Overview of EOR in Unconventional Reservoirs

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Presenter

Xueying Xie, Ph.D.
Principal and Director
Subsurface Technology
Simulation & Design
Oxy

Description

Unconventional reservoirs retain substantial oil after primary depletion, but ultra-low permeability, heterogeneous rock properties, complex hydraulic-fracture networks, and conformance limitations reduce the effectiveness of conventional EOR methods. This talk reviews EOR technologies, key unconventional EOR challenges, and the current status of gas/CO₂ and chemical huff-and-puff processes that leverage existing horizontal wells and stimulated reservoir volume. Main recovery mechanisms include oil swelling, viscosity reduction, vaporization, diffusion, miscibility above minimum miscibility pressure, interfacial-tension reduction, wettability alteration, and improved matrix-fracture fluid exchange. Field pilots in the Bakken, Eagle Ford, and Permian Basins, conducted by multiple operators using various injectants, have demonstrated measurable incremental oil response in unconventional reservoirs. Oxy is expanding EOR into unconventional reservoirs, representing a resource opportunity of more than 2 billion BOE, as highlighted in the Q3 2025 earnings call. Experience in the Permian Basin has demonstrated a practical pathway from laboratory evaluation to field deployment and commercialization, with pilots showing promising incremental oil production. The next milestone is to transition unconventional EOR from successful pilot projects to repeatable commercial-scale developments.