Abstract
The difficulty of deploying remaining oil from unconventional reservoirs and the increasing CO2 emissions has prompted researchers to delve into carbon emissions through Carbon Capture, Utilization, and Storage (CCUS) technologies. Under the confinement of nanopore in unconventional formation, CO2 and hydrocarbon molecules show different density distribution from in the bulk phase, which leads to a unique phase state and interface behavior that affects fluid migration. At the same time, mineral reactions, asphaltene deposition, and CO2 pressurization will cause the change of porous media geometry, which will affect the multiphase flow. This review highlights the physical and chemical effects of CO2 injection into unconventional reservoirs containing a large number of micro-nanopores. The interactions between CO2 and in situ fluids and the resulting unique fluid phase behavior, gas-liquid equilibrium calculation, CO2 adsorption/desorption, interfacial tension, and minimum miscible pressure (MMP) are reviewed. The pore structure changes and stress distribution caused by the interactions between CO2, in situ fluids, and rock surface are discussed. The experimental and theoretical approaches of these fluid-fluid and fluid-solid reactions are summarized. Besides, deficiencies in the application and safety assessment of CCUS in unconventional reservoirs are described, which will help improve the design and operation of CCUS.
Highlights
At present, conventional oil and gas production is decreasing over the years, and the unconventional oil and gas resources, which with rich reserves, have attracted more and more attention
Gs = 160 − 200 Oil samples, methane, and n- Pb is higher in the porous medium than the PVT cell
Higher temperature reduces the effect of porous media on vapor and liquid equilibrium (VLE)
Summary
Conventional oil and gas production is decreasing over the years, and the unconventional oil and gas resources, which with rich reserves, have attracted more and more attention. The low recovery is mainly because the adsorbed and dissolved crude oil in the shale reservoir cannot be effectively utilized in the primary development [1]. Researchers experimentally compared the effects of CO2 Huff-n-Puff and water injection on the enhanced recovery of shale oil. The results show that under different shale properties, CO2 Huff-n-Puff can increase the recovery rate by ~50% (from 33% to 85%), and the overall effect is far better than that of surfactant and water injection [3]. The Rangely Weber unit in Salt Creek field, one of the storage sites for Shute Greek Gas Processing Plant, is the world’s largest extralow permeability sandstone reservoir developed by CO2-WAG miscible flooding [5]. The future research directions and challenges for the research and application of CO2-CCUS are discussed
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