Quantitative Integration of Flow Simulation and 4D Multi-Component Seismic in a CO2 WAG EOR Project

Abstract

Abstract In management of mature oil fields for enhanced oil recovery, 4D seismic imaging plays a very important role. Previously, we published the qualitative results of integrating flow simulation with time-lapse multi-component seismic data for a CO2 EOR project in the thin valley-fill Morrow formation at Postle Field. In this paper, we will present our quantitative approach and results from integrating flow simulation with time-lapse seismic. Three seismic surveys have been acquired at Postle Field to monitor the ongoing CO2 flood. Since presentation of the previous paper, additional seismic and production data has become available which has influenced both the history match of the reservoir flow model and seismic interpretation. Gassmann's fluid substitution method was used to relate the flow simulation results with time-lapse seismic attributes. In addition, a sensitivity analysis was performed using a conceptual model to investigate the effect of various reservoir dynamic parameters on seismic response. Flow simulation and rock physics modeling show that production and injection in the reservoir causes saturation and pressure changes, which affect acoustic and elastic properties of the reservoir. Acoustic impedance calculated from the simulation model was compared to the corresponding results from seismic data. The magnitude of changes of acoustic impedance calculated from the flow simulation is similar in range to that from seismic inversion. The effect of fluid saturation change in the reservoir, particularly CO2 saturation, is greater than the effect of pressure change. Conceptual modeling indicates that the sensitivity of seismic attributes to changes in CO2 saturation and water saturation is weak and may be difficult to detect seismically. On the other hand, to have a relatively big change in acoustic impedance, a big change in pressure is needed. Our research results demonstrate that for a credible dynamic reservoir characterization, an integration of flow simulation and 4D seismic is required which, in turn, could be a viable method to guide field operations. However, this process is challenging in thin reservoirs undergoing CO2 WAG injection.