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Study And Application Of Reservoir Characterization In The Niger Delta, Nigeria, Using Seismic Inversion Technique

Posted on:2015-04-12Degree:DoctorType:Dissertation
Country:ChinaCandidate:F D i e o k u m a T a m u n Full Text:PDF
GTID:1220330431470465Subject:Geophysics
Abstract/Summary:PDF Full Text Request
Over the years, sub surface exploration has been faced with the challenges of reducing the risk of drilling wells that are not hydrocarbon bearing, differentiating dry wells from potentially producing wells and improving hydrocarbon recovery systems. These challenges have led to the development of techniques with relatively better resolution and highly integrative in nature; building confidence level in interpretation and prediction of subsurface targets of interest. It is known that drilling targets since the inception of Seismic reflection method, had been proposed mainly by the identification of "bright spots" or amplitude anomaly. Not all targets were hydrocarbon bearing. This bright spot technology has a fundamental defect which has resulted in drilling many dry holes in the’so called’bright spots. Some were hard rocks, lithology changes or clean water bearing sands.Inversion of seismic data has become one of the well-known oil and gas industry tool used for refining structural interpretation and reservoir geometry, property prediction, as well as reservoir characterization. The ultimate goals of seismic reservoir characterization are to identify reservoirs, delineate them and determine the distribution of their relevant properties such as lithology and porosity, which will provide an early determination of the reservoir’s economic potential. Inversion is a geophysical technique by which seismic reflectivity data is converted to rock properties in the form of P-Impedance, S-impedance and density. These properties are further mapped to distinctive lithology types using derived relationships. An integrated approach of Seismic inversion technique and amplitude versus offset (AVO) analysis was employed to predict reservoir characteristics, sand development, lateral continuity and pore fill in the sedimentary southern Coastal Swamp in the Niger Delta basin in Nigeria. Seismic post-stack and well-log data are applied to estimate rock properties including amplitude, reflection angle, reflection coefficient, impedance, velocity, Poisson’s ratio, porosity, lithology, Lame’s constant, permeability, water saturation, fluid factor, modulus of elasticity and fluid detection in the onshore Coastal Swamp Niger Delta basin.Based on the rock physics models, well log and seismic-inversion-derivatives, elastic attributes such as porosity, Lame’s constant, moduli of elasticity were studied and computed. The zones of interest were obtained by combined analysis of attribute-depth cross-plots and gamma ray log. A total of17reservoir rock-properties and attributes were generated and a total of26cross-plots were used for the analysis of the reservoir zone of interest (1864-2050m) sandstone and shale sequences. Cross-plotting reservoir rock properties and attributes reveal the fluid contents of the reservoirs with distinct separation of the fluids within the reservoir. Comparison of different attributes and rock-properties cross-plots enhances the reliability of hydrocarbon and lithology identification. The analysis reveals possibility of a class3-AVO response between the underlying shales and the overlying charged gas sand reservoir.The result of this study predicted that four identified horizons within the stratigraphic wedge contain sands distributed within the levels in varying amounts. The U2000reservoir is predicted to contain mostly sands with relatively consistent thicknesses. The U1000level is estimated to have relatively good sand but not as extensive as the U2000. The U1000and U2000are predicted to be gas bearing while the U3000and U4000are believed to have very little sands which may not be economically viable.The results from this study would provide support for an exploratory well drilling campaign on the prospect. The results of the study will also provide useful and significant information for Explorationists in identifying likely reservoir rocks. Structural fault trends in relation to the coastline and correlation of deep sequences can be evaluated. Petrophysical parameters such as permeability, porosity, and water saturation, formation factor, Lame’s constants, moduli of elasticity can be predicted. This knowledge enables the reservoir engineer to develop a plan for the number and location of the wells to be drilled into the reservoir, how the rates of production that can be sustained for optimum recovery, and plan for the need for supplementary recovery technology.
Keywords/Search Tags:Reservoir Characterisation, Post-Stack Inversion, Amplitudeversus offset (AVO), Impedance, Porosity, Rock Properties
PDF Full Text Request
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