oa Integrating core and wireline log datasets - a pathway to permeability from AvO seismic?

Improved reservoir modelling and simulation is sought by assigning permeability using AvO seismic. The integration of sidewall-core porosity and permeability with wireline logs represents one possible pathway for differentiating the seismic amplitude responses of different reservoir flow-unit facies.

Two sand facies with differing porosity-permeability trends were defined in the reservoir interval of a Paleocene oil field in a shallow offshore clastic setting. Available sidewall-core data from several wells were added to their respective log datasets as discrete, depth-matched points and used to pinpoint the extraction of relevant log values corresponding to each point. The extracted Vp, Vs and density values enabled calculation of AI and Vp/Vs for each sample. Fluid substitutions using the Gassmann equations were then performed on points within the two sand facies.

A statistical comparison of brine and oil porefill cases for each sand facies in this study showed a clear shift due to the hydrocarbon effect. However, only minor differences were observed in an AI-Vp/Vs cross-plot when the two sand facies with common porefill were overlain. Compositional similarity between the sand facies appears the most likely cause for the lack of significant difference in AvO response. Thin carbonates with high AI are also present in the reservoir interval and lateral variation in carbonate volume of as little as 5-10% would overprint the small differences observed between the sand facies. This method should be revisited for sand facies possessing greater compositional differences or where a larger porosity-permeability distinction between facies exists.