Thats is what they are essentially doing during the EWT -...

Thats is what they are essentially doing during the EWT - Extended Well Test. They need to remove a certain volume of fluid to be able to analyse and determine the extend of the reservoir and associated resource. Please see attached.

The analysis of pressure changes over time, especially those associated with small variations in the volume of fluid. In most well tests, a limited amount of fluid is allowed to flow from the formation being tested and the pressure at the formation monitored over time. Then, the well is closed and the pressure monitored while the fluid within the formation equilibrates. The analysis of these pressure changes can provide information on the size and shape of the formation as well as its ability to produce fluids.