Feldspar Content Research Articles

Evaluation of movable fluid and controlling factors in lacustrine gravity-flow tight sandstone reservoirs: Implications for predicting reservoir quality

Lacustrine gravity-flow tight sandstone reservoirs are rich in petroleum resources, and the presence of movable fluids is essential for the efficient recovery of tight oil. However, characterizing the properties of movable fluids and predicting their content are challenging due to the limited data available on these fluids. To address this research gap, it is imperative to conduct a comprehensive study on the distribution patterns and controlling factors of movable fluids within the lacustrine gravity-flow tight sandstone reservoirs of the Chang-7 Member in the Heshui region of the Ordos Basin. The study utilized a range of analytical techniques, such as thin section analysis, scanning electron microscopy (SEM), high-pressure mercury injection (HPMI), constant-rate mercury injection (CRMI), and nuclear magnetic resonance (NMR). We identified three distinct lithofacies and three types of pore-throat spaces within these lacustrine gravity-flow sandstones. The highest amount of movable fluid was observed in the submicron pore throats, followed by nanopore throats, while the micron pore throats exhibited the lowest amount. Our analysis indicates that petrophysical parameters, mineral composition, and pore throat structures collectively influence the content of movable fluids. Specifically, quartz and feldspar content are positively correlated with the movable fluid content, while clay and carbonate cement content are negatively correlated. Fine sandstones with massive bedding typically have a high content of movable fluids, which is associated with elevated quartz and feldspar content. In contrast, very fine sandstones to siltstones with parallel or ripple beddings have a very low content of movable fluids, characterized by high levels of carbonate and clay cementation. The study also suggests that the lower limit of the pore throat radius of movable fluid is about 0.03 μm. These findings offer novel insights for evaluating and predicting high-quality lacustrine gravity-flow tight sandstone reservoirs, enabling more effective exploration and development strategies.

The effect of high-energy ball milling on enhancing the mechanical properties, light transmittance, and thermal shock resistance of bone china porcelain

A bone china grouting slurry was prepared using two different milling methods: low-energy ball milling (Named LBC) for 24 h and high-energy ball milling (Named HBC) for 1 h. Bone china green bodies were formed by grouting, and the dried green bodies were calcined at different temperatures points in the temperature range from 1235 °C to 1255 °C. The slurry characteristics, as well as the structure and properties of the calcined samples, were analyzed and evaluated. The particle sizes of LBC and HBC slurry D50 are 5.819 μm and 3.571 μm, respectively, accounting for 80.4% and 98.7% of their respective proportions. The particle size distribution range of HBC samples was relatively concentrated, and the viscosity of the two slurries was 1040 mPa·s and 2800 mPa·s, respectively. The ball milling method significantly influenced the formation of product phases. The content of calcium feldspar and β-TCP phases in HBC samples calcined at 1245 °C was higher than that in their LBC counterparts, while the quartz content in LBC was higher than that in HBC samples. The water absorption and porosity of the HBC samples were lower than those of the LBC samples, with a flexural strength of 205 MPa, heat shock temperature difference of 190 °C, and light transmittance of 5.18%/3.73 mm, which were 22.4%, 26.7%, and 4.2% higher than those of the LBC samples, respectively. These results indicate that bone china prepared using the high-energy ball milling method exhibits excellent performance.

Onset and tempo of ignimbrite flare-up volcanism in the eastern and central Mogollon-Datil volcanic field, southern New Mexico, USA

The Cenozoic ignimbrite flare-up (40–18 Ma) generated multiple volcanic fields in the southwestern United States and northern Mexico resulting from asthenospheric mantle upwelling after removal of the Farallon slab. The correlation of tuffs to one another and to source calderas within these volcanic fields is essential for determining spatiotemporal patterns in volcanism and magma geochemistry, which have been used to deduce migration of the Farallon slab at depth and associated mantle melting. However, the correlation of Eocene–Oligocene tuffs in the southwestern U.S. is difficult because of post-emplacement erosion and faulting. This study focuses on spatiotemporal patterns of the initial episode of ignimbrite flare-up activity (ca. 36.5–33.8 Ma) in the Mogollon-Datil volcanic field in south-central New Mexico, USA. We show that alkali feldspar major and trace element geochemistry is an effective tool for correlating tuffs when combined with high-precision, single-crystal 40Ar/39Ar geochronology and bulk-rock geochemistry. Using these data, we correlate several tuff units and differentiate other tuffs that have the same eruption age but very different geochemistry, and we conclude that there was a broadly northwestward migration in volcanism over time. The new tuff correlations are used to investigate spatiotemporal variations in magma geochemistry, erupted volumes, and recurrence intervals during the initial episode of Mogollon-Datil volcanic field volcanism. Early-erupted tuffs restricted to the eastern Mogollon-Datil volcanic field share similarities with western U.S. topaz rhyolites, which suggests that the silicic magmas were generated by partial melting of mafic lower crustal rocks. We also find differences in the compositions, crystallinities, and mineral assemblages between the early- and late-erupted tuffs. The early-erupted tuffs tend to have single-feldspar mineralogies, lower feldspar Or contents, large negative Eu anomalies, and low-whole–rock Ba concentrations. Conversely, late-erupted tuffs have two feldspar plus quartz assemblages, lesser Eu anomalies, higher whole-rock Ba concentrations, and feldspars have higher Or contents. Thus, we suggest that for some of the early eruptions, after magmas underwent crystal fractionation in the crust, the silicic melt largely separated from the crystalline mush prior to eruption, whereas late-erupted tuff magmas underwent crystal fractionation at near the eutectic minimum and were remobilized and erupted with a larger proportion of their crystalline mush. Using our new ages, correlations, and previously published data, we find that the initial phase of Mogollon-Datil volcanic field volcanism produced at least 15 eruptions between 36.5 Ma and 33.8 Ma, with a minimum total erupted volume of ~1350 km3 and an average recurrence interval of 170 k.y. However, eruptions were generally smaller in volume (most <15 km3) than in other coeval fields, and most eruptions (n = 11) occurred in the first 1.2 m.y. (ca. 36.5–35.3 Ma) of activity. Altogether, our work sheds new light on variations in the composition, timing, and migration of volcanism during the initial phase of Mogollon-Datil volcanic field activity and highlights the utility of feldspar geochemistry in both “fingerprinting” tuffs and elucidating magma evolution.

Evolution characteristic and mechanism of microstructure, hydraulic and mechanical behaviors of sandstone treated by acid-rock reaction: Application of in-situ leaching of uranium deposits

The main difficulty in understanding the effects of chemical-physical composite stimulation for low-permeability sandstone-type uranium deposits is clarifying the influence of acidification on pore response mechanism and permeability-mechanical properties evolution during loading-deformation-failure process. Therefore, the acid-rock reaction experiment was first performed, the multiple testing methods (X-ray Diffraction, thin-section identification, high-pressure mercury intrusion porosimetry, stress-seepage coupling experiment) were then conducted, the evolution laws and mechanisms of reservoir physical characteristics after acidification were finally clarified. Results show that after the acid-rock reaction, the contents of calcite, feldspar and kaolinite of samples are decreased and the quartz content is increased, the permeabilities of samples are all promoted, the peak strength, elastic modulus, and shear modulus of samples are reduced and the Poisson’s ratio is raised. The acid-rock reaction changes the energy storage performance and promotes the plasticization of samples. It is suggested to adopt a lower sulfuric acid concentration (2 g/L) and longer reaction time (>45 d) for the ISL of uranium deposits. This work has important theoretical and practical significance for an in-depth understanding of the enhanced mining of low-permeability sandstone-type uranium deposits.

Sandstone Porosity Evolution and Reservoir Formation Models of the Paleogene Huagang Formation in Yuquan Structure of West Lake Sag, East China Sea Basin

The West Lake Sag is abundant in oil and gas reserves, primarily in the Huagang Formation reservoir which serves as the primary source of production. The level of exploration is rather high, but there are still some unresolved issues, such as an unclear understanding of pore evolution features and reservoir growth mode. To tackle the aforementioned problems, this study employs optical microscopic examination, scanning electron microscope analysis, inclusion analysis, isotope analysis, X-ray diffraction analysis, and other techniques to elucidate the primary factors governing reservoir development and establish an analytical model regarding the cause of the sandstone reservoir. The results are as follows: (1) The sandstone reservoirs of the Huagang Formation of the Yuquan (abbreviated to YQ) Structure are now in the mesomorphic A stage as a whole, and minerals such as 4-phase authigenic quartz, 2-phase illite, 2-phase chlorite, 1-phase kaolinite, 1-phase ammonite mixing layer and 2-phase carbonate were formed during the diagenesis. (2) Feldspar and carbonate solution pores make up the majority of the reservoir space. About 10% of the porosity is made up of carbonate solution pores, which are the most prevalent reservoir space. Carbonate solution pores are primarily made up of metasomatic carbonate solution pores and cemented carbonate solution pores. Feldspar solution pores come next, contributing roughly 6.2% of the porosity. At 1.8%, residual intergranular holes are the least common. (3) The four main processes listed below are responsible for the creation of pores in the sandstone of the Huagang creation. The early carbonate cements resist the destruction of mechanical compaction and effectively preserve intergranular volume. The high content of feldspar provided a material basis for later dissolution. Early chlorite surrounding the edges of particles reduced the damage of authigenic minerals to porosity. The faults and cracks formed by the later structural inversion connected to the acidic water in the atmosphere, causing the dissolution of carbonate minerals and feldspar in the sandstone of the Huagang Formation. (4) Carbonate dissolution + feldspar dissolution type, carbonate dissolution type, and feldspar dissolution type are the three main types of reservoir formation in the Huagang Formation; the first two types mainly develop in the Upper Huagang Formation, while the latter mainly develops in the lower part of the Huagang Formation. The research results are conducive to the establishment of a geological prediction model for high-quality reservoirs of different geneses in the Huagang Formation and promote the exploration process of deep-seated hydrocarbons in the West Lake Sag.

Mineral and fluid transformation of hydraulically fractured shale: case study of Caney Shale in Southern Oklahoma

This study explores the geochemical reactions that can cause permeability loss in hydraulically fractured reservoirs. The experiments involved the reaction of powdered-rock samples with produced brines in batch reactor system at temperature of 95 °C and atmospheric pressure for 7-days and 30-days respectively. Results show changes in mineralogy and chemistry of rock and fluid samples respectively, therefore confirming chemical reactions between the two during the experiments. The mineralogical changes of the rock included decreases of pyrite and feldspar content, whilst carbonate and illite content showed an initial stability and increase respectively before decreasing. Results from analyses of post-reaction fluids generally corroborate the results obtained from mineralogical analyses. Integrating the results obtained from both rocks and fluids reveal a complex trend of reactions between rock and fluid samples which is summarized as follows. Dissolution of pyrite by oxygenated fluid causes transient and localized acidity which triggers the dissolution of feldspar, carbonates, and other minerals susceptible to dissolution under acidic conditions. The dissolution of minerals releases high concentrations of ions, some of which subsequently precipitate secondary minerals. On the field scale, the formation of secondary minerals in the pores and flow paths of hydrocarbons can cause significant reduction in the permeability of the reservoir, which will culminate in rapid productivity decline. This study provides an understanding of the geochemical rock–fluid reactions that impact long term permeability of shale reservoirs.

Origin and evolution of soil materials of the Paleo-Chadian linear-dune landscape in the Far North Region of Cameroon

The mineralogy and micromorphology of associated red Arenosols and both yellow and grey Gleysols of the Paleo-Chadian linear-dune landscape of the Far North Region of Cameroon were studied in order to obtain information about depositional environments and pedogenic processes. Differences between the red soils and both others include a significant difference in clay content, which is much higher in the grey and yellow soils. The composition of the clay fraction is also different, with kaolinite and illite as main mineral phases in the red soils, whereas smectite is strongly predominant in the grey soils and a major phase in the yellow soils. Mössbauer spectroscopy analysis reveals a predominance of hematite as iron oxide mineral in the red soils, in contrast to goethite-predominance in the yellow soils. Thin section observations reveal poor sorting of the coarse fraction, differences in feldspar content, and an absence of reworked clay aggregates, as well as the presence of pore-related carbonate features in the grey soils and iron oxide nodules in the grey and yellow soils. The obtained results indicate that the red soils are derived from a different parent material than the other soils. The grey soils developed on flood-related fluvial deposits in interdune depressions, whereas the red soils formed on aeolian sands and the yellow soils show a mixed origin. In the interdune depressions, hydromorphic conditions led to iron reduction and pedogenic carbonate enrichment.

Mapping global distributions of clay-size minerals via soil properties and machine learning techniques

Clay-size mineral is a vital ingredient of soil that influences various environment behaviors. It is crucial to establish a global distribution map of clay-size minerals to improve the recognition of environment variations. However, there is a huge gap of lacking some mineral contents in poorly accessible remote areas. In this work, machine learning (ML) approaches were conducted to predict the mineral contents and analyze their global abundance changes through the relationship between soil properties and mineral distributions. The average content of kaolinite, illite, smectite, vermiculite, chlorite, and feldspar were predicated to be 28.69 %, 22.30 %, 12.42 %, 5.43 %, 5.03 %, and 1.44 % respectively. Model interpretation showed that topsoil bulk density and drainage class were the most significant factors for predicting all six minerals. It could be seen from the feature importance analysis that bulk density notably reflected the distribution of 2:1 layered minerals more than that of 1:1 mineral. High drainage favored secondary minerals development, while low drainage was more benefited for primary minerals. Moreover, the content variation of different minerals aligned with the distribution of corresponding soil properties, which affirmed the accuracy of established models. This study proposed a new approach to predict mineral contents through soil properties, which filled a necessary step of understanding the geochemical cycles of soil-related processes.

Lithofacies assemblage and effects on diagenesis in lacustrine tight sandstone reservoirs: Samples from Upper Triassic Yanchang Formation, Ordos Basin, China

Lacustrine basins are rich in unconventional oil and gas resources and the heterogeneity of matrix reservoir quality seriously affects its development. Previous studies have recognized that diagenesis is the key factor affecting the heterogeneity of matrix reservoir quality, but diagenesis controlled by lithofacies assemblages is poorly studied. In this study, tight sandstones in the Triassic (Ladinian-Carnian) Chang 7 Member of Ordos Basin were taken as examples. Lithofacies, lithofacies assemblages, diagenesis evolution and distribution were investigated by casting thin section analysis, scanning electron microscopy (SEM), X-ray diffraction (XRD), fluid inclusion and carbon-oxygen isotope. The results indicate that eight lithofacies assemblages in Chang 7 exhibit variations in lithofacies, sand-mud ratio and grain size rhythm, controlling the distribution and intensity of diagenesis. Variations in average proportion of lithofacies assemblages are linked to lake level cycles. Compared to cementation, the mechanical compaction has a higher adverse effect on primary porosity of tight sandstones in Chang 7. Siltstone lithofacies show stronger compaction and cementation (mainly clay cementation), whereas fine sandstone lithofacies exhibit stronger dissolution, especially FSpc (fine sandstone with parallel or cross-bedding). Modest proportions of illite (<4%) and chlorite (<1.5%) in fine sandstones tend to form clay coatings, resisting compaction and preserving more porosity. Conversely, abundant pore-filling illite (>4%) and chlorite (>1.5%) result in a noticeable decline in porosity. Particle size and sorting affect reservoir quality by controlling compaction strength. The origin of carbonate cement in sandstones is closely related to mud-rich lithofacies within lithofacies assemblages. Carbonate cementation preferentially occurs in fine sandstones within 0.4 m from the sand-mud interface and the thickness of adjacent mud-rich lithofacies is greater than 0.1 m. Interfaces between fine sandstones serve as fluid migration pathways and bidirectional erosion, facilitated by high porosity and feldspar content. In contrast, the clay-rich matrix in siltstones acts as a barrier hindering fluid migration, creating unidirectional erosion in fine sandstones near the interfaces between siltstones and fine sandstones. Ultimately, five evolution processes linking diagenesis with lithofacies assemblages are summarized, highlighting the differential reservoir quality. This study contributes to understanding the mechanism behind diagenetic variations in tight sandstones and the reservoir evaluation. Consequently, it offers geological reference for the development of unconventional oil and gas resources in comparable lacustrine basins.

Characteristics and correlations of rock components, structure, and physical properties of deep clastic reservoirs in the LD-X area of Yinggehai basin, western South China Sea

Deep clastic rocks in the LD area of the western South China Sea have undergone complex and historical processes of burial, thermal evolution, and diagenesis. As important factors affecting the porosity and permeability, rock components and structures can exhibit pronounced differences with complex lithologies in the vertical direction. In this study, we used a comprehensive method to analyze the lithological characteristics through thin-section observation, scanning electron microscopy imaging, cathodoluminescence, back-scattered electron imaging (on microprobe)), X-ray diffraction patterns of clays, grain size measurement, porosity–permeability analyses, and special imaging logging. The clastic rocks in the study area are dominated by quartz, feldspar, and debris, with the main lithology being subfeldspathic sandstone. The fillings are dominated by carbonate cement, and the clays are mostly illite. The sandstone is mostly grain-supported, moderately rounded, and fine-to medium-grained with poor-medium sorting. Porosity values are mostly in the range of 5–15%, whereas permeability values are in the range of 0.05–10.00 mD. Porosity and permeability are positively correlated with the quartz and feldspar contents and grain size and negatively correlated with the rock debris and carbonate cementing materials and sorting coefficient. These different correlations indicate that the rock components are closely related to the physical properties of the reservoirs. Sandstones with better physical properties generally have higher compositional and structural maturities. On this basis, a conceptual model of the evolution of rock components, structure and physical properties in the LD area is developed. It is verified by the logging profile that rock grouping can reflect both the good and bad physical properties, while simultaneously indicating the development patterns of high-quality reservoirs in the study area.

Changes in Total and Available K Contents in Feldspar and Mica Co-pyrolyzed with Poultry Litter at Different Temperatures

Plant available potassium (K) content is very low in K-bearing mineral ores present in Sri Lanka and that restrict their use in crop production as K fertilizer sources. Heating of minerals can increase their plant available forms of nutrients. The objective of this experiment was to study the effect of direct heating of K-bearing minerals at different temperatures and co-pyrolyis with poultry litter (PL) at different rates on their total and available K contents. Poultry litter was co-pyrolyzed with 0, 1 and 5% (w/w) of feldspar and mica at 350, 500, 650 and 900 ℃. K-bearing minerals were also directly heated at these temperatures. With direct heating the mineral, total K contents of feldspar (6.2%) and mica (4.5%) were significantly (p&lt;0.001) increased by 10% and 18%, respectively at 500 ℃ and then decreased by 33 and 65%, respectively at 900 ℃. Available K contents in feldspar (0.05%) and in mica (0.03%) either decreased significantly (feldspar) or did not change (mica) upon direct heating. Increasing pyrolysis temperature up to 650 ℃ increased both total (4.2 to 6.4%), and available K (3.2 to 6.1%) contents in poultry litter biochar (PLB). Co-pyrolysis of PL with feldspar or mica at 1 or 5% rates did not improve the total or available K contents in PLB at these temperatures. We concluded that heat treatment of locally available feldspar and mica or co-pyrolyzing them with PL are not effective technologies to increase their utilization in agriculture.

Provenance and tectonic setting of greywacke and siltstone of the Nampala gold deposit, Southern Mali

The petrographical and geochemical analyses of greywacke and siltstone samples from the Nampala gold deposit of the Paleoproterozoic Birimian supergroup, Southern Mali, have been carried out to make inferences on the provenance, tectonic settings, and weathering history of the sediments. Petrographical investigations revealed that greywackes can be classified as feldspathic wackes, with immature to moderately mature sediments, with the siltstones being immature. Geochemically, greywackes show features that resemble typical wacke sedimentary rocks, whereas the siltstones are arkose to litharenite. Overall, Nampala sedimentary rocks experienced low intensity of paleoweathering with &lt;70 CIA and &lt;90 CIW values and have not undergone significant sediment recycling having &gt;1 CIV values. Their quartz and feldspar contents, together with the ratio of Al2O3/TiO2 and La/Sc, suggest the derivation of sediments from felsic igneous rocks, with a possible minor contribution from mafic proto-source rock. The petrographic and geochemical features of the greywackes and siltstones are consistent with siliciclastic rocks formed in an active continental margin, similar to other sedimentary rocks of the Paleoproterozoic Birimian terrane. These findings put positive constraints on the subduction-accretion geodynamic model proposed for the evolution of the Birimian terrane of the West African Craton.

Molybdenum tailings calcination for phase composition of Si-Ca-K-Mg fertilizers: Modification of phase transformation and its effects on plant growth

The high value and comprehensive utilization of molybdenum tailings for the production of fertilizer of calcium silicon magnesium potassium (Si-Ca-K-Mg fertilizer) was investigated, considering the abundant potassium feldspar (K-feldspar) content in the tailings. The effects of calcination temperatures, times, and additives (CaCO3 and CaSO4) on reaction degree, final product type, and phase transition process were studied. The results indicated that at 1200 °C, calcination time of 120 min and m(molybdenum tailings):m(CaCO3):m(CaSO4) = 1:0.7:0.2, the final product met Type I product requirements according to Chinese national standards GB/T36207-2018 as well as extremely low heavy metal contents. In the calcination process, CaO resulted from CaCO3 absorbs the liquid phase produced during K-feldspar decomposition to form CaSiO3, facilitating the K-feldspar decomposes into KAlSiO4. Simultaneously, the Ca2+ in CaSO4 replaces undecomposed K-feldspar’s K+. Additionally, CaO reacts with Al2O3, MgO, and SiO2 to produce gehlenite (Ca2Al2SiO7) and akermanite (Ca2MgSi2O7), providing plants with Ca, Mg, and Si elements. The nutrients of the fertilizer were readily assimilated by plants, improving acidic soil without causing any harm to the soil or vegetation. This work offers new ideas for large-scale and high-value utilization of molybdenum tailings as well as addressing the shortage of soluble potassium resource in China.

Detailed Characterization of Pore Results of Continental Shale Reservoir in Fengcheng Formation, Mahu Sag.

The exploration potential of shale oil in the Fengcheng Formation of the Mahu Sag, located in the Junggar Basin, is significant. However, there is a notable dearth of research on shale oil within this formation. This study addresses this gap by focusing on the pore structure and associated development factors of the Fengcheng Formation in Mahu Sag. A total of 113 samples from well X of the Fengcheng Formation were meticulously selected for analysis. The mineral components and pore structure of these samples were characterized using advanced techniques, including X-ray diffraction (XRD), low-temperature nitrogen adsorption (LTNA), high-pressure mercury injection (HPMI), and scanning electron microscopy (SEM). The findings reveal that, despite a relatively low content of clay minerals in the Fengcheng Formation, their presence is intricately linked to pore development. The high content of feldspar in the formation contributes significantly to the formation of clay minerals through dissolution processes. This dual influence plays a crucial role in shaping the overall pore development within the Fengcheng Formation. In addition, a comparative analysis was conducted with shale samples from other wells within the Fengcheng Formation in Mahu Sag, as well as from different basins, such as the Songliao Basin and Ordos Basin. Different from Qingshankou Formation in Songliao Basin and Yanchang Formation in Ordos Basin, the samples from Fengcheng Formation in Mahu Sag are composed of a large number of felic minerals and carbonate minerals with less clay minerals. This study underscores the paramount importance of mineral components and their respective content in influencing the pore development of shale oil reservoirs. The unique characteristics of the Fengcheng Formation in Mahu Sag, as revealed through comprehensive analyses, contribute valuable insights to the understanding of shale oil exploration potential in the Junggar Basin.

Effect of Mineral Composition and Particle Size on the Failure Characteristics and Mechanisms of Marble in the China Jinping Underground Laboratory.

In deep underground engineering, the deformation, failure characteristics, and mechanism of surrounding rock under the influence of grain sizes and mineral compositions are not clear. Based on CJPL-II variously colored marbles, the differences in grain size and mineral composition of the marble were analyzed by thin-section analysis and XRD tests, and the effect of intermediate principal stress on the mechanical properties of marble was investigated. Both SEM and microfracture analysis were coupled to reveal the failure mechanisms. The results highlight that the crack initiation strength, damage strength, peak strength, and elasticity modulus of Jinping marble exhibit an increasing trend with an increase in intermediate principal stress, while the peak strain initially increases and subsequently decreases. Moreover, this study established negative correlations between marble strength, brittleness characteristics, and fracture angle with grain size, whereas positive correlations were identified with the content of quartz, sodium feldspar, and the magnitude of the intermediate principal stress. The microcrack density in marble was found to increase with larger grain sizes and decrease with elevated quartz and sodium feldspar content, as well as with increasing intermediate principal stress. Notably, as the intermediate principal stress intensifies and grain size diminishes, the transgranular tensile failure of marble becomes more conspicuous. These research findings contribute to the effective implementation of disaster prevention and control strategies.

Petrographic characterization of Late Jurassic to Early Cretaceous sandstones in the offshore Bredasdorp Sub-basin, South Africa: An example of a dynamic recycled provenance interpretation

The Mesozoic syn-rift sediments of the Bredasdorp Sub-basin were deposited during the structural inversion of the orogenic Cape Fold Belt (CFB), a crucial time during the break-up of Gondwana. The Late Jurassic to Early Cretaceous non-marine to marine sediments of the Bredasdorp Sub-basin were studied to infer their composition, parent-rock lithologies, tectonic settings and their dynamic response to tectonic perturbations. The knowledge on the provenance terrains in the Bredasdorp Sub-basin is poorly understood and therefore this research shed light on these provenance terrains. Petrographic quantitative analysis revealed that the mineralogical composition of the sediments comprises mainly of litho-quartzose and feldspatho-litho-quartzose sediments. Modal petrographic data indicates a recycled orogen provenance on QFL plots suggesting the occurrence of a collisional provenance terrain. This setting can be interpreted as the reactivation of the CFB structures eroding the Bokkeveld Group (and younger Karoo Supergroup) and the Table Mountain Group metasediments (and Pre-Cape sediments). The shedding of these sediments in the Bredasdorp Sub-basin were coeval with the deposition of the D-V, V-BUSM and BUSM-1AT1 ‘informal’ sequences. Furthermore, an evolving recycled provenance from sedimentaclastic (un-dissected) to basementaclastic (dissected) sediments are proposed and could be a defining characteristic to the enigmatic offshore Jurassic-Cretaceous stratigraphic nomenclature.During the deposition of the D-V Sequence, a spatial variation in provenance due to intrabasinal uplifted fault blocks (possibly reactivated shear zones) occurred between the erosion of the Bokkeveld Group (and Karoo Supergroup) and the Table Mountain Group (TMG) metasediments. The deposition of the V-BUSM Sequence showed a similar compositional trend within their provenance terrain but showed a stronger correlation to an increased quartz and feldspar content. This is possibly due to the erosion of the dominant TMG, which was further supported by the occurrence of distinct type 3 polycrystalline quartz. The deposition of the BUSM-1AT1 sequence saw an increase in plutonic lithic fragments and feldspar content, indicative of an igneous source, which was attributed to the erosion of the proximal Cape Granite Suite. This distinction is crucial in creating a unifying stratigraphic nomenclature for the Jurassic-Cretaceous sequences of South Africa. A dynamic recycled orogen is envisaged for the Bredasdorp Sub-basin and therefore the use of these type of dynamic models should be incorporated in provenance models especially if there is a well-documented geological setting.

Evaluation of Sedimentary Characteristics of the Chang 9 Oil Layer Formation in the Yanchang Formation, Ordos Basin

Shallow-water deltas are a subject of sedimentary research and represent a significant target for oil and gas exploration. The Yanchang Formation of the Triassic in the Ordos Basin comprises numerous shallow-water delta blocks. This paper addresses the core issues pertaining to the sedimentary facies, sedimentary characteristics and sand body distribution of the Chang 9 oil layer formation of the Upper Triassic in the Ordos Basin. Guided by the relevant theories and methods of contemporary sedimentology and sedimentary geology, the reservoir characteristics are described and studied in detail through ordinary thin sections, cast thin sections, graphical representations of particle size and scanning electron microscopy experiments. The experimental results indicate that the porosity in the study area ranges from 3% to 12% and that the permeability is between 0 and 1.5 × 10−3 μm2, which is consistent with classification as an ultra-low-porosity and ultra-low-permeability reservoir. The Chang 9 sandstone is composed of feldspar sandstone and lithic feldspar sandstone. The average content of quartz is low, at less than 31%, while the average content of feldspar is high, at more than 34%. The average content of rock debris is between 10% and 20%. Therefore, the compositional maturity of the Chang 9 sand body is generally low. The particle size distribution exhibits a positive deviation, indicating that the sediments in the sand body are primarily coarse-grained components. The kurtosis of the particle size–frequency curve is observed to vary from flat to very sharp. The Chang 91 lake is classified as a shore shallow lake with basin subsidence and lake transgression. The Chang 9 period saw the development of the Chang 91 sedimentary facies into a semi-deep lake–deep lake environment. The vertical structural style of the Chang 9 oil layer formation in the basin can be roughly summarized into three basic structural types: the sedimentary structures observed in the area include box-shaped upward thinning, bell-shaped upward thinning and funnel-shaped upward thickening. The delta front area in Chang 9 is notable for its size and the prevalence of underwater distributary channel microfacies. The sand body distribution is stable, with sand layer thicknesses ranging from 15 to 30 m. The evaluation and summary of the sedimentary characteristics of the Chang 9 oil layer formation provide a geological basis for future exploration and development in the study area.

Interpretable knowledge-guided framework for modeling reservoir water-sensitivity damage based on Light Gradient Boosting Machine using Bayesian optimization and hybrid feature mining

Reservoir water sensitivity damage significantly contributes to production declines in low-permeability oil and gas fields. An accurate and rapid assessment of water sensitivity is essential for effective mitigation or prevention strategies. Facing the intricate challenge of predicting high-dimensional water sensitivity damage, this study leverages trends in intelligent drilling and completion technologies. It adopts a Knowledge-guided, Bayesian Optimization-enhanced Light Gradient Boosting Machine (KBO-LightGBM) for modeling, augmented by Multiple Imputation by Chained Equations and Synthetic Minority Over-sampling Technique (MICE-SMOTE) to address missing and unbalanced data issues in oil and gas fields, thereby enhancing the scientific efficacy of data processing. The framework's precision and practicality were confirmed using data from 270 natural core samples across 15 oil fields. Findings include a correlation coefficient of 0.9679 on the test set, a root mean square error of 3.4797, and a mean absolute percentage error of 4.0936%. Interpretability analysis identified formation water mineralization, burial depth, feldspar content, and initial porosity as the predominant factors affecting water sensitivity. This research distinguishes itself with a broader dataset, covering 15 parameters of formation fluids and rock components. Weighting factor αDK and scale βDK were designed to integrate empirical correlations into LightGBM's loss function, theoretically mitigating model overfitting. Hence, the intelligent framework proposed herein accurately predicts reservoir water sensitivity damage, aiding in the development of reservoir damage control strategies.

Controls of carbon isotope fractionation during gas desorption in overmature marine shales

Carbon isotope fractionation serves as a crucial tool for assessing gas-in-place content and the gas-adsorbed ratio of shale gas during production. However, a significant gap exists in the understanding of the mechanism and impacts of diverse composition and organic matter on carbon isotope fractionation. To address this gap, this study conducted adsorption and desorption experiments on ten shale samples from the Longmaxi Formation. Various integrated analytical techniques were employed, encompassing X-ray diffraction, bitumen reflectance measurement, total organic carbon (TOC) content analysis, stable carbon isotope analysis, low-pressure gas adsorption tests, and field emission scanning electron microscopic observations. The results reveal that methane dominates the shale gas, with the carbon isotopes exhibiting a distinctive full reversal, attributed to the redox reaction between the ethane and water or transition metals. Differential adsorption capacities of shale led to varied carbon isotope distribution during desorption experiments. Increased micropore quantity in shale is anticipated to augment its adsorption capacity, while elevated feldspar content constrains adsorption due to the absence of intraparticle pores. Consequently, a negative correlation is observed between feldspar content and shale gas fractionation. Although intraparticle pores exist in carbon minerals, their connectivity and low carbonate content limit adsorption capacity in clay-rich shale. Deep burial depletes slit pores in clay minerals, resulting in a low adsorption capacity in clay-rich shale. Notably, the over-mature stage exhibits a substantial increase in micropores within organic matter, positively correlating with carbon isotope fractionation. The positive correlation between quartz content and TOC content is attributed to the positive relationship between the quartz content and carbon isotope fractionation. Additionally, the isotopic values of desorbed gas exhibit significant variability when TOC content exceeds 2.0%, remaining stable when TOC content is less than 2.0%.

Acoustic emission features of granite from different rockburst areas in Sangzhuling Railway Tunnel

In order to investigate the acoustic emission (AE) features of rocks in different (medium and strong) rockburst areas, the Sangzhuling Railway Tunnel granite in China was taken as an example, the mineral composition of rocks in different rockburst areas was analyzed by using XRD (X-ray diffraction) method. The Original rock cores of different rockburst areas were processed into standard rock specimens (diameter 50 mm, height 100 mm) in different directions (transverse, oblique and longitudinal). AE feature parameters (event number, ringing count and energy) of standard rock specimens during indoor uniaxial compression test were obtained by using AE technique. The variation law of AE feature parameters of rocks in different rockburst grade areas was then analyzed. The AE features of failure precursor of rocks in different rockburst areas were therefore discussed. It shows that compared with rocks in medium rockburst area, the content of quartz and feldspar of rocks in strong rockburst area is high, while the content of biotite is low; the rock in the strong rock burst area released more energy during the failure process with about 2–3 times that of the rock in the medium rock burst area; the cumulative ringing curve of rock in medium burst area is a stepped type, while the cumulative ringing curve of rock in strong burst area is the smoothed type; the end of the second and first AE quiet period may be regarded as the failure precursor of rocks in medium and strong rockburst area, respectively. The results presented herein are important for understanding the mechanisms of rockburst.