On-site coreflood experiments were conducted at Prudhoe Bay field, Alaska using side streams of produced water taken directly from produced water injection (PWI) lines. The objectives were to determine how rapidly the formation injection face is plugged by produced water re-injection, the location and mechanism of damage, and the impacts of bacterial growth on the extent and rate of damage.
In core tests where produced water was not filtered prior to injection, 90% permeability damage occurred within 24 hours of injection startup. This is inconsistent with field observations where injection well decline is observed to occur over weeks or months, when seen at all. Field observations are consistent with previously-described (growing) thermal fractures that dominate injection performance, thereby minimizing deleterious effects of sand face plugging.
In core tests where produced water was filtered, little damage was observed; this demonstrates that removable components in produced water are responsible for face damage. However, when cores were first inoculated with bacteria-laden water and then flooded for several days with filtered produced water, deep damage (inches) was seen. This suggests PWI wells can suffer injectivity damage over time due to bacterial growth.
Once damage had occurred, addition of biocide did not restore permeability.