Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02905095 2015-09-28
LIQUID CONTAINMENT STRUCTURES AND FRAC PONDS WITH MAT
FOUNDATIONS
TECHNICAL FIELD
[0001] This document relates to liquid containment structures and frac
ponds with
mat foundations, and related methods.
BACKGROUND
[0002] A frac pond is a large above-ground structure for storing water,
referred to as
frac water, adjacent a well site for use in fracturing the formation
penetrated by a well. Frac
ponds are made of plural C-ring panels with heights of 3-4m or higher, and a
synthetic liner
that sits atop a graded dirt, sawdust, or sand bed. Frac ponds are designed to
hold volumes of
1000-15000 m3 of water. Other mechanisms for storing frac water include a
conventional
tank farm.
SUMMARY
[0003] Containment structures and ponds for retention and storage of
liquid, such as
water, are disclosed, for example liquid used in the oil and gas industry.
Some embodiments
include a floating mat system underlying an above-ground, in some cases open-
topped,
containment structure. Others include a mat foundation with a recessed drain
below a floor
liner.
[0004] A liquid containment structure comprising: a perimeter wall forming
a basin
with an interior sidewall surface and a floor; a liner spread across the
floor, up, and in some
cases over the top edge of, the interior sidewall surface; and a platform
underneath the liner,
the platform formed of a network of mats.
[0005] A liquid containment structure is also disclosed comprising: a
perimeter wall;
a floor liner bounded by the perimeter wall; and a platform underneath the
floor liner, the
platform formed of a plurality of mats laid edge to edge and whose upper faces
collectively
define a support surface, the floor liner conforming to the shape of the
support surface.
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[0006] A method is also disclosed comprising: laying a plurality of mats
edge to edge
over a ground surface to form a platform; erecting a perimeter wall on,
around, or on and
around the platform; and installing a floor liner on the platform within an
area bounded by
the perimeter wall, in which the perimeter wall and floor liner form a liquid
containment
structure. The floor liner conforms to the shape of a support surface
collectively defined by
upper faces of the plurality of mats.
[0007] Cross laminated rig mats lacking connectors are also disclosed.
[0008] In various embodiments, there may be included any one or more of
the
following features: A drain channel is defined in the support surface below a
portion of the
floor liner, with the portion of the floor liner extending downward into the
drain channel.
The portion of the floor liner conforms to the shape of the drain channel. The
drain channel
is defined at least in part by a lateral gap between adjacent mats. The drain
channel is defined
at least in part by a channel member that has in cross section a pair of side
walls and a
channel base. The channel member has in cross section a pair of opposed
laterally extending
flanges, each flange extended from a respective side wall, and the flanges are
secured to an
underside of respective mats bordering the drain channel. The drain channel is
collectively
defined by a series of channel members connected end to end. A collective
base, defined by
respective bases of the series of channel members, slopes downward with
decreasing
distance from the perimeter wall. The collective base has an apex between
axial ends of the
collective base, and the collective base slopes downward from the apex towards
each of the
axial ends. Each axial end terminates prior to reaching the perimeter wall.
The drain channel
bisects a floor area bounded by the perimeter wall. The liquid containment
structure is
located adjacent a well site. The liquid containment structure forms a frac
pond filled at least
partially with water. The perimeter wall comprises a ring formed by plural
arcuate wall parts.
The platform has a rectangular shape, and the perimeter wall is erected on top
of the
platform. The plurality of mats float relative to one another. Each mat is
formed of a
plurality of layers stacked one on the other and laminated together, in which
each layer
comprises a plurality of boards laid edge to edge relative to one another. The
liquid
containment structure is assembled adjacent a well site, and well treatment
liquid is stored
within the liquid containment structure, and a fracturing operation is carried
out on a
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formation penetrated by a well at the well site using the well treatment
liquid. A kit for
assembling the platform.
[0009] These and other aspects of the device and method are set out in the
claims,
which are incorporated here by reference.
BRIEF DESCRIPTION OF THE FIGURES
[0010] Embodiments will now be described with reference to the figures,
which are
not drawn to scale, in which like reference characters denote like elements,
by way of
example, and in which:
[0011] Fig. 1 is a perspective view of a liquid containment structure.
[0012] Fig. 2 is a top plan view of the structure of Fig. 1 with the liner
removed and
the perimeter wall shown in dashed lines, for clarity.
[0013] Fig. 3 is a perspective view of a drain channel used in the
structure of Fig. 1.
[0014] Fig. 4 is a side elevation section view taken along the drain axis
of the drain
channel of Fig. 3 from end to apex to end.
[0015] Figs. 5-6 are perspective and top plan views of a channel member of
the drain
channel of Fig. 3.
[0016] Fig. 7 is a section view taken along the 7-7 seetion lines from
Fig. 1.
[0017] Fig. 8 is a side elevation partial section view of a hook and set
screw lifting
system.
[0018] Fig. 9 is a perspective view of a method of lifting and positioning
a mat used
in the structure of Fig. 1.
[0019] Fig. 9A is a close-up perspective view of the area marked 9A from
Fig. 9.
[0020] Fig. 10 is a side elevation view of a method of fracturing a
formation
penetrated by a well.
DETAILED DESCRIPTION
[0021] Immaterial modifications may be made to the embodiments described
here
without departing from what is covered by the claims.
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[0022] In the conventional fracturing of wells, producing formations, new
wells or
low producing wells that have been taken out of production, a formation can be
fractured to
attempt to achieve higher production rates. Proppant and fracturing fluid are
mixed in a
blender and then pumped into a well that penetrates an oil or gas bearing
formation. Various
chemicals may be added to the fracturing fluid, such as gelling agents,
breakers, activators,
and surfactants. High pressure is applied to the well, the formation fractures
and proppant
carried by the fracturing fluid flows into the fractures. The proppant in the
fractures holds
the fractures open after pressure is relaxed and production is resumed.
Conventional
fracturing fluids include water, frac oil, methanol, and others, water being
the least expensive
and most commonly used option. A fracturing operation may require large
amounts of water,
and such volumes are stored or otherwise made accessible to the frac operator
to ensure that
the frac can be completed.
[0023] Referring to Fig. 1, a liquid containment structure, such as a frac
pond 10, is
illustrated. The pond 10 may have a perimeter wall 12, a floor liner 14, and a
platform 16.
The floor liner 14, which may be a synthetic geomembrane, may be bounded by
the
perimeter wall 12. The floor liner 14 may be part of a larger liner system 18
that extends up
and in some cases over a top rim 20 of the perimeter wall 12. For example,
liner system 18
includes floor liner 14 and a wall liner part 22. A top part 21 of the wall
liner part 22 may
wrap over top rim 20 and secure to the wall 12 in a suitable fashion such as
using clamps or
ties. The liner system 18 may be supplied to the site in one or more rolls,
and may be
assembled by unrolling or by fusing smaller sections or panels of membrane
together.
[0024] Referring to Figs. 1 and 2, the platform 16 may be formed of a
plurality of
mats 24. Referring to Figs. 2 and 9, each mat 24 may have a top face 26, a
base face 28, and
edges 30, such as side edges 30' and end edges 30", separating the faces 26
and 28. The
faces 26 and 28 may define an outer perimeter 32 with a rectangular shape when
viewed
from above or below, although other shapes may be used. Referring to Fig. 2,
the mats 24
may be laid edge to edge. For example, referring to the relationship between a
mat 24G and
adjacent mats 24A-F, the end edges 30"G of the mat 24G contact or otherwise
sit in close
proximity adjacent the end edges 30"F and 30"C of adjacent mats 24F and 24C,
respectively. Similarly, the side edges 30'G of mat 24G may contact or
otherwise sit in close
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proximity adjacent the side edges 30'A, 30'B, 30'D, and 30'E, of respective
adjacent mats
24A, B, D, and E. When laid in place the mats 24 form a network as identified
by the
intersecting side and end lines of the edges of the mats.
[0025] The plurality of mats 24 may float relative to one another, for
example if the
side edges 30' and end edges 30" lack connectors to interconnect with adjacent
mats on all
edges. Thus, referring to mat 24G, there are no connector between mat 24G and
adjacent
mats 24A-F. By lacking connectors, the mats 24 float on the ground surface 19,
and will
each adopt a unique and distinct orientation depending on the grade and
settling of the
ground surface 19 underlying the respective mat 24. Theoretically, the
floating of the mats
24 may lead to corners 25 (Fig. 9) of mat protruding above adjacent mats 24
and thus may
lead to puncture of the floor liner 14 above the mat 24. However, the floating
of the mats 24
is believed to actually reduce the occurrence of protrusions relative to a
platform of
interconnected mats. Such a result is believed to be due to the fact that in a
floating platform
settling effects under a mat 24 are confined to the respective mat 24, while
in a platform of
interconnect mats, settling effects under one mat necessarily translate to
adjacent mats,
which are chained to the respective mat. In practice the weight of the pond
water 92 has been
found to keep the mats 24 sufficiently level, and to reduce occurrence of
corners protruding
from settling action.
[0026] Referring to Fig. 9A, mats 24 may be formed of a plurality of
layers, such as
layers 34A, 34B, and 34C shown, stacked one on the other and laminated
together, for
example with hydrophobic adhesive such as a polyurethane adhesive. Each layer
34 may
comprise a plurality of boards 36 laid edge 38 to edge 38 relative to one
another so that the
top and base faces of each mat may collectively define top and base surfaces,
respectively.
Each board 36 may have side edges 38', such as edges 38'A and 38'B of adjacent
boards
36A and 36B, respectively. Each board 36 may also have end edges 38", such as
end edges
38"A shown for board 36A. Each board 36 may define a longitudinal axis, with
such axes,
for example axes 40C, of boards 36 in each layer, such as layer 34C, arranged
perpendicular
to, or otherwise crossing, the longitudinal axes, such as axes 40B, of boards
36 in adjacent
layers, such as layer 34B, in a configuration referred to as cross-lamination.
The boards 36 in
each layer may be arranged in an abutting relationship with adjacent boards,
to avoid voids
CA 02905095 2015-09-28
between the boards 36. Each layer, or in some cases only the top layer 34C,
may be planed to
provide a smooth top face 26 from edge to edge. Example boards that may be
used include
two by four or two by six wooden boards, although other suitable materials and
sizes may be
used. Mats 24 may lack a metal structural frame interior, and may be made of
suitable wood
such as Douglas Fir or Spruce Pine Fir. Once the layers are arranged and
laminated, the mat
24 may be compressed in a press to reduce mat thickness and increase rigidity
and strength.
The top face 26 of each mat 24 may lack fasteners, such as screws, even ones
that are
countersunk to be flush with a plane defined by the top face 26. Other
suitable materials,
such as polymers, and other suitable designs, such as plural boards laminated
together face to
face and retained within an external support structure, may be used for mats
24.
[0027] Referring to Figs. 2 and 7, upper faces, for example top faces 26,
may
collectively define a support surface 17 for the liner 14. The rigid mats 24
may be arranged
so that adjacent top faces 26 are flush with one another to provide a single
contiguous
support surface 17. The surface 17 is intended to have a planar shape but in
practice will
always have an undulating shape as a result of imperfectly planed grading
below the mats
24.
[0028] Referring to Fig. 7, the floor liner 14 may conform to the shape of
the support
surface 17. Conform is understood to mean that, at least under the hydrostatic
pressure of
liquid retained above the liner 14, the shape of the liner 14, for example at
least a bottom
face 23 of the liner 14, assumes and follows the shape of the support surface
17, for example
in a fashion similar to the shape that a conformal coating may take on the top
face 26,
ignoring the gathering action of excess slack in the liner 14. For example the
platform 16
may be located directly underneath the floor liner 14, such that the bottom
face 23 rests
directly upon the support surface 17. Nominal air gaps may be present between
the liner 14
and support surface 17. In some cases a flexible material may be positioned
between liner 14
and support surface 17. In either case, the shape of the support surface 17
may dictate the
shape of the liner 14.
[0029] The liner 14 may be made of flexible material. The liner 14 may
comprise
two or more layers of material, and is liquid impervious in order to contain
liquid within the
structure 10. The liner 14 may be resistant to damage from ultraviolet light.
The liner 14 may
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comprise a polymeric material, such as polyethylene. The thickness of the
liner 14 may vary,
for example between 1 and 50 mm, though other suitable thicknesses may be
used. The liner
14 may be treated to resist damage from sharp objects. The entire liner system
18 may be
made of the same material, and when installed may comprise a single integral
liner. The
elastomeric membrane or liner 14 may be formed of plural sheets or panels
adhered or
welded together at overlapping seams by a suitable adhesive, with such
connection being
applied on site or off site prior to install. The liner 14 may be a rubber
liner.
[0030] Referring to Figs. 1, 2, and 7, a drain channel 42 may be defined
in the
support surface 17. Referring to Fig. 7, the drain channel 42 may be below a
portion 44 of
the floor liner 14. The portion 44 of the floor liner 14 may extend downward
into the drain
channel 42, for example so that the portion 44 conforms to the shape of the
drain channel 42.
The drain channel 42 may be defined at least in part by a lateral gap 64
between adjacent
mats 24.
[0031] The drain channel 42 may be defined at least in part by a channel
member 62.
The channel member 52 may have, in cross section relative to a drain axis 72,
a pair of side
walls 46, a channel base 48, and in some cases mat fastening elements such as
a pair of
opposed laterally extending flanges 56. The side walls 46 and base 48 are
illustrated as being
formed by straight pieces of material with clear transitions, although other
suitable shapes
are possible, including a U-shape where there is no clear boundary between the
side walls 46
and base 48. Each flange 56 may be extended from a respective side wall 46.
The flanges 56
may be secured, for example by passing fasteners 58 through holes 60 in
flanges 56 and into
respective holes in mats 24, to an underside / base face 28 of respective mats
24 bordering
the drain channel 42. Other suitable securing methods may be used, including
securing the
flanges 56 over the top faces 26 of the mats 24. In some cases loose alignment
mechanisms
are used such as dowels within aligned holes or slots, and in other cases no
securing method
is used and the drain channel 42 is laid within a correspondingly shaped
channel within the
ground surface 19 and permitted to float relative to the mats 24.
[0032] Referring to Figs. 2 and 3 the drain channel 42 may be collectively
defined by
a series of channel members 62 that are connected end to end. Referring to
Fig. 5, each
channel member 62 has opposed axial ends 66. Referring to Fig. 3, axial ends,
for example
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ends 66'A and 66'B of respective members 62A and 62B, may abut or overlap one
another
along the drain axis 72. Adjacent channel members 62 may connect to one
another.
Referring to Fig. 3, a collective base 65 may be defined by respective bases
48 of the series
of channel members 62. Referring to Figs. 1, 3 and 4, the collective base 65
may slope
downward with decreasing distance from the perimeter wall 12. Sloping is
understood to be
defined such that when the structure 10 is deployed in the field, the downward
slope is
downward in a vertical direction to permit gravity to draw liquids down to
pool at the axial
ends 70 of the drain channel 42. Thus, the drain channel 42 increases in depth
the closer the
channel 42 gets to the perimeter wall 12. Referring to Figs. 3 and 4, the
collective base 65
may have an apex 68 between axial ends, defined in this case by end plates 70,
of the
collective base 65. The collective base 65 may slope downward from the apex 68
towards
each of the axial ends 70. Referring to Fig. 4 the increases in depth over the
span of base 65
from apex 68 to each end plate 70 is illustrated by reference numeral 74.
[0033] A drain channel 42 with an apex and dual sloped sections may be
used to
channel liquid toward each end plate 70, where the liquid can then be removed
from the
structure 10 at a location adjacent the end plate 70. Thus, the water may be
removed by
pumping or draining from two outlet locations at once. The channeling effect
may be
achieved with only a single sloped section, for example where the apex 68 is
located at or
near one of the end plates 70. A suitable slope may be used, for example with
less than or
equal to a 1.0% drop in slope.
[0034] Referring to Fig. 2, each axial end 70 may terminate prior to
reaching the
perimeter wall 12, for example if end plates 70 abut mats 24H as shown.
Referring to Fig. 1,
terminating the drain channel 42 prior to the wall 12 avoids potential
complications that may
arise from placing the wall 12 over a void created by a drain channel 42 that
runs underneath
the wall 12. In other cases the channel 42 may run under the wall 12, for
example to an
outlet. A hose or pipe 78 or other suitable outlet may be used to withdraw
liquid from the
structure 10.
[0035] Referring to Fig. 2, the drain channel 42 may bisect a floor area
15 bounded
by the perimeter wall 12. Other suitable arrangements and orientations of
channel 42 may be
used, for example a cross-shaped channel 42, or plural channels 42 running
parallel or at
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other angles relative to one another. Referring to Fig. 7, when laying out the
liner 14 over the
support surface 17, extra slack may be provided over the drain channel 42 to
provide
sufficient extension of portion 44 into the drain channel 42. The weight of
liquid, such as
water 92, stored in the structure 10 presses down on the portion 44 during
use, and forces the
portion 44 to conform to the shape of the drain channel 42. Air gaps 54 may
form between
the channel 42 and liner 14. The side walls 46 and base 48 of the channel 42
may be
concavely shaped when viewing the interior of the drain channel 42. The walls
46 may be
pitched at relatively shallow angles such as obtuse angles formed between
walls 46 and base
48. The drain channel 42 may have rounded transitions 71 between parts, in
order to reduce
the chance of puncturing the liner 14. The top corner edges 73 of mats 24 may
be rounded
for the same reason.
[0036] Referring to Figs. 1 and 10, the structure 10 may be assembled as
follows. In
one case the structure 10 is assembled adjacent a well site, for example where
a well 82
penetrates a hydrocarbon bearing formation 86. Referring to Fig. 1 a plurality
of mats 24
may be laid edge to edge over a ground surface 19, for example a graded
surface of
compacted earth or a surface of earth that has had the subsurface removed to
form a
relatively level horizontal plane.
[0037] Referring to Fig. 9, the mats 24 may be laid by a suitable method,
for example
by lifting with a crane cable 116. As shown, cable 116 connects to a beam 114,
which
connects by cables 112 to four lifting points defined by holes 100 penetrating
the top face 26
of mat 24. Other suitable numbers of lifting points may be used. Referring to
Fig. 8, lifting
devices, such as comprising set screw 102, may be located within holes 100.
Screw 102 may
penetrate up to the lowest layer 34A of mat 24, in some cases without
penetrating out of the
base face 28 of mat 24. Set screw 102 may have an interior bore 104 threaded
to receive a
male threaded part 106 depending from a base 108 that mounts a lifting loop
110, which may
be connected to cables 112 (Fig. 9) to lift the mat 24. Such a lifting device
may be provided
by a RAMPATm insert. After lifting the mat 24 into place, the part 106 may be
unthreaded
from the screw 102, leaving the screw 102 behind in the mat 24, with the screw
102 being
recessed below the support surface 17 to avoid protruding into the liner 14.
In other cases the
set screw 102 is also removed prior to laying the floor liner 14 overtop.
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[0038] Referring to Fig. 1, the perimeter wall 12 may be erected on as
shown,
around, or on and around the platform 16. In the example shown the wall 12 has
the shape of
a ring, which is formed by assembling of a series of plural arcuate wall parts
94. Each part
94 may be lifted and maneuvered into place, for example using a forklift,
picker, or crane,
and each C-ring part 94 may be secured to adjacent parts 94 to provide a
secure structure.
Each part 94 may have an upstanding vertical part 98 and a base flange part 96
extended
laterally from part 98 for providing stability to the part 94 and the wall 12
itself.
[0039] The foundation pad 16 may have a rectangular shape, and the
perimeter wall
12 may be erected on top of the platform 16. The combination of a ring-shaped
wall 12 and
square platform 16 creates areas at the corners of the platform 16 that may be
used to form a
foundation for other equipment, such as equipment related to the function of
the structure 10.
In other cases the platform 16 may have a shape that corresponds to the shape
of the wall 12,
for example a circular shape with a diameter sufficient to extend to or past
base flanges 96 of
the wall 12, or a shape that extends to but not under the wall 12 in order to
support the floor
liner 14 but not the wall 12.
[0040] The floor liner 14 may be installed on the platform 16 within an
area 15
bounded by the perimeter wall 12, in which the mats 24, perimeter wall 12, and
floor liner 14
form the liquid containment structure or basin 10. If a wall liner 22 is used
the wall liner 22
may be secured to the wall 12. Once assembled the structure 10 may be filled
with liquid,
such as water, thus forming a primary containment structure or pond.
[0041] Referring to Fig. 10, the structure 10 may form a frac pond filled
at least
partially with water. Water is one example of well treatment liquid that may
be stored within
the liquid containment structure 10. A fracturing operation may be carried out
on a formation
86 penetrated by well 82 at the well site using the frac water in pond 10.
Fracturing
equipment 84, such as pumps, gel trucks, controllers, blenders, proppant
trucks, fluid lines,
and other suitable equipment may be used to carry out the frac. Lines 87
convey frac water to
the equipment 84, while lines 88 convey liquid into and in some cases out of
the well 82.
During the fracturing operation, well treatment liquid is injected and
pressured up above the
fracturing threshold of the formation 86, in order to form fractures 90, into
which injected
proppant remains after pressure reduction in order to prop up and retain
permeability through
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fractures 90. Flowback water may be sent via lines 89 to pond 10, and such
flowback may be
treated, for example recycled, to remove contaminants prior to or after
storage in structure
10. Flowback may be trucked off-site and disposed of, or injected into an
injection well.
[0042] End plates or axial ends 70 may incorporate ports, such as outlets
to the
exterior of the pond 10. In some cases ground cover mats 24 may interconnect
with one
another, for example by the use of mating fingers, tongue and groove, or other
interconnection systems. In some cases no channel members 62 are used, for
example if a
channel 42 is dug within ground surface 19 and mats 24 laid with a gap 64
across the
channel 42. In some cases the mats 24 may have dimensions of up to forty feet
long, with
widths, such as eight feet, sized to fit on a conventional semi-trailer,
without requiring a pilot
vehicle or wide load precautions to be taken. Holes 60 in channel members 62
may form
slots to permit lateral play with fasteners. The drain channel 42 may be
defined by aligned
channels within the top faces 26 of adjacent mats 24. Insulation may be
provided in wall 12
to limit heat transfer between the ambient environment and water 92.
[0043] Unless context dictates otherwise, words such as vertical,
horizontal, top,
bottom, base, lateral, and other such descriptive words are intended to have
relative
meanings, and are not restricted to absolute orientations defined with respect
to the direction
of gravity on the surface of the earth. The wall 12 may be installed after or
during the
installation of the liner 14 in some cases. Although a rectangular shaped
platform 16 is
shown, other suitable shapes are possible such as polygons, circles, ovals,
and others. Mats
and wall parts may be lifted by other suitable methods such as by grappling
with an
excavator or loader. The pond 10 may incorporate a lid, such as a floating lid
(not shown).
The ground surface below the platform may be sloped towards the drain channel
to channel
fluids to the drain channel.
[0044] In the claims, the word "comprising" is used in its inclusive sense
and does
not exclude other elements being present. The indefinite articles "a" and "an"
before a claim
feature do not exclude more than one of the feature being present. Each one of
the individual
features described here may be used in one or more embodiments and is not, by
virtue only
of being described here, to be construed as essential to all embodiments as
defined by the
claims.
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