3D Inversion of Time-lapse CSEM Data from Dynamic Reservoir Simulations of the Harding field, North Sea

Recent studies have inferred the feasibility of time-lapse controlled-source electromagnetic (CSEM) methods for the monitoring of offshore oil and gas fields. The time-lapse CSEM inverse problem is highly constrained though inherently 3D since the geometry of the reservoir is established prior to production from high resolution seismic surveys; rock and fluid properties are measured from well logs; and multiple history matched production scenarios are contained in dynamic reservoir models. 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 pre-production in 1996 to decommissioning in 2016. CSEM data were simulated for each state. We demonstrate how 3D inversion can be used for monitoring the oil-water contact from pre-production to end of oil production in 2011, and for monitoring of the gas-water contact 2011 to 2016 during gas production. In particular, we show that focusing regularization is able to recover sharp resistivity contrasts across the oil-water and gas-water boundaries, whereas smooth regularization fails to recover an adequate resistivity contrast.