Multiscale Non-Equilibrium Compositional Modeling of Cyclic Gas Injection in Shale Reservoirs

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

The shale matrix is a multiscale porous medium featuring nanopores, macropores, and micro-fractures, exhibiting distinct transport mechanisms and phase behaviors. This study challenges the assumptions of local thermodynamic equilibrium within each matrix grid and recognizes the significant discrepancy in time scales of fluid transport within nanopores and macropores. This disparity leads to non-equilibrium mass transfer between these distinct scales of pores. Accordingly, we propose a multiscale, multiphase, multicomponent transport model for simulating cyclic gas injection in shale reservoirs while accounting for non-equilibrium thermodynamics in the shale matrix. The multiscale porous media encompasses nanopores, macropores, and micro-fractures. The fluid transport within the nanopore and macropore is modeled using a species transport-based equation, incorporating viscous flow, molecular diffusion, and Knudsen diffusion. Darcy's law is applied in micro-fractures and hydraulic fractures. Phase behaviors in nanopores are computed employing a pore-size dependent Peng-Robinson equation of state (PR-C-EOS), while the PR-EOS governs other porous mediums. Non-equilibrium mass transfer between each pair of porous mediums is derived based on multiple interacting continua (MINC) theory. We simulate the cyclic CO2 injection with a ternary component oil-methane, propane, and n-octane-within a shale matrix. Sensitivity analyses are conducted to analyze the effect of soaking time, natural fracture (micro-fracture) permeability, and pore volume fraction on CO2 cyclic injection enhanced oil recovery (EOR). During the injection phase, CO2 rapidly fills the pore volume of natural fractures and then transfers to macropores and nanopores via nonequilibrium mass transfer. Even during the soaking period, when CO2 injection ceases, non-equilibrium mass transfer continues to significantly change the fluid composition within these continua. Increasing the soaking time remains an effective method to improve oil recovery. A longer soaking period allows more CO2 to move into macropores and nanopores through non-equilibrium mass transfer, thereby promoting CO2 mixing with crude oil. In addition, CO2 cycle injection is an effective method for increasing oil recovery across all volume fractions. Nevertheless, enhanced oil recovery is greater when the macropore volume fraction is higher, primarily because CO2 can be injected more easily into macropores and mixed with the oil. Such a multiscale transport model facilitates a comprehensive understanding of the gas EOR mechanism and provides a valuable framework for designing effective EOR methods for shale reservoirs.

Original languageEnglish (US)
Title of host publicationSociety of Petroleum Engineers - SPE Annual Technical Conference and Exhibition, ATCE 2024
PublisherSociety of Petroleum Engineers (SPE)
ISBN (Electronic)9781959025375
DOIs
StatePublished - 2024
Event2024 SPE Annual Technical Conference and Exhibition, ATCE 2024 - New Orleans, United States
Duration: Sep 23 2024Sep 25 2024

Publication series

NameProceedings - SPE Annual Technical Conference and Exhibition
Volume2024-September
ISSN (Electronic)2638-6712

Conference

Conference2024 SPE Annual Technical Conference and Exhibition, ATCE 2024
Country/TerritoryUnited States
CityNew Orleans
Period9/23/249/25/24

All Science Journal Classification (ASJC) codes

  • Fuel Technology
  • Energy Engineering and Power Technology

Fingerprint

Dive into the research topics of 'Multiscale Non-Equilibrium Compositional Modeling of Cyclic Gas Injection in Shale Reservoirs'. Together they form a unique fingerprint.

Cite this