Water‐Filled Porosity 2D Imaging—Part II: Laboratory and Downhole Applications

Heterogeneous reservoirs, especially shaly formations, are challenging in reservoir characterization. Porosity and fluid distributions vary in both vertical and lateral directions. High‐resolution oil‐based mud (OBM) conductivity images are commonly acquired to help to characterize formation conductivity heterogeneities. With calibrated formation conductivity from the conductivity images, water‐filled porosity () 2D images may be obtained by using Archie type models, provided formation shaliness, water salinity and Archie parameters are given. However, at the OBM pad‐based imager operating frequencies (tens of megahertz to megahertz), porous rock interfacial polarization is very complex. Factors such as water‐filled porosity (), water salinity and water‐phase tortuosity () interact among themselves non‐linearly and all contribute to the overall responses of rock conductivity and dielectric permittivity. The complex interfacial polarization challenges or even invalidates Archie model assumptions sometimes. A new theoretical workflow to derive and 2D images without Archie assumptions is provided in a separate paper. In this article, we apply the new workflow first on laboratory outcrop rock slab data then on downhole well data to evaluate the new theoretical workflow. Compatibility analysis is performed on both datasets. Following the rock parameter configuration guidelines provided from the theoretical study, and images can be inverted jointly without Archie assumptions. Inversion uncertainty is also computed. For the downhole data, the Archie model–based , image is also derived as a comparison. Results of the case studies indicate that in the sections containing interbedded sub‐inch layers with high variation of dielectric effect, the Archie‐based water‐filled porosity image tends to underestimate . In addition, in the clastic gas‐bearing intervals where the image resistivity tends to be high, Archie‐based image values are lower than both the multifrequency dielectrics interpretation and the new dielectrics‐inverted image, because water‐phase tortuosity image value is high in that interval. The case study examples validate the new theoretical workflow and can derive an accurate 2D image without Archie assumptions. The data comparison results also indicate the compatibility between the OBM pad‐based imager data and multifrequency dielectrics data in clean formation. In the shaly formation, most likely due to anisotropy response difference between the two tools, the measurement data are not compatible; thus, the new workflow is not applicable. After the joint inversion, we can derive a 2D water‐filled porosity image and a 2D water‐phase tortuosity image that represent better the pore scale interfacial polarization. In heterogeneous rocks with complex pore systems, the separation of and from rock conductivity and permittivity responses can improve the accuracy of and provide additional information to improve rock facies classification.