Carbonate reservoirs of different rock types have wide ranges of porosity and
permeability, creating zones with different reservoir quality and flow properties. This
research addresses how seismic technology can be used to identify different carbonate
rock types for characterization of reservoir heterogeneity. I also investigated which
seismic methods can help delineate thin high-permeability (super-k) layers that cause
early water breakthroughs that severely reduce hydrocarbon recovery.
Based on data from a Middle East producing field, a typical geologic model is
defined including seal, a thin fractured layer, grainstone and wackestone. Convolutional,
finite difference, and fluid substitution modeling methods are used to understand the
seismic signatures of carbonate rock types.
Results show that the seismic reflections from the seal/fractured-layer interface
and the fractured-layer/grainstone interface cannot be resolved with conventional
seismic data. However, seismic reflection amplitudes from interfaces between different
carbonate rock types within the reservoir are strong enough to be identified on seismic
data, compared with reflections from both the top and bottom interfaces of the reservoir.
The seismic reflection amplitudes from the fractured-layer/grainstone and the grainstone/wackestone interfaces are 17% and 23% of those from the seal/fracturedlayer
By using AVO analysis, it may be possible to predict the presence of the
fractured layer. It is observed that seismic reflection amplitude resulting from the
interference between the reflections from overburden/seal and seal/fractured-layer does
not change with offset.
The thin super-k layer can also be identified using fluid substitution method and
time-lapse seismic analysis. It shows that this layer has 5% increase in acoustic
impedance after oil is fully replaced by injecting water in the layer. This causes 11%
decrease and 87% increase in seismic reflection amplitudes from the seal/fractured-layer
interface and the fractured-layer/grainstone interface after fluid substitution,
These results show that it is possible to predict carbonate rock types, including
thin super-k layers, using their seismic signatures, when different seismic techniques are
used together, such as synthetic wave modeling, AVO, and time-lapse analysis. In future
work, the convolutional model, AVO analysis, and fluid substitution could be applied to
real seismic data for field verification and production monitoring.
- Sun, Yuefeng Mollie B. & Richard A. Williford Professor