Effect of gas type on liquid injectivity in a surfactant-alternating-gas foam process

Foam is injected into geological formations in a number of applications, including enhanced oil recovery, CO2 sequestration, and soil remediation. Surfactant-Alternating-Gas (SAG) is one of the most common methods of foam injection. Injectivity is a key factor in a SAG foam process for both economics and diversion. Depending on process goals and local availability, varies types of gas can be injected. Previous studies suggest that gas properties play an important role in the evolution of gas and liquid injectivity in a SAG process. However, the mechanisms of the effect of gas type on injectivity remain poorly understood. In this study, various types of gas, N2, CO2 and Kr, are employed to investigate the effect of gas type on fluid behavior and injectivity in a SAG process. In one experiment, we partially pre-saturate injected liquid with CO2 to explore the effect of gas-dissolution capacity on liquid injectivity. We observe that the process of dissolution of trapped gas into liquid fingers is strongly affected by gas solubility. The lower the gas solubility in water, the slower the gas dissolution process, and the slower the rise in liquid injectivity. The gas-dissolution process takes much longer with injection of partially pre-saturated liquid than with unsaturated liquid. The propagation of the collapsed-foam front during gas injection is also affected by the gas type: the greater the solubility of water in gas, the faster the foam-collapse process. One practical implication is that CO2 SAG foam injectivity is substantially better than foam made with other gases. The data sets include: cross-sectional water saturation profile during liquid injection following Nitrogen foam obtained from CT scan. Foam scan data for various types of gas at the same superficial velocity. The sectional pressure gradient data during gas injection following foam, liquid injection following foam and a period of gas injection. Researchers can directly draw the curve of pressure gradient change against pore volumes liquid/gas injection in various scenarios.

泡沫注入地质地层的应用场景十分广泛，涵盖强化采油（enhanced oil recovery）、二氧化碳封存（CO₂ sequestration）以及土壤修复等多个领域。表面活性剂交替气体（Surfactant-Alternating-Gas, SAG）工艺是最为常用的泡沫注入方法之一。注入能力是SAG泡沫工艺中同时关乎经济性与分流调控效果的核心因素。根据工艺目标与当地气源可得性，可选用不同类型的气体开展注入作业。已有研究表明，气体性质对SAG工艺中气体与液体注入能力的演化过程具有显著影响，但气体类型对注入能力的作用机制仍未得到充分阐释。
本研究选用氮气（N₂）、二氧化碳（CO₂）及氪气（Kr）等多种气体，探究气体类型对SAG工艺中流体行为与注入能力的影响。其中一组实验通过向注入液体中预溶入部分CO₂，以探究气体溶解能力对液体注入能力的调控作用。研究发现，圈闭气体溶解进入液流指进区的过程显著受气体溶解度影响：气体在水中的溶解度越低，其溶解进程越缓慢，液体注入能力的提升速率也越慢；相较于未预饱和的注入液体，预溶部分气体的注入液体对应的气体溶解过程耗时显著更长。此外，气体注入阶段坍塌泡沫前缘的扩展过程同样受气体类型影响：气体对水的溶解度越高，泡沫坍塌进程越快。该研究的一项实际应用启示为：采用CO₂的SAG泡沫注入能力，显著优于其他气体配制的泡沫体系。
本数据集包含以下内容：氮气泡沫实验后液体注入阶段的计算机断层扫描（CT）截面水饱和度剖面数据；相同表观流速下不同气体类型的泡沫CT扫描数据；泡沫阶段后气体注入、泡沫阶段后液体注入以及阶段性气体注入过程中的截面压力梯度数据。研究人员可直接绘制不同工况下压力梯度随液体/气体注入孔隙体积变化的曲线。