Estimation of rock physics properties from seismic attributes — Part 2: Applications

Abstract

The estimation of quantitative rock physics properties is of great importance for reservoir characterization and monitoring in CO 2 storage or enhanced oil recovery as an example. We have combined the high-resolution results of full-waveform inversion (FWI) methods with rock physics inversion. Because we consider a generic and dynamic rock physics model, our method is applicable to most kinds of rocks for a wide range of frequencies. The first step allows determination of viscoelastic effective properties, i.e., quantitative seismic attributes, whereas the rock physics inversion estimates rock physics properties (porosity, solid frame moduli, fluid phase properties, or saturation). This two-step workflow is applied to time-lapse synthetic and field cases. The sensitivity tests that we had previously carried out showed that it can be crucial to use multiparameter inputs to accurately recover fluid saturations and fluid properties. However, due to the limited data availability and difficulties in getting reliable multiparameter FWI results, we are limited to acoustic FWI results. The synthetic tests are conclusive even if they are favorable cases. For the first time-lapse fluid substitution synthetic case, we first characterize the rock frame parameters on the baseline model using P-wave velocity estimations obtained by acoustic FWI. Then, we obtain an accurate estimation of fluid bulk modulus from the time-lapse P-wave velocity. In the Marmousi synthetic case, the rock frame properties are accurately recovered for the baseline model, whereas the gas saturation change in the monitor model is not estimated correctly. On the field data example (time-lapse monitoring of an underground blowout in the North Sea), the estimation of rock frame properties gives results on a relatively narrow range, and we use this estimation as a starting model for the gas saturation inversion. We have found that the estimation of the gas saturation is not accurate enough, and the use of attenuation data is then required. However, the uncertainty on the estimation of baseline rock frame properties is not critical to monitor gas saturation changes.

Rain and small earthquakes maintain a slow-moving landslide in a persistent critical state

“…Velocity of P and S waves as a function of saturation. In order to model the impact of the variation of the water table height upon the surface wave velocities, we used the Biot-Gassmann equations 45 as done in other studies 46,75,76 . These equations give the velocity of Vp and Vs as a function of the porosity and their fluid saturation.…”

Quantitative seismic characterization of CO2 at the Sleipner storage site, North Sea

“…For example, resistivity is highly sensitive to CO 2 saturation (Park et al, 2013;Eliasson et al, 2014). Even if the resolution of a CSEM resistivity image is lower than FWI results, a combination of seismic and CSEM inputs can be easily implemented via the proposed two-step approach for rock physics inversion (Dupuy et al, 2016a). In addition, the combination of different inputs via joint rock physics inversion will be mandatory for pressure-saturation discrimination.…”

“…More details are given in Appendix C, and examples of the implementation of the rock physics inversion method are given by Dupuy et al (2016aDupuy et al ( , 2016b.…”

Monitoring fluid saturation in reservoirs using time‐lapse full‐waveform inversion

“…During the inversion, the gradient is scaled using equation 6. 1: Elastic properties in this study for minerals and fluids where cs is set to 20 (Dupuy et al, 2016a;.…”