Horizontal Wells in Water Supply Applications

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Horizontal Wells in Water Supply Applications
By Louis B. Fournier, Ph.D.

          ore than 2000 horizontal wells have been            consist of a vertical central shaft, called a caisson.

M         completed for environmental remediation
          purposes since 1988. Directionally drilled
horizontal wells have been used for many remedia-
                                                              The caisson is manufactured from reinforced con-
                                                              crete and serves as a collection point for water that
                                                              enters the system through a network of radically ori-
                                                                                                                          Using directionally drilled horizontal
                                                                                                                          wells to extract water from aquifers
tion applications including ground water extraction           ented well screens. In general, the caisson is con-
for pump-and-treat systems, total fluids extraction,          structed in place using the open caisson method with
                                                                                                                          causes less drawdown over a wider
air sparge, biosparge, soil vapor extraction, nutrient        multiple lifts.                                             area, so that upwelling does not or
injection, and ground water containment/migration                  Laterals can be either drilled or hydraulically
control.                                                      projected. A packer and pumping system is used to           may not occur.
     Only a few directionally drilled horizontal wells        control water during lateral installation. This wet
have been installed in the United States for potable          well or pumping station allows entry for periodic
water supply. It is anticipated that the use of these         inspection of the system and permits any required
                                                                                                                          1. Any length screen can be installed with direc-
wells in this application will grow dramatically as           maintenance to be performed. The caisson can be
                                                                                                                               tional drilling. In remediation applications,
human population increases and the demand for                 completed with a pump house or flush grade top slab
                                                                                                                               screen lengths have commonly reached approxi-
potable water increases proportionately. Because              to minimize visual impact on the surroundings.
                                                                                                                               mately 1500 feet long, but this is not considered
much of the population growth is expected in                       The system can pump from subsurface aquifers
                                                                                                                               to be the maximum possible length. Increased
today’s relatively undeveloped nations, it is likely          or from nearby rivers by inducing flow to the cais-
                                                                                                                               screen lengths serve to increase the volume of
that much of the increase in water demand will                son. In riverbank infiltration systems, river water is
                                                                                                                               water pumped from the well.
be in these areas as well. But it is also likely that         filtered by the formation to remove solids and parti-
                                                                                                                          2. Longer screens also can result in a lower
continuing population growth in certain areas of              cles. Such systems have been installed around the
                                                                                                                               entrance velocity for pumped water. Lower
the United States will fuel the demand for water.             world to enhance water production from available
                                                                                                                               entrance velocities generally reduce well plug-
Horizontal water supply wells will play a part in             sources, whether it is ground water, river water, lake
                                                                                                                               ging and, therefore, create a decrease in the need
meeting this demand.                                          water, or water from canals. One manufacturer and
                                                                                                                               for or the frequency of maintenance.
     For example, continuing development brought              consultant on these types of wells, Collector Wells
about in part by the baby boomers reaching retire-            International Inc., on its Web site, describes such         3. In the extreme, a long enough well may reduce
ment age will increase water demand in Florida.               wells being used in Sioux Falls, South Dakota;                   the need for multiple screens oriented radially
The increase is not only related simply to population         St. Helens, Oregon; Jacksonville, Florida; and                   from the central caisson and therefore could
growth; it is also related to the need for more busi-         Crystal City, Missouri. Similar projects are being               result in construction of a smaller caisson or no
nesses, recreational areas, restaurants, etc. to serve        evaluated for Delaware, Ohio; El Paso, Texas; and                caisson. A pump could even be placed within
the incoming flux of retirees — all of which require          other cities within the United States and around the             the header of the horizontal well in some
water supply for their activities.                            world.                                                           applications.
     Installing more vertical water supply wells to                The water supply system for Noida, India, illus-       4. In general, radial collection wells must be placed
accommodate the increased water demand is one                 trates the future of water supply systems around the             in unconsolidated formations consisting of sand
option, as is increasing water production from exist-         world. The rate of water supply in Noida per day is              or gravel deposits. Directionally drilled wells, in
ing vertical wells. However, both face a common               59.4 gallons (225 liters) per capita. There are 184              contrast, can be placed in consolidated rock or
limitation. Excessive pumping down of a water sup-            tube wells, 6 Ranney wells, 33 overhead tanks, and               sand and gravel deposits. Directionally drilled
ply aquifer in coastal areas can result in upwelling of       23 underground reservoirs. The total supply capacity             horizontal wells can also be placed in fractured
underlying salt water layers into these vertical water        is 78.52 million gallons (302 million liters) a day              rock formations where rain water has been cap-
supply wells. Such upwelling can result in a salt-            and the water treatment is by online filtration and              tured in the fractures. When placed in vertically
contaminated drinking water supply and system that            chlorination.                                                    oriented fractures, horizontal wells offer the
can no longer be used for its intended purpose.                    The water supply is adequate and is shortly to be           opportunity to traverse many fractures so that
Using directionally drilled horizontal wells to extract       supplemented with Ganga (Ganges) water, which is                 they meet water production requirements.
water from aquifers causes less drawdown over a               being brought to the area through a project launched             On islands and in coastal areas around the world,
wider area, so that upwelling does not or may not             a few years ago. An ambitious plan is also under            placement of horizontal wells beneath the ocean
occur. Hence the use of horizontal wells for with-            way to set up rain water harvesting facilities in           floor or beaches might offer a non-visible way of
drawing ground water under conditions that exist in           Noida as an alternate source through advanced and           extracting salt water for desalination units. One such
Florida appears to offer substantial long-term bene-          indigenous technology.                                      project is in the planning stages in Mexico, where
fits and less risk of eventual salt contamination of               As a result of the investment in its water supply      industry and human uses have outpaced the ability
drinking water supply aquifers.                               (followed by improvements in the sewage treatment           of typical ground water supplies to meet demand.
                                                              system), Noida has established a congenial atmos-           Another has been installed in the Caribbean.
Radial Collector Wells                                        phere for industrial growth by attracting industrial             In areas where water-bearing zones are thin and
     In the past, horizontal wells have been used for         giants and information technology companies from            water production is hampered by the inability of a
water supply purposes when installed as part of a             India and abroad to establish a permanent base for          single vertical well to achieve production require-
Ranney or similar system wherein screened horizon-            their operations.                                           ments, the choice is to install either many vertical
tal spurs are installed radially into a central caisson            Similarly, radial collection wells at the Okhla        wells, each with small production, or a single hori-
from which water is pumped. Generically, these are            Water Works provide about 5 million gallons of              zontal well centered in the thin water-bearing zone.
referred to as radial collector wells. These systems          water per day to south and southwest Delhi, India.          Several thousand feet of horizontal screen could be
                                                                                                                          installed over a larger area for water collection.
                                                              Directionally Drilled                                       Water could be removed with a single water pump
Louis Fournier, Ph.D., is the president of STAR               Horizontal Water Wells                                      for each well. As a very rough approximation, the
Environmental LLC, an environmental consulting firm that                                                                  total length of well screen in the ground in an area is
specializes in horizontal well design and applications. The
                                                                  It is anticipated that directionally drilled horizon-   proportional to the quantity of water that can be pro-
company is located at 175 North 15th Street, Ponchatoula,     tal wells, when used for water intake, could increase       duced. Thus, in order to meet the production capabil-
LA 70454. He can also be reached at (985) 370-0708 and        water production over radial collector well systems.        ities of a horizontal well with, say, 1000 feet of
starcompany@erols.com.                                        Directionally drilled horizontal wells offer several
                                                              major benefits over normal radial collector wells.          horizontal directions/continues on page 36
34/ June 2005 Water Well Journal                                                                                                                                        NGWA.org
horizontal directions/from page 34                         Institute described the installation of a 10-inch-         choice of using a series of vertical pump wells or a
                                                           diameter HDPE well using a chain trencher. The             horizontal well for water production. Let’s say that
screen, the total number of vertical wells required,       purpose was to have a low-cost installation in a rural     the horizontal well could place 1000 feet of screen
say, with 20 feet of screen each, would be 50.             community. It was estimated that the project reduced       in the ground, and you know the cost of that effort.
    With today’s concerns about terrorism, there may       total project costs by 66% of that of a traditional ver-   Now, let’s say you could use vertical wells and each
be advantages of having a single wellhead rather           tical well water supply system.                            vertical well would have 50 feet of screen in the
than a vertical wellfield to protect. A directionally            Longbore Inc., a horizontal well drilling compa-     ground in contact with the water-bearing formation.
drilled horizontal well can provide such a wellhead        ny which specializes in the installation of long direc-    Dividing 1000 by 50 gives the number of vertical
with minimal impact on overlying structures and            tionally drilled horizontal wells, installed 10 wells      wells that will provide the same total length of
facilities. Moreover, the need to interconnect vertical    with screens ranging from 702 to 840 feet long at          screen as the single horizontal well (20 vertical
wells is eliminated.                                       depths varying from 37 to 42 feet below grade. Total       wells). The total cost of installing these 20 vertical
                                                           well lengths were 1274 to 1547 feet. Longbore com-         wells can be compared with the cost of installing the
Cost Comparisons                                           pleted the wells at a former Department of Defense         single horizontal well. To this must be added mani-
    Articles have been published that detail the cost      facility. The subsurface is composed of sand and           folding costs for the vertical wells, pump costs, site
comparisons of horizontal versus vertical wells for a      gravel with cobbles up to 12 inches in diameter.           access costs, and all other related costs. Keep in
variety of applications. These articles compare costs      The well screen and casing consisted of SDR-11,            mind that the horizontal well will likely have a sin-
of different soil and ground water remediation tech-       65⁄8 inches in diameter HDPE. The screen was               gle pump, a single point of exit for the well, and no
nologies for various cleanup projects. Such cost           designed with 0.020-inch slots. The drilling fluid         manifolding costs.
comparisons are not directly applicable to water pro-      consisted of bentonite and a mixed metal hydroxide             Compared with typical collector wells, the key
duction projects, but they do contain some very            viscosifier. Well development was performed using          benefit of the use of directionally drilled wells will
important and directly applicable concepts.                chemical treatment along with overpumping. Each            likely be the elimination of the costs (and difficul-
    In general, the use of directionally drilled hori-     well produced up to 80 gallons per minute, but was         ties) related to the installation of the caisson.
zontal wells for pumping ground water does not in          pumped at approximately 25 gpm for the treatment               Directionally drilled horizontal wells offer many
and of itself save substantial amounts of money over       activities.                                                advantages over alternative water production sys-
vertical wells in the same application — only per-               The costs of radial collection well systems ver-     tems, which are just now being fully realized and
haps 20% of the total project cost. However, there         sus directionally drilled horizontal well systems have     appreciated. For emerging nations, they offer the
can be very substantial savings in total project costs     not been compared in the literature. Intuitively,          possibility of lower-cost water supply. They also
if other factors are considered, such as access issues     directionally drilled horizontal wells should be sig-      offer the advantage of being able to be installed in
and well manifolding costs. That is, it is difficult and   nificantly less expensive. For example, a riverbank        virtually any water-bearing formation.
costly to install a vertical wellfield with a large num-   filtration system was installed along the Missouri             The techniques and tools for directional drilling
ber of wells over a wide area all of which must be         River by the Board of Public Utilities, Kansas City,       are rapidly being developed in support of ground
manifolded together, particularly in a residential or      Kansas, in 1997. This collector well was designed to       water and soil remediation applications. The use of
urban area. By contrast, if one or two horizontal          produce up to 28,000 gpm (40 mgd) to meet expand-          these techniques and tools in water supply applica-
wells can be installed with minimal impact on over-        ing demand. The reinforced concrete collector well         tions is relatively straightforward and potentially
lying structures and no manifolding requirements,          caisson (20-foot-diameter) was constructed to a            enormously beneficial.        WWJ
then these costs and difficulties are eliminated.          depth of 124 feet below grade (and 17 feet above)
    Horizontal water wells are often more effective        for a total height of 141 feet. A total of 14 lateral      Bibliography
at producing water than vertical wells in lower per-       screens were installed adjacent to and beneath the         A&L Horizontal Potable Water Well. www.alunderground.
meability formations. For a pump-and-treat remedia-        riverbed for a total screen length of 2800 feet.               com/waterwel.htm (accessed April 14, 2005).
tion project at Williams Air Force Base in Mesa,           Conceptually, this same screen length could be             Bardsley, David. 2001. Horizontal wells work. Water Well
Arizona, models estimated that one horizontal well         placed in the ground using directional drilling with           Journal, vol. 55, no. 11: p. 68 (available online at
could replace 80 vertical wells due to the low perme-      two to three horizontal wells. Using in-well pumps,            www.org/ngwapdf/NovHDD.pdf).
ability of the formation.                                  the total system cost should be significantly reduced.     Collector Wells International Inc. www.collectorwellsint.com
    Over the years, horizontal wells with 1000 feet                                                                       (accessed April 12, 2005).
or more of screen have been rather routinely               Conclusions                                                Fournier, Louis B. 2002. Directionally drilled horizontal
installed for ground water and soil remediation.               Directionally drilled horizontal wells offer an            wells offer cost savings and technical advantages over
On Long Island, New York, four remediation wells           opportunity to significantly reduce the costs and dif-         alternative soil and groundwater remediation systems.
                                                                                                                          Remediation Journal, vol. 13, issue 1: pp. 87–98.
were installed under a lined petroleum terminal            ficulties of conventional water product wells and
about 45 feet below grade. Each had approximately          systems in a number of ways. In principle, horizon-        Horizontal Environmental Remediation Wells: Case
                                                                                                                          Histories. www.angelfire.com/biz/horizontalwells/
1220 feet of screen. At the Savannah River DOE site        tal wells can be viewed as a logical alternative to
                                                                                                                          Pg06.HW.Case.Hist.html (accessed April 12, 2005).
in Aiken, South Carolina, two directionally drilled        both vertical water wells and Ranney collector type
                                                                                                                      Kaback, Dawn. Horizontal Environmental Wells—Part 1
horizontal wells with over 1440 feet of screen were        systems. Their key feature is their ability to get more
                                                                                                                          (available online at www.drilleronline.com).
installed. In Ann Arbor, Michigan, a well with 1400        screen into the ground and, therefore, increase water
                                                                                                                      Krug, John D., P.E. 1993. Minimizing water supply costs
feet of screen was installed from a residential area to    production due to an increased use of the water-
                                                                                                                          in rural communities. Plastics Pipe Institute Insider
a remote treatment facility.                               bearing formation. Secondary benefits include                  Newsletter, vol. 3, no. 3: pp. 1–3 (available online at
    A major advantage of directional drilling for          reduced volumetric flow of water per unit of screen,           www.plasticpipe.org/pdf/newsltr/Fall1997.pdf).
such installations is that the wells can be put in place   which may result in decreased operation and mainte-        Longbore Inc. Case History. www.longbore.com/us/
without disruption of overlying facilities and struc-      nance costs.                                                   CaseHistories1.htm (accessed April 12, 2005).
tures. However, this is not the only method of instal-         One back-of-the-envelope way of comparing the          Water Resources—Ranney Collector Wells. www.ranney
lation that has shown the benefits and savings of          cost of different water production systems and alter-          method.com/default.html (accessed April 12, 2005).
horizontal wells in water production applications.         natives is by computing the cost per foot of “screen
An article published in 1997 by the Plastics Pipe          in the ground.” For example, suppose you have the

36/ June 2005 Water Well Journal                                                                                                                                        NGWA.org