Speaker
Description
Surfactant-Alternating-Gas (SAG) (also known as FAWAG) is the most common method of injection for foam EOR. Injectivity is a key factor of a foam EOR process for both process economics and diversion. We have examined liquid injectivity after a period of gas injection. During gas injection following foam, a bank of collapsed, or greatly weakened, foam propagates slowly from the inlet. During subsequent liquid injection, liquid quickly saturates the collapsed-foam region and then fingers through the weakened-foam bank ahead of the collapsed-foam bank in a way similar to liquid injection directly after foam. Mobility then rises substantially, as liquid dissolves gas trapped within the fingers. Over time, the fingers also grow slowly outwards as they dissolve surrounding trapped gas. Thus gas solubility is crucial to liquid mobility and liquid injectivity.
In this study, we conduct coreflood experiments in a Berea sandstone core sample with permeability 160 mD at 90°C with 40 bar back-pressure. Various types of gas, nitrogen, CO2 and krypton, are adopted to investigate the effect of the gas solubility in water on the fluid behavior and injectivity in a SAG foam process. We examine gas injection following foam and liquid injection following a similar amount of gas injection. In one experiment, we partially pre-saturate injected liquid with CO2.
We observe the same sequence of banks with the various types of gas. The liquid-finger sizes are similar, indicated by similar liquid break-through time during liquid injection following foam. The times for foam dry-out and collapse during gas injection following foam injection are also comparable among the gases. However, the process of dissolution of trapped gas into liquid fingers is strongly affected by the gas solubility, as expected. The lower the gas solubility in water, the slower the gas dissolution process, and the slower the rise in injectivity. The gas-dissolution process takes about 7 times longer with injection of liquid partially pre-saturated with CO2 than with unsaturated liquid injection. The plateau value of pressure gradient during liquid injection is also affected by the gas type, in agreement with data on steady-state foam strength. One practical implication is that CO2 SAG foam injectivity is substantially better than for foam made with other gases.
| Participation | Unsure |
|---|---|
| Country | China |
| MDPI Energies Student Poster Award | No, do not submit my presenation for the student posters award. |
| Time Block Preference | Time Block B (14:00-17:00 CET) |
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