Recommendations and Comparisons for Selecting Artificial-Lift Methods(includes associated papers 28645 and 29092 )

Abstract

Distinguished Author Series articles are general, descriptive representations that summarize the state of the art in an area of technology by describing recent developments for readers who are not specialists in the topics discussed. Written by individuals recognized as experts in the area, these articles provide key references to more definitive work and present specific details only to illustrate the technology. Purpose: to inform the general readership of recent advances in various areas of petroleum engineering. Summary Selecting the proper artificial-lift method is critical to the long-term profitability of most producing oil and gas wells. This paper compares the main selection attributes for the current eight major artificial-lift methods and provides practical guidelines, based on practical and proven technology, on the performance and operating capabilities of the methods. This paper covers beam pumping, progressing cavity pumping, electric submersible pumping, hydraulic reciprocating pumping, hydraulic jet systems, continuous gas-lift systems, intermittent gas-lift systems, and plunger lift. Introduction Correct selection of an artificial-lift method is important to the long-term profitability of most producing oil wells. Proper artificial-lift method selection also is very important for gas wells that load up with liquid and for coalbed methane wells that must be dewatered. A poor choice can reduce production and increase operating costs substantially. Once a decision has been made on the type of lift to install on a well, it rarely is reviewed to determine that the method selected was and still is the best choice for existing conditions. In addition, changing the type of lift costs money and implies that the wrong system was selected initially. Although prudent production engineering requires continuous review of the performance of the lift method to modify operating parameters or even to evaluate changing the method, once a method is chosen, it usually stays in place. A starting point in any selection process is to review current practices.Fig. 1 shows a review of about 500,000 U.S. oil wells on artificial lift. This database consists of a wide variety of conditions and a large number of operators. Various types of sucker-rod pumps are used on about 85% of the wells. Gas lift, mostly continuous flow, comes in a distant second with less than 10% usage. Electric submersible pumps (ESP's) are used only 4% of the wells. All other lift methods (hydraulic reciprocating pumps, progressing cavity pumps, and plunger lift) represent less than 5% total usage. Remember that about 400,000 of these wells are classified as stripper wells that produce <10 BOPD. When the stripper wells are excluded, the 100,000 orso remaining U.S. oil wells are relatively high-rate artificially lifted wells. Most of these wells (53%) are gas lifted. About 27% are on rod pumping, 10% are on ESP's, and <10% are on hydraulic pumps and jets. All other methods total less than 1%. By far, the majority of offshore gas-lift wells are on continuous gas lift. Proper selection of the best lift method usually is based on strong opinions. Operating personnel normally select the lift method with which they are most familiar. Equipment suppliers or even in-house experts on a specific method usually recommend that their favorite method can be made to fit the requirements. This "force-fit" selection usually results in the extension of the capabilities or operating experience of the selected lift method. We typically find that improvements made solve a new problem encountered as a result of a poor original choice. Thus, we must establish the normal and, more importantly, the practical operating capabilities of the major lift methods. This paper compares eight major artificial-lift methods (Figs. 2 through7). Hydraulic reciprocating and jet pumps are combined in Fig. 5 because their surface requirements are comparable; however, they have different downhole designs, applications, and capabilities. Similarly, continuous and intermittent gas lift are combined in Fig. 6.