We carried out time-lapse analysis in a producing Niger Delta X-field, by first investigating the response and sensitivity of rock properties/attributes to lithology and pore fill in 3-D cross plot domain and by Gassmann's fluid substitution modeling. Furthermore, 4-D seismic data were inverted into acoustic impedance volumes through model based inversion scheme. This served as input into a multi-attribute neural network algorithm for the extraction of rock attribute volumes based on the results of the petrophysical log analysis. Subsequently, horizon slices of rock properties/ attributes were extracted from the inverted seismic data and analyzed. In this way, we mapped hydrocarbon depleted wells in the field, and identified probable by-passed hydrocarbon zones. Thus, the integration of well and time lapse seismic (4-D) data in reservoir studies has remarkably improved information on the reservoir economic potential, and enhanced hydrocarbon recovery factor.

Integrating seismic amplitudes and spectral attribute analysis has successfully mapped, validated and characterised hydrocarbon-saturated channel sands by high-amplitude low-frequency anomaly. The aim of the study was targeted at using these novel geophysical tools to improve characterisation of tertiary clastic reservoir in the field. These attributes were extracted along H4 seismic horizon and analysed independently for structure, lithology and hydrocarbon saturation. The result of the analysis shows that both attributes complimented each other in mapping the hydrocarbon-saturated reservoir channel sands. However, the spectral attributes in combination with spectral-based Red, Blue and Green (RGB) colour blending attribute map reveal finer and subtle details of the channel structure and stratigraphy which hitherto were not apparent in the seismic amplitude maps. The channel sands trend NE–SW, broadening towards the southwest and bounded by major growth faults to the northeast and southwest, respectively. It is thick to the southwest and thins to the northeast. By-passed hydrocarbon prospect was delineated to the northeast of the existing wells, and as such, infill wells can be drilled in these areas to recover hydrocarbons.

Production-induced subsidence due to compressibility and fluid property changes in a Niger delta field has been investigated using well log and 4D seismic data sets. The objective of the study is to evaluate changes in time lapse seismic attributes due to hydrocarbon production and infer to probable ground subsidence. Petrophysical modeling and analysis of well data revealed that Density (ρ), Lambda rho (λρ) and Acoustic impedance (Ip) are highly responsive to changes in reservoir properties. These properties and water saturation attribute were subsequently, extracted from time-lapse seismic volumes in the immediate vicinity of well locations. Result show that monitor horizon slices exhibit appreciable increases in ρ, λρ, Ip and water saturation values compared to the base data, especially around the well locations. These increases in relative values of rock/attribute properties between the time-lapse surveys for a constant overburden stress are obvious indications of pore pressure and fluid depletion in the reservoir. Depletion in these properties increases the effective stress (pressure) and the grain-to-grain contact of the reservoir matrix, with a corresponding decrease in compressibility. Consequently, pore and matrix volume decreases, the reservoir compacts and the ground subsides. However, this is suspected to be small and at the reservoir scale due to low initial reservoir porosity and the relatively large lateral dimension compared to the thickness of the reservoir.

Reservoir characterization plays a significant role in the exploration, development, and production of hydrocarbon reservoirs. The use of integrated approach in characterization improves on the accuracy, certainty, and robust interpretation of reflectivity data. The study aimed to integrate reflectivity and spectral attributes to adequately characterize hydrocarbon reservoirs in MUN onshore Niger delta field. Well log and rock physics analyses identified and delineated reservoirs, discriminated lithology, characterized fluid, and established relations between elastic and reservoir properties for field-wide interpretation of the reflectivity data. The wells were tied to the reflectivity data, and H4 seismic horizon was mapped. Subsequently, sweetness, reflectivity and spectral attributes were extracted along H4 horizon after inversion and spectral decomposition of the reflectivity data and independently interpreted. Channel-like structure with high-amplitudes, low-to-moderate acoustic impedance (Ip), lambda–rho (λρ) and mu–rho (µρ) attribute values, and high-amplitude low-frequency spectral attributes (15–35 Hz), respectively, characteristics of hydrocarbon saturated channel sands were delineated. The channel reservoir sand is thick, porous with low volume of shale and low to moderate water saturation. Analysis of data further shows that reflectivity attributes provided a better description of fluid characteristics than the sweetness and spectral attributes, but are less sensitive to structure and exaggerated the shape and limits of the channel sands. However, the spectral attributes seem to be more robust than the reflectivity attributes in providing subtle structural and stratigraphic details of the reservoir as well as delineating by-passed hydrocarbons in the field.

Rock Physics Modelling and Seismic Inversion were carried out in an Onshore Niger Delta Field for the purpose of characterizing a hydrocarbon reservoir. The aim of the study was to integrate rock physics models and seismic inversion to improve the characterization of a selected reservoir using well-log and 3D seismic data sets. Seven reservoir sands were delineated using suite of logs from three wells. In this study, the sand 4 reservoir was selected for analysis. The result of petrophysical evaluation shows that the sand 4 reservoir is relatively thick (62 ft) with low water saturation (0.33), shale volume (0.11) and high porosity (0.32). These results indicate reservoir of good quality and producibility. Cross-plot of property pairs (acoustic impedance (I p) vs. lambda-rho (λρ) and mu-rho (µρ) vs. lambda-rho (λρ) color-coded with reservoir properties reveals three distinct probable zones: hydrocarbon sand, brine sand and shale. Results show that low I p , λρ and µρ associated with hydrocarbon charged sands correspond to low S w and V sh and high ϕ. The integration of rock physics models and inverted rock attributes effectively delineated and improved understanding of already producing reservoirs, as well as other hydrocarbon charged sands of low S w , V sh , and high ϕ to the east of existing well locations, which indicate possible bypassed hydrocarbon pays. The results of this work can assist in forecasting hydrocarbon prospectivity and lessen chances of drilling dry holes in MUN onshore Niger delta field.