4D AVO Analysis for Pressure and Water flooding Discrimination on Norne Field

Time-laps seismic is still playing a key role in reservoir management on the aging Norne Field. The focus in this paper is the Norne G-segment, where many different 4D effects have been observed since 2001. A combination of pore pressure changes and waterflooding have made it challenging to understand the true water flooding history and to understand where remaining oil reserves are located, especially by analyzing full offset seismic data alone. By introducing 4D AVO, an improved separation of fluid and pressure 4D effects was seen. 4D AVO includes pre-stack seismic modelling and analysis of pre-stack gathers and near and far offset amplitudes. 4D AVO response for pressure shows typically a very different signal compared to fluid effects. Seismic modelling shows that this can be explained by opposite changes of AI and Vp/Vs for pressure variation, while for waterflooding AI and Vp/Vs changes in same direction. 4D relative inversion for changes in acoustic impedance and Vp/Vs confirmed the opposite signal for AI and Vp/Vs for pore pressure variation compared to waterflooding. A potential undrained target area is defined, and this area will be considered for infill drilling.