Three Pump Intake Pressure (PIP) calculation methods available for sucker rod lifted wells are discussed in detail in this paper. The values of PIP obtained from Acoustic Fluid level measurements, in wells with moderate pump submergence, yield PIP estimates that agree with those from pump fluid load analysis. If PIPs determined using these methods do not agree, then the operator can reduce the error by using the techniques discussed to make adjustments to certain parameters affecting the fluid load. Field data for a significant group of wells are used to compare the PIP results of the three methods. The results show that the PIP computed using the maximum and minimum pump card loads usually calculates too low of a PIP, while the PIP computed using the valve test loads are usually too high. Data processing techniques for improving the quality of the results from dynamometer data are presented. The pros and cons of using each method are discussed.
Downhole pump submergence is defined as the amount (height) of liquid that exists above the pump intake. Since the early times of oilfield pumping pump submergence has been the parameter most used for monitoring and troubleshooting well operation. Acoustic determination of the depth to the liquid in the wellbore was introduced in the 1930s by C.P. Walker who also outlined graphical methods to obtain the pressure distribution in the well(1,2,3). The advent of digital data acquisition and processing provided the tools to routinely convert fluid level measurements to estimates of downhole pressure distribution in the wellbore4. Today, pump submergence is easily converted to pressure at the depth of the pump intake.
Figure 1 shows schematically the wellbore configuration and pressure distribution that exists in a well producing by means of a downhole pump means regardless of the type of artificial lift system employed. The measured depth to the fluid level is determined by acquiring and processing an acoustic signal round trip travel in the casing-tubing annulus. The casing-head pressure is measured and is used to compute the pressure at the bottom of the annular gas column using the gas properties and the geothermal temperature profile. Then the pressure at the depth of the pump intake is computed using the gradient of the annular fluid below the gas/liquid interface. The Pump Intake Pressure (PIP) determined acoustically is the pressure in the casing-tubing annulus at the depth specified as the pump intake. Depending on the configuration of the piping installed below the pump (strainer, gas anchor, mud joint, etc) this PIP may or may not be equal to the pressure at the actual pump intake but in general this value is considered to be equal to the pump intake pressure.
In rod pumping, the measurement of pump rod load as a function of plunger position was first introduced by Gilbert's development of a mechanical downhole dynagraph that was installed at the bottom of the rod string and just above the pump plunger5.
