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Determination of Reservoir Properties from Poisson Impedance Pre-stack Inversion

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Document pages: 7 pages

Abstract: In this study Poisson impedance pre-stack seismic inversion has been extensively studied to determine reservoir properties in Gamma field Niger Delta, from high resolution seismic data and well logs. Three main classifications of lithology (sand, sandy-shale and shale) were discriminated based on the well log Crossplot between gamma ray and Poisson impedance. Also, well log Crossplot between density and Poisson ratio, formed three major clusters which are probably shale, brine and hydrocarbon zones. The sand lithofacies shows low values of gamma ray (< 57 API) and PI (< 5200 ft s*g cc) while shale lithofacies possesses high values of gamma ray (> 57 API) and PI (> 5600 ft s*g cc). Hydrocarbon zones show low values of PI (<4995 ft s*g cc) while brine and shale zones have intermediate PI (Between 5100 to 5388 ft s*g cc) and high values PI (> 5508 ft s*g cc) respectively. The value of scale factor, c was calculated to be 1.38, which was obtained from the inverse of the slope of the regression line between the P-impedance (Ip) and a scaled version of the S-impedance (Is). The scale factor was used in calculation of Poisson impedance. Inversion of the seismic data was also carried out to generate horizon slices of Poisson Impedance away from the wellbore. Results show that anomalously low values of Poisson impedance (Between 4862 to 5168 ft s*g cc) were observed in both cross-sections and horizon slices indicating the presence of hydrocarbon sands.

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