Arabian Journal of Geosciences最新文献

We have investigated granodiorite and dolerite dykes around the Bingo carbonatite cropping out in the western branch of the East African Rift System (EARS), eastern Democratic Republic of Congo (DRC). These dominantly N-S fracture-controlled dykes are emplaced in an older orthogneiss basement surrounding a Neoproterozoic carbonatite-bearing alkaline intrusive complex. Petrographic and geochemical studies of the granodiorite and dolerite intrusions were carried out to constrain the petrogenesis and tectonic setting of the rocks. Granodiorite is medium to coarse-grained, contain plagioclase of oligoclase to andesine composition, quartz, K-feldspar, hornblende, biotite and accessory magnetite, titanite, ilmenite, and zircon. Dolerite exhibits an ophitic texture with lath-shaped, randomly oriented plagioclase of andesine to labradorite composition embedded in large orthopyroxenes and clinopyroxenes. Accessory minerals include serpentine, altered olivine, amphiboles, magnetite, and ilmenite. The granodiorite is a metaluminous to weakly peraluminous, calc-alkaline. It is enriched in LREE (La_N/Yb_N = 10.91–22.28) and depleted in HREE with insignificant Eu (0.9–0.95) and negative anomalies in some high field strength elements (HFSEs) notably Ta, Nb, and Ti, which suggest melts generated in volcanic arc tectonic setting. The LREE (La_N/Yb_N = 1.97–2.92) for dolerite and the Eu anomaly ((Eu/Eu*)_N 0.85–0.92) suggest a mantle-derived MORB melt probably contaminated by crustal materials during ascent. Emplacement of the dykes was aided by crustal extension and associated fracturing to develop dyke swarms of basic, calc-alkaline, and alkaline rocks.

Microstructure determinations and magnetic parameter measurements are conducted on the Neoproterozoic Boula-Ibi granitic pluton (BIGP) in the western domain of the Neoproterozoic Central African Fold Belt (NCAFB) in Cameroon. We deciphered the deformation and emplacement of the BIGP that contributed to highlight the magmatic sinistral kinematic context of its emplacement in the belt. It is emplaced in a basement made of monzonite, syenite, and gneiss. The magnitude of the magnetic susceptibility, dominantly ferromagnetic, is controlled by magmatic magnetite of different size ranging from single- to multi-domains as confirmed by thermomagnetic and hysteresis curves. The degree of magnetic anisotropy value is < 1.2 and AMS ellipsoids, of both oblate and prolate shapes, imply that flattening and shearing components have both influenced the granitic pluton emplacement. Microstructure data reveal that the pluton emplaced as syn- to late-tectonic magma that registered magmatic to solid state deformations with the drop in temperature in a progressive deformation. The magnetic fabrics of the BIGP strike NW–SE and NE-SW, with low plunges of lineation and moderate dips of foliation and display a sigmoidal S-type pattern, inferring a magmatic sinistral shearing context of the emplacement during transpressive tectonic. This tectonic is correlated to the transpressive D₂ deformation event of regional tectonic. Microstructures, kinematic markers, S-shape of the magnetic fabrics, and the emplacement age (596–566 Ma) of the BIGP indicate that it was emplaced during the transition period between the sinistral D₂ and the dextral D₃ deformation events in the NCAFB history in Cameroon.

Lithologic and elastic interpretations of reservoir rocks and minerals are critical steps in hydrocarbon exploration and production. In this work, we developed an anisotropic micromechanical scheme known as the Mori–Tanaka-Benveniste Method (MTBM) to compute the effective elastic properties of isotropic and anisotropic composites. This led to the creation of new Anisotropic Rock Physics Templates (ARPTs), represented as Ternary Diagrams based on Young’s moduli and Poisson’s ratios, considering factors such as mineralogy, porosity, pore fluid type, and pore geometry. An essential aspect of this research is the pore aspect ratio ((alpha)), a critical parameter influencing pore shape and significantly impacting rock characterization, pore fluid behavior, and mineralogy. We explored an isotropic scheme with a pore aspect ratio of (alpha =1) (spherical pores). We compared it against established methods, including the Perfectly Disordered Method (PDM), Self-Consistent Method (SCM), and classic models like the Hashin–Shtrikman schemes, using Berea sandstone as a reference sample. The resulting ARPTs were constructed as Ternary Diagrams based on calcite, quartz, and clay, utilizing pore aspect ratios of 0.1 and 0.5 (representing aligned spheroidal pores). These templates were applied to various anisotropic samples and formation data, including Bazhenov, Niobrara, Lockatong, Woodford, Chicopee, and a Shale sample from 5000 ft depth, where they demonstrated a strong fit. MTBM provides analytical solutions in a tensorial form that minimizes numerical complexity, presenting a significant advantage over classical self-consistent approaches. This innovative integration of micromechanical modeling with petrophysical analysis enhances the understanding of reservoir characteristics and supports more effective hydrocarbon exploration and production.

During the shale oil development process in the Mahu Sag, there is a significant difference in the initial crude oil production after soaking, which is considered to be related to the soak. Therefore, 7 wells in the research area were selected to study the relationship between various parameters in soaking and initial crude oil production under similar control engineering parameters. Selecting parameters with strong correlation to establish a multiple linear regression equation with initial crude oil production and predict the initial crude oil production of Well M57. The results indicate that the initial oil production is negatively correlated with pressure drop rate, porosity, and soaking time. Establishing a multiple linear regression equation as Y =  − 127.1823A—5.20913B + 1.35608C + 73.81473 and predicting initial oil production of well M57 is 16.58 m³/d. Based on the relationship between pressure drop rate and soak time, the pressure curve is divided into four phases. The reasonable soak time is between the lower and upper limits. The favorable soak time for initial crude oil production is between the II and III stage. This study fills the gap in predicting the initial production of shale crude oil in Mahu Sag and can provide guidance for the efficient development of shale oil in the region in the later stage.

This paper presents a comprehensive study on predicting bulk density in missed intervals of the Nubian reservoir in the Sirt Basin, Libya, leveraging both empirical and machine learning methodologies. Bulk density is one of the most significant and crucial parameters for rock physics modeling, geomechanical analysis, and reservoir characterization; however, this measurement is not present in all intervals of the Nubian reservoir in the Sirt Basin to predict an accurate, reliable prediction and save cost. Empirical equations such as Gardner, Lindseth, and Khandelwal models, alongside machine learning algorithms including random forest (RF), multi-layer perceptron (MLP), and support vector machine (SVM), are employed using conventional logs that were collected from four vertical wells. The data set undergoes a pre-processing step before being divided into 50%, 20%, and 30% for training, testing, and validation, respectively. The optimization is performed using the Grid search CV function. Based on the findings, using machine learning rather than empirical models to predict bulk density is more effective. The machine learning model achieves a higher correlation coefficient above 0.89 and lower mean absolute error than the empirical approaches. Conclusively, a predicted bulk density by supervised machine learning approaches can be used as a reference in all intervals that lack the density log.

This paper presents the results of a comprehensive analysis of five gamma ray logs from the offshore western Niger Delta, Nigeria. The investigation was aimed at using gamma ray logs to estimate the shale volume, identify lithology, correlate between formations, and establish the comparative rate of accretion of deposits of the five studied wells. Five lithologies were recognized, namely, sandy mudstone, shale/mudstone, fine-medium grained sandstone, argillaceous sandstone, and coarse-grained sandstone. The lithology thicknesses varied down the profile of the studied wells due to the discrepancy in the subsidence with erosion and onlap of sediments. The shale volume (Vsh) investigation revealed low Vsh values for argillaceous, fine-medium, and coarse-grained sandstones and high values for shale/mudstone and sandy mudstone lithologies. However, lithologies are discriminated into three types of formation, namely, clean formation (Vsh < 10%), shaly formation (Vsh ranged from 10 to 30%), and shale formation (Vsh is more than 33%). These differentiated lithologies consist of laminated, structural, and dispersed shale, respectively. It is shown that when the Vsh values increase, the Vsh/lithological thickness ratios increase, and when the Vsh/lithology thickness ratios increase, the lithology thicknesses decrease. The graphic correlation revealed that for 1 m of sediment accretion in MOX4 well, 0.10 m, 0.30 m, 0.31 m, and 0.42 m of rocks were accumulated in MOX1, MOX2, MOX3, and MOX5 wells, correspondingly. These comparative rates of sedimentary particle accumulation proved that there were either fewer erosion occurrences or extra accommodation gaps within MOX4 than in MOX1, MOX2, MOX3, and MOX5 wells.

The northern region of Ethiopia, particularly the Dichinama locality, holds significant potential for marble resources. Saba Dimension Stone Private Limited Company is currently mining at three key locations in this region: Lidge, Ela-wedizare, and Dugub. However, the company faced challenges with the existing mine layout, which resulted in decreased production capacity. To address this, a comprehensive research initiative was conducted to assess the current mine design and develop a new open-pit layout. The study included geological mapping, rock characterization, sampling, laboratory testing, and geotechnical evaluations, alongside an in-depth analysis of geological formations such as joints, faults, and shear zones. Geotechnical techniques, including rock mass rating (RMR), rock quality designation (RQD), and slope mass rating (SMR), were utilized to inform the development of the new mine design. The findings from the laboratory tests and geotechnical analysis were applied to create a revised mine layout. The new open-pit design has led to significant improvements in production and recovery rates. Specifically, production volumes are projected to increase from 9976 to 12,470 m3 at Ela-wedizare, from 36,150 to 45,187.5 m3 at Lidge, and from 4620 to 5775 m3 at Dugub. Recovery rates are also expected to improve, from 20.5 to 25.6% at Ela-wedizare, from 23.4 to 29.3% at Lidge, and from 35.7 to 44.6% at Dugub. This research underscores the importance of advanced geological and geotechnical approaches in optimizing mining procedures and improving operational efficiency in the Dichinama marble resource region. The implementation of the new design has helped Saba Dimension Stone Private Limited Company overcome prior obstacles, achieving substantial gains in both productivity and recovery.

Rock slope stability, having a plane mode of failure, can be assessed by different methods. The traditional analytical approaches used in the analysis are limited to those in which the upper slope surface is horizontal and the tension crack is inclined, and generally imply the resolution of nonlinear equations which require an exhaustive calculation. The aim of this study is to develop a systematic analytical solution for estimating the safety factor of a rock slope with an inclined upper surface. By employing the basic assumptions of the limit equilibrium method, simplified expressions considering the nonlinear Barton-Bandis and linear Mohr–Coulomb failure criteria were proposed to analyze the stability of a slope with no tension cracks and sliding on a planar failure surface. Furthermore, some other expressions for the normal stress, length of the planar failure line, and self-weight of the block masses are presented. Finally, the relationships between the derived closed-form solutions and some main parameters, such as the height, cohesion, total unit weight, internal friction angle, slope face angle, failure plane angle, basic friction angle, joint roughness coefficient, and joint compressive strength and upper surface angle, are illustrated with typical examples. These results are in good agreement with practical case studies in literature and numerical simulation results. This method can be effectively utilized in rock and soil slope engineering to provide a reference for preventing and controlling planar slope failure.

This research focuses on characterizing the Late Miocene Qawasim Formation in the El Basant Gas Field, located in the Eastern part of the East Nile Delta onshore, 12.5 km south of El Manzala Lake, covering approximately 30.66 km². By integrating well-log analysis from five wells and seismic data interpretation from 30 2D seismic lines, this study identifies opportunities for enhancing our understanding of the subsurface geology, reservoir characterization, and reservoir potential of the El Basant Gas Field. The study area is characterized by step normal faults oriented northeast-southwest and northwest-southeast. Lithological analysis reveals abundant shale and sandstone facies, indicating significant gas potential. Petrophysical analysis confirms the Qawasim Formation as the primary reservoir, with a net pay thickness of about 23 m, effective porosity of around 34%, and hydrocarbon saturation of about 52%. A detailed 3D model assessed the influence of structural setting, facies, and petrophysical properties on the Qawasim Formation. Integrating these findings, two highly prospective locations were identified, with estimated Gas Initial In Place (GIIP) values of approximately 29.563 million cubic feet.