bluuebunny/crossref_metadata_2025 huggingface dataset:
A New Oriented Perforation Strategy for Fracturing Deep and Tight Gas Reservoirs
Authors: Xia K. , Mahmood T. , Cui Y.
Published: November 2022

Hydraulic fracture initiation can be a challenging issue for fracturing deep and tight gas reservoirs, which generally requires a high breakdown pressure for clustered perforation hydraulic fracturing treatment. Oriented perforation represents a potential solution to alleviate this issue, which can not only lower breakdown pressure but also deliver a better oriented fracture geometry. In this paper, we present a new strategy to tackle this issue, which includes a framework to calculate the breakdown pressure, optimum perforation direction, and a new perforation cluster layout design. The optimum perforation direction is defined as the one, along which hydraulic fractures can be initiated with the lowest breakdown pressure for a perforation cluster. It can be used to control the perforation device rotating and fired at the right direction in subsurface. Further we present a new perforation cluster layout design, which can alleviate the near wellbore fracture tortuosity and deliver a better fracture initiation when it is aligned along the optimum perforation direction in the subsurface. The two parts of the strategy working together, fracture initiation from a perforation cluster can be achieved a lot of easy than using the conventional perforation method. This new perforation strategy can further alleviate the near wellbore fracture tortuosity, minimize fluid flow restriction and reduce pressure friction loss during hydraulic fracturing treatment. Otherwise multiple and reoriented nonplanar fractures originated from the wellbore perforation cluster likely lead to a premature screen-out, which can negatively impact fluid injection to achieve a desired stimulation performance. Hydraulic fracturing treatment in deep and tight gas reservoirs can be improved through the following actions: calculating breakdown pressure and optimum perforation direction, using new perforation cluster layout design, and aligning the perforation cluster in the optimal direction in subsurface.
Third-Order Padé Thermoelastic Constants of Solid Rocks
Authors: Yang J. , Fu L. Y.
Published: November 2022

Classical third-order thermoelastic constants are generally formulated by the theory of small-amplitude acoustic waves in cubic crystals during heat treatments. Investigating higher-order thermoelastic constants for higher temperature is a challenging task because of more undetermined constants involved. However, even at low temperatures, these Taylor-type thermoelastic constants encounter divergence in characterizing the temperature-dependent velocity changes of elastic waves in solid rocks as a complete polycrystal compound of different mineral lithologies. Therefore, we propose third-order Padé-type thermoelastic constants derived by the approximation of Padé rational function to the total strain energy. The Padé thermoelastic constants are characteristics of a reasonable theoretical prediction for acoustic velocities of solid rocks even at high temperature. The results demonstrate that the third-order Padé thermoelasticity can characterize thermally induced velocity changes more accurately than the conventional third-order Taylor thermoelasticity, and have the same accuracy for the corresponding higher-order thermoelastic model. The Padé approximation could be considered a more versatile model for describing thermal velocity changes for polycrystals and solid rocks. The physics of the Padé coefficients is relevant to the thermal expansion mismatch and thermally induced deformation of microcracks.

Introduction

Temperature significantly changes the mechanical and physical properties of rocks, which becomes importance in many fields of earth sciences and geological engineering. Temperature-induced variations in elastic properties generally present strong nonlinearity even at low temperature because of the differential thermal expansion of multimineral rocks. The classical theory of thermoelasticity is formulated on account of the Taylor power series of the Helmholtz free energy functions (Dillon, 1962). The resulting second- and third-order thermoelastic constants have been widely used for crystals, but with certain insufficiencies in representing the temperature-dependent velocity changes of elastic waves for rocks like a completely polycrystal compound of varying mineral lithologies. The investigation of higher-order thermoelastic constants could be useful for understanding the nature of nonlinear behavior in heating rocks, but involves more undetermined constants and becomes a challenging task. As a more effective alternative, this article addresses a nonlinear thermoelasticity for solid rocks relied on the Padé approximation of Helmholtz free energy functions.
Geomechanical Modelling of Borehole Breakouts and Compaction Bands in High-porosity Sandstones
Authors: Bere A. B.
Published: November 2022

Predicting the nature and extent of deformation adjacent to wellbores can be critical for successful subsurface operations. The ability to capture the onset and evolution of failure can permit more efficient operations and circumvent or minimize the effects of well-known operational issues such as wellbore instability and sand production. In this paper, the behaviour of porous sandstones is investigated through replication of experimental testing conducted by Haimson (2004). In this work the deformation near the excavated section for highly porous sandstones was documented and analyzed, with contrasting deformational styles observed that are tentatively attributed to mineral composition. The requirements for predicting these styles are discussed and presented within a novel three-field modelling framework that incorporates a sophisticated constitutive model. Application of the workflow and results for breakout and sand control studies is discussed, along with potential future extensions to the capabilities of the constitutive model.

Introduction

Instability of subsurface excavations is critical and can pose serious problems affecting the timing and success of a project. Prediction of such instabilities has long been recognised as a key factor in many industries. Understanding the failure mechanisms is vital for the optimisation of well production as instabilities affect drilling efficiency, resulting in lost circulation, breakouts, or hole closure and even in loss of the open-hole section due to stuck and damaged drill pipe (Lang et al., 2011). Nevertheless, such instabilities are useful for informing on stress directions and magnitudes (Haimson and Song, 1993). Borehole logging has been long used to estimate stress directions, based on the location of the breakouts around the well (Brudy et al., 1997; Zoback et al, 2003; Kingdon et al., 2016). In addition, several studies have suggested that the characteristics and dimensions of the breakouts, if properly measured, can also inform on the magnitudes of far-field stresses.
PFC Modelling on Natural Weak Planes of Laminated Shale and Their Influences on Tensile Fracture Propagation
Authors: Anyimah Peter Owusu , Meng Leifeng , Cheng Shizhong , Chakma Nabayan , Sheng Mao , Shahid Arshad Shehzad Ahmad
Published: November 2022

Laminated shale reserves various natural weak planes involving some bedding planes, natural fractures and mineral dykes. The obvious phenomenon of the interactions between hydraulic fractures and bedding weak planes were observed involving arrest, crossing, and diversion in previous works. Moreover, the bedding angles, cement mineral compositions of natural weak planes, and net pressure of hydraulic fracture were considered as the primary factors to determine the type of interaction. However, the rock failure modes and characterization of weak planes from micromechanics has been yet addressed. In this paper, a Particle Flow Code (PFC) model on natural weak planes of laminated shale was proposed by considering micromechanical properties including the cohesive strength, stiffness, elastic modulus, and friction angle. The PFC model was validated by the three-point bending tests on a typical laminated shale. The influence of weak plane angles, elastic modulus, and strength of weak planes on tensile fracture propagation were obtained. Their interaction types and dominant failure mode from tensile to shear were analyzed. It concludes that fractures divert in the inclined angles and low strength of natural weak planes, crossing occurs in the opposite case.

Introduction

Shale oil and gas formation normally reserves various natural weak planes involving the weak bedding planes, natural fractures and mineral dykes. It is evident that the natural weak planes affect hydraulic fracture geometry. The obvious phenomenon of the interactions between hydraulic fractures and bedding weak planes were observed involving arrest, crossing, and diversion in previous works. Moreover, the bedding angles, cement mineral compositions of natural weak planes, and net pressure of hydraulic fracture were considered as the primary factors to determine the type of interaction. However, the rock failure modes and characterization of weak planes from micromechanics has been yet addressed.
Geomechanical Approach of Induced Seismicity using Cohesive Zone Elements
Authors: Pouya Amade , Deptulski Rafael , Ahn Kyeung Hye , Rebel Estelle , Boisson Michel
Published: November 2022

This study aims to demonstrate the capability to account for seismic and aseismic responses due to fault reactivation using a cohesive zone model in a Finite Element framework. We adopt an elastic-damage-plastic formulation to predict the fault reactivation while considering unilateral effects observed in geomaterials. In a conceptual 2D problem representing two layers of rock separated by an existing fault, we apply displacement-driven and stress-driven shear loading to provide a first characterization of the instabilities and energy dissipation. Qualitative and quantitative analyses of the dissipative process are provided through the shear stress field and the evolution of the shear stress, displacement, and energy balance. We obtain through the present model the total of dissipated energy thanks to the energy balance. Also, while the elastic energy variation can be positive or negative depending on the type of boundary conditions (stress-driven or displacement-driven), the radiated elastic energy is always positive during seismic events. It is so a good candidate to determine the seismic moment.

Introduction

Instabilities in faulted mechanical systems are at the heart of numerous recent studies related to micro-seismic phenomena induced by human activities. Increasing interest to assess the potential for activation of existing faults in geologic sites has been observed in different applications such as CO2 sequestration (Nguyen et al., 2019), waste-water disposal (Walsh and Zoback, 2015), recovery of hydrocarbons (Davies et al., 2013), geothermal facilities (Majer et al., 2007) and nuclear waste disposal (Urpi et al., 2019). Several previous studies showed that both natural and anthropogenic factors determine fault reactivation phenomena (McGarr, 2014; Segall and Lu, 2015; Fan et al., 2016). The lack of long-term historical monitoring of seismic activity in candidate sites to host in-deep geological applications is an important drawback to assess the risks through empirical models. For this reason, numerical models were mainly used to predict fault reactivation response (e.g. finite element method (Haddad and Eichhubl, 2020), discrete element method (Langhi et al., 2010), finite difference method (Lee et al., 2013)).
Discrete Element Study on Rock Failure Mechanism by Shaped PDC Cutter Under Formation Conditions with In-Situ Stress and Temperature
Authors: Yao Jianlin , Liu Bin , Zhu Haiyan
Published: November 2022

Polycrystalline diamond compact (PDC) bits have been widely used in drilling process due to their high efficiency and great reliability. To investigate rock failure mechanism and further improve the performance of PDC bits, a series of single cutter tests have been conducted in previous studies. However, most of them were performed under atmosphere conditions. That is, the effects of temperature and in-situ stress were ignored due to the limitation of experimental facility, which restricts the developing of novel bits. To solve the aforementioned problem and deeply study the rock failure mechanism of PDC bits, numerical simulation researches were conducted based on the discrete element method (DEM). Firstly, a numerical triaxial test model was established to calibrate microscopic parameters of rocks that collected from Sichuan basin Ziliujing formation. Then, boundary conditions such as bottom hole temperature, surrounding pressure and hydrostatic pressure were loaded to rocks, thus simulating the actual bottom conditions. Based on this model, rock failure characteristics under the impacts of cutters with different shapes (cylindrical cutter, triangular prismatic cutter, ridge cutter, V-cutter) and different cutting parameters (cutting depth, back rake angles, etc) were studied. The results indicate that the triangular prismatic cutter has the greatest rock-breaking efficiency in our studies, followed by V-cutter and cylinder cutter. The triangular prismatic cutter can obtain the highest rock cutting efficiency when the cutting depth, back rake angles and the diameter of cutter are equal to 2 mm, 20 degrees and 16 mm respectively. The present study provides an in-depth understanding on rock failure mechanism and a basis for the development of efficient PDC bits.

Introduction

The Sichuan Basin is rich in natural gas resources and is one of the major gas production regions in China. However, the corresponding geological conditions are complex. Under the impacts of high temperature and high pressure at the bottom hole, the formation rock becomes highly abrasive and poorly drillable, resulting in a significant decrease in the drilling speed. To improve the drilling efficiency and enhance the performance of PDC bits, it is necessary to carry out studies on cutting and investigate rock failure mechanisms under the actual bottom hole temperature and pressure.
Selection of Sand Control Completion Techniques Using Machine Learning
Authors: Laoufi H. , Megherbi Z. , Zeraibi N. , Merzoug A. , Ladmia A.
Published: November 2022

Sand production is one of the major problems in many oil and gas assets around the world. Uncontrollable sand production can affect hydrocarbon recovery and increase operational costs. This paper aims to develop a classification approach to suggest the optimal sand control method using machine learning algorithms. Four different models have been used, namely K-Nearest Neighbors, Support Vector Machine, Random Forest and Decision Tree. After extensive exploratory data analysis, nine parameters were included in the model: Sorting coefficient D10/D95, Mass fraction smaller than 44 micron, Well deviation angle through the pay zone, Pay-zone true vertical thickness, Bottom hole pressure, Maximum oil rate, Maximum gas rate, Permeability, Well type. By comparing the different models in this study Random Forest classifier achieved the highest evaluation metrics: f1-score of 0.9568, precision of 0.9580, and recall of 0.9568 respectively. These results combined with the confusion matrix to assess the model performance have shown that up to a certain level machine learning methods can ensure the adequate completion for the candidate well. The proposed work turns out to be a potential approach that rises to the level of a decision support tool and thus can help engineers set the right completion option.

Introduction

Sand production has always been one of the major concerns for the oil and gas industry. It is the result of the migration of failed sand grains because of the drag forces caused by fluids flow from an unconsolidated reservoir. Generally, this phenomenon leads to technical problems such as erosion of downhole equipment and surface facilities, production loss, well access obstruction, and economic effects represented by the additional cost of sand disposal. Sand control is, therefore, necessary to mitigate the effect of sand production on hydrocarbon wells. Judhan (2016) defined sand control as all the techniques that allow hydrocarbons production without sand grains production in the wellbore. Sand control consist of two methods: passive and active. Passive sand control methods are generally used to reduce sand during the first stage of production when the sanding rate is low, as this latter gradually increase, active sand control will be required.
Reducing Uncertainty in the Pore Pressure Profile of the Most Important Unconventional Argentinian Play: Vaca Muerta
Authors: Rodríguez L. G. , Moreno Cardenas J. P. , Mónaco A. , María S. , Osorio Gallego J. G. , Alvarez J. B. Angel
Published: November 2022

In the centre of the Neuquén Basin, the Vaca Muerta formation is a 400 m thick over-pressurized shale characterized by presenting a 100% marl lithology with Total Organic Carbon (TOC) contents that can exceed 10 wt.%. This condition causes important logs distortion since it reduces their dependence on the rock matrix, being even almost impossible to determine facial changes by conventional mudloging visual techniques.

This work is focused in La Calera block, an unconventional asset operated by Pluspetrol S.A (in partnership with YPF S.A.) where a theoretical and operational crosschecked methodology was established as to reduce the Vaca Muerta pore pressure uncertainty.

Data from LCa.x-3001, the first unconventional exploration well in the block, was used to calibrate a Bowers’ pore pressure model, including lithology descriptions, operational and drilling events, and MPD tests. In addition, kerogen corrected synthetic sonic logs were incorporated in the pore pressure estimation workflow as a more accurate input, avoiding logs distortion.

The pore pressure model built for the Vaca Muerta formation show highly precise results, being implemented to date on 40 unconventional wells, with optimal performance, neither well loss nor Geological/Geomechanical NPTs.

Finally, X-Ray Fluorescence (XRF) from a Vaca Muerta horizontal well was used as a crosschecking input since it acts as an accurate indicator of facial changes and paleoenvironmental variations, existing high correlation between some elemental concentrations and the pore pressure variations.

Introduction

On the west part of Argentina, the Neuquén basin has been producing oil and gas from several proved conventional plays for more than 100 years (Carbone et al., 2020). In the last decade, Vaca Muerta has become a world-class example of an unconventional reservoir, being by its own the Argentina's most important energy source, with estimated resources around 20 to 40 Bbbl (Billion barrels) of oil (Gutiérrez Schmidt et al., 2014) and 150 to 250 TCF (Trillion Cubic Feet) of gas. Considering the country current consumption, it can supply its energy demands for the next 100 years.
3D Geomechanical Reservoir Modelling in Faulted Reservoirs
Authors: Markou N. , Papanastasiou P.
Published: November 2022

In this study, we present a three-dimensional (3D) geomechanical reservoir model for a faulted and compartmentalized reservoir in the Eastern Mediterranean. A series of alternative production scenarios performed using a simulation model that accounts for consolidation and plasticity deformation of the rocks. Plastic yielding is mainly developed in fault slip zones of narrow extent whereas it appears that there is low risk of plastic behavior in the main reservoir. The slip conditions become complex in the fault contact surfaces where local areas close to fault connections are more pronounced to slip creating localized areas of smaller faulted zones. Displacement magnitudes, are controlled by the structural boundary conditions and the geometrical shape of each fault block. Overall, the higher displacements develop in the near fault region while in the remote from the fault area the vertical displacement is nearly constant as it is clearly governed by the reservoir depletion. Furthermore, changes of normalized permeability can be drawn in the 3D space providing additional insights of heterogeneous distribution.

Introduction

Petroleum geomechanics become important in reservoirs highly impacted by faults mechanics and overpressure zones. An operator has to well define the fault structural geometry of the field and assess early in the producing life of a reservoir whether production will be affected by the presence of naturally occurring fractures though some faults and fractures cannot be identified even at the early stages of a field production. Reservoir depletion increases the stress carried by the load-bearing grain frame of the reservoir rock. Stress analysis can be extended to identify rock failure conditions that can lead to the creation of new faulted systems in the subsurface formations. Geomechanics play an important role in identifying the stress conditions in a faulted reservoir system and the potential of slip activation of an existing fault. Extensive accounts on the importance of reservoir geomechanics can be found in the classical books of Fjaer et al., (2008) and Zoback, (2010). Finite element analysis can be used to simulate the tectonic movement to match borehole observations (Plumb et al., 1998).
A Multi-Physics Fields Coupling Model for Supercritical CO2 Seepage in Shale Formation
Authors: Bai Bing , Yao Bowen , Chen Mian , Jin Yan , Liu Di , Zhang Yu , Sun Mingwei
Published: November 2022

Supercritical carbon dioxide (ScCO2) can protect shale formation from hydration damage. When ScCO2 is utilized to develop shale oil and gas resources, it is necessary to establish the multi-physics fields coupling model to describe ScCO2 seepage in shale formation. The multi-physics model describing water-based fluid seepage is not capable explaining ScCO2 flow because of a great variation in physical properties of ScCO2 with pressure and temperature. In this study, a thermal–hydro–mechanical coupling model is constructed to describe ScCO2 seepage based on the transport and thermodynamic properties of CO2, combined with the effect of ScCO2 on mechanical properties of shale. The finite element method is used to solve the distribution of formation temperature, pore pressure and stress with time and position. The results show that compared with water seepage, the variation of formation temperature is greater, the pore pressure is lower, the stress difference near the wellbore in the direction of minimum in-situ stress is bigger, and the tangential stress in the direction of maximum in-situ stress is lower when adsorption-induced strain is neglected. The radial stress and tangential stress decrease with increasing time. This research can provide theoretical basis for wellbore stability analysis and fracturing evaluation when using ScCO2 as the drilling fluid and fracturing fluid, separately.

Introduction

As one of the unconventional resources, shale oil and gas resource is an important alternative to widely used conventional resources, which is attracting worldwide attention (Jin and Chen, 2019). Currently, the commercial exploitation technologies are massive hydraulic fracturing and horizontal drilling for developing shale gas resource. However, shale formation contains clay mineral, the hydration damage will be produced when clay mineral meets water. In the process of drilling or fracturing with water–based fluid, wellbore collapse or poor fracturing stimulation may be encountered due to hydration swelling. Meanwhile, hydraulic fracturing operation will consume a large amount of water resource, which limits the application of hydraulic fracturing in water–lacking area. In order to avoid formation damage and conserve water resource, the technology of drilling or fracturing with supercritical CO2 is proposed (Wang et al., 2018; Wen et al., 2020).
Intelligent Evaluation on Drillability of Shale Gas Formation in N2 Region of Changning Field in Sichuan, Southwest China
Authors: Zheng Haiyan , Lin Botao
Published: November 2022

Formation drillability evaluation plays an essential role in the exploitation of shale gas reservoirs. Currently, the common methods for evaluating formation drillability mainly include experimental methods, such as scratch tests and micro-drilling tests, and regression analysis. However, the applications of experimental methods and regression analysis cannot reasonably assess drillability due to a lack of well-core information and describe the strong heterogeneity of shale formations. In this study, a data-driven model based on the constrained K-means (CKM) method was proposed to evaluate shale formation drillability, which can solve the problems related to core sample limitation and heterogeneity of the formation. First, a regular evaluation model was built against the conventional cluster methods, such as K-means, DBSCAN, and GMM. Secondly, the closed pairwise constraints were generated based on domain knowledge. Finally, the evaluation model was established by applying pairwise constraints to the K-means clustering generation process. The value of normalized mutual information (NMI) ranges from 0.86 to 0.93 based on the proposed model, which has been improved by 50% over the conventional cluster methods. The results show that the drillability index of the Longmaxi Formation ranges from 5 to 7, whereas the index value of the Wufeng Formation averages at 8-9, which demonstrates that the Wufeng Formation is more difficult to drill compared to the Longmaxi Formation. The drilling practices in the field demonstrated that the actual drilling rate of the Wufeng Formation was lower than that of the Longmaxi Formation, which is in accord with the model predictions.

Introduction

As an essential unconventional oil and gas resource, shale gas reservoirs have enormous extraction and economic value. Shale drillability characterizes the resistance of shale to drill, which is a crucial type of information requested for the bit type selection, borehole track design (Chen, 2021; White, 1969), and drilling implementation (White, 1969; Chen et al., 2017). Inaccurate evaluation of rock drillability has resulted in a slow drilling rate and severe drill bit wear, leading to procrastination in construction and significant financial losses. Many investigators considered that geomechanical properties (rock type, rock mass jointing), machine parameters (drilling machine type, bit pressure, rotary speed), and operational process determine the drillability of rock (Saeidi et al., 2013; Yetkin et al., 2016). The methods toward getting drillability are majorly implemented in two ways: indoor rock core experimental and numerical model (Gan et al., 2021).
Log CCS vs App CCS
Authors: Etaje D. C. , Hulog R. , Trivadi A. , Le A. , Shor R.
Published: November 2022

Confined Compressive Strength (CCS) offers a more accurate indication of rock hardness and rock formation drillability, which is useful in optimizing the drilling operation. PhiDrillSim is a machine learning app that predicts the CCS using neural network techniques. The goal is to predict the Confined compressive Strength using the Neural network technique based on the operation dataset, which will be used to train the neural network model. A specific operation dataset will be provided for the training of the model in the app. It will predict the CCS model of the rock formation and compare it with the actual CCS collected. Preliminary results show that the accuracy of the predicted CCS values is consistent with the CCS calculations using the log data method. There are various methods of calculating the CCS of the formation, with varying degrees of cost and difficulty. Furthermore, the accuracy of CCS measurements directly affects the drilling cost of operations, affecting drill-string durability and operational time. This paper explores the accuracy of the PhiDrillSim App in comparison with a log data method in calculating and predicting the formation of CCS.

CCS Description

Rock strength is essential in the drilling process. Confined Compressive Strength (CCS) is a geomechanical rock property that indicates the rock strength when confined to some medium. (Fabian, 1994). Since UCS is widely used, the classification of rock formations based on UCS is readily available. Moreover, the estimation of rock strength classification is based on UCS. CCS then will be related to UCS using the equation proposed by Caicedo et al., 2005.
Phytochemical constituent and oxidative potencies of acetone, methanol and aqueous leaf extracts of Acalypha Wilkesiana grown at the Kaura Namoda plant nursery
Authors: Bamidele Hassan , Abass Ahmed , Hussaina Tanko
Published: November 2022

As a result of increased interest in the production of plant-based drugs for the treatment of many diseases has become a significant reason why people have become more coversant in the use of traditional medicine for the treatment of mild and serious illness. Due to increase in the thrust for the production of plant-based drugs, this present study was carried out to compare the phytochemical constituents and antioxidant potencies of acetone, methanol and aqueous leaf extracts of Acalypha wilkesiana collected from Kaura Namoda Botanical Garden in Zamfara State-Nigeria. The antioxidant activities was evaluated using various assays; The total phenolic content of aqueous, methanol and acetone leaf extract were 15.58 0.66 mg GAE/g, 14.10 2.17 mg GAE/g and 8.70 0.01 mg GAE/g respectively. Total flavonol contents; 207.10 11.53 mg QE/g, 196.08 5.53 mg QE/g and 112.04 8.27 mg QE/g respectively. Total flavonoid contents; 240.99 9.50 mg QE/g, 252.52 3.73 mg QE/g and 123.88 5.58 mg QE/g respectively. FRAP values were 679.14 0.45 mmol/g, 611.90 7.09 mmol/g and 292.07 11.38mmol/g respectively. ABTS activity of aqueous, methanol and acetone leaf extract were 24.30 5.86 mg AAE/g, 14.49 1.02 mg AAE/g and 7.00 0.57 mg AAE/g respectively, methanol leaf extract had the highest percentage DPPH Inhibition value of 42.64 5.13, followed by aqueous (31.77 4.08) at 0.25mg/ml while aqueous had the highest (52.63 0.67), followed by methanol extract (44.80 2.80) at 0.50mg/ml. Aqueous extract had the highest percentage inhibition of Nitric Oxide with a value of 59.74 1.30, followed by methanol extract (46.11 2.54) at 0.25mg/ml. inhibition for aqueous was also highest at 0.5 mg/ml. Aqueous extract had the highest percentage lipid peroxidation inhibition value of 22.66 2.93, followed by methanol leaf extract with the value of 18.89 0.80 while at 0.50mg/ml methanol leaf extract had the highest percentage inhibition of lipid peroxidation (39.42 3.10), followed by aqueous leaf extract with the value of 31.48 1.61. The results showed that aqueous and methanol leaf extract of Acalypha wilkesiana displayed potent antioxidant effects with the aqueous having an edge. This present study therefore supports the view that Acalypha wilkesiana can be used in the management of oxidative stress and other related diseases.
Some differences in turnover kinetics of penams and cephems catalyzed by classes A and C ?-lactamases
Authors: Adediran Suara , Praff Rex
Published: November 2022

The differences in the kinetic mechanism of catalysis of class A and class C ?-lactamases are shown by the manner by which these enzymes catalyze the hydrolyses of the penicillins and the cephalosporins. The hydrolysis of cephalosporins that are good substrates of the class C P99 ?-lactamase, where deacylation of an acyl-enzyme intermediate is rate-determining, has been shown to involve a free enzyme isoform (Adediran et al, 2021). We describe here how reconversion of this isoform to the native enzyme is accelerated by bases (e.g. imidazole) and salts (e. g. sodium chloride). The hydrolysis of penicillins by the P99 enzyme, where deacylation is also rate-determining, is not affected by imidazole and sodium chloride, a result that suggests that an enzyme isoform does not accumulate as an intermediate in turnover of this class of substrate. In support of these conclusions, solvent deuterium kinetic isotope effects on kcat values were changed by the presence of imidazole for turnover of cephalothin by the P99 enzyme but unaffected for benzylpenicillin turnover. The hydrolyses of cephalosporins and penicillins by the class A TEM-2 ?-lactamase were not affected by imidazole and sodium chloride and thus also may not involve an accumulating free enzyme isoform. Solvent deuterium kinetic isotope effects and proton inventories on the class A PC1 and P99 ?-lactamase-catalyzed hydrolyses of benzylpenicillin at saturating concentrations showed the deacylation transition states of these two classes of enzymes to be different with respect to proton motion.
ORIGINAL RESEARCH ARTICLE: Antioxidant capacity and antibacterial activity of some phyto-spices against some bacterial isolates of foods origin
Authors: Ado Aliyu , Ahmed Ismaila , Umar Sadisu , Lambu Zakari , Haruna Musa , Adamu Sabo , Shehu Adamu , Mohammed Yasir , Ahmed Usman , Babaji Haruna
Published: November 2022

Spices that are mostly of plant origin are used in the preparation of almost all processed food to enhance palatability, tastiness, sweetness, and its overall acceptability, without taking into consideration of its medicinal values. The study was conducted to determine the antioxidant capacity and antibacterial activity of the extracts ofAllium sativum,Syzygium aromaticum, andZingiber officinale against some bacterial isolates of foods origin including Bacillus cereus, Escherichia coli,Salmonella typhi,Shigella dysentriae,andStaphylococcus aureus. Bacterial isolates of food origin were collected from the laboratory unit of the Department of Microbiology, Kano University of Science and Technology, Wudil. Antioxidant capacity of the extracts used was determined using 2,2-diphenylpicrylhydrazyl (DPPH) assay while agar disc diffusion techniques were used in the determination of the antibacterial activity. Results show that extracts of the spices exhibited a strong antioxidants capacity that ranges from 89.5% to 97.5% at high concentrations of the extracts with methanol extracts being the most active. Methanolic extracts shows zone of inhibition ranging from 16.45mm to 5.26mm while that of aqueous extracts were 10.32mm to 4.32mm. Meanwhile isolates of E. coli and S. aureus were the most sensitive with 16.45 and 15.32. This study concluded that the antibacterial effect of methanolic extract of Allium sativum extract was stronger in comparison, followed by Syzygium aromaticum and Zingiber officinale against five test bacteria isolated of food origin. Therefore, this study revealed that spices produced using Allium sativum, Syzygium aromaticum and Zingiber officinale have an antibacterial property and can be used for food preservation.
Prelim
Authors: Journal System
Published: November 2022

Prelim
Editorial
Authors: Unterhalter Elaine , Allais Stephanie
Published: November 2022

This special issue of the Journal of Higher Education in Africa examines global debates concerned with higher education as a public good, in the context of the lived realities, political and economic constraints as well as opportunities in contemporary Africa. While the articles draw on research and analysis conducted from 2017 to 2019, and were completed before the seismic changes associated with the COVID pandemic, the framing ideas regarding a contextualised understanding of the relationship between higher education and the public good are highly resonant with the processes of the COVID conjuncture. In this Editorial, we distil the key ideas that have shaped this collection of works, describe the research study that connected them, and draw out some of the implications of the findings for thinking about higher education and the public good in the light of the major disruptions of 2020–2021 for higher education in many African countries.
Theorising the Relationship of Higher Education and the Public Good in Africa
Authors: Unterhalter Elaine , Allais Stephanie
Published: November 2022

This article explores conceptualisations of the public good role of higher education and considers their application to higher education in African countries. The article starts by delineating a number of different ways in which higher education and the public good are linked, grouping these together as instrumental and intrinsic versions of the relationship between higher education and the public good. In considering the connections and disjunctures between these two formulations and the way studies on higher education in contemporary Africa have engaged with this debate, we argue for discussing the importance of processes that link or have the potential to connect instrumental and intrinsic visions of higher education and the public good. We discuss these, drawing on a set of framing ideas associated with conditions of possibility and forms of social contract, which, we argue, express a less abstract form of this discussion, more responsive to the complexities of context associ ted with actual higher education institutions and the systems they work in.
The Nigerian University System, Corruption and Erosion of the Public Good
Authors: Ibrahim Jibrin
Published: November 2022

This article examines the nature, causes and implications of the decline of the public good within Nigeria’s university system over the past three decades. In that period, there has been a significant shortfall in the finances of the university system from federal and state governments, creating the material basis for its inability to recruit, retain and manage quality academic and non-academic staff. Essentially, it highlights how the self-interest of academics, expressed through their powerful union, the Academic Staff Union of Universities (ASUU), has engaged in a struggle with government to improve the remuneration of academics rather than the quality of academic services. At the same time, corruption has sapped the system and led to significant levels of exploitation of students, in general, and the sexual harassment of female students. The public good within the university system is rooted in the constitutional provision that directs governments to provide quality and free education at all levels. But governments have failed in this mission, and families have had to pay for their children’s quality education. This outcome has created massive inequality, with only the wealthy able to ensure quality education for their children, usually abroad. This has weakened the commitment of those in authority to push for the return of quality education at the national level. The result is that the Nigerian state appears to have provoked a class struggle in which poorly educated youth and the lump n classes are marginalised and excluded from the ladder of social mobility.
The Other Side of the Story: The Costs of Being a Public Good Academic
Authors: Ndaba Mthobisi
Published: November 2022

This article argues that the relationship between higher education and the public good should be understood not only from a macro-level point of view, in terms of how higher education systems and institutions contribute to the public good. It should also be understood from a micro-level point of view. Drawing on a qualitative study of the role of academics in higher education’s contribution to the public good, this article demonstrates that micro-level- focused research allows for a deeper and richer insight into the intricacies of this relationship. It does this from the vantage point of the costs of being a public good academic, as recounted by fifteen academics from two universities in South Africa. The perceptions of these academics indicate that the costs of producing public good at universities in South Africa are more than just the financial costs covered by student fees, government subsidies and donor funding. They include relational, psychological and career-related costs, as well as those related to personal resources and identity contingencies, which academics must deal with in advancing the public good. This article concludes that further micro-level-focused research can uncover more nuanced aspects of the complex relationship between higher education and the public good.
Researching the Public Good: Reflections on Experiences of Doing Research on Higher Education and he Public Good in South Africa
Authors: Ngcwangu Siphelo
Published: November 2022

This article discusses the experience of doing research on higher education and the public good in South Africa within a bigger project titled ‘Higher Education, Inequalities and the Public Good: Perspectives from Four African Countries’. Qualitative data was collected through key informant interviews by a team of eight researchers who concentrated on specific groups of stakeholders as per the themes of the research. The aim of the interviews was to understand the perceptions of stakeholders both within and outside the university system on the public good role of university education in South Africa. This article focuses on three key issues: locating the research in the context of South Africa’s democratic transition, methodological challenges and pitfalls, tensions, and missing questions/silences. We were doing our research in the aftermath of the student protests of 2015 and 2016, and many of the stakeholders we interviewed were actively involved in making sense of the issues that the students raised. The research team formulated the ‘DNA’ framework for analysing qualitative data from the stakeholders, which refers to the descriptive, normative and analytic aspects of the data that pointed to a unique way in which we could frame our findings. By reflecting on the research process and our positionality in it, the paper contributes to the general field of qualitative research studies, bringing in the dynamics of conducting research in large-scale cross-national projects.
Θέατρο στη φυλακή: Παράθυρο στην κοινωνία
Authors: Παυλίδης Στυλιανός
Published: November 2022

«Το ελάχιστο τρεμούλιασμα πόνου στο πιο ασήμαντο άτομο ακόμα, κάνει μία τεράστια σχισμή στην κουρτίνα της δημιουργίας». Ίσως με αυτή τη σκέψη ο Μπύχνερ οδηγήθηκε να γράψει το «Βόυτσεκ» ή μήπως με την άλλη που χαρακτήριζε την άποψη του για την αθλιότητα της παραγωγικότητας στη βιομηχανική κοινωνία; «Η πρώτη ύλη της βιομηχανικής κοινωνίας, είναι η ανθρώπινη σάρκα». Μπορεί να είναι και οι δύο μαζί ή και όλες οι άλλες που προκαλούν και ξεσηκώνουν τη βαθιά, τρυφερή και ουμανιστική σκέψη του νεαρού δόκτορα της ιατρικής και των φυσικών επιστημών παρασέρνοντάς τον σε ένα στρόβιλο αντιδράσεων ενάντια στην καταπιεστική εξουσία και την κοινωνική εξαθλίωση της εποχής. Έτσι το 1834 (!), σε ηλικία μόλις 19 ετών ιδρύει την πρώτη λέσχη για τα ανθρώπινα δικαιώματα και λίγο πριν πεθάνει, στα 23 του χρόνια, γράφει το αριστούργημα «Βόυτσεκ», θεμέλιο λίθο του σύγχρονου θεάτρου.
Μακροχρόνιες Επιδράσεις της Διάρκειας και της Έντασης της Θεραπείας σε Χρήστες Αλκοόλ χωρίς Προηγούμενη Θεραπευτική Εμπειρία
Authors: Moos Rudolf H. , Moos Bernice S.
Published: November 2022

Στόχοι: Αυτή η μελέτη εξέτασε την επιρροή της διάρκειας και της έντασης της πρώτης επαφής με τη θεραπεία σε άτομα με διαταραχές από τη χρήση αλκοόλ που δεν είχαν προηγούμενη εμπειρία θεραπείας όσον αφορά τα βραχυπρόθεσμα και μακροπρόθεσμα αποτελέσματα και την επίδραση στα αποτελέσματα από την επιπρόσθετη και καθυστερημένη θεραπεία. Σχεδιασμός και συμμετέχοντες: Ένα δείγμα ατόμων με εξάρτηση από το αλκοόλ (Ν= 473) από κέντρα ενημέρωσης και παραπομπής και από μονάδες αποτοξίνωσης μελετήθηκε στην αρχή και στον 1ο χρόνο, στα 3 χρόνια, και στα 8 χρόνια μετά τη θεραπεία. Μετρήσεις: Σε κάθε σημείο επαφών, οι συμμετέχοντες συμπλήρωσαν ένα ερωτηματολόγιο που αξιολογούσε τη χρησιμότητα της θεραπείας από την τελευταία αξιολόγηση και τα προβλήματα αλκοόλ, τα τρέχοντα ψυχολογικά και κοινωνικά τους προβλήματα. Συμπεράσματα: Σε σύγκριση με τα άτομα που δεν δέχτηκαν καθόλου θεραπεία, τα άτομα που ξεκίνησαν θεραπεία σχετικά σύντομα και έλαβαν μακρύτερης διάρκειας θεραπεία είχαν καλύτερα βραχυπρόθεσμα και μακροπρόθεσμα αποτελέσματα όσον αφορά τα προβλήματα με το αλκοόλ και καλύτερα βραχυπρόθεσμα αποτελέσματα όσον αφορά την κοινωνική λειτουργικότητα. Τα άτομα που έλαβαν μακρύτερης διάρκειας επιπρόσθετη θεραπεία είχαν καλύτερα αποτελέσματα όσον αφορά προβλήματα με το αλκοόλ από τα άτομα που δεν έλαβαν καμία επιπρόσθετη θεραπεία. Ωστόσο για τα άτομα που καθυστέρησαν την είσοδο στη θεραπεία, η διάρκεια της θεραπείας δεν συνδέθηκε με τα αποτελέσματα της θεραπείας. Γενικά, η ένταση της θεραπείας δεν συνδέθηκε με καλύτερα αποτελέσματα. Συμπεράσματα: Η γρήγορη είσοδος και η διάρκεια της θεραπείας για τις διαταραχές από τη χρήση αλκοόλ μπορεί να παίζουν σημαντικότερο ρόλο από την ένταση της θεραπείας. Αυτοί που παρέχουν θεραπεία ίσως πρέπει να δομήσουν τα προγράμματά τους δίνοντας έμφαση στη συνοχή, κι όχι στην ένταση της φροντίδας.
Μέτρηση της προβληματικής ενασχόλησης των εφήβων με τα ηλεκτρονικά παιχνίδια
Authors: Tejeiro Salguero Ricardo A. , Bersabι Morαn Rosa M.
Published: November 2022

Στόχοι: Ορισμένοι ερευνητές υποστηρίζουν πως για κάποιους ανθρώπους η ενασχόληση με τα ηλεκτρονικά παιχνίδια αποτελεί εξαρτητική συμπεριφορά που παρουσιάζει ομοιότητες με την τοξικοεξάρτηση. Στόχος μας ήταν να σχεδιάσουμε και να κατοχυρώσουμε μια κλίμακα μέτρησης των προβλημάτων που σχετίζονται με την εμφανώς εξαρτητική χρήση με όλα τα είδη ηλεκτρονικών παιχνιδιών, και με όλα τα διαφορετικά συστήματα ηλεκτρονικών παιχνιδιών, καθώς, επί του παρόντος, δεν υπάρχει εργαλείο που να μπορεί να χρησιμοποιηθεί γι’ αυτό το σκοπό. Σχεδιασμός: Αναθεωρήσαμε τα κριτήρια του DSM-IV (APA, 1994) για την τοξικοεξάρτηση και τον παθολογικό «τζόγο», και συμβουλευτήκαμε τη βιβλιογραφία για τις εξαρτήσεις στοχεύοντας στη δημιουργία μιας σύντομης κλίμακας Προβληματικής Ενασχόλησης με τα Ηλεκτρονικά Παιχνίδια, (PVP·Problem Video Game Playing), η οποία θα μπορούσε να εφαρμοστεί εύκολα και γρήγορα. Συμμετέχοντες: Η κλίμακα εφαρμόστηκε σε 223 εφήβους ηλικίας 13-18 ετών στην Ισπανία,. Ευρήματα: Η ψυχομετρική ανάλυση έδειξε πως η Προβληματική Ενασχόληση με τα Ηλεκτρονικά Παιχνίδια, (PVP) δείχνει να είναι μονοδιάστατη και έχει αποδεκτή εσωτερική συνοχή (Cronbach’s alpha) στο .69. Η μορφή των σχέσεων μεταξύ στις τιμές της κλίμακας και στους εναλλακτικούς τρόπους μέτρησης της προβληματικής ενασχόλησης με τα ηλεκτρονικά παιχνίδια υποστηρίζει την αξιοπιστία του θεωρητικού μοντέλου (οι υψηλότερες τιμές στην κλίμακα σχετίζονταν με μεγαλύτερη συχνότητα ενασχόλησης με τα παιχνίδια, με τη μέση και τη μεγαλύτερη διάρκεια ενασχόλησης κάθε φορά, με την αντίληψη του εφήβου και των γονιών του σχετικά με την υπερβολική ενασχόληση και με τη βαθμολογία στην κλίμακα Σοβαρότητας της Εξάρτησης). Συμπεράσματα: Τα αποτελέσματά μας επιβεβαιώνουν πως η υπερβολική χρήση των ηλεκτρονικών παιχνιδιών σχετίζεται με έναν αριθμό προβλημάτων που παρουσιάζουν ομοιότητες με το σύνδρομο εξάρτησης και η κλίμακα Προβληματικής Ενασχόλησης με τα Ηλεκτρονικά Παιχνίδια δείχνει να είναι ένα χρήσιμο εργαλείο για τη μέτρηση τέτοιων προβλημάτων. Λέξεις κλειδιά: ηλεκτρονικά παιχνίδια, εξάρτηση, εθισμός, εφηβεία, στάθμιση κλίμακας