Quantification of the microstructure, effective hydraulic radius and effective transport properties changed by the coke deposition during the crude oil in-situ combustion

Qianghui Xu, Wei Long, Hang Jiang, Bin Ma, Cheng Zan, Desheng Ma, Lin Shi - Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Department of Thermal Engineering, Tsinghua University, Beijing, China ; iCore Digital Reservoir Group, Katy, TX 77450, United States ; State Key Laboratory of Enhanced Oil Recovery, Research Institute of Petroleum Exploration & Development, China National Petroleum Corporation, Beijing 100007, China ; Research Institute of Tsinghua University in Shenzhen, 518055, China

Coke deposition during crude oil in-situ combustion (ISC) is an important phenomenon that significantly impacts the pore topology and permeability.

In this study, X-ray computed microtomography and a specific image processing procedure were used to reconstruct the micro-tomographic images of packed beds with coke deposition. From the reconstructed images, the microstructural parameters related to the transport were analyzed, such as the effective porosity, the constrictivity and the geodesic tortuosity. The Lattice Boltzmann method was used to simulate the species diffusion and fluid flow through the microstructures to quantify the mass diffusivity and permeability. The experimental work was performed to validate the digital microstructures and the simulated permeability. The effects of the coke deposition on the pore topology and the permeability were analyzed. The coke deposition pattern showed significant deposition in the pore throat. Analyses of the pore size distribution lead to a more reasonable geometric approach to measure the effective hydraulic radius for the better permeability prediction. Based on the effective transport properties and the microstructural parameters, a developed permeability relation was introduced by factorizing the permeability into two distinct contributions from the characteristic length and the microstructural effect. The permeability model describes the main influences of all the relevant geometric parameters on the permeability reduction by the coke deposition.

How PerGeos is used

The reconstructed data was imported into Avizo 8.0 from FEI for further image processing to label the different materials in the reconstructed digital image. Fig. 2 illustrated the detailed steps of image processing with the image labeled with the corresponding serial number of each step. The fundamental of the image processing was the gray-intensity contrast among difference phases and the morphological characteristics between glass bead particles and the coke. A line was drawn to probe the gray-scale intensity variation along the line across different components in order of the glass bead, the pore, the coke, the pore and the glass bead, as illustrated in Fig. 1a. Their gray-intensity differences were observed since their different density and atomic number leaded to the variations in the X-ray attenuation.