The offset dependent variation of the acoustic impedance has been used throughout the lifecycle of oilfields to discriminate pressure and saturation differences. While there are many ambiguities caused by overburden, tuning, morpho- and lithological effects the analysis provides additional insights to the distribution of pore pressure and fluids in a given rock physics framework. An experimental design assessing the sensitivity of AVO effects in a rock physical context is proposed. The methodology is applied to a planned CO2 injection test at the Svelvik CO2 Field Laboratory, South of Oslo, Norway. The geology is inspired from a recent site characterization (Bakk et al., 2012) and is supplemented with different conceptual features. The information present for the site is translated into a scenario based ensemble of static models.
A detailed understanding of the underlying rock physics model is required not only to design the monitoring campaigns before injection, but will provide the basis to alter the underlying parameters defining the magnitude and sensitivity of simulated and measured acoustic impedances. Distinguishing pressure and saturation related changes of the acoustic impedance is subject to the sensitivities of the properties used to derive the underlying seismic P- and S-velocities as well as densities. These uncertainties can induce a non-negligible variability in the footprint of a seismic image of the CO2 plume. This allows to explain subtle heterogeneities of highly simplified simulations. Designing cost efficient surveys to obtain an effective coverage of the injected CO2 and discrimination of fluid and saturation related pore effects require a rigorous approach in the quantification of the rock physical properties upfront.
Presentation Date: Wednesday, October 17, 2018
Start Time: 9:20:00 AM
Location: Poster Station 3
Presentation Type: Poster