Surface geophysics has good coverage, but is limited in vertical resolution and quality, especially in areas with complex overburden. To realize high-fidelity reservoir characterization and monitoring, we foresee the need to bring geophysics closer to the reservoir to transfer geophysical measurements more in line with the resolution obtainable by logs. Sensors, and probably sources, need to be deployed tens or hundreds of meters below the surface. We envision this happening for targeted applications in areas from 10 to 100 km2.

Setting the stage

Reservoir engineers need geophysics to fill in the gap in information between the wells to help with reservoir management and improve recovery. This translates into a need for ultra-high vertical resolution for reliable reservoir properties, and monitoring. The realities of surface geophysics in the Middle East and many other areas with complex overburden are rather unappealing. Surface seismic on the Arabian peninsula can provide structural information with perhaps 50-100 ft vertical resolution. Mature areas are covered by multiple legacy surveys each escalating in cost, but from an engineer’s perspective with little added value. Engineers build billion-cell reservoir simulation models with 25x25 m grids which are not routinely populated using seismic data. As a geophysicists, we never stop trying to improve data fidelity and quality and we have had some successes using higher channel counts and wide azimuth acquisition, but far too often what we extract is only incrementally better than legacy data. A revolution is needed in geophysical data acquisition to achieve our goals. As we discovered in 4D trials with buried receivers (Bakulin et al., 2012) we have the beginnings of a solution. All of us are familiar with the concept of resolution and associated trade-offs (Figure 1): to see big picture – one needs to be high above the target and to see details one needs to be close. We have largely concentrated on these two extremes for a very long time; we perfected our surface geophysics to image large volumes but at low resolution and we use logging to see incredible details but very locally. Yet developments in these two areas did not fulfill the engineers needs that we outlined earlier. We think this can be changed by bringing geophysics closer to the reservoir, i.e. by literally burying sensors and perhaps sources below near-surface complexities, in deeper boreholes and in producing boreholes.

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