Downhole Separation Research Articles

Downhole Separation of Petroleum Fluids

Oil–water separation is one of the oldest practices in the purification of water or oil. Environmentally concerned organizations pay more attention to the purification of water, while oil companies concentrate on the purification of oil. Water management is particularly an important issue in the production of hydrocarbons, because volumes of water steadily increase as a field ages. In fact, increasing costs of water handling such as separation, disposal, treatment, maintenance, and environmental risks make the oil production scheme uneconomic. Recently, several downhole oil/ water separation technologies have been proposed to reduce water volume in the oil production, but they are not yet technically efficient and cost effective. One of the most recent technologies introduced is membrane separation technology. In the past, polymeric membranes have been used for liquid–liquid separation. These membranes induce high pressure drop and are very expensive. This study identifies a novel material that allows oil to pass through it but not water. After in-depth investigations, a surprising capability of Xerox bond paper having different basis weight (24 lb, 32 lb) was discovered. This material was found to permeate oil selectively from an oil/ water mixture. The recovery of oil was more than 85%, which is high in separation efficiency. The oil permeation flux through the paper surface was measured as a function of various operating parameters. The permeation of oil flux was possible only at finite pressure difference. The recovery of oil was increased with the increase of oil concentration in the feed mixture. The permeation of flux was affected with filtering medium thickness, feed flow rate, and pressure, but these parameters did not affect the ultimate oil recovery.

Applications of Nanotechnology in Oil and Gas E&P

Special Feature: Applications of Nanotechnology in Oil and Gas E&P Saeid Mokhatab, U. of Wyoming; Mariela Araujo Fresky, Imperial College, London; and M. Rafiqul Islam, Dalhousie U. Over the next 30 years, global energy demand is projected to rise as high as almost 60%, a challenging trend that may be met only by revolutionary breakthroughs in energy science and technology. The industry needs stunning discoveries in underlying core science and engineering. Breakthroughs in nanotechnology open up the possibility of moving beyond the current alternatives for energy sup-ply by introducing technologies that are more efficient and environmentally sound. Nanotechnology is characterized by collaboration among diverse disciplines, making it inherently innovative and more precise than other technologies. Such a technology may be the cornerstone of any future energy technology that offers the greatest potential for innovative solutions. "Nano" denotes a thousand millionths (10−9), with a nanometer equaling a millionth of a millimeter. That corresponds to the width of 10 hydrogen atoms. So the nanotechnologist is concerned with building new structures and substances by manipulating molecules and atoms on this scale. Technically, nanotechnology is the art and science of building materials that act at the nanometer scale. It builds at the ultimate level of finesse, one atom at a time, and it does it with molecular perfection. In a general sense, nanotechnology is the ability to create and manipulate matter at the molecular level that makes it possible to create materials with improved (or, more accurately, altered) properties, such as being both lightweight and having ultrahigh strength, and greater capabilities such as in electrical and heat conductivity. Another research approach is known as top-down nanofabrication, which involves working with bulk materials and reducing them to nanometer size. This is most common in currently used technology development schemes. Nanotechnology is exciting because the science and engineering behind it are largely unknown. In fact, most scientists are aware that the laws that govern materials at nanoscale are very different from those that have been widely accepted in larger scales (Islam 2004). Recent work by Nobel Prize physicist Richard Smalley of Rice U. supports this hypothesis. He discovered that carbon nanotubes (Fig. 1) and fullerenes (buckyballs), nanoparticles of carbon, which are conventionally characterized as graphite, behaved in ways unlike graphite (Smalley and Yakobsonb 1998; Zhou et al. 2005). Potential Benefits Scientific inquiry in the energy area is scattered and unfocused, with various groups working separately to gain research dollars for uncoordinated pursuits that lack a clear road map to a better energy future (Baker Inst. Study 2005). But nanotechnology is poised to impact dramatically on all sectors of industry (Fig. 2). In oil and gas applications, nanotechnology could be used to increase opportunities to develop geothermal resources by enhancing thermal conductivity, improving downhole separation, and aiding in the development of noncorrosive materials that could be used for geothermal-energy production. Nanoscale metals already have been used to delineate ore deposits for geochemical exploration (Wang et al. 1997).

A Review of Downhole Separation Technology

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 94276, “A Review of Downhole Separation Technology,” by O.O. Ogunsina, SPE, and M.L. Wiggins, SPE, U. of Oklahoma, prepared for the 2005 SPE Production and Operations Symposium, Oklahoma City, Oklahoma, 17–19 April. Downhole oil/water separation (DOWS) allows water to be separated in the wellbore and injected into a suitable injection zone downhole while oil, with traces of water, is produced to the surface. After introduction of DOWS in the 1990s, several trial applications were undertaken to test the technology. These trials allowed information to be collected on DOWS feasibility. The full-length paper reviews the status of downhole separation technology and presents an extensive list of references. Introduction Produced water is water produced to the surface from hydrocarbon-bearing formations during oil and gas extraction and can include formation water, injection water, and any chemicals added downhole. Conventional production processes involve producing both oil and water to the surface and then separating them at the surface. Surface separation is accomplished by use of separation and dehydration equipment including skimmer vessels, plate coalescence, hydrocyclones, and, in some cases, crossflow membrane filters to reduce the oil content in the water phase and improve water quality before disposal. As a reservoir matures and oil and gas production peaks, often there is an associated increase in water cut and a corresponding increase in both lifting and water-disposal costs. The increased water cut also necessitates additional maintenance for production equipment and downhole treatment for corrosion, bacteria, and scale. Although producers still have a variety of choices in either disposing of the water or reusing it, there is a growing concern from the public related to the handling of this waste product. Public concern about the environmental impact of produced-water disposal has become a major issue, especially related to surface damage caused by spillage or subsurface contamination of drinking water caused by poor injection practices. Environmental regulations pertaining to produced-water management are expected to become more stringent in the future, requiring new practices and techniques to manage produced water. DOWS technology was introduced to the oil and gas industry in the 1990s, and work to assess its feasibility was sponsored by the U.S. Dept. of Energy in 1999. DOWS, unlike conventional separation processes, separates oil and gas from produced water at the bottom of the well and injects the separated produced water into another formation, usually deeper than the producing formation, while the oil and gas are pumped to the surface. Depending on DOWS type, typical DOWS project costs (procurement and installation) range from U.S. $120,000 to$300,000. Although reports show that some DOWS projects have had payback periods as short as 2 months, the relatively high project costs suggest that the design life or time to failure is a critical factor for the success of a DOWS project. The degree and duration of benefit that can be realized with DOWS technology depend on the characteristics of the producing well, reservoir rock and fluid properties, and the robustness of the separator/pump assembly.

Use of a Bubble Tracking Method for Prediction of Downhole Natural Separation Efficiency

For any pumping artificial lift system in the petroleum industry, the free gas significantly affects the performance of the pump and the system above the pump. A model, though not a complete two-phase flow model, has been developed for the effective prediction of separation efficiency across a wide range of production conditions. The model presented is divided into two main parts, the single-phase flow-field solution and the bubble-tracking method. The first part of the model solves the single-phase liquid flow field using the computational fluid dynamics approach. Then, a simple bubble-tracking method was applied to estimate the down-hole natural separation efficiency for two-phase flow. A comparison between the results of the model and the experimental data was conducted. It shows a very good agreement with the experimental data for lower gas void fractions (bubble flow regime).

Evaluating offshore technologies for produced water management using GreenPro- I—a risk-based life cycle analysis for green and clean process selection and design

Sustainable development and environmental protection require green products, processes, and waste management strategies. The selection and design of green and clean processes and products involve handling a huge set of data related to the environment, economics and technologies. Therefore, it is essential to employ a comprehensive technique to guide decision-making under uncertainty that can incorporate these factors. The paper presents decision-making under uncertainty based on life cycle analysis and considering environmental, technological, and economical drivers in the analysis. The methodology, GreenPro-1, is applicable at any stage of a process design and can be used to evaluate the environmental burdens of a product or a process throughout its life cycle, and to identify and assess opportunities to make improvements. A weighting scheme is used to integrate various criteria and policies so that a most appropriate alternative can be selected. The GreenPro-1 methodology is applied to a case study for offshore produced water management. In the first stage, 14 best available technologies (BAT) for treatment of produced water are evaluated individually using cradle-to-gate life cycle analysis. In the second stage, seven treatment strategies are developed from BAT and are further investigated. A treatment strategy that combines a hydrocyclone and produced water re-injection proved to be the best system among selected strategies. The combination of hydrocyclone and adsorption was found to be the next best treatment strategy. Two other noteworthy strategies were membrane and centrifuge combination, and down-hole separation and injection.

Lower-Cost Facilities: Where Are They?

Lower-Cost Facilities: Where Are They?

Recent Advances in Production Engineering

Abstract The purpose of this paper is to identify the most important advances in petroleum production engineering in the past decade. Of course, a review paper in the allotted space simply cannot do justice to all new technologies, especially those that are gradual advances to established techniques. We then expound upon two technologies that we feel already have made or have the capacity to make quantum impacts on the petroleum industry. These are high-permeability fracturing (often referred to in the vernacular as frac-pack and variants) and complex well architecture (which deals with wells with a main or "mother" bore from which branches are drilled). At the end of this paper, we have added a Bibliography section that includes several recent papers which, while not individually referenced in the text, add important contributions to the body of knowledge and experience in the two areas that we write about. Introduction Petroleum production is a mature engineering discipline where progress often comes from pushing the limits. One of the most obvious examples is the evolution of off-shore technology: first leaving on-shore, then going "deepwater" and now "ultra deepwater." As subsea oil and gas developments reach ever deeper into the oceans (currently 2,500 m), new challenges for topside, subsea and downhole equipment arise. In artificial lift, progressive cavity pumps have been successfully applied where emulsions and/or solids production make ESP's less reliable. Downhole separation (both gravity and cyclone based) of oil and water, and reinjection of the latter within the same wellbore, are major improvements, especially because the costs of water lifting, processing and disposal from the surface costs are ever increasing(1, 2). Subsea flow assurance becomes a major constituent of production(3) and multiphase pumping provides a viable option, changing the economics of marginal off-shore locations(4). If one can predict the long term impact, however, the most influential change is the evolution of real-time monitoring and control of both surface and downhole conditions(5-7). Multiphase metering systems offer a significant increase in functionality over traditional test separators. The continuous monitoring of all produced fluids and the possibility of remote intervention are transforming the way engineers do their job. Combining logging, imaging, and 3D visualization techniques with continuously available engineering data such as pressure, temperature, and saturation coming from permanent ownhole instrumentation, allow engineers to improve the management of their reservoirs and individual wells within it(8). Many of the improvements are driven by progress elsewhere. The most convincing example is the evolution of the technology of sensing and transmitting data. Since this technology is driven by consumer electronics, it is not surprising that the price of a microchip, equivalent in computing power to yesteryear's mainframe, is only a couple of dollars, but increases tremendously for every additional 10 degrees, and/or 689.5 kPa (100 psi) temperature and/or pressure rating. The bottleneck for the newest technology to penetrate into our wells is reliability under high-temperature, high-pressure (HTHP) and chemically hostile conditions(9). Pressure and temperature are only the first things to look at.

Laboratory Study Investigating Emulsion Formation in the Near-Wellbore Region of a High Water-Cut Oil Well

Summary An experimental study was conducted to determine the morphology of oil/water mixtures produced into a high water-cut well. This information is important for determining the feasibility of downhole oil/water separation. Core-flow and microflow experiments were performed to simulate the two-phase flow process in the near-wellbore region of a high water-cut well. In the core-flow experiments the morphology of oil/water mixtures leaving different types of porous media was observed and the droplet-size distribution was determined for different fluid properties and flow parameters. In the microflow experiments the flow regimes and breakup mechanisms of the oil phase in the pore space were visualized and observed. The experimental results show that the oil/water mixture emerging from the porous medium depends strongly on its wettability. When the porous medium is oil-wet, the produced oil is mainly in the form of large drops that are formed at the porous end face. From water-wet porous media, small oil droplets are produced at high flow rates; their sizes are typically of the pore size's order and are formed inside the porous medium. A correlation between the droplet size and relevant fluid, and flow and porous-medium parameters has been developed, allowing for the assessment of circumstances in which downhole separation can be problematic. The experimental results have also shown that in water-wet porous media a transition from capillary-dominated to dispersed flow takes place in the capillary number range investigated (10-5<Nc<10-3).

Development of a Downhole Oil/Water Separation and Reinjection System for Offshore Application

Summary Hydrocyclone-based systems for downhole separation of produced oil and water and subsequent disposal of the produced water by reinjection within the same wellbore have been successfully applied in a number of onshore wells. Benefits of these systems include reduced produced water lifting and disposal costs, as well as a significant reduction in liquid load on surface processing facilities.1 Reduction in surface equipment requirements is of primary interest in offshore applications, where significant reduction in the size and cost of surface separation facilities promises to extend field life and make marginal developments economically viable. Further development of downhole separation and reinjection systems is underway in order to provide a range of hardware systems suitable for a variety of offshore applications.

Natural Downhole Separation and Its Impact on Production Performance

Summary This article deals with phenomena associated with gravity-induced separation along the completed interval of inclined wells. The model developed computes liquid accumulation and production performance. From the results it is shown that both the overall inflow performance and the gas-liquid ratio observed at the surface are affected by the downhole separation. It is shown that downhole separation may be constrained by either backseepage to the reservoir or countercurrent flooding along the wellbore. The liquid backflow rate limit due to flooding has been derived explicitly, providing a design parameter for downhole separation devices.

Downhole Separator Produces Less Water and More Oil

This article is a synopsis of paper SPE 50617, "Downhole Separator Produces Less Water and More Oil," by P.H.J. Verbeek and R.G. Smeenk, Shell Intl. E&P, and D. Jacobs, BEB Erdgas und Erdol, originally presented at the 1998 SPE European Petroleum Conference, The Hague, The Netherlands, 20-22 October.

Development and Testing of a Compact Liquid-Gas Auger Partial Separator for Downhole or Surface Applications

Summary In some applications, complete separation of liquid and gas is not required and removing only a portion of the gas is sufficient. One application that was developed fully is separation of gas from one well for raw gas lift of other wells. This can be done either on the surface or downhole. The auger separator is a new, patented device that was initially developed to fit inside production tubing and, thus, is an ultra-compact separator design. It differs from other separators in that it requires no complex controls or power to operate and, for most applications, has a diameter of only a few inches. The multiphase fluid enters an auger section where the pitch of the stationary auger blade causes the flow to rotate. Centrifugal forces created by this rotation cause the liquid to flow along the outer wall with the gas flowing in the center. A portion of the gas is ported through a crossover to the annulus in downhole applications or to a gas line in surface applications. The downhole separator can be placed by wireline in the tubing. The surface version is placed as a spool piece in the production line. Equations were developed to predict performance and were incorporated into a spreadsheet for ease of design. Laboratory tests were performed to validate the predictions and to explore various design details. Following successful lab testing, the prototype separator, which was 3½ in. in diameter, was placed downhole inside 4½-in. tubing. The separated gas was ported to the annulus through a gas-lift mandrel. This test showed that the equipment could be placed in the well with wireline, that downhole separation was feasible, and that the theoretical pressure-drop calculations were accurate. Following this test, an 8-in.-diameter auger separator was designed for separation of gas on the surface as a full-scale pilot test. This was placed in the production line from a well, and the separated gas was used to provide raw lift gas for other wells on the drillsite. These two field tests showed that partial separation was feasible with this device, and that the equations used for design were reasonable. The surface auger separator was left in place after the test and continues to provide lift gas. This paper presents the concept, design equations, laboratory test results, and field-test results of both a downhole and a surface application. Although raw gas lift is an application that has been fully developed, other potential uses also are discussed.

Downhole Oil/Water Separator Development

Abstract A feasibility study and subsequent equipment prototype design work completed by the Centre for Frontier Engineering Research have led to the development of some novel downhole oil/water separator systems for improving the economics and recovery of oil from conventional and heavy oil reservoirs. The basic concepts and driving forces behind the systems that have been developed are based on several ideas and technologies which were brought together with the objective of producing a lower cost alternative for handling production and reinjection of water from maturing, high water oil ratio (WOR) reservoirs. These systems are currently in the prototype development phase in preparation for field testing. The downhole oil/water separation systems have the potential to achieve large, perhaps order of magnitude, savings in lifting costs through significant reductions in the volume of water that must be produced to surface. In most cases, these cost reductions would be accompanied by increased revenue, through reactivation or increased production from wells that are currently shut-in or constrained by the limits of the current lifting system or surface facilities. Other potential benefits include reduced exposure to environmental liability from high volume water spills or contamination of fresh water aquifers. The main requirement for application of these systems is that a suitable water disposal zone be accessible from the producing wells. Introduction Numerous conventional oil wells, especially in North America and Southeast Asia, are becoming less economic due to high lifting costs and reduced recoveries. Much of the cost increase is in managing the ever increasing volumes of water that must be lifted to surface, separated, treated, pipe lined and reinjected back into the formations. Meanwhile ultimate recoveries are being eroded by shutting off production from specific reservoir zones through recompletions to reduce wafer inflow and by the eventual early abandonment of wells which leaves much of the original oil in place. The downhole separation project was initiated to help operators keep wells on production longer, economically producing more oil from existing mature reservoirs. A review of field production data showed that most rod pumped wells were being shut-in at WOR's of between 10 to 15 m3 of water per m3 of oil, which is reflected in overall field WOR's of 10 or less. Figure 1 shows the production history for the Leduc D-3A pool which is almost exclusively on rod pump and where the oil leg is reduced to the point where conventional water shut-off techniques are relatively ineffective. However, oil reserves in this pool are almost three million m3 of oil per meter of oil zone, so there is a strong incentive to implement a production method that is capable of economically producing the oil leg down to the last few centimetres. FIGURE 1: Leduc D-3A production. (Available in full paper) Figure 2 shows the production history for the Redwater D-3A pool where there is less of a discrete oil zone and most wells are produced with electric submersible pumps, which circulate high volumes of water to sweep the dispersed oil to the wellbore.