The effect of wellbore gas segregation after the production was shut-in at wellhead.
The bottomhole gas is moving up to the wellhead valve and carrying a high downhole pressure along.
The effect leads to a temporary (but could be a long-lasting) pressure increase (sometimes above formation pressure).
It is eventually followed by pressure decline due to balancing with formation pressure but this may take a long time.
The usual practice is to bleed the gas off before well intervention.
The effect often creates a confusion during the Pressure Build Up Surveys and leads to the wrong estimation of the actual rformation pressure (see Fig. 1).
|
Fig. 1. A sample of a Gas Hump during the BUS after 1,000 hrs of constant rate production. If the BUS period has been < 24 hours it may easily mislead an analyst with the much higher than actual formation pressure estimation. |
