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Optimization of Gas–Water Synergistic Huff-n-Puff Development for Tight Conglomerate Reservoirs in the Mahu Area
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DOI：10.3390/pr14162581.png)
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Abstract
En 中文
Tight conglomerate reservoirs in the Mahu area are characterized by strong heterogeneity, complex fracture–matrix interactions, and rapid pressure depletion after volumetric fracturing, which severely restricts the sustainable production of horizontal wells. To clarify the applicability of post-fracturing energy replenishment and enhanced oil recovery strategies, this study establishes single-fracture and field-scale numerical models for tight conglomerate reservoirs and systematically investigates the effects of gas injection timing, injection volume, fracture conductivity, injection media, gas–water ratio, and well-pattern cooperation on huff-n-puff performance. The results show that immediate gas injection after fracturing is not the optimal strategy because the injected gas mainly migrates through hydraulic fractures and has limited contact with matrix oil. For the base-case single-fracture model, a favorable injection timing was obtained when oil production entered a slow-decline stage and the reservoir pressure decreased to approximately 3–4 MPa below the bubble-point pressure, resulting in a simulated recovery-factor increase of 12.3% relative to the reference case. CO2 shows strong advantages in oil swelling, viscosity reduction, diffusion, and extraction, whereas water injection provides more effective pressure maintenance. Therefore, a gas–water synergistic huff-n-puff mode can simultaneously improve matrix oil mobilization and reservoir energy replenishment. The optimal gas–water ratio should be dynamically adjusted during different cycles, with a higher CO2 proportion in the early stage and an increased water slug proportion in later cycles to compensate for pressure depletion. At the field scale, a cooperative scheme of edge-water injection and central gas injection is proposed. Edge-water injection forms a high-pressure barrier that suppresses gas channeling, extends CO2 retention time, and promotes deeper gas migration into the matrix. Field-scale simulation results indicate that this scheme increases the simulated cumulative oil production by 6.9% compared with the reference scheme. This study provides a practical gas–water synergistic development strategy for improving oil recovery in Mahu and similar tight conglomerate reservoirs.
Keywords:
tight conglomerate reservoir
gas–water synergistic huff-n-puff
gas injection for enhanced oil recovery (EOR)
development strategy
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