Abstract

This paper summarizes the opening remarks of the panel members on a panel discussion of â??Selection of Artificial Lift Methodâ?¿. This is not a co-authored paper in the normal sense. It is a paper with five sections, each section independently authored by a panel member.

Reservoir and Well Considerations

In artificial lift design the engineer is faced with matching artificial lift capabilities and the well productivity so that an efficient lift installation results. With the increasing cost of energy, it is becoming more important that the best efficiency possible be obtained. In the typical artificial lift problem, the type of lift has already been determined and the engineer has the problem of applying that system to the particular well. The more basic question, however, is how do we determine what is the proper type of artificial lift to apply in a given field. Each of the four major types of artificial lift will be discussed a little later by one of the panel members. This introduction will attempt to look at some of the reservoir and well factors that should be taken into consideration in making this initial basic decision on the type of artificial lift to use.

There are certain environmental and geographical considerations that may be overriding issues. For example, sucker rod pumping is by far the most widely used artificial lift method in the United States. However, if we are in the middle of a densely populated city or on an offshore platform with forty wells contained in a very small deck area, sucker rod pumping may be eliminated as a viable means of lift to be considered. These geographic and environmental considerations may simply make our decision for us; however, there are many considerations that need to be taken into account when these conditions are not predetermining factors.

Among the most important factors to consider are reservoir pressure and well productivity. If producing rate vs. producing bottom-hole pressure is plotted, one of two relationships will usually occur. Above bubblepoint pressure, it will be a straight line. Below bubblepoint pressure, a curve as described by Vogel will occur. These two types of productivity relationships are shown in Figure 1. Some types of artificial lift are able to reduce the producing pressure to a lower level than other types. The reward for achieving a lower producing pressure will depend on the type of productivity relationship. For example, a well in a reservoir with 2000 psi reservoir pressure and a producing pressure of 500 psi will be producing 75 percent of the maximum rate if the well has a straight line productivity relationship. On the other hand, if it is following a Vogel curve relationship, it will be producing 90 percent of the maximum rate. The characteristics of the reservoir fluids must also be considered. Paraffin is a much more difficult problem with some kinds of lift than others. The production of solids from the formation along with the well fluids needs to be considered. Sand can be very detrimental to some types of lift and much less so on others. The producing gas-liquid ratio is very important to the lift designer. Gas is a significant problem to all of the pumping methods. Gas lift, on the other hand, utilizes the energy contained in the produced gas and simply supplements this source of energy.

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