Production Engineering Fundamentals and Long-Stroke Rod Pumping
E-Book, Englisch, 598 Seiten
ISBN: 978-0-12-417212-8
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: Adobe DRM (»Systemvoraussetzungen)
Gabor Takacs is a professor and was head of the Petroleum Engineering Department at the University of Miskolc, Hungary from 1995 to 2012. He has more than 35 years of teaching and consulting experience in the production engineering field. He was acting director of the Petroleum Engineering program at The Petroleum Institute in Abu Dhabi, UAE from 2007 to 2010, and taught at Texas Tech University from 1988 to 1989. He is also currently a technical editor for an oil and gas journal, and received the Society of Petroleum Engineers Distinguished Lecturer award for 1995-96. Gabor regularly teaches short courses internationally and is a well-known consultant and instructor on production engineering and artificial lift topics. Gabor earned an MS and PhD degree in petroleum engineering, both from the University of Miskolc.
Autoren/Hrsg.
Weitere Infos & Material
Chapter 1 Introduction to Sucker-Rod Pumping
Abstract
The first section of this chapter presents an overview of artificial lift methods and classifies available methods into two main groups: gas lifting and pumping. The second section compares artificial lift technologies according to their lifting capacities, system efficiencies, and other important factors. Finally, the short history of sucker-rod pumping is given, along with typical applications and detailed advantages and limitations. Keywords
Advantages; Artificial lift; Gas lift; History of sucker-rod pumping; Lifting capacity; Limitations; Overview; Pumping; System efficiency Chapter Outline 1.1 Artificial Lift Methods 1 1.1.1 Gas Lifting 2 1.1.2 Pumping 2 1.1.3 Artificial Lift Populations 3 1.2 Comparison of Lift Methods 4 1.2.1 Lifting Capacities 4 1.2.2 System Efficiencies 5 1.2.3 Further Considerations 6 1.3 Main Features of Sucker-Rod Pumping 7 1.3.1 Short History 7 1.3.2 Applications 9 1.3.3 Advantages, Limitations 11 References 12 1.1. Artificial Lift Methods
Usually, oil wells in the early stages of their lives flow naturally to the surface and are called flowing wells. Flowing production means that the pressure at the well bottom is sufficient to overcome the sum of pressure losses occurring along the flow path to the separator. When this criterion is not met, natural flow ends and the well dies. The two main reasons for a well's dying are: • its flowing bottom hole pressure drops below the total pressure losses in the well; or • pressure losses in the well become greater than the bottom hole pressure needed for moving the well stream to the surface. The first case occurs due to the removal of fluids from the underground reservoir; the second case involves an increasing flow resistance in the well. This can be caused by: • an increase in the density of the flowing fluid as a result of decreased gas production; or • various mechanical problems like a small tubing size, downhole restrictions, etc. Artificial lifting methods are used to produce fluids from wells that are already dead or to increase the production rate from flowing wells. The importance of artificial lifting is clearly seen from the total number of installations: according to one estimate there are approximately two million oil wells worldwide, of which about 50% are placed on some kind of artificial lift [1]. There are several lifting mechanisms available for the production engineer to choose from. One widely used group of artificial lift methods uses some kind of a pump set below the liquid level to increase the pressure of the well stream so as to overcome the pressure losses occurring along the flow path. Other lifting methods use compressed gas, injected from the surface into the well tubing to help the lifting of well fluids to the surface. Although all artificial lift methods could be grouped based on the two basic mechanisms just discussed, their traditional classification is somewhat different, as discussed in the following. 1.1.1. Gas Lifting
All versions of gas lifting use high-pressure gas (in most cases natural gas, but other gases like N2 or CO2 can also be used) injected in the well stream at some downhole point. In continuous-flow gas lift, a steady rate of gas is injected in the well tubing, aerating the liquid and thus reducing the pressure losses occurring along the flow path. Due to the reduction of flow resistance, the well's original bottom hole pressure becomes sufficient to move the gas/liquid mixture to the surface and the well starts to flow again. Therefore, continuous-flow gas lifting can be considered as the continuation of flowing production. In intermittent gas lift, gas is injected periodically into the tubing string whenever a sufficient length of liquid has accumulated at the well bottom. A relatively high volume of gas injected below the liquid column pushes that column to the surface as a slug. Gas injection is then interrupted until a new liquid slug of the proper column length builds up again. Production of well liquids, therefore, is done by cycles. The plunger-assisted version of intermittent gas lift, a.k.a. plunger lift, uses a special free plunger traveling in the well tubing and inserted just below the accumulated liquid slug in order to separate the upward-moving liquid from the gas below it. These versions of gas lift physically displace the accumulated liquids from the well, a mechanism totally different from that of continuous-flow gas lifting. 1.1.2. Pumping
Pumping involves the use of a downhole pump to increase the pressure in the well to overcome the sum of flowing pressure losses occurring along the flow path up to the surface. Pumping can be further classified using several different criteria, e.g., the operational principle of the pump used. However, the generally accepted classification is based on the way the downhole pump is driven and distinguishes between rod and rodless pumping. Rod pumping methods utilize a string of metal rods connecting the downhole pump to the surface driving mechanism which, depending on the type of pump used, generates an oscillating or rotating movement. Historically, the first kinds of pumps to be applied in water and oil wells were of the positive-displacement type, requiring an alternating vertical movement to operate. The dominant and oldest type of rod pumping is walking-beam pumping, or simply called sucker-rod pumping (SRP). It uses a positive-displacement plunger pump and its most well-known surface feature is the pumping unit featuring a pivoted walking beam. The need for producing deeper and deeper wells with increased liquid volumes necessitated the evolution of long-stroke sucker-rod pumping. Different units were developed with the common feature of using the same pumps and rod strings as in conventional sucker-rod pumping, but with substantially longer pump stroke lengths. The desired long strokes did not permit the use of a walking beam, and completely different surface driving mechanisms had to be invented. The basic types in this class are distinguished according to the type of surface drive used: pneumatic drive, hydraulic drive, or mechanical drive long-stroke pumping. A newly emerged rod pumping system uses a progressing cavity pump that requires the rod string to be rotated for its operation. This pump, like the plunger pumps used in other types of rod pumping systems, also works on the principle of positive displacement, but does not contain any valves. Rodless pumping methods, as the name implies, do not utilize a rod string to operate the downhole pump from the surface. Accordingly, other means (other than mechanical) are used to provide energy to the downhole pump, such as electric or hydraulic. A variety of pump types can be utilized in rodless pumping installations, including centrifugal, positive displacement, or hydraulic pumps. The most important kind of rodless pumping is electrical submersible pumping (ESP), utilizing a multistage centrifugal pump driven by an electrical motor, both contained in a single package and submerged below the fluid level in the well. Power is supplied to the motor by an electric cable run from the surface. Such units are ideally suited to produce high liquid volumes. The other lifting systems in the rodless category all employ a high-pressure power fluid that is pumped down the hole. Hydraulic pumping was the first method developed; such units have a positive-displacement pump driven by a hydraulic engine, contained in one downhole unit. The engine or motor provides an alternating movement necessary to operate the pump section. The hydraulic turbine-driven pumping unit consists of a multistage turbine and a multistage centrifugal pump section connected in series. The turbine is supplied with power fluid from the surface and drives the centrifugal pump at high rotational speeds, which lifts well fluids to the surface. Jet pumping, although it is a hydraulically driven method of fluid lifting, completely differs from the rodless pumping principles discussed so far. Its downhole equipment contains a nozzle through which the power fluid pumped from the surface creates a high-velocity jet stream. The kinetic energy of this jet is converted into useful work by the jet pump, lifting the commingled stream of the power fluid and the well's produced liquids to the surface. The downhole unit of a jet pump installation is the only oil-well pumping equipment known today that contains no moving parts. 1.1.3. Artificial Lift Populations
There are no reliable estimates on the distribution of each artificial lift method in the different parts of the world. One generally accepted fact is, however, that sucker-rod pumping installations are the most numerous worldwide; in the US there were about 350,000 such installations in 2007 [1]. The charts in Fig. 1.1, available from the Artificial Lift Research and Development Council (ALRDC) web page [2], present estimates on the number of different installations...
