Olawale Olakunle Osinowo

3D Electrical Resistivity Imaging (ERI) for subsurface evaluation in pre-engineering construction site investigation

Abstract Three Dimensional (3D) Electrical Resistivity Imaging (ERI) was carried out for pre-construction foundation investigation of a proposed engineering construction site within the University of Ibadan Campus, south-western Nigeria, where some distressed structures (offices and hostels) have been reported to show stress induced cracks attributed to incompetent foundation support from rocks upon which they were constructed. The 3D grid of resistivity data generated along parallel and equally spaced profiles stations presented the resistivity distribution of the subsurface as well as delineated zones of relatively high resistivity values (450–4500Ωm) in the east and lower resistivity zones (15–300Ωm) in the west. The study also delineates zones of isolated low resistivity values (10–50Ωm) at the mid and west end of the field. The generated resistivity distribution sections, maps and 3D model indicate spatial variation in resistivity value which varies both laterally and vertically. The variation which is attributed to differences imposed by underlying rock’s structural and geological rock composition resulted from complex rock coexistence as schist (quartz- and amphibolitic-schist) and quartzite coexist as underlying rocks of the proposed construction site, especially since these rocks respond to weathering differently. The generated subsurface resistivity model guided selection of geotechnical investigation points which captures spatial variation in subsurface physical properties as recorded by the measured subsurface resistivity. Better guided geotechnical investigation provided needed information required to design appropriate foundation support for the proposed engineering structure.

Reservoir description and characterization of Eni field Offshore Niger Delta, southern Nigeria

Integration of structural and horizon mapping of 3D seismic volume, petrophysical studies of over sixty (60) wireline logs, stratigraphic analyses, reservoir property modeling and production information have been adopted to study Eni field that has been experiencing production decline with increase in water output. Generated reservoir structural framework and spatial reservoir property distribution have proved useful to guide the optimal placement of proposed wells and also provide information needful for the development of best production plan that would guarantee effective oil drainage from the delineated reservoir compartments.

Petrophysical Properties’ Evaluation for Reservoir Characterization of AK Field, Onshore Eastern Niger Delta, Southern Nigeria

In this study, well log derived petrophysical parameters of four (4) delineated clastic reservoirs in AK field, located onshore eastern Niger Delta have been effectively employed to characterize and assess hydrocarbon prospect potential of the field. Wireline well log data, such as gamma ray, resistivity log suite, Compensated Neutron Log (CNL) and Formation Density Compensated (FDC) were studied and analyzed for qualitative and quantitative evaluation of the formation units in the field. Lithologic discrimination aided the identification of sandy units, while fluid identification and discrimination defined the hydrocarbon saturated reservoir units in the field. Other derived parameters such as porosity, permeability, water saturation, hydrocarbon saturation, Net To Gross (NTG), net hydrocarbon pay, Bulk Volume Water (BVW) among others were employed to quantitatively characterize the delineated reservoir units, especially to establish their hydrocarbon potential. Four (4) sandy reservoir units, A1, A2, A3 and A4 which ranged in thickness from about 60-350 ft were identified from four exploratory wells AK-01, AK-02, AK-03 and AK 04 to be hydrocarbon bearing. The clastic reservoirs presented medium to relatively high formation porosity (0.27-0.38), low to average permeability value (61.6-685.5 mD) and significant to high hydrocarbon saturation (0.42-0.97). A plot of true formation resistivity values (Rt) against water saturation (Sw) indicate that all reservoir units encountered in well AK-01 are oil saturated. However, only reservoir sands A1 and A2 are predominantly oil reservoirs in well AK02 while sands A3 and A4 plot in oil and water field. In well AK-03, reservoir A1 contains only oil while the remaining reservoirs contain oil and water. The reservoir units as encountered in well AK-04 show slightly different fluid saturation pattern as reservoir A1 contains only oil, A4 is gas saturated while the remaining two reservoir units (A3 and A4) plot in the field of both water and oil.