Rock physics analysis for time‐lapse seismic at Schiehallion Field, North Sea

Abstract

A B S T R A C TRock physics analysis plays a vital role in time-lapse seismic interpretation because it provides the link between changes in rock and fluid properties and the resulting seismic data response. In this case study of the Schiehallion Field, we discuss a number of issues that commonly arise in rock physics analyses for time-lapse studies. We show that: 1 Logarithmic fits of dry bulk (K dry ) and shear (G dry ) moduli vs. effective pressure (P eff ) are superior to polynomial fits. 2 2D surface fits of K dry and G dry over porosity (φ) and effective pressure using all the core data simultaneously are more useful and accurate than separate 1D fits over φ and P eff for each individual core. 3 One average set (facies) of K dry (φ, P eff ) and G dry (φ, P eff ) can be chosen to represent adequately the entire Schiehallion reservoir. 4 Saturated velocities and densities modelled by fluid substitution of K dry (φ, P eff ), G dry (φ, P eff ) and the dry bulk density ρ dry (φ) compare favourably with well-log velocities and densities. 5 P-and S-wave impedance values resulting from fluid substitution of K dry (φ, P eff ), G dry (φ, P eff ) and ρ dry (φ) show that the largest impedance changes occur for high porosities and low effective pressures. 6 Uncertainties in K dry (φ, P eff ) and G dry (φ, P eff ) derived for individual cores can be used to generate error surfaces for these moduli that represent bounds for quantifying uncertainties in seismic modelling or pressure-saturation inversion.

Investigation of core data reliability to support time-lapse interpretation in Campos Basin, Brazil

“…Similar result was observed in Schiehallion Field by Meadows et al (2005). Other studies in the same basin and other parts of the world are needed to verify how general this conclusion is.…”

Rock Physics Analysis and Time-lapse Rock Imaging of Geochemical Effects Due to CO2 Injection into Reservoir Rocks

“…The model scheme performs a mere fluid substitution treating the rock-fluid interaction as a purely mechanical problem. It is a common practice in the literature to include the time-variant effects on the properties of the fluid and the rock frame due to the variation of physical parameters such as stress and temperature (Nur et al, 1984;Lumley, 2001;Meadows et al, 2005). Nevertheless, data interpretation almost never includes geochemical effects on the properties of the frame.…”

Seismic detection of fractures from injection illustrated through a field example

“…There are many intermediate steps and options in this process (such as convolution versus fullwaveform modeling) that we omit from this article for brevity (for examples, see Meadows et al, 2005, or Johnston, 2013. In 4D modeling, the velocity-stress dependence is usually obtained by laboratory measurements on core samples.…”