Abstract
Previous studies performed in Abu Dhabi oilfields, United Arab Emirates, revealed the direct link of seismic wave attenuation to petrophysical properties of rocks. However, all those studies were based on zero offset VSP data, which limits the attenuation estimation at one location only. This is due to the difficulty of estimating attenuation from 3D seismic data, especially in carbonate rocks. To overcome this difficulty, we developed a workflow based on the centroid frequency shift method and Gabor transform which is optimized by using VSP data. The workflow was applied on 3D Ocean Bottom Cable seismic data. Distinct attenuation anomalies were observed in highly heterogeneous and saturated zones, such as the reservoirs and aquifers. Scattering shows significant contribution in attenuation anomalies, which is unusual in sandstones. This is due to the complex texture and heterogeneous nature of carbonate rocks. Furthermore, attenuation mechanisms such as frictional relative movement between fluids and solid grains, are most likely other important causes of attenuation anomalies. The slight lateral variation of attenuation reflects the lateral homogeneous stratigraphy of the oilfield. The results demonstrate the potential of seismic wave attenuation for delineating heterogeneous zones with high fluid content, which can substantially help for enhancing oil recovery.
Highlights
Enhanced oil recovery (EOR) aims to improve oil and gas production by facilitating the flow of fluids
Such sensitivity might be useful for enhancement oil recovery studies, since it can help to delineate the zones with great hydrocarbon potential, which are usually noticed by their high intrinsic attenuation anomalies
We suggest that in the reservoir zones, energy losses are dominated by intrinsic attenuation, which is the result of fluidrelated mechanisms, such as wave induced fluid flow (WIFF) mechanism known to be significant in the reservoir zones
Summary
Enhanced oil recovery (EOR) aims to improve oil and gas production by facilitating the flow of fluids. Conventional methods used for investigating naturally fractured reservoirs are generally based on petro-physical well-logs, such as sonic, gamma ray, and resistivity logs or on core description. Such data are obtained in the vicinity of the well location and at small scale. By looking at the dominant direction of the extracted maximum curvature, Ali, et al [4] successfully defined the dominant orientation of fractures in a reservoir of an offshore Abu Dhabi oilfield, and found that it is parallel to the NNE-SSW and NE-SW directions Such methods are sensitive to any geological feature causing seismic anisotropy other than fractures, such as lithological alignment
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