Overcoming the Challenges Faced in a 4D Project on a Jurassic Carbonate Field, Offshore Abu Dhabi

The time-lapse 4D seismic method has been proven an effective tool for monitoring reservoir dynamics, especially in turbidite environments, but this technology faces many challenges in Middle East carbonate fields. There were three main difficulties: i) Acquisition repeatability: The monitor seismic survey was not initially designed for 4D; its objective was a full azimuth 3D survey for reservoir characterization. Thus, its acquisition geometries were different to the baseline survey; ii) Environment: The water depth of the field is less than 20 m, which generates severe shallow water multiple noises; and iii) Signal strength: The 4D signals were relatively weak due to the nature of the rigid carbonate rock frame. To overcome these challenges, we applied several methods: i) Least-squares migration to minimize the 4D acquisition differences; ii) Iterative cascading demultiple filtering; and iii) 4D signal interpretation with the integration of well production profiles and reservoir dynamic simulation. Ultimately, we identified meaningful 4D signals from 4D inversion that are coherent with our reservoir simulation and well production. In general, water rise from the aquifer was higher than observed in the dynamic model and the model showed heterogeneous water sweep. We also observed an unswept area based on 4D inversion. Whilst results are coherent with production data, they are far from challenging the production data as the noise level remains high. However, these results are favorable and have positively impacted the decision for future 4D, with better acquisition designs to meet the future reservoir management and development needs.