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

Abstract

Well logs and three-dimensional (3-D) partial angle stacks and full angle stack seismic volumes are used inthis 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 latePliocene gas sandstone reservoir, offshore Nile Delta. The inversion was performed using a deterministicwavelet set. Rock physics was used to enhance the VP, VS, and density volumes from the inversion. The presentstudy performed in three phases: AVO analysis, pre-stack inversion, and lambda-mu-rho (LMR) analysis. Theresults from the different crossplots, such as P-Impedance vs. Vp/Vs, show that the gas sands are clearlyseparated from brine sands and shale. By maximizing the potential offered from the elastic properties such asλρ, μρ and Vp/Vs ratio we were able to define the limits and cutoffs which sufficiently separate the gas sandbodies. The resulted volumes were used to better define the late Pliocene reservoir and optimize a new welllocation. 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 amplitudedata. The chance of success was increased and a new well is proposed to drain the gas in the eastern flank ofChannel 1.