Investigation of Pore-Scale Remaining Oil Dynamic Evolution in Heterogeneous Marine Carbonate Using Real-Time Computed Tomography Scanning

Primary and secondary oil recovery are the main early-stage production methods of carbonate reservoirs. However, its intrinsic complex pore structure causes production reduction during the process of depletion production. The distribution of oil and brine varies in the pore space during water flooding. The core to solve the problems is to figure out the dynamic evolution of remaining oil. In this work, three heterogeneous marine carbonate samples were made to carry out water injection experiments using real-time computed tomography scanning. The oil saturated samples and those after injecting 3, 5, 10, and 20 PV (pore volumes) brine were scanned, and 3D images were reconstructed. The oil and brine were segmented from 3D images by the gray value discrepancy. The pore network models were built to calculate and analyze some typical pore structure parameters such as pore and throat radii, coordination number, and tortuosity. Different types of remaining oil were classified by shape factor and Euler number. The oil saturation decreases and the distribution of different types of remaining oil changes accordingly during water flooding. The proportions of isolated oil ganglia and branched remaining oil are larger. The influence of flow rate and permeability on the changes of remaining oil was analyzed. After injecting 20 PV, almost all of the oil ganglia with a radius greater than 20 mu m is displaced. Only a few residual oil ganglia with an equivalent radius of 2-20 mu m is left.

Automated summary

Primary and secondary oil recovery are the main early-stage production methods for carbonate reservoirs. This study conducted water injection experiments on three heterogeneous marine carbonate samples using real-time computed tomography scanning. The distribution of oil and brine in the pore space, as well as the changes in remaining oil during water flooding, were analyzed by segmenting 3D images and building pore network models.