Azimuthal anisotropy analysis of walkaround vertical seismic profiling vertical seismic profiling: a case study from Saudi Arabia

Understanding fracture orientations is important for optimal field development of fractured reservoirs because fractures can act as conduits for fluid flow. This is especially true for unconventional reservoirs (e.g., tight gas sands and shale gas). Using walkaround Vertical Seismic Profiling (VSP) technology presents a unique opportunity to identify seismic azimuthal anisotropy for use in mapping potential fracture zones and their orientation around a borehole. Saudi Aramco recently completed the acquisition, processing and analysis of a walkaround VSP survey through an unconventional tight gas sand reservoir to help characterize fractures. In this paper, we present the results of the seismic azimuthal anisotropy analysis using seismic traveltime, shear‐wave splitting and amplitude attenuation. The azimuthal anisotropy results are compared to the fracture orientations derived from dipole sonic and image logs. The image log interpretation suggests that an orthorhombic fracture system is present. VSP data show that the P‐wave traveltime anisotropy direction is NE to SW. This is consistent with the cemented fractures from the image log interpretation. The seismic amplitude attenuation anisotropy direction is NW to SE. This is consistent with one of the two orientations obtained using transverse to radial amplitude ratio analysis, with the dipole sonic and with open fracture directions interpreted from image log data.     

Locational analysis of slums and the effects of slum dweller’s activities on the social,economic and ecological facets of the city: insights from Kumasi in Ghana

GeoJournal - Slum development has become a major urban planning and management problem due to the challenges they pose to the larger urban environment. Activities of slum dwellers are...     

Mapping of prospectivity and estimation of number of undiscovered prospects for lode gold,southwestern Ashanti Belt,Ghana

In the southwestern part of the Ashanti Belt, the results of fractal and Fry analyses of the spatial pattern of 51 known mines/prospects of (mostly lode) gold deposits and the results of analysis of their spatial associations with faults and fault intersections suggest different predominant structural controls on lode gold mineralisation at local and district scales. Intersections of NNE- and NW-trending faults were likely predominantly involved in local-scale structural controls on lode gold mineralisation, whilst NNE-trending faults were likely predominantly involved in district-scale structural controls on lode gold mineralisation. The results of the spatial analyses facilitate the conceptualisation and selection of spatial evidence layers for lode gold prospectivity mapping in the study area. The applications of the derived map of lode gold prospectivity and a map of radial density of spatially coherent lode gold mines/prospects results in a one-level prediction of 37 undiscovered lode gold prospects. The applications of quantified radial density fractal dimensions of the spatial pattern of spatially coherent lode gold mines/prospects result in an estimate of 40 undiscovered lode gold prospects. The study concludes finally that analysis of the spatial pattern of discovered mineral deposits is the key to a strong link between mineral prospectivity mapping and assessment of undiscovered mineral deposits.     

Living conditions and social determinants of healthcare inequities affecting female migrants in Ghana

This paper is concerned with the living situation of female migrants in Ghana. We draw on the available research literature to examine the living conditions of female migrants paying special attention to the underlying interrelated factors impacting on their accessibility and utilization of orthodox healthcare. While a plethora of interconnected economic, social, cultural and institutional elements are key factors influencing the living conditions particularly, healthcare access and utilization, policy efforts undertaken to address the situation seem to focus only on the economic dimension. Three broad initiatives requiring active participation of multi-sectoral actors are outlined in efforts towards improving the situation.     

How do Ghana’s landfills affect residential property values? A case study of two sites in Accra

Like many countries in sub-Saharan Africa, Ghana lacks well-engineered sanitary landfill sites. Increased urbanization and concomitant real estate growth lead landfills to compete with residential land use, resulting in closer proximity between landfill sites and residential neighborhoods. The effects of landfills on the property values of nearby residential communities have been the subject of much debate in the developed world, where state-of-the-art and environmentally well-engineered landfills are common. However, academic and other research is inconclusive on the effects of landfills on property values in the developed countries. This paper addresses this knowledge gap by exploring the effects of landfills on residential property values in Ghana, using the Oblogo and Mallam landfills in Accra as a case study. Our analysis indicates that while landfills do depress nearby residential property values, the effects are contingent on property location relative to the level of urbanization in a community, and year of completion and total costs of property development.     

The changing rainy season climatology of mid-Ghana

Daily rainfall data are examined through the temporal analysis of various definitions of variable temporal units (VTUs) consisting of combinations of various starting dates and durations over mid-Ghana. These VTUs are independent of, yet encompass, the starting dates and durations of the major and minor rainy seasons. Within each VTU, total rainfall and number of rainy days are calculated to describe the rainfall characteristics of the unit. Means and variances of each variable are calculated for each unit over two 20-year periods, 1951–1970 (P1) and 1981–2000 (P2). In P2, the major and minor rainy seasons have undergone varying degrees of desiccation. This reduction in rainfall is, however, not temporally or spatially uniform. The widespread decline of mean rainfall totals and number of rainy days during the minor rainy season, often associated with greater inter-annual variability, is particularly threatening to the production of a second crop.     

Anisotropic elastic full‐waveform inversion of walkaway vertical seismic profiling data from the Arabian Gulf

Borehole seismic addresses the need for high‐resolution images and elastic parameters of the subsurface. Full‐waveform inversion of vertical seismic profile data is a promising technology with the potential to recover quantitative information about elastic properties of the medium. Full‐waveform inversion has the capability to process the entire wavefield and to address the wave propagation effects contained in the borehole data—multi‐component measurements; anisotropic effects; compressional and shear waves; and transmitted, converted, and reflected waves and multiples. Full‐waveform inversion, therefore, has the potential to provide a more accurate result compared with conventional processing methods. We present a feasibility study with results of the application of high‐frequency (up to 60 Hz) anisotropic elastic full‐waveform inversion to a walkaway vertical seismic profile data from the Arabian Gulf. Full‐waveform inversion has reproduced the majority of the wave events and recovered a geologically plausible layered model with physically meaningful values of the medium.     

Assessment of coastal communities’ vulnerability to floods using indicator-based approach: a case study of Greater Accra Metropolitan Area,Ghana

Coastal towns along the coast of Africa are among the most vulnerable to climate change impacts such as flooding and sea level rise. Yet, because coastal conditions in many parts of the region are poorly understood, knowledge on which population groups are at the most risk is less known, particularly in the Greater Accra Metropolitan Area (GAMA) of Ghana, where the capital city Accra is located. Without adequate information about the risk levels and why, the implementation of locally appropriate adaptation plans may be less effective. This study enriches our understanding of the levels of flood risks along the coast of GAMA and contributes knowledge to improve understanding of place-specific adaptation plans. The study uses data from a 300-household survey, stakeholder meetings, and interviews with local community leaders to construct an integrated vulnerability index. The index includes seven components made up of: dwelling type; house and house environment; household socioeconomic characteristics; experience and perception of flood risk; household and community flood adaptation strategies; house location, and physical characteristics. Our findings show that exposure to floods, particularly from local flash floods is relatively high in all communities. However, significant differences in sensitivity and adaptive capacity of the communities were observed due to differences in location, socioeconomic characteristics, and perception of risks to flooding and sea level rise. The complexity of factors involved in the determination of local-level vulnerability requires that the implementation of adaptation strategies needs to involve cross-sectorial partnerships, involving local communities, in building a comprehensive multi-risk adaptation strategy.