Rudarsko-geološko-naftni zbornik

Fluvial sedimentology of the river Ethiope sediments, Niger Delta, Southern Nigeria

Israel Aruoriwo Abiodun ETOBRO — 2024-04-28

Despite modern advances in the study of rivers globally, there remains a plethora of work to be done especially in the area of fluvial sedimentology of some present-day river systems. Previous studies on fluvial sedimentology of the sediments of the river Ethiope (in southern Nigeria) are meagre. Grain size analytical methods are indispensable to infer siliciclastic sediments' hydrodynamic conditions, transportation mode(s), and sedimentary environments. Twenty-eight samples (n=28) of the river Ethiope sediments were selected and studied using granulometric analyses (mechanical sieving and pebble morphometric methods). The granulometric analyses results revealed that the obtained sediments were comprised of 82.75% sand, 9.33% gravel, and 7.92% mud. A ternary diagram of sand-gravel-mud shows the sediments are mainly gravelly sand, with few indicating slightly gravelly sand, gravelly muddy sand, muddy sand, and sandy gravel. The grain size statistical analysis shows that the river Ethiope sediments consist of medium to coarse, poorly-sorted to moderately well-sorted, strongly coarse skewed to strongly fine skewed, and very platykurtic to extremely leptokurtic sands. The pebble morphometric analysis revealed that the pebbles range in shape from bladed (B) 22%, compact-bladed (CB) 17%, compact (C) 16%, compact-platy (CP) 16%, compact-elongated (CE) 12%, platy (P) 5%, to elongated (E) 5%. The integration of bivariate plots, ternary diagrams, and C-M patterns plotted for the sediments of the river Ethiope indicated a fluvial environment with sediments characterised by low to moderately high energy that transport sediments of different sizes and grades through saltation, traction, and suspension modes. This study also confirms that sediment transport modes such as saltation, traction, and suspension typify river environments. In general, the existing sedimentologic models derived from grain size analysis of sediments and pebble morphometric methods obtained from modern-day rivers can be applied to better understand transport modes, sedimentary processes, and palaeoenvironments of their ancient counterparts.

Geochemistry and petrography of metamorphic sole amphibolites from the Slatina Quarry, Mt. Zrinska Gora, Croatia

Marija Putak Juriček — 2024-04-28

The investigated Mt. Zrinska Gora amphibolites are a part of the metamorphic sole of the Banovina ophiolite complex. Mineral composition and other petrographic characteristics of amphibolites and adjacent peridotite were investigated by polarised microscopy and chemical analyses of rocks were obtained by a combination of inductively coupled plasma mass and emission spectrometry. The main minerals in these garnet-bearing amphibolites are amphibole and plagioclase with accessory garnet, sphene, spinel, opaque mineral ± clinopyroxene ± quartz ± actinolite ± zoisite-clinozoisite ± prehnite ± pumpelyite and ± clay minerals. Kelyphitic corona is developed around garnet. The amphibolites have nematoblastic, nematogranoblastic, porphyroblastic and porphyroclastic textures and homogenous to foliated structures. The presence of clinopyroxene in some of the investigated amphibolites points to their possible formation under P‒T conditions of upper amphibolite facies. The greenschist facies retrograde metamorphism and subsequent surface weathering of amphibolites is also evident. The chemical composition of rocks indicates that protoliths of most amphibolites were tholeiitic basalts, initially formed in island arcs and the adjoining back-arc basins. During the intraoceanic subduction in Jurassic Neotethys Ocean basalts/basaltic tuffs of island arc tholeiite affinity and back-arc basin basalts, positioned on the top of the down-going oceanic slab, were welded to the base of the hot over-riding mantle wedge, metamorphosed to amphibolite rocks and obducted together with ophiolites on the Adria continental margine. The new described amphibolite type having peridotite protolith characteristics originated as the consequence of the hydration of the bottom part of the overlying mantle wedge.

Zonation of Seismic Vulnerability Levels in South Bengkulu Regency, Indonesia for Disaster-Based Regional Planning

Arif Ismul Hadi — 2024-04-28

The accurate prediction and prevention of earthquakes remains challenging. Consequently, the primary approach to mitigate the impact of earthquakes is through disaster risk reduction efforts. One significant strategy involves conducting seismic vulnerability analyses based on disaster scenarios. This study aims to identify and map areas with varying levels of seismic vulnerability, analyzing the factors contributing to vulnerability in the South Bengkulu Regency. Secondary data, including peak ground acceleration (PGA) values, were collected, along with microtremor data obtained through the Horizontal to Vertical Spectral Ratio (HVSR) method. The recorded microtremor data serve as input parameters for PGA, Modified Mercalli Intensity (MMI), Seismic Vulnerability Index (K_g), shear wave velocity (V_s), and the time-averaged shear wave velocity for the first 30 m depths (V_s30) values. The findings reveal that, overall, seismic vulnerability in the South Bengkulu Regency can be categorized as low. However, specific areas, particularly in the southwestern and northeastern zones, exhibit relatively higher levels of vulnerability. The heightened vulnerability in these areas is attributed to elevated PGA values, despite the region's generally high soil density, which acts as a mitigating factor against earthquake threats.

Effects of porosity on the strength and mechanical behaviour of porous geo-materials under cyclic loading

Abolfazl Dalirnasab — 2024-04-28

Most rocks in nature are porous and usually saturated with different fluids such as water, oil, and gas. The conventional and unconventional hydrocarbon reservoirs are mainly associated with sedimentary formations. The main rocks of these reservoirs are sandstone (porous rock), limestone and oil shale (tight rock), which are associated with varying porosity. Hence, porosity serves as a fundamental parameter for most reservoir rocks. In this research, the effect of porosity on the mechanical behaviour of geo-materials and its fatigue behaviour was investigated. For this purpose, a total of five geo-material sample groups with varying porosities were prepared and designated, i.e. groups A, B, C, D, and E. Group A exhibited the highest porosity 20-21.5%, while group E had the lowest porosity 2-3%, respectively. The conventional quasi-static strength tests and cycle loading tests with constant frequency and amplitude were performed on the samples and different results were obtained. The samples belonging to group E, with the lowest porosity (2-3%), exhibited the highest mechanical strength, elastic modulus and fracture toughness values and the lowest Poisson's ratio compared to those of higher porosity samples. During the cyclic loading period, the fatigue stress-life graph of the E group has the lowest slope compared to the other groups. It means that the slope of the graph increases as the porosity increases in all groups. Therefore, the E group has the lowest porosity and the longest fatigue life time, i.e. porosity and fatigue resistance have an inverse correlation.

A Review of Chan Plot Application and Recent Advanced Models for Diagnosing Excessive Water Production

Ahmed Hamdoon — 2024-04-28

Water is one of the major fluids associated with the operational cycle of the oil industry that must be carefully considered due to its environmental, treatment facility, and economic impacts. Over the years, various methods have been developed to identify excessive water production. These methods range from reliable and expensive ones, such as well-logging records, to less accurate methods that utilize available production and water-oil ratio data, such as the Chan plot. The Chan plot emphasizes that well production can exhibit various patterns of excessive water production, including constant water-oil ratios, normal displacement, channeling, and coning. However, manual interpretation of these plots is often confusing due to the noise present in the actual data. Machine learning models have improved interpretation accuracy, but limitations remain in detecting evolving water production patterns. This paper reviews the application of Chan plots and their integration with existing diagnostic tools for diagnosing excessive water production. It then focuses on a recent advanced model that leverages machine learning specifically designed to improve the interpretation of Chan plots. The review highlights the limitations of traditional interpretation techniques and explores how the recent advanced model can address these limitations. Additionally, the paper briefly discusses the potential of an interactive model for the continuous monitoring of water production patterns. Finally, the paper offers recommendations for future research directions.

Numerical Analysis of Borehole Heat Exchanger Performance in Shallow Gravel Aquifers and Clay-dominated Soil

Amalia Lekić Brettschneider — 2024-04-28

The performance of geothermal heat extraction in shallow aquifers depends on both Borehole Heat Exchanger (BHE) and soil or aquifer properties. In this work, an analysis of the thermal yield of a shallow geothermal reservoir was made numerically with the finite element method used to simulate heat and mass transfer in the three-dimensional reservoir. The main parameters for analysis which have been considered are the geometry and physical parameters of the BHE and grout, as well as aquifer matrix and groundwater fluid. Physical parameters are thermal conductivity, flow conductivity, expansion coefficient, porosity, volumetric heat capacity, anisotropy and dispersivity. The numerical tests have been performed in single BHE line source configuration representing numerically modelled thermal response test for the estimation of sustainable heat extraction. The domain size was a 100x100 meter rectangle with a depth of 200 meters. Three main lithological configurations have been modelled: gravel aquifer with low and high convection of groundwater fluid, as well as a shallow geothermal reservoir dominated by clay material without convection. For selected cases, the analysis for temporal and spatial discretization was also made. Three-dimensional transient modelling was made in FEFLOW^® software with pre- and post-processing done in user-defined Python scripts. The results show the most influential parameters to be considered when setting up the real case simulation of geothermal heating and cooling, as well as optimal temporal and spatial discretization set-up with respect to expected thermal gradients in the reservoir.

Geological investigations and production planning by identification of the discontinuities and rock mass blocks in dimension stone quarries: a case study

Mohammad Hossein Jalalian — 2024-04-28

The dimension stone industry faces a significant environmental challenge due to the large amount of waste produced during the production process. About 51.3% of the materials extracted from dimension stone quarries worldwide end up as quarry waste. The presence of discontinuities and fractures primarily causes this waste. However, by examining the characteristics of these discontinuities and fractures and identifying in-situ blocks of the rock mass, it is possible to reduce the amount of waste produced during dimension stone quarrying. This study focuses on an abandoned quarry bench of the Lashotor quarries complex in the Isfahan Province, Iran. Due to high waste production, the quarry bench was left unused. The study aimed to identify the in-situ blocks of the quarry bench by examining the characteristics of the rock mass's discontinuities and fractures. The authors used a modified algorithm to identify and grade all the quarry bench blocks based on the target market. The study revealed that some blocks in the abandoned quarry bench could be supplied to the target market, and the bench has the potential for block extraction. The algorithm's modification based on the shape factor of blocks is an important innovation that increases the accuracy of block determination compared to previous methods. Overall, this algorithm can be used as a decision-making tool in extracting or not extracting the quarry bench of dimension stone quarries and implementing an optimal cutting pattern to reduce waste production.

Simultaneous Evaluation of Criteria and Alternatives for Mining Method Selection (Case studies: Gol-E-Gohar No. 3 Iron ore and Chahar-Gonbad Copper ore)

Farhad Samimi Namin — 2024-04-28

Selecting a mining method is an essential step in the initial phases of mining. The selection of an inappropriate mining method can have consequences, such as the potential loss of a portion of the ore deposit. Sometimes, changing the mining method can result in high costs that render the entire project economically unfeasible. For the past two decades, qualitative patterns and numerical scoring have been replaced by multi-criteria decision-making methods. In this study, the Simultaneous Evaluation of Criteria and Alternatives (SECA) multi-criteria decision analysis method was introduced for the first time in the selection of mining methods. The SECA was used to select the mining method in two ore bodies: Gol-E-Gohar No. 3 Iron ore and Chahar-Gonbad Copper ore. The final ranking compared with the results obtained from the fuzzy TOPSIS decision-making method. The satisfactory results indicated that the open-pit method was selected as the appropriate approach for both cases. The SECA method has lower computational complexity because it does not require the use of weight vectors as inputs. However, it does require a precise decision matrix. This method can be considered the foundation of artificial intelligence for selecting a mining method.

Laboratory investigation of the effect of sodium silicate and bentonite on the mechanical properties of the grout behind the segment in mechanized excavation

Erfan Khoshzaher — 2024-04-28

Nowadays, the use of Tunnel Boring Machines (TBM) in tunnelling has increased in urban environments. One of the effective parameters in the excavation process is the use of grout behind the segments to prevent ground settlement and penetration into the tunnel. The investigation of the effects of two-component grout (bentonite and sodium silicate) on the mechanical properties of the grout plays a crucial role in mechanized excavation. Therefore, this article aims to investigate the effect of various parameters on the properties of the two-component grout. Eight different mixing designs were considered in this research. Gel-time tests, viscosity test, water bleeding test, uniaxial compressive strength tests (UCS), and direct shear tests were conducted for each mixing design. The UCS tests were performed for eight mixing designs and at four different ages of the grout, while the direct shear test was conducted for five mixing designs at the age of one day. The results showed that increasing the sodium silicate content from 4% to 9.4% reduced the Gel-time to 7 seconds, and increasing the bentonite content from 2.3% to 4.58%, increased the marsh funnel time to 12 seconds. The uniaxial compressive strength of the grout increased to 0.682 MPa at the age of 28 days. Finally, by conducting the direct shear test on the grout and obtaining the parameters of cohesion and internal friction angle, it was determined that these two parameters depend on the values of bentonite and sodium silicate, and they change with the increase or decrease of these grout components.

Determining Rock Fragment Size Distribution Using a Convolutional Neural Network

Elmira Sharifi — 2024-04-28

Fast and relatively accurate determination of the fragment size distribution of a muck-pile is still a challenge in mining operations and the existing measurement methods are inefficient. In this research, a new algorithm to determine fragment size distribution due to blasting was presented, using the image processing technique. In the newly proposed approach, delineating of the fragmented rock particles, as the main core of processing, was carried out, using a convolutional neural network. Two networks were defined and trained by 150 laboratory and 150 field data images. Also, 30 laboratory and 30 field data images were applied to carry out the validation visually, and by using F1-scores. For the two laboratory and field networks and results obtained by Split-Desktop software automatic edge detection on the same images, the F1-scores are equal to (0.98, 0.74) and (0.99, 0.85) respectively. Also, for determination of fragment size distribution by laboratory data network and Split-Desktop software automatic edge detection on the same images, the Root Mean Square Error (RMSE) for F30 and F80 are equal to (0.36, 1.20) and (0.31, 1.24) respectively. These indicate better performance of the proposed approach for both rock edge detection and fragment size distribution over Split-Desktop software automatic edge detection.

Seamless precise kinematic positioning in the high-latitude environments: case study in the Antarctic region

Reha Metin ALKAN — 2024-04-28

Scientific activities in the Antarctic regions have increased daily within the last decades to achieve many different projects. The ice sheet over 98% of the Antarctic continent, the coldest, driest, and windiest place in the world and has the largest desert, makes it very difficult to conduct any kind of study and research. Among them, precise hydrographic surveying should be conducted for many different applications that require reliable and accurate positioning. The output from these surveys plays a vital role in understanding sea level changes, global warming, sea ice movement, navigation and many others. The harsh atmospheric and topographic conditions of the region pose additional challenges to surveyors in the use of conventional terrestrial measurement techniques and satellite-based positioning methods (GNSS) to make positioning. Low quality and noisy GNSS observations with low satellite elevations made their positioning vulnerable to cycle slip, multipath, and discontinuity in Antarctica. This study analyses the performance of the post-processed kinematic Precise Point Positioning (PPP) based on the web-based online GNSS processing service for marine surveying in the high-latitude environment. Within this frame, two realistic experiments were carried out on board a ship and zodiac boat during the 6th Turkish Antarctic Expedition (TAE). The results show that the PPP coordinates using an online GNSS processing service provide kinematic positioning with centimetre level of accuracy using a single GNSS receiver. The general results showed that the PPP technique allows for much faster and accurate positioning in remote and high-latitude areas at a lower cost.

Determination of Lakebed Sediment Distribution based on Underwater Electrical Resistivity Tomography Data

Jasna Orešković — 2024-04-28

Electrical resistivity tomography (ERT) in an aquatic environment is usually measured using two basic systems. One system uses floating electrodes, which is usually applied in shallow water, and the other uses underwater cables with integrated electrodes, which is often carried out as a mobile system. The aim of this research was to test an underwater ERT measurement with floating cables on the water surface, but with electrodes submerged at the water bottom. This type of cable spread makes it possible to lay all the electrodes vertically to the bottom without the distance between them being reduced by the uneven topography and various underwater obstacles. Prior to the field survey that was conducted in a 40 m – deep lake, the response of common electrode arrays was tested using synthetic models. Two models were used that correspond to the geological condition in the field, higher resistivity bodies in a lower resistivity environment and a model with inverse relationship of resistivity to the first one. The Wenner‑Schlumberger and dipole-dipole arrays resolved the resistivity range, size and shape of the bodies very well and were therefore used in the field. The field data quality was very good and it was shown that ERT measurements in freshwater depths of more than 40 metres can provide very good results. As expected from the modelling, the dipole-dipole array led to a high-resolution resistivity model that enabled the characterisation of the lakebed sediments.