GAS SAND DETECTION USING ROCK PHYSICS AND PRE-STACK SEISMIC INVERSION, EXAMPLE FROM OFFSHORE NILE DELTA, EGYPT

Well logs and three-dimensional (3-D) partial angle stacks and full angle stack seismic volumes are used in
this study with the purpose of detecting gas sands using rock physics and pre-stack inversion workflows.
Integration of pre-stack inversion and rock physics analysis can improve the characterization of the late
Pliocene gas sandstone reservoir, offshore Nile Delta. The inversion was performed using a deterministic
wavelet set. Rock physics was used to enhance the VP, VS, and density volumes from the inversion. The present
study performed in three phases: AVO analysis, pre-stack inversion, and lambda-mu-rho (LMR) analysis. The
results from the different crossplots, such as P-Impedance vs. Vp/Vs, show that the gas sands are clearly
separated from brine sands and shale. By maximizing the potential offered from the elastic properties such as
λρ, μρ and Vp/Vs ratio we were able to define the limits and cutoffs which sufficiently separate the gas sand
bodies. The resulted volumes were used to better define the late Pliocene reservoir and optimize a new well
location. The pre-stack inversion and AVO/rock physics studies resulted in a new Gas Initial In Place (GIIP)
calculation that was doubled in the P50 case from the original estimation based only on the seismic amplitude
data. The chance of success was increased and a new well is proposed to drain the gas in the eastern flank of
Channel 1.