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English Difusión del agua en el mundo y las características terapéuticas y nutricionales del agua de mar. http://aprchile.cl/index.php/articulos-de-aprchile/hidrogeologia/english Mon, 09 Dec 2019 10:51:51 +0000 Joomla! 1.5 - Open Source Content Management es-es Technical Memorandum 006-6 - Entrance Velocity: Its Importance to Well Design. http://aprchile.cl/index.php/articulos-de-aprchile/hidrogeologia/english/1700-technical-memorandum-006-6-entrance-velocity-its-importance-to-well-design http://aprchile.cl/index.php/articulos-de-aprchile/hidrogeologia/english/1700-technical-memorandum-006-6-entrance-velocity-its-importance-to-well-design

Introduction

Among the many important parameters that figure into the design and operation of water wells, perhaps none engenders more misunderstanding than does the concept of maximum entrance velocity through water well screen. A commonly accepted design concept, proffered some 60 years ago as a general guideline for well design, is that water wells should be constructed with sufficient open area within the well screen so that during pumping the calculated entrance velocity will not exceed 0.1 feet per second (ft/second). Over the years, this concept has been the subject of model simulations and desktop studies which have shown it to be an ultra-conservative design parameter. While it is readily acknowledged that entrance velocity is an integral component of well design, model studies clearly indicate that the range of acceptable entrance is actually considerably higher than 0.1 ft/second, as will be described in this memorandum. For the well designer, this has important relevance when selecting the type and amount of well screen for a new well.

This memorandum is intended as a primer on entrance velocity for water wells. As such, important considerations are introduced and briefly explained. Well designers, particularly those new to water well design, are encouraged to investigate the various references presented herein for more detailed explanations of this subject. Other related and pertinent technical memoranda on well design have been prepared by Roscoe Moss Company and are available upon request.

Well Screen Open Area

Several types of well screens are available for construction of high-capacity water wells. Among these, the three most commonly installed in production wells for municipal, industrial, and agricultural use are: 1) louvered screens; 2) wire-wrapped screens; and 3) mill-slotted screens. Each of these options offers a range of open area per linear foot, as determined by the number of openings (i.e., slots) per linear foot and their dimensions (i.e., length and width). General information on open area for these screens is presented below.

ENVIADO POR RAÚL CAMPILLO U., HIDROGEÓLOGO

 

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contacto@aprchile.cl (Javier) Hidrogeología English Sun, 13 Nov 2011 22:46:48 +0000
Technical Memorandum 006-5 - Case Study: The Performance of Louvered Screen and Non-Select Filter Pack Material. http://aprchile.cl/index.php/articulos-de-aprchile/hidrogeologia/english/1699-technical-memorandum-006-5-case-study-the-performance-of-louvered-screen-and-non-select-filter-pack-material http://aprchile.cl/index.php/articulos-de-aprchile/hidrogeologia/english/1699-technical-memorandum-006-5-case-study-the-performance-of-louvered-screen-and-non-select-filter-pack-material

Introduction

The generally accepted criteria for filter pack material suitable for use in gravel envelope water wells is for it to be composed of well-rounded, water-worn siliceous rock washed free of deleterious matter. Many designers specify that the midsize of the pack material should be about 4 to 6 times larger than the midsize of the aquifer. Filter packs that meet such criteria are herein referred to as “select”. Select filter pack materials are readily available in the U.S. from commercial aggregate suppliers who typically offer a variety blended materials to meet specific size parameters. However, the fact is that select materials are not always available. For instance, well drilling contractors working in rural areas or overseas seldom use select filter pack materials. They have no recourse but to use locally available aggregate that is angular, calcareous, randomly sorted, and rife with deleterious matter. Such was the case in the Republic of the Philippines where a score of gravel envelope wells were installed.

This memorandum presents a narrative describing a major ground water development project that relied upon the performance of louvered well screen to overcome the inherent negative characteristics of non-select filter pack materials.

The Program

The Metropolitan Water Works and Sewage System (MWSS), the principal water utility for metropolitan Manila, meets a large portion of its daily water demand by pumping ground water from a network of deep wells located throughout Metro Manila and the Marikina Valley. As the population of Metro Manila increased, MWSS had to increase its water supply. It began by upgrading the well system. MWSS funded a two-part program that consisted of 1) rehabilitating existing wells and 2) drilling new wells. MWSS embarked upon a major ground water development program and drilled 25 high-capacity production wells in the span of about 30 months.

Part 1 - Redeveloping Existing Wells

MWSS had a large system of production wells that had been poorly maintained. Therefore, the initial effort was to rehabilitate approximately 60 existing wells. Many existing wells dated back to the end of WWII, had been drilled by cable-tool rigs, and were completed with mill’s knife perforations. In general, they were generally no longer serviceable. Approximately 60 wells less than 20 years old had been drilled by mud-rotary rigs and were completed with mill-slotted casing. Those wells were scheduled for rehabilitation.

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contacto@aprchile.cl (Javier) Hidrogeología English Sun, 13 Nov 2011 22:44:48 +0000
Technical Memorandum 006-4 - Efficiency Loss and Its Relationship to Plugging of Well Screens by Fine Sediment and Encrustation http://aprchile.cl/index.php/articulos-de-aprchile/hidrogeologia/english/1698-technical-memorandum-006-4-efficiency-loss-and-its-relationship-to-plugging-of-well-screens-by-fine-sediment-and-encrustation http://aprchile.cl/index.php/articulos-de-aprchile/hidrogeologia/english/1698-technical-memorandum-006-4-efficiency-loss-and-its-relationship-to-plugging-of-well-screens-by-fine-sediment-and-encrustation

Introduction

Most well owners, well designers, well drilling contractors and, certainly, Roscoe Moss Company share a common goal of constructing highly efficient wells that promote cost-effective, long-term service. This goal is most regularly achieved when the well is constructed with highly efficient well screens that are properly developed. However, after being put into operation some wells experience a noticeable decline in efficiency within a relatively short time. Experience has shown that often such changes occur when well screens become plugged by fine sediment or encrustations. This memorandum discusses these conditions and various methods that can be used to ameliorate their effects.

Well Efficiency

Well efficiency is defined as the ratio of actual specific capacity to the theoretical specific capacity. (Specific capacity is ratio of the production rate to the drawdown required for produce that yield.) A well that is highly efficient exhibits less drawdown and requires less energy to deliver the water to ground level, resulting in less cost to the owner. (The reader is referred to Technical Memorandum 005-1 which explains well efficiency and power costs.) However, when well screens become plugged with sediment or encrusted, the total open area of the screen is effectively reduced so that ground water is no longer available to freely enter the well. Pumping under these conditions, a well will usually exhibit greater drawdown (i.e., due to the increased head loss) and lower specific capacity.

Plugging Phenomenon

During the development phase of well construction, remnant drilling fluid and cuttings adhering to the well bore and filter pack are agitated and loosened so that they can be drawn into the well. Similarly, as development proceeds fine sediment (down to silt size) from the aquifer is also captured and pulled into the well with the net effect of enhancing the formation’s permeability near the borehole wall. As a result, ground water flow from the aquifer is more easily accomplished.

ENVIADO POR RAÚL CAMPILLO O., HIDROGEÓLOGO

 

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contacto@aprchile.cl (Javier) Hidrogeología English Sun, 13 Nov 2011 22:41:35 +0000
Technical Memorandum 006-3 - Monitoring During Water Well Development: Collecting Pertinent Data and Evaluating the Results. http://aprchile.cl/index.php/articulos-de-aprchile/hidrogeologia/english/1697-technical-memorandum-006-3-monitoring-during-water-well-development-collecting-pertinent-data-and-evaluating-the-results http://aprchile.cl/index.php/articulos-de-aprchile/hidrogeologia/english/1697-technical-memorandum-006-3-monitoring-during-water-well-development-collecting-pertinent-data-and-evaluating-the-results

Introduction

Over the years, the practices of water well design and water well construction have evolved considerably from a time when cable tool drilling was the state-of-the-art approach and well designs were uncomplicated. In today’s water well industry, well designers and contractors are able to take advantage of advanced technologies of drilling, construction, and materials that are presently available. They routinely combine complex drilling methods with highly durable and corrosion resistant materials to install wells in varied hydrogeologic and water quality conditions. Despite the marked advancements within the industry, however, one constant has been the fact that well owners continue to expect that their completed facilities will provide efficient, productive, and long-term service. Such expectations are both natural and reasonable. Yet, they are only achievable if after construction the well is properly developed and then later redeveloped periodically during its useful life.

At the time of construction, the key development objectives are: 1) to remove remnant drilling fluid and cuttings from the borehole wall, formation, filter pack and well screen; and 2) to create an optimum interface between the filter pack and the water-bearing formation. For filter pack wells, well development also consolidates and stabilizes the filter pack material.

Later, during its operation, it is common for a well to experience a decline in efficiency and/or production. When this happens, it should be redeveloped by mechanical and/or chemical treatment methods in order to improve its efficiency and productivity.

Whether during initial development or follow-up redevelopment, it is essential to carefully monitor the well’s response over time. It is simply not enough to assume that a well can be developed (or redeveloped) within a fixed number of hours. The proper approach is to carefully monitor the well’s responses in real-time and discontinue the work when the well’s performance has been restored to a satisfactory level. How that monitoring can be performed is explained in this memorandum.

Development Methods

Well development (and redevelopment) methods are categorized as either mechanical methods or chemical methods. Mechanical methods include: bailing, swabbing with a surge block or dual-swab, airlift pumping, jetting, and pumping with a test pump. Generally, wells are developed initially by swabbing and bailing followed by a period of airlift pumping and/or jetting. The final stage of mechanical developing is usually pumping with a test pump.

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contacto@aprchile.cl (Javier) Hidrogeología English Sun, 13 Nov 2011 22:38:33 +0000
Technical Memorandum 006-2 - Gravel Pack Design: The Nexus of Theory, Experience and Personal Preference. http://aprchile.cl/index.php/articulos-de-aprchile/hidrogeologia/english/1696-technical-memorandum-006-2-gravel-pack-design-the-nexus-of-theory-experience-and-personal-preference http://aprchile.cl/index.php/articulos-de-aprchile/hidrogeologia/english/1696-technical-memorandum-006-2-gravel-pack-design-the-nexus-of-theory-experience-and-personal-preference  

Introduction

It is widely accepted that a properly designed and installed, graded gravel pack will enhance a well’s efficiency and will control the migration of fine formation sand into the well. These and other value-added aspects of a gravel pack are collectively the reasons that the majority of municipal, industrial, and agricultural water wells are completed with gravel envelopes. However, while there is general agreement on the utility of a graded gravel pack, there seems to be no consensus on the best approach to designing the gravel pack. As with most things engineered, there is no shortage of opinions on gravel pack design.

Over the past 80+ years since Karl Terzaghi authored Theoretical Soil Mechanics in 1943, numerous technical papers and articles have described various approaches to engineer a gravel pack. Typically, they espouse the importance of various gravel pack design considerations such as pack thickness, grain size sorting (or grading), the ideal uniformity coefficient and effective size, and parameters for the pack-aquifer ratio. Each author offers various charts, ratios, and design criteria, all intended to guide the designer toward the selection of an appropriately graded gravel pack for a given formation.

Faced with the myriad opinions on gravel pack design, the designer is faced with an important decision: Which method(s) should I choose? Based on our own personal experiences, we believe that many designers make this choice based on factors such as:

• Understanding of the various design methods

• Guidance from colleagues or directions from supervisors

• Personal preference

In surveying the various gravel pack selection methods, it is apparent that every design method is guided by two tenets. Ultimately, the gravel pack should:

• Enhance the efficiency of the well, and

• Control the migration of sand from the formation to meet the performance requirements of the project.

ENVIADO POR RAÚL CAMPILLO U., HIDROGEÓLOGO.

 

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contacto@aprchile.cl (Javier) Hidrogeología English Sun, 13 Nov 2011 22:36:15 +0000
Technical Memorandum 006-1 - Preparation and Planning for Well Rehabilitation. http://aprchile.cl/index.php/articulos-de-aprchile/hidrogeologia/english/1695-technical-memorandum-006-1-preparation-and-planning-for-well-rehabilitation http://aprchile.cl/index.php/articulos-de-aprchile/hidrogeologia/english/1695-technical-memorandum-006-1-preparation-and-planning-for-well-rehabilitation

Introduction

Benjamin Franklin is credited with the now-famous quotation about certainty when he observed the following: “Certainty? In this world nothing is certain but death and taxes”.

Most would agree that his observation remains on point today; however, had old Ben been discussing water wells, he might well have said: “Certainty? For water wells, nothing is certain but rehabilitation followed by another episode of rehabilitation”.

The one certainty for water wells is that at some time within their useful lifetimes most of them will need some type of rehabilitation to improve their performance. The frequency of rehabilitation is something that is unique to each facility. Some wells have been known to operate well beyond 10 years before needing attention, while others require rehabilitation at intervals as short as 2 to 3 years. Many variables are known to contribute to reduced performance including well screen and casing corrosion, incrustation, wear due to sanding, and, in some cases, structural failure.

The key to effective and cost-controlled well maintenance is the process of identifying the cause(s) responsible for reduced performance. This can be a difficult task. However, if the well operator has properly maintained complete records and understands what data are needed to assess well performance, it can be a relatively straightforward exercise to evaluate and diagnose well problems. It all begins with gathering data that can be used to identify an effective course of remedial action.

This memorandum briefly describes the types of information that are most often needed to formulate a remedial action plan for well rehabilitation.

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contacto@aprchile.cl (Javier) Hidrogeología English Sun, 13 Nov 2011 22:32:29 +0000
Technical Memorandum 005-9 - Joining Dissimilar Metals With A Mechanical Connector http://aprchile.cl/index.php/articulos-de-aprchile/hidrogeologia/english/1694-technical-memorandum-005-9-joining-dissimilar-metals-with-a-mechanical-connector http://aprchile.cl/index.php/articulos-de-aprchile/hidrogeologia/english/1694-technical-memorandum-005-9-joining-dissimilar-metals-with-a-mechanical-connector

Introduction

Most high-capacity water wells are constructed of casing and well screen manufactured from a single type of steel such as low-carbon steel, copper-bearing steel, high-strength low-alloy steel, or stainless steel (Types 304 and 316L). However, there are exceptions such as when well screen manufactured from a noble metal (stainless steel) is welded to casing manufactured from a less noble metal. This direct coupling of two highly dissimilar metals typically promotes the occurrence of galvanic corrosion unless some suitable control measure, such as a mechanical connector, is employed. This memorandum provides a brief overview of galvanic corrosion and describes the design and use of a mechanical connector that is supplied by Roscoe Moss Company (RMC).

Galvanic Corrosion

Galvanic corrosion is a common form of corrosion that is induced when two dissimilar metals are in direct contact with one another under water. When a galvanic couple of this type is formed, the more positive (noble) metal functions as a cathode and will corrode slower than it would by itself. The less noble of the metals functions as an anode and will corrode faster than it would by itself. Two significant effects of galvanic corrosion that affect the operation of water wells are: 1) an increase in sand production caused by the widening of the screen openings which allow aquifer material and even gravel pack to enter the well; and 2) structural failure of the casing or well screen caused by a loss of collapse strength for the affected casing and/or screen.

Galvanic corrosion is preventable, controllable, and predictable. One way to qualitatively assess the relative tendency of various metals to corrode if connected to one another is to refer to each metal’s position in the galvanic series (See the reference list for sources of information on this topic). If two metals are close together on the table, then they have a greater potential to corrode if they are coupled. Unfortunately, however, the galvanic series does not forecast the rate of corrosion; nevertheless, it is a reliable qualitative guide.

ENVIADO POR RAÚL CAMPILLO U., HIDROGEÓLOGO.

 

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contacto@aprchile.cl (Javier) Hidrogeología English Sun, 13 Nov 2011 22:28:50 +0000
Technical Memorandum 005-8 - Landing Rings: An Alternative Handling Accessory for Water Well Casing and Screen http://aprchile.cl/index.php/articulos-de-aprchile/hidrogeologia/english/1692-technical-memorandum-005-8-landing-rings-an-alternative-handling-accessory-for-water-well-casing-and-screen http://aprchile.cl/index.php/articulos-de-aprchile/hidrogeologia/english/1692-technical-memorandum-005-8-landing-rings-an-alternative-handling-accessory-for-water-well-casing-and-screen  

 

Introduction

The typical large diameter water well is constructed by welding together a string of blank casing and scree and lowering it with an elevator into the borehole to the prescribed depth. As the well construction proceeds the assembled string may be held at the surface by a heavy-duty landing clamp so that each additional joint of casing or screen can be connected by welding. Most casing and screen are supplied with either welding collars or lugs. If welding collars are attached, the well is constructed by positioning the landing clamp under the collar and then tightening it around the casing or screen joint. However, if lugs (4 or more small, rectangular pieces of steel equally spaced around the circumference and welded to of the casing and screen) are attached, the landing clamp is positioned under the lugs.

 

The choice between welding collars and lugs is largely a matter of the contractor’s preference unless one or the other is called out in the construction specifications. Welding collars are described in Technical Memorandum 005-6 by Roscoe Moss Company (RMC).

Use of landing rings to support the string during installation is a third option for casing and screen handling. RMC manufactures landing rings and attaches them to casing and screen at the factory on request. This memorandum describes their design and use.

Description

A landing ring is a type of handling accessory that has one function in common with a welding collar: it supports the string of casing and screen during installation. Some contractors prefer to use landing rings to construct very deep wells requiring an extremely heavy string of casing and screen. Commonly, landing rings are attached only to the upper joints of blank casing that bear the greatest the loads during the latter stages of well construction. Some contractors also prefer to use landing rings when handing large diameter casing (18-, 20- and 24-inch diameter). There are no formal guidelines or specific parameters for the use of landing rings. Most contractors rely upon their personal experience. RMC has manufactured landing rings for many years, understands their use, and is available to provide technical assistance on them.

Landing rings are sometimes used in place of lugs because the ring has a much greater surface area to support the load of casing and screen. Another consideration relates to welding. RMC typically attaches the bottom edge of the 3-inch wide landing ring about 13 inches below the lower edge of a welding collar. In the field, as each joint of casing or screen is installed and the landing ring is lowered onto the landing clamp, the welding collar is positioned 13 inches higher. This added height above the rig floor or ground surface is probably most appreciated by the welder(s) who can work in a more comfortable upright position. Considering that it can take as much as 24 hours or more to install a long string of casing and screen, this is an added benefit most appreciated by the welding crew.

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contacto@aprchile.cl (Javier) Hidrogeología English Mon, 07 Nov 2011 17:37:18 +0000
Technical Memorandum 005-7 - Monitoring Sand Content: The Rossum Tester http://aprchile.cl/index.php/articulos-de-aprchile/hidrogeologia/english/1691-technical-memorandum-005-7-monitoring-sand-content-the-rossum-tester http://aprchile.cl/index.php/articulos-de-aprchile/hidrogeologia/english/1691-technical-memorandum-005-7-monitoring-sand-content-the-rossum-tester  

 

Introduction

The bane of many well operators is sand that is produced during pumping. While it is not uncommon for a small quantity of sand to be discharged during start up, chronic sand production will usually accelerate the normal wear of impellers and other pump parts and clogs meters and valves. If left uncontrolled, sanding also increases the frequency of equipment maintenance and replacements, and causes nuisance problems for pipelines and water storage facilities. Whether the cause for sand production is design related or the result of corrosion, it is important to monitor the quantity of sand that is discharged from the well on a regular schedule.

 

Sand production is a key criterion of new wells and should be carefully monitored when the well is developed and pump tested. During the early stage of well development, the quantity of sand discharged often exceeds 50 milligrams per liter (mg/l). Such concentrations are expected and even desirable. Precise measurements of sand content during this phase of well completion can be made with an Imhoff cone or other suitable device. However, in the later stage of well development and during performance testing, accurate sand content measurements are needed. In fact, most operators cite a specific criterion in well construction specifications that defines the upper limit of sand production that is acceptable. Generally, this can range from 15 mg/L to less than 1 mg/L.

During a well’s life, sand production may increase for various reasons. For example, corrosion of casing and/or screen may allow for passage of sand into the well. Or, a poorly selected gravel pack might be unable to filter fine sand from passing through the well screen. In either case, if routine sand monitoring were conducted, the change in sand content could signal the problem to the well owner.

For monitoring sand content during a pump test or at regular intervals during a well’s life, American Water Works Association (AWWA) Standard A-100 suggests the use of the Rossum Sand Tester (RST). An RST is easy to operate, low in cost, reliable, and widely used in the water industry.

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contacto@aprchile.cl (Javier) Hidrogeología English Mon, 07 Nov 2011 17:31:46 +0000
Technical Memorandum 005-6 - The Utility and Efficacy of Welding Collars http://aprchile.cl/index.php/articulos-de-aprchile/hidrogeologia/english/1690-technical-memorandum-005-6-the-utility-and-efficacy-of-welding-collars http://aprchile.cl/index.php/articulos-de-aprchile/hidrogeologia/english/1690-technical-memorandum-005-6-the-utility-and-efficacy-of-welding-collars  

 

Introduction

For the majority of projects, the process of well design is a relatively straightforward exercise in which sound engineering principles are combined with the experience of the designer to select specific methods and construction materials to meet or exceed the performance objectives of the client. While there is no denying the obvious importance of performance objectives such as production capacity and efficiency, it is easy to overlook the importance of selecting materials that will facilitate the contractor’s efforts to construct the well. This memorandum explains how the welding collars enable a contractor to more easily complete the well installation in a safe and timely manner.

 

Types of Connections Steel well casing, louvered well screen and continuous wire-wrapped (CWW) well screen are manufactured in various lengths usually ranging from 10 to 40 feet. These individual joints are assembled at the job site, connected to one another, and lowered into the borehole as a continuous string. The four types of connections most often used in the water well industry are: 1) plain end; 2) threaded and coupled; 3) bell and spigot; and 4) welding collars. Most large diameter wells (i.e., greater than 12 inches in diameter) are constructed with casing and well screen that have plain ends or welding collars; both are described below.

Plain Ends. Casing and screen with plain ends are manufactured with either beveled or square edges depending upon the wall thickness; connections are made by butt welding in the field. Plain ended casing and screen have smooth sides and a uniform outside diameter (O.D.). With a uniform O.D., a tremie pipe and/or other ancillary pipes will lie flat up against the casing and screen minimizing their cross sectional diameter. An added benefit of the uniform O.D. is that gravel is more easily placed and consolidated in the annulus.

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contacto@aprchile.cl (Javier) Hidrogeología English Mon, 07 Nov 2011 17:27:31 +0000