AU2018267548B2

AU2018267548B2 - A method and system for borehole fracture zone sealing for drilling circulation mud loss control

Info

Publication number: AU2018267548B2
Application number: AU2018267548A
Authority: AU
Inventors: Ross Robson
Original assignee: Earth Technics Pty Ltd
Current assignee: Earth Technics Pty Ltd
Priority date: 2017-11-23
Filing date: 2018-11-19
Publication date: 2024-02-29
Anticipated expiration: 2038-11-19
Also published as: AU2018267548A1

Abstract

A method and apparatus for sealing fracture zones (loss zones) within boreholes where drilling circulation has been lost may comprise inserting a pair of conduits into the borehole having a pressurisation conduit operably coupled to an inflatable packer at the distal end of the conduits and a sealant conduit operably coupled to a delivery tube passing through the inflatable packer. When the distal end of the packer reaches a level just above the loss zone, the pressurisation conduit is pressurised with air to inflate the packer in order to set the packer in place. When set in this manner, the delivery tube extends beneath the packer and is held thereby. A set amount of hydrophilic polyurethane is injected via the sealant conduit to be injected into the loss zone below the packer and via the delivery tube. The set amount of hydrophilic polyurethane may be chased down the sealant conduit by an inert non-compressible substance, such as biodegradable vegetable oil. Once injected beneath the packer, the polyurethane expands when in contact with water to typically between 5 - 7 times the original volume, the polyurethane being forced into the loss zone fractures within the confined space enclosed by the packer above. The polyurethane sets in about two minutes. Thereafter, the conduits (polypipes) are broken from the packer and delivery tube by way of a breakable joiner for retrieval. 9 Il/ I 101 100 1121/ 102 107 --- 106 113 108 110 F5 1\l04 Figure 1

Description

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Figure 1

A method and system for borehole fracture zone sealing for drilling circulation mud loss control Field of the Invention

[1] This invention relates generally to a method and system for sealing fracture zones within boreholes where drilling circulation mud has been lost. The method applies especially, but not necessarily, for exploration boreholes.

Background of the Invention

[2] Exploration boreholes are typically of 100 mm in diameter and varying depths, sometimes down to 1,000 metres. .

[3] A series of connectable drillrods having a drillbit at a distal end thereof (a "drill string") is caused to rotate and drills the borehole.

[4] Drilling "mud", typically water with additives, is injected via the drill string causing drill cuttings to return to the surface under pressure.

[5] However, drilling mud is sometimes lost to localised fracture zones in the surrounding rock (called a "loss zone") such that the cuttings no longer return to the surface.

[6] This is problematic in that the borehole can become clogged with the cuttings and jam the drill string. Furthermore, the rock cuttings are needed for identification and sampling. (It has been estimated that between 10 and 20 percent of drilling costs on deeper exploration boreholes are caused by lost circulation problems. If circulation cannot be recovered, the borehole may have to be abandoned, invariably before the target depth or zone has been reached)

[7] As such, conventional arrangements for eliminating the loss zone comprise retracting the drill string (soon after encountering the loss zone) and inserting a concrete injecting drill string or tubing to inject concrete. The concrete is injected in order to seal the fractures of the loss zone. The concrete is injected both adjacent to and above the loss zone

[8] Typically, the concrete is emplaced within the loss zone and to a level quite high above the loss zone (typically 20 to 50 metres) in order to confer the requisite hydrostatic pressure to force the concrete into the loss zone fractures. (The borehole is not pressurised and uses the weight of the concrete column to provide the hydrostatic pressure.)

[9] The concrete is then left for about a day or so whereafter the drill string is reinserted into the borehole in order to drill through the concrete and continue the borehole drilling process.

[10] However, such an approach is expensive in that a day may be lost in injecting and allowing the

concrete to set and a further day or two lost in drilling through the set concrete, especially in that a

relatively long column of concrete is typically set.

[11] Furthermore, approximately 30% of concrete seals fail, requiring one or more repeats of the "cementing up" process

[12] The present invention seeks to provide a way which will overcome or substantially ameliorate

at least some of the deficiencies of the prior art, or to at least provide an alternative.

[13] It is to be understood that, if any prior art information is referred to herein, such reference

does not constitute an admission that the information forms part of the common general knowledge

in the art, in Australia or any other country.

Summary of the Disclosure

[14] There is provided herein a method and apparatus for sealing fracture zones (loss zones) within

boreholes where drilling circulation has been lost.

[15] The method comprises inserting a pair of conduits into the borehole. The pair of conduits

comprise a pressurisation conduit operably coupled to an inflatable packer at the distal end of the

conduits and a sealant conduit operably coupled to a delivery tube passing through the inflatable

packer.

[16] Preferably, the pair of conduits are coaxial and, furthermore, flexible (such as "poly pipe") so

as to allow feeding from a motorised trellis or coiled drum.

[17] When the distal end of the packer reaches a level just above the loss zone, the pressurisation

conduit is pressurised with air to inflate the packer in order to set the packer in place. When set in this

manner, the delivery tube extends beneath the packer and is held thereby.

[18] A set amount of hydrophilic polyurethane is injected via the sealant conduit to be injected

into the loss zone below the packer and via the delivery tube. The set amount of hydrophilic

polyurethane may be chased down the sealant conduit by an inert non-compressible substance, such

as biodegradable vegetable oil.

[19] Once injected beneath the packer, the polyurethane expands when in contact with water to

typically between 5 - 7 times the original volume, the polyurethane being forced into the loss zone

fractures within the confined space enclosed by the packer above. The polyurethane sets in about two

minutes.

[20] Thereafter, the conduits (polypipes) are broken from the packer and delivery tube by way of

a breakable joiner for retrieval.

[21] The drill string is then reinserted into the borehole to continue drilling.

[22] As can be appreciated, the presently provided methodology greatly reduces the time involved

in sealing the loss zone. Specifically, the packer may be set and the hydrophilic polyurethane injected

and set relatively quickly. It is envisaged that drilling may recommence within 2 - 3 hours with the

present methodology.

[23] Furthermore, the reinserted drill string and drill bit will very easily drill through the packer,

set polyurethane and delivery tube (which may be a perforated aluminium tube) as compared to a

column of concrete having substantial length as per prior art methods. (The prior art method requires

the drilling out of the concrete which is invariably extends 20 and 50 metres in length).

[24] According to one aspect, a method for borehole fracture zone sealing for drilling circulation

mud loss control, comprises inserting a pair of conduits into the borehole, the pair of conduits

comprising a pressurisation conduit operably coupled to an inflatable packer at a distal end of the

conduits and a sealant conduit operably coupled to a delivery tube passing through the inflatable packer, when the distal end of the conduits reaches a loss zone, pressurising the pressurisation conduit

to inflate the inflatable packer; injecting hydrophilic polyurethane fluid via the sealing fluid conduit

such that the polyurethane is injected into the borehole beneath the packer; retrieving the conduits,

leaving the packer and delivery tube in place.

[25] The method may comprise injecting a set amount of hydrophilic polyurethane. The hydrophilic

polyurethane may be chased with a liquid. The liquid may be an oil. The oil may be vegetable oil.

[26] The delivery tube may be rigid. The delivery tube may be metallic. The delivery tube may

comprise aluminium.

[27] The delivery tube may comprise a plurality of apertures there along.

[28] The method may comprise allowing the hydrophilic polyurethane to set for approximately ten

minutes.

[29] The method may further comprise a breakable joiner interfacing the conduits and the packer

and the delivery tube. The breakable joiner may sever under tension.

[30] The packer may comprise a rubberised bladder.

[31] The method may further comprise a gland arrangement at a proximal end of the conduits for

separating out the pressurisation and sealant conduits. The conduits may be coaxial. The conduits may

be flexible. The conduits may comprise polyethylene pipes.

[32] Other aspects of the invention are also disclosed.

Brief Description of the Drawings

[33] Notwithstanding any other forms which may fall within the scope of the present invention,

preferred embodiments of the disclosure will now be described, by way of example only, with reference to the accompanying drawings in which Figure shows a system for borehole fracture zone sealing for drilling circulation mud loss control, in accordance with an embodiment.

Description of Embodiments

[34] Figure shows a system 100 for borehole 106 where a localised rock fracture zone has allowed

drilling mud to be lost into the rock strata. This is a lost circulation zone 110 (or loss zone) and requires

sealing in order that drill mud circulation can be recovered and drilling of the borehole can be

progressed (drilled deeper). In summary, the borehole 106 has a loss zone 110 via which drilling mud

111 is lost to the surrounding rock strata.

[35] As such, for sealing the loss zone 110, the drill string is removed, and the apparatus shown in Figure 1 inserted.

[36] The apparatus comprises a pair of conduits 107 comprising a pressurisation conduit 102

operably coupled to an inflatable packer 103 at a distal end of the conduits and a sealant conduit 101

operably coupled to a delivery tube 104 passing through the inflatable packer 103. A gland

arrangement 112 may separate the pressurisation conduit 102 and the sealant conduit 101 at a

proximal end of the conduits 107.

[37] In a preferred embodiment, the pair of conduits are coaxial as is shown in Figure 1 and further

manufactured from a suitably flexible material, such as "poly piping" so as to allow the conduits 107

to be trellis or drum fed. A conduit trellis or drum housing polypipe of a suitable length may be on

standby for drilling operations which may, for example, be truck mounted and motor driven. When

required, the conduit may be lowered down the borehole 106 from a motorised trellis or the like or

alternatively lowered inside an open ended drill string which would terminate in depth above the level

of setting the packer. (in order that the packer be set against the rock wall of the borehole)

[38] The conduits 107 are lowered into the borehole 106 until the distal end of the packer reaches

a depth a little above the top of the loss zone 110. The conduits 107 may comprise depth markings to

allow an operator to gauge the depth of insertion.

[39] Once at the requisite depth, the pressurisation conduit 102 is pressurised to inflate the packer

103.

[40] As such, the packer 103 swells to set within the borehole 106 as shown in Figure 1. The packer

103 may comprises a suitably resilient rubberised bladder, for example.

[41] In a preferred embodiment, the delivery tube 104 is substantially resilient so as to extend

rigidly from beneath the set packer 103.

[42] In embodiments, the delivery tube 104 may be manufactured from aluminium. Aluminium is

a relatively soft metal which may be relatively easily drilled through by the drillbit subsequently as

described in further detail below.

[43] The delivery tube 104 may comprise a plurality of apertures therealong to allow the

hydrophilic polyurethane to escape into the borehole 106 adjacent to the loss zone 110.

[44] A set amount of hydrophilic polyurethane 105 (preferably the closed cell type) is then injected

via the sealant conduit 101.

[45] In embodiments, the delivery tube 104 may comprise a one-way valve 108 at an entrance

thereof to prevent water rising within the sealant conduit 101 which may prematurely react with the

hydrophilic polyurethane within the sealant conduit 101.

[46] In embodiments, the set amount of hydrophilic polyurethane 105 may be chased by a non

compressible substance that does not react of the polyurethane, such as biodegradable vegetable oil or the like.

[47] The hydrophilic polyurethane 105 is injected via the delivery tube 104 beneath the packer

103.

[48] Beneath the packer 103, the hydrophilic polyurethane 105 comes into contact with water and

swells to typically 5 - 7 times the original volume. Within the confined space closed off by the packer

103 above, the expanding hydrophilic polyurethane 105 will force any free water in the confined space

into the rock fractures ahead of the rapidly expanding polyurethane mass 105., thereby sealing the

loss zone 110. (The expanded polyurethane fills and blocks the rock fractures for a distance of up to

300mm from the borehole walls)

[49] Typically, the hydrophilic polyurethane 105 sets within about ten minutes. (Can be made to

set faster with additives)

[50] Thereafter, the conduits 107 are retrieved, leaving the packer 103, delivery tube 104 and set

hydrophilic polyurethane 105 in place. (The delivery tube 104, and the base of the packer 103 will be cemented in place by the polyurethane 105).

[51] In this regard, the conduits 107 may connect to the packer 103 and delivery tube 104 by way

of a breakable joiner 109. A breakable joiner 109 may be engineered to disconnect under tension,

which will be applied by the motorised trellis at the surface.

[52] Once the conduits 107 are retrieved from the borehole, the drill string is reinserted into the

well to recommence drilling in the normal manner, wherein the drillbit drills through the in-place set

packer 103, delivery tube 104 and set polyurethane 105.

[53] In an embodiment, the pressurisation conduit comprises a diameter of 38.1 mm and the

sealant conduit 101 comprises a diameter of 25 mm.

[54] As can be appreciated, the present system and methodology may save at least 2 days of "drill

rig time" after the sealing of a loss zone has been undertaken and may furthermore seal rock fracture

zones (loss zones) within boreholes with more success and certainty than the current art form.

[55] The foregoing description, for purposes of explanation, used specific nomenclature to provide

a thorough understanding of the invention. However, it will be apparent to one skilled in the art that

specific details are not required in order to practice the invention. Thus, the foregoing descriptions of

specific embodiments of the invention are presented for purposes of illustration and description. They

are not intended to be exhaustive or to limit the invention to the precise forms disclosed; obviously,

many modifications and variations are possible in view of the above teachings. The embodiments were

chosen and described in order to best explain the principles of the invention and its practical applications, they thereby enable others skilled in the art to best utilize the invention and various

embodiments with various modifications as are suited to the particular use contemplated. It is

intended that the following claims and their equivalents define the scope of the invention.

Claims

Claims 1. A method for borehole fracture zone sealing for drilling circulation mud loss control, the method comprising: inserting a pair of conduits into the borehole, the pair of conduits comprising a pressurisation conduit operably coupled to an inflatable packer at a distal end of the conduits and a sealant conduit operably coupled to a delivery tube passing through the inflatable packer, when the distal end of the conduits reaches a loss zone, pressurising the pressurisation conduit to inflate the inflatable packer; injecting hydrophilic polyurethane fluid via the sealing fluid conduit such that the polyurethane is injected into the borehole beneath the packer; and retrieving the conduits, leaving the packer and delivery tube in place.
2. A method as claimed in claim 1, wherein the method comprises injecting a set amount of hydrophilic polyurethane.
3. A method as claimed in claim 1, wherein the hydrophilic polyurethane is chased with a liquid.
4. A method as claimed in claim 3, wherein the liquid is an oil.
5. A method as claimed in claim 4, wherein the oil is vegetable oil.
6. A method as claimed in claim 1, wherein the delivery tube is rigid.
7. A method as claimed in claim 6, wherein the delivery tube is metallic.
8. A method as claimed in claim 7, wherein the delivery tube comprises aluminium.
9. A method as claimed in claim 6, wherein the delivery tube comprises a plurality of apertures there along.
10. A method as claimed in claim 1, wherein the method comprises allowing the hydrophilic polyurethane to set for approximately ten minutes.
11. A method as claimed in claim 1, further comprising a breakable joiner interfacing the conduits and the packer and the delivery tube.
12. A method as claimed in claim 11, wherein the breakable joiner severs under tension.
13 A method as claimed in claim 1, wherein the packer comprises a rubberised bladder.
14. A method as claimed in claim 1, further comprising a gland arrangement at a proximal end of the conduits for separating out the pressurisation and sealant conduits.
15. A method as claimed in claim 1, wherein the conduits are coaxial.
16. A method as claimed in claim 1, wherein the conduits are flexible.
17. A method as claimed in claim 16, wherein the conduits comprise polyethylene pipes.
18. A method as claimed in claim 16, wherein the conduits are fed from a motorised trellis or

coiled drum into the borehole.
19. A method as claimed in claim 1, wherein the conduits comprise external depth markings.
20. A method as claimed in claim 1, further comprising inserting a drill string into the borehole

and boring through the packer, delivery tube and set hydrophilic polyurethane.