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

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.

Analysis of the Behavior of a Chaotic Dynamic System under Different Types of Couplings and Several free Dynamics

In this paper, we analyze how the behavior of a chaotic dynamical system changes when we couple it with another. We focus our attention on two aspects: the possibility of chaos suppression and the possibility of synchronization. We consider a Symmetric Linear Coupling and several free dynamics. For each of them we study the evolution of the coupling behavior with the coupling strength constant, defining windows of behavior. We extend the analysis to some other couplings. This is a survey paper.

Compressive Deformation Behavior of Thick Micro-Alloyed HSLA Steel Plates at Elevated Temperatures

The hot deformation behavior of a heavy micro-alloyed high-strength low-alloy (HSLA) steel plate was studied by performing compression tests at elevated temperatures. The hot compression tests were carried out at temperatures from 923 K to 1,223 K with strain rates of 0.002 s−1 and 1.0 s−1. A long plateau region appeared for the 0.002 s−1 strain rate, and this was found to be an effect of the balancing between softening and hardening during deformation. For the 1.0 s−1 strain rate, the flow stress gradually increased after the yield point. The temperature and the strain rate-dependent parameters, such as the strain hardening coefficient (n), strength constant (K), and activation energy (Q), obtained from the flow stress curves were applied to the power law of plastic deformation. The constitutive model for flow stress can be expressed as σ = (39.8 ln (Z) – 716.6) · ε(−0.00955ln(Z) + 0.4930) for the 1.0 s−1 strain rate and σ = (19.9ln (Z) – 592.3) · ε(−0.00212ln(Z) + 0.1540) for the 0.002 s−1 strain rate.

Influence of Material Properties on Hydraulic Conductivity and Strength of Aggregates Used for Pavement Base

The hydraulic conductivity and strength of several aggregates (limestone, gravel and recycled concrete) are very important for pavement base construction. To study the influence of fines content on hydraulic conductivity and strength, constant/falling head permeability and CBR tests were performed. The results show that hydraulic conductivity exponentially decreases as fines content increases. Their values were also found to vary significantly as a function of aggregate type, gradation, and density. Particle degradation of recycled concrete aggregates is higher than crushed limestone and gravel, which leads to lower hydraulic conductivity values.

Analysis of Starch Bubble Breakage during Extrusion Expansion by Finite Elements Method

Major factors that influenced the breakage of starch bubbles during extrusion expansion such as the initial bubble radium, the initial cell wall thickness, the initial cell wall temperature, the initial cell wall moisture content, the stress strength constant of starch and the changes of failure stress of bubble wall, stress of bubble wall, bubble radium, cell wall thickness, pressure different with time were investigated and the critical breaking points for each operation parameters under certain conditions were determined. The results showed that the smaller the initial bubble radium, the higher the initial cell wall thickness, and within certain range, the lower the initial temperature, the lower the initial moisture content, and the higher the stress strength constant of starch, the lower the tendency the bubble broke.

LATTICE WAVE TRANSMISSION THROUGH ONE-DIMENSIONAL DEFECTED CHAIN

By using Green's functional method, we investigated the influence of different strength constants at defected bonds and the junction's size on the transmission properties of the lattice wave in a one-dimensional chain. The heat currents of several defected chains are also calculated. The results show that correlation transmission between two defected bonds in a chain different from electron behaviors. Furthermore, for a large-size junction embedded in a chain, the transmission of high frequency phonons will disappear while having smaller strength constant in the junction than in two semi-infinity chains. On the other hand, for larger strength constant than in two semi-infinite chains, all phonons can transport through the junction with a certain transmission value, although the number of transmission peaks decreases. Finally, the lower frequency lattice waves have better transmission through a junction with a series of strength constants according to the Fibonacci sequence.

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

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.