Detection of Hydrocarbons in Carbonate Lithological Packages Using Amplitude vs. Offset Inversion of Seismic Data: Case History from Alberta, Canada: ABSTRACT

Abstract

Amplitude vs. offset (AVO) analysis has been used since the late 1970s to find hydrocarbon accumulations. The method is usually used in clastic sediments, although some geophysicists have maintained that AVO inversion works in carbonate reservoirs that have a reflector associated with them. Previous workers compiled laboratory data from carbonate cores collected throughout the world. This data demonstrated the change in Poisson's ratio with a change in pore fluids or mineralogy. Because Poisson's ratio reflects changes in pore fluids or mineralogies in carbonates, AVO inversion can be used to determine the lithology and pore fluid changes. Four common depth points for seismic lines on a Mesozoic reef complex in Alberta, Canada, were analyzed using SAMPLE (Seismic Amplitude Measurement for Primary Lithology Estimation, Terra Linda Group's AVO inversion). The locations ranged from fore-reef facies to back-reef facies, including two locations in the productive porosity of the main reef. SAMPLE analysis of the first location showed a tight shaly limestone of the Waterways Formation corresponding to the lime mud in front of the reef complex. In the reef complex, both the analyses showed hydrocarbons in the Swan Hills Formation. In the back-reef location, the AVO inversion showed tight limestones with no hydrocarbonsmore » present. Thus, AVO inversion, SAMPLE, can determine whether the zone of interest is a tight limestone or shaly limestone, and whether it is wet. SAMPLE also indicates the presence of hydrocarbons in limestones at the second and third locations on the productive reef. Thus, AVO inversion can distinguish between hydrocarbon-bearing and nonhydrocarbon bearing zones on the basis of interval velocity and Poisson's ratio.« less