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Simulation of high water-cut in tight oil reservoirs during cyclic gas injection
Zhang, Chi
Zhang, Chi
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2019
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Data from a pilot test imply substantial water production after gas injection, which may impede oil production, but the underlying mechanisms are poorly understood. A compositional model is developed to study possible mechanisms for high water-cut pilot results. First, eight pseudo-components were used to match the PVT lab results of a typical oil sample from the Wolfcamp shale. A lab-scale model was then established in our simulation study to match the results of gas huff-n-puff experiments in cores, in which key parameters were identified and tuned. A half-stage field model consisting of five fractures was built, where stress-dependent permeability was represented by compaction tables. In addition, a sensitivity analysis was conducted to examine the roles of different mechanisms behind the abnormal high water-cut phenomenon. Our simulation results have shown that initial water saturation, IFT-dependent relative permeability, reactivation of water-bearing layers, and re-opening of unpropped hydraulic fractures may affect the water-cut after gas injection. Among them, re-opening of unpropped hydraulic fractures was the most critical factor. This study also optimized the period of injection and soaking phases and well bottom-hole pressure to improve the economic benefits of production operations.
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