Adaptive scaling for an enhanced dynamic interpretation of 4D seismic data

Abstract

A B S T R A C TIn this study, importance is drawn to the role of engineering principles when interpreting dynamic reservoir changes from 4D seismic data. In particular, it is found that in clastic reservoirs the principal parameters controlling mapped 4D signatures are not the pressure and saturation changes per se but these changes scaled by the corresponding thickness (or pore volume) of the reservoir volume that these effects occupy. For this reason, pressure and saturation changes cannot strictly be recovered by themselves, this being true for all data interpretation. This understanding is validated both with numerical modelling and analytic calculation. Interestingly, the study also indicates that the impact of gas saturation on the seismic can be written using a linear term but that inversion for gas saturation can yield at best only the total thickness/pore volume of the distribution. The above provides a basis for a linear equation that can readily and accurately be used to estimate pressure and saturation changes. Quantitative updates of the static and dynamic components of the simulation model can be achieved by comparing thickness or pore volume-scaled changes from the simulator with the corresponding quantities on the inverted observations.

Seismic History Matching Using a Fast-Track Simulator to Seismic Proxy

“…In our case, as we are dealing with relatively small changes, one obvious form for f(ΔR, G) can be obtained by a linear polynomial (Falahat et al 2013) (2)…”

“…The coefficients are functions of the reservoir geology, rock properties and fluid properties. As the main reservoir variability is supplied by the baseline amplitude, the weighting coefficients a i can be assumed fixed across the reservoir (Falahat et al, 2013).…”

“…Arguments in favour of quadratic terms for pressure and saturation change have been provided by Meadows (2001), Cole et al (2001) and Meadows and Lumley (2002). At a practical level, the linear version of this proxy is found to be useful for the purposes of directly inverting to pressure and saturation changes (Landro 2001, Falahat et al, 2013Floricich et al, 2006;MacBeth et al, 2006), thus in this study we applied the linear version, the accuracy and robustness of this proxy for history matching purposes will be tested in the next section.…”

“…The main assumption behind the equation 2is that modelled seismic response might be decomposed into effects of P/S (pressure/saturation) changes linearly. Although it is a data-driven assumption with limited physical basics, it has been proved in literature (Falahat, 2013, Fursov, 2015 to be successful on synthetic or real field data. However, considering the complexity of the seismic attribute, reservoir geometry and other considerations, this proxy (equation 2) would have different performance based on specific cases.…”

Enhancement of dynamic reservoir interpretation by correlating multiple 4D seismic monitors to well behavior

“…From the engineering perspective, these 4D signals contain crucial information for updating reservoir models. A number of specialized techniques have been developed to extract quantitative reservoir engineering information, especially pressure and saturation changes, from these 4D seismic signatures (Landrø, 2001;Mac-Beth et al, 2006;Falahat et al, 2013). After obtaining quantitative reservoir dynamic changes, workflows have also been proposed to close the loop between the observed and predicted 4D seismic and production history, to improve the reliability of reservoir simulation models for efficient well planning and production strategies (Staples et al, 2005;Landa and Kumar, 2011;Souza et al, 2011;Ayzenberg et al, 2013;Alerini et al, 2014;Ayzenberg and Liu, 2014;Tian et al, 2014).…”