Limestone Samples Research Articles

Early Ordovician to Early Permian tectonic evolution of the northern Western Kunlun Orogen (NW China): Insights from the Omixia Complex and surrounding rocks

The Palaeozoic tectonic evolution of the Western Kunlun Orogen plays an important role in deciphering the Tethyan tectonic evolution. This study provides new geochronology, geochemistry and Lu–Hf isotopic data of igneous rocks from the Omixia Complex in the eastern section of the northern Western Kunlun, as well as detrital zircon ages from turbidites and meta‐sediments north of it. From the Omixia Complex, the determined ages of five ultramafic–mafic rock samples are approximately 470, 456, 429, 401 and 382 Ma. Two samples of acidic rocks from the same complex yielded ages of approximately 438 and 378 Ma. One pegmatitic plagiogranite sample exhibits feature of accretionary arc granites, while other samples show geochemical characteristics of island arc tholeiite and E‐MORB. Additionally, four turbidite matrix and two limestone samples, with a major peak around ca. 480–500 Ma, have the youngest zircon ages ranging from ca. 481 to 387 Ma, paralleling the age range of igneous rocks in the ophiolitic mélange. The εHf(t) values of these samples reveal a broad spectrum of crustal and mantle processes. The youngest zircon ages of five meta‐sedimentary rock samples north of the Omixia Complex range from ca. 581 to 535 Ma, with peak ages concentrated around ca. 0.9–1.0 Ga. Their provenance characteristics differ from the turbidite matrix in the southern Omixia Complex and from the meta‐sediments in the northern Tiklik terrane with peak ages of ca. 0.8 Ga. A younger limestone sample yielded youngest zircon age of ca. 294 Ma, which is unconformably overlain the Omixia Complex and surrounding older rocks. Based on these new results, combined with previous data, we propose a new tectonic model for the eastern section of the northern Western Kunlun Orogen, suggesting a continuous evolution process of multi‐terrane subduction–accretion collage from the Early Ordovician to the Middle Devonian in the Paleo‐Tethys Ocean, which evolved into an Andean‐type active margin in the Early Permian, contributing to the substantial continental growth of the southern Tarim Craton.

Inhibition Studies of Expansion Damage in Medium-Low Reactivity Limestone by Fly Ash.

Expansion damage in medium-low reactivity dolomite limestone poses significant challenges in construction and engineering projects. This study investigates the potential of fly ash in inhibiting expansion damage in such limestone formations based on RILEM AAR-5 method. Through a series of laboratory experiments, various proportions of fly ash instead of cement, respectively, were prepared and subjected to varying alkali content conditions immersion tests to simulate expansion conditions. The expansion rates and extents were monitored and compared between pure limestone samples and those mixed with different proportions of fly ash. Additionally, scanning electron microscopy (SEM) analysis was employed to investigate the microstructure of the dolomite limestone-fly ash mixtures to understand the inhibition mechanisms. Results indicate that fly ash demonstrates promising inhibitory effects on expansion damage in medium-low reactivity dolomite limestone across the addition of 40% fly ash and alkali content of 0.70%. The reaction products are calcite, brucite, and a mixture of Mg-Si-Al phases and the reaction area is within 100 μm from the boundary when the cement alkali content is 1.50% without any fly ash. However, no reaction products were found at the boundary after adding 40% fly ash when lowering the cement alkali content to 0.70%. This research contributes to a better understanding of the interaction between fly ash and dolomite limestone in inhibiting expansion damage, providing valuable insights for engineering applications.

Investigation of fracture mechanisms in smooth blasting of limestone samples: numerical and experimental approaches

Investigation of fracture mechanisms in smooth blasting of limestone samples: numerical and experimental approaches

A laboratory study on the durability of limestone wastes in harsh environments for their suitability as aggregate in concrete

One of the critical environmental issues in the Chegeni area (Lorestan Province, western Iran) is the production of a large volume of limestone wastes during the quarrying operations. Releasing limestone wastes in the areas neighboring the quarries has caused visual damage to the environment, and adverse effects on the quality of the soil, running water, and groundwater used for agricultural and drinking water purposes. One solution to this issue can be recycling limestone wastes to produce building materials. In the present study, a comprehensive laboratory program is planned for the durability evaluation of the limestone wastes under harsh environments for their suitability as aggregate in concrete. For this purpose, five aging tests, including freeze-thawing (F-T), salt crystallization (SC), acid attack (AA), wetting-drying (WD), and heating-cooling (HC), were conducted on the limestone sample up to 60 cycles. After every 10 cycles, the physico-mechanical characteristics of the sample, including porosity (n), Brazilian tensile strength (BTS), point load index (PLI), and P-wave velocity (Vp) were determined. Moreover, the pores structure modification of the sample subjected to aging tests was examined through scanning electron microscopy (SEM). Data analyses revealed that the sample is highly vulnerable to the AA and SC processes but is durable against FT, WD, and HC actions. These results were in good agreement with the SEM data such that the sample exposed to AA and SC underwent more changes in their pore structure compared to FT, WD, and HC. Among the physico-mechanical characteristics, the Vp and PLI had the highest and the lowest accuracy, respectively, in the durability evaluation of the sample exposed to aging tests. Based on the data analysis, limestone wastes can be used as aggregate in concrete in environments with the possibility of FT, WD, and HC. However, this type of concrete is not suitable for conditions with occurrences of the AA and SC. Finally, in addition to reducing the environmentally harmful impacts of the study area, using limestone wastes as aggregate in the construction of concrete can also be a practical solution for sustainable development from an economic viewpoint. The results of the present study can be used for assessing limestone wastes produced in other areas of Iran and the world.

H2-enriched gaseous fuel production via steam-gasification of biomass by using lime-based sorbents

The main objective of the present study was to compare the catalytic activity of selected limestones (Göynük, Dikmen, Polatlı Yolu, Kınık Tüneli and Köserelik) in terms of H2-rich syngas production from biomass gasification. In order to achieve this goal, an ASPEN plus-based model for biomass gasification integrated with carbonation reaction was developed. Tar formation was also considered and the gasification process was carried out based on Gibbs free energy minimization. A combined effect of temperature (600-710 °C), steam/biomass ratio, S/B (0.58-1.58), and limestone/biomass ratio, L/B (0-2.0) on gas composition, H2 yield (HY) and gas yield (GY) was also studied. An increase in both S/B and L/B was beneficial for H2 enrichment. The CO2 content declined sharply from 16.83 vol% to 10.28 vol% with increasing L/B from 0 to 1.5; however, a marginal reduction in CO2 content was observed with further increase in L/B. The highest HY (51.01 g/kg) was produced with Dikmen followed by Göynük, Polatlı Yolu, Kınık Tüneli and Köserelik. The results also showed that the limestone samples with high CaO content in general exhibits a better H2 production capacity than limestones with low CaO content. To the best of our knowledge, no simulation study has been presented to compare the catalytic activity of different limestones in terms of H2 production.

Expanded pore-emanated cracking model for brittle failure of sedimentary rocks under triaxial compression

Brittle fracture and its relationship to deformation and strength have been a fundamental area of research in rock mechanics. This paper presents an expanded pore-emanated cracking model to better understand the fracture behaviors and predict the compressive strength of sedimentary rocks. This proposed model is developed to account for a triaxial compression condition using the triaxial compression test results on sandstone, limestone and siltstone samples from Wyoming, USA and experimental data on sedimentary rocks collected from published literature. The normalized critical crack length is determined from the proposed model through which the peak compressive strength is estimated when the stress intensity at the crack tip reaches a critical value called the fracture toughness. Results indicate that the rock porosity and pore radius have an inverse relationship with the compressive strength. Adopting the porosity-permeability relationship, the pore radius is calculated in terms of porosity and grain size. Next, the effect of grain size is implicitly included in the model and negatively correlated with the compressive strength. Moreover, a new approach is proposed for the estimation of fracture toughness based on the pore radius and confining pressure. The predicted compressive strengths from the proposed model show a good agreement with the measured strengths with a mean bias (i.e. average ratio of the measured to predicted strengths) of 1.014. The influence of ϕ and KIC on σ1 was thoroughly studied using parametric study. The study concludes that the effect of ϕ is more prominent than KIC on σ1. At a constant porosity of 0.1, the stress ratio decreases from 0.0082 to 0.0078 when KIC increases from 0.1 to 0.2, indicating a 5% decrease in stress ratio. Whereas, at a constant KIC of 0.1, the stress ratio increases from 0.0082 to 0.014 when the porosity increases from 0.1 to 0.2, indicating 71% increases in stress ratio and therefore compressive strength.

Petrography and Geochemistry of Limestone Upper Cretaceous Kometan Formation (Azmir Anticline): A Preliminary Assessment for Cement Production Suitability in the Kurdistan Region Northeast Iraq

A succession of slightly siliceous limestone of the Kometan Formation is studied geochemically and strati graphically. The studied area is located on the SW limb of the Azmir anticline at the northeastern of Sulaimaniyah city. The studied section is situated at longitudes 45°38'310"E and latitudes 35°36'129''N inside the Folded Zone, Kurdistan Region, northeastern Iraq. The exposed section is sampled for lab studies, and inspected by eyes and hand lenses in the field. In this study, petrographic and geochemical analyses of 17 limestone samples were carried out. This study aims to investigate the major oxides of the limestone samples, using the X-Ray Fluorescence (XRF), for preliminary assessment for possible cement production. A petrographic study was also carried out, in order. Depending on the petrographic study, three major microfacies were recognized: lime mudstone microfacies, lime wackestone microfacies, and lime packstone microfacies, which subdivided into four submicrofacies are planktonic foraminifera lime mudstone submicrofacies, planktonic foraminifera lime wackestone submicrofacies, and planktonic foraminifera lime packstone submicrofacies and heterohelix lime packstone submicrofacies. The geochemical analysis shows that a range of variations in constituents: LOI (35.90% to 42,72%), SiO2 (3.77% to 14.66%), CaO (42.59% to 49.95%), Al2O3 (0.44% to 2.22%), Fe2O3 (0.02% to 0.78%) and MgO (1.50% to 2.26%); K2O and Na2O are present in traces. The high CaO (49.95%) indicates that calcite is the primary carbonate mineral. Due to mineralogical considerations, CaO with LOI shows a positive correlation, whereas CaO with SiO2 shows a negative correlation. The low MgO contents in calcitic limestone and calcitic limestone with chert nodules recommend a lack of dolomitization process. The silica modulus and lime saturation factor from geochemical data indicated that the siliceous limestone samples from the Kometan Formation and Azmir Anticline can be used in the cement-making process provided they are processed for silica removal treatment to reduce its percentage to less than 8%, as required level, where the CaO can be automatically enriched. Depending on field observation, petrography, and geochemistry analysis, we conclude that the source of the chert or silica minerals is diagenetic processes and depositional environment origin.

Estimation of shear strength parameters of intact limestones using miniature triaxial test

Determination of the strength parameters of intact rock samples is an important requirement in rock engineering. On the other hand, proposing a simple method as an index to estimating the strength parameters is one of the tasks of engineering geology. The conventional triaxial test (CTT) is one approach used to determine shear strength parameters (φ and c) that requires standard core cylindrical samples. As it is not possible to prepare standard core samples or collect rock block samples to prepare standard cores under all conditions, the shear strength parameters should be determined using samples having non-standard geometry and dimensions. For this purpose, a miniature triaxial test (MTT) device is introduced and used as an index test to apply triaxial loading on small cubic rock samples in order to estimate their shear strength parameters. The repeatability of the MTT results was determined by performing 27 MTT on 6 × 6 × 6 mm3 polymethyl methacrylate (PMMA) cubic samples. The results showed that the values measured by the device were repeatable with over 97% similarity. The internal friction angles (φ) of the mortar samples obtained from the CTT on cylindrical samples and MTT on the 6 × 6 × 6 mm3 samples are similar. However, the cohesion (c) value measured from the MTT test is nearly double the value obtained from the CTT test. The shear strength parameters of 12 different intact limestone samples from the Asmari Formation located in the Siyakouh section were obtained by performing CTT on standard NX core samples and MTT on the 6 × 6 × 6 mm3 samples. The correlation between the φ and c from the CTT and MTT had coefficients of determination (R2) of 0.92 and 0.88, respectively. The precision of the empirical relation for the CTT-MTT correlation was evaluated and showed that shear strength values estimated by the MTT had about 90% similarity with the measured shear strength values from the CTT.

X-ray Diffraction Line Profile Analysis of Natural Calcite Minerals found in Southern Philippines by Williamson-Hall Method

This study employs the Williamson–Hall (W–H) models to examine the microstrains and crystallite sizes of CaCO3 occurring as calcite in limestone samples found in General Santos City and Sarangani Province, Southern Philippines. Using both the Uniform Deformation Model (UDM) and Uniform Stress Deformation (USDM) models, computations for average sizes were established to be identical, implying minimal strain influence. The consistency of resulting measurements extends to the microstrain, revealing uniform results for all samples. Correlation between crystallite sizes and microstrains in the calcite crystals was observed, where high-purity calcites exhibited larger crystallite sizes and microstrains. The crystallite sizes decrease with microstrains for calcites with higher Mg concentration, a finding that can be attributed to lattice distortion and the formation of defects. The release of stress forms these defects, thereby resulting in a reduction of microstrains. Moreover, the distinctly variable responses to strain exhibited by the samples could be influenced by either their anisotropic properties or other additional components. The W–H models, used jointly with UDM and USDM consistently predicted crystallite sizes, and thus offer valuable insights into the uniform stress responses of calcites. These promising results notwithstanding, USDM is shown to be especially relevant for anisotropic samples owing to the display deviations of crystallite sizes, a key feature of anisotropic natural calcites. The microscopic analysis is expected to provide additional understanding regarding the state of the limestone samples.

Freeze–Thaw Performance Trends of Short-Term Cured Cement-Stabilized Aggregate Quarry By-Product Materials

Recent research studies conducted at the Illinois Center for Transportation focused on sustainable applications of quarry-by-products (QB) as pavement foundation materials and demonstrated the superior durability performance of dolomitic aggregate materials exposed to long-term cementitious reaction and repeated freezing and thawing. This study investigated the influence of QB chemical composition on the strength of cement-stabilized samples exposed to freeze–thaw cycles. Dolomitic QB materials from different quarries in Illinois and with different magnesium oxide (MgO) content, and a control limestone sample were chemically characterized by X-ray fluorescence and X-ray diffraction techniques. The QB materials were then stabilized with 3% cement and subjected to a 7-day curing period, followed by freeze–thaw conditioning. Unconfined compressive strength and resonant frequency tests were conducted to examine how the percentage of MgO and dolomitic minerals could alter the strength/stiffness with freeze–thaw cycles. Optical microscopy analysis was also performed to observe the extent of microstructure damage with freezing and thawing. Over the course of the applied freeze–thaw cycles, no notable minerology effect on strength or stiffness characteristics was observed for the short-term curing. Instead, performance was predominantly governed by physical properties, such as the particle size distribution, which played a more significant role after short-term curing. Well-graded QB materials with optimum packing, following Talbot’s equation with a 0.45 exponent, consistently exhibited the highest strength after any freeze–thaw cycle. The next phase of research, focusing on long-term curing, is expected to provide more insights into the chemical and mineralogical effects of QB materials on durability performance.

Evaluation of Cherts in Gumushane Province in Terms of Alkali Silica Reaction

Alkali–silica reaction (ASR) occurs when alkali oxides coming from the cement composition in concrete come together with reactive silica and moisture coming from the aggregate. Additional maintenance and repair costs caused by the development of ASR in concrete cause the cost to increase. However, thanks to the measures taken against ASR in the early period, it contributes to the creation of sustainable and durable concrete structures. The article investigated the usability of cherts with eight different chemical compositions as aggregates in ready-mixed concrete plants in Gümüşhane. Cherts have been investigated for alkaline reactivity and are intended to be used largely as a source for concrete plants. ASR length changes of the samples prepared according to ASTM C1260 standard were determined after 3, 7, 14, and 28 days of the curing period. Microstructural examination, ultrasonic P-wave velocity, and bending and compressive strength experiments supporting ASR were carried out. The obtained test results were compared between the reference (limestone) sample and each other, as well as with the values specified in the standards. The compressive and bending strength values of the samples increase depending on their ASR. It was observed that the crack structures and types increased depending on the increase in the crack values.

Rock weathering: The effects of varying rock moisture on controlled weathering cycles in low porosity limestone

Examples of rockwall weathering processes include diurnal heating and cooling, diurnal and seasonal freezing, wetting and drying and thawing/seasonal active-layer thawing. These stress-loading processes often occur synergistically and cause a weakening of the rockwall through the propagation of sub-critical cracks. The Acoustic Emissions (AE) released by these cracking events can be measured in order to quantify the weathering efficacy. While the effects of thermal cycling are well studied, rock moisture content and its control on these weathering processes is rarely considered in detail.To better understand rock moistures effect on weathering processes we subjected Wetterstein limestone samples with different starting moisture contents (0 %, 25 %, 50 %, 75 %, 100 %) to thermal cycling above (5 to 35 °C) and below (5 to −10 °C) freezing and a longer freezing cycle with gradual stepped thawing (10 to −10 °C). In addition to this we simulated wetting and drying cycles at a constant temperature. For all of these weathering cycles, relative efficacy was assessed by amount of AE hits and change in effective porosity.Rock moisture was found to have little effect on the overall AE count and effective porosity increase over shorter thermal cycling. However, freeze-thaw cycling was shown to have similar weathering effect to thermal cycling of 3 K greater thermal gradient above freezing. Meanwhile longer duration freezing cycles see an increase of rock moisture create 4× as many cracking events compared to dry samples. More re-freezing events are seen in lower saturation samples and when considered with the synergistic effects of wetting and drying in natural open systems, the presence and mobility of pore water are considered to be more important than the quantity.

Simultaneous removal of fluoride and arsenic from drinking groundwater using limestones from Bajío Guanajuatense, Mexico

Numerous groundwater wells in Mexico exceed the maximum allowable fluoride (F−) and arsenic (As) drinking water concentration requirements, posing an environmental and health risk to the population that relies solely on these wells for drinking water sources. Since encouraging results have been obtained utilizing native limestones to remove some toxic elements from contaminated water, the ability of the limestone rock outcrop to the south of the Sierra de Guanajuato in Mexico to remove As and F− from groundwater was assessed. A sampling campaign was conducted in the study area, focusing on wells exhibiting elevated concentrations of arsenic (As) and fluoride (F−) in compliance with international standards. This water was employed in the treatment experiment involving limestone rocks. The rock sampling process involved a reconnaissance campaign covering the study area and outcrop points of limestone rocks. Representative limestone samples were collected and subsequently subjected to mineralogical and geochemical characterization. Using rock samples, synthetic water, and groundwater from contaminated wells in the region, batch experiments were conducted to evaluate the As and F− removal capacity of limestone. The batch testing consisted of water–rock interactions at various times with different samples of limestone rocks, grain sizes, and water containing distinct concentrations of both elements, artificial and groundwater extracted close to the limestones outcrop. The results indicate that the rock with the highest calcium carbonate (CaCO3) content and the smallest grain size (< 0.05 mm) removes the highest concentrations of both As and F−, with As removal being superior. The removal mechanisms were studied using scanning electron microscopy with energy-dispersive spectroscopy (SEM–EDS) images, saturation index calculations, and Eh–pH diagrams,. Fluoride precipitation was favored when the pH of the solution was slightly acidic, whereas sorption was favored when the pH was higher. The results obtained are encouraging for the removal of high levels of As, and to a lesser extent for F−; consequently, the use of regional limestone rocks could be a viable option for improving the water quality ingested by rural inhabitants in the study area. Calcium carbonate (CaCO3) concentration can be used to identify limestone rocks with the potential to effectively remove As and F− in other locations.

Multiscale investigation of pore structure heterogeneity in carbonate rocks using digital imaging and SCAL measurements: A case study from Upper Jurassic limestones, Abu Dhabi, UAE.

This study presents a comprehensive analysis of rock properties for a selected group of six carbonate reservoir rock samples revealing complex structures at various length scales. Experimental laboratory methods as well as image analysis techniques were conducted in this study to characterize the macro- and micro-pores in mud- and grain-dominated limestones samples from the Upper Jurassic Arab Formation (Arab D member). Mercury Injection Capillary Pressure (MICP), porosimeter, and permeameter lab measurements were employed to assess the pore network heterogeneity and complexity. In addition, a multiscale rock imaging approach was implemented to detect grain and pore phases at several length scales using Thin Sections (TS), Scanning Electron Microscopy (SEM), Focused Ion Beam Scanning Electron Microscopy (FIB-SEM), as well as 3D X-ray Computed Tomography (CT), and micro-computed tomography images (MCT). Furthermore, the multifractal analysis method was applied on the MICP and FIB-SEM to characterize quantitatively the heterogeneity of the pores in the studied samples. Heterogeneous samples 3R, 4M, 5W, and 6M display the highest non-uniformity degree Δα values, falling within the range of [1.21, 1.39] based on FIB-SEM images. Samples 1G, 2R, 3R, and 5W exhibit more heterogeneous pore structure, with Δα values ranging from 0.73 to 1.49 based on the MICP experiments. The results and findings confirm the effectiveness of multifractal parameters Δα and the asymmetry degree in the vertical axis Δf(α) in quantifying and characterizing rock heterogeneity.

Research on the Influence Mechanism of Moisture Content on Macroscopic Mechanical Response and Microscopic Evolution Characteristic of Limestone

The uniaxial compression experiments and acoustic emission (AE) monitoring are conducted to investigate the macroscopic mechanical behavior and microscopic fracture characteristics of limestone samples with varying moisture contents. The findings revealed that as the moisture content increases from 0 to 6.6%, there is a decrease in peak stress and an increase in peak strain. A clear trend towards greater complexity in fracture characteristics is observed with increasing moisture content. In addition, AE activities demonstrate a heightened frequency, accompanied by an elevation in the corresponding multifractal parameter Δα as the moisture content rises. These variations are attributed to the increase in moisture content, which promotes the proliferation of small-scale microcracks and inhibits their evolution into large-scale microcracks. Consequently, the damage and failure process of the limestone samples transitions from being predominantly controlled by a few large-scale microcracks to being collectively influenced by a multitude of small-scale microcracks as the moisture content increases. In conjunction with the Criterion of Microcrack Density, the correctness of the analysis above is substantiated through mathematical derivation. Further, a quantitative model that links the microcrack system to moisture content is established based on the multifractal parameter Δα. Following this, a characterization model that depicts the macroscopic mechanical properties of limestone affected by moisture content is developed. This model effectively encapsulates the quantitative relationship between moisture content and the macroscopic characteristics of limestone and is validated through fitting experimental data. This research contributes to understanding the macroscopic mechanical response and microscopic fracture characteristics of limestone samples with different moisture contents, providing valuable insights and guidance for ensuring safety during engineering construction processes.

Diammonium Phosphate Treatment for Sustained Hydraulic/Acid Fracture Conductivity in Chalk and Limestone Formations

Summary The sustained conductivity of hydraulic/acid fractures is crucial for the continuous and effective production of hydrocarbons. However, hydraulic fractures in soft carbonate formations often experience a reduction in conductivity due to rock deformation and creeping under in-situ stresses. One approach to resolve this issue is to stiffen the fracture surfaces using a consolidating agent. This study examines the application of diammonium hydrogen phosphate (DAP) as an additive to improve the hydraulic/acid fracture conductivity in Indiana limestone and Austin chalk slabs. Initially, flat slabs of Indiana limestone and Austin chalk were subjected to acidization using 15% and 10% hydrochloric acid (HCl) for 10 minutes and 5 minutes, respectively. The resulting surface texture changes were measured using a profilometer. Subsequently, half of the samples underwent treatment in 1 M DAP under 1,000 psi and 75°C for 72 hours. The surface stiffness of the samples was evaluated using nondestructive impulse hammering before and after acid injection and DAP treatment, while hydraulic/acid fracture conductivity was determined using an API conductivity setup. Following acid injection, the experimental results demonstrate that the stiffness of all the samples was diminished to different degrees. However, intact Indiana limestone samples exhibited increased stiffness after treatment with DAP. Acidized Indiana limestone samples showed partial restoration of their original stiffness with DAP treatment. In contrast, DAP treatment fully restored the stiffness of Austin chalk samples and further enhanced it, resulting in a twofold to fivefold increase. The increased stiffness observed in the treated samples had a direct impact on short- and long-term conductivity. Treated Indiana limestone fractures exhibited double the conductivity of untreated fractures. The improvement in Austin chalk conductivity was even more significant after DAP treatment, resulting in seven to eight times higher conductivity in the treated hydraulic/acid fractures. It is worth noting that there was little to no correlation between surface roughness and conductivity, highlighting the significant influence of fracture stiffness on conductivity.

Experiments and modeling of fracture evolution during percolation of CO2-acidified brine through fractured limestone samples

Shunbei Oil and Gas Field has a special type of fault-controlled carbonate reservoir at depths of more than 7,000 m in Tarim Basin, China. The scale and distribution of faults determine the reservoir space distribution. The interaction among faults, geological fluid and carbonate rock and the overall impact towards the reservoir formation are hot issues of interest to scholars at home and abroad. In this study, we focused on the fractured carbonate reservoir of Yijianfang Formation in Shunbei area, and carried out dissolution experiments and 3D numerical calculations to mimic the interaction between CO2 brine fluid and fractured carbonate reservoir along the fracture. This study combines microscopy, scanning electron microscopy and XCMT scanning, aquous cation concentration analysis, numerical simulations together to compare the changes such as fracture surface area, fracture volume, and cations concentration after the reaction. In order to understand the effects of fluid transformation qualitatively and quantitatively. The research shows the main fracture is the dominant place of physical mass transfer and chemical reaction, and the overall reaction is mainly calcium carbonate dissolution. The sample physical heterogeneity and the hydraulic property jointly control the fracture and cation spatiotemporal evolution and affect the overall reservoir physical property finally. In this study, a three-factor coupled fracture-fluid-rock geological model for the fractured carbonate reservoirs is proposed, and the potential locations for the reservoir space are presented.

Experimental Study of Energy Design Optimization for Underwater Electrical Shockwave for Fracturing Applications

Underwater electrical shockwave can be used as a waterless, chemical-free, and environmentally friendly fracturing technique. A detailed experimental study was performed to develop a correlation between the optimum energy required to generate a shockwave that could be used in fracturing rock samples with the wire weight and diameter as independent factors. In addition, the effect of the water volume on the Underwater Electrical Wire Explosion (UEWE) was investigated to quantify the effect of the wellbore fluid volume in the fracturing process. The effect of increasing the discharge energy on the current waveform rising rate, peak amplitude, and fracturing geometry was investigated. A baseline for implementing the shockwave fracturing method on cement and limestone samples was defined to be used in future work. The results show that the water volume has a significant effect on the results of the experiment. A correlation was developed that defined the optimum minimum energy required to burn a certain wire weight with consideration to the wire diameter. Using the optimum required energy or higher will increases the current peak amplitude with the same current waveform rise rate, which leads to higher energy deposition into the wire and prevents the premature breakdown of the wire. The generated shockwave was used to successfully fracture cement and limestone cubic samples.

Comparison of machine learning and statistical approaches to estimate rock tensile strength

Tensile strength is very important in drilling operations. The main objective of this study was to assess petrography, physical, and mechanical properties and predict the Brazilian tensile strength of sedimentary rocks by leveraging key parameters such as Schmidt hardness, compressional wave velocity, density, and porosity. A diverse array of predictive models was employed, encompassing simple regression, multivariate linear and nonlinear regression, backpropagation artificial neural network, gaussian process regression, classification and regression tree, K-nearest neighbor, random forest, and support vector regression. Based on thin section analysis and X-ray diffraction, the samples were identified. The sandstone samples were meticulously categorized into two distinct groups: arenite and litharenite. Additionally, the limestone samples were stratified into the categories of packstone to mudstone based on texture. The highest failure mode frequency of the samples under the Brazilian tensile strength test was identified as central fracturing. Upon meticulous examination, it was discerned that compressional wave velocity exerted the most substantial influence on Brazilian tensile strength estimates, while density exhibited the least impact. Comparing the outcomes derived from the diverse modeling techniques, it was unequivocally established that the support vector regression model showcased the highest level of performance for forecasting Brazilian tensile strength. This was evidenced by the remarkable coefficient of determination of 0.99 along with an impressively low root mean square error of 0.03.

INVESTIGATING THE RELATIONSHIP BETWEEN PORE CHARACTERISTICS, FRACTAL DIMENSION, AND PERMEABILITY OF LIMESTONE USING HIGH-PRESSURE MERCURY INTRUSION, SEM ANALYSIS, AND BP NEURAL NETWORK

In this study, limestone samples from a coal mine in the North China region were selected for analysis. High Pressure Mercury Intrusion (HPMI) and Scanning Electron Microscopy (SEM) experiments were conducted to explore the impact of pore characteristics and fractal dimension of limestone on permeability. Additionally, regression analysis and a Backpropagation Neural Network (BPNN) were employed to predict permeability. The results of this study reveal that the pore-throat distribution of the limestone samples is non-uniform, indicating significant heterogeneity. The difference of pressure curve morphology affects the permeability. Utilizing multivariate regression analysis, a relationship was established between permeability and parameters such as mean radius, porosity, and fractal dimension. Furthermore, the BP neural network was effectively employed to predict permeability values, with small discrepancies between predicted and measured values. This study establishes a link between microstructural attributes and macroscopic permeability providing a robust theoretical foundation for permeability assessment and engineering applications pertaining to limestone.