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

Abstract

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 μm is displaced. Only a few residual oil ganglia with an equivalent radius of 2–20 μm is left.

Fine Modeling of Multiscale Fracture Cavity Fusion in Fault Solution Reservoirs Based on Multiscale Discrete Crack Modeling Method

“…Marinković et al conducted a composite hydrogeothermal investigation of the post-Neotethys Late Paleogene Neogene crustal core complex in the Kopaonik Mountains of the southwestern Serbian Plateau. The fractured carbonate reservoirs in Tahe Oilfield are different from conventional porous sandstone reservoirs and other karst carbonate reservoirs. − The main storage space of oil reservoirs is mainly composed of cracks and caves formed by structural deformation and collapse, as well as pores and caves formed by karst processes. − The large karst caves are the most important storage space, and cracks are the main connecting channels. − Due to the different types of karst caves and cracks of different scales, their morphology and scale are different, making it difficult to establish a unified geological model using a single method. − Therefore, different modeling methods are used to establish discrete models for different constituent elements. − Then, the discrete models were integrated into a wpore, establishing a three-dimensional distribution model of the fractured and vuggy reservoir. − …”

“… 37 − 38 39 Then, the discrete models were integrated into a wpore, establishing a three-dimensional distribution model of the fractured and vuggy reservoir. 45 − 56 …”

Flow Patterns and Pore Structure Effects on Residual Oil during Water and CO2 Flooding: In Situ CT Scanning

“…The displacement experiment is an effective method for exploring both flow patterns and the efficiency of utilization by employing microfluidic models, − real sandstone models, ,,, and technologies such as nuclear magnetic resonance, − laser confocal techniques, − and CT scanning technology. − CT scanning technology has emerged as a significant method used in various fields, including but not limited to enhanced oil recovery (EOR), − carbon dioxide storage, , environmental remediation, , and reservoir modeling at the pore scale. − The nondestructive and high-accuracy evaluation offered by CT scanning technology places it at the forefront of the choices for the study of the flow pattern and distribution of residual oil. For example, Zhang et al utilized in situ CT scanning and QEMSCAN to acquire multicomponent 3D digital models and investigate the impact of wetting on microscale residual oil.…”

Pore-Scale Experimental Investigation of the Residual Oil Formation in Carbonate Sample from the Middle East

“…Jing initially explored the residual oil morphology of carbonate cores at different PVs by micro-CT and also quantified the residual oil in different states. The results show that when the injection multiplier exceeds 20 PV, a large amount of residual oil is displaced [20]. Guo analyzed the pore structure of four samples through fractal dimensions.…”