Abstract
4D seismic technology is becoming routinely incorporated in reservoir management by some of the majors—to improve reservoir characterization for EOR, identify unswept oil, GOC, hydraulic communication, infill well locations. To estimate changes in seismic properties due to production, generating the reservoir's theoretical seismic response is indispensable—for guiding interpretation and quantification in terms of saturation and pressure change.
Simulating the reservoir's seismic response to potential rock and fluid distributions is essential for relating 4D seismic information to production—especially for inverting seismic information to an estimate of acoustic impedance change and Poisson's Ratio change. The choice between 1D-, 2D-, 3D-raytrace or full elastic seismic simulation depends on the structural complexity of the reservoir and overburden, the reservoir's elastic profile, and the potential artifacts from differences in the seismic acquisition & processing parameters.
Given the potential pitfalls and limitations of both modeling and data, it is necessary to visually relate geologic, engineering and geophysical information (shared-earth-modeling) to guide the quantification of seismic information for reservoir model updating and history matching. Relating different data types measured at different scales requires a case dependent development of rock physics transforms and downscaling methodologies for updating the high-resolution geologic model with results from the flow-simulator.
To illustrate the above in the context of potential impact on reservoir management, three examples are shown:
Deepwater Brazil water-injected oil field with evolving critical gas: 4D seismic analysis of two 3D surveys; utilizing 1D and 3D raytrace modeling.
North Sea gas-injected oil producing field: 4D seismic analysis of three 3D seismic surveys acquired during 8 producing years; utilizing 1D seismic modeling.
North Sea reservoir: synthetic AVO time-lapse seismic study comparing 2D raytrace and 2D HybriSeis (raytracing above reservoir, full elastic modeling of reservoir).
