- Copyright © 2000 Society of Exploration Geophysicists
In the E&P business, by far the largest component of geophysical spending is driven by the need to characterize (potential) reservoirs. The simple reason is that better reservoir characterization means higher success rates and fewer wells for reservoir exploitation … and that increased investments in subsurface work are paying off in an overall reduction in E&P cost. Future geophysical spending will depend primarily on our continued contribution to overall E&P cost control by further improvements in reservoir characterization.
What are we after in reservoir characterization? Ultimately, it must be a model consistent with all available subsurface information. Some key reservoir model parameters to which geophysical measurements can contribute include:
fluid content and properties
rock type and porosity
flow conduits and flow barriers
changes over time for all of the above
and all of the above, not in map form but spatially
We are continually doing a better job of determining these reservoir parameters and are now at a stage that, in many cases, the challenge is no longer to predict the presence of hydrocarbons. The challenge is quantification and risk assessment and making accurate spatial predictions of reservoir parameters so reservoirs can be exploited with as few wells as possible.
Quantitative seismic reservoir characterization: the past
From a geophysical perspective, reservoir characterization has traditionally used seismic amplitude data. This dates back to when seismic amplitudes were used for “bright spot” detection. Shortly afterward, the first attempts were made to invert amplitude data to directly recover rock property parameters, primarily acoustic impedance. Seismic amplitudes and amplitude attributes characterize the reflection properties of an interface, and only indirectly the surrounding rocks. In contrast, rock property parameters derived from seismic directly characterize the rocks, meaning they can be directly and quantitatively related to other key reservoir parameters. A second advantage is that rock property …