Abstract
This case study showing the usefulness of the Common Depth Point (CDP’s) analysis to assess the amplitude response which is similar at two cases (gas-bearing and dry sands) after stack, using the Amplitude Versus Offset (AVO) analysis and the pre-stack inversion to understand the reservoir configuration and its relationship to the different amplitude response. The results led to a high success of exploration ratio as the positives vastly outweigh the negatives. Several lessons have been learned, which how to differentiate between the similar amplitude responses for two dry and gas discovery wells-by understanding the relationship between the near traces (near offset) and the far traces (far offset) from the CDP gathers in order to reduce the amplitude anomalies to their right justification. Consequently, a variation in the reflectivity strength is observed, which is controlled by the mechanical properties of the rocks: compression wave (VP), shear wave (Vs) and density. These properties are affected by litho logy and fluid contents. The analysis of the CDP’s gathers and the inversion results help in validating the prospects before drilling and in determining the response of the seismic amplitude deviation with the offset, so it is possible to confirm the amplitude anomaly if it is related to hydrocarbon or not.
Highlights
The Nile Delta region discovered gas reserves reach to about 58 Tcf until now (Nini et al, 2010), from different stratigraphic levels, ranging from the Oligocene to the Plio-Pleistocene, it is considered the greatest prolific region for production of gas in Egypt
The Amplitude Versus Offset (AVO) modeling is broadly used in detection of hydrocarbon, lithology determination and fluid analysis, according to the fact that seismic amplitude is affected by the physical properties changes above and below the boundaries
After the quantitative seismic interpretation for the different stratigraphic levels in the concerned area and application of the AVO detailed study, it is observed that, same amplitude response has occurred in both two drilled wells gas
Summary
The Nile Delta region discovered gas reserves reach to about 58 Tcf until now (Nini et al, 2010), from different stratigraphic levels, ranging from the Oligocene to the Plio-Pleistocene, it is considered the greatest prolific region for production of gas in Egypt. Seismic inversion is the convert the seismic data to a measureable rock-properties or fluid contents useful as for the hydrocarbon reservoirs (Hampson et al, 2005). It involves extraction of acoustic impedance from seismic data (P-impedance the product of the density and P-wave velocity) that help to make predictions of important reservoir properties like lithology and porosity. Inversion can be applied to the pre-stack seismic data to generate both the shear and acoustic impedance cubes volume use the inversion results for calculation of pore fluid with mean fluid indication (elastic impedance) (Russell, 2014: Hampson and Russell, 2006) Inversion can be applied to the pre-stack seismic data to generate both the shear and acoustic impedance cubes volume use the inversion results for calculation of pore fluid with mean fluid indication (elastic impedance) (Russell, 2014: Hampson and Russell, 2006) (Figs. 16 and 17)
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