ارزيابي بازچرخاني گاز در مخزن داراي تركيب كلاهك گازي و آبخوان (كلاهك گازي–گاز محلول–آبخوان)

Managing hydrocarbon recovery in tilted reservoirs, characterized by a complex drive mechanism combining a primary gas cap, dissolved gas expansion, an‎d an active bottom water layer, presents a significant technical challenge. In such systems, the simultaneous rise of the water-oil contact surface (WOC) an‎d the simultaneous fall of the gas-oil contact surface (GOC) often leads to premature fluid breakthrough, leaving substantial oil reserves unrecovered. This research eva‎luates the technical feasibility an‎d efficiency of a strategic gas recycling scheme as a proactive reservoir management tool, aiming to stabilize the fluid contact surfaces an‎d maximize the recovery factor. The study utilizes a high-resolution, three-phase numerical simulation model developed using the CMG IMEX black oil simulation software (2018). A three-dimensional Cartesian grid with a tilted stratigraphic structure was constructed to represent the reservoirʹs structural dip. To achieve high accuracy in representing the physics of water an‎d gas flow near oil wells, a Local Grid Refine (LGR) strategy was implemented using a 5×5×5 subgrid configuration. This methodology compared two main scenarios: natural depletion (baseline), gas recycling to maintain pressure. Production was subject to strict operational constraints, including a maximum gas oil ratio (GOR) of 3000 m³/m³ an‎d a maximum water-to-capture ratio (WCUT) of 0.9. The results show that gas recycling successfully maintains reservoir pressure significantly above the baseline for natural depletion, preserving oil fluidity an‎d the natural energy of the gas cap. Spatial visulation of saturation profiles confirms that reinjecting the produced gas creates a downward reservoir gradient that effectively inhibits the upward migration of the lower aquifer. This intervention effectively delayed water breakthrough in downward-dip wells (OP5 an‎d OP6), significantly reducing the cumulative costs of water production an‎d treatment. In contrast, for the updraft wells (OP2 an‎d OP3), which are more susceptible to the gas cone phenomenon, the study implemented a perforation management strategy. By gradually shutting down the upper perforation intervals as the gas reservoir expan‎ded, the model mitigated gas interference an‎d extended the productive life of the wells. The final analysis reveals that the optimal gas recycling scenario, followed by strategic gas cap discharge at the critical oil depletion point, achieved a significantly higher oil recovery factor compared to the natural depletion criterion. The results highlight that the synergy between pressure maintenance, perforation management, an‎d high-resolution gas cone modeling is essential for optimizing recovery in multi-drive systems. This research provides a technical framework for operators to balance pressure support in the early stages an‎d gas cap recovery in the later stages, ensuring maximum volumetric flow an‎d long-term field profitability.

محسن محمدي

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