Analysis of Differential Waveform of Time-lapse Seismic Data in Deep Water of West Africa

Post-stack time-lapse seismic data is always used to interpret the change of thick reservoir. The difference between baseline seismic data and monitoring seismic data cannot be identified directly by analyzing the changes of travelling time in thin reservoir because the change is too small. Differential Waveform can effectively reflect the change of P-wave velocity of thin reservoir and the reservoir change caused by hydrocarbon production or gas/fluid injection. The original P-wave velocity of the reservoir and the surrounding rock does not affect the differential waveform of time-lapse seismic data. The differential waveform is determined by the change of P-wave velocity of the reservoir. When P-wave velocity of the thin reservoir increased during oilfield development, the differential waveform is Positive Waveform(wave trough above wave peak). When P-wave velocity of the thin reservoir decreases, the differential waveform is Negative Waveform(wave peak above wave trough). The study area is located in the deep water of West Africa. Water injection has been used to improve the recovery efficiency. Baseline seismic survey was acquired in 1998 and monitoring seismic survey was acquired in 2011. The change of reservoir caused by oilfield development is identified by analyzing differential waveform of time-lapse seismic data.