This work represents the first part of a three -stage research program that consists of: a) lab scale test; b) field scale test in an experimental well and c) adjustment of existing mathematical models based on experimental test and actual oil wells.The objective of this first stage was not to develop mathematical correlations that can be applied in the field, but to gather well controlled data that can be used to look for trends and test simple theoretical models.The experimental results of liquid fall-back measurements in intermittent gas lift are presented. The variation of liquid fall-back with changing injection pressures, amount of gas injected and initial liquid column above the plunger are described. The plunger velocity is measured by means of proximity sensors able to detect the metallic plunger. The amount of liquid produced is determined in two ways: a) by using a weighting tank separator at the tubing outlet and b) by using pressure transducers in the bottom of the production tubing which measure liquid column height, before and after the gas injection.The experimental work was carried out using 2 3/8" tubing of 63 ft in length. The liquid being lifted was water and compressed air was used to lift the water.
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractCurrently in Lake Maracaibo there are nearly 2000 wells on Intermittent Gas Lift (IGL) with an average production of 150 BPD, so a method to estimate the IPR curves in such wells is necessary and important. Considering that in IGL the bottom hole flowing pressure is an instantaneous value continuously changing, then the correct and precise way to determine the IPR curve is through a production test along with a downhole pressure survey. However, many times this method is not economically convenient in highly depleted wells, as it does in a typical intermittent gas lift well. Since there is no publication reported on this subject, the purpose of this work is to get the equations that relate Vogel's model with field data for IGL wells and a numerical method to solve these equations in order to obtain an IPR estimation. Through these equations more realistic values can be obtained, and therefore a better match can be reached between simulators' outputs and field data. These equations will help the field engineer to properly analyze and design these types of wells.
Engineers have used standard techniques for decades when analyzing sucker rod wells, such as: API 11L standard, wave equation numerical simulation, acoustic logs and dynamometer card acquisition and processing. Each technique has a particular goal and they complement each other. API 11 was developed in the fifties as an easy and hand computation procedure for estimating the production and operational parameters (loads, stresses, torque, etc). Later in the eighties the desktop computers came into the market making the wave equation approach reasonable and popular. The acoustic logs and dynamometer card have been diagnosis tools in the field, which have been boosted by the portable computers. However, none of these tools is able to generate the pump performance curve equivalent to those provided by the electrical submergible pump (ESP) or progressive cavity pump (PCP) manufacturers. Piston pump manufacturers cannot generate that curve at the factory because they only can measure the pump's slippage (leaks in valves and piston walls) but the pump performance also depends on the following parameters: rod and tubing stretching, the rod fundamental frequency, which change in each completion. In the present paper the approach and algorithm to generate the Piston-Tubing-Rod Performance Curve (PTRPC) is shown, which gives a new complementary tool for engineers. Some examples show usefulness of this innovative concept in Sucker Rod Pumping. Finally, the way to introduce the PTRPC in a Nodal Analysis is presented. Introduction Sucker Rod pumping (SRP) is one of the most widely applied artificial lift methods around the world because the operational conditions of the majority of the wells fits within the application window of this method [1]. SRP can handle easily rates up to 1200 BPD, used at depths up to 8000 ft, outstanding resistance for thermal process (600°F), suitable for gas handling, excellent performance with extremely viscous fluids, and very good overall mechanical efficiency (60%). In addition, SRP is a robust and reliable method, easy and economical to operate; besides field engineers feels comfortable operating SRP not only for the acquired experience but also for the huge amount of literature knowledge in this area. Contrary to the appearance, SRP is a very difficult method to be simulated proper and accurately, because there are many phenomena involved: The piston compression process, the rod dynamic and stress analysis, the surface unit geometry and kinematic. At the begging of the 20th century the engineering computations for equipment sizing were based on static analysis. Later in 1939 Mills[2] introduced the acceleration factor into the static analysis to correct the minimum and maximum polished rod loads as well as the effective plunger stroke. Even though Mills' contribution was a considerable advance, as wells became deeper it was not good enough for a proper sizing and understanding of the dynamometer card. In 1954, a group of users and manufacturers of SRP undertook a study based on analogical simulation obtaining as result a set of graphs, tables and charts representative of the dynamic of the piston-rod-surface unit system. These results together with a defined procedure were so useful and practical way to analyze and calculate SRP equipment that was published as the API 11L [3] standard by the American Petroleum Institute. These sets of graphs are the numerical solution of the differential equations that govern the system taking into account many completion details (unit geometry, piston and rod diameters, etc.). With this graphical solutions the field engineers in the fifties and sixties had a hand computation procedure that replaced a simulation running at mainframes, huge and expensive computers affordable for big corporations and available for computer skilled professionals only. The API 11L has been widely used but people are unaware of its assumptions and approximations, such as: low fluid viscosity, vertical wells, one phase fluid, the rod's dynamic is similar to ten strings coupled in serial.
Summary Ultrasound or a high-frequency (20 kHz to 100 kHz) pressure wave has been used in diagnosis and treatments in different areas, such as: medicine, dentistry, civil engineering, and many other industrial applications. In the oil industry, there are applications (i.e., pipeline inspections, fluid velocity measurements, etc.), but to the present, these applications in formation stimulation have been incipient, and only a few lab and field test experiences have been reported. Stimulation with ultrasound is not a common operation offered by oil service companies. To visualize the real potential of ultrasound in oil well stimulation, it is necessary to understand the wave phenomenon, its properties, the parameters that define its behavior, and its interaction with the propagation media. This basic knowledge and the understanding of the different formation damage mechanisms are the keys to comprehend the real potential and application window of the ultrasound in oil well stimulation. This paper presents the theoretical basis of ultrasound and wave phenomena that must be considered when considering stimulation with ultrasound. Finally, some suggestions about the application window of this technology are given. Introduction Ultrasound has been applied in many areas, such as diagnosis, quality control, inspections, cleaning, etc. Industrial cleaning is achieved by flaking out the particles with a mechanical action of the pressure waves (Fig. 1). Usually, the piece is submerged in fluids inside a container with walls that have ultrasonic sources. Clearly, there is a great difference with an application for oil well stimulation, in which the source is running inside the hole, and the cleaning area is around the source. Each application has a particular frequency and power associated according to the sample dimensions and the purpose. For example, the power and frequency used for control echography in pregnant mothers are different than ones used in muscular therapeutic treatments. In the first case, it is enough to detect an echo with high resolution (higher frequencies). In the second case, energy is required to be transferred to the tissue, but high resolution is not required (lower frequencies). It is clear that the purpose and the propagation media affect the ultrasound parameters, highlighting the importance to understand which are the damage mechanisms in which ultrasound can be applied and vice versa. The advantage of applying ultrasound comparing with conventional stimulation is that no invasion or external fluids are required. Ttherefore, fluid/rock interaction analysis is avoided, and the placement as well as the associated equipment and risky operation of handling high pressures at the wellhead is also avoided. Additionally, ultrasound allows underbalance treatments without shutting in the well. Ultrasound cleaning is not a common tool offered by service companies in the field. Only field tests in China and Russia have been reported with more qualitative than quantitative information making these tests inconclusive. Recent references about lab experiences and tool prototypes suggest the potential of this technology. However, ultrasonic stimulation has little understanding of the phenomena taking place in the porous media, and how the waves are interacting with the matrix and the trapped particles. The parameters for suitable cleaning with ultrasonic treatment are not well defined, and how these parameters change while the wave is propagating in the porous media is also not clear. Power requirements for stimulation and effective penetration depend on the elastic media (matrix), the radial geometry, and completion (i.e., either open, gravel packed, or case hole). Wave phenomena as reflection, transmission-refraction, diffraction, and interference must be considered; otherwise, a successful application in Russia can be a failure in other places, because change in one or more parameters considerably affects the wave.
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