Low porosity fractured reservoirs have been successfully described using a combination of high resolution geometrical information from borehole images together with deeper penetrating log evaluation methods.
Borehole images from acoustic or electrical scanning tools provide statistics of fracture distribution, first order estimates of fracture opening and porosity, and a basis for geological inference. Their drawback is that, in this environment, the events on the images bear a strong overprint of the drilling process. Deeper penetrating but lower resolution techniques such as Stoneley wave reflectance and deep resistivity log inversion are used to distinguish the deep and permeable fractures that may contribute to flow.
By making some assumptions about the nature of the porosity in basement reservoirs we develop a new method to estimate the porosity and the fraction of this porosity due to fractures. This method makes use of the Kuster-Toksoz acoustic scattering model and requires low frequency measurements of compressional and shear velocities.