Page 8 - Acoustic Fluid Level Measurements

Visualizing Well Performance 1-1

resentation of conditions that exist within the wellbore, University of Texas at Austin
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Visualizing Well Performance

In this chapter:
• Principles of well production
• Relation between flow rate and pressure drawdown
• Characteristic performance of flowing wells and pumping wells
• Calculation of pressure distribution in the wellbore from fluid level surveys and casing pressure measurements
• Determining present operating conditions in relation to well potential

This introductory chapter addresses the widespread need An accepted rule of thumb is that the producing
for oil and gas field operators to continually verify that bottomhole pressure (PBHP) should be less than 10%
wells are being produced close to their optimum capacity of the static bottomhole pressure (SBHP) to ensure
and in the most cost-effective manner. The analysis is to that the maximum production is being obtained from
be made based on data obtained at the surface without the well. This requires measurement or calculation of
entering the wellbore and must yield an accurate rep- both the producing and the static bottomhole pressures.
Petroleum Extension-The
The PBHP must be obtained while the well is being
at the bottom of the well, at the sand face, and within produced under normal conditions, and the SBHP
the reservoir. As such, it is not an easy task, since fairly must be obtained when the well has been shut-in long
complicated processes are involved in the flow of gas, enough that the surface and bottomhole pressures in the
oil, and water mixtures in wellbores. Operators are often wellbore have stabilized and inflow from the reservoir
confused by the apparently contradictory evidence that has practically ceased.
may be obtained. Well performance is defined as the relationship between
The objective of this chapter is to present in simpli- the fluid flow rate and the pressure drawdown between
fied terms some of the basic concepts of well performance the wellbore and the formation pressure. This relation
analysis and to recommend a procedure to be followed may take several forms, all of which are approximations
in obtaining, organizing, and analyzing data acquired of the actual behavior. The most common forms are:
with acoustic fluid level instruments to visualize the • The productivity index (PI), defined as flow
performance of oil and gas wells. rate/drawdown, expressed in barrels per day
(bbl/day) per psi 1,2
DETERMINING OPTIMUM AND CURRENT • The inflow performance relationship (IPR),
WELL PERFORMANCE defined as a functional relationship between
flow rate, flowing BHP, and static BHP, the most
The principal question that must be answered is: “Is the common of which is Vogel’s relation 3
well producing all the fluid that it is capable of producing
without problems and within the guidelines for optimum In order to answer the principal question stated
reservoir management?” If the answer is negative, then earlier, it is thus necessary to be able to determine the
additional questions must be answered to pinpoint the current well performance and to compare it to what is
reason(s) why the well is operating below its potential. considered optimum for the particular well.

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