scholarly journals Experimental Study on the Stress Sensitivity and Influence Factors of Shale under Varying Stress

2018 ◽  
Vol 2018 ◽  
pp. 1-9 ◽  
Author(s):  
Zhonghu Wu ◽  
Yujun Zuo ◽  
Shanyong Wang ◽  
Jibin Sunwen ◽  
Leilei Liu
Keyword(s):  
Mechanical Properties ◽  
Mineral Composition ◽  
Effective Stress ◽  
Influence Factors ◽  
Clay Content ◽  
Sensitivity Coefficient ◽  
Stress Sensitivity ◽  
Factors Affecting ◽  
Porosity And Permeability ◽  
Shale Reservoir

Shale reservoirs are characterized by extremely low permeability and high clay content. To further study the stress sensitivity of a shale reservoir, the Lower Cambrian shale in north Guizhou was utilized. Through laboratory testing, the relationships between the shale porosity and permeability and the effective stress were established, and the stress sensitivity of shale was analysed. The mechanical properties and mineral composition of this shale were studied by rock mechanics testing and X-ray diffraction. The main factors affecting the stress sensitivity were analysed. The results show that the porosity and permeability of this shale decrease with increasing effective stress; the shale reservoir permeability damage rate is 61.44 ~ 73.93%, with an average of 69.92%; the permeability stress sensitivity coefficient is 0.04867 ~ 0.05485 MPa−1, with an average of 0.05312 MPa−1; and the shale reservoir stress sensitivity is strong. Shale stress sensitivity is related to the rock mineral composition and rock mechanical properties. The higher the clay content in the mineral composition, the lower the elastic modulus of shale, the higher the compressibility, and the greater the stress sensitivity coefficient.

scholarly journals Stress sensitivity of porosity and permeability under varying hydrostatic stress conditions for different carbonate rock types of the geothermal Malm reservoir in Southern Germany

2021 ◽  
Vol 9 (1) ◽  
Author(s):  
Daniel Bohnsack ◽  
Martin Potten ◽  
Simon Freitag ◽  
Florian Einsiedl ◽  
Kai Zosseder
Keyword(s):  
Effective Stress ◽  
Hydraulic Properties ◽  
Rock Strength ◽  
Pore Network ◽  
Stress Sensitivity ◽  
Stress Conditions ◽  
Rock Matrix ◽  
Effective Stresses ◽  
Rock Types ◽  
Porosity And Permeability

AbstractIn geothermal reservoir systems, changes in pore pressure due to production (depletion), injection or temperature changes result in a displacement of the effective stresses acting on the rock matrix of the aquifer. To compensate for these intrinsic stress changes, the rock matrix is subjected to poroelastic deformation through changes in rock and pore volume. This in turn may induce changes in the effective pore network and thus in the hydraulic properties of the aquifer. Therefore, for the conception of precise reservoir models and for long-term simulations, stress sensitivity of porosity and permeability is required for parametrization. Stress sensitivity was measured in hydrostatic compression tests on 14 samples of rock cores stemming from two boreholes of the Upper Jurassic Malm aquifer of the Bavarian Molasse Basin. To account for the heterogeneity of this carbonate sequence, typical rock and facies types representing the productive zones within the thermal reservoir were used. Prior to hydrostatic investigations, the hydraulic (effective porosity, permeability) and geomechanical (rock strength, dynamic, and static moduli) parameters as well as the microstructure (pore and pore throat size) of each rock sample were studied for thorough sample characterization. Subsequently, the samples were tested in a triaxial test setup with effective stresses of up to 28 MPa (hydrostatic) to simulate in-situ stress conditions for depths up to 2000 m. It was shown that stress sensitivity of the porosity was comparably low, resulting in a relative reduction of 0.7–2.1% at maximum effective stress. In contrast, relative permeability losses were observed in the range of 17.3–56.7% compared to the initial permeability at low effective stresses. Stress sensitivity coefficients for porosity and permeability were derived for characterization of each sample and the different rock types. For the stress sensitivity of porosity, a negative correlation with rock strength and a positive correlation with initial porosity was observed. The stress sensitivity of permeability is probably controlled by more complex processes than that of porosity, where the latter is mainly controlled by the compressibility of the pore space. It may depend more on the compaction of precedented flow paths and the geometry of pores and pore throats controlling the connectivity within the rock matrix. In general, limestone samples showed a higher stress sensitivity than dolomitic limestone or dolostones, because dolomitization of the rock matrix may lead to an increasing stiffness of the rock. Furthermore, the stress sensitivity is related to the history of burial diagenesis, during which changes in the pore network (dissolution, precipitation, and replacement of minerals and cements) as well as compaction and microcrack formation may occur. This study, in addition to improving the quality of input parameters for hydraulic–mechanical modeling, shows that hydraulic properties in flow zones largely characterized by less stiff, porous limestones can deteriorate significantly with increasing effective stress.

Stress sensitivity of sandstones

Geophysics ◽  
1996 ◽  
Vol 61 (2) ◽  
pp. 444-455 ◽  
Author(s):  
Jack Dvorkin ◽  
Amos Nur ◽  
Caren Chaika
Keyword(s):  
Elastic Modulus ◽  
Effective Stress ◽  
Elastic Moduli ◽  
Hydrostatic Stress ◽  
Clay Content ◽  
Stress Sensitivity ◽  
High Porosity ◽  
Effective Pressure ◽  
Critical Porosity ◽  
Difference Formula

Our observations made on dry‐sandstone ultrasonic velocity data relate to the variation in velocity (or modulus) with effective stress, and the ability to predict a velocity for a rock under one effective pressure when it is known only under a different effective pressure. We find that the sensitivity of elastic moduli, and velocities, to effective hydrostatic stress increases with decreasing porosity. Specifically, we calculate the difference between an elastic modulus, [Formula: see text], of a sample of porosity ϕ at effective pressure [Formula: see text] and the same modulus, [Formula: see text], at effective pressure [Formula: see text]. If this difference, [Formula: see text], is plotted versus porosity for a suite of samples, then the scatter of ΔM is close to zero as porosity approaches the critical porosity value, and reaches its maximum as porosity approaches zero. The dependence of this scatter on porosity is close to linear. Critical porosity here is the porosity above which rock can exist only as a suspension—between 36% and 40% for sandstones. This stress‐sensitivity pattern of grain‐supported sandstones (clay content below 0.35) practically does not depend on clay content. In practical terms, the uncertainty of determining elastic moduli at a higher effective stress from the measurements at a lower effective stress is small at high porosity and increases with decreasing porosity. We explain this effect by using a combination of two heuristic models—the critical porosity model and the modified solid model. The former is based on the observation that the elastic‐modulus‐versus‐porosity relation can be approximated by a straight line that connects two points in the modulus‐porosity plane: the modulus of the solid phase at zero porosity and zero at critical porosity. The second one reflects the fact that at constant effective stress, low‐porosity sandstones (even with small amounts of clay) exhibit large variability in elastic moduli. We attribute this variability to compliant cracks that hardly affect porosity but strongly affect the stiffness. The above qualitative observation helps to quantitatively constrain P‐ and S‐wave velocities at varying stresses from a single measurement at a fixed stress. We also show that there are distinctive linear relations between Poisson’s ratios (ν) of sandstone measured at two different stresses. For example, in consolidated medium‐porosity sandstones [Formula: see text], where the subscripts indicate hydrostatic stress in MPa. Linear functions can also be used to relate the changes (with hydrostatic stress) in shear moduli to those in compressional moduli. For example, [Formula: see text], where [Formula: see text] is shear modulus and [Formula: see text] is compressional modulus, both in GPa, and the subscripts indicate stress in MPa.

Some factors affecting the relation between the clay minerals in soils and their plasticity

Clay Minerals ◽  
1966 ◽  
Vol 6 (3) ◽  
pp. 179-193 ◽  
Author(s):  
M. J. Dumbleton ◽  
G. West
Keyword(s):  
Physical Properties ◽  
Clay Minerals ◽  
Mineral Composition ◽  
Clay Content ◽  
Liquid Limit ◽  
Particle Aggregation ◽  
Sedimentation Analysis ◽  
Factors Affecting ◽  
Artificial Mixtures ◽  
Clay Mineral Composition

AbstractThe clay mineral composition is one of the factors that affect the physical properties of soils, and a knowledge of it is required to promote a fuller understanding of the origin of these properties. The relationships between the clay content and the plastic and liquid limits of natural montmorillonitic and kaolinitic soils and of artificial mixtures have been examined and compared. Factors affecting the relationships are discussed, and illustrated by the effect of particle aggregation on the measurement of the liquid limit of tropical red clays and on the sedimentation analysis of the Keuper Marl. The effect of muscovite and of silt-sized material on the position of soils on the Casagrande classification chart has also been examined.

Synergistic Effects of Micronano Structures on Porosity and the Permeability of Shale Under Varying Effective Stresses and Temperatures: A Case Study of Fresh Outcrops from Lower Silurian Longmaxi Formation Shale in the Southern Sichuan Basin, China

2021 ◽  
Vol 21 (1) ◽  
pp. 120-138
Author(s):  
Xiaojing Yue ◽  
Ying Li ◽  
Erping Bi ◽  
Honghan Chen
Keyword(s):  
Mineral Composition ◽  
Sichuan Basin ◽  
Synergistic Effects ◽  
Sensitivity Coefficient ◽  
Stress Sensitivity ◽  
Black Shales ◽  
Stress Release ◽  
Longmaxi Formation ◽  
Pore Sizes ◽  
Lower Silurian

To study the changes in porosity–permeability and the characteristics of the pore structure of shale under stress and high temperature, the Lower Silurian Longmaxi Formation shale in the southern Sichuan Basin, China, was investigated under conditions of continuous pressurization and heating. In addition, the pore compression coefficients and permeability stress sensitivity coefficients were analyzed and quantified. The mineral composition of these black shales was analyzed using scanning electron microscopy (SEM) and nuclear magnetic resonance (NMR). Our results reveal that the porosity and permeability of the shales exponentially decreases with increasing stress, reflecting that microfracture development during increasing stress causes the pores in these shale samples to enlarge. However, the pore compressibility and stress sensitivity coefficient vary for each sample, and the quantitative results indicate an overall decrease with increasing stress, suggesting that the shale deformation is nonlinear during stress release. Based on the mineral composition analyses and SEM measurements, we conclude that the nonuniform changes during stress release are related to the complexity of the shale mineral compositions and the different intercrystalline/ interlaminar pores of the different minerals, which are affected in different ways by pressure. The NMR measurements reveal that the mesopores are most developed in the shale samples, the pore volumes of the micro- and macropores are small, and the nanoscale pores are mainly from 1–60 nm in diameter. The different types of pore sizes decrease with increasing stress, indicating that the porosities measured experimentally reflect the synergistic effects of the different pore sizes on porosity. As the temperature increases, the permeability of the shale decreases significantly, which is primarily caused by the thermal expansion effect. The high clay mineral content of the shales also causes their permeabilities to be sensitive to temperature.

scholarly journals Permeability experiments with overburden pressure of coal measure reservoirs and numerical analysis of its stress sensitivity: A case study of Qinshui Basin, China

2020 ◽  
Vol 38 (5) ◽  
pp. 1690-1705
Author(s):  
Dan Zhou ◽  
Kunjie Li ◽  
Haichao Wang ◽  
Yi Jin ◽  
Zhongliang Ru ◽  
...  
Keyword(s):  
Effective Stress ◽  
Coalbed Methane ◽  
Low Pressure ◽  
Stress Sensitivity ◽  
Coal Measure ◽  
Main Trend ◽  
Overburden Pressure ◽  
Negative Exponential Function ◽  
Qinshui Basin ◽  
Porosity And Permeability

The commingled exploitation of coal measure reservoirs has become the main trend in the development of coalbed methane (CBM) in the central and southern Qinshui Basin. In fact, the porosity and permeability (P&P) of coal measure reservoirs and the evolution of their stress sensitivity are a focus of the basic theory of commingling exploitation. In this study, the coal measure reservoirs in this area are taken as the research object, and the P&P characteristics and stress sensitivity of coal measure reservoirs under different overburden pressure conditions were investigated by P&P experiments on coal, sandstone, and mudstone. The results show that the P&P decreases as a negative exponential function with the increase in effective stress, and the initial porosity and initial permeability of coal are both significantly higher than those of mudstone and sandstone. Besides, the permeability stress sensitivity coefficients of coal, mudstone, and sandstone all decline with a wavy trend with the increase in effective stress. Coal is more sensitive to stress than mudstone and sandstone in the medium and low pressure stages (Pc<5 MPa), while their stress sensitivities tend to become equal in the medium and high pressure stages (Pc>5 MPa). Since the type of coal rich in organic matter is soft rock, it is more susceptible to damage and deformation in the medium and low pressure state (Pc<5 MPa). In contrast, sandstone and mudstone contain more brittle minerals such as cuttings, quartz, and clay minerals, which are, in general, more resistant to deformation, and are less sensitive than coal at the medium and low pressure stages. Finally, a stress sensitivity model based on the Langmuir equation was proposed in this study. With the aid of the model, the stress sensitivities of porosity and permeability of coal, sandstone, and mudstone were analyzed accurately.

Improving the Strength of Abrasive Wheels and Optimizing the Control over the Strength of Composite Abrasive Materials

2019 ◽  
Vol 946 ◽  
pp. 380-385
Author(s):  
Boris A. Chaplygin ◽  
Viacheslav V. Shirokov ◽  
Tat'yana A. Lisovskaya ◽  
Roman A. Lisovskiy
Keyword(s):  
Mechanical Properties ◽  
Test Results ◽  
Key Factors ◽  
Special Equipment ◽  
Material Density ◽  
Factors Affecting ◽  
Control Factors ◽  
Reinforcing Material ◽  
Special Studies ◽  
First Time

The strength of abrasive wheels is one of the key factors affecting the performance of abrasive machining. The paper discusses ways to improve the strength of abrasive wheels. The stress-state mathematical model presented herein is a generalization of the existing models. It is used herein to find for the first time that there are numerous optimal combinations of the elastic modulus and reinforcing material density, which result in the same minimum value of the objective function. It is found out that increasing the radius of the reinforcing component while also optimizing the mechanical properties of its material may increase the permissible breaking speed of the wheel several times. We herein present a regression equation and a nomogram for finding the optimal combination of control factors. Conventional methods for testing the mechanical properties of materials, which have been proven reliable for testing metals and alloys, are not as reliable for testing abrasive materials, as the test results they generate are not sufficiently stable or accurate. We therefore propose an alternative method that does not require any special equipment or special studies.

scholarly journals Survey on Public Psychological Intervention Demand and Influence Factors Analysis

2021 ◽  
Vol 18 (9) ◽  
pp. 4808
Author(s):  
Fang Su ◽  
Bingjie Fan ◽  
Nini Song ◽  
Xue Dong ◽  
Yanxia Wang ◽  
...  
Keyword(s):  
Risk Perception ◽  
Family Size ◽  
Psychological Intervention ◽  
Control Period ◽  
Influence Factors ◽  
Negative Influence ◽  
Internet Survey ◽  
Psychological Status ◽  
Factors Affecting ◽  
Epidemic Period

Major public health emergencies would have a negative influence on the psychology of the public, and an effective psychological intervention can help them to relieve some emotions, such as tension and panic. However, differences in individual environments affect people’s psychological intervention demands and intervention mode choices. Therefore, it is of great theoretical and practical value to analyze and identify the key factors affecting these demands and choices. Based on a nationwide sample of 24,188 respondents from the “Internet Survey of Residents’ Behavioral Changes and Psychological Conditions during the Epidemic,” the different characteristics of public psychological intervention demands and choices under different factors are explored in this paper. The results demonstrate that: (1) the psychological status of Chinese people was relatively stable during the epidemic period, and there were 1016 respondents who had subjective demands for a psychological intervention, (2) age, gender, occupation type, residence, family size, risk perception, psychological status, education level, and fixed expenditure all significantly affect public psychological intervention demands, and (3) risk perception, psychological status, age, gender, and family size will impact the choice of psychological intervention methods. The above results can provide a decision-making basis for the construction of a psychological intervention system in psychological crisis management during the post-epidemic prevention and control period, as well as reference and suggestions for handling psychological stress of similar sudden crisis events in the future.

scholarly journals Evaluation of Bleeding Resistance in Chip Seal and Asphalt Emulsion Residue Rheology

Coatings ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 670
Author(s):  
Preeda Chaturabong
Keyword(s):  
Influence Factors ◽  
Application Rate ◽  
Test Methods ◽  
Test Results ◽  
Asphalt Emulsion ◽  
Aggregate Gradation ◽  
Factors Affecting ◽  
Promising Tool ◽  
Chip Seal ◽  
Asphalt Emulsions

Chip seal bleeding is influenced by many factors, including design inputs, material properties, and project-specific conditions. It reduces the surface texture of the pavement and thus compromises the safety of the traveling public. Even though factors that bring about premature bleeding are known, currently, no laboratory test methods for evaluating bleeding in chip seals have been specified. The objective of this paper is to present the results of an investigation of the influence factors of asphalt emulsion residue properties measured by the ASTM D7405 multiple stress creep and recovery (MSCR) test, as well as other factors related to chip seal bleeding resistance as measured by the modified loaded wheel test (MLWT). In this study, the MSCR test was used as a tool for evaluating the performance of asphalt emulsions because it has been identified as a potential test related to bleeding in the field. In addition, MLWT was selected as a tool for evaluating chip seal bleeding performance in the laboratory. The results of the MLWT showed that the emulsion application rate (EAR), aggregate gradation, and emulsion properties were significant factors affecting bleeding. The MSCR test was found to be a promising tool for the performance evaluation of asphalt emulsion residue, as the test was able to differentiate between emulsion chemistries and modifications in terms of sensitivity to both temperature and stress. In relation to chip seal bleeding resistance, only the creep compliance (Jnr) obtained from the MSCR test results was identified as a significant property affecting potential for bleeding.

scholarly journals A Review of Factors Affecting the Mechanical Properties of Maraging Steel 300 Fabricated via Laser Powder Bed Fusion

Metals ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 1273 ◽  
Author(s):  
Barry Mooney ◽  
Kyriakos Kourousis
Keyword(s):  
Mechanical Properties ◽  
Maraging Steel ◽  
Processing Parameters ◽  
Powder Bed Fusion ◽  
Laser Powder Bed Fusion ◽  
Factors Affecting ◽  
Powder Bed ◽  
Porosity Defects ◽  
Research Findings ◽  
Microstructure Density

Maraging steel is an engineering alloy which has been widely employed in metal additive manufacturing. This paper examines manufacturing and post-processing factors affecting the properties of maraging steel fabricated via laser powder bed fusion (L-PBF). It covers the review of published research findings on how powder quality feedstock, processing parameters, laser scan strategy, build orientation and heat treatment can influence the microstructure, density and porosity, defects and residual stresses developed on L-PBF maraging steel, with a focus on the maraging steel 300 alloy. This review offers an evaluation of the resulting mechanical properties of the as-built and heat-treated maraging steel 300, with a focus on anisotropic characteristics. Possible directions for further research are also identified.

scholarly journals Spatial variation in porosity and permeability of the Rupel Clay Member in the Netherlands

2016 ◽  
Vol 95 (3) ◽  
pp. 253-268 ◽  
Author(s):  
Hanneke Verweij ◽  
Geert-Jan Vis ◽  
Elke Imberechts
Keyword(s):  
The Netherlands ◽  
Spatial Variation ◽  
Clay Content ◽  
Burial Depth ◽  
Southeastern Part ◽  
Boom Clay ◽  
The North ◽  
Sealing Capacity ◽  
Porosity And Permeability ◽  
Permeability Data

AbstractThe spatial distribution of porosity and permeability of the Rupel Clay Member is of key importance to evaluate the spatial variation of its sealing capacity and groundwater flow condition. There are only a limited number of measured porosity and permeability data of the Rupel Clay Member in the onshore Netherlands and these data are restricted to shallow depths in the order of tens of metres below surface. Grain sizes measured by laser diffraction and SediGraph® in samples of the Rupel Clay Member taken from boreholes spread across the country were used to generate new porosity and permeability data for the Rupel Clay Member located at greater burial depth. Effective stress and clay content are important parameters in the applied grain-size based calculations of porosity and permeability.The calculation method was first tested on measured data of the Belgian Boom Clay. The test results showed good agreement between calculated permeability and measured hydraulic conductivity for depths exceeding 200m.The spatial variation in lithology, heterogeneity and also burial depth of the Rupel Clay Member in the Netherlands are apparent in the variation of the calculated permeability. The samples from the north of the country consist almost entirely of muds and as a consequence show little lithology-related variation in permeability. The vertical variation in permeability in the more heterogeneous Rupel Clay Member in the southern and east-southeastern part of the country can reach several orders of magnitude due to increased permeability of the coarser-grained layers.

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