Repeatability of Marine CSEM Imaging for Reservoir Monitoring

Recent studies have inferred the feasibility of time-lapse controlled-source electromagnetic (CSEM) methods for the monitoring of offshore oil and gas fields. However, survey repeatability is difficult as transmitter and receiver positions will vary, and the resistivity of the water column may vary with season. Moreover, cultural noise due to sub-sea infrastructure may increase as the field is developed. These effects will influence the CSEM data. Using Archie's Law, rock and fluid properties from dynamic reservoir simulations of the Harding field in the North Sea were converted to resistivity, from preproduction in 1996 to decommissioning in 2016. CSEM data were simulated for each state, where the transmitters and receivers were varied within the tolerance of today's best practice. Even with imperfect survey repeatability, we demonstrate how 3D imaging can be used for monitoring the oil-water contact from preproduction to the end of oil production in 2011, and for monitoring of the gas-water contact from 2011 to 2016 during gas production.