Abstract
Recent advances in micro-CT techniques allow imaging heterogeneous carbonates at multiple scales and including voxel-wise registration of images at different resolution or in different saturation states. This enables characterising such carbonates at the pore-scale targeting the optimizing of hydrocarbon recovery in the face of structural heterogeneity, resulting in complex spatial fluid distributions. Here we determine effective and total porosity for different pore-types in a complex carbonate and apply this knowledge to improve our understanding of electrical properties by integrating experiment and simulation in a consistent manner via integrated core analysis. We consider Indiana Limestone as a surrogate for complex carbonate rock and type porosity in terms of macro- and micro-porosity using micro-CT images recorded at different resolution. Effective and total porosity fields are derived and partitioned into regions of macro-porosity, micro-porosity belonging to oolithes, and micro-porosity excluding oolithes’ rims. In a second step we use the partitioning of the micro-porosity to model the electrical conductivity of the limestone, matching experimental measurements by finding appropriate cementation exponents for the two different micro-porosity regions. We compare these calculations with calculations using a single cementation exponent for the full micro-porosity range. The comparison is extended to resistivity index at partial saturation, further testing the assignment of Archie parameters, providing insights into the regional connectivity of the different pore types.
Highlights
Electrical resistivity measurements of partially saturated rock are commonly used to estimate the productivity and size of oil and gas reservoirs
Numerical capabilities to carry out electrical conductivity calculations directly on tomographic images were established [11,12,13,14,15] and morphological transforms applied to carry out resistivity index calculations [16,17,18]
Integrated approaches combining experiments with tomogram-based numerical modeling were presented for non-Archie behavior of clean sandstones [19,20,21] including for pressure-dependent return to Archie behavior of Fontainebleau sandstone at high confining pressures [21] and more recently carbonates [22], where the effect of films on the RI behavior of dualporosity carbonate rock is assessed with network models derived from tomograms acquired via micro-CT
Summary
Electrical resistivity measurements of partially saturated rock are commonly used to estimate the productivity and size of oil and gas reservoirs. In recent years digital core analysis has made significant advances in particular for the analysis of heterogeneous rocks with complex micro-structure like carbonates. The analysis of transport properties like electrical conductivity for heterogeneous carbonates via digital core analysis requires balancing field of view (FOV) and resolution. We distinguish between two micro-porosity types that are prominent in terms of their X-ray density and geometrical features in order to assess their relative impact on resistivity index behavior (see Fig. 2). We test the hypothesis that type II RI behavior can be reproduced directly from tomographic images by carefully addressing associated numerical problems originating from the choice of resolution; namely strong partial volume effects at partial saturations. Microstructure and porosity types of Indiana limestone. [a] SEM image illustrating the main porosity types and solid phases; Ach: allochems, detrital skeletal remains of marine
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
