Improvement in Foamability/stability Test Rigs for CO2 Foam EOR Screening Evaluation

摘要

To screen effective foaming agents for CO2 Foam EOR, foamability/stability test is performed as visual evaluation and/or slimtube apparatus under high pressure and high temperature (HPHT) condition in reservoir. There are several ways for generating foams: i.e. bubbling, stirring, and mixing through porous media (ex. sandpack, glassbeads, etc.). The bubbling method is usually applicable in the open system at ambient pressure condition. The mixing through porous media is applicable in HPHT condition, but mainly used in flooding tests in which mixing efficiency might be minimal because of just one time chance for injectants (CO2 and foaming agent) to create foam. The stirring can be applied into closed/ pressurized system such as PVT apparatus that provides visual observation through glass cell/window. In this paper, stirring and mixing-through-porous-media were used in the foamability test rig and the slimtube apparatus, respectively. The existing rigs in our laboratory were modified for evaluating CO2 foam. In general, magnetic stirring system is equipped in PVT apparatus to equilibrate fluid samples, however; the iron magnets could not be resistant to our experimental condition. Then, polytetrafluoroethylene (PTFE)-encapsulated magnetic stirrer was used as alternative material. The PTFE stirrer was wheel shape with 4 blades on both surfaces of upper and lower for more stirring power. From material aspects, PTFE is universal chemical/corrosion resistance under existence of oil and hydrocarbon gas mixture, however; our experimental environment (mixing of CO2 + formation water) rapidly becomes severer as pressure/temperature increase. The stirrer was expanded and chipped due to CO2 corrosion, and stuck in cylinder-shape metal device location at the bottom of glass cell, although it was originally set with small clearance to rotate freely. This expansion resulted insufficient stirring power to create foams. In the slimtube flooding test to evaluate apparent viscosity increase by CO2 foam, a visual cell was equipped at the downstream location of the sandpack to check ideal foam creation. However, our first trial was failed and required modification. This paper demonstrates how we improved the foam creation sufficiently under the reservoir condition for appropriate evaluation.