A: Unfortunately, when we developed PC-PUMP, we could not anticipate every possible situation. In the past several years, C-FER has corrected most of the situations which we were aware of which could cause this error. If you get this error, click on the “send” button in the error message and email it to C-FER. It is virtually impossible for us to diagnose your problem with these error messages without having the PC-PUMP data file (.pcp file), but in most cases we can determine the problem and suggest a correction or work-around for you once we see the .pcp file. When these problems are reported to C-FER, we strive to fix them in a new version of PC-PUMP as soon as it is feasible to do so.

A: PC-PUMP checks the input in the wellbore survey to ensure it meets certain criteria (for example each survey point must be at a deeper measured depth than the previous one). PC-PUMP, however, does not check everything. This error is most likely caused by an incorrect value in the survey. You can probably find the problem by scanning your inputs for a number that looks out of place. If not, save the file and email it to C-FER for diagnosis.

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.

A: When you specify a higher flow rate and you have an IPR active, PC-PUMP uses a lower pressure at the perforations (as defined by your IPR). At lower pressure, more gas comes out of solution before entering the pump. The free gas reduces the amount of volume within the pump occupied by liquid. PC-PUMP calculates pump speed based on the efficiency you’ve specified, the liquid flow rate you’ve specified, the proportion of the volume filled by liquid, and the pump displacement. As the amount of gas increases, the pump must run at a higher speed to achieve the liquid flow rate you’ve specified. This is indicative of a problem you would encounter in trying to pump off a gassy well by increasing the pump speed—you may find that above a certain speed you get very little incremental liquid flow rate.

A: This can happen in some cases with very gassy wells. As the pressure at the perforations decreases (as happens when the flow rate is increased with an IPR) more gas comes out of this solution. Some or all of this gas goes up the casing annulus (depending on the free gas separation value, and on whether the pump intake is above or below the perforations). This gas serves to decrease the overall density of the fluid in the casing. The fluid level is determined by calculating what depth of fluid is necessary for there to be the required pressure at the perforations. The pressure at the perforations is determined from the IPR, but is also the sum of the casing head pressure, the hydrostatic pressure due to the gas column (normally very small) and the hydrostatic pressure due to the liquid column. The hydrostatic pressure due to the liquid column depends on the fluid level and the fluid density. In some cases, as the density decreases, the fluid level must be higher in the well (i.e. at a lower mKB or ftKB value) to achieve the required pressure at the perforations. In some extreme cases, it will not be possible to calculate a fluid level. In these cases, you will either get Error 813 or Error 8002 (both these error messages are shown above). Interestingly, in many of these cases, you will see that at higher flow rates a valid result can once again be obtained.

A: PC-PUMP calculates power requirements based on straight-forward energy calculation. PC-PUMP converts these power requirements into a cost per day by multiplying the power requirement (in kW) by 24 hours to get a total energy per day (in kWh/d), and then multiplying this by the Power Cost value (in $/kWh, or, in newer versions of the program, other currency units per kWh, depending on your International settings in Windows) stored in the program to get a total cost per day. You can set the Power Cost value in the Prime Mover tab of the Surface Equipment Selection window. The default value that is used comes from the Defaults tab of the Edit-Preferences window. PC-PUMP uses $0.05/kWh unless you have changed it, or unless the currency setting is not dollars (in which case a default value would have been entered when the program was installed or first run on your computer). The values you have entered for electric motor efficiency and power factor will have an effect on the results. Note that some power companies will charge other fees beyond the energy costs, such as demand charges and power factor charges. These are not included in the result provided by PC-PUMP.

A: In reality, negative pressures are not physically possible. In single phase mode, PC-PUMP will give an error in this case even though it will complete the calculation and show a result—if this was a multiphase case, the program would not complete the calculation. What is causing this is excessive flow losses between the perforations and the pump intake. If you are in surface drive, this is most likely to occur if you have a tail joint, and is more likely to occur if the tail joint is very long or of a small tubing size. If you are in downhole drive mode, you probably have a very small clearance between the motor and casing (or a shroud that is causing there to be a small clearance either between the casing and the shroud OD or between the shroud OD and the motor, or both). In either surface or downhole drive, high flow rates or very viscous fluids will exacerbate the problem.

A: This occurs only in multiphase flow. Many of the correlations that are used to determine fluid properties (such as dead and live oil viscosity, solution gas ratio, bubble point, etc.) were not designed to work in heavy oil. Those correlations which were intended for use in heavy oil may only be applicable to oils from certain regions. With heavy oil, there is much more regional variation in properties (for oils with the same API gravity) than there is with medium or light oil. PC-PUMP will allow to continue your calculation—this is just a warning message and not an error. We do recommend, however, that you enter your oil’s actual dead oil viscosity at several temperatures in the Advanced Viscosity window. This will remove one correlation and should significantly improve the accuracy of the results.

A: This is in relation to the single-phase, specify fluid composition option. PC-PUMP makes several assumptions about the way the sand affects the density. If these assumptions are correct, the density calculation will be accurate at any sand cut, but if they are not correct, the accuracy will decrease as the sand cut increases; 10% was chosen as the limit at which to issue a warning. The four assumptions used are: 1) The sand cut is based on the level of the sand in a test tube after being spun in a centrifuge. 2) The water cut is based on the difference in the levels of the sand and the oil/water interface in the test tube. 3) The sand has a porosity of 40%. 4) The porosity of the sand is filled entirely with water (even if the water cut is specified as 0%).