The influence of pore system change during CO₂storage on 4D seismic interpretation

Abstract

A 4D seismic forward model constitutes the foundation of 4D seismic inversion. Here, in combination with the Gassmann equation, the Digby model is improved to calculate the S-wave velocity, and the resulting equation is verified using rock testing results. Then, considering the influences of changes in the pore pressure, CO2 saturation and porosity on the P- and S- wave velocities, rock testing results from a CO2 injection area in the Weyburn field are used to calculate the P- and S-wave velocities of the reservoir. These P- and S-wave velocities are found to overlap under different pressure conditions with or without considering porosity variations. Therefore, two-layer models and well models are developed to simulate synthetic seismograms; the models considering porosity variations may provide greater seismic responses and different Amplitude Versus Offset (AVO) trends in the synthetic seismogram profiles than those without considering porosity variations. Thus, porosity variations must be considered when establishing 4D seismic forward models.

Subsurface fluid injection and energy storage

“…Ma et al [5] present geochemical modeling of CO 2 -brine-rock interactions in a deep saline aquifer in the Jianghan Basin, Hubei Province, China. Li and Ma [6] reported the influence of pore system change during CO 2 storage on 4D seismic interpretation, and the proposed methodology is expected to be used in China's Shengli Oilfield CO 2 -EOR project. Zhang et al [7] used the the TMVR_EOSG module of the TOUGHREACT code to simulate the feasibility of acid gas (59% CO 2 and 41% H 2 S) injection in a carbonate formation of the Tarim Basin, Xinjiang, China.…”