During hydrocarbon recovery, fluid replacement takes place in reservoirs, affecting the reservoir... more During hydrocarbon recovery, fluid replacement takes place in reservoirs, affecting the reservoir properties and consequently altering the production model and forecast. These attributes were utilized to refine fluid replacement modeling (FRM). This research aims to generate geological models capable of serving as predictive tools for reservoir monitoring. The FRM was carried out using rock-physics analysis of the wells of X-field, onshore Niger Delta, while the reservoirs' stress state was determined using Dynamic Rock-Physics Template (RPT). Rock-physics modeling was used to characterize the reservoirs dynamically and estimate their geomechanical responses due to fluid replacement. As hydrocarbons were replaced by brine, the FRM showed a consistent increase in density (ρ) attributed to a gradual rise in bulk and shear moduli. Gas dissolution resulted from the unusual reduction of compressional wave velocity (Vp) from 3.92 to 3.86 km/s in reservoir D of well A1. As hydrocarbon is replaced by water, the reservoir's shearing strength decreases. Reservoir B of well A2 has comparatively low resistance to deformation and rock strength of 18.40 GPa and 77.70 MPa, while 34.29 GPa and 142.85 MPa were recorded for reservoir D (well A1), while 34.29 GPa and 142.85 MPa were recorded for reservoir D (well A1), respectively, at 100% S w. The increase in young modulus and strength (138.86-142.85 MPa) in reservoir D (well A1) implied mechanical and well-bored stability. Pore pressure depletion in reservoir B (well A2) from RPT could induce well instability. This study highlights tailored production strategies to mitigate destabilizing effects, stressing the relationship between pore pressure depletion, stress redistribution, and fluid migration for sustainable hydrocarbon exploitation and well integrity.
Electrofacies and depositional systems of sequence penetrated in 'Ray' Field, Niger Delta were an... more Electrofacies and depositional systems of sequence penetrated in 'Ray' Field, Niger Delta were analyzed, using well log and 3-D seismic data, with a view to enable accurate prediction of source and reservoir rocks in the study area. Lithofacies were delineated through analysis of well logs using signatures of gamma ray, cross-plot of neutron-density logs and seismic facies analysis. The identified lithofacies were subjected to electrofacie analysis through diagnostic characteristics of gamma ray log indicative of a given depositional environment. Sands of different environments were subjected to seismic attribute and petrophysical analyses to assess the hydrocarbon potentials of such reservoirs. Results showed the presence of four lithofacies: Shale, Heterolithic, Shaly-Sandstone and Sandstone Facies. The electrofacies analysis revealed five depositional systems of Shoreface, prodelta, distributary, tidal and fluvial systems. Lateral variations of lithology and facies distribution, as well as presence of channels were imaged by seismic attribute. The sand units of the distributaries and tidal channels having thickness of 70 m and 65 m, and porosity of 16% and 24% respectively were viewed to have good quality for hydrocarbon reservoir.
An integrated approach to reservoir characterization involving seismic attributes extraction and ... more An integrated approach to reservoir characterization involving seismic attributes extraction and Articial Neural Network (ANN) analysis of the reservoirs of X eld, onshore, Niger Delta was carried out to assess the effectiveness of ANN as a tool for hydrocarbon reservoir study. ANN is a relatively new technique and imitation of the human brain in its basic form. In this study, it was used in the prediction and classication of reservoir properties and facies from well logs and seismic. Facies classication on logs was executed using an empirical relationship between selected logs such as gamma ray (GR), density (DEN) and resistivity (RES) logs which were cross-plotted against one another to determine data suitability. Facies classication on seismic was employed to predict facies distribution without well control. Two attributes, Root Mean Square (RMS) and Relative Acoustic Impedance (RAI) were selected based on their capability to discriminate lithologies. Facies classication on logs showed correlation between GR and DEN, GR and RES, DEN and RES logs to be 69%, 35% and 36% respectively. These values fell within the acceptable range. Facies classication on seismic revealed 44% correlation between RMS and RAI. Hence, ANN analysis effectively distinguished reservoir sands from non-reservoir sands and accurately identied lithologies penetrated by the wells of the Field. The unsupervised neural network was able to distinguish water and hydrocarbon-bearing sands. This technique had proven to be an effective tool for facies distribution studies and could be employed for generation of leads and prospects for hydrocarbon exploration.
Sand_K2 is a thin, sub-seismic reservoir in 'KUTI' Field, Deepwater Niger Delta having indistinct... more Sand_K2 is a thin, sub-seismic reservoir in 'KUTI' Field, Deepwater Niger Delta having indistinct impedance contrast with the surrounding shale wish made conventional seismic interpretation impossible. Rock physics transformation of petrophysical properties of Sand_K2 into petroelastic parameters, which allows sub-seismic reservoir to be imaged from seismic data, has been carried out. The reservoir's lithofacies and their petrophysical properties were determined using well data. Rock physics analysis was implemented to model the seismic response of the reservoir. The rock physics analysis was achieved through multivariate cross-plot of petro-elastic parameters of the Sand_K2. Sand_K2 has a thickness of 32.8m, shale volume of 12%, average porosity of 33% and acoustic impedance of 4200 to 5000 (m/s)(g/cc). The presence of shale and clay minerals increases the acoustic impedance and P-wave velocity of the reservoir above 4800 (m/s)(g/cc) and 2500 m/s respectively; while decreasing its porosity and rigidity (Mu-Rho) below 36% and 6.0 (Gpa*g/cc) respectively. The effect of hydrocarbon reduced acoustic impedance below 4775 (m/s)(g/cc). Similarly, the hydrocarbon effect reduced the reservoir's incompressibility (Lambda-Rho) below 25 (Gpa*g/cc). Rock physics modelling provided calibration data from which cutoff values were determined for improved identification and interpretation of sub-seismic reservoirs awayfrom the wellbore, consequently reducing exploration risks.
Rock physics modelling has been employed in studying the elastic behaviors of reservoir SAND_K2 i... more Rock physics modelling has been employed in studying the elastic behaviors of reservoir SAND_K2 in the 'KUTI' Field, Niger Delta under a plausible production scenario of increasing water saturation. The study aimed to investigate how variation in reservoir fluid saturation will influence seismic attributes and determine the characteristics of expected time-lapsed (4-D) seismic signals that may be generated due to the effects of production. Multivariate cross-plot analyses of petro-elastic parameters were carried out to establish the seismic characteristics of the target reservoir with different pore fluids in its natural state before production. Fluid replacement modelling was applied to calculate measurable changes in the reservoir's seismic characters by steadily increasing the water saturation from its initial value to 100%. Synthetic logs of petro-elastic parameters were created for different values of water saturation and combined into property cross-plots to predict the dynamic seismic response of the reservoir as brine gradually replaced hydrocarbon. Results showed that fluid changes from hydrocarbon to brine produced significant and quantifiable seismic signatures for timelapse monitoring investigation. At some future points in the production history of the field under increasing water saturation conditions, the density, P-wave velocity and acoustic impedance of SAND_K2 increase and produce a negative seismic difference data of P-wave amplitude. Based on the responses of reservoir SAND_K2 under modelled production conditions, the study concluded that rock physics analysis can help to optimize and enhance the success of time-lapse monitoring of the KUTI Field.
The study investigated the importance and image behavior of integrated geophysical methods in map... more The study investigated the importance and image behavior of integrated geophysical methods in mapping contaminant spread beneath the surface of a pollution site in Ogoniland, Southern Nigeria. Electrical Resistivity Tomography (ERT) and Ground Penetrating Radar (GPR) techniques constrained by Vertical Electrical Sounding (VES) data were employed to investigate the electrical properties of hydrocarboncontaminated soils that resulted from recent oil spills/leakage into the environment. Five (5) ERT and GPR lines and twenty-nine (29) VES data were acquired at the spill site. Basically, the electrical signatures from the resistivity measurements were able to image the subsurface layers and the associated contamination zone. GPR equally imaged the subsurface stratigraphy to a depth of 10.0 m beneath the surface. The interpretation of the five (5) ERT data showed consistency in the resistivity structure indicative of contaminant plumes with anomalously high electrical resistivity in the range of 1000-10,000 Ωm, a possible indication of hydrocarbon contamination. On the GPR radargram, regions of high electrical resistivities were in agreement with reduced GPR reflection behavior (shadow zones) and were limited to the near surface of the surveyed areas. Vertical electrical sounding delineated layers with high resistivity predominantly within the second and fourth geoelectric layers within pollution depths of 2.4 m and 11.9 m, respectively. As a result, the underground aquifer, relatively between 7.5 and 10.5 m, has been infiltrated by hydrocarbons. It can be seen from the study that geoelectric measurements on the surface can describe the distribution of hydrocarbon resistive zones as well as their conductive behavior that may be linked with the biodegradation of oil spills in the subsurface. Thus, the employment of these integrated methods for contaminant monitoring, hydrogeologic studies and remediation planning reduced the uncertainties, and they are of extensive relevance in mapping the geological behavior of polluted soils in contamination sites.
Characterization of complex sand reservoirs in deepwater of Niger Delta was carried out through p... more Characterization of complex sand reservoirs in deepwater of Niger Delta was carried out through petrophysical and rock physics evaluation of well log data from three wells. Petrophysical analysis to determine clay volume, porosity, lithologies and hydrocarbon saturation were made. Rock physics was studied in velocity-porosity plane to analyze the influence of depositional and diagenetic features on the reservoirs. Cross-plots of different elastic parameters, using linear regression and cluster analysis, were generated for lithologic and fluid fill identification and to differentiate between the hydrocarbon bearing sands, brine sands and shale. Variance attribute was extracted on seismic time slice in order to image the complex sand distribution in the area. Three reservoirs of turbidite origin were identified within the upper fan to lower fan area. Petrophysical results revealed gas bearing reservoir units with less than 20% shale volume and porosity of 25-31%. Lambda-Mu-Rho (LMR) cross-plots for the reservoirs show gas saturated data cloud and trend. Ratio-Difference (R-D) cluster analysis of elastic rock properties shows a distinct trend and data cloud that represents lithofacies units and fluid fills. The study concludes that the reservoirs simulated contact cement and friable models with properties that ranged from highly porous, well sorted and poorly consolidated sand to fairly sorted and highly cemented sands. The results provide a model that increases the possibility of finding reservoir sand, while mitigating the risk involved in finding hydrocarbons.
The Niger Delta is a prolific hydrocarbon producing belt in the southern Nigeria sedimentary basi... more The Niger Delta is a prolific hydrocarbon producing belt in the southern Nigeria sedimentary basin on the continental margin of the Gulf of Guinea. This study used well log suites to delineate the hydrocarbon reservoirs, depositional environments and lithostratigraphy of the Duski Field, Onshore Niger Delta, Nigeria. A comprehensive interpretation of the three wells revealed five (5) reservoir units with low volume of shale and thickness variations between 24m and 60.20m. The average porosity values ranged from 12% to 34%, with high hydrocarbon saturation in all the reservoir sands. Generally, porosity and permeability values decrease with depth in all the wells. Cross-plots of water saturation (Sw) and porosity ( ) (Buckles plot) revealed that some reservoirs were at irreducible water saturation; hence producing water-free hydrocarbons. Therefore the hydrocarbon accumulation of this field is commercially viable and promising. This study revealed that the reservoir sand units were deposited within marginal marine depositional environment which include fluvial channel, transgressive marine, progradational and deltaic settings.
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