| Autor: |
N. K. Khatri, P. K. Chaudhury |
| Rok vydání: |
2019 |
| Předmět: |
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| Zdroj: |
Petro-physics and Rock Physics of Carbonate Reservoirs ISBN: 9789811312106 |
| DOI: |
10.1007/978-981-13-1211-3_15 |
| Popis: |
Since compression-wave velocity Vp and shear-wave velocity Vs are affected differently by variation in rock properties and pore fluids, seismic amplitude variation with offset (AVO) and multicomponent seismic emerges as a key tool for exploration and reservoir evaluation. Compression-wave and shear-wave velocities of water-saturated sandstones and shales often closely obey a linear relationship, mudrock equation. Reflections from the interface of such layers exhibit the well-defined background trend of decrease in AVO. Layers with Vp and Vs not honoring the mudrock equation are elastically anomalous. Hydrocarbon-saturated sands and the carbonate rocks are two of the several cases which do not honor the mudrock equation, and therefore, their Vp/Vs (Poisson ratio) is different for the same Vp than had they been honoring the mudrockline relation. Such layers when interfaced with layers honoring the mudrock equation generate the seismic responses anomalous to the background AVO response. Low-impedance and low-Poisson ration hydrocarbon-saturated sands in clastic regime reflect negative amplitudes increasing with offsets (termed as class III AVO anomaly). First offshore well in deepwater in Mahanadi Basin was drilled to probe the amplitude anomaly showing increase in amplitudes with offsets. Well encountered limestone encased in incompacted shale generating increasing amplitude with offset . AVO response was computed from well logs to help explaining the observed AVO anomaly of increase in amplitudes with offset from limestone. Anomaly could not be explained from approximated Aki and Richards (Quantitative seismic: theories and methods. W. H. Freeman and Company & Co. New York 1980) relations of Zoeppritz equation alone. Angle of incidence approaching critical 40° at about offset of 2000 m at shale-limestonetop interface depth caused the amplitude to increase with offset. Case study is presented to show how such expressions can, prior to drilling, be inferred as generated by other than hydrocarbon sands. |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
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