FRACTAL MODEL FOR HETEROGENEOUS EFFECTIVE DIFFUSION AND ITS APPLICATION IN COMPOSITIONAL SIMULATIONS OF CO2 FLOODING IN TIGHT RESERVOIRS

Mingyu Cai, Shugang Yang, Shuangxing Liu, Kunfeng Zhang, Ming Xue, Xingchun Li, Yuliang Su and Lei Li
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Mingyu Cai: CNPC Safety and Environmental Protection, Technology Research Institute, Huanghe, North Road No. 1, Shahe Town, Changping District, Beijing 102206, P. R. China
Shugang Yang: CNPC Safety and Environmental Protection, Technology Research Institute, Huanghe, North Road No. 1, Shahe Town, Changping District, Beijing 102206, P. R. China
Shuangxing Liu: CNPC Safety and Environmental Protection, Technology Research Institute, Huanghe, North Road No. 1, Shahe Town, Changping District, Beijing 102206, P. R. China
Kunfeng Zhang: CNPC Safety and Environmental Protection, Technology Research Institute, Huanghe, North Road No. 1, Shahe Town, Changping District, Beijing 102206, P. R. China
Ming Xue: CNPC Safety and Environmental Protection, Technology Research Institute, Huanghe, North Road No. 1, Shahe Town, Changping District, Beijing 102206, P. R. China
Xingchun Li: CNPC Safety and Environmental Protection, Technology Research Institute, Huanghe, North Road No. 1, Shahe Town, Changping District, Beijing 102206, P. R. China
Yuliang Su: ��School of Petroleum Engineering, China University of Petroleum (East China), Changjiang West Road 66, Economic Technical, Development Zone, Qingdao 266580, Shandong Province, P. R. China
Lei Li: ��School of Petroleum Engineering, China University of Petroleum (East China), Changjiang West Road 66, Economic Technical, Development Zone, Qingdao 266580, Shandong Province, P. R. China

FRACTALS (fractals), 2025, vol. 33, issue 01, 1-17

Abstract: The extremely low porosity and permeability in tight reservoirs make diffusion effects significant and non-negligible. Accurately estimating diffusion coefficients is critical for predicting CO2-enhanced oil recovery and CO2 storage (CCUS–EOR) in such reservoirs. However, predicting effective vapor–liquid phase diffusion in porous media and incorporating it into large-scale compositional simulations remains a major challenge. This study combines fractal theory with Fick and Maxwell–Stefan diffusion frameworks, proposing a simplified fractal diffusion model that incorporates fractal parameters and porosity to better characterize CO2 and in situ oil diffusion in heterogeneous tight reservoirs. Numerical models were developed using MATLAB to simulate both immiscible and miscible CO2 flooding within multiphase, multicomponent flow equations while considering diffusion effects. The results reveal that diffusion significantly increases the area influenced by CO2 and improves the uniformity of CO2 concentration along the flow path. Confined phase behavior in micro- and nanopores enhances diffusion, increasing CO2 mole fractions in displacement zones. In immiscible flooding, CO2 extraction of lighter oil components results in higher residual oil density compared to models that neglect diffusion. This fractal-based model for heterogeneous effective diffusion, combined with insights into the role of diffusion in CO2 flooding in tight reservoirs, offers important implications for developing more effective CCUS–EOR strategies.

Keywords: Effective Diffusion; Fractal Theory; Compositional Simulation; CO2–EOR; Tight Reservoir (search for similar items in EconPapers)
Date: 2025
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DOI: 10.1142/S0218348X25500021

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