High resolution geochemical data are rare for Australian salt deposits. Recent studies by Chemostrat Australia in the Adavale, Officer and Polda basins have analysed Neoproterozoic and Paleozoic massive halite deposits using inductively coupled plasma–optical emission spectrometry and –mass spectrometry (ICP-OES-MS), yielding quantitative data for 50 elements. Supporting X-ray diffraction (XRD) and energy-dispersive X-ray fluorescence (ED-XRF) data has elucidated internal variability of the principal rock forming minerals to produce lithostratigraphic models. Further resolution of the internal architecture of the massive salt deposits using trace elements highlights subtle variabilities in the composition and abundance of non-evaporitic components, principally the accessory heavy minerals and clays. This has allowed for the definition of chemical sub-units within the salt. It is likely that these variations reflect changes in sediment influx and climate and thus can be utilised for regional correlation.

In the oil and gas industries, lithology classification (characterization of rock samples) is used to improve accuracy in locating new reservoirs. Compared to geochemical analysis of physical rock samples in laboratory settings, wireline logging (measuring petro-physical properties of rocks using a variety of sensors lowered down a given borehole) provides a more cost-effective method of obtaining rock data for classification and characterization. However, this is a challenging task due to the complexity of well log data, and often expert knowledge is required to analyze and interpret this data. Within the remit of automatic well log data analysis, a new fuzzy inference system for sedimentary rock class classification is presented here. The performance of this system was evaluated on the data provided in the FORCE 2020 Machine Learning Competition. The system, which only used three fuzzy rules to map four well logs to three rock classes, had a classification accuracy of 74

Real-time chemostratigraphy is a workflow deployed at wellsites to remove stratigraphic uncertainty and support drilling operations. This study presents the chemostratigraphic wellsite workflow which, during drilling operations, support either the placement of casing points (using predefined geochemical markers to target a depth above a specific stratigraphic feature) or aid geosteering. Geosteering is typically employed during the drilling of a horizontal well and is done to keep the drill within a certain zone or horizon to maximise production. Wellsite chemostratigraphy has been effectively deployed to wellsites within multiple basins around the globe and has recently been utilised in the Perth Basin. The wellsite workflow starts before the deployment, with offset wells analysed by inductively coupled plasma (ICP) spectroscopy within a laboratory-based setting. This builds the correlative element-based framework and identifies the trends required to assist with either core placement, casing point, or geosteering. Samples are analysed by energy dispersive x-ray fluorescence units (these data are then used to confirm the zone previously defined) and can be identified at wellsite using the onsite tool, the selected elements of which are those less likely to be affected by drilling mud contamination and loss of circulation material (LCM). However, during drilling operation, there may be instances where LCM must be added to the drilling muds, which may have an effect on the data quality for certain elements. With a dedicated ICP spectrometry elemental database behind the wellsite operation, machine learning tools may be employed to ‘repair’ correlation critical elements.

The Neoproterozoic to Middle Ordovician sedimentary rocks of the Officer Basin, Australia, are difficult to correlate, in part because biostratigraphic studies of acritarchs and stromatolites are localised, stable isotope studies are rare, and seismic models are technically challenged by the occurrence of basaltic and halite prone-sections. Hence, the elemental chemostratigraphic framework presented here provides an independent stratigraphic model for the Neoproterozoic to Middle Ordovician sedimentary rocks of the Officer Basin. A total of six chemostratigraphic megasequences have been geochemically defined and assigned to the existing litho stratigraphy; these have been further subdivided into twenty-eight chemostratigraphic sequences. The chemostratigraphic zonation has been established based on elemental changes attributed to provenance and climatic variation which can be used for correlation as they convey regional, rather than local, changes in sedimentation. The elemental data reveals that there is lateral variation within the established lithostratigraphy (e.g., within the members of the Observatory Hill and Hussar formations), which suggests localised sediment source input to different areas of the basin.

Presented within this study is an example of high resolution chemostratigraphic zonation of the Wilcox Group. Elemental data from Inductively Coupled Plasma - Optical Emission Spectrometer (ICP-OES) and Inductively Coupled Plasma - Mass Spectrometer (ICP-MS) has been used to chemostratigraphically evaluate the Wilcox Group interval. The geochemical data has been integrated with palynological data (Cornick et al. 2023) and x-ray diffraction mineralogical data to develop a multi-disciplinary approach to stratigraphic zonations and correlations.

The Cretaceous and Paleogene marine sedimentary rocks that crop out along southern coastal Tanzania have been the focus of the Tanzanian Drilling Project (TDP) since 2001. The comprehensive lithological and chro-nostratigraphic examination of over forty shallow cores by the TDP culminated in the formal definition of the Kilwa Group: a claystone-dominated succession comprising five formations deposited in middle to outer shelf and upper slope marine environments along a passive continental margin. Onshore, the TDP has cored important palaeoclimatic events within the Kilwa Group. Offshore, the group forms the reservoir and seal of several gas fields discovered in southern Tanzania.The formations of the Kilwa Group cored onshore, have been differentiated from each other largely by vari-ations in subsidiary lithologies (sandstones and limestones), rather than by diagnostic characteristics of their dominant lithology (olive grey claystone). To test and refine the lithostratigraphy of the Kilwa Group, a forensic examination of the claystones using whole-rock inorganic geochemistry, mineralogical analysis and detailed biostratigraphy, is employed in this study.1210 core samples collected from 20 onshore TDP boreholes and 185 cutting samples acquired from three wells located in offshore in Blocks 1 and 4 are examined by inductively-coupled plasma optical emission spec-troscopy and mass spectrometry, whole-rock and clay fraction X-ray diffraction analysis and heavy mineral analysis using Raman spectroscopy. The different methodologies are used to produce a claystone-based che-mostratigraphic framework for the Kilwa Group that comprises three sequences, five packages and six units, and links the shallow subsurface rocks onshore to the deep subsurface stratigraphy offshore.The multidisciplinary geochemical and mineralogical approach reveals that variations in detrital quartz, feldspars (K and Na), heavy minerals, phosphatic minerals and clay minerals (particularly illite, smectite and kaolinite) are key for defining the claystone-based stratigraphy of the Kilwa Group. The variation in the abun-dance of these mineral through time highlight mostly temporal changes in depositional environment, chemical weathering and sediment provenance that occurred in Tanzania during the Cretaceous and Paleogene.Integration of the chemostratigraphic framework with detailed biostratigraphic information from the study sections and comparison with the published lithostratigraphy of the Kilwa Group onshore reveals that all three stratigraphic schemes are in broad agreement. Nevertheless, refinements are proposed based on the new che-mostratigraphic results. It is suggested here that the top and base of the Kilwa Group is older than previously reported (base-Albian and intra-Rupelian, respectively, rather than the end of both stages) and in most cases, the geochemical data suggests that most of the Kilwa Group formations, as cored onshore, are thinner than formerly proposed. Only the Masoko and Lindi Formations are interpreted to be thicker than previously defined by the TDP.

This study proposes an integrated multidisciplinary workflow for the correlation of wells within the Gulf of Mexico. Integrating wellsite biostratigraphy and chemostratigraphy. Wells previously analysed for biostratigraphy have been subjected to elemental analysis by Inductively Coupled Plasma - Optical Emission Spectrometer (ICP-OES) and Inductively Coupled Plasma - Mass Spectrometer (ICP-MS) analysis, as well as x-ray fluorescence (XRF) in a simulated wellsite situation. The newly implemented workflow in this study exhibits a robust correlation between biostratigraphy and chemostratigraphy, leading to a more confident identification of major intra Wilcox surfaces.

A prerequisite to understanding the evolution and resource potential of a basin is to establish a reliable stratigraphic framework that enables the correlation of rock units across multiple depocentres. Establishing a stratigraphic model for the Adavale Basin is challenging due to its structurally complexity, lack of well penetration and its lateral changes in facies. Biostratigraphy appears broad-scale, and despite providing chronostratigraphic control for the Lower Devonian Gumbardo Formation when combined with U/Pb zircon geochronology, the rest of the Devonian succession is hampered by a lack of microfossil assemblages and their poor preservation. The aim of this study is to establish an independent chemostratigraphic correlation across the Adavale Basin using whole rock inorganic geochemistry. Within this study, a total of 1489 cuttings samples from 10 study wells were analysed by Inductively Coupled Plasma – Optical Emission Spectrometry and Inductively Coupled Plasma – Mass Spectrometry for whole rock geochemistry, in order to establish an independent chemostratigraphic zonation scheme. Based on key elemental ratios selected to reflect changes in feldspars, clay minerals and provenance, the Devonian-aged stratigraphy is characterised into four chemostratigraphic mega-sequences that encompass the Gumbardo Formation (Mega-sequence 1); the Eastwood Formation, the Log Creek Formation and the Lissoy Sandstone (Mega-sequence 2); the Bury Limestone and the Boree Salt formations (Mega-sequence 3); and the Etonvale and the Buckabie formations (Mega-sequence 4). These mega-sequences have been further subdivided into a series of chemostratigraphic sequences that can be correlated across the study wells, establishing a regional correlation framework.

A multidisciplinary workflow (Sandtrak®) showcases cross-validation methodologies and integration of different data streams in the Palaeocene-Eocene Wilcox Group, to achieve a high-resolution provenance analysis and reservoir zonation. The techniques utilized include elemental ICP, Raman heavy mineral analysis, QXRD and zircon geochronology, a suite of techniques which allows understanding of sediment provenance variations in a way that is accurate and allows high-resolution changes to be identified. The analysis results of the three wells included in this study show a clear correlatable subdivision of the Wilcox Group.

Abstract This paper shows how heavy minerals and single-grain varietal studies can be conducted on silt (representing c. 50% of world's sediments) sediments to obtain quantitative data as efficiently as for sand-sized sediments. The analytical workflows include heavy mineral separation using a wide grain-size window (15–355 μ) analysed through integrated optical analysis, Raman spectroscopy, QEMSCAN microscopy and U–Pb dating of detrital zircon. Upper Jurassic–Cretaceous silt-sized sediments from the Mandawa Basin of central-southern Tanzania have been selected for the scope of this research. Raman-aided heavy mineral analysis reveals garnet and apatite to be the most common minerals together with durable zircon, tourmaline and subordinate rutile. Accessory but diagnostic phases are titanite, staurolite, epidote and monazite. Etch pits on garnet and cockscomb features on staurolite document the significant effect of diagenesis on the pristine heavy mineral assemblage. Multivariate statistical analysis highlights a close association among durable minerals (zircon, tourmaline and rutile, ZTR) while garnet and apatite plot alone reflecting independence between the three groups of variables with garnet increasing in Jurassic samples. Raman data for garnet end-member analysis document different associations between Jurassic (richer in A, Bi and Bii types) and Cretaceous (dominant A, Ci and Cii types) samples. U–Pb dating of detrital zircon and their statistical integration with the above-mentioned datasets provide further insights into changes in provenance and/or drainage systems. Metamorphic rocks of the early and late Pan-African orogeny terranes of the Mozambique Belt and those of the Irumide Belt acted as main source of sediment during the Jurassic. Cretaceous sediments record a broadening of the drainage system reaching as far as the Usagran–Ubendian Belt and the Tanzanian Archean Craton.

This study represents an integrated stratigraphic study on the stratigraphy of the Triassic and Lower Jurassic sequences of the well Spoonbill C-30, from the Jeanne d’Arc Basin. This basin formed as a result of a failed triple rift system that developed during the North Atlantic Mesozoic Rift. Overall, across the Grand Banks penetrations of the Lower Jurassic and Triassic are limited with the key sections occurring in the southern wells of the Jeanne d’Arc, Carson and Whale Basins. The deposition during the Tethys Phase of rifting (during the Late Triassic – Early Jurassic) sediments are predominantly deposited in continental and lacustrine settings. There were some marine incursions resulting in the deposition of salts and carbonates, which are contemporaneous with equivalent salt deposits across the Scotian Shelf (Enachescu, 2013).

Reservoir quality primarily reflects the properties of porosity and permeability, the ability to store a fluid and transport it between the particles that make up the rock. Reservoir quality data is predominantly measured during the acquisition of routine core analysis (RCA) data on core plugs. From the plugs subsequent analysis, such as petrography, scanning electron microscopy (SEM) or QEMSCAN may be carried out. However, these techniques are time consuming and costly, requiring specialist equipment, therefore this study presents a supplementary technique; the application of whole rock inorganic geochemistry for reservoir quality assessment.

Summary Reservoir quality reflects the sandstones porosity and permeability; the measurements of this data is collected during routine core analysis (RCA). Additional analysis, such as petrography, SEM or QEMSCAN may then be carried out on these samples. However, this is costly and time consuming, requiring specialist equipment. This study demonstrates how the complementary technique of whole rock geochemistry may be applied to reservoir quality assessment. Changes within the whole rock geochemistry reflects changes within the mineralogy which can be used as a preliminary assessment of the mineral phases likely to be controlling reservoir quality. Geochemical analysis allows the pre-screening of samples to ensure effective sampling for additional techniques and provides a means to model the reservoir quality into equivalent reservoir sections that have been only sampled by ditch cuttings. The study utilises whole rock geochemical data from the Mizzen wells (Flemish Pass Basin, Grand Banks, Canada) to demonstrate the mineralogical controls on the reservoir quality within the core of Mizzen F-09 which is then used to determine the thin section placement. In addition, the geochemical data has then been used to predict reservoir quality within equivalent sections of Mizzen L-11 and O-16, which are only sampled by cuttings.

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The Namurian and Westphalian sequences from the onshore well Scaftworth-B2, located in the Gainsborough Trough, central England, have been analysed for whole-rock inorganic geochemical data via inductively coupled plasma optical emission spectrometry (ICP-OES) and mass spectrometry (MS). The changes within key elements, and elemental ratios, results in a chemostratigraphic zonation scheme consisting of eight chemostratigraphic sequences and 13 chemostratigraphic packages, providing the type zonation for the Bowland Shale and overlying formations. Mineralogical data are provided by whole rock X-ray diffraction (XRD) and are used to calibrate the mineral modelling in order to generate a modelled mineral log for the study well. Furthermore, the modelled mineralogy is then used to calculate a relative brittleness for the samples, which can then be collaborated with traditional rock properties data at a later date. Elemental data can also be used to model the relative abundance of detrital quartz and biogenic silica; while total silicon is detected by ICP, biogenic silica is not detected by XRD owing to its amorphous nature. Enrichment factors calculated from the inorganic elemental data suggest that the sediment was deposited in an unrestricted marine setting, which experienced periods of anoxia.

Provenance analysis has traditionally focused on sandstones, which are much easier to analyse than conglomerates - which must be analysed in the field with limited tools - and mudrocks - which cannot be dealt with easily with classical optical methods. However, it is important to recognise that the silt fraction transported in suspension actually represents the majority of the sediment in large river systems and the predominant grain-size in major deltas and submarine fans, as well as in most of ancient sedimentary basins and reservoirs. Quantitative provenance analysis of silt represents a step forward in provenance studies as it provides the access to an unexplored world where detrital minerals can be easily identified and their history reconstructed. The technique can be applied to both siltstone and shale making it attractive for the hydrocarbon industry, particularly in the area of research of Unconventional Plays. This contribution is therefore intended to prove the validity and efficacy of the method and its possible application to both QPA studies and to hydrocarbon exploration. The latter is located in the onshore Mandawa basin in southern Tanzania. where hydrocarbon exploration is particularly important for the presence of huge deep-water gas fields.

The Upper Devonian (Frasnian) Duvernay Formation of Alberta is a proven, areally extensive source rock and has become a major and active shale resource play. The Duvernay is conformably overlain by the Ireton Formation and conformably overlies platform carbonates of the Cooking Lake Formation in the East Shale Basin and the Majeau Lake Formation in the West Shale Basin, where the Cooking Lake Formation is absent (e.g. Stoakes and Creaney, 1984). Although productive, the Duvernay consists of a carbonate shale sequence characterised by significant lateral facies variations that produces exploration and development challenges when targeting sweet spots and modelling changes in mineralogy for fracture optimisation. However, the lack of reliable biostratigraphy and variable log response, and lateral facies variation ensures that chronostratigraphic correlation is poor, which in turn hampers regional play fairway mapping. For example, the Duvernay is believed to be age equivalent to the Muskwa Formation, although these plays have different organic and mineralogical characteristics, which implies that more detailed time resolved palaeoenvironmental reconstructions of the Upper Devonian are required. This study demonstrates a proof of concept study of the application of C-isotope chronostratigraphy in combination with elemental chemostratigraphy to constrain the correlation of Duvernay both on a field to sub regional scale.

The Athabasca Oil Sands of northeastern Alberta represent one of the largest reserves of hydrocarbons in the world. Barren fluvial sandstones of the Lower Cretaceous (Aptian) McMurray Formation form the principal reservoir in this play. However, despite extensive research, the detailed correlation of these stacked amalgamated sandstone sequences remains problematic. The incising nature of the McMurray Formation’s deposition has resulted in a complex stratigraphic architecture. In many cases this results in heavily oil saturated sand-on-sand contacts thereby making it difficult to distinguish individual channel sequences. Furthermore, the McMurray Formation sandstones are mineralogically mature (typically comprising >95% quartz) with only minor to trace amounts of feldspars, clays and heavy minerals. As a result, the differentiation and correlation of individual channel packages is challenging using bulk mineralogical data from petrographic or XRD methods. The present study aims to ascertain whether individual channel packages can be differentiated and correlated using a forensic multi-disciplinary approach including high-resolution chemostratigraphy, heavy mineral analysis and zircon U-Pb geochronology. Datapages/Search and Discovery Article #90224 GeoConvention © 2014, FOCUS Adapt, Refine, Sustain Calgary, Alberta, Canada, May 12-16, 2014

Summary The Permian Rotliegend Group is a prolific reservoir interval holding a significant proportion of north west Europe’s gas reserves, and as such is one of the most studied stratigraphic intervals. The study area is on the margin of the Rotliegend sandstone fairway and straddles the Netherlands/German median line An integrated approach to stratigraphy has been undertaken, incorporating different techniques on different lithology types including inorganic geochemistry, petrography, heavy mineral analysis, zircon geochronology and palynology, and has resulted in a high resolution stratigraphic framework independent of lithology or facies. This study introduces a new chemostratigraphic breakdown for the basal Rotliegend section which, when integrated with the other techniques can help understand the early basin fill geometry and architecture. This study also extends the chemostratigraphic breakdown of the upper Carboniferous into the German North Sea allowing new calibration when mapping the Base Permian Unconformity subcrop. The improved stratigraphic understanding has had a significant impact on hydrocarbon prospectivity in the study area.

Summary The Siciny-2 well is an ideal example to demonstrate the technique of chemostratigraphy. The sediment is described as monotonous mudstone and sandstone successions, while the well itself is drilled in the Fore-Sudetic Monocline, located in the south-west portion of the Polish Basin and is heavily affected by the Variscan orogeny, and then by latter inversion events. All these hurdles can prove problematic for traditional subsurface correlation techniques. Within this example the study well is sub-divided into four chemostratigraphic sequences and eighteen chemostratigraphic packages using elements associated with provenance, weathering and palaeoproductivity. Intergrated biostratigraphy, which recognises six biozones, highlights the occurrence of marine bands, and shows how the geochemical data can be used to highlight marine bands. Furthermore, from the geochemical characterisation of the Carboniferous and Permian a new top Carboniferous pick is identified.