Seismic monitoring of oil production: A feasibility study

David E. Lumley, Amos Nur, Sverre Strandenes, Jack Dvorkin and James Packwood

We perform a feasibility study on the likelihood of seismically detecting and interpreting the time-varying changes in a North Sea reservoir during solution-gas-drive oil production from a horizontal well. This study integrates reservoir engineering fluid-flow simulations, rock physics measurements and transformations, and prestack seismic modeling and migration on a real but anonymous North Sea reservoir model. Our hydrocarbon recovery monitoring analysis includes:

• Integrating reservoir fluid-flow simulation results (pore pressure; temperature; and oil, gas and water saturations) as provided by Norsk Hydro.
• Integrating reservoir geology information on relevant rock properties (porosity, dry elastic constants and density) measured from core data.
• Computing spatial distributions of compressional and shear wave velocities in the reservoir using Gassmann's formula and the fluid-flow simulation results of oil production.
• Simulating multi-offset surface seismic monitor surveys over the reservoir during oil production using a Kirchhoff elastic modeling algorithm.
• Mapping the differences between seismic responses as a function of reservoir production time using prestack seismic imaging methods.

We calculate spatial distributions of reservoir rock properties from the fluid-flow simulation data, and map the associated seismic responses at three production-time snapshots: prior to any oil production (Base Survey), after 56 days (Monitor 1), and after 113 days (Monitor 2) of oil production. Multi-offset seismic surveys are simulated for each of these three production times. Using realistic seismic acquisition parameters, we are able to successfully detect and monitor dynamic gascap expansion in the reservoir during the fluid-flow simulation of the oil production process. Evidence of gas coning is clearly visible in the prestack-migrated difference sections at realistic seismic noise levels and frequency bandwidth.

64th Ann. Internat. Mtg., Soc., Expl. Geophys., Expanded Abstracts, 319-322, (1994).