陆相页岩凝析气衰竭及注气吞吐长岩心实验研究

Experimental study on depletion development and gas injection huff-n-puff in long cores for continental shale condensate gas

  • 摘要: 陆相页岩凝析气藏在开发过程中,当地层压力低于露点压力后会发生反凝析,导致凝析油滞留,而目前对该类气藏衰竭开发特征及注气吞吐关键参数的认识尚不明确。通过长岩心物理模拟实验,揭示了页岩凝析气藏衰竭开采特征,明确了注气吞吐增油机理并优化了关键参数。选用四川盆地复兴地区涪页10HF井岩心与复配地层流体,按正交设计方法开展衰竭开采实验,系统研究不同压降速度下的生产特征。在衰竭开采结束后进行注气吞吐实验,以优化参数并提高凝析油采出程度。实验全程监测压力、油气产量、生产气油比及产出气组分,结束后通过核磁共振分析含油饱和度分布。衰竭实验表明,生产气油比呈现“驼峰”形态,证实反凝析油参与流动,快速衰竭因气体夹带效应,凝析油采出程度(24.77%)高于慢速衰竭(22.62%)。注气吞吐实验中,CO2因具有抑制反凝析和强抽提重烃的双重机制,增油效果显著优于CH4。在总注气量约束下,较高注入压力可获得更高最终采收率,但需更多吞吐轮次,从较低压力开始注气虽采收率略低,但经济性更优。研究明确了陆相页岩凝析气藏衰竭开采的反凝析动态特征,论证了注CO2吞吐是提高凝析油采收率的有效技术途径。其核心优势在于通过相态调控抑制反凝析,并通过强抽提作用采出滞留烃。参数优化表明,注气时机需在采收率与经济效益间权衡,建议在较低地层压力下启动CO2吞吐,并配合适度焖井,以实现高效开发。

     

    Abstract: During the development of continental shale condensate gas reservoirs, once the formation pressure falls below the dew point pressure, retrograde condensation occurs, leading to condensate oil retention. However, the depletion development characteristics and key parameters of gas huff-n-puff in such reservoirs remain poorly understood. This study aims to reveal the depletion development characteristics of shale condensate gas reservoirs, clarify the oil enhancement mechanisms of gas huff-n-puff, and optimize key parameters through long-core physical simulation experiments. Using core samples from the well FY10HF and reconstituted formation fluids from Fuxing area, Sichuan Basin, depletion production experiments were conducted according to the orthogonal design method to systematically investigate production characteristics under different pressure decline rates. After depletion production, gas huff-n-puff experiments were performed to optimize parameters and improve condensate oil recovery degree. Throughout the experiments, pressure, oil and gas production, producing gas-oil ratio, and produced gas composition were monitored. After the experiments, nuclear magnetic resonance (NMR) was used to analyze the oil saturation distribution. The depletion experiments indicated that the producing gas-oil ratio exhibited a "hump" shape, confirming the participation of retrograde condensate oil in flow. Due to the gas stripping effect, rapid depletion achieved a higher condensate oil recovery degree (24.77%) than slow depletion (22.62%). In the gas huff-n-puff experiments, CO2 demonstrated significantly better oil enhancement performance than CH4, owing to its dual mechanisms of inhibiting retrograde condensation and strongly extracting heavy hydrocarbons. Under the constraint of total injection gas volume, a higher injection pressure led to a higher ultimate recovery factor, but required more huff-n-puff cycles. Starting gas injection at a lower pressure, while resulting in a slightly lower recovery factor, proved to be more economical. This study clarifies the dynamic characteristics of retrograde condensation during depletion development in continental shale condensate gas reservoirs, and demonstrates that CO2 huff-n-puff is an effective technical approach for enhancing condensate oil recovery. Its core advantages lie in suppressing retrograde condensation through phase behavior control and recovering retained hydrocarbons through strong extraction. Parameter optimization indicates that the timing of gas injection requires a trade-off between recovery factor and economic benefit. It is recommended to initiate CO2 huff-n-puff at lower formation pressures, combined with appropriate shut-in time, to achieve effective development.

     

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