Visualizing the internal physical characteristics of carbonate sediments with magnetic resonance imaging and petrography

Magnetic resonance (MR) images are analyzed in conjunction with petrographic data to evaluate the textural characteristics of rocks dominated by fabric-selective dolomitization. The magnetic resonance imaging (MRI) measurements reveal the three-dimensional geometry of the physical sedimentary structures and the trace fossils that influenced dolomitization and porosity development.

Because MRI images represent composites of nuclear spin density and MR relaxation times, each of which can be related to pore size, stronger MRI image intensity must be calibrated to known porous zones by integrating petrological data with MR data. Pairing of MR images with petrography helps map the distribution of porosity in diagenetically altered rock.

The data presented herein show the potential of a new class of MRI technique as an imaging tool for low-porosity rocks. The results demonstrate that MRI technology can significantly enhance petrological studies. Notable results include 1) the successful resolution of the porosity distribution in carbonate rocks characterized by low porosity (generally less than 6%); 2) the successful acquisition of the three-dimensional data required to model the porous network; and 3) recognition that the complex distribution of porosity and its relationship to the matrix show that this fabric represents a dual porosity/permeability system and may reduce the resource quality of similarly burrowed carbonate rocks.