Webinar Series
Wednesday, August 26th
9:00am – 10:00am US Central Time
Why the Sonic Saturation Model Works: From Gas Shales to Low API Black Oil Reservoirs
John Omovie, Goshey Energy Services LLC
Sheyore John Omovie is CEO and Principal Consultant of Goshey Energy Services LLC, with over 20 years of experience in petrophysics, rock physics, and reservoir characterization across major U.S. and international basins. He has held technical roles with Oxy, Apache Corporation, EOG Resources, and Baker Hughes.
Dr. Omovie is the inventor of a patented sonic-log-based saturation technology (U.S. Patent No. 12,242,011 B2) that estimates water saturation from compressional and shear sonic logs, without requiring resistivity or formation-water resistivity. The technology is commercialized as plug-ins for SLB Techlog and Geoactive Interactive Petrophysics and has been validated across a broad range of conventional and unconventional reservoirs worldwide. He holds a Ph.D. in Geophysics from the University of Houston and is a Licensed Professional Geoscientist in Texas, and has presented technical papers at SPWLA, OTC, URTeC, and IMAGE conferences.
ABSTRACT:
A sonic-based saturation model (Omovie, 2024; Omovie, 2025a) estimates water saturation (Swt) from compressional and shear sonic logs without requiring formation resistivity or brine resistivity. Unlike conventional resistivity-based saturation models, the new model is particularly effective in low-resistivity, low-contrast (LRLC) reservoirs and unconventional reservoirs where Archie's assumptions often break down. This webinar addresses a fundamental question: why does the model work, and how broadly does it apply?
The answer lies in the physics of fluid substitution at the ultrasonic and sonic scales. Where patchy saturation dominates, a prevalent condition at both scales, the Vp/Vs ratio varies nearly linearly with Swt. Omovie and Dvorkin (2025) demonstrate this linearity through rock physics modeling across clean sands, shaly sands, and carbonates with varying porosities, and confirm it using ultrasonic laboratory measurements and wireline log data from conventional reservoirs. This linearity is the rock physics foundation that makes the model both accurate and robust across a wide range of reservoir conditions. The model exploits this relationship by estimating Swt from the perpendicular distance of measured Vp-Vs data from fully brine-saturated and fully hydrocarbon-saturated end-member trends in Vp-Vs space. It has been validated across more than 20 wells and 15 formations spanning an exceptionally broad range of reservoir types. In conventional reservoirs, applications include deepwater offshore Gulf Coast gas and oil sands, gas condensate reservoirs in the North Slope of Alaska, and LRLC shaly sand reservoirs where resistivity-based models incorrectly indicate wet intervals. In unconventional reservoirs, applications span gas shale reservoirs, including Haynesville and Marcellus, and organic shale oil and tight sand formations in the Midland and Delaware sub-basins of the Permian Basin and the Powder River Basin. For black oil reservoirs, where the oil-brine compressibility contrast is smaller than for gas, the model remains effective down to API gravities at the boundary between medium and heavy crude, as demonstrated on offshore Gulf Coast reservoirs with oil gravity as low as 22° API. A key practical advantage of the sonic model is its relative insensitivity to brine salinity. Sensitivity analysis shows that while Archie's Swt prediction can shift by over 30 absolute percentage points across a plausible salinity range of 10,000 to 50,000 ppm, the sonic model Swt remains essentially unchanged (Omovie, 2025b), a decisive advantage in LRLC and frontier exploration settings.
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