Wellbore Volume (Vw)

Wellbore volume represents the fluid filled volume, below the wellhead valve, that is in communication with the perforations. It can include any combination of tubing, casing, and/or annular volume based on the wellbore configuration (e.g., with no packer present). Wellbore volume is the cause of afterflow or wellbore storage. The larger the volume, the longer the duration of wellbore storage-dominated flow. Occasionally, part of the formation near the wellbore may act as an extension of the wellbore volume. This explains why wellbore storage determined from analysis does not usually match that calculated from the physical dimensions of the wellbore.

For non-conventional analysis and modeling (Slug / PITA / CCT), wellbore volume is used in calculating the influx rate, or the afterflow rate into the wellbore at the sandface.