Dynamic Reconstruction of Working-Gas Space in High-Water-Cut Oil Reservoirs Converted to Underground Gas Storage
Abstract
Conversion of mature waterflooded oil reservoirs to underground gas storage (UGS) is controlled by cyclic gas-oil-water flow rather than by simple repressurization of a depleted hydrocarbon pore volume. At the onset of storage operation, residual oil and movable or capillary-trapped water occupy a substantial fraction of the pore space, whereas the connected gas volume required for repeatable injection-withdrawal cycling is only partially developed. This review synthesizes the conversion process from pore to reservoir scale around four coupled controls: liberation of liquid-occupied pore volume, establishment and persistence of gas-phase connectivity, hysteretic relative-permeability and capillary-pressure responses to drainage-imbibition reversals, and the resulting injectivity, withdrawal deliverability, and working-gas capacity. Evidence from cyclic core flooding, high-pressure/high-temperature (HPHT) micromodel experiments, special core analysis (SCAL), reservoir simulation, and field studies indicates that usable gas-storage space is a dynamic, history-dependent flow property rather than a fixed fraction of geological pore volume. A phenomenological three-stage evolution is identified, comprising initial flow-path establishment, sweep expansion, and quasi-stable cycling, with channel-dominated and balanced-expansion responses representing two mechanistic end members. The review further links pore-scale trapping, film flow, remobilization, gas-oil compositional mass transfer, reservoir heterogeneity, and aquifer influx to cycle-conditioned saturation functions and reservoir-scale performance. Liquid-displacement metrics are therefore most informative when evaluated jointly with gas saturation, gas mobility, sweep efficiency, and cyclic recoverability. This distinction prevents produced-liquid volume from being conflated with field-scale working-gas volume. The central implication is that liquid removal and gas-phase connectivity must evolve concurrently before geometrical pore volume can be converted into repeatedly recoverable working-gas space.
Article Type: Review article
Cited as:
Zhang Q, Zheng DW, Shi L, et al. 2026. Dynamic Reconstruction of Working-Gas Space in High-Water-Cut Oil Reservoirs Converted to Underground Gas Storage. GeoStorage, 2(3), 258-273.
DOI:
https://doi.org/10.46690/gs.2026.03.05Keywords:
Underground gas storage, high-water-cut oil reservoir, cyclic injection-withdrawal, three-phase relative permeability, hysteresis, working-gas capacityReferences
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