothem in the Oread Limestone at Stop 3 and possibly another cyclothem at the optional Stop 4. Siliciclastic cyclothems are dominated by shale and may contain an incised valley filled partly by fluvial or estuarine sandstone. The Lawrence Shale, which we will see at Stops 2 and 3, contains such features. While many cyclothems are incomplete, both types of cyclothem may contain dark gray to black, fissile, phosphatic core shale beds, commonly a meter or less thick, and an underlying transgressive deposit beneath. Overlying deposits represent regression or progradation of the shoreline: either lime mudstone grading to grainstone or clay-rich marine shale grading to coarse siltstone or fine sandstone. Paleosols and fossils of marine invertebrates are common and indicate that deposition took place in both marine and non-marine conditions. Some marine deposits show a paleosol overprint. The deposits indicate that the area was a shelf during the Late Pennsylvanian where relief was very low, and very laterally extensive deposits formed as sea level rose and fell. The alternation of shale-rich and limestone-rich intervals plus the feet-per-mile dip to the WNW create the characteristic topographic expression of cuestas with gently sloping caps that are underlain by limestone. While glacial deposits are mostly restricted to northern and east-central Douglas County, Pleistocene glaciers influenced the erosional and drainage patterns of the area.

Distribution of chromium, copper, lead and zinc in soil from kimanis, papar, sabah

This paper discusses the distribution of selected heavy metals namely chromium (Cr), copper (Cu), lead (Pb) and zinc (Zn) in soil from Kimanis, Papar, Sabah. Fourteen soil samples were collected from soil originated from sedimentary rock of Crocker Formation and Quaternary deposit. The Crocker Formation consists of thick sandstone unit and inter-bedded sandstone and shale unit with the age of Late Eocene to Early Miocene. The physico-chemical analysis of soil include the pH value, moisture content, organic content and particle size. Soil of Crocker Formation were classified as sandy loam and sandy clay loam, while Quaternary deposit were classified as sand, sandy loam, sandy clay loam and clay with loam. The result of analysis shows the soils were acidic with pH values range from 3.06-5.65. Organic matter content ranges from 0.98%-7.63% and moisture content were 13.8%-60.51%. All heavy metals were analyzed using ICP-OES. The result of analysis indicated that Zn shows the highest value then followed by Cu, Pb and Cr. Soil sample from Crocker Formation show significantly high Zn and Cu content, where SC6 and SC7 have Zn value of 274.36 μg/g and 127.82 μg/g respectively, whereas 127.98 μg/g of Cu. The distribution of heavy metals in soil samples are controlled by the mobility and leaching process during chemical weathering and also adsorption by clay particles and organic matter as well as the human activities within the area.

Characteristics and formation mode of salt-bearing series in typical rift valley basin, Eastern China

The Shulu Sag is a typical rift valley basin in Eastern China, where the formation mechanism of Cenozoic salt-bearing series has been poorly understood. In this paper, petrologic analysis, X-ray powder Diffraction (XRD) analysis and the analysis of halite ion concentrations of the first member of the Shahejie Formation from two drilling cores were conducted to interpret the formation mechanism of these salt-bearing series in Shulu Sag. The results indicated that the salt-bearing series is mainly composed of calcilutite or mudstone at top and bottom, and anhydrite-bearing halite and thin interbeds of salt-bearing calcilutite and dark grey shale in the middle part. These thin interbeds with porphyritic or petalshaped glauberite crystals or some thinner dark grey shale interbeds separated halites into several members with the average thickness of only 9~12 cm in the two drilling holes. This typical rhythmic pattern due to frequent alternation of concentration was evidenced by the variation of chemical composition and hydrogen isotopes of halite fluid inclusions. The presence of large number of primary fluid inclusions within chevron crystals and vertically oriented bottom-growth crystals showed that the halite were precipitated in shallow water (<60 cm). These features are direct evidence for this frequent alternation of dissolution and concentration of brines and terrigenous detrital-chemical shallow-water sedimentary model of these small rift-valley basins in Eastern China.

Influences of sandstone superimposed structure and architecture on waterflooding mechanisms: A case study of Kumkol Oilfield in South Turgay Basin, Kazakhstan

Abstract Taking the Kumkol oilfield of high water cut in the South Turgay Basin, Kazakstan as an example, this article built the architecture models of meandering river sandstones, braided river sandstones and delta sandstones, and analyzed the influence of the superimposed structure characteristics between different types of sandstones and internal architecture features on warterflooding mechanisms and effects. The meandering river sandstones are mainly characterized by lateral accretion shale beddings inside, with simple overlay-relationship in sand bodies. In meandering river sandstones, injected water almost sweeps through the bottom of sand bodies and the bottom part of the sandstones is previously waterflooded, and the thickness ratio of strong and moderate waterflooded zone is about 51.8%. Braided river sandstones are characterized by nearly horizontal interlayers inside, with low heterogeneity and uniform waterflooding sweep vertically, and the thickness ratio of strong and moderate waterflooded zone is as high as 81.7%. The superimposed structure and architecture of delta sandstone is relatively complicated; different types of sandstones overlay each other frequently and shale interbeds are developed in sandstones. The injected water is obstructed not only by impermeable or low-permeable layers between sand bodies but also by shale interbeds in sandstones, with low sweep range of injected water, and the thickness ratio of strong and moderate waterflooded zone is only 32.6%. The braided river sandstone has low rising velocity of water cut and high no-water recovery degree, and its waterflooding development effect is the best. The waterflood sweep of delta sandstones is poor, with fast rising velocity of water cut and low no-water recovery degree, and its waterflooding development effect is the worst. The waterflooding development effect of meandering river sandstones is moderate among these three types of sandstones.

Sequence stratigraphy of the Eocene turbidite reservoirs in Albacora field, Campos Basin, offshore Brazil

This article describes a 250-m (820-ft)-thick upper Eocene deep-water clastic succession. This succession is divided into two reservoir zones: the lower sandstone zone (LSZ) and the upper sandstone zone, separated by a package of pelitic rocks with variable thickness on the order of tens of meters. The application of sequence-stratigraphic methodology allowed the subdivision of this stratigraphic section into third-order systems tracts. The LSZ is characterized by blocky and fining-upward beds on well logs, and includes interbedded shale layers of as much as 10 m (33 ft) thick. This zone reaches a maximum thickness of 150 m (492 ft) and fills a trough at least 4 km (2 mi) wide, underlain by an erosional surface. The lower part of this zone consists of coarse- to medium-grained sandstones with good vertical pressure communication. We interpret this unit as vertically and laterally amalgamated channel-fill deposits of high-density turbidity flows accumulated during late forced regression. The sandstones in the upper part of this trough are dominantly medium to fine grained and display an overall fining-upward trend. We interpret them as laterally amalgamated channel-fill deposits of lower density turbidity flows, relative to the ones in the lower part of the LSZ, accumulated during lowstand to early transgression. The pelitic rocks that separate the two sandstone zones display variable thickness, from 35 to more than 100 m (115–328 ft), indistinct seismic facies, and no internal markers on well logs, and consist of muddy diamictites with contorted shale rip-up clasts. This section is interpreted as cohesive debris flows and/or mass-transported slumps accumulated during late transgression. The upper sandstone zone displays a weakly defined blocky well-log signature, where the proportion of sand is higher than 80%, and a jagged well-log signature, where the sand proportion is lower than 60%. The high proportions of sand are associated with a channelized geometry that is well delineated on seismic amplitude maps. Several depositional elements are identified within this zone, including leveed channels, crevasse channels, and splays associated with turbidity flows. This package is interpreted as the product of increased terrigenous sediment supply during highstand normal regression.

Geochemical discrimination of the Upper Ordovician Kinnekulle Bentonite in the Billegrav-2 drill core section, Bornholm, Denmark; pp. 264–270

The content of the trace elements Ti, Nb, Zr and Th has been analysed in 34 Upper Ordovician bentonites from the Billegrav-2 drill core, Bornholm, Denmark. The section contains two 80–90 cm thick bentonites, which potentially may represent the Kinnekulle Bentonite, as well as several rather thick but composite bentonite layers with thin terrigenous shale interbeds. Comparison of the four immobile trace elements with data from the Kinnekulle Bentonite reported from other locations in Baltoscandia indicate that the 80 cm thick bentonite between 88.30 and 89.10 m in the Billegrav-2 core represents this marker bed. The other thick (90 cm) bentonite in the Billegrav-2 core, exceeding the thickness of the Kinnekulle Bentonite, belongs to the Sinsen or uppermost Grefsen Series bentonites. Bentonites in the Grefsen Series frequently contain much higher concentrations of trace elements than the Kinnekulle Bentonite.

The Mianwali and Tredian Formations: An Example of the Triassic Progradational Deltaic System in the Low-Latitude Western Salt Range, Pakistan

The Nammal Gorge, Salt Range, Pakistan, preserves a record of the interacting Triassic open-marine carbonate sedimentation, cyclic siliciclastics progradation and fluctuating relative sea level. The sediments at the bottom in the Mianwali Formation, show bivalves and ammonoids rich wacke- to packestone lithofacies (i.e. ML 1 and ML 2), which indicates an open-marine depositional setting. The overlying shale of the Mianwali Formation (i.e. ML 3), has ammonoids and gastropods, the lower part of which indicates a relatively deep-marine depositional setting. Upwards, the ML 3 grades into the sandstones and shales (i.e. ML 4), which show ripple marks, mudcracks, bioturbation, graded, and cross bedding and syndepositional deformation. These features indicate deposition in delta lobe/shoreline sub-environments, with a high siliciclastic input. The lower part of the overlying Tredian Formation contains interbedded shale and sandstone (i.e. TL 1), having large scale slumps, which indicate deposition in cyclic, proximally located varied sub-environments of the delta topsets/channels and in the flood plain environments. The overlying thick, coarse, conglomeratic sandstone (i.e. TL 2) has planar, trough cross bedding and lenticular channelized bedding, which indicates a fluvial to continental environment. Further up, in the Tredian Formation, the presence of dolomite (i.e. TL 3) represents marine transgression. The facies association in the Mianwali and Tredian formation indicates many coarsening upward cycles representing the progradation of individual delta lobes. This study therefore proposes that, subsequent to the Permian-Triassic paraconformity, an open-marine depositional setting established in this area that gradually built up into a progradational deltaic system.