Geo-electrical investigation for groundwater potential of Ihievbe Ogben, Edo North, south western Nigeria

This study was carried out within Ihiebe Ogben community in Akoko Edo LGA, Nigeria to investigate the ground water potential of the Basement Complex rocks using Vertical Electrical Sounding (VES) that deploys Schlumberger Array configuration. Evaluation of hydrogeological parameters shows fractured/ weathered basement thickness, resistivity values of the fractured basement, overburden thickness and basement relief having values between 1.5-7.9m, 64.5-503.9 Ωm, 5.2-15.7m and 136.8-160.7m respectively. Prospectivity ranking map was generated from these parameters and was used to rank the area around the VES stations. The results show that the most prospective areas with the highest ranking of 8,7 and 6 correspond to areas around VES station 6,1 and 2 respectively, restricted to the Eastern – Northwestern region of the study area.Keywords: Groundwater, Vertical Electrical Sounding, Fractured basement, prospectively rankin

Provenance and tectonic setting of Leuma Field sediments, Coastal Swamp Depobelt, Niger Delta Basin, Nigeria

Geochemical analysis of sediments recovered from NS-1 well and NS-2 well, Leuma Field, Coastal Swamp Depobelt, Niger Delta Basin was done to establish tectonic setting and provenance. Data for ten major elements and forty-three trace elements were obtained from two boreholes. The geochemical signals display systematic  stratigraphic trends in the two wells that depict one source terrain. To determine the provenance of NS-1 well and NS-2 well sediments, Th/Co vs La/Sc plot was utilized which inferred that the sediments from NS-1 and NS-2 wells were derived from felsic source rocks. TiO2 versus Ni bivariate plot was also used to establish the provenance and it revealed that the source of the sediments penetrated by NS-1 and NS-2 wells is predominantly acidic in nature. The provenance of NS-1 and NS-2 wells sediments was further confirmed by considering the ratios of Thorium/Scandium (Th/Sc), Thorium/Cobalt (Th/Co), Chromium/Thorium (Cr/Th) and Lanthanum/Scandium (La/Sc). For NS-1 well, Thorium/Scandium (Th/Sc) range from 1.12-2.01, Thorium/Cobalt (Th/Co) range from 0.91-1.66, Chromium/Thorium (Cr/Th) range from 4.21-16.04 and Lanthanum/Scandium (La/Sc) range from 3.69-8.78. For NS-2 well, Thorium/Scandium (Th/Sc) range from 0.95-2.05, Thorium/Cobalt (Thko/Co) range from 0.94-1.91, Chromium/Thorium (Th/Cr) range from 4.32-15.43 and Lanthanum/Scandium (La/Sc) range from 2.58-6.66. These values inferred that the sediments recovered from NS-1 and NS-2 wells were transported from felsic source rocks.Inorganic geochemical results infer that the tectonic setting for NS-1 and NS-2 wells facies is passive continental margin

Post Drill Pore Pressure Prediction for Geo-hazard Assessment of Offset Wells in Hamoru Field

Understanding the distribution and variation of subsurface formation pressure is key to preventing geo-hazards associated with drilling activities such as kicks and blow out. To assess and prevent such risk in drilling offset wells in the Hamoru field, prediction of pore pressure was done to understand the pressure regime of the field using well logs in the absence of seismic data. Two commonly used methods for formation pressure prediction; Bower’s and Eaton’s methods were adopted to predict pore pressure and determine the better of the two methods that will be more suitable for the field. The cross-plot of Vp against density disclosed that compaction disequilibrium is the prevalent overpressure mechanism. The prediction of Pore pressure with Eaton’s method gave results comparable to the acquired pressure in the field, typical of what is expected when compaction disequilibrium is the dominant overpressure mechanism. Since the result of Bower’s method over estimated formation pressure, Eaton’s method appears to be the better choice for predicting the formation pore pressure in the field. Analysis of the predicted pore pressure reveals the onset of overpressure at depth of 2.44 km. The formation pressure gradient ranges from 10.4 kPa/m to 15.2 kPa/m interpreted as mild to moderately over pressure. Keywords: Geohazard, over-pressure, Eaton’s method, Bower’s method, normal compaction tren

Neural Network Prediction of P-wave Log for Reservoir Characterization in the Niger Delta Basin

This study present a new technique that integrates several logs for P-wave prediction to minimize some errors and uncertainties associated with most estimation methods. The adopted method involves application of an artificial neural network technique that integrates density, resistivity and gamma ray logs for data training and the prediction of P-wave log. The results obtained gave correlation coefficient of 0.77, 0.24 and 0.42 between the acquired P-wave log and the acquired density, resistivity and gamma ray logs respectively, to demonstrate the relationship between P-wave log and the selected logs for the prediction process. The correlation coefficient of the estimated P-wave from Gardner and Faust methods with the acquired P-wave log are 0.64 and 0.59 respectively, while that of the neural network derived P-wave gave a better correlation coefficient of 0.81. Cross plot validation of P-wave derive Acoustic Impedance against density for both lithology and fluid discrimination revealed clusters for neural network derived P-wave parameter similar to the acquired P-wave derived parameters. Results of the presented neural network technique have been demonstrated to be more effective than results of the two conventional techniques. Keywords: Sonic log, Gardner’s method, Faust method, Neural network, Cross plot

PRESSURE ANALYSIS AND FLUID CONTACT PREDICTION FOR ALPHA RESERVOIR (A PARTIALLY APPRAISED FIELD) ONSHORE NIGER DELTA.

The study field is green, with limited well penetrations. The objective reservoir (Alpha Reservoir) is a relatively shallow one, with 6 wells penetration. Two of the wells are wet (Water-Up-To) while the rest penetrated hydrocarbon bearing intervals (Gas-Down-To). As pressure data was not acquired in the water leg of the reservoir, pressure gradient analysis was done with the field-wide hydrostatic profile for contact and fluid prediction. Also, an evaluation of the possibility of having an oil rim within the region of fluid-type uncertainty was carried out. The predicted results revealed that the objective reservoir has the potential of having oil rim of a possible gradient 0.20psi/ft., with a column height of less than or equal to 20ft. Such an oil column if present is deemed insignificant. Therefore, the reservoir can be developed as a non- associated gas reservoir with a predicted Gas-Water-Contact of 7529ftss. http://dx.doi.org/10.4314/njt.v36i3.2

Geochemical Approach and Industrial Utilization of Some Marble Bodies from Ubo River Area and Environs, Southwestern Nigeria

Marble bodies occur in Ubo River Area as lenses of rocks. Seven (07) marble samples were obtained, analyzed and subjected to X-Ray Flourescence (XRF) analysis to determine both the major and trace elemental composition of the samples. The analysis revealed high CaO values (52.23-58.10 wt. %) and moderate values for SiO2 (7.50-10.43wt. %), fairly low values for Al2O3 (2.30 – 4.21 wt. %), Fe2O3 (2.62 – 5.15 wt. %), MgO (0.42 – 0.7 wt. %), MnO (0.01 – 0.06 wt. %), K2O (0.32 – 1.55 wt. %) and Na2O (0.01 – 0.03 wt. %), respectively. Variation plots involving Na2O/Al2O3 vs K2O/Al2O3 reveal sedimentary progenitors for the rocks. The fairly high SiO2 and low K2O content is an indication of the environment of deposition and may have been in a shallow marine environment with fair input of classic sediments into the system. The relatively high CaO content, moderate SiO2content and fairly low Al2O3 and Fe2O3 values indicates a fair degree of purity of the parent rock, hence its suitability as a raw material in the industrial sector. Keywords: Clastic, Deposition, Environment, Progenitor, Marble, Chemica

Deep Play prospectivity of U- Field onshore Niger Delta Basin

This study Integrated structural interpretation with some aspects of regional stratigraphy concepts that allowed for the prediction of sand fairways and their gross depositional environment to evaluate the unpenetrated deep prospect of the U-Field onshore Niger Delta. Gross Depositional Environment model was established based on an integration of evidences from seismic, well data and paleo-bathymetric profile of wells within the area. Sequence stratigraphic analysis derived from an integration of both biostratigraphic data and chronostraigraphic chart, enabled the definition of an objective interval both on the strike and dip directions between 23.2 Ma MFS and 26.2 Ma MFS. This interval fell within the Shelf Margin Gross depositional environment with characteristic wedge-like gently dipping seismic facies geometry on seismic. The target reservoirs are sequences of potential LST/TST shelf margin sand packages which have a potential analogue along the strike direction. The prospect trap consists of a four-way dip closure with both a three way and two way components. The main risks identified for this prospect are reservoir presence and seal integrity. The geologic risk assessment result performed gave a possibility of success value of 0.4, which is considered acceptable at the exploration stage. &nbsp

Shear wave estimation for rock physics reservoir evaluation of jay field in the Niger Delta basin

Shear wave logs are one of the key data required for most Amplitude Versus Offset (AVO) studies and quantitative seismic interpretation. Despite its overwhelming importance, it is hardly available in most wells due to its very high cost of acquisition. In the absence of shear wave logs in the field, the Castagna’s empirical relationship that relates P-wave and S-wave velocities and Biot-Gassman’s Fluid substitution equations were adopted for its estimation. The results obtained revealed that Castagna’s empirical relationship underestimated the Shear wave log in the field, even after Biot-Gassman’s Fluid substitution model was applied to define P-wave of the brine filled scenario. A cross plot of Mu-Rho versus Lambda-Rho presented low values for Mu-Rho due to the underestimated shear wave used. To correct for the underestimation, a modified form of the Castagna’s Equation constants were establish. This was achieved by generating several linear regression equations that defines the relationship between P and S-wave for brine sands in the field. The cross plot of Mu-Rho versus Lambda-Rho done with the modified shear wave gave very good results as expected for both fluid and lithology discrimination. Keywords: Shear Wave, Castagna’s Equation, Biot-Gassman’s Equation, Rock Physics, Cross plot

Fluid replacement modelling analysis for C4 reservoir characterisation onshore Niger Delta Basin

This study applied Gassman’s fluid substitution theory to model the sensitivity of several saturations of gas and oil in the C4 reservoir using well log data, to determine the applicability of rock physics analysis to evaluate the reservoir in the undrilled area of the field. Results of fluid substitution modeling for gas revealed that P-wave velocity decreased significantly at 5% gas saturation. Upon further increments in the gas saturation, the P-wave velocity remained relatively constant, revealing the difficulty in differentiating between economical and sub- economical gas saturation on seismic. Oil substitution showed that as the saturation of oil introduced into the reservoir increases, the P-wave velocity and density decreases accordingly. The 80% oil saturation model appeared to be greater than the insitu P-wave and density. Hence it can be concluded that the insitu oil saturation may be greater than 80% oil. In both fluid substitution scenarios, the S-wave models remained constant irrespective of the fluid saturation. Cross plot of Vp/Vs ratio against P-impedance and Mu-rho against Lambda-rho technique were done to validate the modeling results. The techniques discriminated both the lithology types and fluid contrast in the reservoir. Hence, it can be applied in the evaluation and characterization of the C4 reservoir in the undrilled area of the field from inversion results.Keywords: Forward-Modelling, Fluid-Substitution, P-wave, S-wave, Fluid-Saturation, Rock Properties, Petrophysical Evaluatio

Amplitude variation with offset modelling and crossplot analysis for reservoir characterization in Montero field, central swamp depobelt, onshore Niger Delta Basin, Nigeria

The study area is a partially appraised green field with few well counts. The recent drive to minimize the number of appraisal to save cost and still fully understand the subsurface geology underlying the field for proper characterization lead to the application and advancement of quantitative seismic interpretation techniques for field appraisals. In this study, well based Rock physics Crossplot Analysis and Amplitude Versus Offset (AVO) forward modelling feasibility were carried out in Montero Field to assess the applicability of the techniques for characterization and prospectivity of undrilled areas. Results from two conventional cross plot techniques (Vp/Vs ratio against Acoustic impedance and Lambda-Mu-Rho) gave very good lithology and fluid discrimination (that can be relied on in the absence of neutron log for fluid typing and contact definition). AVO modelling results reveals the presence of type I,II,III and IV AVO  gas sand classes for sands B, B2, A2 and A respectively. &nbsp