Gas Sand Detection Using Rock Physics and Pre-Stack Seismic Inversion a Real Example from Offshore Nile Delta

Review Article

Austin J Earth Sci. 2017; 3(1): 1021.

Gas Sand Detection Using Rock Physics and Pre-Stack Seismic Inversion a Real Example from Offshore Nile Delta

El-Mowafy H*

Department of Geology, Al-Azhar University, Egypt

*Corresponding author: :Hamed Z. El-Mowafy, Department of Geology Al-Azhar University, Egypt and Geoscientist Consultant, Houston, Texas. 6327 Borg Breakpoint Dr, spring, Texas, 77379, USA

Received: February 02, 2017; Accepted: March 17, 2017; Published: March 30, 2017


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 prestack 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 cross plots (e.g. 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.

Keywords: Gas sand; AVO; Pre-stack inversion; Rock physics


Vp: p-wave velocity; Vs: s-wave velocity; AVO: Amplitude Versus Offset; λρ: lambda-rho; μρ: mu-rho; GIIP: Gas Initial in Place


The Nile Delta Basin covers an extensive area including onshore, shelf and deepwater environments. The Nile Delta offshore is rapidly emerging as a major gas province. High-quality three-dimensional (3-D) seismic data, coupled with data from thirteen consecutive successful deep-water exploration and appraisal wells, have highlighted clear phases of erosion and deposition within the upper Pliocene deep-marine slope channels [1]. Scarab field is part of the offshore Nile Delta and lies in West Delta Deep Marine (WDDM) concession, 50–100 km offshore in the deep water of the present-day Nile Delta (Figure 1). A series of successive exploration and appraisal wells drilled by BG Egypt and Rashpetco encountered gas-bearing sands in slope canyon settings on the concession (Figure 2). The Scarab field is submarine delta slope canyon system, with complex turbiditic channel-levee reservoirs. They record delta front submarine flows, mass wastage and related slope processes on the proto-Nile Delta. Detailed studies of the geometry of the canyon systems, from seismic extractions, core data, wire line logs and high-resolution FMI imaging [1] reveal a complex canyon fill.