Note: Descriptions are shown in the official language in which they were submitted.
CA 02212840 1997-08-13
1 FIELD OF THE INVENTION
2 This invention relates to a temporarily blinded sand exclusion
3 liner and to the method for emplacing or landing the liner so that it is
fully
4 inserted into the desired position in the wellbore.
6 BACKGROUND OF THE INVENTION
7 Sand exclusion liners (also known as "sand control screens")
8 are commonly used in wells producing from a sand formation or reservoir.
9 These wells usually are completed "open hole". That is, the wellbore is
drilled
vertically down through the overburden to the top of the sand reservoir and
11 cased. The end plug of the casing is then drilled out and the wellbore is
12 whipstocked and drilled horizontally through the reservoir. The horizontal
13 section of the wellbore is left uncased or "open hole". A perforated liner
is
14 then run into the well at the end of a pipe string and landed or positioned
to
extend from the end of casing through the horizontal section of the wellbore.
16 The liner is sealed at its inner end to the casing's bottom end, so that
the
17 former is an extension of the latter. A production tubing string is then
run into
18 the well to extend into the liner bore.
1 g The function of the liner is to allow produced fluid to enter the
production string while simultaneously screening or rejecting mobilized sand
21 grains seeking to enter with the fluid.
22 One specific, commercially available sand exclusion liner will
23 now be described, by way of example. The liner is formed of tubular steel
24 joints coupled together end to end by threaded couplings. Some of the
joints
have screen sections. The screened joints each comprise a base pipe having
2
CA 02212840 1997-08-13
1 transverse perforations extending through the pipe side wall. Steel rods
2 extend across the perforated section, parallel to the axis of the pipe. The
rods
3 are welded to the outside surface of the base pipe at spaced intervals
around
4 its circumference. A stack of vertically spaced apart steel rings is
positioned
over the rods; the rings are individually welded to the rods. The rings each
6 have a generally triangular cross-section so that the slot, formed between a
7 pair of adjacent, vertically spaced apart rings, has increasing width from
the
8 outside in. This is commonly referred as a "keyhole" opening or slot. In
9 summary, the liner comprises one or more joints, some blank and some
having a perforated base pipe carrying means for screening sand to prevent it
11 entering the perforations.
12 The present invention was developed in connection with
13 experimental wells in which liners were to be landed in horizontal
wellbores
14 completed in an unconsolidated sand reservoir.
Two problems needed to be addressed.
16 Firstly, the liner has a tendency to pile up sand ahead of it as it
17 is advanced along the horizontal wellbore. Or alternatively sand may slump
in
18 around the liner. In both cases, it can become difficult or impossible to
keep
19 advancing the liner to get it fully inserted to the desired landing
position. It is
common oilfield practice to remove sand blockages by circulating oil or
drilling
21 fluid down through a non-perforated tubular string and out of the annulus
or
22 vice versa, to fluidize and remove the sand. However, in the case of a
23 perforated liner, the circulating fluid will reverse prematurely through
the
24 perforations and not reach the end of the liner. Thus, circulating fluid to
wash
3
CA 02212840 1997-08-13
1 out sand blockages preventing full insertion of the liner in a horizontal
2 wellbore is not available as a solution.
3 Secondly, it will be desirable in some cases to be able to keep
4 the liner and the positioning string to which it is attached empty or "dry'
when
easing it into the horizontal section of the wellbore. If the liner/string
unit is
6 filled with the fluid filling the wellbore, then the liner will bear against
the
7 bottom surface of the horizontal wellbore section wall. Being heavy and with
8 little string weight to help force it along, the liner is difficult to
advance. If the
9 liner/string unit can be kept empty, then buoyancy will assist in easing the
liner along the horizontal wellbore.
11 With this background in mind, it was therefore one objective of
12 the invention to modify a liner so that it could be "circulated into" the
wellbore.
13 It was a second preferred objective to provide a liner that could be
"floated
14 dry" into the wellbore.
16 SUMMARY OF THE INVENTION
17 In accordance with the invention, the side wall openings of each
18 screened section of the liner are temporarily blinded with heat-liquefiable
solid
19 sealant. The sealant selected is capable of remaining solid and in place
when
exposed to reservoir temperature and pressure as well as circulating
21 pressure, yet it will liquefy when contacted by steam, hot oil or water. By
22 temporarily blinding the openings with a pressure-resistant sealant,
circulation
23 can thereafter be carried on through the full length of the assembled
liner.
4
CA 02212840 2001-04-18
1 Suitable materials for use as the sealant are wax, asphalt or roofing tar.
2 The preferred material is wax because it leaves no residue when liquefied or
melted.
3 Tests with a mixture of wax and roofing tar indicated that the seal would
adequately
4 hold pressure but tar residue after melting would partly block the screen
openings.
We have successfully used petroleum wax having a melting point of about
60°C as
6 the liner sealant in wells having a vertical depth of 160 meters and
reservoir
7 temperature and pressure of 8°C and about 350 psi.
8 We have used two approaches in blinding the openings. In earlier
9 experiments, an internal sleeve of sealant was formed by placing a tubular
mandrel
within the bore of an upstanding liner joint and pouring hot sealant into the
annular
11 space between the mandrel and joint. The sealant would penetrate out into
the
12 screen openings. On cooling, the mandrel would be extracted leaving a
circulation
13 bore extending through the sleeve. It was believed that the thick sleeve
was needed
14 to resist pressure. However, in later tests involving wax sleeves, the
sleeve was
bored out and the sealant in the openings was found to be adequately resistive
to
16 leakage under pressure.
17 Preferably, a one-way valve is attached to the leading end of the liner.
18 This allows the liner to be run "dry" or empty into the fluid-filled
wellbore. Buoyancy
19 thus can assist in advancing the liner through the horizontal wellbore.
In one aspect, broadly stated, the invention comprises a method for
21 landing a sand control liner in a horizontal wellbore penetrating a
subterranean sand
22 reservoir, comprising providing a tubular liner having upper and lower ends
and a
23 side wall forming screen sections having openings for enabling formation
fluid to
24 enter the bore while screening out sand carried by the fluid, said openings
being
temporarily blinded by a heat-liquefiable solid sealant; running the blinded
liner into
s
CA 02212840 2001-04-18
1 the wellbore on the end of a tubular string and, on encountering a sand
blockage,
2 circulating fluid through the full length of the blinded loner to remove the
blockage;
3 and when the liner has reached its landing position in the wellbore, then
contacting
4 the sealant with hot fluid to liquefy it and open the openings for the
production of
fluid.
6 In another aspect, broadly stated, the invention comprises a blinded
7 sand control liner joint for running into a wellbore penetrating a fluid-
producing
8 subterranean sand reservoir, said liner having upper <~nd lower ends,
comprising a
9 tubular liner formed of joints connected end-to-end, some of the joins
having
transverse openings forming a screen section for admitting fluid and rejecting
sane;
11 heat-liquefiable solid sealant blinding the openings, said sealant being
selected to
12 remain solid and in place at circulating pressure but to liquefy when
contacted by
13 steam; said liner forming an open central longitudinal bore; and one way
valve
14 means, attached to the liner at its lower end, for preventing the ingress
of fluid into
the liner bore from its lower end by permitting fluid to be pumped through the
valve
16 means from the liner bore.
17 DESCRIPTION OF THE DRAVNINGS
18
19 Figure 1 is a schematic showing a method for constructing the blinded liner
joint;
21 Figure 2 is a side sectional view showing a blinded liner joint having a
sleeve,
22 together with the top centralizes, bottom sealing and centralizing cap and
forming
23 mandrel used in constructing the sleeve, with some structural details
omitted to
24 simplify the drawing;
Figure 3 is a plan view of the top centralizes;
6
CA 02212840 1997-08-13
1 Figure 4 is a side sectional view of the bottom cap;
2 Figure 5 is a partly broken away perspective view of the wire-
3 wrapped screen section of the joint shown in Figure 1;
4 Figure 6 is an expanded perspective view of the "wire wrap" and
rods, showing keyhole apertures; and
6 Figure 7 is a side sectional view of the blinded liner equipped
7 with a one-way valve, ready for running into the wellbore.
8
g DESCRIPTION OF THE PREFERRED EMBODIMENT
Having reference to Figure 7, a blinded liner 1 comprises a
11 series of screened joints 2, separated by blank joints 2a, connected
together
12 end-to-end by threaded connections. Each screened joint 2 has an internal,
13 annular, solid sleeve 3 of sealant blinding its openings 4.
14 The liner joint 2 shown in Figures 2, 5 and 6 is conventional. It
comprises a steel base pipe 5 having transverse perforations 6. Rods 7 are
16 welded to the outside surface 8 of the base pipe 5. These rods 7 extend
17 longitudinally of the base pipe at positions spaced around its
circumference.
18 A spirally wrapped steel wire 9 forming of vertically spaced apart steel
rings
19 10 is positioned over the rods 7 and perforations 6. The rings 10 are
welded
to the rods 7. They have generally triangular cross-sections so that
21 "keystone" apertures 11 are formed between them. In summary, the liner
joint
22 2 comprises a perforated base pipe 5 carrying an external "wire wrap"
screen
23 12 positioned over the perforations 6. (The term "openings" used in the
24 claims is intended to mean the fluid passageways formed by the combination
of the keystone apertures 11, spaces 13 between the rods 7 and perforations
7
CA 02212840 1997-08-13
1 6. ) The keystone apertures 11 are operative to screen out or reject coarse
2 sand grains carried with produced fluid.
3 To form or construct the sleeve 3, the following procedure is
4 practiced. A tubular mandrel 20 is centrally positioned within the bore 4 of
a
vertically oriented joint so as to extend coaxially and longitudinally
thereof.
6 The mandrel 20 is inwardly spaced from the inside surface 21 of the base
7 pipe 5, to cooperate therewith to form an annular space 22. The bottom end
8 of the mandrel 20 rests on and is centered by the bottom cap 23, which is
9 threaded onto the lower end of the base pipe 5. The bottom cap 23 seals the
bottom of the annular space 22. A centralizes 25 has openings 27 so that
11 liquid sealant may be poured into the annular space 22.
12 As previously stated, the preferred sealant is petroleum wax
13 having a melting temperature of about 60°C.
14 The outside surface 28 of the screen 12 is wrapped with a
wrapping 30 of silicon-coated paper held in place with duct tape. Hot liquid
16 sealant 32 is poured into the annular space 22. The sealant penetrates the
17 openings perforations 6, spaces 13 and apertures 11. On cooling, the
sealant
18 forms a solid sleeve 3 having "fingers" extending into and sealing the
19 passageways. The sealant provides a liquid-tight seal. The solid sealant
plugs within the tapered keystone apertures 11 are particularly resistive to
21 displacement by internal pressure during circulation.
22 The mandrel 20 can then be loosened by heating it internally
23 and removed, together with the centralizes 25. The bottom cap 23 is
24 unscrewed from the base pipe 5. This leaves a central bore extending
longitudinally through the sleeve 3.
8
CA 02212840 1997-08-13
1 In later tests, the sleeve 3 has been bored out and it has been
2 determined that the "fingers" alone are adequate to provide the pressure-
3 holding seal of the passageways, that is needed.
4 A one-way valve 34 is attached to the leading end of the first
joint of the liner. The remaining joints are then connected and the liner is
6 ready to be run into the wellbore.
7 Pressure Test
g If fluid, such as water, oil or drilling mud is to be circulated
9 through a blinded liner, there will be pumping pressure ("circulation
pressure")
acting on the fluid moving through the liner. The wells in which the liners
were
11 to be run were quite shallow, having a vertical depth of about 160 meters.
12 These wells were being completed in the Athabasca oil sands in Alberta. It
13 was therefore anticipated that the blinded liner would be subject to a
pressure
14 differential across the sealant-filled screen openings in the order of 200
psi.
It was desirable to bore out the sealant sleeve in each joint
16 before running it into the wellbore, so the full diameter of the base pipe
would
17 be open. However, it was a concern that the fingers of sealant might blow
out
18 or leak if such internal pressure was applied.
1 g Therefore, a pressure test was carried out on a wax-sealed,
bored-out liner joint, to determine the strength of the seal.
21 More particularly, a blank coupling was threaded onto one end
22 of the test joint and a coupling having a 2-inch inlet was threaded onto
the
23 other end. The joint was filled with water and pressure tested at 200 psig
for
24 3 hours without leakage. The pressure was then increased to determine the
9
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1 upper limit for pressure containment - the seal did not leak until a
pressure of
2 about 800 psig was applied.
3 Field Test Involvin4 Circulation
4 Wax-blinded liners were tested in a pair of wells extending
horizontally about 750 meters into an unconsolidated oil sand at a depth of
6 about 160 meters. The reservoir temperature and pressure were 8°C and
7 about 200 psi.
g The wells were completed with about 750 meters of 7-112 inch
9 diameter wire-wrapped liners comprising 40 foot joints, each having about 10
feet of screen. In each case, the joints had been sealed with an internal
11 sleeve of wax extending into the screen openings. The internal sleeve had
12 been bored out before use in the well.
13 The liner for the first well was fully inserted without any need to
14 circulate to clear sand blockages. Once in place, it was circulated with
water
to remove drilling fluid and observations of fluid return volumes and samples
16 of water indicted that the wax seal remained in place throughout
emplacement
17 and circulation.
1 g The second well provided proof that the wax sealed liner could
19 be used to circulate drilling fluid and clear sand blockage from the
wellbore.
The liner was being run into the horizontal wellbore and had completed about
21 500 meters of the planned 750 meter insertion without incident with a
modest
22 "pulldown" force on the liner of about 7000 daN. At about the 540 meter
point,
23 a sand blockage was encountered and the pulldown force required jumped
24 from 7000 daN to 30,000 daN, thereby ending any possibility of pushing the
liner further into the wellbore. The liner was pulled back about 1 meter using
CA 02212840 1997-08-13
1 a very high pullback force of 50,000 daN. Drilling fluid was then circulated
in
2 through the liner and out the annulus for about 0.5 hours. Running of the
liner
3 was then recommended. The liner moved forward into the well to the full
4 depth of 750 meters with a pulldown force of 7000 daN. After full insertion,
water was circulated through the liner. Observations of water returns
6 indicated that the wax seal still remained in place after circulation to
remove
7 the sand blockage.
8 Field Test Involvin4 Seal Removal
g In another well, having a horizontal wellbore extending about
500 meters, a 7-1/2 inch diameter wire-wrapped liner having blinded joints
11 was inserted without incident. The blinded joints contained a wax sleeve
12 having a 4-inch bore. After emplacement, the sleeve was bored out with a
13 drill bit. Steam was then circulated through the liner and back up the
annulus
14 for 24 hours. After about 24 hours, the circulation pressure dropped,
indicating that the screen openings were being cleared. Subsequently, the
16 well was placed on production and oil was satisfactorily produced through
the
17 liner openings.
11
