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Artificial Lift Techbook 2016

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ARTIFICIAL LIFT TECHBOOK: CASE STUDY 34 | May 2016 | hartenergy.com First, how does one know when to recalibrate the fow-rate model? This would be required if there is a degradation in pump performance, which could be caused by either wear, free gas and/or viscosity. Second, how does one calibrate the algorithm if no physical test is possible at all using a test separa- tor and/or a multiphase fowmeter? The solution to both these problems was pro- vided by a new Schlumberger proprietary pump diagnostic algorithm called the Pump Health Indi- cator (PHI). Traditional pump condition moni- toring is based on comparing the measured pump differential head with the "as new" head at a given fow rate. The weakness of this process is that it not only requires an accurate fow-rate measurement but also an in situ measurement of pump specifc gravity to convert measured pump differential pres- sure to head, both of which often are unavailable. The new method also compares "actual" to "as new" condition, but instead of performing the analysis at a given fow rate, it is done at a given pump differ- ential pressure, which is readily available from real- time data and removes the dependence on fow rate. Furthermore, the value compared is the pump differential pressure divided by pump absorbed power ratio (DP/Power). This value also can be measured with existing instrumentation and most importantly is indepen- dent of specifc gravity. Where the actual and reference DP/Power val- ues are equal, the pump is deemed to be in good condition. Conversely, where the values differ, it is an indication that there is pump degradation. In actual fact, one can demonstrate mathemati- cally that the PHI is equal to the ratio of head, fow and efficiency degrada- tion factors thereby pro- viding a holistic indicator of pump performance. In a recent remote well case study, there was insuf- fcient traditional testing over the 16-month produc- tion period to know whether a single calibration of the calculated liquid rate provided a reliable trend or whether recalibration was required. The PHI was calculated (Figure 1) and an excellent match obtained over the entire 16-month period with the exception of the last nine days prior to ESP failure, thereby confrming that a single calibration was suffcient. Furthermore, as fuid analysis confrmed the absence of gas and/or viscosity, it was possible to use the PHI to calibrate the power model during the frst few months of the ESP life when one knows that pump wear is negligible and there- fore PHI must be equal to 1.0. In other words, the PHI enables calibration of the liquid rate model if there is no gas, viscosity or wear degradation of the pump, which is the case on most ESP applications during the frst few months of operation. The resulting liquid rate trend is shown in Fig- ure 2, which illustrates how fow-rate transients are captured thereby enabling reservoir simulation to match the fowing pressures both during transient and steady state conditions. This becomes a pow- erful tool for monitoring depletion at the well scale and thereby optimizing drawdown. n References available. FIGURE 2. A high-frequency fow-rate trend, including transient fow rates, enables pressure simulation and matching during both steady and transient state conditions thereby quantifying depletion. (Data courtesy of Schlumberger) Pressure, psi Elapsed time, days Reservoir pressure Flow rate, rbpd

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