bluuebunny/crossref_metadata_2025 huggingface dataset:
Effekt der „low-dose PDT“ auf die choriokapilläre Perfusion bei cCRCS
Authors: Reifeltshammer E. , Feucht N. , Lohmann C. P. , Maier M.
Published: December 2021

Hintergrund

Bei Patienten mit chronischer Chorioretinopathia centralis serosa (cCRCS) soll die „low-dose photodynamische Therapie“ (PDT) über eine kurzfristige choriokapilläre Minderperfusion zu einem langfristigen vaskulären Umbau mit konsekutiver Reduktion der vaskulären Hyperpermeabilität und Leckage führen. Ob sich die verminderte Perfusion gänzlich normalisiert, bleibt jedoch ungeklärt. Hauptziel der retrospektiv angelegten Studie war es, das choriokapilläre Flusssignal nach „low-dose PDT“ mittels optischer Kohärenztomographie-Angiographie (OCT‑A) zu analysieren.

Patienten und Methoden

Eingeschlossen wurden 19 im Rahmen der „low-dose PDT“ belichtete Areale an 16 Augen. Neben der Erhebung von Visus und Metamorphopsien wurden ein „enhanced depth imaging-OCT“ (EDI-OCT) und eine OCT-Angiographie mit Zentrierung auf das bei der „low-dose PDT“ belichtete Areal angefertigt. Im Rahmen der vorliegenden Studie wurden das choriokapilläre Flusssignal sowie die chorioidale Dicke innerhalb eines genormten Bezirks sowohl im Bereich der PDT-Applikation als auch in einem unbeleuchteten Referenzareal in direkter Nähe mit gleicher Exzentrizität in Bezug auf die Fovea centralis retrospektiv ausgewertet.

Ergebnisse

Es konnten im Mittel eine Abnahme des choriokapillären Flusssignals um 33 % (p < 0,001) im belichteten Areal gegenüber dem Referenzareal sowie eine im Durchschnitt um 71 µm (p = 0,001) verminderte Aderhautdicke im Vergleich zum Referenzareal gezeigt werden; 7 von 10 Patienten beklagten trotz „low-dose PDT“ langfristig Metamorphopsien, jedoch ergab sich durch die Therapie bei fast der Hälfte der Patienten eine Visusverbesserung.

Schlussfolgerungen

Durch die OCT-Angiographie konnte gezeigt werden, dass die „low-dose PDT“ im Bereich der Choriokapillaris ein vermindertes Blutflusssignal zurücklässt und somit das vaskuläre Remodelling die thrombosebedingte Hypoperfusion nicht gänzlich kompensiert.
Submergence of the filamentous Zygnematophyceae Mougeotia induces differential gene expression patterns associated with core metabolism and photosynthesis
Authors: Fürst-Jansen Janine M.R. , de Vries Sophie , Lorenz Maike , von Schwartzenberg Klaus , Archibald John M. , de Vries Jan
Published: December 2021

The streptophyte algal class Zygnematophyceae is the closest algal sister lineage to land plants. In nature, Zygnematophyceae can grow in both terrestrial and freshwater habitats and how they do this is an important unanswered question. Here, we studied what happens to the zygnematophyceaen alga Mougeotia sp., which usually occurs in permanent and temporary freshwater bodies, when it is shifted to liquid growth conditions after growth on a solid substrate. Using global differential gene expression profiling, we identified changes in the core metabolism of the organism interlinked with photosynthesis; the latter went hand in hand with measurable impact on the photophysiology as assessed via pulse amplitude modulation (PAM) fluorometry. Our data reveal a pronounced change in the overall physiology of the alga after submergence and pinpoint candidate genes that play a role. These results provide insight into the importance of photophysiological readjustment when filamentous Zygnematophyceae transition between terrestrial and aquatic habitats.
Mitral regurgitation severity dynamic during acute decompensated heart failure treatment
Authors: Bugała Kamil , Rubiś Paweł , Hołda Mateusz K. , Konieczyńska Małgorzata , Bijak Piotr , Płazak Wojciech
Published: December 2021

Acute decompensated heart failure (ADHF) treatment leads to significant hemodynamic changes. The aim of our study was to quantitatively analyze the dynamics of mitral regurgitation (MR) severity (evaluated by transthoracic echocardiography) which occur during the treatment of ADHF and to correlate these changes with the clinical condition of patients as well as heart failure biochemical markers. The study included 27 consecutive adult patients (40.7% females, mean age 71.19 ± 11.2 years) who required hospitalization due to signs of acute HF. Echocardiographic assessment was performed upon admission and discharge together with clinical and laboratory evaluation. Significant reduction in dyspnea intensity [0–100 scale] (81.48 ± 9.07 vs. 45.00 ± 11.04 pts, p < 0.001), body weight (84.98 ± 18.52 vs. 79.77 ± 17.49 kg, p < 0.001), and NT-proBNP level (7520.56 ± 5288.62 vs. 4949.88 ± 3687.86 pg/ml, p = 0.001) was found. The severity of MR parameters decreased significantly (MR volume 44.92 ± 22.83 vs. 30.88 ± 18.77 ml, p < 0.001; EROA 0.37 ± 0.17 vs. 0.25 ± 0.16 cm2, p < 0.001; VC 6.21 ± 1.48 vs. 5.26 ± 1.61 mm, p < 0.001). Left atrial area (35.86 ± 9.11 vs. 32.47 ± 9.37, p < 0.001) and mitral annular diameter (42.33 ± 6.63 vs. 39.72 ± 5.05. p < 0.001) also underwent statistically significant reductions. An increase in LVEF was observed (34.73 ± 13.88 vs. 40.24 ± 13.19%, p < 0.001). In 40.7% of patients, a change in MR severity class (transition from a higher class to a lower one) was observed: 6/8 (75%) patients transitioned from severe to moderate and 6/18 (33.3%) patients transitioned from moderate to mild class. Treatment of ADHF leads to a significant reduction in MR severity, together with significant reductions in left atrial and mitral annular dimensions. Quantitative measurement of MR dynamics offer valuable assistance for ADHF management.
Genetic signature of immigrants and their effect on genetic diversity in the recently established Scandinavian wolf population
Authors: Åkesson Mikael , Flagstad Øystein , Aspi Jouni , Kojola Ilpo , Liberg Olof , Wabakken Petter , Sand Håkan
Published: December 2021

Transboundary connectivity is a key component when conserving and managing animal species that require large areas to maintain viable population sizes. WolvesCanis lupusrecolonized the Scandinavian Peninsula in the early 1980s. The population is geographically isolated and relies on immigration to not lose genetic diversity and to maintain long term viability. In this study we address (1) to what extent the genetic diversity among Scandinavian wolves has recovered during 30 years since its foundation in relation to the source populations in Finland and Russia, (2) if immigration has occurred from both Finland and Russia, two countries with very different wolf management and legislative obligations to ensure long term viability of wolves, and (3) if immigrants can be assumed to be unrelated. Using 26 microsatellite loci we found that although the genetic diversity increased among Scandinavian wolves (n = 143), it has not reached the same levels found in Finland (n = 25) or in Russia (n = 19). Low genetic differentiation between Finnish and Russian wolves, complicated our ability to determine the origin of immigrant wolves (n = 20) with respect to nationality. Nevertheless, based on differences in allelic richness and private allelic richness between the two countries, results supported the occurrence of immigration from both countries. A priori assumptions that immigrants are unrelated is non-advisable, since 5.8% of the pair-wise analyzed immigrants were closely related. To maintain long term viability of wolves in Northern Europe, this study highlights the potential and need for management actions that facilitate transboundary dispersal.
Fabrication of graphene–ZnO heterostructure-based flexible and thin platform-based UV detector
Authors: Kumar Ashish , Varghese Arathy , Janyani Vijay
Published: December 2021

This work presents the performance evaluation of Graphene/ZnO Schottky junctions grown on flexible indium tin oxide (ITO)-coated polyethylene terephthalate (PET) substrates. The fabricated structures include chemical vapour deposition grown graphene layer on ITO-coated PET substrates. Polymethyl methacrylate assisted transfer method has been employed for the successful transfer of graphene from Cu substrate to PET. The smaller D-band intensity (1350 cm−1) compared to G-band (1580 cm−1) indicates good quality of carbon lattice with less number of defects. High-quality ZnO has been deposited through RF sputtering. The deposited ZnO with grain size 50–95 nm exhibited dislocation densities of 1.31270 × 10–3 nm−2 and compressive nature with negative strain of − 1.43156 GPa. Further, the electrical and optical characterization of the devices has been done through device I–V characterization and UV detection analysis. The UV detection capability of the device has been carried out with the aid of a UV-lamp of 365 nm wavelength. The fabricated graphene/ZnO photodetector showed good response to UV illumination. The device performance analysis has been done through a comparison of the device responsivity and detectivity with the existing detectors. The detectivity and responsivity of the fabricated detectors were 7.106 × 109 mHz1/2 W−1 and 0.49 A W−1, respectively.
Promoting educational innovations and change through networks between higher education teachers
Authors: Stasewitsch Elena , Dokuka Sofia , Kauffeld Simone
Published: December 2021

Innovation in higher education teaching is essential to respond to global challenges and actively improve teaching (e.g. through new technologies), necessitating the implementation of educational reform programmes that fund educational innovations. Although currently deployed strategies frequently promote networks between innovators to diffuse educational innovations, little is known about the efficiency of these networks or whether they promote innovation diffusion. This study investigates a network comprising 88 higher education teachers who received funding for their educational innovations in a German university. We collected longitudinal data by asking higher education teachers from whom they adopted innovative teaching ideas and requesting self-reports on innovative teaching climate. Our findings show that the teachers’ social network had a smaller path length and more clustering than might be expected by chance. This observation might indicate that the examined educational innovation network exhibits a small-world property and allows efficient exchange of ideas among the teachers. In line with our hypotheses, the network’s initial tendency toward hierarchy and homophily decreased over time in response to strategies and network interventions. In summary, this study provides initial empirical support that educational reform programmes can create efficient educational innovation networks, facilitating innovation diffusion and promoting change in higher education teaching.
Effects of muscle shortening on single-fiber, motor unit, and compound muscle action potentials
Authors: Rodriguez-Falces Javier , Malanda Armando , Navallas Javier
Published: December 2021

Even under isometric conditions, muscle contractions are associated with some degree of fiber shortening. The effects of muscle shortening on extracellular electromyographic potentials have not been characterized in detail. Moreover, the anatomical, biophysical, and detection factors influencing the muscle-shortening effects have been neither identified nor understood completely. Herein, we investigated the effects of muscle shortening on the amplitude and duration characteristics of single-fiber, motor unit, and compound muscle action potentials. We found that, at the single-fiber level, two main factors influenced the muscle-shortening effects: (1) the electrode position and distance relative to the myotendinous zone and (2) the electrode distance to the maxima of the dipole field arising from the stationary dipole created at the fiber-tendon junction. Besides, at the motor unit and muscle level, two additional factors were involved: (3) the overlapping between the propagating component of some fibers with the non-propagating component of other fibers and (4) the spatial spreading of the fiber-tendon junctions. The muscle-shortening effects depend critically on the electrode longitudinal distance to the myotendinous zone. When the electrode was placed far from the myotendinous zone, muscle shortening resulted in an enlargement and narrowing of the final (negative) phase of the potential, and this enlargement became less pronounced as the electrode approached the fiber endings. For electrode locations close to the myotendinous zone, muscle shortening caused a depression of both the main (positive) and final (negative) phases of the potential. Beyond the myotendinous zone, muscle shortening led to a decrease of the final (positive) phase. The present results provide reference information that will help to identify changes in MUPs and M waves due to muscle shortening, and thus to differentiate these changes from those caused by muscle fatigue.

Graphical abstract
Turkish Migration Policy from the 1960s Until Today: What National Development Plans Tell Us
Authors: Kilic Hakan , Biffl Gudrun
Published: December 2021

This paper is on migration and migration policy transition of Turkey. The focus is on the Turkish National Development Plans from the 1960s until today and the socio-political and economic context. We identify three distinct periods. The first period of the 1960s is characterized by an explicit support of out-migration to reduce population pressure and on remittances to promote economic growth. The second period from the 1970s to 2000 is marked by diaspora policies of Turkey relative to Europe, thereby acknowledging the role of the Turkish diaspora in the promotion of Turkish economic development and international relations. Since the year of 2000, Turkish migration policy turned to the promotion of highly skilled immigration, aiming at the promotion of technological progress towards a knowledge society with the support of intellectual elites. The policy transition towards the promotion of highly skilled immigration goes hand in hand with institutional and legal changes, which we specify.
Translation and validation of an extended German-language version of the Perceived Locus of Causality Questionnaire (PLOCQ-G) in a sample of physical education students
Authors: Wolf Julia , Kleinert Jens , Pels Fabian , Vogelsang Anna
Published: December 2021

The aims of this study were to translate and validate an extended German-language version of the Perceived Locus of Causality Questionnaire (PLOCQ), a questionnaire that assesses behavioural regulations in the physical education (PE) context. Items assessing integrated regulation were added given that the original PLOCQ omits this factor. The sample consisted of 223 students from different German secondary schools. Psychometric analyses provided support for the six factors and 24-item model. Inter-correlations among the factors predominantly mirrored a simplex-like structure, except for the correlations between introjected and identified regulation and integrated regulation and its adjacent forms of regulation. Construct validity was demonstrated with positive correlations between the autonomous forms of regulation on the one hand and task orientation, perceived competence, and enjoyment on the other. Overall, this study showed that the PLOCQ‑G with six factors and 24 items has good psychometric properties and can be used to assess behavioural regulations in German PE students.
Prediction of penetration rate in drilling operations: a comparative study of three neural network forecast methods
Authors: Brenjkar Ehsan , Biniaz Delijani Ebrahim , Karroubi Kasra
Published: December 2021

Optimizing purposes of the drilling process include reduction in time, saving costs, and increasing efficiency, which requires optimization of controllable variables and variables affecting the drilling process. Drilling optimization is directly related to maximizing the rate of penetration (ROP). However, estimation of ROP is difficult due to the complexity of the relationship between the variables affecting the drilling process. The main goal of this study is to develop three computational intelligence (CI)-based models including multilayer perceptron neural network optimized by backpropagation algorithm (BP-MLPNN), cascade-forward neural network optimized by backpropagation algorithm, and radial basis function neural network optimized by biogeography-based optimization algorithm (BBO-RBFNN) to estimate ROP. Also, in order to broaden the comparisons, some conventional ROP models from the literature were employed. The required data were collected from the well log unit and the final drilling reports of four drilled wells in two different oil fields in southwestern Iran. Firstly, all data were preprocessed to remove outliers; then the overall noises of the data were reduced by implementing Savitzky–Golay smoothing filter. In the next stage, nine input variables were selected during a feature selection step by combining the BP-MLPNN and NSGA-II algorithm. The results of this study showed that developed CI-based models more accurate than conventional ROP models. Also, a survey of statistical indices and graphical error tools proved that BBO-RBFNN model has the highest performance to predict ROP with values of APRE, AAPRE, RMSE and R2 equal to  − 0.603, 5.531, 0.490 and 0.948, respectively.
Lithology and fluid discrimination using rock physics-based modified upper Hashin–Shtrikman bound: an example from onshore Niger Delta Basin
Authors: Okeugo C. G. , Onuoha K. M. , Ekwe A. C.
Published: December 2021

The Ozifa reservoir is proven reservoir that cuts across the Northern and Greater Ughelli depo-belts of the Niger Delta Basin. This reservoir possesses heterogenous character southward of the field, making elastic properties, lithologies and fluid types difficult to describe accurately. In this study, rock physics template was applied to porosity and acoustic impedance (AI) crossplot clusters to illustrate rock–fluid relationships using modified Hashin–Shtrikman upper bound, Voigt upper bound and Reuss lower bound, as an input in the template. Values of acoustic impedance and porosity were used as lithofacies classification parameters for discrimination of lithofacies and fluid types. Our result showed that modified Hashin–Shtrikman upper bound line when applied in acoustic impedance (AI) and porosities (φ) crossplot domain discriminated gas-filled reservoirs from brine filled reservoirs and shale effectively. Similarly, results from crossplot showed clear separation of shale, heteroliths filled with brine and gas bearing sand, which was not plausible using conventional petrophysical analysis. This approach was successfully applied in analysing lithofacies and fluid relationship in different well locations and serves as a model for successful prediction of different lithology and fluid types, a major requirement for determining effects of geological variables such as sorting, clay distributions on the reservoir connectivity and optimum production using time-lapse (4D) seismic interpretation.
Effect of bio-based flow improver on the microscopic and low-temperature flow properties of waxy crude oil
Authors: Eke William Iheanyi , Kyei Sampson Kofi , Ajienka Joseph , Akaranta Onyewuchi
Published: December 2021

Wax formation creates flow assurance problems in the production and transportation of waxy crude oil. Flow improvers are added to waxy crude in order to reduce handling cost. Bio-based flow improvers derived from cheap renewable resources are attractive as cost-effective, eco-friendly alternatives to the conventional additives. Natural cashew nut shell liquid extracted from waste biomass (Anacardium occidentale shells) was derivatized and applied as flow improver for waxy crude oil. Effect of the additive on wax formation in crude oil was studied by cross-polarized microscopy, while the change in oil flow properties was evaluated using a rotational coaxial cylinder viscometer. Micrographs of the waxy crude were processed and analyzed with image J software. The microscopic properties of the wax crystals were characterized using Feret diameter, crystal area, aspect ratio, circularity, solidity and boundary fractal dimension. The pour point of doped crude oil was depressed by − 18 °C and the wax area fraction reduced by 40% due to wax inhibitive effect of the additive. The presence of the additive resulted in evolution of smaller, rounder and more regular wax crystals with smoother and more even surfaces indicated by reduction in the Feret diameter, aspect ratio and boundary fractal dimension of wax crystals in doped oil, and an increase in crystal circularity and solidity. The shear stress and viscosity of doped oil were reduced by 86.8% and 85.0%, respectively. The flow improvement effect of the CNSL derivative is linked to its effect on morphology and microstructure of wax crystals in the crude oil.
Developing a new algorithm for numerical modeling of discrete fracture network (DFN) for anisotropic rock and percolation properties
Authors: Hosseini Erfan , Sarmadivaleh Mohammad , Chen Zhongwei
Published: December 2021

The role of natural fractures in future reservoir performance is prominent. The fractured porous media is composed of an interconnected network of fractures and blocks of the porous medium where fractures occur in various scales and have a strong influence either when most of the flow is concentrated and them or when they act as barriers. A general numerical model for discrete fracture networks (DFN) is usually employed to handle the observed wide variety of fracture properties and the lack of direct fracture visualization. These models generally use fracture properties’ stochastic distribution based on sparse and seismic data without any physical model constraint. Alternatively, a DFN model includes usual numerical geomechanical approaches like boundary element and finite element. But here, a geostatistical methodology has been used to generate a DFN model. In this paper, an alternative modeling technique is employed to create the realization of an anisotropic fractured rock using simulated annealing (SA) optimization algorithm. There is a notable positive correlation between fracture length and position. There are three principal subjects in a study of fractured rocks. Firstly, the network’s connectivity, secondly, fluid flows through the system, and thirdly, dispersion. Here, connectivity of generated networks is considered. Continuum percolation is the mathematical model to study the geometry of connected components in a random subset of space. Different random realizations from the S.A. algorithm in four different sizes of L = 100, 150, 200, 250 at post-threshold condition are used as disordered media in percolation theory to compute percolation properties using Monte Carlo simulation. The percolation threshold (critical fracture density) and two crucial scaling exponents (β and υ) that dictate the model’s connectivity behavior are estimated to over 200 realizations.
New insights into guar gum as environmentally friendly polymer for enhanced oil recovery in high-salinity and high-temperature sandstone reservoirs
Authors: Musa Tagwa A. , Ibrahim Ahmed F. , Nasr-El-Din Hisham A. , Hassan Anas. M.
Published: December 2021

Chemical enhanced oil recovery (EOR) processes are usually used as additives for hydrocarbon production due to its simplicity and relatively reasonable additional production costs. Polymer flooding uses polymer solutions to increase oil recovery by decreasing the water/oil mobility ratio by increasing the viscosity of the displacing water. The commonly used synthetic water-soluble polymer in EOR application is partially hydrolyzed polyacrylamide (HPAM). However, synthetic polymers in general are not attractive because of high cost, environmental concerns, limitation in high temperature, and high-salinity environment. Guar gum is an environmentally friendly natural water-soluble polymer available in large quantities in many countries and widely used in various applications in the oil and gas industry especially in drilling fluids and hydraulic fracturing operations; however, very limited studies investigated on guar as a polymer for EOR and no any study investigated on its uses in high-temperature and high -salinity reservoirs. The objective of this study is to confirm the use of guar gum as a natural polymer for EOR applications in sandstone reservoirs and investigate its applicability for high-temperature and high-salinity reservoirs. The study experimentally investigated rheological characteristics of a natural polymer obtained from guar gum with consideration of high temperature (up to 210 °F) and high salinity (up to 20% NaCl) and tested the guar solution as EOR polymer. The results of this study show that the guar solution can be used as an environmentally friendly polymer to enhance oil recovery. Based on the results, it can be concluded that guar gum shows shear-thinning behavior and strongly susceptible to microbial degradation but also shows a very good properties stability in high temperature and salinity, where in low shear rate case, about 100 cp viscosity can be achieved at 210 °F for polymer prepared in deionized water. Guar polymer shows good viscosity in the presence of 20% NaCl where the viscosity is acceptable for temperature less than 190 °F. Also, the flooding experiment shows that the recovery factor can be increased by 16%.
Judgment method of working condition of pumping unit based on the law of polished rod load data
Authors: Han Chuanjun , Yue Yang
Published: December 2021

At present, oil companies are committed to applying the theory and means of mathematics or data science to the research of oilfield data rules. However, for some old oil wells, aging equipment, complex environment and backward management, cause the authenticity and accuracy of the data collected by the equipment cannot be determined. According to the actual engineering demand of the old wells, this paper proposes a method based on principal component analysis, cluster analysis and regression analysis to mine and analyze the data of polished rod load of old oil wells, so as to judge the working conditions of the oil wells. Combined with the application of this study in several operation areas of some oilfields, the findings of this study can help for better understanding of the working condition information hidden in "big data" of oilfield. Meanwhile, the PCA method can reduce the complexity of the original data, the regression equation can calculate the size of the polished rod load more accurately, and the prediction model can effectively judge the working conditions of the old oil wells on site.
Prediction performance advantages of deep machine learning algorithms for two-phase flow rates through wellhead chokes
Authors: Barjouei Hossein Shojaei , Ghorbani Hamzeh , Mohamadian Nima , Wood David A. , Davoodi Shadfar , Moghadasi Jamshid , Saberi Hossein
Published: December 2021

Two-phase flow rate estimation of liquid and gas flow through wellhead chokes is essential for determining and monitoring production performance from oil and gas reservoirs at specific well locations. Liquid flow rate (QL) tends to be nonlinearly related to these influencing variables, making empirical correlations unreliable for predictions applied to different reservoir conditions and favoring machine learning (ML) algorithms for that purpose. Recent advances in deep learning (DL) algorithms make them useful for predicting wellhead choke flow rates for large field datasets and suitable for wider application once trained. DL has not previously been applied to predict QL from a large oil field. In this study, 7245 multi-well data records from Sorush oil field are used to compare the QL prediction performance of traditional empirical, ML and DL algorithms based on four influencing variables: choke size (D64), wellhead pressure (Pwh), oil specific gravity (γo) and gas–liquid ratio (GLR). The prevailing flow regime for the wells evaluated is critical flow. The DL algorithm substantially outperforms the other algorithms considered in terms of QL prediction accuracy. The DL algorithm predicts QL for the testing subset with a root-mean-squared error (RMSE) of 196 STB/day and coefficient of determination (R2) of 0.9969 for Sorush dataset. The QL prediction accuracy of the models evaluated for this dataset can be arranged in the descending order: DL > DT > RF > ANN > SVR > Pilehvari > Baxendell > Ros > Glbert > Achong. Analysis reveals that input variable GLR has the greatest, whereas input variable D64 has the least relative influence on dependent variable QL.
Analysis of bottom hole pressure of unsteady flow in dual-medium fracturing vertical well
Authors: Hailong Liu
Published: December 2021

In order to improve the validity of bottom hole pressure model, and simplify its calculation process, a mathematical model of instantaneous pressure for unsteady flow was established by considering the crossflow between the fractures and matrix. Different conditions, including the reservoir top has constant pressure, were considered. The basis for obtaining bottom hole pressure is to solve diffusivity equation with the integration of axisymmetric transformation and similar methods, which is presented for the first time. Different from the traditional method of using the Green’s function and source solution, this paper uses Laplace transformation, axisymmetric transformation and similar methods, separation of variables to obtain the analytical solution of Laplace domain. Then, the Stephenson Numerical method was used to obtain the numerical solution in a real domain. The results of this method agree with the numerical simulations and actual test data, suggesting the validity and accuracy of this method. Finally, the sensitivity analysis revealed that the pressure curve can be divided into eight stages, namely, early linear flow, continuous flow transition section, fracture linear flow, formation linear flow, crossflow, transitional flow, pseudo-radial flow and boundary control flow. The advantage of the analytical solution utilized in this paper is to incorporate exchange coefficient and skin factor efficiently, providing a theoretical basis for optimizing production pressure difference and determining the reasonable productivity.
Correction to: A numerical investigation on the performance of hydraulic fracturing in naturally fractured gas reservoirs based on stimulated rock volume
Authors: Al-Rubaye Ali , Mahmud Hisham Khaled Ben
Published: December 2021

In the original publication of the article, the corresponding author name was incorrectly published as Ali Al-Rubaie; it should read Ali Al-Rubaye.
Basin margin sediment wedge build out of the Eastern Niger Delta: application of shelf-edge trajectory pattern studies
Authors: Anyiam Okwudiri A. , Hoggmascall Nicholas , Amogu Daniel K.
Published: December 2021

The understanding of how basin margin sediment wedge builds out causes shelf-edge migration with time is approached based on shelf-edge trajectory pattern analysis using a high-resolution mega-merge seismic data from the eastern Niger Delta, Nigeria. The study focuses on a seismic dip transect traversing the Greater Ughelli, Central Swamp, Coastal Swamp and the Shallow Offshore Depobelts of the Niger Delta. On the regional dip transects, shelf-edge sediments occur as clinoform-bearing wedges at and immediately updip of the shelf-slope break. The shelf edge is deeply buried (> 2–4 s, twt), around the Greater Ughelli and Central Swamps. But with changing structural style, sudden change of ascending shelf edge around the Central Swamp was observed. The huge listric growth fault in the Coastal Swamp; around Bonny area, once again cut the shelf edge into half, rotated it along the listric fault and buried it distally. Several depositional packages show low to moderate ascending shelf-edge trajectory with progradational to aggradational clinoform growth that is characterized by thin sand sheets across most of the shelf and upper slope, though few are also characterized by progradational clinoform growth with thick sand on the shelf, upper-tolower slope and basin floor. The deposition is usually on the Outer Shelf Terrace (OST) which is regressive in a flat and rising trajectory style. This study has demonstrated that accommodation and sediment flux are the dominant controls on how the study basin’s sediment wedge built out, whereby limited accommodation promotes sediments with significant shelf-edge advance and descending trajectories, while increasing accommodation promotes ascending trajectories and increased deposition on the outer shelf. The greater sediments on the Outer Shelf Terrace and the shelf margin than on the slope gives more hydrocarbon prospectivity search around the outer shelf and shelf margin.
Viscosity models for bitumen–solvent mixtures
Authors: Alade Olalekan S. , Al Shehri Dhafer A. , Mahmoud Mohamed , Olusegun Samuel , Lawal Lateef Owolabi , Kamal Muhammad Shahzad , Al-Nakhli Ayman
Published: December 2021

Viscosity is the resistance of a material to continuous deformation exerted by shear force. High viscosity, which is sometimes greater than 1 million mPa s, at the initial reservoir conditions, is a major challenge to recovery, production, and transportation of bitumen. Addition of organic solvents or diluents with bitumen leads to significant viscosity reduction and forms the basis for the steam/solvent-assisted recovery methods of extra-heavy oil and bitumen. Therefore, modeling and predicting viscosity of bitumen–solvent mixture has become an important step in the development of solvent-assisted system. The aim of this article is to present a concise survey of the various viscosity models that have been proposed to predict the viscosity of bitumen–solvent mixtures, and make comparative discussion on their applicability. Available reports revealed that the accuracy of a model to predict the viscosity of bitumen–solvent mixtures depends on various factors including the type and concentration of solvents, and the properties of the bitumen. Thus, no model has been found to have absolute capability to predict the viscosity for all mixtures. Therefore, there is room for further improvement on the viscosity modeling of bitumen–solvent system for wider applications.
Numerical simulation investigations of coalbed methane drainage performance with multilateral well
Authors: Liu Songze , Wei Jianguang , Ma Yuanyuan , Liu Hongliang , Liu Xuemei , Yan Bingxu
Published: December 2021

A novel multilateral well for coalbed methane extraction was proposed in the study. There is a main wellbore at the longitudinal center of coal seam and four lateral wells at the horizontal center in the multilateral-well system. Compared with traditional drainage holes, multilateral-well system has a better performance on coalbed methane development. A hydraulic-mechanical coupling model of multilateral well was established, the pressure and permeability ratio distribution of the gas extraction process were analyzed comprehensively. The sensitivity analysis of lateral number, length distribution and intersection angle of multilateral-well system were studied. The results indicate that there is a minimum gas pressure distribution around the multilateral well and the overall permeability of coal seams increases with production time and the permeability around the multilateral well is larger than the area away from the multilateral well which induced by the gas desorb and matrix shrink. The quantity of lateral wells has a positive effect on cumulative production. When the total length of lateral wells is equal, the uniformity and symmetry of lateral length distribution are two key factors on the gas extraction performance. The minimum intersection angle has a positive effect on cumulative production. This study provides a better alternative for traditional drainage hole to obtain greater coalbed methane performance.
Analysis of subsurface structural trend and stratigraphic architecture using 2D seismic data: a case study from Bannu Basin, Pakistan
Authors: Ishaq Kashif , Wahid Sohail , Yaseen Muhammad , Hanif Muhammad , Ali Shehzad , Ahmad Jawad , Mehmood Mubashir
Published: December 2021

The present study is focused on the subsurface geology of Bannu Basin, a part of western Indus foreland Pakistan. For this purpose, some regional seismic profiles and deep exploratory wells data have been used in integration.A total of ten mappabale seismic reflection events have been identifed which are representative of specific geological units. In general, based on the seismic the formation trends, the horizons are dipping in the northwest direction of the study area. The area generally deepens toward the northwest due to sediments load toward the northwest. The seismic profile MWI-83 shows a unique faults bounded anticlinal structure that has also been mapped on the two-dimmensional contour maps. This could be regarded as potential hydrocarbon entrapment. The regional seismic profiles are contoured for the entire grid in both time and depth domain to obtain the clearer image of the subsurface individual stratigraphic units. The 2D contour maps for Lower Permian aged Warcha Sandstone, Middle Triassic aged Tredian Formation and Early Jurrasic aged Datta Formation have been prepared using gridded TWT of the seismic profiles. The time and depth contour maps of the Datta Formation and Tredian Formation show a four way clouser oriented in the southeast dierction. The area of the closure was computed which is 24 Sq km approximately. Furthermore, the formation tops of the five wells have been used to correlate the wells for understanding the lateral and vertical variations in the stratigraphic layers. The correlation shows that the Datta Formation’s thickness increases at the centre of the basin whereas decreases on the east and south flanks of the basin. Reasons of Wells failure were concluded on the basis of the final well report and concluded that these well failure occur due to poor quality of the data and also due to some mechanical problems. Reservoircharacterization using statistical rock physics and petrophysics coupled with core data analysis can provide further insights into the hydrocarbon exploration.
Geological mapping and mineral prospectivity using remote sensing and GIS in parts of Hamissana, Northeast Sudan
Authors: Mohamed Mohamed Taha AlMakki , Al-Naimi Latifa Shaheen , Mgbeojedo Tochukwu Innocent , Agoha Chidiebere Charles
Published: December 2021

In recent years, various geological activities and different mineral prospecting and exploration programs have been intensified along the Red Sea hills in order to elucidate the geological maps and to evaluate the mineral potentials. This study is therefore aimed at testing the viability of using remote sensing and geographic information system (GIS) techniques for geological mapping and prospecting for gold mineralization in the area. The study area is located in northeast Sudan and covers an area of about 1379 km2. Different digital image processing techniques were applied to Landsat 8 Operational Land Imager image in order to increase the discrimination between various lithological units and to delineate wall rock alteration which represents target zones for gold mineralization. Image sharpening was performed to enhance the spatial resolution of the images for more detailed information. Contrast stretching was applied after the various digital processing procedures to produce more interpretable images. The principal component analysis transformations yielded saturated images and resulted in more interpretable images than the original data. Several ratio images were prepared, combined together and displayed in RGB color composite ratio images. This process revealed the existence of alteration zones in the study area. These zones extend from the northeast to the southwest in the acid meta-volcanic and silica barite rocks. The enhanced satellite images were implemented in the GIS environment to facilitate the final production of the geological map at scale 1:400,000. X-ray fluorescence analyses prove that selected samples taken from the wall rock alteration zones are gold-bearing.
Improving drilling performance through optimizing controllable drilling parameters
Authors: Bani Mustafa Ahmed , Abbas Ahmed K. , Alsaba Mortadha , Alameen Mamoon
Published: December 2021

The prediction of the drilling rate of penetration (ROP) is one of the key aspects of drilling optimization due to its significant role in reducing expensive drilling costs. Many variables could affect ROP, which can be classified into two general categories; controllable operational variables and uncontrollable or environmental variables. Minimizing the drilling cost can be achieved through optimizing the controllable drilling parameters. As a direct result, the drilling speed will be increased while maintaining safe practices. The primary purpose of this study is to address the simultaneous impact of controllable parameters such as weight on bit (WOB), revolutions per minute, and flow rate (FR) on the rate of penetration (ROP). Response surface methodology was applied to develop a mathematical relation between operational controllable drilling parameters and ROP. To accomplish this, actual field datasets from several wells drilled in Southern Iraq in different fields were used. The second purpose of this study was to identify all prospective optimal ranges of these controllable parameters to obtain superior drilling performance with an optimum ROP. The obtained results showed that the developed model offers a cost-effective tool for determining the maximum ROP as a function of controllable parameters with reasonable accuracy. In addition, the proposed model was used to estimate optimal combinations of controllable drilling parameters for various depths. The results have shown that FR has the most significant effect on ROP variation with a sum of squares values of 23.47. Applying high WOB does not permanently improve ROP but could result in reducing ROP for some cases. The developed mechanical specific energy model for polycrystalline diamond compact (PDC) bit with vertical and deviated wells can estimate combinations of controllable drilling parameters. The developed model can be successfully applied to predict and optimize the drilling rate when using PDC bits, hence reducing the drilling time and the associated drilling cost for future wells.
Study on the microscopic pore structures of the four different kinds of lithological reservoirs in the basin of Western China
Authors: Liu Tianqi , Xiong Shengchun , Yu Jiayi , He Ying , Song Peng , Chu Shasha , Lin Wei , Hou Haitao
Published: December 2021

In the basin of western China, four different kinds of lithological reservoirs are developed, including low-permeability sandstone, sedimentary tuff, shale and volcanic rock. There is generally a large difference in the micropore structure characteristics and distribution laws due to different reservoirs. The reserving capacity as well as the porous flowability, mechanism and laws are determined by the micropore structure characteristics and distribution laws of hydrocarbon reservoirs. Low-temperature nitrogen adsorption and desorption technology, high-pressure mercury injection experiment and nuclear magnetic resonance (NMR) testing technology are applied to study the micropore size, quantity, structure and distribution laws of four different kinds of lithological reservoirs as well as their similarities and differences of corresponding relation with macroporosity–permeability physical parameters. This paper also studies the movable fluid and nonlinear seepage flow characteristics of four different kinds of lithological reservoirs.
Influence of different pore structure types on the occurrence features of movable fluid in Chang-10 reservoir in Wuqi–Ansai Oilfield
Authors: Gao Yong-li , Li Pan , Li Teng
Published: December 2021

Chang-10 reservoir in Wuqi–Ansai oilfield of Ordos Basin is restricted by its strong microscopic heterogeneity, complicated microscopic pore structure and unclear oil–water movement rules. The technology of nuclear magnetic resonance (NMR) is an excellent method to quantitatively evaluate the reservoir fluid of different pore structure types, and the microscopic experiments such as cast thin slices, scanning electron microscope (SEM) and high-pressure mercury injection were also used to analyze the differences in the occurrence features of fluid of different pore structure types and their influencing factors. The experimental results show that the sandstone types of Chang-10 reservoir in Wuqi–Ansai Oilfield are mainly medium-fine arkose and lithic arkose. The pore types are mainly intergranular pore, feldspar pore, turbiditic zeolite pore and cuttings pore. The combination type of pore-throat belongs to mesopore–micropore and microlarynx–microlarynx. By mercury injection experiment analyzed the characteristic of capillary pressure curve, Chang-10 reservoir in Wuqi–Ansai Oilfield pore structures is classified into Type I, Type II, Type III and Type IV due to the different movable fluid occurrence features. The occurrence features of movable fluid are obviously controlled by the pore-throat, and the orders of control effect from strong to weak are from Type I, Type II, Type III to IV The saturation of movable fluid gradually becomes low when the pore-throat radius decreases.
Pre-acid system for improving the hydraulic fracturing effect in low-permeability tight gas reservoir
Authors: Li Nianyin , Chen Fei , Yu Jiajie , Han Peihong , Kang Jia
Published: December 2021

Hydraulic fracturing is an important technical means to improve the development effect of low-permeability oil and gas reservoirs. However, for low pressure, low-permeability, tight, and high-clay sandstone gas reservoirs, conventional propped fracturing can cause serious damage to the reservoir and restrict the fracturing effect. The pre-acid fracturing technology combines acid treatment technology with sand-fracturing technology. A pre-acid system that meets special performance requirements is injected before fracturing. The pre-acid reduces the formation fracture pressure and removes clay damage. During acid flowback, the fracturing fluid is promoted to break the gel, dissolve the fracturing fluid residue and polymer filter cake, clean the supporting cracks, and effectively improve the fracturing effect. This study analyzes the process principle and technical advantages of the pre-acid fracturing technology based on the laboratory evaluation of the fracturing damage mechanism of low-permeability tight gas reservoirs. To meet the performance requirements of low-permeability tight gas reservoirs and pre-acid fracturing technology, a set of polyhydrogen acid system with long-lasting slow reactivity, low damage, and low corrosion was developed and used as the pre-fracturing acid. The acid system is mainly composed of the main agent SA601 and the auxiliary agent SA701. Then, on the basis of laboratory experiments, this acid system is used as the fracturing pre-acid to evaluate the fracturing improvement effect. The results show that the fracturing fluid system can better dissolve the fracturing fluid filter cake and remove the fracturing fluid damage.
Influence of top management commitment towards the effective implementation of TQM in Iraqi oil companies
Authors: Aletaiby Abbas Abdulhameed , Rathnasinghe Akila Pramodh , Kulatunga Pramodh
Published: December 2021

By raising performance, Total Quality Management (TQM) transforms any industry that is in a state of substantial structural change and facing increased competition. However, Iraq as one of the main global oil suppliers is still lagging on the TQM journey due to decreasing quality levels, particularly in management systems. Thus, this study aims to facilitate TQM in Iraqi Oil Companies by reviewing the TQM practices and the significance of Top Management Commitment (TMC) towards eliminating the barriers for implementation. To achieve this aim, the study utilises a mixed research approach and a single holistic case study strategy by triangulating literature and data collected from one of the leading Iraqi oil companies. The research identified TMC as the most influential factor for effective TQM implementation and six barriers. Furthermore, the research reveals the relationship between the top management commitment required for successful TQM implementation and barriers in that journey. This study will be the first of its kind in the Iraqi oil industry which will lead to a better understanding of TQM practices in Iraq and will encourage other researchers to extend this study through further work.