Geomechanical modelling of stress magnitude and orientation across fault and its relation to hydraulic fracturing

With intense exploration around the world, easily extractable hydrocarbons are getting more and more difficult to find. Major conventional hydrocarbon accumulations have been targeted and are being produced; but increased world’s consumption has led petroleum exploration and production industry to consider exploiting targets that were not believed to be economical. Tight reservoirs include shale gas, shale oil, coal seam gas (CSG) and tight sands. This concept has changed the conventional view of shales from being source and seal rock to unconventional perception –as reservoir. These reservoirs have minimal porosity and permeability which is not sufficient to produce at economic rates. Developing these reserves may require hydraulic fracturing to create a predictable network of fractures with height of several hundred feet through which hydrocarbons can easily flow towards borehole. Even if these reservoirs are fracture stimulated at best of the knowledge and skills; production from two wells in the same field is never the same. For a successful fracturing treatment, it is necessary to understand impact of existing fractures, faults and stress regimes in the subsurface. Geologic structures influence the stress field locally and show deviation from the regional trend of stress pattern. This study utilizes geomechanical modeling with static elastic moduli to depict stress magnitude and orientation around faults. For the purpose, stress magnitudes estimated by Reynolds et al., (2006) are used. Strike-slip stress regime prevails in at the depth interval selected. A thorough study using different lithologies, σH azimuth and fault size is carried out. Stress concentrate at the fault tips on opposite quadrants of the fault tips. Fluctuation in stress magnitude increases with increase in fault size. However, the variation diminishes after fault size of 1500 meters. These models help in understanding the orientation of fractures during hydraulic fracturing and help to recognize stress barriers that may affect production from an unconventional reservoir.Thesis (M.Sc.(Petrol.Geosc.)) -- University of Adelaide, Australian School of Petroleum, 201

Study on borehole stability in fractured rocks in deep drilling conditions

Wellbore or borehole stability is a serious and expensive problem in mining and petroleum industry. With the development of new exploration and production technologies, Australian miners are looking for mineral deposits in deep seated environments. Borehole instabilities can be encountered at any stage in the life of a well, including drilling, completion and production. Borehole instabilities are the main cause of difficulties encountered during drilling. This results in significant expenditure, excessive loss of time, sometimes it results in loss of borehole. One of the most integral part of rock formation is the presence of joints and fractures at a small scale. According to some researchers most of the rock formations have fractures at some scale. When boreholes are drilled in such formations, instability is a major concern. In order to accurately predict the behaviour in fractured media, the matrix and fracture deformations as well as fluid flow in fractures need to be fully coupled. A number of factors influence borehole instabilities in fractured rocks. This may include solid-fluid interaction (rock and chemically active mud), complex stress conditions, probable borehole deviation, heterogeneity in the formation and drilling operations. Vertical boreholes are usually stable where overburden is the maximum stress (σ1). However, drilling vertically does not guarantee a stable hole. Instability in a borehole is dominated by the in-situ stress system. When an undisturbed rock is penetrated by drill bit, the in-situ stresses are redistributed. As a result, in-situ stresses tend to concentrate around the excavation. This is presented by an increase in stress concentration in the vicinity of the borehole and induced stresses near intersection of discontinuities and fracture tips. These induced stresses can lead to rock failure of the borehole wall. This thesis represents three journal publications which represent simulation of an unsupported and mud supported vertical borehole in two dimensional and threedimensional analyses. Because the nature of rock media is considered as fractured with single permeability along discontinuities, Discrete Element Model (DEM) was considered to be the best tool for investigations. First of all, Numerical investigation on the behaviour of an unsupported vertical cylindrical borehole in heavily fractured rock mass is presented. DEM based code Universal Distinct Element Code (UDEC) is used as the simulation tool. With taking into account the in-situ stress conditions in Cooper basin, South Australia. A borehole of 0.15 m radius in the centre of the model was simulated comprising of two fracture sets. The vertical stress applied correlates with the 1.5 km depth of the Cooper basin. The effect of fracture orientation and in-situ horizontal stress ratio (σH /σh) on the stability of the rock mass around the borehole was investigated. It has been shown that the induced stresses due to excavation lead to the development of a yielded zone around the borehole. Borehole stability criteria relevant to the extent of yielded zone and maximum displacement around the borehole were introduced into stability analysis. Results show that when the in-situ stress ratio increases the rock blocks at borehole wall tend to move towards the centre of borehole, consequently yielded zone around the borehole increases. Similarly, the fracture orientation changes the angle of borehole fracture intersection which aids in displacement increase as well as the location of block detachment. Furthermore, the change in fracture orientation highly influences the formation of yielded zone. Secondly, a 3D discrete element model is presented which is developed to simulate a borehole drilled in fractured rock mass. A model with overbalanced drilling conditions is simulated in this study. In doing so, different depths of a borehole, MB-1 borehole, in Northern Perth basin was simulated. The developed model was validated against log measurements of Caliper log. Rock strength was found to be one of the governing factor in controlling the stability. Thereafter, hydro-mechanical models were generated and it was observed that high mud flow rates and high pore pressure increased the instability around borehole. Furthermore, a parametric study was performed to investigate the influence of viscosity and fluid flow on the stability. Shear displacement linearly increase with an increase in the flow rate while fluid pressure decreases due to the increase in fracture’s aperture with an increase in the flow rate. Similarly, increase in viscosity caused increase in fracture shearing and therefore instability around borehole. After most important rock mass and operational parameters were analyzed, their influence was determined. A detailed stress analysis of 3D model of Northern Perth basin was carried out. Apart from the regional stress constraints, stress distribution in a smallscale area has several influencers. Constraining these localized stress perturbations is a key element in analyzing borehole stability and related underground excavations. As a final part of this study stress perturbation near the well bore and fracture tips was analyzed. As part of the study a regional model with three major faults was generated which was further used to estimate boundary stresses on descriptive smaller model termed as ‘base model’. In addition to the magnitude of stresses at tips of discontinuity, it was observed that when stress tensor pass through a material of low stiffness in this case, a discontinuity, it tends to rotate parallel to the discontinuity. A borehole in such rock mass determined that yield zone is in agreement with high stresses along discontinuities. Base model was further subjected to strength anisotropy and stress anisotropy analysis. Effect of stress anisotropy on stress perturbation is found to be very significant whereas strength anisotropy which was studied by changing of friction angle and cohesion in one of the discontinuities slightly affected stress perturbation. In both cases, due to the effect of discontinuities the induced stress field is non-linear.Thesis (Ph.D.) -- University of Adelaide, School of Civil, Environmental & Mining Engineering, 201

Environmental Influences on the Behavioural and Emotional Outcomes of Children: A Network Analysis

Background: Intellectual developmental disorders are a serious source of health morbidity with negative consequences for adults as well as children. However, there is limited evidence on the environmental, trace element, behavioural, and emotional outcomes in children. Here, we investigated whether there is any association between child behaviour and emotional outcomes and micronutrients using network analysis. Methods: A cross-sectional study was conducted in 9-year-old children within a Pacific Island Families study birth cohort. Elemental concentration was determined in children’s toenails after acid digestion and analysed using inductively coupled plasma mass spectrometry. We used network analysis to identify closely associated trace elements and tested the directions and strength of these trace elements. MANCOVA were used to identify the significant associations between individual elements and the behavioural/emotional function of the children using the children behaviour checklist (CBCL). At the final step, quantile regression analysis was used to assess and quantify the identified associations between CBCL function scores and manganese, adjusted by sex, ethnicity, and standardized BMI. Results: Three major nutrient networks were identified. In the Mn network, Mn was strongly positively associated with Al (0.63) and Fe (r = 0.65) and moderately associated with Pb (r = 0.45) and Sb (r = 0.42). Al was also strongly associated with Fe (r = 0.9). Children in the second or third clinical group, with an elevated externalized CBCL score, had a much higher mean and median level of Mn as compared to the normal range group. The aggression score was significantly associated with Mn concentration and sex. Higher Mn concentrations were associated with a higher aggression score. A 1 ug/g unit increase in Mn was associated with a 2.44-fold increase (95% confidence interval: 1.55–4.21) in aggression score, and boys had higher median aggression score than girls (difference: 1.7, 95% CI: 0.9–2.8). Attention and rule breaking scores were both significantly associated with Mn concentration. Higher Mn concentrations were associated with higher attention behaviour problem and rule breaking scores. A 1 ug/g unit increase in Mn was found to be associated with a 1.80-fold increase (95% confidence interval: 1.37–2.82) in attention score, and a 1.46-fold increase (95% confidence interval: 1.01–1.74) in the rule breaking score. Thought score was not significantly associated with Mn concentration (p = 0.13) but was significantly lower in boys (p = 0.004). Conclusions: Exceeding Mn levels is potentially toxic and has been identified to be associated with worse externalized children’s behavioural health and emotional well-being. Future studies are necessary to find the exposure paths so that advice shall be provided to family and care providers in public health and environmental protection

Assessment of Determinants of Paediatric Diarrhoea Case Management Adherence in Pakistan

Worldwide, diarrhoea in children under five years of age is the second leading cause of death. Despite having high morbidity and mortality, diarrhoeal diseases can be averted by simple and cost-effective interventions. The Integrated Management of Childhood Illness (IMCI) has proposed the use of Oral Rehydration Salt (ORS) and zinc together with adequate food and fluid intake for the management of acute non-dysenteric watery diarrhoea in children. In the past, few studies examined the determinants of adherence to diarrhoea case management. Therefore, this study measured the determinants of therapeutic and dietary adherence to diarrhoea case management using the third and fourth wave of Pakistan Demographics and Health Surveys (PDHS) datasets. Data from 4068 children between 0 to 59.9 months with positive history of diarrhoea were included, while data on children with dysentery, severe dehydration, and co-morbid condition was excluded. This study reported therapeutic adherence in less than 10% of children in Pakistan, while dietary adherence was reported in 39.2% of children (37.7% in 2012–2013 and 40.7% in 2017–2018). A significant improvement in therapeutic (0.8% in 2012–2013 and 8.1% in 2017–2018) and dietary adherence (37.7% in 2012–2013 and 40.7% in 2017–2018) was reported in the 2017–2018 survey compared to the 2012–2013 survey. In general, children over the age of one year (compared to children <1 year) and of the richer/richest socioeconomic class (compared to poorest/poorer socioeconomic class) showed higher therapeutic and dietary adherence. Therapeutic and dietary adherence among diarrhoeal children can be improved by increasing the awareness and accessibility of ORS, zinc, and essential foods

Association of pesticides and kidney function among adults in the US population 2001–2010

Chronic kidney disease of unknown cause is prevalent in a range of communities; however, its etiology remains unclear. We examined the association between pesticide exposures and the risk of kidney function loss using four waves of the National Health and Nutrition Examination Survey (NHANES) to identify a pathological pathway. We pooled data from four cross-sectional waves of NHANES, with 41,847 participants in total. Exposure to malathion increased the risk of low kidney function (aOR = 1.26, 95% CI = 1.01–1.56) in the adjusted model. Increased risk of low kidney function was not found among those exposed to 2,4-D (aOR = 0.88, 95% CI = 0.72–1.09), 3,5,6-trichloropyridinol (aOR = 0.96, 95% CI = 0.83–1.12), and 3-PBA (aOR = 1.03, 95% CI = 0.94–1.13). Our findings provide evidence of altered kidney function in people exposed to malathion, highlighting the potential of organophosphate pesticides’ role in renal injury

Association of Allergic Symptoms in the First 2 Years of Life With Sleep Outcomes Among Chinese Toddlers

Background: Previous studies have linked allergic symptoms to sleep in children, but the associations might be different when considering different types of allergic symptoms or sleep outcomes. Moreover, the combined effects of multiple allergic symptoms remain unclear in early life. This study aimed to investigate the associations between multiple allergic symptoms and sleep outcomes in early life. Methods: We included 673 toddlers aged 2 years from a birth cohort in Guangzhou, China. We identified allergic symptoms (skin, eyes and nose, gastrointestinal tract, mouth and lips, and wheeze) within 2 years via standard questionnaires. Sleep outcomes including sleep duration and quality over the past month were assessed based on the Chinese version of the Brief Infant Sleep Questionnaire. Associations between allergic symptoms and sleep outcomes were examined using multivariable linear regression and logistic regression. Results: Compared to children without allergic symptoms, children with allergic nasal and ocular symptoms had higher odds of frequent nighttime awakenings (OR = 1.41; 95% CI: 1.03, 1.93) and irregular sleep (OR = 1.45, 95% CI: 1.05, 2.00); children with allergic gastrointestinal symptoms slept 0.28 h less during nighttime (95% CI: -0.48, -0.07) and 0.25 h less per day (95% CI: -0.43, -0.08), and had 59% higher odds of irregular sleep (95% CI: 1.24, 2.04). We also found significant association of multiple allergic symptoms with shortened nighttime sleep duration and increased irregular sleep. Whereas, allergic skin, mouth and lips, and wheeze symptoms were not significantly associated with sleep outcomes. Conclusion: Allergic symptoms within 2 years of age were adversely associated with sleep outcomes, which highlight the importance of early screening of allergic symptoms in toddlers in order to improve their sleep outcomes

Final technical report : The International Alcohol Control (IAC) Study - Working Meeting, Torino, Italy, 7th and 8th June 2014

This is part of a funding proposal report. Funding received was used to support costs associated with the preparation, facilitation and hosting of the IAC study meeting in Torino, Italy. In addition the financial support enabled three low and middle income (LMIC) researchers and one member of the New Zealand IAC study team to attend the working meeting. IAC survey data was shared from participating countries; cross-country analyses were discussed and planned; and methodological issues encountered by the different research teams were discussed

Use of Serum Homocysteine to Predict Cardiovascular Disease in Korean Men with or without Metabolic Syndrome

The aim of this study was to examine whether serum homocysteine (Hcy) levels correlated with cardiovascular disease (CVD) depending on the presence or absence of metabolic syndrome (MetS) in Korean men. We conducted a case-control study, including 138 CVD and 290 non-CVD age-matched control subjects. The subjects were divided into four subgroups: 34 CVD/MetS, 104 CVD, 77 MetS, and 213 normal subgroups. The mean Hcy was significantly higher, whereas HDL and intake of vitamin B1 and B2 were lower in the CVD group (P < 0.05) than non-CVD group. When compared to the control group, subjects with CVD/MetS, CVD and MetS exhibited high Hcy levels, with the highest observed in the CVD/MetS subgroup (P < 0.001). Multivariate stepwise linear regression between CVD and markers of CVD showed Hcy significantly correlated with CVD (P < 0.05). To predict CVD based on Hcy, Hcy threshold of 11.72 µM in non-MetS subjects had an area under the curve (AUC) of 0.664 (95% CI 0.598-0.731). In MetS subjects, the AUC was 0.618 and Hcy threshold was 13.32 µM (95% CI 0.509-0.726). The results of our study show that the presence of MetS needs to be considered when using Hcy levels for predicting CVD

Health of Pacific children in New Zealand: association between selected elements, behaviour and body-size

In childhood environmental and dietary exposure to toxic and non-toxic elements may affect development and growth. The elemental concentrations of scalp hair and toenails may reflect chemical uptake via the diet, or environment. Very little is known about the relationship between elemental concentrations in scalp hair and toenails and behavioural and growth characteristics of children in New Zealand. The Pacific Islands Families (PIF) study has provided a unique opportunity for children of age six and nine years to explore such relationships. The overall aim of this research was to collect and analyse the scalp hair and toenails of Pacific children (and in some cases from their mothers) resident in South Auckland, New Zealand (as part of the PIF population study) for calcium, magnesium, iron, manganese, zinc, copper, selenium, iodine, cobalt, chromium, nickel, molybdenum, antimony, arsenic, aluminium, boron, mercury, lead and cadmium. Three questions were addressed: (1) what is the relationship between mercury in scalp hair, reported to originate from fish consumption to behavioural problems; (2) what is the relationship between mercury in toenails and behavioural characteristics and specific behavioural domains (particularly aggression, rule breaking, attention and social problems); and (3) in a population where three out of four children are defined as obese or overweight is there any relationship between elemental concentration in toenails and current body-size? The first study was a nested case-control study which recruited children (with and without behavioural problems) and their mothers to study the effects of mercury through seafood diet and dental amalgams on child behaviour. Hair samples were collected from both mothers and their children as a biomarker for mercury exposure. The second and third studies were cross-sectional studies designed to explore the association of elements on behavioural problems as identified by mothers (using the child behaviour checklist) and body-size categories (using the International Obesity Task Force’s (IOTF) cut-off points). Toenail clippings were collected as a biomarker for elemental assessment for these studies. The biological measurements (scalp hair and toenail) were carried out using inductively coupled plasma mass spectrometry (ICP MS). The existing multi-disciplinary, longitudinal PIF information provided additional data on confounding factors and co-variants on these samples. In the first study (n=92 mother and child pairs), almost 20% of both mothers (median hair: 0.32 µg/g mercury) and 18% of children (median hair: 0.43 µg/g mercury) exceeded the Environmental Protection Agency’s (EPA) threshold for mercury of 1 µg/g Hg but were lower than the World Health Organization’s (WHO) threshold of 1.6 µg/g Hg. There was no conclusive evidence on child behavioural problems and hair mercury concentrations. A direct correlation was observed between mothers and their children's hair mercury concentrations (r = 0.79 (95% CI 0.65, 0.88). In the next study (n=278 children; 160 boys, 118 girls), 21% of children had toenail mercury concentrations above 1 µg/g Hg with girls having higher mercury concentrations (24%) than boys (18%). Aggressive behaviour and seafood diet was associated with toenail mercury exposure after adjusting for gender, ethnicity and income levels (OR: 2.15 95% CI 1.45, 3.18 p-value< 0.05; OR 1.38 95% CI 0.83, 1.2 p value <0.05, respectively). Within the final study, three out of four children were defined as obese or overweight; however, no significant correlation was found between body-size categories and toenail elemental concentrations. The elemental interaction of selenium-mercury and zinc-copper had an association with the different body-size categories (p value 0.03; and p value 0.02, respectively). It was observed that the mean toenail selenium (0.35 µg/g Se), calcium (868 µg/g Ca) and zinc (129 µg/g Zn) concentrations were lower than the required optimal health concentrations for toenails (selenium 0.75 µg/g Se; calcium 900 µg/g Ca; zinc 160 µg/g Zn) amongst these children. Toenail mean lead (0.86 µg/g Pb), cadmium (0.21 µg/g Cd) and mercury (0.72 µg/g Hg) concentrations were also higher than the optimal health requirements. Ethnic differences in relation to toenail elemental concentrations were observed for manganese, cobalt, iron, chromium, antimony, aluminium, mercury, lead and cadmium. Boys had higher concentrations for calcium, magnesium, manganese, copper, zinc, iron, antimony arsenic, aluminium, boron and lead than girls. Toenail clippings are a better biomarker for elemental status within Pacific people than scalp hair samples. Overall, this research contributes to the understanding of the elemental concentrations for Pacific people using scalp hair and toenail clippings as biomarkers in terms of associations with health outcomes (particularly child behavioural problems and body-size categories). Mercury in toenails demonstrated a moderate association with a specific behavioural domain – aggressive behaviour – while elemental interactions such as zinc-copper and mercury-selenium seemed to influence the body-size categories in these children even though single elements did not show any associations on body-size categories. Furthermore, some possible explanations for both the conclusive and inconclusive results that have so far emerged, and suggestions for potential ways forward in this area of research are discussed

Localized stress field modelling around fractures using three-dimensional discrete element method

Understanding of field stress condition in fractured rock mass is required to investigate stability of underground excavations. To analyze stress perturbation in fractured rock mass, a regional model is generated using a DEM based code, 3DEC.Three major steep faults were considered in the model. The regional model then was used to estimate stresses on the boundaries of smaller descriptive model termed as the base model. Stresses were observed to vary in magnitude at the intersection of discontinuity sets and stress drop was observed at the discontinuity. In addition, stress tensors in the model were observed to rotate parallel to the discontinuity. A vertical borehole in base model revealed that high stresses concentrated along discontinuities may result in forming yield zones around the borehole. Furthermore, the base mode was subjected to strength and stress anisotropy analysis. Effect of stress anisotropy on stress perturbation was significant, whereas, stress values slightly changed by strength anisotropy. In both cases, due to the effect of discontinuities the induced stress field was non-linear and fluctuating. Effect of stress anisotropy on stress perturbation found to be more significant for the maximum principal stress as compare with the minimum principal stress.Ehtesham Karatela, Abbas Taher