The task of minimizing pitfall in quantitative reservoir assessment and evaluation is an integral aspect of any promising petroleum exploration and evaluation project. The Niger Delta oil province in Nigeria is chiefly composed of several pay zones with many stratigraphic intervals of sand and shale formations in varying proportion. Whereas conventional seismic interpretation technique poses certain degree of uncertainty in reservoir characterization, seismic inversion constraint by log data brings significant improvement in interpretation that reduces uncertainty in the delineation of reservoir characteristics, volume and distribution. In this present study, post-stack seismic inversion and seismic attributes analysis were used to evaluate the potentials and prospects of mapped reservoirs in a field, offshore depobelt, Niger Delta. The implementation of the tasks consists of mapping of structural framework, horizon picking, log editing and correlation, wavelet extraction, building of low-frequency model, acoustic impedance inversion and crossplot analysis of reservoir properties and attributes. A hybrid approach (formulated using Greenberg-Castagna equation) specific for the Niger Delta depobelts was used to estimate and generate shear wave velocity for the wells. Results obtained from inversion depict an acoustic impedance values in the range 150-280 ft/s g/cc and V P ∕V S of 1.25-2.50 at a depth range of 9250-9280 ft within the hydrocarbon-bearing sands in the two wells. Region of low acoustic impedance (representing high reservoir porosity) coupled with a corresponding low V P ∕V S ratio (indicating hydrocarbon accumulation) is presumed to have high prospects for exploration and well development. Altogether the degree of correlation between the inverted and actual impedance was found to be about 90% across the wells. It is evident that the acoustic impedance slice at 3000 ms depicts low acoustic impedance sand within 18,500-20,000 ft/s g/cc at the northeastern and southeastern regions of the field. High reflection amplitudes (bright spots) signifying hydrocarbon accumulation are also revealed on seismic attribute maps with surrounding shale diaper as the source rock. This study has revealed the prospect (i.e., existence of active petroleum system of probable economic value) of the delineated field in the Niger Delta depobelt.

The occurrence of collapsible and unstable subsurface materials (clay, silt, peats etc.) in alluvial deposits and other soil deposits throughout the world and the difficulties with building on them have long been recognized. Accordingly inclusive site investigation of subsurface condition is important for construction of engineering structures and buildings on land reclaimed from wetland such as marsh or swamp with soft compressible clays and peat materials. Peatlands common in most coastal areas of Lagos, Nigeria are characteristic waterlogged locations. These areas characterized by low human and economic activities in the past are now considered for building residential houses due to the surging population of the metropolis. Problem usually arises when there is uneven soil settlement which might results in disastrous collapse of structures. This study presents a subsurface geophysical mapping of a site reclaimed by sand filling in Victoria Island, Lagos, using integrated electrical resistivity techniques. The geoelectric data acquired through vertical electrical sounding (VES) and electrical resistivity imaging (ERI) techniques were processed and interpreted to provide a detailed characterization of the subsoil profile and soil parameters of the study area. VES technique employed Schlumberger configuration because of its obvious deeper current penetration, while for ERI, a combination of Werner, dipole-dipole and pole-dipole were utilized. Results from the two procedures show a maximum of four geoelectric strata, with the second and third layers consisting either sandy clay (50 Ωm < ρ < 140 Ωm) or peat/clay (ρ < 50 Ωm). These middle layers are sandwiched between the topsoil and the last layer (composed mainly of sand, ρ > 140 Ωm). Due to the lateral discontinuous and inhomogeneous nature of these sandwiched layers of high compressibility and low shear strength, the possibility of occurrence of subsidence and differential settlement is high. This might result in minor or major failure in building and engineering structures built on such soils. Sand medium encountered at shallow depth of about 0.6-0.9 m, beneath VES 7, 8, 14 and 19, could have been a suitable layer for foundation of buildings and structures except that it is directly underlain by peat/clay. Other locations with competent sand layers for which deep foundation might be required lie at depth within 9.5-30.8 m. Thus, this study has revealed both the lateral and vertical variation with depth of the subsurface strata within the study area. This would assist local structural engineers and builders in designing appropriate and adequate foundation of structures in this area.