Abstract

The seismic response to hydrocarbons has long been recognised as a potential means of directly predicting petrophysical and fluid properties in the subsurface. An integrated workflow that draws on the latest developments in prestack and poststack seismic inversion, incorporating AVO, AI and EI inversion, allows better distinction between seismic anomalies caused by lithology and those caused by hydrocarbons. By creating relationships between these inversion attributes and logged petrophysical properties it is possible to produce petrophysical property volumes and by mathematical manipulation of impedance cubes, create volumes of rock properties such as bulk modulus, rigidity and incompressibility.

Recent developments in seismic inversion techniques allow us to draw more direct information about the reservoir properties and fluid content than can be obtained using "direct" hydrocarbon indicators or conventional AVO attributes such as normal incidence reflectivity and gradient sections. Prestack AVO inversion produces a series of AVO reflectivity volumes by separating out the P-wave and S-wave reflectivities from the data and these can be used to derive secondary attributes more closely related to fluid properties. Poststack inversion of these reflectivities generates elastic and acoustic impedance volumes that can be correlated with well data to derive relationships with known petrophysical properties.

An integrated workflow adds considerable value over isolated attributes as it combines the latest technology in both prestack and poststack seismic inversion, Seismic modelling, attribute interpretation and reservoir fluid prediction, leading towards a thorough understanding of the seismic response to hydrocarbons and a rapid economic assessment of hydrocarbon prospects.