Tag Archives: Basement

Modeling Crustal Structures of Southern Nigeria Basins from Aeromagnetic Data: Implication on Hydrocarbon Prospectivity (Published)

Aeromagnetic data has been used by many authors worldwide in evaluation of subsurface basin configuration.This study covers parts of five basins (Niger Delta, Calabar Flank, Anambra Basin, Mamfe Basin, and Lower Benue Trough) in Nigeria.The study utilized twenty aeromagnetic maps on a scale of 1:100,000. The maps were digitized manually along flight lines and a total of 16,689 data points obtained. The data was processed using computer techniques including map merging,  reduction to pole, polynomial and power spectrum filtering for residual and regional anomaly separation,and forward and inverse 2.5D saki modeling .Results obtained from power spectrum depth analysis indicate depth to magnetic sources vis – a –vis sediment thickness  from the Niger delta area (2.75km -3.75km), Anambra basin (1.5 km – 2.6 km ), Calabar Flank (1.3 km – 2.3 km ), Mamfe basin (2.0 km – 3.4 km ), and Lower Benue Trough (1.5 km – 3.2 km ). Also,  depth to basement results from forward and inverse modeling indicate the Niger Delta has thickness of sediments ranging between 1.0 km- 8.0 km, Anambra basin (1.4 km – 2.7 km ),Calabar Flank (0.8 km- 2.5 km), Mamfe Basin (1.0 km – 2.7 km), and Lower Benue Trough (1.4 km – 2.7 km). Also, results from modeled number of intrusives indicate that the Calabar Flank has five intrusives , Niger Delta has four intrusives , Mamfe basin has six intrusives , Anambra basin has five intrusives, and Lower Benue Trough has four intrusives. The implications of the increased number of intrusives is that generated hydrocarbons might be converted to gas ,this is more likely in areas around Calabar Flank, Mamfe basin and Anambra basins, given the high number of occurrence of intusives within these areas. whereas  areas around the Niger Delta and Lower Benue Trough with significantly increased depth and lower number of intrusive are less proned to excessive heat from the intrusive and may produce more oil .The study support futher exploration activities within the Niger Delta and Lower Benue Trough areas.

Keywords: Aeromagnetics, Basement, Configuration, Intrusives, Power Spectrum

AZIMUTHAL SQUARE ARRAY RESISTIVITY SOUNDING OF SHALLOW SUBSURFACE FRACTURE DISTRIBUTION IN PARTS OF THE EASTERN BASEMENT COMPLEX OF NIGERIA (Published)

Azimuthal square array resistivity sounding method was carried out at twelve (12) locations within Parts of the Eastern Basement Complex of Nigeria. The field data were collected using ABEM Terrameter with other accessories. For square – array, the location of measurement point is the centre point of the square and array size of 28m and 42m, 56m and 70m were used and each square was rotated in 150 increments about the centre point for a total of 3600.Data were analyzed using Origin pro. 8.0 Software. The results of the study showed the presence of fracture zones and seven (7) of the fracture zones were oriented in the NE – SW direction, while six (6) were oriented in the NW – SE direction indicating that the study area is has good potentials for ground water development.

Keywords: Abem Terrameter, Basement, Fracture, Groundwater, Resistivity, Square Array

APPLICATION OF GEOELECTRICAL TECHNIQUE IN DELINEATING GEOLOGICAL STRUCTURES AROUND GANAWURI AREA, NORTH CENTRAL NIGERIA (Published)

Geophysical investigation involving the use of geoelectrical technique has been carried out to delineate buried geological structures around the proposed Ganawuri Dam Site North Central Nigeria. The objective of this study is to establish the depth to fresh basement in the area using the VES technique with a view to delineating those near surface structures that could be deleterious to any construction work embarked upon within the area and to proffer a befitting recommendation that would necessitate the construction of a dam to impound the flowing stream and develop a reservoir which could be used for irrigation. The area is underlain by the Crystalline Basement rocks composed of granite gneiss, with late diorite, basalts and pegmatite intrusions. The older units have been intruded by the biotite granite of the Younger Granite province, occurring as a ridge bordering the north eastern margin of the area. ABEM Terrameter SAS 1000C model was used and the symmetrical Schlumberger configuration adopted. A total of twenty (20) Vertical Electrical Sounding (VES) stations were established and fully occupied along three (3) different profiles (AA/, BB/ and CC/) in the study area. Preliminary input data from the field were fed into Zohdy software to generate real resistivities and depths to geoelectric layers. Three (3) geoelectric layers were interpreted. The first geoelectric layer is a thin lateritic top surface with resistivity range of 270-4100 ohm-m with average thickness of 1.94m. The second geoelectric layer is interpreted as the weathered basement with resistivity range of 16-3510 ohm-m and the thickness ranges from 1.06-29.2m. This layer was observed to be very clayey at VES points 5, 6, 7, 10, 12, 16 and 17. The third interpreted geoelectric layer represents the fresh basement with infinite resistivity trend and thickness. The VES section delineated presence of fault/shear zones at 13m, 22m, 13-41m and 13-21m at VES 2, 3, 18 and 19 respectively along profile AA/. Along profile BB/, fault/shear zones were observed at 25-36m below 27m and 28m at VES 13, 14 and 15 respectively. Fault/shear zones were equally delineated between 11-17m at VES 10 along profile CC/. These shear zones are known for their structural weaknesses. Any construction work to be sited within the area should take into account these zones and geotechnical method such as grouting should be applied to seal off these shear zones.

Keywords: Basement, Ganawuri, Geoelectric Layer, Schlumberger array, Seepage, Shear zone