Application of AVO attributes for gas channels identification, West offshore Nile Delta, Egypt

Abstract The offshore part of the Nile Delta is considered one of the most prolific provinces for gas production and for future petroleum exploration. Amplitude Variation with Offset (AVO) analysis supported by composite logs considered as one of the best-advanced techniques enables the interpreter to understand the seismic data. It is used to generate a new view of the output results, especially for the identification of gas zones as gas channels by using pre-stack AVO attributes that based on the intercept product gradient (A*B) and the Scaled Poisson's Ratio Change. Free gas, regardless of the percentage show obvious AVO anomaly. Well log data, including gamma-ray, resistivity, and Vp sonic logs are used in the seismic data to well tie and in the generation of the synthetic seismogram. Seismic data conditioning processes with check-shot correction is performed to improve the resolution of the reflection events and signal to noise ratio. AVO attributes technique, as a direct hydrocarbon indicator, including AVO gradient analysis and AVO crossplot separate the gas levels in the sand-shale sequences. The identified gas-bearing zones consistent with well log data responses. As the main conclusion, we show the visual evidence for the gas-bearing zones by interpreting different AVO responses due to the changes in fluid and rock types

Identification of gas zones and chimneys using seismic attributes analysis at the Scarab field, offshore, Nile Delta, Egypt

Seismic attributes supported by composite logs are the best way that can enable the interpreter to understand seismic data very well and generate a new view of the output results. Detection of the reservoir zone can be enhanced by analyzing wells log data based on Gamma-ray, Resistivity, and Vp sonic logs respectively. Composite logs of Scarab-1, Scarab-De, Scarab-Da, Scarab-Dd, and Scarab-2 wells indicate the lateral and vertical variation of the gas reservoir in El Wastani Formation. However, there are several seismic attributes that can be used to support reservoirs identification. For enhancement the detection of the hydrocarbon reservoirs, it is important to carefully analyze the 2D seismic data, which in this study will be primarily prepared to enhance seismic attributes results for the identification of gas chimneys, gas zones as channels, enhance stratigraphic and structural interpretations. In this article, we have performed data conditioning, quality control and seismic well ties including the preliminary wavelet extractions to get accurate output. Then, we have extracted of several classes of physical, geometrical and complex attributes as a direct hydrocarbon indicator to identify the gas zones, channels and chimneys and to identify the faults and discontinuities. The main contribution of this work is to provide a more detailed seismic reflection image supported by several seismic attributes classes and well logs to show a visual and quantitative evidence to identify the gas channels and gas chimneys with improving the detection of the faults and discontinuities. Keywords: Seismic attributes, Offshore nile delta, Gas channels, Gas bearing sand zones, Gas chimney, Well loggin