Abstract
This paper proves the soundness of supercritical CO2 displacement for enhancing gas recovery of a tight gas reservoir via laboratory investigations and compositional modeling. First, a novel phase behavior experimental device with a screened supercritical CO2 dyeing agent were first presented to better understand the mixture characteristics between supercritical CO2 and natural gas. The mass transfer between two vapor phases was also measured. Then, based on experimental results, the compositional model considering the influence of CO2 diffusion on the gas recovery and critical property adjustment of supercritical CO2 was established. The miscibility process and mixing properties, such as density, viscosity, and the flowing velocity vector, of supercriticalCO2 and natural gas were visualized through a 3D display, which obtained a better understanding of the flooding mechanism of Enhanced Gas Recovery (EGR) via supercritical CO2. Finally, with experiments and numerical simulations, the main benefits of CO2 EGR were shown, which were partial miscibility between CO2 and natural gas, pressure maintenance, and CO2 displacement as a “gas cushion.” In general, experiments and numerical simulations demonstrate that CO2 EGR can be seen as a promising way of prolonging the productive life and enhancing recovery of tight gas reservoirs.
Highlights
Due to various industrial activities, and in particular the burning of fossil fuels, the concentration of CO2 in the atmosphere has continually risen since the industrial revolution, which has triggered global warming and poses a serious threat to human survival and socio-economic development [1]
CO2 with a dyeing agent was injected into the device, and the natural gas was injected from the upper part under constant pressure with 9 MPa
Non-equilibrium and diffusion experiments proved that there was a weak diffusion between supercritical CO2 and natural gas
Summary
Due to various industrial activities, and in particular the burning of fossil fuels (coal, oil, and natural gas), the concentration of CO2 in the atmosphere has continually risen since the industrial revolution, which has triggered global warming and poses a serious threat to human survival and socio-economic development [1]. Long-term geologic storage is considered as an important solution for CO2 reduction. Depleted natural gas reservoirs are potentially important targets for carbon sequestration using direct carbon dioxide (CO2 ) injection with two remarkable advantages: (i) available volume, and (ii) integrity against gas escape. The accumulation and entrapment of natural gas testifies to the integrity of natural gas reservoirs for containing gas for long periods of time. The IEA (International Energy Agency) has estimated that as much as 140 GtC could be sequestered in depleted natural gas reservoirs worldwide (IEA, 1997) [2]. These aspects of natural gas reservoirs for carbon sequestration are widely recognized
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