Gas evolution and expansion are natural phenomena in petroleum wells. However, gas is detrimental to pumping artificial-lift (AL) systems, causing incomplete pump fillage and reduced pump efficiency. Pumping AL systems may also be involved in high GLR applications for gas well deliquification. It then becomes essential to separate the gas before the pump's intake in these applications to preserve the life of the pump. Various downhole separators with questionable efficiencies are available today. In this study, an automated experimental separation facility is presented and applied to test the efficiency of two downhole separators. The setup includes a 31-ft horizontal section followed by a 27-ft vertical section that houses the separator. The performance of the separators is evaluated at different air (34 - 215 Mscf/d) and water rates (17 - 867 BPD). The multiphase-flow loop is equipped with pressure transducers and control valves for effective flow control. Data acquisition and process control are performed using LabVIEW™. A newly designed packer-type centrifugal downhole separator is evaluated over a wide range of flow rates and compared to a basic gravity-type separator without the centrifugal part. The performance and outlet flow stability of the separators are compared. Liquid separation efficiency is a measure of the fraction of the inlet liquid produced at the tubing return line. Output flow stability is measured by looking at the ratio of standard deviation over the average flow rate. Separation efficiency is close to ideal (100%) for liquid rates up to 500 BPD for both separators. The efficiency slightly decreases at higher liquid rates, but stays above 80%. This decline in efficiency is more noticeable for the gravity separator compared to the centrifugal, and it is sharper for higher gas rates (over 300 SCF/STB). The centrifugal separator provides a more stable output flow rate with less fluctuations compared to the gravity type. Various flow patterns in the separator outlet and the casing are visualized and recorded. With declining rates of production from oil fields and the need to de-liquefy gas wells, efficient artificial lift is necessary. This system provides a unique and novel tool to simulate the dynamics of flow in wellbores and identify the best tools to improve the efficiency.
Pumping artificial lift techniques, such as rod pumps and ESPs, are applied for gassy wells more than ever before. This has made the downhole separators a critical part of most such installations. There are multiple categories of downhole separators, with various techniques developed to assess and improve their performances, but no general guidelines are established for their application. This paper aims to classify the separator types and review their performances in the open literature. In addition, various data sets are collected and put together to evaluate and rank downhole centrifugal separators using data analysis and machine learning (ML) techniques. A comprehensive literature review is conducted to collect the available downhole separator performance data. Experiments and Computational Fluid Dynamic (CFD) simulations are the techniques used by the researchers. This information is collected to identify the optimum conditions for each separator type, considering the effects of liquid and gas rates and other flow parameters. The data collected from various research projects over the last 20 years are combined to make a comprehensive downhole separation databank. These data are analyzed using various machine learning algorithms to rank the performances of downhole separators at various operating conditions. Various downhole separators have been tested in the open literature, including poor-boy separators, two-stage separators, packer-type separators, rotary and spiral separators with different designs, etc. A critical factor that adds to the uncertainty is the separator's control system, which significantly affects its efficiency. The available data show that most separators provide separation efficiencies higher than 80% if the downstream casing valve is adequately controlled. The separation efficiencies decline as the liquid and gas rates increase past an upper limit. The collected data from multiple previous studies form a broad dataset. Data analysis is used to compare the performances of different downhole separator classes, and machine learning is applied to identify a robust prediction model. This paper gathers, interconnects, and examines several available research works through data analytics. The results provide a fundamental source and a valuable guideline for downhole liquid-gas separation, particularly in artificial lift applications.
Downhole gas separators are often the most inefficient part of a sucker rod pump system.This paper presents laboratory data on the performance of five different gas separator designs. Only continuous flow was studied. Field data is presented on two of the designs.The field data indicates that success or failure of the gas separator is dependent upon the fluids and wellbore pressures as well as the mechanical design of the gas separator.Successful and unsuccessful examples of gas separator performance in the field are shown along with field fluid data properties. Introduction Patterson[1] studied some different down-hole gas separation designs for coal bed methane operations in Wyoming.In these designs the inlet to the gas separators were smaller than normally used and along with some baffles, thought to allow gas to vent from inside the gas separator, obtained good gas separation in the field installation. While field installations provide the ultimate validation of gas separator performance, it is extremely difficult to isolate the influence of each design parameter. It was these installations which prompted the laboratory study of the gas separator geometry to understand if the "rules-of-thumb" used by the industry for gas separator design were valid. One of the most common sources of inefficiency in oil well pumping installations (rod pumps, ESPs of PC pumps alike) is gas interference, which prevents the pump from delivering liquid at the design rate. Although this is a well known effect, there seems to be limited understanding of the mechanisms that control gas interference and this often results in the use of remedies, such as installing downhole gas separators, that are ineffective or even detrimental to the pumping system performance. The objectives of this paper are to give a clearer insight on the mechanisms of gas interference in pumping wells and to present the results of recent laboratory and field studies on the flow characteristics and performance of some downhole gas separators. In a pumping installation, one of the principal functions of the wellbore is to operate as a two-phase (gas-liquid) separator so that the pump (which is designed to pump liquid) can operate efficiently. Although this concept appears to be obvious, it seems to be totally ignored by most operators when they design completions and install hardware (gas anchors and the like) to combat the effects of gas interference. In these applications, the separation of gas from liquid is achieved through GRAVITY separation without the introduction of other mechanisms (centrifugal forces, nozzles, etc.). Thus, the difference in density between the gas and liquid is the main driving force to be used for separation. This also implies that forces that oppose the effect of gravity, such as viscous drag caused by high fluid velocity and turbulence, will be detrimental to the separation process. Thus, high velocity of liquid or gas should be avoided if possible. The Pumping Wellbore as an Efficient Gas-Liquid Separator The preferred pumping installation for maximum pump efficiency requires installing the pump intake BELOW the lowest point of fluid entry into the wellbore and requires having an open casing-tubing annulus from the bottom to the wellhead. This configuration is shown in Figure 1A. Gas and liquid enter the wellbore through the perforations and liquid flows to the bottom of the well under the action of gravity. The lighter gas bubbles rise through the liquid forming a gaseous liquid column, from the bottom of the perforated interval to the fluid level, then gas flows through the casing-tubing annulus to the wellhead where it exits to the flow line. Practically 100% liquid accumulates at the bottom of the well and enters the pump intake to be discharged by the pump into the tubing. This completion is similar to the surface facility vertical two-phase separator shown in Figure 1B. To be equivalent both the x-sectional area for flow diameter to length ratios would have to be the same. The gas-liquid mixture enters the vessel about two-thirds up the vessel wall. The gas outlet is at the top of the vessel; Liquid falls to the bottom and accumulates in the "quieting chamber" of the vessel where it flows to the pump intake through the liquid outlet.Proper operation of the separator requires that the liquid retention time be sufficient for most of the gas bubbles to rise to the gas/liquid interface and that the gas velocity be low enough for most of the liquid droplets to fall to the gas-liquid interface. These are the two criteria used for correctly sizing the separator to meet the flowing requirements. The unusual characteristics of this "equivalent separator" are that:It would have to be built with 4 to 7 inch diameter pipeIt would be at least 30 feet tallIt would not have liquid level controls The capacity of a 2-phase separator is defined in terms of liquid and gas capacity as a function of operating pressure and gas and liquid densities
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.