Permeability Derivation from Sonic Stoneley Wave Attenuation Measurements: Application in a Giant Carbonate Field from Middle East

Abstract

Permeability is one of the most important parameters that is required in reservoir simulation, field development, and reservoir management. An innovative permeability derivation method and workflow has been developed using Stoneley wave attenuation mechanism (not Stoneley wave velocity as discussed in some previous studies). The workflow was applied to the sonic waveform data acquired from a vertical well in a giant carbonate field in Middle East. The workflow includes (a) extraction of Stoneley-wave attenuation rigorously from the waveform data, and (b) fast inversion from Stoneley-wave attenuation to permeability. Validation of the method and workflow were performed by comparing the results with core permeability and MDT mobility data. Results from this application indicate that low-frequency monopole waveforms provide good quality Stoneley wave data, and that Stoneley wave attenuation responds to permeability changes. The Stoneley-wave attenuation log extracted from the low-frequency monopole waveforms shows variability, and the permeability log obtained using the inversion workflow through different reservoir intervals has a good overall correlation with core permeability. The main reservoir interval is over 100 feet thick. Porosities are generally high throughout the interval, but permeabilities vary by several orders of magnitude due to pore type changes. The Stoneley wave attenuation permeability trend corresponds very well to vertical changes in the dominant pore system. Stoneley-derived permeabilities distinguish between microporosity in lower section with permeabilities in 1-20 millidarcy range, and mixed-pores in the upper section with permeabilities in the 10's to 100's of millidarcy range. The sonic permeability is also picking up tight streaks (stylolite zones with cementation) that have low porosity and permeability and can act as flow baffles within the reservoir. These results show that Stoneley wave attenuation is responding to changes in carbonate pore systems, and that Stoneley-derived permeabilities can provide useful permeability estimates in the absence of core data.