Q: I’m trying to use an IPR, but I keep getting error messages. What is wrong?

A: There can be several reasons for this. First of all, any time you are having problems either in multiphase mode or if you are using an IPR (or both), try using flow rate as an input. This removes some problems associated with iterating to a solution. (If you are in multiphase and using an IPR, look at the next two questions below as well.) You must also remain within the limits of your IPR. The following error indicates that you are trying to draw the well down below the maximum flow rate permitted using the IPR:

In this case, the IPR reached a producing pressure of 0 at a flow rate of 148 m³/d, and the user tried to obtain a flow rate of 200 m³/d. When an IPR is selected, the flow rate can never be higher than the flow rate calculated by the IPR at a producing pressure of 0. If you are getting this message when you are specifying pump speed instead of flow rate, it is because PC-PUMP is having difficulty accounting for the gas going through the pump—try specifying flow rate instead.

In this case, PC-PUMP has not been able to locate the fluid level—it’s trying to put it below the pump, which is not allowed (unless there is a tail joint, in which case the fluid level may not go below the bottom of the tail joint). If you’ve specified a flow rate, PC-PUMP calculates a producing pressure from the IPR. It will then calculate where the fluid level should be. If the casing head pressure is greater than the producing pressure, it will fail with the above error message. Try a lower flow rate to increase the producing pressure, or determine if you can use a lower casing head pressure.

This message also indicates that the program cannot calculate a valid fluid level. It is often caused by large amounts of gas flowing up the annulus. This gas decreases the effective density of the fluid, meaning it needs more height to reach the required pressure at the perforations. In some cases, the fluid column may go all the way to surface, at which time this error message will be reached. Such a well will actually produce some liquid (along with a lot of gas) up the annulus, and PC-PUMP does not allow this.

This message is similar to the previous two. If you get this error, you need to check the same things. Your flow rate could be too high or too low for the circumstances, or you may need to adjust your casing head or tubing head pressure.

In general, if you are having problems of this nature, a good idea would be to run a batch comparison with flow rate as the batch parameter. Enter flow rates from just over zero to just under the maximum value from the IPR (i.e. the flow rate at zero producing pressure). See what range the calculation will allow and try to stay in that range.

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