Introduction
To begin:
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Supercharging: Supercharging is a dynamic condition which extends the hydrostatic pressure of mud in the wellbore beyond the filter-cake into the reservoir.
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Interference: In the context of flow and buildup, interference refers to declining pressures during the buildup period due to offset production.
Example 1: Canadian Gas Well
In this field example, the Bourdet (Well Testing) derivative. This analysis was performed using PanSystemTM.
As can be seen by the plot on the left, the pressure data begins to decline although it was not clear if it was due to supercharging or nearby production interference.
With respect to the derivative analysis, the analyst has chosen to assume that the last data prior to the collapse of the derivative is the best estimate of permeability. In this scenario, one could consider the estimate PESSIMISTIC if true radial flow occurs later.
However, one cannot easily determine where the effects of the declining pressure actually begin influencing the pressure derivative. It is possible that radial flow occurred earlier, and the actual permeability estimate is OPTIMISTIC.
Example 2: Canadian Gas Well
In this example of gas well 15-27-068-06W6, declining pressures during the buildup portion is present. This analysis was using WellTestTM. This well was fracture stimulated.
Although there is an “apparent” radial flow period, it could be optimistic as the radial flow regime may be an artefact of the declining pressures. We know that the radial flow does not occur any earlier as much of the flow appears to be dominated by Bilinear (1/4) slope.
It is also possible to interpret the early-time data as radial flow. But it is Predico’s position that this apparent radial flow is more likely due to a combination of:
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Missing early-time data, and
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Transition to Bilinear flow
Below, a hand-drawn wellbore storage flow period has been added. This “valley“ can be reproduced with simulation when a fracture model is combined with wellbore storage.
