4D Fast Track Advanced Interpretation on Dalia Field, Block 17, Angola

The Dalia field, located deep offshore Angola in Block 17, is composed of confined and unconfined unconsolidated turibidites sands aged from Miocene. After 30 development wells, a first 4D seismic survey was acquired in order to monitor these development wells, understand reservoir communications, but also prepare the next development and infill wells. Due to the fact that sands are very unconsolidated and with a low burial, 4D effects are very strong: time shifts larger than 10 ms are observed due to fluid changes. Post-stack processing and interpretation techniques were optimized in order to fully interpret 4D and integrate it into the reservoir model. For fast track interpretation purposes, performed within a 2 months time frame, we used amplitude difference cube and dV/V attribute (i.e. relative P-wave velocity change) issued from warping. Starting from these attributes, advanced interpretation and upscaling techniques were applied. 4D anomalies were compared to dynamic monitoring parameters such as MDT and PLT measurements in order to calibrate it. 4D seismic data was useful to understand areas of water injection, depletion, rise of the WOC, fault sealing character and reservoirs communications.