bluuebunny/crossref_metadata_2025 huggingface dataset:
The Dilemma of Human Relations and Access to Land at the Face of Game Conservation Policies in Mara Region, Tanzania, 1920s – 2014
Authors:   University of Dar es Salaam, Magoti Iddy Ramadhani
Published: October 2022

Tanzania is one of the countries in sub-Saharan Africa which has great number of conserved and protected areas, and aspires to protect more areas. However, there is a growing concern among Tanzania’s people who live around conserved areas that their rights to access land and other natural resources around is being impinged. As a result, conflicts emerge between local people and those who call themselves 'conservationists'. Increase of population of both human beings and wild animals continues to aggravate the problem. In light of that thinking, this paper examines game conservation policies and their far-reaching implications on human relations and access to land in Mara region. The main assumption is that changes of land use from human settlement, grazing, cultivation and hunting land to game reserves and controlled areas creates pressure on the meagre remaining land surface. This situation, in turn, affects the pre-existing human relations and the future prospects of the surrounding communities. The paper builds its analysis from both secondary and primary sources such as review of books and journal articles, archival research and oral in-depth interviews conducted in the area. The findings show that conservation practices in Tanzania prioritize animal rights at the expense of human population thereby creating dilemma on human relations and survival. Finally, the paper reveals that there has been an emerging trend for conservation for the interest of the foreign investors; that investors and some government officials benefit more than the local community around.
Navigating through German Colonial Past in Tanzania through Artistic Productions
Authors:   University of Dar es Salaam, Shule Vicensia
Published: October 2022

There are various works of arts that represent German colonial history in Tanzania. Such artistic productions linked to cultural productions depict not only the history of Tanzania in relation to the colonial past but also reflect the current struggles to overcome the colonial legacy. This study is informed by qualitative research methods including observations, interviews and documentary review. The study is based on the interpretation of artistic productions and linkages to decoloniality discourse. Six artistic works were used as a case study. These were Nkhomanile (2006), Mkwawa (2011), MV Liemba (2015), Maji Maji Flava (2016), Skull X 2016) and Mangi Meli Remains (2018). The study argues that the artistic productions under review depict German colonial history in Tanzania. The depiction underscores the exploitative, violent and brutal nature of that history. Significantly, the colonised did not sit back and watch because they had resisted the German occupation of their land as most of the productions illustrate. However, such artistic productions are informed mostly by the funding agencies and audiences which appear predefined for such productions. Therefore, it is important to research further on the nature and behaviour of the audience of the artistic productions linked to the historical colonialism.
Using Airborne Laser Scanning Data to Assess the State Historical Garden Complexes
Authors: Dudzińska Anna , Szpakowska Barbara
Published: October 2022

The aim of the study was to assess the possibility of applying GIS analysis for investigations into the state of preservation of a baroque garden complex. The article presents a method based on Airborne Laser Scanning data (LIDAR) which can be used for analysis of revalorization of historical garden complexes. The research was conducted in a rural park in Siemczyno, Zachodniopomorskie Voivodship, Poland. The analysis was made by means of the ENVI and ArcMap programs. The article presents an analysis of the terrain microstructure, which was used for assessment of changes in the terrain. It is a significant element used for planning public space. The research results were compared with the park inventory data of 1973. The research proved that LIDAR data analysis could be used for assessment of the state of preservation of historical garden complexes. It might also be used for preparation of park registration documentation or revalorization plans.
Production Potential and Income of Agricultural Holdings in Poland
Authors: Strzelecka Agnieszka , Zawadzka Danuta , Kurdyś-Kujawska Agnieszka
Published: October 2022

The aim of this article is to assess the impact of production potential on the income obtained by agricultural holdings in Poland. The Farm Accountancy Data Network FADN data from 2015 was used to achieve this aim. Empirical verification of factors determining the production potential and their impact on agricultural holding income was carried out using the logistic regression model. The dependent variable was taken to be the probability that the agricultural holding would achieve annual family farm income exceeding the median value of PLN 46149,18. It was established that four variables had a statistically significant positive effect on the studied phenomenon: area of agricultural land, share of leased land in the agricultural land area, total labor expenditure and technical labor infrastructure. This means that an increase in the level of these factors increases the probability of obtaining an above median value of income by agricultural holdings.
Trajectories of the Development of Small Towns in Terms of the Urban Resilience Concept — the Demographic Dimension
Authors: Konecka-Szydłowska Barbara
Published: October 2022

The paper aims to determine the trajectories of the development of small towns in terms of the urban resilience concept in a demographic dimension. It makes it possible to answer the question of how towns adapt to contemporary socio-economic processes. The subject of the research is a set of small towns in Wielkopolskie Voivodship. The period of the study involves the years 2003–2016 which enables us to grasp the changeability of development conditions related to transformation, globalization, and integration processes as well as the economic crisis. The research is conducted with the use of indexes of change dynamics with a fixed basis. Analysis provides for a diversified size structure of small towns, their location and administrative functions performed. In 2003–2016 the trajectories of the resilience of Wielkopolskie small towns were diversified. The basic criterion influencing their course is the size structure of a given center and its location, whereas administrative functions are of minor significance. The smallest towns (of a mixed type — i.e., roller-coster with elements of avant-garde type) seem the most resistant to external disturbances, have a higher degree of resilience and thus adapt better to contemporary socio-economic changes in the demographic dimension. An important external disturbance which clearly modifies the values of the selected indexes of resilience and vulnerability dynamics as well as the course of the trajectories of the development of towns with a diversified size structure was an economic crisis strengthened by globalization and integration processes.
Accessibility of Polish and Nordic Cittaslow Towns
Authors: Zawadzka Alicja
Published: October 2022

The main objective of this article is to indicate transport accessibility (according to two criteria: fly&60 and 6×60×60) and information accessibility (on the Internet) of all Polish (28 ) and all Nordic (9 ) towns — members of the International Network of Cities Where Living is Good. The research was conducted using non-reactive methods: content analysis and desk research. The analysis has shown that the fly&60 criterion is met by eight Cittaslow towns (seven Polish and one Nordic), and the 6×60×60 criterion — by five towns (four Polish and one Nordic), which confirms the thesis on the peripheral nature of Cittaslow cities, which in fact may be perceived as an attracting factor. Their location, away from frequently used routes, may attract (some of them already do so) tourists seeking alternative forms of leisure, following a growing global trend of sustainable tourism. The level of accessibility to online information on the Cittaslow towns is varied, but rather low.
Role of Rail in Passenger Border Traffic between Poland and Ukraine — a Dynamic Approach
Authors: Komornicki Tomasz , Kowalczyk Karol
Published: October 2022

Changes in the functions of Polish borders at the turn of the 20th and 21st century resulted in a reorientation of transport connections with countries of the former Soviet Union. One of the consequences of the phenomenon are considerable transformations in the scope of degree of use of rail transport in cross-border passenger traffic. The objective of the article is the dynamic assessment of the importance of railways in passenger traffic between Poland and Ukraine in the years 1990–2016 (including limited data for 2018), with consideration of the infrastructural and organizational factors. The analyses employed data on traffic of persons and vehicles on railway and road border crossings. They provided the basis for the determination of changes in the position of rail towards other modes of cross-border transport. The second source is Network Train Timetable (in Polish: Sieciowy Rozkład Jazdy Pociągów), used for the preparation of maps of connections functioning in selected time intervals. The analyzed period was characterized by a continuous decrease in the importance of rail in bilateral passenger traffic. It proved completely inflexible towards systemic and geopolitical transformations and intermodal competition of bus transport, and from 2013 also air transport. The spatial layout of rail connections suggested initial de-concentration involving several border crossings, and then concentration on two main lines. The vast general increase in traffic that occurred in recent years in the Ukrainian direction constitutes a chance for increasing the role of rail transport in a situation of overload of road border crossings.
Technical Efficiency of Polish Independent Public Health Care Centres: Data Envelopment Analysis Approach
Authors: Podgórska Joanna
Published: October 2022

In the face of the growing demand for health services, which can be observed in Poland (as well as in many other countries), it is extremely important to make effective allocation decisions in relation to financial resources (at the disposal of health sector decision-makers). The pace of demographic, technological and market changes forces an increase in financial expenditures on health, while at the same time the resources allocated to these objectives are still lacking. The present paper assesses the technical efficiency of 24 independent public health care centers (IPHCCs) in 2010–2014 with the use of the data envelopment analysis method and evaluates changes in the examined efficiency categories using the Malmquist Index. The research has shown that independent public health care institutions in Poland are facing the problem of debt and inefficiency. It has also been established that the level and method of financing health services in Poland contribute to a large extent to the technical inefficiency of IPHCCs, and that the increase in IPHCCs’ revenues leads to an increase in their technical efficiency. The conclusions of this paper provide, on one hand, the basis for in-depth research into the efficiency of public health entities and, on the other, guidance that can be used in the practical management of public health entities and in the shaping of national health care policy.
Increased Employment Rates and the Nature of the Economic Growth in Poland’s Voivodships
Authors: Zieliński Mariusz
Published: October 2022

The purpose of the article is to study the impact of basic production factors (level of employment and value of fixed assets) on the economic growth rate in different regions of Poland. The hypothesis presented in the article is that in the process of economic growth, the human factor (level of employment) plays a greater role than the fixed assets. The hypothesis was verified using the data published by the Central Statistical Office in the Statistical Yearbooks of the Regions for the years 2000 and 2015. The results of the study confirm the validity of the formulated hypothesis. Also, the author of the article made the effort to identify the voivodships characterized by extensive and intensive economic growth.
Labor Market Segmentation as an Important Factor in Research of Labor Immigration. Comparative Analysis Based on the Opolskie Voivodship Empirical Findings
Authors: Kubiciel-Lodzińska Sabina , Ruszczak Bogdan
Published: October 2022

The purpose of this paper is to draw attention to the need of taking into account the existence of dual labor markets in the majority of developed countries when analyzing research results on labor immigration. The countries most affected with this duality are the ones where immigration is still on the increase; amongst others, Central and Eastern European countries. Selected qualitative and quantitative research methods were implemented in the study. The data source was a structured questionnaire interview conducted in 2007–2008, among 91 employers and the comparison research carried out again in 2014–2015 with 263 participating entrepreneurs. In accordance with the dual labor market theory, the employers were divided into those who offered employment in the primary or the secondary labor market. The research carried out in the Opolskie Voivodship, Poland showed that those employing a foreign labor force were driven by different reasons in the primary or the secondary sector of the labor market. It was also determined that taking into account the segmentation of the labor market in analyses of results of research on labor immigration positively affected their interpretation and provided more precise conclusions.
Internal and External Costs in Sustainable Development of the Healthcare System in Poland. Case Study of the John Paul II Specialist Hospital in Głuchołazy
Authors: Malik Krzysztof , Jasińska-Biliczak Anna , Grochowski Mariusz
Published: October 2022

The article’s goal is to study internal and external cost as part of the sustainable development paradigm. To illustrate such a problem the role and a scope of presented costs in the health care system are discussed. The practical example from Opolskie Voivodship — the John Paul II Specialist Hospital in Głuchołazy — is presented. For achievement of this aim a literature review is conducted from the scope of health-care economics and its sustainable development as well as internal and external costs (desk research). An analysis of data (data analysis) is performed on the example of the specific hospital (case study). After such analysis it is possible to state that it is necessary to have knowledge regarding the occurrence of diseases in the population and the total (including external) values of social and economic costs of untreated diseases. In order to achieve this, it is necessary to, first of all, implement educational programs. This also applies to general medical practitioners, because, as practice shows, patients are often diagnosed at the stages of disease when effective treatment is nearly impossible.
Knowledge Management Models. State of the Art
Authors: Andreasik Jan
Published: October 2022

In this article knowledge management models are classified into the following groups: 1. Resource models. 1.1. Holistic models. 1.2. Pyramidal models. 2.Process models. 2.1. Knowledge value chain models. 2.2. Branch models of organizational processes. 2.3. Spiral models. 3. Knowledge creation models. 4. Semantic models. As the summary the operationalization of knowledge management models is presented.
SIMULATION RESEARCH ON THE GRASPING PROCESSOF THE SOFT ROBOT GRIPPER
Authors:   Le Quy Don Technical University, Phung Van Binh
Published: October 2022

Thisarticlepresents a method to simulate the dynamics of the grasping process of a soft robotic gripper that is made of silicon. The pneumatically actuated soft fingers are composed of interconnecting hollow chambers. Each soft finger is modeled as a series of line-segment links using a multibody dynamics approach. Numerical simulations using Abaqus/CAE software are used to determine the system's dynamic parameters. The soft gripper’s model is then integrated into the robotic manipulators that are built on MSC Adams software. The interaction between soft grippers and objects is modeled according to the Hertz contact theory. The proposed model allows for the investigation of soft gripper gripping capacity with various types of objects and different moving velocities and accelerations. The simulation shows that the soft gripper can hold a spherical object and a cylindrical object with the same mass of 300 g at a maximum acceleration of 9.9 m/s2and 3.6 m/s2respectively. The results of the study are being used to improve the design of the robot's soft gripper.
Ayurvedic Management of Duchene Muscular Dystrophy (DMD) A Case report
Authors: Belavadi Dr. Santosh N.
Published: October 2022

Duchene muscular dystrophy is inherited X-linked recessive disorder. Females will typically be carriers for the disease while males will be affected. Dystrophin is essential for cell membrane stability. Deficiency leads to reduction in three glycol proteins in the dystrophin associated protein complex that link dystrophin to laminin with cell membranes. This occurs in people without a known family history of the condition. Because of the way the disease is inherited, males are more likely to develop symptoms than are women. In this Clinical study enlightening about 2 cases of Duchene muscular dystrophy, the concept in Ayurveda the entities like Astimajjagatavata and Pakkharoga, and the treatment carried out in this disease are Sarvanga Abhyanga (whole body massage) Musthadiyapanabasti followed by Shamanayogas(palliative medicines) like Ajamamsa Rasayana, Balarishta and cap Bontone followed by Physiotherapy.
Training the knowledge assimilating activities in a way which developes the detection and solving problems capability in teaching vector - relationships within a triangle topic at highschool
Authors:   Vinh University, Nghe An, Viet Nam, Tam DAO , Thi Thu Hien TRAN ,   Graduate students of course 24, Math teaching methods, Vinh University
Published: October 2022

In this article, we clarify the knowledge assimilating activities and propose a number of training measures for student in the knowledge assimilating activities, thereby contributing to the development of capability of detecting and solving problems.
Triterpenoids from the fruit of Fissistigma oldhamii (Hemsl.) Merr. in Vietnam
Authors:   Vinh University, Nghe An, Viet Nam, Cong Dung VO , Dinh Thang TRAN ,   Vinh University, Nghe An, Viet Nam
Published: October 2022

Two triterpenoids, taraxer-14-en-6α-ol and taraxerol, were isolated from the fruit of Fissistigma oldhami (Hemsl.) Merr. (Annonaceae). The structures of the isolated compounds were established by spectroscopic methods (UV, IR, MS, 1H-NMR, 13C-NMR, DEPT, COSY, HSQC and HMBC). These compounds were isolated from this plant for the first time.
Inheritance of morphological and bioagrological characteristics of sesame (Sesamum indicum L.)
Authors:   Vinh University, Nghe An, Viet Nam, Tai Toan NGUYEN , Tu Nga TRAN ,   Faculty of Agronomy, Vietnam Academy of Agriculture, Van Liet VU ,   Faculty of Agronomy, Vietnam Academy of Agriculture, Cong Thanh NGUYEN ,   Vinh University, Nghe An, Viet Nam
Published: October 2022

The experiment was carried out to research on the inheritance of capsule hairiness, branch, number of capsule per leaf axil and number of locule per fruit in sesame. The results in the F1 generation of cross made for hairiness revealed that hairiness, branching, one capsule per leaf axil and 4 locules per fruit was dominant to hairless, monostemed, three capsules per leaf axil and 8 locules per fruit. Chi-square values obtained for all the crosses in F2 progeny showed a good fit for a monogenic inheritance with the F2 phenotypic ratio of 3:1. The information presented in this research was beneficial for sesame breeding and reaching to ideal plant type.
Measures taken in teacher training at colleges of education to increase students’ self-confidence in applying information technology into their academic activities and practicum
Authors:   Ba Ria - Vung Tau Pedagogical College, Tu Anh TRAN
Published: October 2022

This article presents the current state of confidence among full-time students at Ba Ria - Vung Tau College of Education when they apply information technology into their academic activities and practicum as well as the causes of such situation. The paper also offers some measures to be taken with a view to building up students’ confidence in this aspect, which include changes in the teaching content of Computer Science; innovations in dealing with the course on “The Application of Information Technology in Teaching”, creating favorable conditions for students in terms of learning facilities and friendly study environment.
Governance of university brand
Authors:   Vinh University, Nghe An, Viet Nam, Xuan Khoa DINH , Minh Hung PHAM ,   Vinh University, Nghe An, Viet Nam
Published: October 2022

This paper is concerned with the theory of brand governance and its application to building brand and model of university brand governance in Vietnam. University brand governance encompasses all that include management of human resources, quality, finance… with a view to improving the university’s quality and prestige in the context of globalization and the 4th Industrial Revolution.
Tyre Parameterization Tests: Dynamic vs. Static
Authors: Becker Carl , Els Schalk
Published: October 2022

Agricultural vehicles are used more on asphalt roads and needs to be safe in an evasive maneuver or during an emergency brake scenario. The designers of these vehicles require tyre parameterization data to obtain accurate and representative simulation results of these vehicles. The standard laboratory tyre testing procedures are not always possible on very large tyres. The limitations in the form of the actual size of the tyre and the required loads on the tyre cannot always be accommodated by the current equipment available to conduct dynamic tests. This study investigates how the tyre parameterization results compare between a dynamic/rolling tyre test and a static/non-rolling tyre. This is in an attempt to parameterize tyre models using largely or only static test data. Tests are conducted on a smaller agricultural tyre where dynamic tyres test results are compared to static tests.
A Preliminary Wellbore In-Situ Stress Model for Utah FORGE
Authors: Ye Zhi , Fang Yuan , Ghassemi Ahmad , McLennan John
Published: October 2022

Knowledge of the in-situ stress is very important to the geothermal reservoir development as well as to the planned R&D activities at the Utah FORGE. Whereas the vertical stress (Sv) and the minimum horizontal principal stress (Shmm) can reliably be determined through density logs and hydraulic fracturing tests, respectively, the determination of the magnitude of maximum horizontal principal stress (SHmax) is challenging. In this paper, we established a preliminary wellbore in-situ stress model for the Utah FORGE based on the drilling-induced fractures and wellbore breakouts observed in borehole image logs. We utilize stress polygon (frictional faulting theory), wellbore failure analysis, drilling-induced fractures, and borehole breakouts to constrain the magnitude of the SHmax in the well 78B-32 where both tensile and compressive failures occur. The constrained SHmax is in the range 0.83-0.98 psi/ft. The results are compiled to obtain a wellbore in-situ stress profile for the well 78B-32 which is in good agreement with other data.

1. INTRODUCTION

Understanding the magnitude and orientation of in-situ stress is important to many subsurface science and engineering problems. In the development of an Enhanced Geothermal System (EGS), the knowledge of in-situ stress impacts several aspects such as reservoir characterization, deep well drilling, hydraulic stimulation, and induced seismicity.

Constraining the in-situ stress requires the determination of a stress tensor with six independent unknowns (the magnitudes of three principal stresses and their orientations). In most geological settings within the Earth’s upper crust, we can assume that the three principal stresses are vertical stress (Sv), and two horizontal principal stresses (Shmin and SHmax). In general, the magnitude of vertical principal stress (Sv) is obtained by integrating the density logs, and the magnitude of minimum principal stress (Shmin) can be measured through hydraulic fracturing tests (e.g., DFIT, leak-off test, microfrac test). In addition, the orientations of Shmin and SHmax can be identified using observed wellbore failures (breakouts and drilling-induced fractures), crossed-dipole sonic logs, and seismic focal mechanisms. However, the determination of the magnitude of maximum horizontal principal stress (SHmax) is challenging.
How Grooves Can Improve Casing Tripping-Out from the Cemented Borehole
Authors: Xie Xiyang , Ytrehus Jan David , Taghipour Ali , Kulkarni Raghavendra
Published: October 2022

Field observation shows a challenge to pull out a cemented casing without cutting it into pieces due to the limitation of pulling force. Required force can often be beyond the capacity of pulling equipment and it can also be beyond the material strength of the casing causing failure if one should be able to use excessive force for removal. For cases where removal of the cemented casing is necessary different approaches have been considered. Introducing grooves to the casing lowers the pulling force to remove it from the cemented wellbore and has been conceptually considered. This method has been demonstrated successfully in lab-scale experiments. The simulations, based on lab-scale geometry, verify the experimental observation and frictional cohesion, the key parameter to control pulling force, is quantified. The field-scale simulation indicates a significant reduction of the pulling force even with small grooves (5 mm width). The peak of the pulling force also illustrates the possibility of pulling a 10-meter grooved casing without cutting it into pieces. This study demonstrates a potential to shorten the non-productive time and save cost on plug and abandonment tasks.

1. INTRODUCTION

Pulling a 20-inch surface casing from cemented borehole encounters challenges. In a field scenario, the evaluated pulling force can be more than 1000 tons to trip out a 10-meter surface casing. The downhole pulling tool limits the pulling force up to 350 tons in many situations. This allows only a 3-meter casing section to be pulled out at each run. With such restrictions, a 10-meter casing would be cut into 3 pieces (3 meters for each piece) and pulled out one by one. These restrictions increase the non-productive operational time and cost. Therefore, novel technics are demanded to lower the pulling force if mechanical casing removal is to be applied further. The aim is to pull at least one 10-meter casing at once.
Mechanism Analysis of the Regular Pipe Sticking in Extended-Reach Drilling in the Eastern South China Sea
Authors: Zhao Jun , Huang Wenjun , Gao Deli , Zhao Lipeng
Published: October 2022

In the drilling process of extended-reach wells in the eastern South China Sea, the problem of regular pipe sticking is quite prominent. In order to effectively control it, this paper studies the mechanism of regular pipe sticking. It is thought that there are two main reasons: (1) A large number of open hole keyways are formed because connectors grind cuttings bed and wellbore; (2) Serious local cuttings accumulation at the connectors because of axial motion. Based on the above analysis, the mechanical resistance coefficient is introduced to characterize the local resistance of connectors. In this way, an amended drag & torque model is built. The case study shows that the local resistance and additional torque of each connector are about 360 N and 25 N·m during backreaming, and 350 N and 21 N·m while drilling. Furthermore, the mechanical resistance coefficient increases with the increase of cuttings bed thickness and the decrease of formation strength.

1. INTRODUCTION

In the 1920s, the United States first used extended-reach wells to develop offshore oil and gas fields, which indicated that the directional drilling technology was developed to a new level (Gao, 2018). At present, extended-reach well has become the key technology for developing complex oil and gas resources in ocean, beach, lake, etc (Gao, 2019).

Since the first extended-reach well was drilled in 1997, more than 70 extended-reach wells have been drilled in the eastern South China Sea, which made important contributions to the effective development of oil and gas resources (Shi, 2008; Gao, 2009). However, serious regular pipe sticking caused huge economic and time losses. Fig. 1 shows its typical performance. During the drilling process, pipe sticking occurs frequently and usually takes a single drill pipe as a period, but the circulation of drilling fluid and the rotation of drill pipe string are not suffocated. According to statistics, it takes about 0.5~4 hours to deal with a stuck point, and sidetracking is even required in some severe cases. In general, about 70% of the lost time was related to pipe sticking (Alshaikh, 2018).
Numerical Simulation of Wellbore Closure Due to Shale Creep: Potential for Annular Sealing Barrier Formation
Authors: Morales-Monsalve C. B. , Fontoura S. A. B. , Rosero-Argote S. , Lomba R. F. , Machado L. , Carrera S. , Ezechiello I.
Published: October 2022

The abandonment of an oil well at the end of its operational life must adhere to strict regulations to ensure that no leakage from the reservoir surrounding the wells occurs. The high costs of plug and abandon (P&A) operations have prompted the oil industry to investigate the possibility that certain rock formations around the well could deform enough during the well’s life to close the uncemented annular and strongly touch the casing, thereby promoting the formation of an impermeable barrier. This paper describes a protocol for numerical simulation of uncemented annular wellbore closure in shale sections. The simulation is carried out in plane strain and axisymmetric conditions using the commercial finite element code ABAQUS. The short-term drilling displacements are modeled using the rock’s elastic response, and the creep behavior is evaluated using poroviscoelastic behavior. The results show that, depending on the hypotheses used, the annular space can be closed in a variety of time spans. Finally, the contact pressure developed between the casing string and the rock formation upon full annular space closure is shown, as well as its variation over time.

1. INTRODUCTION

Nowadays, the worldwide process of well abandonment and decommissioning is accomplished through wellbore annular cementation; this procedure is carried out to prevent fluid (oil and gas) leakage from the well to the surface (Williams et al., 2009). With the goal of improving this process, the Brazilian Institute of Petroleum (IBP) developed the document "Guidelines for Well Abandonment," which emphasizes the creep potential of some sedimentary rock formations, particularly evaporites and shales, and how this property can act as permanent barriers in parts of casing wells and non-cemented wells (IBP, 2017). This unique mobility characteristic should ideally be observed throughout the field, giving it a regional character rather than being restricted to the location of a well. Furthermore, in order to consider this option as a possible substitute for the reliable isolation provided by a cement barrier during field abandonment, the rock formation, upon closure of the annular space, must have low permeability and be able to withstand the stresses, fluid pressures, and temperature that will be applied over time (Fjaer et al., 2016).
A Comprehensive Case Study on Lost Circulation of Changqing Mizhi Block in Perspective of Geomechanics
Authors: Li Xingbao , Ban Fansheng , Zhu Yujie , Luo Jiangwei , Chen Shaoyun , Jin Sheng , Che Zhenhua , Dong Jingnan
Published: October 2022

Drilling mud loss is of crucial importance in drilling. Lost circulation will extend the well construction period, cause investment losses, and even cause serious downhole accidents. In the Mizhi block of Changqing Oilfield targeted by this research, serious leakage occurred in many wellbore drilling processes, which has seriously affected the development of the block and caused economic losses. This paper focuses the mud loss during the drilling process of more than 200 wells in the Mizhi block, and counts the key loss data such as the lost horizons, the amount of lost drilling fluid, the average leak rate, and the density of the drilling fluid, and fully analyzes the possible reasons of the lost circulation. Collecting logging data, modeling geomechanics of some key wells and formations and taking cores. Finally, the geomechanical model is established. Analyzing the logging data and the specific leakage situation, the leakage mainly comes from fracture, and the leakage horizons mainly locate at the bottom of the Liujiagou Formation, the entire interval of the Shiqianfeng Formation and the top of the Shihezi Formation. Most of the mud loss sections are sand-mudstone interbeds. Geomechanical analysis shows that the rock mechanical strength of the entire interval is difficult to support the stability of the wellbore under the drilling fluid density of 1.1 grams per cubic meter, but the block loss pressure is generally between 1.1 - 1.2 grams per cubic meter. Collapse and leakage coexist in the wellbore. This study gives the method of drilling fluid optimization, and gives the possible reasons for the leakage from the perspective of geomechanics, which has important guiding significance for the further development of the Mizhi block.

1. INTRODUCTION

During drilling or completion operations, when the pressure of the effective drilling fluid density in the wellbore is greater than the formation pressure, the fluid will flow to the formation along the leakage channel around the wellbore, resulting in lost circulation. (MD Hashmat et al. 2016)Loss of circulation not only causes a large amount of drilling fluid loss, but also may cause a series of other drilling accidents, such as stuck pipe, blowout and even wellbore scrapped and other serious consequences.(Zhang et al.2016) Ultimately, it increases the non-operation time of drilling and causes huge economic loss. The time consumed to deal with lost circulation accounts for about 10% of drilling operation time, and the economic loss in drilling caused by lost circulation is as high as 2 billion US dollars every year.(Arshad Umar et al.2014) If the leakage appears in the reservoir, it will also cause reservoir damage, thus affecting the subsequent production of oil and gas. Therefore, lost circulation is regarded as one of the most complex and harmful accidents in drilling operations.
Modelling Stress Evolution in Cement Plugs During Hydration
Authors: Moghadam A. , Corina A. N.
Published: October 2022

In this work, we have developed a methodology to model the stress evolution in cement plugs during hydration. The model begins with the slurry state of cement and calculates the water consumption and void creation over time as the hydration reactions progress. The void volume change due to chemical shrinkage is imported into a coupled mechanical model that calculates the pore pressure drop and the resulting change in stresses. The results of the proposed modelling methodology are verified using lab experiments from the literature. The results provide new insights in understanding cement behavior under lab and field conditions. Under most scenarios, cement’s pore pressure drops to saturation pressure of water which leads to partial evaporation of the remaining pore water. This pore pressure drop controls the radial stress change, according to the theory of poroelasticity. For a plug set under an initial pressure of 5 MPa, the radial stress drops to 1.6 MPa after 20 hours of curing. This stress drop can cause the cement to debond from the casing, if the fluid pressure above the plug exceeds the final radial stress. This methodology can be extended to annular cements and initial cement stress after placement can be readily calculated.

1. INTRODUCTION

Zonal isolation in active and abandoned wells is paramount to ensure minimal fugitive methane emissions and to protect shallow freshwater aquifers. Wells penetrate different strata and can create a leakage pathway in case of a damaged cement sheath. This has been linked to methane emissions to the atmosphere (Schout et al., 2019), and aquifers (Osborn et al., 2011). Historically, oil and gas wells have been the main culprit in providing the leakage pathway for unwanted fluids. As more geothermal, energy, and carbon storage wells are drilled as part of the energy transition, zonal isolation challenges require more attention due to the long expected lifetime for these wells and unique operating conditions.
Effect of Interlaminar Difference on Height Propagation Behavior of Hydraulic Fracture in Lucaogou Shale
Authors: Zhang X. H. , Zhang S. C. , Zou Y. S. , Li J. M. , Wang J. C. , Zhu D. Y. , Zhou G. J. , Yang C.
Published: October 2022

The shale oil reservoir of Lucaogou Formation is characterized by complex lithology changes in vertical direction and lamination. To simulate the lithology variation of shale oil formation, downhole cores with different lithologies were prepared and bonded to layered samples. After that, the influence of interlaminar difference on propagation behavior of hydraulic fractures (HFs) was investigated through laboratory hydraulic fracturing and mechanical characteristics analysis. The result shows that mechanically weak bedding planes (BPs) leads to obvious anisotropy of rock mechanical properties. The rock samples is unstable when loaded along the parallel BPs direction, the tensile strength decline significantly, which is about 20% of the tensile strength measured perpendicular to BPs. The brittleness of rock samples measured parallel to BPs is greater than that measured perpendicular to BPs, by about two times. This results in HFs induced by low-viscosity slickwater are easily arrested by BPs, can not penetrate interlayer. HFs induced by high viscosity gel can penetrate the bonding interface. The difference of tensile strength between layers increases, the decrease degree of fracture width increases 2.5 times. This will impede proppant placement in interlayer. This research results provide a basis for the optimization of hydraulic fracturing of Lucaogou shale oil reservoir.

1. INTRODUCTION

The reservoirs of Lucaogou Formation in Jimusar sag, Junggar Basin are saline lacustrine and delta facies (Zou et al., 2020; Nie et al., 2011). The variation of climate and source supply intensity as well as the periodical fluctuation of lake level lead to the longitudinal lithology variation, and BPs development (Li et al., 2020; Zhang et al., 2021; Yang et al., 2018; Zhi et al., 2019 ). The influence of interlayer difference and BPs on reservoir fracture propagation is unclear. The selection of fracturing techniques and engineering parameters lacks theoretical support, and HFs height and vertical fracturing volume are limited (Lei et al., 2021; Jiang et al., 2021;). Understanding the influence of interlayer difference and BP structure on fracture propagation is the key to optimize hydraulic fracturing strategy, which is of great significance to improve the adaptability of fracturing process parameters and realize the overall utilization of multi-layer sweet spot body.
Development and Evaluation of a Novel Delayed Crosslink, Low Friction, High-Density Brine-Based Fracturing Fluid for Ultra-Deep Fracturing Stimulation
Authors: Xu Hang , Zhou Fujian , Wu Hao , Li Yuan , Sheng Lianqi , Yao Erdong
Published: October 2022

Using heavyweight brines as a base for fracturing fluids is an effective method for solving the problem of exorbitant surface pressure during the deep well fracturing process. However, higher fluid densities can lead to higher friction pressures, and with the well depth increases, the travel time to the mudline prolongs, resulting in the demand for extended crosslink delay times. Therefore, fracturing fluids that provide flexibility in density, lower friction and extended crosslink times are required for effective stimulation in ultra-deep reservoirs. This paper presents details of laboratory studies to develop and evaluate a novel weighted fracturing fluid. The main additives of the novel system were sequentially synthesized, including modified guar gum, a new weighting agent and an organic boron-zirconium crosslinker. Afterwards, a series of lab experiments were carried out to test the comprehensive performances of the novel system, such as temperature and shear resistance, friction reduction, gel breaking performance and core damage rate. The optimal formula of fracturing fluid was 54.3 wt.% weighting agent + 0.4 wt.% modified guar gum + 1.0 wt.% pH regulator + 0.5 wt.% crosslinker. Results show that the novel weighted fracturing fluid is a good choice for ultra-deep reservoir hydraulic stimulation and hence improving the recovery.

1. INTRODUCTION

Advancement of exploration and drilling technologies impel the oil and gas industry to extend the depth for hydrocarbons. Achieving efficient development of deep oil and gas is an important way for China’s recent oil and gas exploration and development (Xu et al., 2022; Lei et al., 2021; Wei et al., 2021). For major high-temperature and ultra-deep reservoirs in West China, hydraulic stimulation is facing some particular challenges. For instance, where the true vertical depth is more than 6000 m, there the rock fracturing pressure is often over 100 MPa and the temperature beyond 150 °C (Zhu et al., 2021; Ma et al., 2022). The traditional fracturing fluid system is difficult to play a role in the high-temperature deep well-fracturing process, and the weighted fracturing fluid system is a potential solution for deep well fracturing stimulation. At present, the formula of the weighted fracturing fluid system is not mature enough, and the upper limit of the density that can be weighted is restricted by economic and environmental protection (Wang et al., 2019; Yang et al., 2020; Qiu et al., 2009). Meanwhile, the weighted fluid system does not possess excellent friction reduction performance and cannot meet the requirements of deeper well fracturing stimulation. Therefore, it is essential to carry out the research on a novel weighted fracturing fluid system with high density, low friction and other excellent performances.
Numerical Investigation of Particle Bridging near Fracture Entrance
Authors: Han Yanhui , Luo Bo , Chang Frank , Li Wenwen
Published: October 2022

Particle transport and bridging inside fractures is an important subject in wellbore drilling and completion. For example, when drilling naturally fractured formations, depleted formations, and offshore formations where fractures can be easily induced or reactivated, loss circulation material (LCM) containing high loading of solid particles is commonly used to seal the pre-existing or newly created fractures to prevent mud loss. The particles are expected to bridge the fracture at the entrance area to maximize the sealing effectiveness and efficiency. A different example is the well completion with hydraulic fracturing, in which the proppant particles are injected with fracturing fluids to keep the fractures open after the fracturing pressure is released. To maximize the opening area of the fractures thus the well productivity, the placement of the proppant particles is expected to reach the far region of the fractures, so the particle bridging near the fracture entrance should be avoided. On the other hand, should the objective be promoting multiple fractures, particle bridging against a pre-existing or dominant fracture is beneficial to redirect the fracturing fluid into less conductive fractures. The ability to predict the bridging location and time with given solid particle size and concentration, fluid viscosity and operating parameters will help design drilling fluid, LCM, fracturing fluid, and diverting materials. In this work, a simulator is developed for numerically experimenting the particle bridging in the entrance area of a fracture. The fluid flow in the fracture is simulated by pipe network flow model. The equation of particle advection with fluid is solved using the upwind numerical scheme. The particle bridging is evaluated using a blocking criterion proposed in the literature. After all the implemented computational components are tested and verified, extensive parametric studies are then performed to experiment how various parameters, including particle size and concentration, fluid viscosity and injection rate, influence the particle bridging location and time near the entrance area. Accordingly, a few recommendations are provided to assist the design and selection of diverting and LCM agents.
Laboratory Characterization of a Synthetic Sandstone for Tunnel Rockburst Study
Authors: Wibisono D. Y. , Arora K. , Gutierrez M.
Published: October 2022

Assessment of rockburst potential in the rockmass is one of the main challenges in tunnel design. The phenomenon of rockburst is often linked with brittle failure characteristics of the rock leading to high strain-energy release and spalling, fractures, and damage around the tunnel boundary. This paper develops a synthetic sandstone as a model material for bursting rocks prepared in the laboratory to advance the study of the rockburst phenomenon. The synthetic sandstone is composed of fine-grained F-75 Ottawa sand, type I/II cement, and water. The brittle behavior of the material was studied based on the full stress-strain curve observed in the synthetic sandstone. Also, the synthetic rockburst-susceptible rock suitability is evaluated using several empirical criteria, such as strength brittleness index, burst energy coefficients, a brittleness index modified, and a strain energy storage index. The laboratory tests found that the material can be easily reproduced in different shapes and geometry with repeatable properties. The elemental testing damage characterization of the synthetic sandstone shows that the material is similar to bursting rock. The synthetic sandstone will be further expanded in laboratory-scale physical model testing using a true-triaxial cell to study the complex problem of rockburst.

1. INTRODUCTION

The sudden, violent manner of rockburst is a complex phenomenon that remains a significant hazard for many deep underground excavations (Simser, 2019). Understanding the primary cause of rockburst and its interdependence enables engineers to make more informed risk management and mitigation decisions. One approach to improve the understanding of the failure process for the excavation is building a reproducible physical model under controlled circumstances in different shapes and geometry (Klammer et al., 2017).

Although categorized as medium strength rocks, historical evidence has shown that rockburst can occur in this lithology (Q. M. Gong et al., 2012; Naji et al., 2019; Sun et al., 2016). Researchers have attempted to produce artificial rocks similar to natural sandstone in the past few decades. The efforts include a sintering process of natural sand grains with artificial beads, artificial cement, 3D printing, and chemical reaction utilization (David et al., 1998; Huang and Airey, 1998; Ishutov et al., 2015; Osinga et al., 2015; Rice-Birchall et al., 2021). However, these methods necessitated extensive resources and were considered limited in terms of ease of preparation.