Carbonates and Evaporites最新文献

Lithofacies and palynofacies were investigated from deposits of the Laopanga Basin to provide sedimentation conditions and their evolution during the Cenozoic Era. Deposition occurred in an active tectonic setting giving rise to six facies including laminated, reeds/fossils-rich, bubble mat, massive, packed fragmental and botryoidal lithofacies and various microfacies (mudstone, wackestone, packstone, grainstone and floatstone). They record precipitates in the form of travertines, pure sinters and carbonate sinters interfingering with alluvial deposits (conglomerates, sandstones and claystones with silica and carbonate cements) as a result of tectonics and climate fluctuations. Sedimentation has been affected by several erosional events which affected the sedimentary basin. The precipitates suggest different temperature of deposition, ranging between 30 °C to 70 °C, likely related to lateral gradients from proximal to distal deposits. The mixing of sinters and travertines suggests a geothermal upflow and outflow and a probable migration of the spring controlled by tectonics related likely to reactivation of the Precambrian fault during the Cenozoic period. Freshwater algal and fungal remains such as Chomotriletes minor and the fern monolete spores Laevigatosporites sp. point to freshwater inflow from terrestrial habitats. Occurrence of other monolete spores such as Polypodiaceoisporites sp. indicates a similar marshy environment. Microbial communities (i.e. cyanobacteria) including coalesced silica spheres and filamentous bacteria reflect their influence on the chemical deposits, in active hydrothermal systems. The mixed precipitates and alluvial/terrigenous deposits are reported elsewhere as for example in the alluvial deposits in Namibia, Italy and Tunisia, meanwhile, the case ofinteraction between travertine-sinter-terrigenous deposits is exceptional.

Reservoir characterization, crucial for oilfield development, aims to unravel intricate non-linear relationships within real-world data. Conventional methods, rooted in simplistic theories, often lead to uncertainties and inaccuracies in workflows. Leveraging the power of deep learning, this study introduces a pioneering approach: a hybrid neural network model merging convolutional and Long Short-Term Memory (LSTM) RNN layers. Focused on effective porosity modeling for the Ghar Member of the Asmari Formation in western Iran, the study utilizes post-stack seismic data and well-log information. By effectively deciphering spatio-temporal information within the data, our methodology allows for spatially aware predictions of effective porosity values, a capability not addressed by previous studies. The hybrid neural network model predicts effective porosity values for the entire reservoir, creating a 3D grid of porosity. It leverages CNN and RNN layers to decipher spatio-temporal information within the data, thereby enabling the model to make spatially aware predictions. The model achieved a mean squared error (MSE) of 0.005, generating clear 3D porosity models with greater detail compared to traditional machine learning and geostatistical methods. This innovative methodology represents a step forward in reservoir characterization, offering improved precision and efficiency. It holds promise for advancing oilfield development practices in the future.

The stratigraphic problem of the Jurassic-Cretaceous boundary (JKB) is still the object of a warm international debate. Around this limit, the Upper Tithonian substage has been the subject of significant stratigraphic investigations throughout the Tethyan Realm areas. On the southern Tethys Margin of the Maghreb, our recent works in NE Algeria have revealed sections, where good Upper Jurassic outcrops are considered as promising for the definition of a Global Standard Section and Point (GSSP) for the Jurassic-Ctretaceous boundary. In this line of interest, a high resolution calpionellid biozonation of Upper Tithonian successions from two bed-by-bed sampled key sections in the Aurès (Jebel Azreg) and Aïn Yaghout Mounts (Jebel Toumbaït) of NE Algeria is proposed here for the first time. The Crassicollaria and Calpionella Zone limits, encasing two subzones and six stratigraphic horizons, are identified. Within these sections, calpionellid distribution and resulting biostratigraphic units fit the standards referred to for the Tethyan Realm. The identified marker bioevents and associations confirm the high biostratigraphic potential of calpionellids for the JKB definition in the North Africa Maghrebian Chains. Correlation transects reveal important thickness and facies variations interpreted as the result of a synsedimentary tectonic control implying NW–SE, E-W and NE-SW major faults that led to the individualization of a mozaic of highs and depressions where Upper Tithonian deposits onset. A proposed interpretative model replaces the Upper Tithonian study successions in their regional geodynamic context.

This research article presents a comprehensive work on sedimentological study of the Yamama Formation in the Saudi Arabia, aiming to enhance understanding of its depositional environments, diagenetic evolution, and reservoir properties of the formation. Integrated field and petrographic studies are used to interpret microfacies, depositional environment and diagenetic history of the Yamama Formation near Riyadh, Saudi Arabia. Field investigations show that the formation is thin- to thick-bedded, massive to nodular limestone with small patches of shale and marl. Petrographic studies show four distinct microfacies, i.e., mudstone MF-I, wackestone MF-II, packstone MF-III, grainstone MF-IV. The microfacies and their associations represent homoclinal ramp depositional setting designated on the basis of the relative percentage of allochems and orthochems. The diagenetic history, which includes eogenetic, mesogenetic, and telogenetic stages, is discussed as follows: The eogenetic stage includes burrowing, micrtization, neomorphism, and drusy mosaic cementation; the mesogenetic stage includes compaction (mechanical and chemical) and dissolution. The telogenetic stage is evident from calcite-filled fracture veins crosscutting the rock unit. The reservoir properties are directly dependent on both depositional and diagenetic processes. The reservoir quality of the formation has been significantly reduced by the precipitation of different types of cements during the diagenetic processes, as observed in the detailed paragentic sequence; however, during the late stage, fracturing has enhanced the reservoir quality significantly during the late stage.

The freshly exposed carbonate rock succession of the Ewekoro Formation (Palaeocene) was investigated to interpret its palaeoredox conditions and depositional environments based on microfacies, mineralogy and geochemical variations. Wackestone, packstone and mudstone are three carbonate microfacies identified from petrographic observations. Calcite is the dominant mineral phase, while quartz, dolomite and lizardite are minor phases. The dominance of CaCO₃ and the low SiO₂ and Al₂O₃ in the limestones indicate a low detrital contribution during precipitation. The low U and U/Th ratios are associated with an environment characterised by oxygen-enrichment, while redox proxies of Ni/Co, V/Cr and V/(V + Ni) show substantial oxygenation (oxic to anoxic) in their respective sedimentary environments. The mean rare-earth elements contents in the examined samples (45.03 ppm) are greater than the characteristic values (28 ppm) in marine carbonates. The rare earth and Yttrium signature of these limestones shows a seawater-like pattern. However, the somewhat lower average Y/Ho ratio (35.70) than conventional seawater (44–74) implies that freshwater input in a coastal setting modifies the seawater to some extent. Except for a few elements, these samples are comparable to those of shallow-marine carbonates, formed in a seawater-influenced environment. The REEs data obtained from these limestones has provided baseline information on geochemistry with a potential to better understand the regional paleogeographic conditions of the Ewekoro Formation.

The Early Triassic Kangan Formation in southern Iran and Persian Gulf, equivalent to the Upper Khuff Formation in the neighboring Arab countries hosts vast natural gas resources in the Persian Gulf. The current study discusses sedimentary facies, diagenesis, depositional setting and reservoir characteristics of the Triassic Kangan Formation within a sequence stratigraphic framework across a section passing from the central to northern Persian Gulf. For this purpose, a comprehensive analysis was conducted using well logs, cores and thin sections from four wells. In this respect, fifteen microfacies representing four facies’ belts ranging from peritidal to lagoon and barrier (shoal) settings of a shallow marine carbonate ramp environment were identified. The Kangan Formation has undergone marine, meteoric and burial diagenesis severely impacting its reservoir quality through dolomitization, dissolution and cementation. Analysis of sedimentological and petrophysical characteristics enabled the recognition of three third-order and seven fourth-order depositional sequences. This unit’s persistent and complex diagenetic history, spanning since the Lower Triassic, has significantly altered reservoir quality by reshaping pore types, size and geometry. Dolomitization and dissolution have notably improved the reservoir quality of the Kangan Formation in the central Persian Gulf. However, towards the northern Persian Gulf, the presence of anhydrite in the form of cement, nodules and interbeds has adversely affected reservoir quality. Consequently, the Kangan Formation behaves as a tight gas carbonate reservoir in the Coastal Fars structural zone of Zagros. Therefore, the Coastal Fars and the northern Persian Gulf can be conceptualized as the inner part of a large-scale paleo-ramp environment (inner ramp), whereas the central Persian Gulf lies within its mid-ramp and basin environment.

Coring is essential for understanding subsurface rock properties and optimizing reservoir characterization. This study explores the application of the Multi-Resolution Graph-Based Clustering (MRGC) method for efficient sample selection in coring programs. Through a detailed analysis of well logs and core data, focusing on mechanical properties like rock strength and elasticity, geomechanical units are identified using the MRGC method. By aligning selection criteria with program objectives and integrating various data sources, the MRGC method optimizes sample selection, offering a comprehensive insight into subsurface geomechanical properties while minimizing core sample requirements. The systematic and targeted sample selection facilitated by the MRGC method ensures that core samples accurately represent the geomechanical characteristics of different field layers. By incorporating petrophysical logs and geomechanical parameters, a model was developed for formations in Gachsaran, Asmari, and Pabdeh-Gorpi-Gadovan. Ultimately, 11 geomechanical units were distinguished from 12 coring wells based on 4 input parameters using the MRGC method. This method improves sample selection accuracy and efficiency, validates geomechanical unit definitions, and offers valuable insights into subsurface geomechanics.

China, being the world’s largest consumer of potassium fertilizer, faces significant challenges due to limited potassium reserves. Qarhan Salt Lake stands out as a reservoir containing 296 million tons of low-grade solid potash ore (KCl), establishing itself as the premier potassium fertilizer production base in China. The extraction of low-grade solid potash ore via liquefaction technology, leading to the generation of potassium-rich brine, emerges as a pivotal strategy for sustainable potash exploitation in the region. This approach offers a promising solution to mitigate the potassium salt shortage in China. This paper systematically examines the transformation in KCl content of solid potash ore within the Bieletan section of Qarhan Salt Lake before (2007) and after liquefaction (2022). The study employs quantitative assessments to determine liquefaction volume and efficiency. Results reveal that, at a shallow depth of 23.20m, the average KCl content of solid potash ore decreases from 2.15% before liquefaction to 1.00% after liquefaction. This observed decrease of 1.15% (53% reduction) underscores the substantial impact of liquefaction. A total of 136.94 million tons of KCl are dissolved, providing a sustainable resource for approximately 15 years or more. During the initial stages of liquefaction (2007–2008), a rapid decline in the KCl content of solid potash ore is noted, with liquefaction efficiency significantly influenced by the positioning of the brine mining channel. As liquefaction progresses, efficiency diminishes, although the overall efficiency surpasses that of the Huobuxun section at the eastern extremity of Qarhan Salt Lake. This study holds significant implications for refining the solid potash liquefaction mining strategy in Qarhan Salt Lake, providing valuable guidance for future optimization efforts.

The late Cretaceous Fort Munro Formation in the western Sulaiman Range represents medium to thick-bedded, dark grey limestone displaying rich skeletal components, particularly larger benthic foraminifera (LBF), and bivalves. Three sections from the western Sulaiman Range, namely Spera Ragha, Murree Brewery, and Hanna Lake, were studied for detailed microfacies analysis and diagenetic investigation. A total of nine microfacies have been recognized, including 1 mudstone, 4 wackestone, 2 packstone, and 2 grainstone. Considering the proportionate prevalence of biota, their groupings, and the existence of a micritic matrix in different microfacies, it is deduced that the Fort Munro Formation was deposited inner to middle ramp setting. The inner ramp setting is more widespread than the corresponding middle ramp and is characterized by sub depositional environments including semi-restricted, storm-induced skeletal shoals, lagoons, low energy and protected inner ramp, storm induced skeletal shoals, and open marine. The Fort Munro Formation has undergone significant diagenetic alteration due to various diagenetic events. These events have altered the primary and secondary porosities. The observed diagenetic processes include micritization, cementation, dissolution, neomorphism, mechanical compaction, stylolitization, fractures and veins formation. Paragenetic sequence reveals that the studied carbonates are modified in marine, meteoric, and burial diagenetic environments. Detailed diagenetic analysis of the Fort Munro Formation reveals that most of the primary as well as secondary porosities are deteriorated by the precipitation of different type of cements in a variety of diagenetic environments.