Geomechanical properties of the Permian black shales in the southern main Karoo Basin: lessons from compositional and petrophysical studies

2021 ◽  
Author(s):  
C. Geel ◽  
E.M. Bordy ◽  
S. Nolte
Keyword(s):  
Compressive Strength ◽  
Constant Strain Rate ◽  
Black Shales ◽  
Triaxial Deformation ◽  
Geomechanical Properties ◽  
Karoo Basin ◽  
Young’S Moduli ◽  
Shale Composition ◽  
Strength Constant ◽  
Deformation Tests

Abstract Permian black shales from the lower Ecca Group of the southern main Karoo Basin (MKB) have a total organic carbon (TOC) of up to ~5 wt% and have been considered primary targets for a potential shale gas exploration in South Africa. This study investigates the influence of shale composition, porosity, pressure (P) and temperatures (T) on their geomechanical properties such as compressive strength and elastic moduli. On average, these lower Ecca Group shales contain a high proportion, ~50 to 70 vol%, of mechanically strong minerals (e.g., quartz, feldspar, pyrite), ~30 to 50 vol% of weak minerals (e.g., clay minerals, organic matter) and ~0 to 50 vol% of intermediate minerals (e.g., carbonates), which have highly variable mechanical strength. Constant strain rate, triaxial deformation tests (at T ≤100°C; P ≤50 MPa) were performed using a Paterson-type high pressure instrument. Results showed that the Prince Albert Formation is the strongest and most brittle unit in the lower Ecca Group in the southern MKB followed by the Collingham and then the Whitehill Formation. Compressive strength and Young’s moduli (E) increase with increasing hard mineral content and decrease with increasing mechanically weak minerals and porosity. On comparison with some international shales, for which compositional and geomechanical data were measured using similar techniques, the lower Ecca Group shales are found to be geomechanically stronger and more brittle. This research provides the foundation for future geomechanical and petrophysical investigations of these Permian Ecca black shales and their assessment as potential unconventional hydrocarbon reservoirs in the MKB.

scholarly journals Influence of snow type and temperature on snow viscosity

2013 ◽  
Vol 59 (213) ◽  
pp. 87-92 ◽  
Author(s):  
Louis Delmas
Keyword(s):  
Mechanical Properties ◽  
Constant Strain Rate ◽  
Ice Crystals ◽  
Triaxial Deformation ◽  
Influence Of Temperature ◽  
Slab Temperature ◽  
Rapid Temperature ◽  
Similar Temperature ◽  
Deformation Tests ◽  
Rapid Drop

AbstractThree spontaneous avalanches were observed in Lia, Longyearbyen, Svalbard, each occurring naturally under similar temperature conditions. Automatic measurements of temperature inside the snowpack led to examination of the triggering of avalanches in cold conditions following a rapid drop in temperature. The mechanical properties of ice depend on the slab temperature and I ask: could a rapid temperature change affect the mechanical properties differently considering a slab consisting of (1) rounded grains or (2) faceted grains? Snow is considered as a foam of ice crystals, and triaxial deformation tests are performed at constant strain rate to examine the influence of temperature and grain type on the mechanical properties. Although the snow densities in the two sample sets were almost identical, some differences due to grain type were observed. In particular, the set with faceted grain snow started to flow at higher stresses than the set with rounded grains.

Some Implications of a Nonlinear Viscoelastic Constitutive Theory Regarding Interrelationships Between Creep and Strength Behavior of Ice at Failure

1989 ◽  
Vol 111 (2) ◽  
pp. 144-148 ◽  
Author(s):  
B. D. Harper
Keyword(s):  
Strain Rate ◽  
Constant Strain Rate ◽  
Nonlinear Viscoelastic ◽  
Uniaxial Creep ◽  
Strength Behavior ◽  
Minimum Strain Rate ◽  
Strength Constant ◽  
Viscoelastic Constitutive Model ◽  
Stress And Strain Rate ◽  
Special Case

This study explores several possibilities for a correspondence in the behavior of ice at failure during uniaxial creep (constant stress) and strength (constant strain rate) experiments. The usual notion of failure in ice is employed (i.e., the occurrence of a minimum strain rate during a creep test and a peak or maximum stress during a strength test), and the behavior at failure is discussed in terms of a recently proposed nonlinear viscoelastic constitutive model for ice. It is demonstrated that no correspondence between creep and strength data can be expected in general; however, several approximate interrelationships do occur for the experimentally motivated special case of a constant (independent of stress and strain rate) failure strain.

scholarly journals Mineral compositional controls on the porosity of black shales from the Wufeng and Longmaxi Formations (Southern Sichuan Basin and its surroundings) and insights into shale diagenesis

2018 ◽  
Vol 36 (4) ◽  
pp. 665-685
Author(s):  
Mei Han ◽  
Chao Han ◽  
Zuozhen Han ◽  
Zhigang Song ◽  
Wenjian Zhong ◽  
...  
Keyword(s):  
Organic Matter ◽  
Pore Size ◽  
Pore Volume ◽  
Total Pore Volume ◽  
Black Shales ◽  
Carbonate Content ◽  
Pore Sizes ◽  
Pore Size Distributions ◽  
Shale Composition ◽  
The Relationship

The effects of brittle minerals in shale diagenesis on shale pores remain controversial and it is difficult to quantify directly. However, the relationship between brittle minerals and shale pores could provide indirect guidance regarding diagenesis processes in post-mature marine shales. In this study, the pore size distribution was determined, and the relationship between pore volume and shale composition was examined in shale samples with different total organic carbon contents from the Wufeng and Longmaxi Formations, with the objective of distinguishing pore size ranges in organic matter and inorganic minerals, respectively, and studying shale diagenesis. The samples of the Wufeng and Longmaxi shales are composed of clay minerals, calcite, dolomite, quartz, feldspar, and some minor components. The pore size distributions, which were determined using nitrogen adsorption isotherm analysis of shale and kerogen, show similar trends for pore sizes less than approx. 6.5 nm but different trends for larger pore sizes. Mercury injection saturation shows that macropores account for 14.4–22% of the total pore volume. Based on a series of crossplots describing the relationships between shale composition and pore volume or porosity associated with different pore sizes as well as on scanning electron microscopy observations, organic matter pores were found to comprise most of the micro-mesopores (pore diameters < 6.5 nm). Organic matter pores and intraparticle pores associated with carbonate constitute the majority of mesopores (pore diameters 6.5–50 nm). Finally, interparticle pores associated with quartz comprise the majority of the macropores. The mesopores associated with carbonate were formed by dissolution during diagenesis, whereas the macropores associated with quartz are the remainders of the original interparticle pores. Mesopore volumes increase with increasing carbonate content while macropore volumes decrease due to the ‘pore size controlled solubility’ effect, which causes dissolved calcium carbonate to precipitate in larger macropores.

Compressive strength behavior of fine-grained frozen soils

1990 ◽  
Vol 27 (4) ◽  
pp. 472-483 ◽  
Author(s):  
Harsha Wijeweera ◽  
Ramesh C. Joshi
Keyword(s):  
Compressive Strength ◽  
Water Content ◽  
Yield Stress ◽  
Constant Strain Rate ◽  
Unit Weight ◽  
Total Water Content ◽  
Total Water ◽  
Frozen Soils ◽  
Fine Grained ◽  
Dry Unit Weight

Constant strain-rate (0.01/s) uniaxial compression-strength tests were conducted on more than 200 saturated samples of six fine-grained frozen soils at temperatures between −5 and −17 °C. Saturated soil samples containing total water contents between 15% and 105% were prepared using a consolidation apparatus specially designed for this purpose. The effect of dry unit weight, total water content, temperature, and soil type on the behavior of peak compressive strength was studied. Test results indicate the peak compressive strength of fine-grained soils is sensitive to changes in the dry unit weight and the total water content. The temperature dependence of the peak compressive strength is represented by a simple power law. An empirical formula has been developed to predict the peak compressive strength of fine-grained frozen soils at a particular temperature using index properties, specific surface area, particle-size distribution, and dry unit weight. A linear relationship exists between the peak compressive stress and the yield stress. Key words: peak compressive strength, yield stress, frozen soils, fine-grained soils, dry unit weight, failure strain, temperature, total water content, slurry consolidation.

A Uniaxial Nonlinear Viscoelastic Constitutive Relation for Ice

1986 ◽  
Vol 108 (2) ◽  
pp. 156-160 ◽  
Author(s):  
B. D. Harper
Keyword(s):  
Strain Rate ◽  
Constant Strain Rate ◽  
Constitutive Theory ◽  
Uniaxial Deformation ◽  
Explicit Dependence ◽  
Deformation And Failure ◽  
Nonlinear Viscoelastic ◽  
Defect Growth ◽  
Special Cases ◽  
Strength Constant

The present paper concerns the description of uniaxial deformation and failure of ice in uniaxial compression in terms of a nonlinear viscoelastic constitutive theory. The constitutive model incorporates explicit dependence upon micro-structural defect growth and assumes the form of a so-called modified superposition integral contaiing a linear kernel which depends only upon time. This last feature will greatly simplify the task of experimentally characterizing the various material properties which appear in the theory. The existence of correspondence principles for the model will also facilitate the solution of practical boundary value problems. Predictions based upon this model will be shown to agree qualitatively with experimental results for creep (constant stress) and strength (constant strain-rate) tests on ice. In addition, specific empirically deduced relationships between stress, strain, strain-rate and time at certain critical points in these standard tests will be shown to result directly from the constitutive theory as special cases.

Uniaxial Constant Compressive Stress Creep Tests on Sea Ice

1995 ◽  
Vol 117 (4) ◽  
pp. 283-289 ◽  
Author(s):  
N. K. Sinha ◽  
C. Zhan ◽  
E. Evgin
Keyword(s):  
Compressive Strength ◽  
Sea Ice ◽  
Strain Rate ◽  
Compressive Stress ◽  
Axial Strain ◽  
Acoustic Emissions ◽  
Constant Strain Rate ◽  
Rate Sensitivity ◽  
Load Test ◽  
Creep Tests

First-year columnar-grained sea ice from Resolute Passage (74° 42′ N, 94° 50′ W), off Barrow Strait in the Canadian High Arctic, was tested under constant uniaxial compressive stress applied normal to the length of the columns. Creep tests were performed at 263 K, 253 K, and 243 K in the stress range of 0.7 to 2.5 MPa, using prismatic samples with dimensions of 50 mm × 100 mm × 250 mm. Because three-dimensional creep data are extremely useful for developing constitutive equations, axial strain was measured in conjunction with the measurements of two lateral strains and acoustic emissions. The deformations were measured using displacement gages mounted on the samples. A description of the experimental procedures and the observations are presented here. One-to-one correspondence has been obtained between the present results on the dependence of minimum creep rate on stress and previous data on the dependence of uniaxial compressive strength on strain rate under constant strain rate. The strain-rate sensitivity of compressive strength can, therefore, be obtained from creep tests which can be performed by using simple dead-load test systems.

A Preliminary Examination of the Effect of Structure on the Compressive Strength of Ice Samples From Multi-Year Pressure Ridges

1985 ◽  
Vol 107 (1) ◽  
pp. 99-102 ◽  
Author(s):  
J. A. Richter ◽  
G. F. N. Cox
Keyword(s):  
Compressive Strength ◽  
Constant Strain Rate ◽  
Strain Rates ◽  
Compression Tests ◽  
Preliminary Examination ◽  
Pressure Ridge ◽  
Test Parameters ◽  
C 23 ◽  
Strain Rate Compression ◽  
Effect Of Structure

A series of 222 uniaxial constant-strain-rate compression tests was performed on vertical multi-year pressure ridge sea ice samples. A preliminary analysis of the effect of structure on the compressive strength of the ice was performed on 78 of these tests. Test parameters included a temperature of −5°C (23°F) and strain rates of 10−5 and 10−3 s−1. Columnar ice loaded parallel to the elongated crystal axes and perpendicular to the crystal c-axis was consistently the strongest type of ice. The strength of the columnar samples decreased significantly as the orientation of the elongated crystals approached the plane of maximum shear. Samples containing granular ice or a mixture of granular and columnar ice resulted in intermediate and low strength values. No clear relationship could be established between structure and strength for these ice types. However, in general, their strength decreased with an increase in porosity.

scholarly journals Physical and geomechanical properties of the Siwalik sandstones, Amlekhganj-Suparitar area, central Nepal Himalaya

2002 ◽  
Vol 26 ◽  
Author(s):  
Naresh Kazi Tamrakar ◽  
Shuichiro Yokota ◽  
Suresh Das Shrestha
Keyword(s):  
Compressive Strength ◽  
Uniaxial Compressive Strength ◽  
Point Load ◽  
Early Pleistocene ◽  
Dry Density ◽  
Modulus Ratio ◽  
Deep Basin ◽  
Geomechanical Properties ◽  
Central Nepal ◽  
Siwalik Group

The Siwalik Group, one of the world's largest fluvial deposits, distributed in the fore deep basin of the rising Himalayas, crops out well in Central Nepal. The group comprises of mudstones, sandstones and conglomerates ranging in age from middle-Miocene to early Pleistocene. Sandstones form the major lithology in the Siwalik Group and distributed pervasively. Forty-four samples of sandstones were tested for physical and geomechanical properties in order to create a database on Siwalik sandstones and to know the variability of these properties with respect to their stratigraphic levels.  Dry density and saturated density of sandstones are 2.10-2.63 g/cm3 and 2.22-2.66 g/cm3, respectively. Porosity is found to vary between 1.93 and 15.2%.They bear weak to strong uniaxial compressive strength (1.29-51.6 MPa), very low to high point­ load strength (0.05-4.53 MPa, measured across bedding), high deformability (secant modulus =0.03-0.98 GPa and tangent modulus = 0.06-1.09)and low modulus ratio (17.8-86.6). The Schmidt hammer hardness in sandstones ranges from 12 to 52. Variation of these properties is independent of stratigraphic level. Dry density and porosity correlate well with uniaxial compressive strength, point-load strength and modulus ratio, and bear highly significant relationships. Hence, dry density and porosity can be used for predicting strength measures for the Siwalik sandstones.

About stress reduction experiments during constant strain-rate deformation tests

2005 ◽  
Vol 96 (6) ◽  
pp. 589-594 ◽  
Author(s):  
Tomas Kruml ◽  
Olivier Coddet ◽  
Jean-Luc Martin
Keyword(s):  
Strain Rate ◽  
Stress Reduction ◽  
Constant Strain Rate ◽  
Deformation Tests
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