Page 13 - Acoustic Fluid Level Measurements

Calculating Wellbore Pressure Distribution from Acoustic Fluid Level Surveys 6-1

Petroleum Extension-The University of Texas at Austin

6

Calculating Wellbore Pressure Distribution
from Acoustic Fluid Level Surveys

In this chapter:
• Pressure distribution in pumping wells
• Classification of wells by wellbore and producing conditions
• Gaseous liquid column gradient
• Liquid level depression test
• Gas-free liquid pump submergence
• Correlations and mechanistic models
• PBHP and SBHP calculations

Acoustic determination of the depth to the liquid in the properties as a function of pressure and temperature and
wellbore was introduced in the 1930s by C. P. Walker , the lengthy iterative computations.
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who also outlined graphical methods for obtaining the The advent of portable digital data acquisition and
pressure distribution in the well. At that time, the main processing provided the tools needed to routinely convert
objective was determining the depth of the gas/liquid fluid level measurements into estimates of downhole
interface in relation to the depth of the pump intake in pressure distribution in the wellbore at the well site .
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order to estimate the pump submergence. Downhole Today, surface pressure and pump submergence are eas-
pump submergence is defined as the amount (height) ily converted to pressure at both the depth of the pump
of liquid that exists above the pump intake. Since the intake and the depth of the producing formation and then
early days of rod pumping applications in the oilfield, reported with an analysis of acoustic fluid level records.
the submergence of the pump has been the parameter
most commonly used for monitoring and troubleshooting
well operation. Often abbreviated FAP for “fluid above WELL PERFORMANCE AND
pump,” it was (and still is today) periodically monitored POTENTIAL ANALYSIS
and recorded. Based on its value, the operation of the As discussed in chapter 1, the producing efficiency of a
pumping system can be adjusted to maintain an adequate well can be determined at a given time using an inflow
submergence, which has been defined as about 100 feet of performance relation (IPR) that expresses the effect on
fluid, to provide sufficient pump intake pressure to force pressure drawdown of the rate of production from the
the fluid into the pump at the operating pumping rate. formation. These relations require knowing the producing
The importance of knowing the pressure distribution bottomhole pressure (PBHP) and the static bottomhole
in the wellbore for detailed analysis of well performance pressure (SBHP) corresponding to a steady production
was recognized early in the 1930s . However, for many flow rate. The simplest relation, applicable to wells
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years it remained a research tool because of the dif- producing primarily liquids, is given by the productivity
ficulties involved in obtaining accurate values of fluid index (PI), defined as “barrels per day of gross liquid

For distribution by Petroleum Extension-The University of Texas at Austin
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