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Geophysical investigations for groundwater in the area around Bauchi town
216A
SITE INVESTIGATIONS:BOREHOLES
mography and specially seismic tomography is being made. (from Author) 965200 Tomographic velocity reconstruction for a fault dominant area M. A. Echeverri, Individual Studies by Participants at the
International Institute of Seismology and Earthquake Enginering, 31, 1995, pp 17-30. Describes current application of travel time tomography to seismic exploration to find out the seismic velocity distribution in different kind of rocks in a fault dominant area. In seismic tomography, both seismic sources and receivers may be buried beneath the surface in two or more bore-holes and the recorded events correspond to direct and reflected arrivals of P and S waves. (from Author) 965201 On the scope and limitations of the electromagnetic method in groundwater prospecting in a Precambrian basement terrain - a Nigerian case study M. O. Olortmfemi, M. A. Dan-Hassan & J. S. Ojo, Journal of African Earth Sciences, 20(2), 1995, pp 151-160. A pre-driUing, geophysical investigation for groundwater development in the Proterozoic basement of the northern central part of Kaduna State, Nigeria, involved the EM method. The amplitude of the EM conductivity measurements correlates more with the weathered layer conductivity than with the overburden thickness. The prediction of groundwater yield from the EM conductivity amplitude is also not feasible as no clearly defined relationship is established between these parameters. The method is not amenable to the mapping of confined fractures that are concealed beneath fresh and infinitely resistive basement rocks. (from Authors) 965202 Ground-penetrating radar used to assess aggregate in catastrophic flood deposits, northeast Alberta, Canada T. G. Fisher, H. M. Jol & D. G. Smith, Canadian Geoteehnical Journal, 32(5), 1995, pp 871-879. Coarse-grained aggregate deposited by a catastrophic flood located north of Fort McMurray, was examined using ground-penetrating radar (GPR) and lithostratigraphic logging techniques. The sedimentary structures mapped from the GPR transects were confirmed in adjacent trench exposures. Suggests that GPR is an efficient methodology for determining volumes of aggregate reserves, thicknesses of aggregate deposits, and mapping sedimentary structures of highenergy fluvial sediments. (Authors) 965203 PASISAR: a new tool for near-bottom very high-resolution profiling in deep water B. Savoye, P. Leon, Y. H. De Roeck, B. Marsset, L. Lopes & J. Herveou, First Break, 13(6), 1995, pp 253-258. Better seismic images of the shallow sub-seabed in deep water, achievable in theory by reducing the Fresnel zone, can be obtained by two different means: the first is to improve the focusing of the seismic source; the second is to deploy the seismic system near the sebed. The PASISAR project makes use of the second method. (from Authors) 965204 On the application of geophysics in the exploration for copper and chrome ores in Albania A. Frasheri, L. Lubonja & P. Alikaj, Geophysical Prospecting, 43(6), 1995, pp 743-757. Some generalized results of geophysical exploration for copper sulphide and chromite ores in Albania are presented. The most important geophysical methods used are electrical prospecting, gravity, magnetics and electromagnetics. Physical properties oftbe ores, genesis and geological problems to be solved have determined the proper choice of any of these methods in the complex exploration. (Authors)
965205 Geophysical investigations for groundwater in the area around Bauchi town E. M. Shemang, J. R. Umaru & A. F. M. Umaru, Journal of Mining & Geology, 30(1), 1994(1995), pp 81-86. A geophysical survey employing seismic refraction and vertical electrical sounding was carried out in parts of Banchi town and environs, using a 12 Channel Dresser R4 Seismograph and an Abem Tetrameter model SAS 300B. The results indicate that the overburden (regolith) in the study area ranges from about 10m to 45m at places. This regolith was seen from the VES study to consist essentially of top soil which is silty sand, and highly weathered basement material, all underlain by fresh crystalline basement. The results of the study suggest that the area South of Grudum hill and most parts of the Barkumbo valley are the best suited for a borehole programme. (from Authors)
Borehole and core logging 965206 Distortion in resistivity logging at shallow depth Tien-Chang Lee & B. N. Damiata, Geophysics, 60(4), 1995, pp 1058-1069. Owing to the proximity of an insulating ground surface, normal resistivity logging at shallow depths can yield an apparent resistivity that exceeds 200% of the formation resistivity for a homogeneous medium. The distortion is more acute for long-normal than for short-normal logging. Three examples from a landfdl site in southern California are presented to show such distortion. The magnitude of the distortion can be reduced by placing the reference-ground potential electrode at a radial distance that is about equal to the spacing between the downhole upper potential electrode and the upper current electrode. It can also be removed by including the radial distance in an array-dependent geometric factor that accounts for the resistivity of the borehole fluid and the proximity oftbe logging device to the ground surface. (from Authors) 965207 Analytical solution of the borehole resistivity casing problem J. R. Wait, Geophysics, 60(4), 1995, pp 1261-1264. There has been a strong interest in understanding how direct current flow is influenced by the presence of a metal casing in boreholes, in particular, when the current electrode is within the cyclindrical borehole, the resulting potential in the external region is severely shielded. Nevertheless, it is possible to exploit the external potential, even though it is very weak. The objective here is to determine analytical expressions for the resultant potentials/Io and Ve in the internal and external regions, respectively. (from Author) 965208 Induction log analysis of thinly laminated sand/shale formation T. Hagiwara, SPE Formation Evaluation, 10(2), 1995, pp 8690. Examines induction log responses to a thinly laminated sand/ shale sequence in a deviated borehole for arbitrary deviation angle and sand/shale composition. The induction log responses in a thinly laminated sand/shale sequence are the same as they would be if the tool is placed in a homogeneous but anisotropic formation with the horizontal and vertical conductivities given respectively by the parallel and the series conductivities of the sequence. Conversely, a thinly laminated sand/shale sequence can be identified as an anisotropic formation by induction logs. (from Author)
SITE INVESTIGATIONS:BOREHOLES
mography and specially seismic tomography is being made. (from Author) 965200 Tomographic velocity reconstruction for a fault dominant area M. A. Echeverri, Individual Studies by Participants at the
International Institute of Seismology and Earthquake Enginering, 31, 1995, pp 17-30. Describes current application of travel time tomography to seismic exploration to find out the seismic velocity distribution in different kind of rocks in a fault dominant area. In seismic tomography, both seismic sources and receivers may be buried beneath the surface in two or more bore-holes and the recorded events correspond to direct and reflected arrivals of P and S waves. (from Author) 965201 On the scope and limitations of the electromagnetic method in groundwater prospecting in a Precambrian basement terrain - a Nigerian case study M. O. Olortmfemi, M. A. Dan-Hassan & J. S. Ojo, Journal of African Earth Sciences, 20(2), 1995, pp 151-160. A pre-driUing, geophysical investigation for groundwater development in the Proterozoic basement of the northern central part of Kaduna State, Nigeria, involved the EM method. The amplitude of the EM conductivity measurements correlates more with the weathered layer conductivity than with the overburden thickness. The prediction of groundwater yield from the EM conductivity amplitude is also not feasible as no clearly defined relationship is established between these parameters. The method is not amenable to the mapping of confined fractures that are concealed beneath fresh and infinitely resistive basement rocks. (from Authors) 965202 Ground-penetrating radar used to assess aggregate in catastrophic flood deposits, northeast Alberta, Canada T. G. Fisher, H. M. Jol & D. G. Smith, Canadian Geoteehnical Journal, 32(5), 1995, pp 871-879. Coarse-grained aggregate deposited by a catastrophic flood located north of Fort McMurray, was examined using ground-penetrating radar (GPR) and lithostratigraphic logging techniques. The sedimentary structures mapped from the GPR transects were confirmed in adjacent trench exposures. Suggests that GPR is an efficient methodology for determining volumes of aggregate reserves, thicknesses of aggregate deposits, and mapping sedimentary structures of highenergy fluvial sediments. (Authors) 965203 PASISAR: a new tool for near-bottom very high-resolution profiling in deep water B. Savoye, P. Leon, Y. H. De Roeck, B. Marsset, L. Lopes & J. Herveou, First Break, 13(6), 1995, pp 253-258. Better seismic images of the shallow sub-seabed in deep water, achievable in theory by reducing the Fresnel zone, can be obtained by two different means: the first is to improve the focusing of the seismic source; the second is to deploy the seismic system near the sebed. The PASISAR project makes use of the second method. (from Authors) 965204 On the application of geophysics in the exploration for copper and chrome ores in Albania A. Frasheri, L. Lubonja & P. Alikaj, Geophysical Prospecting, 43(6), 1995, pp 743-757. Some generalized results of geophysical exploration for copper sulphide and chromite ores in Albania are presented. The most important geophysical methods used are electrical prospecting, gravity, magnetics and electromagnetics. Physical properties oftbe ores, genesis and geological problems to be solved have determined the proper choice of any of these methods in the complex exploration. (Authors)
965205 Geophysical investigations for groundwater in the area around Bauchi town E. M. Shemang, J. R. Umaru & A. F. M. Umaru, Journal of Mining & Geology, 30(1), 1994(1995), pp 81-86. A geophysical survey employing seismic refraction and vertical electrical sounding was carried out in parts of Banchi town and environs, using a 12 Channel Dresser R4 Seismograph and an Abem Tetrameter model SAS 300B. The results indicate that the overburden (regolith) in the study area ranges from about 10m to 45m at places. This regolith was seen from the VES study to consist essentially of top soil which is silty sand, and highly weathered basement material, all underlain by fresh crystalline basement. The results of the study suggest that the area South of Grudum hill and most parts of the Barkumbo valley are the best suited for a borehole programme. (from Authors)
Borehole and core logging 965206 Distortion in resistivity logging at shallow depth Tien-Chang Lee & B. N. Damiata, Geophysics, 60(4), 1995, pp 1058-1069. Owing to the proximity of an insulating ground surface, normal resistivity logging at shallow depths can yield an apparent resistivity that exceeds 200% of the formation resistivity for a homogeneous medium. The distortion is more acute for long-normal than for short-normal logging. Three examples from a landfdl site in southern California are presented to show such distortion. The magnitude of the distortion can be reduced by placing the reference-ground potential electrode at a radial distance that is about equal to the spacing between the downhole upper potential electrode and the upper current electrode. It can also be removed by including the radial distance in an array-dependent geometric factor that accounts for the resistivity of the borehole fluid and the proximity oftbe logging device to the ground surface. (from Authors) 965207 Analytical solution of the borehole resistivity casing problem J. R. Wait, Geophysics, 60(4), 1995, pp 1261-1264. There has been a strong interest in understanding how direct current flow is influenced by the presence of a metal casing in boreholes, in particular, when the current electrode is within the cyclindrical borehole, the resulting potential in the external region is severely shielded. Nevertheless, it is possible to exploit the external potential, even though it is very weak. The objective here is to determine analytical expressions for the resultant potentials/Io and Ve in the internal and external regions, respectively. (from Author) 965208 Induction log analysis of thinly laminated sand/shale formation T. Hagiwara, SPE Formation Evaluation, 10(2), 1995, pp 8690. Examines induction log responses to a thinly laminated sand/ shale sequence in a deviated borehole for arbitrary deviation angle and sand/shale composition. The induction log responses in a thinly laminated sand/shale sequence are the same as they would be if the tool is placed in a homogeneous but anisotropic formation with the horizontal and vertical conductivities given respectively by the parallel and the series conductivities of the sequence. Conversely, a thinly laminated sand/shale sequence can be identified as an anisotropic formation by induction logs. (from Author)