Polymer-based EOR methods in low-permeability reservoirs face injectivity issues and increased fracturing due to near wellbore plugging, as well as high-pressure gradients in these reservoirs. Polymer may cause pore blockage and undergo shear degradation and even oxidative degradation at high temperatures in the presence of very hard brine. Low-tension gas (LTG) flooding has the potential to be applied successfully for low-permeability carbonate reservoirs even in the presence of high formation brine salinity. In LTG flooding, the interfacial tension between oil and water is reduced to ultra-low values (10⁻³ dyne/cm) by injecting an optimized surfactant formulation to maximize mobilization of residual oil post-waterflood. Gas (nitrogen, hydrocarbon gases or CO₂) is co-injected along with the surfactant slug to generate in situ foam which reduces the mobility ratio between the displaced (oil) and displacing phases, thus improving the displacement efficiency of the oil. In this work, the mechanism governing LTG flooding in low-permeability, high-salinity reservoirs was studied at a microscopic level using microemulsion properties and on a macroscopic scale by laboratory-scale coreflooding experiments. The main injection parameters studied were injected slug salinity and the interrelation between surfactant concentration and injected foam quality, and how they influence oil mobilization and displacement efficiency. Qualitative assessment of the results was performed by studying oil recovery, oil fractional flow, oil bank breakthrough and effluent salinity and pressure drop characteristics.

中文翻译：

---

高盐低渗油藏中的低压天然气工艺

低渗透油藏中基于聚合物的EOR方法面临注入问题，并且由于近井眼堵塞以及这些油藏中的高压梯度而导致压裂增加。在非常硬的盐水存在下，聚合物可能会在高温下引起孔堵塞并发生剪切降解甚至氧化降解。即使在高地层盐分盐度的情况下，低强度气体（LTG）驱油也可能成功地应用于低渗透性碳酸盐岩储层。在LTG驱油中， 通过注入优化的表面活性剂配方以最大程度地移动注水后的残余油，油和水之间的界面张力降低到超低值（10 ^-3达因/厘米）。气体（氮气，碳氢化合物气体或CO ₂）与表面活性剂块料一起共注入以生成原位泡沫，从而降低了驱替相（油）和驱替相之间的迁移率，从而提高了油的驱替效率。在这项工作中，通过实验室规模的岩心驱替实验，在微观层面利用微乳液特性研究了在低渗透率，高盐度储层中控制LTG驱替的机理。研究的主要注入参数是注入的sal盐度以及表面活性剂浓度和注入的泡沫质量之间的相互关系，以及它们如何影响油的动员和驱替效率。通过研究油的采收率，油的分流率，油库的穿透力以及废水的盐度和压降特性，对结果进行了定性评估。