3.: Matrix Injection

Under a matrix-injection philosophy, injectivity decline will invariably be observed over time. Factors that can induce declines (Guan et al. 2005) include

It is this last effect that is normally recognized as the main cause of injection decline in water-injection wells, but the other factors mentioned can be significant and should not be ignored. It can be seen from all of these effects that injectivity can change over time even if it were possible to inject completely clean injection water containing no suspended material at all.

There have been many field cases where injection performance has been significantly better than had initially been predicted. In some cases, no long-term declines in injectivity were seen even when upsets in the filtration plant allowed theoretically damaging water to be injected. One possible explanation for such cases could be that, although matrix injection was planned, injection was actually taking place under fractured-injection conditions (possible explanations for this will be discussed later). In any event, these observations led to many fields retiring the water-injection fine-filtration equipment, a change that was made in many North Sea waterfloods.