Note: Descriptions are shown in the official language in which they were submitted.
1,
BOUNDARY LAYER MODIFICATION IN CLOSELY-SPACED
PASSAGES
FIELD
[0001] The present disclosure relates generally to an
apparatus and a
method for removing particulates, especially sand, from multiphase fluid
streams. In
particular, it relates to a filtering device having stacked plates, wherein
the plates
comprise a lip that modifies the boundary layer formed by fluids passing along
the
plates, so as to allow closer spacing of the stacked plates.
BACKGROUND
[0002] Production from wells in the oil and gas industry
often contains
particulates, such as sand. This sand could be part of the formation from
which the
hydrocarbon is being produced, introduced from hydraulic fracturing, fluid
loss
material from drilling mud or fracturing fluids, or from a phase change of
produced
hydrocarbons caused by changing conditions at the wellbore (asphalt or wax
formation). As the sand is produced, problems occur due to abrasion and
plugging
of production equipment. In a typical startup, after stimulating a well by
fracturing,
the stimulated well may produce sand until the well has stabilized, often
lasting for
several months after production commences. Other wells may produce sand for a
much longer period of time.
[0003] Erosion of the production equipment can be severe
enough to cause
catastrophic failure. High fluid stream velocities are typical and are even
purposefully designed for elutriating particles up the well and to the
surface. An
erosive failure of this nature can become a serious safety and environmental
issue
for the well operator. A failure, such as a breach of high pressure piping or
equipment, releases uncontrolled high velocity flow of fluid which is
hazardous to
service personnel. Releasing such fluid to the environment is damaging to the
1
CA 3010532 2018-07-05
environment resulting in expensive cleanup and loss of production. Repair
costs are
also high.
[0004] In all cases, retention of sand contaminates surface equipment
and
the produced fluids and impairs the normal operation of the oil and gas
gathering
systems and process facilities. Therefore, desanding apparatus are required
for
removing sand from the fluid stream. Due to the nature of the gases handled,
including pressure and toxicity, all vessels and pressure piping in desanding
apparatus must be manufactured and approved by appropriate boiler and pressure
vessel safety authorities.
[0005] Trends in the fracturing industry have evolved to where the
amount of
sand pumped downhole is now in the order of 10,000 tonnes (20 million pounds)
per well in multi-stage fractures. Correspondingly, the amount of sand
produced in
flow back operations has increased and it is not unusual for a well to produce
50
tonnes (100,000 pounds) of sand. Desanding capabilities must increase
accordingly.
[0006] It is known to employ filters to remove sand, including fiber-
mesh filter
bags that are placed inside a pressure vessel. The density of the filter bag
fiber-
mesh is matched to the anticipated size of the sand. Filter bags are generally
not
effective in the removal of sand in a multiphase condition. Usually multiphase
flow in
the oil and gas operations is unstable. Large slugs of fluid followed by a gas
mist
are common. In these cases, the fiber-mesh bags can blind off, becoming a
major
cause of pressure drop and they often fail due to the liquid presence. Thus,
filter
bags are avoided in critical applications and due to cost associated with
replacement and subsequent disposal as contaminated waste.
[0007] Other prior-art apparatus use plate filters and/or screens for
removing
sand from an input fluid stream. For example, stacked plate or multiple-disc
type
filters are known, such as in US 4,753,731 to Drori, and US application
US2015/0144546, published May 28, 2015, each of which disclose a plurality of
2
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paired, cooperating disc-like filter surfaces. Such designs are designed to
form
annular pockets between adjacent discs for receiving and holding foreign
particles
separated from the fluid. As stated by Drori, multiple-disc filters have a
number of
advantages over the apertured screen type including removal and retention of
higher quantities of foreign particles, and higher resistance to damage.
However,
these prior-art desanding apparatus have drawbacks such as low or even
marginal
tolerance for pressure drop, and usually physically collapse at differential
pressures
as low as about 100 psi. Another drawback of such prior-art devices is that
the
screens thereof are easily plugged or clogged due to the accumulation of sand
thereon.
[0008] Applicant's US Patent Application No. 15/835,039, filed Dec 7,
2017
and published as US 2018-0161705A1 on June 14, 2018, describes a stacked plate
filter for filtering out sand from a fluid, which comprises parallel, closely-
spaced
plates suitable for excluding sand of a particular diameter. The cross-
sectional
dimension of the passages through which a fluid is conducted, such as the
walls of
spaced stacked plates in a filter, is typically sized to exclude sand and
minimize
pressure drop, which also happens to result in opposing wall spacing that is
far
greater than the sum of the approaching boundary layer displacement from each
wall for the fluid being filtered.
[0009] The closer together that the stacked plates are spaced, the
smaller is
the particulate that can be excluded from the space between the plates.
However,
Applicant notes a problem arises in spacing the plates closer together when
the
fluid being filtered was a liquid. As plate spacing decreased, for a given
fluid flow
rate, the pressure drop was been observed to increase beyond that of the
theoretical. Clearly, the characteristics of liquid, as the process fluid,
behaved
significantly differently from gaseous fluids.
[0010] Therefore, there is a need to further improve the efficiency of
separating smaller particulates from a multiphase fluid in a stacked-plate
filter.
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SUMMARY
[0011] Applicant has determined that the flow of fluids between closely-
spaced walls, such as stacked plate filters, can be subject to significant and
deleterious effects related to the fluid mechanics of the fluid flowing
therethrough.
Applicant believes these are due to boundary layer effects, as referred to
hereinafter.
[0012] Disclosed herein is an apparatus and method to mitigate these
boundary effects and enable closer spacing of walls, such as walls of stacked
plate
filters than was previously possible, while still allowing flow of fluid
therebetween.
[0013] In embodiments, the development of the boundary layer
displacement
is modified to be less than 1/2 the design spacing in a passage and reduce
compensatory increases in the free stream velocity for maintaining like mass
flow
therethrough over a given length of the passage. More particularly, at least
the
entrance to the passage is fit with an inward weir or lip for forming an inlet
spacing
and the passage downstream having a greater spacing therebetween.
[0014] In one aspect, disclosed is a stacked-plate apparatus having at
least
one pair of adjacent plates stacked along an axis, each plate of the pair
comprising
a first edge and a second edge, said adjacent plates having opposing surfaces
that
are parallel to one another and spaced apart axially to form a flow passageway
for
flow of fluid therethrough from a fluid inlet formed by the first edges of the
at least
one pair of adjacent plates, to a fluid outlet formed by the second edges of
the at
least one pair adjacent plates. At least the first plate of the at least one
pair of
adjacent plates has a first lip at the first edge, the first lip extending
axially into the
flow passageway at the fluid inlet, thereby narrowing the flow passageway at
the
fluid inlet to form an inlet gap. The first lip is configured to enhance the
flow of a
fluid towards the fluid outlet, for at least a working distance downstream
thereof, as
compared to a pair of adjacent plates that does not have the first lip.
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[0015] Fluid, as used herein includes liquids and gases. "Gases"
includes
without limitation air, nitrogen, carbon dioxide, carbon monoxide, methane,
ammonia, hydrogen chloride, nitrous oxide, nitrogen trifluoride, sulphur
dioxide and
sulphur hexafluoride. "Liquids" as used herein includes, without limitation
water in all
its forms, for example fresh water, salt water, wastewater, brine and process
water,
liquid hydrocarbons such as heavy (e.g., bitumen), medium and light crude
oils,
alcohol, mercury, glycol, liquid metals.
[0016] In embodiments of the apparatus the second plate of the at least
one
pair of adjacent plates comprises a second lip around the first edge of the
second
plate, the second lip extending axially into the flow passageway at the fluid
inlet and
the second lip is configured to enhance the flow of fluid towards the fluid
outlet, for
at least a working distance downstream thereof, as compared to a pair of
adjacent
plates that does not have the second lip.
[0017] In embodiments of the apparatus, the first lip and/or second lip
has a
planar surface that is generally coplanar with the opposing surfaces of the
plates.
[0018] In embodiments of the apparatus, the first lip and/or second lip
is
rectangular in cross section.
[0019] In embodiments of the apparatus, the first edge is an undulating
edge
of the plate, and in embodiments the undulating edge is a pleated edge.
[0020] In embodiments of the apparatus, the first lip and/or the second
lip is
continuous around the entire first edge of the plate.
[0021] In embodiments of the apparatus, the first lip and the second
lip are
opposite one another at the fluid inlet.
[0022] In embodiments the inlet gap is 100 pm or less across and/or the
opposing surfaces of the at least one pair of adjacent plates are spaced apart
by
200 pm or more.
CA 3010532 2018-07-05
[0023] In another aspect, described herein is a stacked-plate filter
has a
plurality of plates stacked along an axis and adjacent one another, each plate
comprising a central opening forming an inner edge about the axis and an outer
periphery forming an outer edge, said plates being parallel to one another
with the
upper and lower planar surfaces of adjacent plates spaced apart to form a flow
passageway therebetween for flow of fluid therethrough. The filter has a fluid
inlet
at the outer edges of adjacent plates; and a fluid outlet at the inner edges
of
adjacent plates.
[0024] The upper surface of each of the plates has an upper lip around
the
outer edge of the plate and extending axially from the upper surface, the
lower
surface of each of the plates has a lower lip around the outer edge of the
plate and
extending axially from the lower surface and the upper and lower lips of
adjacent
plates oppose one another at the fluid inlet to form an inlet gap.
[0025] The upper and lower lips are dimensioned to enhance the flow of
a
fluid towards the fluid outlet, for at least a working distance downstream
thereof, as
compared to a pair of adjacent plates that does not have the upper and lower
lips.
[0026] In embodiments of the filter the upper and/or lower lip has a
planar
surface that is generally coplanar with the upper and/or lower surface of the
plate,
respectively.
[0027] In embodiments of the filter the upper and/or lower lip is
rectangular in
cross section.
[0028] In embodiments of the filter the outer edge of each plate is a
radially
undulating edge, such as a pleated edge.
[0029] In embodiments of the filter the upper and/or lower lip is
continuous
around the entire outer edge of the plate.
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[0030] In embodiments of the filter the inlet gap is 100 pm or less
across
and/or the upper and lower surfaces of adjacent plates are spaced apart by 200
pm
or more.
[0031] In another aspect described herein is a method of enhancing the
flow
of a fluid through a stacked plate filter that comprises a plurality of plates
stacked
along an axis and adjacent one another, said plates being parallel to one
another
with the upper and lower planar surfaces of adjacent plates spaced apart to
form a
flow passageway having parallel sides therebetween, for flow of fluid
therethrough
from a fluid inlet to a fluid outlet, the method comprising narrowing the flow
passageway at the fluid inlet, to enhance the flow of fluids along the
passageway.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] Various of the drawings below set forth arrangements of features
affecting at least fluid flow and structure considerations which can vary
according to
the process design considerations, and unless specifically noted, proportions
illustrated thereon are not necessarily to scale.
[0033] Figure 1 is an illustration of the displacement effect of the
Blasius
laminar boundary layer formed on a semi-infinite plate, from zero velocity to
about
99% of free stream mean velocity;
[0034] Figure 2 is an illustration of the effect of the minimal Blasius
boundary
layer effect for parallel plates spaced sufficiently apart for formation of a
typical free
stream formed therebetween;
[0035] Figure 3 is an illustration of the overwhelming effect of
Blasius
boundary layer for parallel plates spaced very close together where the
displacement, shown fancifully beyond the wall dimensions, exceeds 1/2 of the
spacing between the plates, a free stream unable to be formed therebetween;
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[0036] Figure 4A illustrates the closely-spaced plates of Figure 3 with
a
stream flow fully influenced by boundary layer effects;
[0037] Figure 4B illustrates a first general embodiment of a design for
boundary layer manipulation between in closely-spaced plates for establishing
free
stream flow therebetween, the opposing plates fit with trip lips;
[0038] Figures 5A and 5B are plan view and cross-sectional side views
of a
plate respectively;
[0039] Figures 5C and 5D are plan view and cross-sectional side views
of a
plate fit with peripheral trip lips, the trip lips sized for demonstrating
their location,
not necessarily their relative proportions to the plate and plate-to-plate
spacing;
[0040] Figure 6 is a perspective view of filter plates of Fig. 5A, 5B
shown in
the process of alignment in a stack, the plates not yet arranged in a facing,
engaged
position;
[0041] Figure 7A is a partial perspective view of a plate fit with
peripheral trip
lips and a spacing boss;
[0042] Figure 7B is a side cross-sectional view of opposing plates of
the
configuration shown in Fig. 7A, each plate having spacing bosses sized to
space
the respective trip lips apart to the design spacing for the design flow
rates;
[0043] Figure 7C is a partial cross-section side view of the periphery
of
opposing plates, the view expanded to illustrate approximate relative
proportions of
one or more trip lips and plate bosses;
[0044] Figure 8 is a graph illustrating the performance of the change
in
pressure drop between two plates, with and without trip lips, for a range of
flow
rates of water therethrough;
8
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[0045]
Figure 9 illustrates radially spaced trip lips to manipulate the boundary
layer downstream of the outermost lip and again, downstream of a second trip
lip
before the boundary layer displacement re-establishes across the flow gap;
[0046]
Figures 10A through 10C each illustrate side cross-sectional views of
opposing plates, more particularly:
[0047] two opposing plates absent any trip lips
[0048] two
opposing plates having optionally two or more radially
spaced trip lips of like height; and
[0049] two
opposing plate having option two or more radially spaced trip
lips of diminishing height;
[0050]
Figure 11 is a plan view of a pair of opposing plates the alignment of the
profile of the periphery offset by plate stack reversal for angular offset of
the profile;
[0051]
Figure 12 is a cross-sectional view of a periphery of the stacked filter
plates of Fig. 11;
[0052]
Figures 13A and 13B are perspective views of four filter plates in axially
exploded view and an operationally stacked view respectively, with plate
bosses
providing inter-plate spacing therebetween;
[0053]
Figures 14A and 14B illustrate a plan view of an alternative embodiment
of a trip-lip plate and a perspective view of an example tooth of the plate of
Fig. 14A
respectively;
[0054]
Figure 14C is a perspective view of an angular portion of the trip-lip
plate of Fig. 14A, illustrating an intermediate tooth formed with a nib boss
thereon;
[0055]
Figures 15A and 15B are perspective views of the example tooth Fig.
14B with a spacing nib boss thereon, and a side cross sectional view of teeth
of
9
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1,
adjacent plates respectively, the teeth of Fig. 14A being spaced by the nib
boss and
illustrating a rejected particle;
[0056] Figure 16 is a graph illustrating the general
pressure drop
performance for a stack of 95 plates with no lip, spaced apart by 100 pm,
tested on
water;
[0057] Figure 17 is a graph illustrating the general
pressure drop
performance for a stack of 406 plates (curves 172 and 182) or 800 plates
(curve
190) which have a nominal 100 pm gap between opposing lips on the plates;
[0058] Figure 18 is a graph illustrating the general
pressure drop
performance in field trials for wells in Colorado, USA, Alberta, Canada, and
British
Columbia, Canada, for a stack of 800 plates which have a nominal 100 pm gap
between opposing 50 pm lips on the plates, line 190 shows the results of the
laboratory flow test for comparison;
[0059] Figure 19 is a graph illustrating the general
pressure drop
performance for a stack of 800 plates (curve 192) which have a nominal 50 pm
gap
between opposing lips on the plates; and
[0060] Figure 20 is a graph illustrating the general
pressure drop
performance for a stack of plates separated by 100 pm and with no lip, showing
that
forward (curve 184) and reverse (curve 194), showing that forward and reverse
flow
are generally the same.
DESCRIPTION
[0061] In testing a stacked plate filter, such as that
disclosed in Applicant's
US patent application US 2018-0161705A1 and published on June 14, 2018, when
plates were spaced about 100 pm apart, pressure drop across the plates rose
sharply with increased flow rate of water therethrough. At 75 pm plate
spacing, fluid
flow was established, but it was unstable. And as time progressed, pressure
drops
CA 3010532 2018-07-05
climbed, and after a number of start-stop tests flow therethrough could no
longer be
established. The filter was essentially blocked. At 50 pm plate spacing, flow
of water
through the plates could not be established at all. As verification that the
plates
were in fact open and not blocked with particulate matter, air was pumped
successfully through the plate filter with expected pressure drops
thereacross.
[0062] While initially attributed to fluid viscosity and surface
tension, Applicant
has determined that the development of a boundary layer within the plate
filter plays
a dominant role in the flow performance of a plate filter. The displacement
effect of
the boundary layer causes a small but finite displacement of the outer fluid
streams
spaced from the wall.
[0063] With reference to Fig. 1, the general behaviour of fluids flowing
over a
flat plate is shown. The solution to boundary layer displacement (dashed line)
was
given by Blasius in 1908 and is illustrated in Fig. 1. In our case of using
closely-
spaced stacked plates to create a filter where the spacing is measured in
microns,
Applicant has determined that the boundary layer displacement becomes
important,
because the boundary layer displacement is as large or larger than the plate
spacing (measured in microns), and the plates confine the space where a
boundary
layer is not allowed to grow to extent of the Blasius displacement.
[0064] As shown in Fig. 2, in a normal case of designing a passage for
fluid
flow for a low pressure drop therealong, opposing plates are spaced
sufficiently
apart such that the normal boundary layer displacement (dashed line) is less
than
the mid-point between the plates and the displacement, to about 99% of the
free
stream mean velocity, is achieved.
CLOSELY-SPACED PLATES FOR FILTERING
[0065] In other design cases, where filtering is the driving factor, the
plates
are arranged in a more closely-spaced manner, to exclude particulates and the
displacement is constrained. As shown in Fig. 3, for a given fluid flow, the
normal
boundary layer displacement is shown fancifully for each plate. Note that the
extent
11
CA 3010532 2018-07-05
of the displacement, generally deemed to be about 99% of the free stream mean
velocity of the fluid, happens to be larger than the spacing of the plates
when
arranged in such closely-spaced and opposing fashion.
[0066] In Fig. 4A therefore, when the flow stream is bounded between
two
plates, and not allowed to grow due to boundary layer displacement, the
resulting
flow streams would need to show a significant increase in velocity in the flow
streams away from the plates to accommodate boundary layer growth and preserve
momentum. In most circumstances with widely spaced passages, boundary layer
effect is small and often ignored for flow design considerations. In the case
of the
flow through the closely-spaced passages of a plate filter, boundary layer
effect is
the dominant factor in the plate design.
[0067] With reference to Figs. 5A, 5C,6, 13A, 14A, generally, a
plurality of
plates 100 are stacked one adjacent the other in parallel, yet spaced,
arrangement.
Each plate is generally planar and each pair of plates 100,100 forms a
generally
uniform passageway or gap 102 therebetween, forming a plurality of gaps
102,102.
Each of the plates can have a central opening 104 for receiving a perforated
fluid
receiving pipe forming a fluid path coupled to a fluid outlet or fluid inlet
(not shown; a
form of which is described in Applicant's co-pending US Patent Application No.
15/835,039, published as US 2018-0161705A1 on June 14, 2018).
[0068] The opening has inner edge 106 forming an inner diameter (ID)
of the
plate, and an outer periphery of the plate has an outer edge 108 forming an
outer
diameter (OD) of the plate. In embodiments with teeth 122, the outer edge 108
is
the edge around and between the individual teeth 122 as shown in Fig. 7A, and
the
OD is formed by an imaginary perimeter that coincides with the tips of the
teeth.
Gaps 102 communicate the fluid passing therethrough radially from in-to-out
(inner
edge to outer edge) or out-to-in (outer edge to inner edge).
12
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[0069] Typically the central opening 104 is fluidly connected to one of
a fluid
inlet or fluid outlet depending on the flow direction. If the central opening
104 is a
fluid inlet, the inner edge, which is fluidly connected to the fluid inlet,
forms a gap
interface. In embodiments, the outer edge is fluidly connected to the fluid
inlet,
forming the gap interface, for flow through the stack from the outer edge to
the inner
edge and the fluid outlet.
[0070] The size of the gap 102 between each pair of adjacent plates
100,100
is sized to exclude particulates from entering therein. When flowing in-to-
out, the
respective pairs of adjacent inner edges 106 exclude particulates from
entering the
gap 102 between adjacent plates and flowing along the gap. When flowing out-to-
in,
the respective pairs of adjacent outer edges 108 exclude particulates from
entering
the gap 102 between adjacent plates and flowing along the gap.
[0071] Referring to Figs. 4A, 5A, 5B, 8 and 10A, as an example, a filter
stack
of eight hundred (800) opposing, parallel and closely-spaced plates 100,100
... was
assembled. Each plate was 152 mm OD X 76 mm ID (6"X3"), with a tooth length of
about 7mm, and each pair of plates was spaced 100 pm apart. A flow of water
was
passed through the filter stack from the outer edge to the inner edge at a
flow rate
of 1000 m3/day. Assuming unbounded flow, the estimated boundary layer
displacement thickness for each plate was about 600 pm. For the plates spaced
100 pm apart therefore, the interplate interference would be less than the at
1/2 the
plate spacing, or 50 pm. Thus, as shown in Fig. 3, the boundary layer
displacement
thickness would be 12 times the plate spacing, inferring boundary layer
interference. The Blasius equation for laminar flow is inversely proportional
to the
square root of the Reynolds number which implies that it would be inversely
proportional to the square root of the fluid stream velocity. To solve this
for the test
conditions, a velocity of close to the speed of sound would be needed to
accommodate the boundary layer growth. This analysis suggests why the 75 pm
plate spacing test were unstable and the 50 pm tests were unable to establish
any
flow of liquid therethrough.
13
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[0072] As shown in Fig. 8, in upper curve 170 for the above
arrangement, as
the flow rate doubles from about 730 m3/d (4600 bbl/d) to about 1500 m3/d
(9400 bbl/d), the pressure drop across the filter stack increases by a factor
of about
five times (6 to 26 psig).
[0073] While the development of a boundary layer requires a
compensatory
increase in the free stream velocity, the embodiments herein significantly
reduce the
extent to which velocities increase and pressure drops increase.
EDGE MISALIGNMENT
[0074] In the prior art, each plate of a stack of plates had been of
like design,
resulting in coincident inner and outer edges, aligning along a perpendicular
to the
plane of the plates. In other words, when the plates happen to be stacked
vertically
and secured together for use, all the inner and outer edges aligned
vertically. As
described in Applicant's co-pending US published patent application US 2018-
0161705A1, Applicant noted that with this prior art arrangement, individual
particles
are often received and become lodged along the aligned and spaced edges of the
gap interface, the aligned edges of the plates imposing retaining forces. In
US
published patent application US 2018-0161705A1, Applicant disclosed a stacked
plate filter with misalignment of the respective and adjacent inlet edges to
mitigate
particle retention and clogging at the filter gap interface. A slight
misalignment of the
edges at the gap interface, such as that being less than the particle radius,
disables
opposing frictional jamming forces that retain particulates.
[0075] Further, as shown in Fig. 5A, each plate 100 has a peripheral
pleated
edge 120 for increasing the surface area thereof and, in embodiments, aids in
angular misalignment. For example, each plate 100 is a gear-like plate having
a
plurality of teeth 122 about the edge thereof. In this embodiment, the central
opening 104 is keyed by having a keyed notch (keyway) 124 to provide alignment
in
addition to the alignment provided by three assembly rods (described later)
for extra
rigidity.
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[0076] Each plate 100 may also comprise a plurality of alignment
holes 128
for coupling to assembly rods 138 as part of the assembly apparatus, as shown
in
Fig. 6. For example, in this embodiment, the plate 100 comprises three
alignment
holes 128A, 128B and 128C. A portion of the plate in proximity with each
alignment
hole 128 has an increased thickness forming a raised-face area or boss 140 on
at
least one side, but which can also be on both sides of the plate 100, for
providing
required spacing between plates when assembled. While the alignment holes 128
and rods 138 aid in assembly, the fine tolerance of the lip misalignment for
particle
rejection relies on more precise angular alignment of adjacent plates. As
shown in
Fig. 6, 13A and 13B, the stack of plates are fit to a centre generally
cylindrical
mandrel. The keyed notch 124 in each of the plates aligns angularly with a key
on
the mandrel. The assembly rods 138 then can be provided with sufficient
tolerance
to avoid jamming during assembly or omitted in their entirely.
[0077] In this embodiment, the teeth 122 are generally of the same
size and
circumferentially uniformly distributed. Each tooth 122 is symmetrical to a
central
axis thereof (not shown). As shown in Fig. 5A, in embodiments, the plate 100
may
be absent of one or more teeth for alignment and/or identification purposes.
[0078] In this embodiment the three alignment holes 128a, 128b and
128c
are located on the plate 100 at a same distance from the center 130 (denoted
"origin" hereinafter) of the plate 100, and at 120 to each other with respect
to the
origin 130. Further, the alignment holes 128 are positioned such that, for
each
alignment hole 128, the tooth 122, or the notch 1126 if the tooth faces a
notch,
adjacent thereto is asymmetrical with respect to an imaginary line between the
origin 130 and the center of the alignment hole 128. In other words, the
imaginary
line between the origin 130 and the center of the alignment hole 128 is offset
from
the central axis of the adjacent tooth 122. For example, the tooth 122a
adjacent to
the alignment hole 128a is asymmetrical to the imaginary line 136a between the
origin 130 and the center of the alignment hole 128a. The tooth 128c faces a
notch
126, which is asymmetrical to the imaginary line 136c between the origin 130
and
CA 3010532 2020-03-30
the center of the alignment hole 128c. Such asymmetry of the teeth 122 results
in
different patterns of the front and rear faces of the plate 100, in terms of
the tooth
positions relative to the alignment holes, and gives rise to angular offset
between
filter plates 100 after assembling.
[0079] As shown in Fig. 6, during assembly, a plurality of filter
plates 100 are
stacked with the alignment holes thereof aligned for receiving assembly rods
138,
each plate arranged alternatingly "facing-up" and "facing-down". Herein,
filter plates
are alternatingly "facing-up" and "facing-down" in that the first or front
faces of each
pair of adjacent filter plates 100 are facing opposite directions such that
among any
three adjacent filter plates, the first faces of the first and third plates
face the same
direction and the first face of the middle plate faces the opposite direction.
[0080] Fig. 11 shows a plan view of a pair of filter plates 100a,
100b stacked
as described above, i.e., one plate "facing-up" and the other "facing-down"
and
alignment holes 128 are aligned. As can be seen, the teeth 122a of plate 100a
are
angularly offset, e.g., about 1 , from the teeth 122b of plate 100b, resulting
in offset
edges of assembled filter plates 100. In embodiments the teeth of adjacent
plates
100a,100b are oriented with respect to an alignment keyway 124, a reference
tooth
being angularly skewed, for example, by less than 1/2 particle size. This
alternate
upright and upside down plate stacking results in in slight misalignment of
the plate
edges at the gap interface, as described in Applicant's copending US published
patent application US 2018-0161705A1.
[0081] Thus, in order to obtain angular separation the plates'
peripheries are
pleated and the alignment holes are slightly offset from a symmetrical radial
through
the pleating profile so that when flipped over, the pleat profile is shifted
angularly
from the adjacent pleat profile. Pleats both provide an increased surface area
as
well as a non-tangential face to allow for angular offset. As shown in Fig.
12, for
providing a shedding interface, one selected magnitude of the misalignment is
at
least 1/2 particle size. Larger or smaller offsets are also employed so as to
cover a
16
CA 3010532 2020-03-30
larger or smaller range of particle diameters. Larger offsets aid in the ease
of
manufacture.
[0082] With the assembly comprising alternate flipping of a single
plate, used
for each of a stack of plates, only one mold is necessary, reducing costs and
reducing errors in assembly. An alternate embodiment is to implement a mold
for
each offset through 360 degrees and thus avoid flipping plates. However, using
an
offset using % degrees, this method would require 720 molds. Another practical
alternate embodiment is to implement two molds, the alignment holes arranged
to
alternate 1/2 degree clockwise and 1/2 degree counterclockwise each
alternating
plate.
[0083] Plates 100 may further comprise plate bosses 142 to space
adjacent
plates 100,100. The plate bosses 142 can be spaced about the plate's
circumference at an intermediate radial orbit. For gap dimensional stability,
plates
100 having a large radial extent, or which are subject to compressive forces
can
benefit from additional tooth bosses 144 (see Figs. 14A,C and 15A,B) spaced
about
the plate's circumference at the pleated edge and spaced circumferentially
intermediate the plate bosses 142. With reference to Figs. 14B, 15A and 15B,
the
pleated edge 120 comprises a plurality of teeth 122 and boss teeth 122S having
tooth bosses 144 thereon.
[0084] The plates 100 can be made of a synthetic material for reduced
fluid
friction and for erosion resistance. One such synthetic is a polymer material
including silica. In one embodiment, the plates are made of a polymer material
containing silica including nylon material. An injection mold process can be
employed to inject the polymer material into a suitable mold for making the
plates.
[0085] In some embodiments, the plates 100 are made of a polymer
material
having a suitable percentage of silica. For example, in one embodiment, the
plates
100 are made of a polymer material, such as Nylenee 5133 HS having about 33%
silica, manufactured by Nylene Canada Inc. of Arnprior, Ontario, Canada. In
another
17
CA 3010532 2018-07-05
embodiment, the plates 100 are made of a polymer such as Vydene R533 NT
having about 33% silica, manufactured by Ascend Performance Materials of
Houston, Texas, United States of America.
[0086] An inert polymer with a silica base is quite chemically neutral
and can
in the order of at least 5x stronger than a stainless material without issues
caused
with H2S stress cracking or oxidation problems associated with carbon steel.
The
polymers are also recyclable.
[0087] Those skilled in the art appreciate that the plates 100 may
alternatively be made of other suitable materials such as carbon steel or
stainless
steel. However, compared to plates made of steel, the polymer plates 100 have
advantages including reproducible manufacturing tolerances in the order of
within
5/10,000ths of an inch. Such tolerances are more difficult to achieve
economically in
materials such as carbon or stainless steel. Polymer plates may have
compressive
strength in the order of at least 10,000 psi, contribute to lowering pressure
drop due
to reduced surface drag, and are also chemically resistant to oilfield
chemicals.
BOUNDARY LAYER MANIPULATION
[0088] With reference to Fig. 4B, 5C and 5D, and returning to
Applicant's
improvement in flow between closely-spaced plates, one embodiment is to create
a
lip 150 (a flow stream trip lip) at the leading (inlet) edge of the plate,
herein shown
located at the outer edge 108 of the plate. In embodiments, lip 150 is an
annular
shoulder or protrusion that extends axially, preferably perpendicularly, from
the flow
surface of the plate into gap 102 at the outer edge 108 of plate 100, around
the
entire outer edge.
[0089] Without being limited to theory, a comparison of Figs. 4A and 4B
shows schematically what the Applicant believes is the effect of lip 150 on
the fluid
mechanics and resulting flow of fluid between two closely-spaced plates. Fig.
4A,
demonstrates a flow passageway (the gap) that is bounded between two plates
separated by a distance 2h. Boundary layer growth (dashed line) begins on each
18
CA 3010532 2018-07-05
plate at the entrance (fluid inlet) to the flow passageway between the spaced
plates,
and is restricted before the fluid can exit the flow passageway between the
plates.
Thus, the plates are too close together to allow free flow to be re-
established and
the flow passageway becomes plugged with fluid ("liquid lock").
[0090] In Fig. 4B, lips 150 at the entrance (fluid inlet) of the flow
passageway
between the spaced plates likewise create an opening having a distance 2h.
Thus,
these plates would exclude the same sized particulates as the arrangement in
Fig. 4A. However, the lips 150 extend for only a short distance along the flow
passageway, and then cause the flow passageway to abruptly enlarge, and fluid
emerging from the gap between the lips is unable to follow the abrupt
deviation of
the boundary. It is believed this abrupt deviation causes pockets of turbulent
eddies
in the flow after the lips (curved arrows), preventing attachment of fluid to
the walls
and moving the formation of the boundary layers further down the walls to a
point
where they do not interfere with one another before the fluid outlet, or the
interference is minimized.
[0091] As demonstrated in the empirical results disclosed herein, it is
believed that this modification or manipulation of the formation of the
boundary layer
by lip 150 enhances the flow of fluid through a passageway, "enhance" meaning
that the flow rate of the fluid at a given pressure drop is increased and/or
the
pressure drop along the passageway at a given flow rate is decreased. Another
theory or explanation for the operation of the invention described herein is
that the
lip (or lips) acts as a nozzle at the entrance to the flow passageway between
the
plates.
[0092] In embodiments lip 150 is dimensioned (short) in the flow
direction so
that a boundary layer is not formed thereon by fluid flowing along the lip.
The wall
spacing immediately following the lip 150, opens to a downstream passage, gap
102, which is of sufficient dimension that a boundary layer does not attach to
the
wall behind the lip 150 for at least a working distance downstream thereof.
For
circular plates, the working distance is normally the radial extent of the
plate from
19
CA 3010532 2018-07-05
I]
inlet edge (edge 108 in this case) to outlet edge (edge 106 in this case). On
linear
passageways, the working distance is simply the length of the plate from inlet
edge
to the outlet edge. Returning to the illustrated generally circular plates, in
instances
where the radial depth of the plate exceeds the working distance, subsequent
and
supplementary lips 150 can be provided as discussed below.
[0093] Without fluid boundary layer attachment to a wall,
there is little or no
boundary layer growth at the upstream inlet to the passage or gap 102 between
the
plates, resulting in a reduced need, or extent of which, to forcibly increase
velocities
to maintain throughput that otherwise would create additional pressure drop.
[0094] As shown schematically in Fig. 4B, and structurally
in Fig. 7B, test
plates were fabricated each with a 50 pm lip 150 (50 pm being the distance
that the
lip extends perpendicularly from the surface of the plate 100 into gap 102), a
100
pm boss 140. When coupled as a pair of opposing, like plates 100,100,
sandwiched
boss-to-boss, a 200 pm gap 102 is created behind the lips 150, to create a
void
large enough to avoid or delay the formation of a boundary layer. This
geometry
provides a 100 pm inlet gap or space between the lips 150,150, equal to the
100
pm spacing of the plain, planar, and lipless plate filter of Fig. 5A.
[0095] For a silica/polymer plate having a body thickness of
about 1.25mm
(1250 um), a 100 pm boss 142, and a 50 pm lip 150, the radial width of the lip
was
designed to be about 1 mm (1000 urn), considered to be about a minimum for
consistency of fabrication and operational strength given the materials used.
In
preferred embodiments the lip 150 maintains the particle-release overlap as
larger
and larger diameter plates are used. For example, for plates angularly offset
by a 1/2
degree rotational offset, on the sides of the teeth, the radial lip would then
need to
be wider for larger diameter plates. The plate filter material is a Nylene
(or similar
material) which is a silica matrix suitable for injection molds. This material
has a low
enough thermal shrinkage (about 3%) that it does not impact the dimensions of
the
molded product. To meet the spacing specifications, machining tolerances were
maintained within 5/10,000" or about 13 um.
CA 3010532 2018-07-05
[0096] Experimental data confirms that this arrangement not only
reduces
pressure drop through a plate filter but also prevents the flow instability
and liquid
lock experienced in the smaller 50 and 75 pm lipless plate filters.
[0097] Returning to Fig. 8, a comparison of pressure drop to flow rate
is
shown for filters using stacked plates with and without lips. Each filter is
an eight
hundred (800) plate stack having an inlet spacing of 100 pm. The space between
stacked plates of filter without lips is 100 pm, and inlet gap or space
between the
lips 150 of stacked plates with lips is 100 pm. Downstream of the lips, the
space
between the plates of the filter with lips was about 200 pm. Referring to
curve 170,
and using curve matching techniques, for a plate filter without any leading
edge lip
150 the pressure differential for water rose rapidly from 6 psi to 26 psi for
the flow
range tested, and had a pressure proportional to the 1.996 power of the flow
rates.
Referring to curve 180, for the plate filter with the lip embodiment, the
pressure
differential for water only climbed from 3 psi to 7 psi for the same range of
flow
rates, and the pressure drop was proportional to the 1.444 power.
[0098] The difference in the powers is attributable to the presence of
the lip
150. This difference in powers becomes more significant as the flow rates
through
the plate filter increase. One advantage of the plate filter fit with a lip
150 is that a
shorter filter stack could be provided, using fewer plates, for the same
performance.
Alternatively, the same number of plates could be used but the filter would be
rated
at a higher throughput.
[0099] In the embodiments shown in Figs. 5C and 14A, designed for out-
to-in
flow, lip 150 is an annular shoulder situated at the outer edge 108 of plate
100,
around the entire outer edge. In other embodiments, where flow is in-to-out,
lip 150
may be at the inner edge 106 of the plate, around the entire inner edge. The
width
of lip 150 may be the same along its length, as shown in Fig. 14A,C, or it may
have
different widths along its length, as shown in Fig. 14B. In embodiments, only
one
surface of a plate has a lip 150, the other surface being flat, so that a
stacked filter
21
CA 3010532 2018-07-05
may be formed in which some of the pairs of adjoining plates 100,100 do not
have
lips 150, or only one of the pairs of adjoining plates 100,100 has a lip 150.
[0100] In the embodiments shown in Figs. 50, 7A-C, 14A-15B, lip 150 is
a
rectangular shoulder in cross section, having a flat/planar surface.
Embodiments of
the lip 150 included herein may have other shapes, geometrical or not, which
extend axially into the gap 102, and which create a suitable obstruction to
the flow
of particulates into gap 102 and function so as to manipulate the boundary
layer as
described herein. For example, lip 150 may be triangular, oval or crescent
shaped
in cross section. The dimensions of the lip 150 will depend on, among other
things,
the dimensions of the plate, the materials used to fabricate the plate, the
types of
fluids and particulates being separated and the operating conditions.
[0101] As introduced above, it is believed that the boundary layer
manipulation by lip 150 has a working distance on a wall before the boundary
layer
reforms or begins to reform downstream and layer displacement again encroaches
on the ability of fluids to flow between plates. In the context of the plates
tested by
Applicant above, a 50 pm high x 1 mm wide lip positively influences free
stream
flow up to a distance of at least about 10X the height downstream, so in this
case at
least about 500 pm. Periodic and repeated introduction of lips, as necessary,
may
improve the flow performance over longer flow distances, and also over shorter
distances. These additional lips also serve to provide an additional "gauge"
of the
outer lip, in the event the outer lip becomes damaged, for example by erosion.
Thus, as shown schematically in Fig. 9 and structurally in Figs. 10B and 10C,
in
embodiments plate 100 includes subsequent lips 150a,b disposed downstream of a
first lip 150, and the subsequent lips 150a,b height can have the same
dimensions
(height, length and shape) as the initial lip 150 at the fluid inlet (Fig
10B), or different
dimensions (Fig. 10C shows lips of diminishing height). The gap 112 between
lips
150 at the fluid inlet sets the particle exclusion dimension.
[0102] Further illustrations of embodiments are described with
reference to
Figs. 14A to 15B. In these embodiments, adjacent filter plates 100,100 provide
gap
22
CA 3010532 2018-07-05
116T that is amenable to the passage of liquid L but not sand S. Lip 150 about
the
periphery of the plate forms a narrow gap 116T for particle exclusion and a
wider
gap 116P therebehind for transport of the liquid L to central opening 105.
Tooth
boss 144 provides additional gap dimensional stability.
[0103] Additional laboratory and field testing demonstrates the
operability of
the apparatus and method disclosed. In laboratory tests a centrifugal pump was
used to flow fresh water through plate stacks with different spacings between
plates
and at various flow rates.
[0104] A stack of ninety-five (95) plates, without a lip 150 and with a
100 pm
space between plates was prepared and ten laboratory trials were conducted,
each
at five discreet pump levels. Flow rates were measured with a container of a
known
volume and a timer. For each flow rate the pump was run long enough to
stabilize
the flow loop and take readings, which was approximately five minutes per
test. No
temperatures were taken during the trials.
[0105] The results, plotted as pressure differential (psig) vs. flow
rate (bbl/d),
are shown in Fig. 16. Of note, each successive trial indicated a lower pump
rate
than the prior trial. At the time, this was attributed to testing error,
filter stack
settling, or filter stack fouling. On further analysis and a result of
additional testing
this time related degradation of filter performance was observed in most
tests.
Figure 16 uses the trend from the last trial (#10), to represent the flow rate
¨
pressure differential relationship.
[0106] When 95 plates without a lip, were spaced apart a distance of 75
pm
between plates, and tested as above, again each successive test had higher
pressure drop than the prior test so much so that at trial #10, no flow was
established.
[0107] Plate molds or injection dies, for manufacturing plates, were
machined
to obtain higher tolerances on the plates. Four dies, for a 0, 25, 50 and 100
pm
nominal spacing between the trip lips of paired plates (i.e., the flow gaps),
were
23
CA 3010532 2018-07-05
machined. The actual plate spacing was measured after the plates were
produced,
as the physical dimensions are influenced by shrinkage of the injected
material, the
size of the dimensioned items, the total force of the injector press and by
relative
proximity of the dimensioned item relative to the injector locations. It was
determined that the lip 150 at the outside edge of the plate had a different
overall
shrinkage than the formed bosses used to separate the plates. In addition, the
design employed two different sizes of bosses, and these had different
shrinkage
characteristics. In many cases, the injector press was insufficient to keep
the dies
completely closed resulting in a small amount of flash material extruded where
the
facing dies meet. This flash, no matter how small can result in an out-of-spec
plate.
To mitigate the effect of flash material on fluid flow between adjacent
plates, the
dies were redesigned so that the flash material, if formed at all, would be
deposited
intermediate the plate inlet edges, away from the facing corners or edges of
the
plate 114 where fluid influx occurs.
[0108] The following plate combinations combine to form the actual flow
inlet
gap between adjacent plate lips. As an example, the 50+50 plate comprises two
plates each with a lip of nominal 50 pm in height (100 pm total), which are
used to
create a nominal 100 pm gap between the lips and a nominal 200 pm space
between the plates. This combination results in an actual total trip lip
height of 127
pm, a flow gap between the lips of 86.36 pm, and space between the plates of
213.36 pm.
INTERPLATE SPACE TRIP LIP HEIGHT AVAIL.
FLOW GAP
in IJM in pm in pm
25+0
.0081 205.74 0.0086 218.44 -0.0005 -12.70
25+25
0.0082 208.28 0.0076 193.04 0.0006 15.24
50+0
0.0082 208.28 0.0073 185.42 0.0009 22.86
50+25
0.0083 210.82 0.0063 160.02 0.0020 50.80
24
CA 3010532 2018-07-05
50+50
0.0084 213.36 0.0050 127.00 0.0034 86.36
100+0
0.0116 294.64 0.0095 241.30 0.0021 53.34
100+25
0.0117 297.18 0.0085 215.90 0.0032 81.28
100+50
0.0118 299.72 0.0072 182.88 0.0046 116.84
100+100
0.0152 386.08 0.0094 238.76 0.0058 147.32
[0109] Laboratory tests were run on a 50+50 plate combination (nominal
100
pm flow gap, actual 86.4 pm flow gap) and a 25+25 plate combination (nominal
50
pm and actual 15.24 pm flow gap). In addition, plates with no lips and spaced
apart
by 100um or 75 pm plates were rerun with the same liquid delivery pumps and
configuration as the plates having the lips, in order to again compare
performance
of a plate stack comprising plates with lip to a stack of plates without a
lip.
[0110] Normal or "out-to-in" flow (from outer edge 108 to inner edge
106) was
performed by running two different pumps at various flow rates to achieve at
least
five different flow rates, measuring flow rate, inlet pressure, outlet
pressure and
temperature. Efforts were made to run the test for each individual flow rate
for at
least one hour in length.
[0111] Reverse flow, or "in-to-out" (from inner edge 106 to outer edge
108)
was performed to establish the impact of the lip on flow. Fluids in normal
flow enter
the fluid inlet and first pass over the lip (if present) and continue through
the
adjacent plates' gap to the fluid outlet. In reverse flow, the fluids flow
through the
adjacent plates' gap from the fluid outlet and exit over the lip (if present).
In reverse
flow, a lip effect on fluid inflow is nullified.
[0112] Of interest, while the lip is believed to modify the boundary
layer, it is
possible that some of the reduction in pressure drop was due to a larger
interplate
spacing behind the trip lip. The nominal interplate spacing of about 200 pm
for
plates with a lip is double the 100 pm space between plates with no lip. It
should be
CA 3010532 2018-07-05
noted that it is possible the "in-to-out" flow is handicapped by additional
turbulence
caused by the mandrel in the centre opening 104 of the plates in the stack,
and
because of the smaller inside diameter of the inner edge 106 (as compared to
the
outer edge 108), this turbulence may therefore be different than that for flow
in the
reverse direction.
[0113] Fig. 17 shows the results of laboratory flow tests done with the
50+50
plate combination in a stack of 406 plates or 800 plates. Pressure
differential is
plotted against forward and reverse viscosity adjusted flow. A comparison of
the
forward or "out-to-in" test (curve 182) where the trip lip is active and the
reverse or
"in-to-out" test where it is not (curve 172), shows that about three times the
flow can
be expected for a given pressure drop (e.g., at 150 kPa, flow is about 200 for
reverse vs. about 600 for forward). This demonstrates that for the given
geometry,
the lip 150 improves flow presumably because of boundary layer modification
resulting from its use. Curve 190 shows the results for a forward flow test on
a stack
filter comprising 800 plates. Curves 182 and 190 are linear, whereas for curve
172
the pressure drop is proportional to the 6.7591 power.
[0114] In running the individual test, for normal flow, it was observed
that
there was some flow instability over the one hour test period. In most flows
trials,
the pressure drop increased and the flow rate decreases as the test proceeded.
The
chart below shows the marked degradation of filter performance over the course
of
the test
[0115] It was observed that there was some flow instability over the
one hour
test period. In most flow trials, the pressure drop increased and the flow
rate
decreased as the test proceeded.
26
CA 3010532 2018-07-05
[0116] Considering the flow profiles across a plate as determined by
Blasius
1908) or the Hagen-Poiseuille flow in small diameter tubes, pressure drop is
proportional to some geometry parameters as well as fluid viscosity and flow
rate,
as follows:
Ai) oc C,1112
[0117] To determine the geometry parameter C, for these trials, the
pressure
drop divided by the viscosity adjusted flow rate (AP/pQ) was plotted over time
(as
what is referred to as a "stability chart). If the geometry parameter is
constant, then
Ap/pQ should be constant and the plots should yield a vertical line. If the
geometry
parameter is not constant, then the Ap/p.Q is not constant, and the plots will
trend
towards horizontal, suggesting that at some point flow will not be
sustainable, i.e.,
there is a point above which flow cannot be established.
[0118] For reverse flow (i.e., in-to-out; equivalent to a no lip test)
the
geometry parameter was found to change over the course of the test, which
suggested that at some point in time, flow might not occur. This point is
approximately 240 m3/d, as shown in Fig. 17.
[0119] For forward flow (i.e., out-to-in; lip active) the geometry
parameter was
also found to change over the course of the test, however the constant was
about
an order of magnitude smaller than the constant for the reverse flow test. At
lower
throughput rates for the forward flow test, the geometry constant was
relatively
stable and appeared to improve over time.
[0120] The 50+50 plate combination (nominal 100 pm actual 86.4 pm
opening between the lips) was used in field trials of an 800 plate stacked
plate filter.
While the laboratory tests were conducted in a controlled environment with a
single-
phase fluid, the fluids in the field tests were multiphase fluids, including
gas, oil,
emulsions, waxes and water.
27
CA 3010532 2018-07-05
[0121] To compare against the single-phase flow data, the field data was
converted to a single pseudo phase by estimating the volumes at flow
conditions in
the filter using industry PVT correlations, estimating the associated
viscosities of the
fluid, accommodating for dissolved gas in solution for the oils and adjusting
the
viscosities for temperature.
[0122] The test data used for the 100 pm plate were based on linear
correlations adjusted for viscosity variations due to temperature variations
that
occurred during the tests and adjusted to the field installations of 800
plates per
filter. No adjustment was made for fouling of the filters due to sand
production.
[0123] Fig. 18 shows a plot of pressure differential (AP, KPa) vs.
viscosity
adjusted flow rate (QVisc m3/d) for various trials. Line 190 shows the results
of the
laboratory flow test for comparison. The Colorado field tests (A) showed
remarkable
correlation to the laboratory data, the well-produced high-pressure gas and
liquid,
the liquid was about 60% water and 40% light condensate. The stacked filter
was
moved to several locations in Colorado. In one location paraffin wax covered
about
80% of the surface of the stacked filter yet the filter was still able to
operate at
pressures that would be considered to be very low considering the amount of
fouling.
[0124] A test for a well in Northern Alberta (0) was a high gas rate
well with
liquid comprising of about 50% water and 50% light oil. The well made
considerable
sand while the filter was running requiring frequent clean outs.
[0125] A well in Northern British Columbia (+) was a high-pressure
condensate rich gas well. The production was nominally 1,000m3/d, pressure
drops
recorded were from almost zero to over 400 kPa. In some cases, this was due to
the wellbore slugging fluids where the instantaneous liquid rate was many
times
higher than the average rate and where sand production caused partial fouling
of
the filter.
28
CA 3010532 2018-07-05
[0126] Considering the instability noted in the laboratory tests, the
field data
was reviewed to see if the instability was demonstrated by an increase in
pressure
drop over time. The pressure drop showed the effects of unstable well flow but
was
generally in line with the decline in well productivity as indicated by the
desander
operating pressure.
[0127] Fig. 19 shows the results of laboratory flow tests done with the
25+25
plate combination in a stack of 800 plates. Diamonds (0) show the reverse flow
test
data, small circles (.) show the forward flow test data and curve 192 shows
the
results for a forward flow test.
[0128] The stability charts for the forward and reverse flow showed
similar
characteristics as the 50+50 plate combination flow test. The forward flow
test with
the 25+25 lip show about a seven times improvement over the reverse flow where
the lip is not effective. This confirms the utility of the lip for smaller
spaces between
the plates and a smaller flow gap. A filter comprising plates with no lip and
15um
space between the plates would not be able to flow any fluid.
[0129] The current test protocol using an extended test period and
taking
temperature into account, was performed on a stacked plate filter with plates
that
did not have a lip and which were separated by a space of 100 pm. The results
(Fig.
20) confirmed earlier observations. A reverse flow test was conducted for a
comparison to the reverse flow tests with plates having a nominal 100 pm flow
gap
and lips. In the plate with no lips, the reverse flow should match the forward
flow,
since there is no lip to influence the forward flow. Fig. 20 shows the
relative
performance of the forward (curve 184) and the reverse (curve 194) flow tests.
Considering the instability of the flow rates, the results were consistent
with the
expectation that the performance should be similar for both directions of
flow.
[0130] While the apparatus and method has been described in conjunction
with the disclosed embodiments which are set forth in detail, it should be
understood that this is by illustration only and the method and apparatus are
not
29
CA 3010532 2018-07-05
intended to be limited to these embodiments. On the contrary, this disclosure
is
intended to cover alternatives, modifications, and equivalents which will
become
apparent to those skilled in the art in view of this disclosure.
CA 3010532 2018-07-05
