Structural interpretation of aeromagnetic data over Nkalagu-Igumale area of the Lower Benue Trough of Nigeria was carried out to determine the depth to magnetic basement and delineate the basement morphology and the structural features associated with the basin and their trends. The aeromagnetic data were subjected to series of computer based image and data enhancement techniques before spectral analysis. Results of the 2-D spectral analysis revealed two depths source models with the depth model (D1) for deep magnetic source bodies which are associated with intra-basement discontinuities and faults ranging from 2.15 to 5.25 km while the depth model (D2) of the shallow magnetic source bodies range from 0.35 to 0.99 km. From an economic viewpoint, the results indicate possible mineralization and existence of a reasonable Cretaceous sedimentary thickness in the area which is deep enough for hydrocarbon accumulation. The average sedimentary thickness obtained in the area is 3.75 km.

Qualitative and quantitative interpretations of aeromagnetic anomalies over Ogoja and Bansara areas of Anambra Basin, Lower Benue Trough of Nigeria were carried out using spectral analysis and source parameter imaging methods. The study area which covers an area of approximately 6050 km 2 lies within latitude 60° 0' to 7° 0' North and longitude 8° 30' to 9° 0' East. The regional anomaly was separated from the total magnetic intensity map to obtain the residual anomaly using first order polynomial fitting technique. The residual data was analyzed spectrally to obtain 18 spectral blocks for sedimentary depth estimates (deep and shallow depths). The edges and causative bodies of the residual anomaly were also sharpened to reduce anomaly complexity as well as fault trend amplification using first, second and horizontal derivatives. The 3-D basement topography map of the study area shows linear depression with deepest sedimentary thickness at the southeastern region of the study area, which implies that the feasibility of hydrocarbon potential will be higher in Bansara area than in Ogoja. The deepest depths obtained from spectral analysis and source parameter imaging are 5437.0 and 5059.9 m, respectively.

Abstract. Electrical resistivity imaging survey was carried out at the proposed site for Kauridan Estate at Ibagwa -Nike, Southeastern Nigerian, in order to investigate the suitability of the subsurface geological structures for the housing estate. The multielectrode ABEM Lung resistivity meter system, employing the Wenner array, was used to acquire 2D resistivity data sets along six parallel profiles in the survey area. The acquired data was processed and interpreted using Res2DINV software to produce the 2D inverse resistivity models. The subsurface images showed that the near surface materials, up to a depth of about 7m from the surface, have moderately high resistivity range of 728 -1100Ωm, and were inferred to be coarse sand and gravel. These materials were underlain by other materials of a lower resistivity range of 164-358Ωm at a depth of 26.2m, which vary from shaley sand -shale. The images did not suggest the presence of clay formations or any other building constraints such as fractures, faults or voids.

Aeromagnetic data over Abakaliki and Ugep areas of the lower Benue Trough were interpreted to determine the depth to magnetic source rocks of the area. The study area covered latitudes 5° 30' and 6° 30'N and longitudes 8° 00' and 8° 30'E with an estimated total area of about 6000 km 2 . Quantitative interpretation was carried out using spectral analysis method to compute for depth to basement while the polynomial fitting method was adopted for the regional-residual separation of the total magnetic intensity. Interpretation of the total magnetic intensity (TMI) over the area showed NE and NW main trends in the study area. The 3-D surface map also showed a linear depression with sedimentary accumulation trending E-W. The spectral analysis over the area showed a sedimentary thickness that ranged from 0.64 to 4.25 km. High sedimentary thickness of over 4 km was obtained at the central part of the study area while the minimum sedimentary thickness of about 0.60 km was obtained at the southern part of the study area which is around Ugep. The maximum sedimentary thickness of about 4.25 km could be capable of hydrocarbon accumulation prospect.

Knowledge of formation pore pressure ahead of the drill bit is not only critical for safe and costeffective drilling of wells but also essential in studying the hydrocarbon trap seal and analyzing the trap configurations. A predrill estimate of the formation pore pressure can be obtained from seismic velocities and employing a velocity-to-effective stress transform. However, limitations abound in the use of seismic velocities for accurate pore pressure prediction. These limitations are traceable to some main factors such as the correctness of the seismic velocities themselves and the accuracy of the local parameters of the pore pressure prediction method used. Knowledge of the sources of overpressure in the formation is also an essential factor. This paper discusses these factors and attempts to put them into context for accurate pore pressure prediction using seismically-derived velocities.