Analysis of P-wave attenuation anisotropy in fractured porous media

Fractures exert a strong influence on fluid flow in subsurface reservoirs, and hence an adequate understanding of fracture properties could provide useful information on how they may be managed optimally to produce oil and gas or to be used as repositories for carbon dioxide (CO2) to mitigate climate change. Since fractures are commonly aligned by the stress field, seismic anisotropy is a key tool in investigating their properties. Velocity anisotropy is now a well-established technique for determining properties such as fracture orientation and density, but in recent years, attention has focused on quantifying azimuthal variations in Pwave attenuation to provide additional information, especially on the fracture size. However, the practical application of this attribute in geophysical exploration is still limited due to the uncertainty associated with its measurement and the difficulty in its interpretation in terms of rock properties. There is still a lack of proper understanding of the physical processes involved in the mechanisms of attenuation anisotropy. In this thesis, I use the seismic modelling approach to study the effects of attenuation anisotropy in fractured porous media using P-waves with the main aim of improving the understanding of these effects and exploring the physical basis of using attenuation anisotropy as a potential tool for the characterization of fractured reservoirs. Fractures with length on the order of the seismic wavelength in reservoir rocks cause scattering of seismic waves which exhibits characteristic azimuthal variations. I study these scattering effects using complementary seismic physical (scale-model laboratory experiments) and numerical (finite difference) modelling approaches. The results of both approaches are consistent in delineating fracture properties from seismic data. The scattered energy is quantified through estimates of the attenuation factor (the inverse of the seismic quality factor Q) and shown to be anisotropic, with elliptical (cos2θ) variations with respect to the survey azimuth angle θ. The minor axis of the Q ellipse corresponds to the fracture normal. In this direction, i.e. across the material grain, the attenuation is a maximum. The major axis corresponds to the fracture strike direction (parallel to the material grain) where minimum attenuation occurs. Empirically, the magnitude of P-wave attenuation anisotropy is greater in fluid-saturated rocks than in dry rocks. I study the influence of fluid saturation on P-wave attenuation through synthetic modelling and compare the attenuation signature to that of dry fractured rocks. The results of the analysis show that the relaxation time strongly controls the frequency range over which attenuation occurs. The magnitude of the induced attenuation increases with polar angle and also away from the fracture strike direction. The attenuation exhibits elliptical variations with azimuth which are also well fitted with a cos2θ function. The magnitude of the attenuation anisotropy is higher in the case of the fluid-saturated rocks. All of these properties of the numerical model are in agreement with the results of empirical experiments in the laboratory. The same crack density can result from many small cracks, from a few large cracks, or from an equal number of cracks of various sizes with varying thicknesses in the same volume of background material. This makes it difficult to distinguish between the anisotropy caused by micro-cracks and that caused by macro-cracks. I study the effects of fracture thickness or aperture on P-wave scattering attenuation through seismic physical modelling, and find that the induced attenuation has a direct relationship with the fracture thickness or aperture. This result indicates the potential of using P-wave attenuation to get information which might be useful in examining the effects of voids in the rocks, and also provides a basis for further future theoretical development to distinguish the effects caused by thin micro cracks and large open fractures. Finally, I study the effects of two types of fluid saturation (brine and CO2 in the supercritical state) on P-wave attenuation through synthetic modelling, with particular attention to varying CO2 saturation using the CO2 properties at the Sleipner gas Field in the North Sea. The presence of CO2 causes more attenuation in the numerical model output than when the rock is saturated with only brine. The induced attenuation increases with decreasing percentage of CO2 saturation and has a maximum magnitude at 10 % CO2 saturation. Further work is needed to quantify the additional effect of fractures on these results

Timing and reasons for antenatal care booking among women in a tertiary health care center in Southern Nigeria

Background: Antenatal care is one of the four pillars of safe motherhood and its benefits in preventing adverse feto-maternal outcome is proven. Commencement of antenatal care early has been shown to be key for this benefit to be fully realized. The aim of this study was to determine the antenatal booking pattern of pregnant women and its determinants in our environment.Methods: A cross sectional study of women attending the booking clinic in the University of Uyo Teaching Hospital, Akwa Ibom State, Southern Nigeria over a three-month period.Results: The mean age of the respondents was 28.5 years. The mean gestational age at booking was 18.3 weeks. The majority of the patients were married (94.1%). 68.1% had a post-secondary education. 33.5% of patients were nultiparous, while 3.5% were grand multiparous. The majority of patients (72.4%) booked late for antenatal care. Age group, marital status, mode of delivery was not significantly associated with timing of booking. High levels of patient’s education, high levels of husband’s education as well as grand multiparity were significantly associated with late booking (P<0.05). Majority (65.4%) of patients claimed that it was safe to book at any time during pregnancy.Conclusions: The majority of women booked late for antenatal care. In our study, we have found that general and health education, subsidisation of cost for antenatal care and introduction of focused antenatal care will help to reverse this trend

Modeling of aquifer geo-hydraulic characteristics with geo-electrical methods at a major coastal aquifer system in Uyo, southern Nigeria

Characterization of aquifer geo-hydraulic properties is essential for groundwater management and conservation. This work demonstrates the use of electrical resistivity surveying data in the characterization of important geo-hydraulic properties within a major coastal aquifer in southern Nigeria. Geo-electrical data acquired along profile lines with the use of Schlumberger array configuration were used to determine the aquifer geo-hydraulic parameters such as aquifer resistivity ρb, water resistivity ρw, porosity Φ, formation factor F, hydraulic conductivity K, transmissivity T, permeability Kp, and tortuosity τ. The resistivity inversion models delineated the occurrence of four lithological layers, with resistivity of the geo-layers ranging from 2.4 to 4,393 Ω m. Contour maps were created to show the distribution of the various geo-electrical and geo-hydraulic parameters over the study area. Regression curves showing the relationship between the geo-hydraulic parameters were generated and used to generate empirical relationships between the parameters. The empirical formulas developed for these geo-hydraulic parameters will aid in future work seeking to characterize aquifer zones and model aquifer geo-hydraulic units. In all, electrical resistivity surveying was found to be a noninvasive, cost-effective, and efficient method of characterizing aquifer geo-hydraulic properties via nonpoint geo-electrical data collected over the earth's surface. HIGHLIGHTS Vertical electrical soundings were undertaken in the study area.; The geo-electrical data were used to generate important aquifer geo-hydraulic parameters such as hydraulic conductivity K and transmissivity T.; The region has locations of low and high resistivity values.; This major coastal aquifer in southern Nigeria has been characterized.; Empirical formulas relating the geo-hydraulic parameters have been generated.

Attitude of antenatal attendees to people living with HIV/AIDS in Uyo, south-south Nigeria

Background: Stigmatization and discrimination of people living with HIV/AIDS has a negative impact on the global efforts to control the HIV/AIDS pandemic. Due to fear of stigmatization and discrimination, many people are reluctant to undergo voluntary counseling and testing, infected individuals are often unwilling to disclose their status and some of them still engage in high-risk behaviours leading to increased transmission of the virus. Study design and setting: A study of the attitudes to people living with HIV/AIDS was carried out among antenatal clinic attendees at the University of Uyo Teaching Hospital with the aim of developing site-specific information and counseling interventions to reduce stigmatization and discrimination of people living with HIV/AIDS. Information was elicited from 265 randomly selected women who booked for antenatal care between September and December 2005 with the use of a self-administered questionnaire. Results: 263 questionnaires were duly completed and analyzed. The mean age of the respondents was 27 ± 5.1 years, majority of them (52.1%) were either unemployed or unskilled workers and 42.9% of them had tertiary education. Awareness and knowledge of HIV/AIDS was high, (95.8%) and (86.7%) respectively. Majority of the respondents (55.6%) were also assessed as having a positive attitude to people living with HIV/AIDS (PLWHA). There was a statistically significant association between good knowledge of HIV/AIDS and a positive attitude to PLWHA (P=0.000) and a high educational status with a positive attitude to PLWHA (P=0.009). Conclusion: combating stigma and discrimination is an important process in controlling the epidemic. Specific information and counseling interventions aimed at dispelling misconceptions about HIV/AIDS should be reinforced

Factors contributing to uterine rupture in women having vaginal births after caesarean section

Context: Ruptured gravid uterus is a common occurrence in our environment with higher risk in scarred uterus. Some women will attempt vaginal delivery at home after a caesarean section had been performed for cephalopelvic disproportion. Objective: To evaluate the various reasons put forward by our women for attempting vaginal delivery at home despite previous caesarean section. Subjects and Methods: Patients with ruptured gravid uterus during labour with history of previous caesarean section were studied using structured interview formats. Their demographic characteristics, social class, booking status, place of attempted vaginal delivery and various reasons for seeking unorthodox care. Close relative of patients were interviewed in unconscious or moribund patients. Results: Some 24(96.0%) of the patient had no antenatal care in the index pregnancy and had laboured in spiritual churches or in traditional birth attendants homes. Ninteen (76.0%) were of low social class. Various reasons for attempting vaginal delivery at TBA's or spiritual churches included lack of funds 9(37.5%) husbands or close relative not available to take decision for hospital delivery 6(25.0%), not appreciating the need for hospital delivery 3(12.5%) and no reason 1(4.2%). There were 12 maternal deaths giving a case fatality rate of 48%. Conclusion: The study shows socio economic factors, dependency on family decisions and belief in supernatural powers as major reasons our women chose unorthodox delivery despite prior caesarean section and recommend ways of preventing it.Keywords: vaginal birth after caesarean section, uterine rupture Tropical Journal of Obstetrics and Gynaecology Vol. 22(2) 2005: 177-17

Calabash Chalk's Geophagy Affects Gestating Rats' Behavior and the Histomorphology of the Cerebral Cortex

Introduction. Calabash chalk contains heavy metals, and this lead to this study on the effect of this chalk on the behavior and the histomorphology of the cerebral cortex of gestating rats. Material & Methods. 24 female rats were equally divided into 4 groups and were mated at preostrous with the males. The day after mating was designated as day 1 of gestation. On gestation days 7–20, groups 1, 2, 3, and 4 animals were treated with 1 mL of distilled water, and 1 mL (200 mg/kg), 2 mL (400 mg/kg), and 3 mL (600 mg/kg) of calabash chalk suspension, respectively. On pregnancy day 21, behavioral tests using the open field and the light/dark mazes were carried out and the animals subsequently euthanized and their brains were routinely processed. Results. There was no difference in ambulatory activities, but group 4 animals had more (P<0.05) transition frequency and were more averse to the dark in the light and dark field, while sections of the cerebral cortex showed a higher (P<0.05) cellular population, hypertrophied pyramidal cells, and vacuolations in the treatment groups. Conclusion. Calabash chalk may have anxiolytic effect especially at high dose in the light and dark field but not in the open field and can stimulate maternal cerebral cortical cellular changes

Remote blood collection from older adults in the Brain Health Registry for plasma biomarker and genetic analysis

IntroductionUse of online registries to efficiently identify older adults with cognitive decline and Alzheimer's disease (AD) is an approach with growing evidence for feasibility and validity. Linked biomarker and registry data can facilitate AD clinical research.MethodsWe collected blood for plasma biomarker and genetic analysis from older adult Brain Health Registry (BHR) participants, evaluated feasibility, and estimated associations between demographic variables and study participation.ResultsOf 7150 participants invited to the study, 864 (12%) enrolled and 629 (73%) completed remote blood draws. Participants reported high study acceptability. Those from underrepresented ethnocultural and educational groups were less likely to participate.DiscussionThis study demonstrates the challenges of remote blood collection from a large representative sample of older adults. Remote blood collection from&nbsp;&gt;&nbsp;600 participants within a short timeframe demonstrates the feasibility of our approach, which can be expanded for efficient collection of plasma AD biomarker and genetic data

Direct Detection of Groundwater Accumulation Zones in Saprock Aquifers in Tectono-Thermal Environments

Some vertical electrical sounding (VES) data from tectono-thermal environments usually plot anomalously on a VES curve, thereby distorting the curve trend at the points of their occurrence. These datasets usually plot noisily in the form of a sudden rise and drop in electrical resistivity values. They constitute abnormal datasets that are usually deleted to recover trends and consequently develop confidence in both the datasets and the modelling and interpretational processes. This study was conducted to assess their origin and consequently gain an understanding of their contributions to groundwater accumulation and transmission in saprock aquifers. The results, supported by co-located drilling and pumping test data, show that these datasets are indicators of subsurface conditions where high-resistivity unconformal structures directly overlie saturated (low-resistivity) porous media, provided that the resistivity of the first breakout point is less than those from subsequent points. Remote sensing data reveal that these types of curves are common in hard rock and metasedimentary environments. Borehole groundwater yields can also be assessed qualitatively from the number and trend of breakoff points. The integrity of the breakoff points must be affirmed by using more sensitive equipment for data acquisition and repeating the measuring process using different potential electrode separations and—where possible—VES profile orientation