case as illustrated in fig3 these functions can be reduced to f q q and f p datum p datum however for a gas reservoirs f p datum p 2 datum is typically a better choice to produce an ipr whilst the measuring points for p datum and q can be chosen in general arbitrarily across the range of possible values it may be advantageous to start a series of such measurement with high enough flow rate such that all zones have a positive contribution and the composite curve for f q is linear as shown on the fig3 the flow rate can be altered in discrete steps and with each step in the flow rate the well should be allowed to return to a stable state before taking the data point after a shut in period prior to the test a well is best cleaned out and stabilized by letting the well produce at a high flow rate and wait until all transient behavior becomes negligible the sampling of the comingled flow is also best performed close to the end of the flow period after the well reached a steady state in the example the comingled samples are collected from a sample outlet built into the flow meter at surface flowing pressure for each zone p 1 p 2 and p 3 and the pressure difference between zones h 1 h 2 and h 3 can be calculated from p datum at surface or any other chosen location and the.