Most often the initial pressure is just before purging portable production test facilities. This operation usually causes one of two patterns. If the wellbore is gas filled, a characteristic drawdown spike occurs. If there is liquid in the hole, the pressure may spike upwards due to increasing the liquid head between gauges and formation (i.e. sucking liquid into the wellbore). Pattern is a good indicator of wellbore fluid composition.
The production flow test, or drawdown, is what sends the #welltest pressure transient signal out into the reservoir. The flow test may be designed as a single point or multi-point (#AOF). The final flowing pressure, before the extended pressure buildup test, is critically important. Multi-point tests may be done as a modified isochronal, with equal flow/shut-in sequences, or flow-after-flow, with equal flow sequences but no shut-in periods (i.e. for high permeability systems). The flowing (and shut-in) pressures, at each step, are also important events for multi-point tests.
Flowing pressures increasing might be due to the near wellbore region cleaning up or liquid loading. Flowing pressures decreasing usually indicates that stabilized conditions have yet to be achieved. Be cognizant of counteracting effects by comparing surface flowing data.