GB2431949A

GB2431949A - Thermoplastic resin to consolidate fractures

Info

Publication number: GB2431949A
Application number: GB0622056A
Authority: GB
Inventors: Angus Lewis-Smith
Original assignee: DOWNHOLE FLUID SOLUTIONS Ltd
Current assignee: DOWNHOLE FLUID SOLUTIONS Ltd
Priority date: 2005-11-07
Filing date: 2006-11-06
Publication date: 2007-05-09
Anticipated expiration: 2026-11-06
Also published as: WO2007052048A3; GB0522653D0; GB2431949B; GB0622056D0; WO2007052048A2

Abstract

A fusible composition for use downhole comprises a polymerisable thermoplastic resin, an initiator and a filler. The thermoplastic resin may be selected from petroleum resins, copolymer alkylaromatic/cycloaliphatic resins, modified resins containing hydroxyl or carboxyl groups, such resins being selectable to be thermally cured yet remain flexible upon curing within selected temperature ranges, say 50-90{C, 90-120{C, 120-140{C, and 140-160{C or above.Also present is a polymerisation initiator, and an inorganic filler such as particulate forms of limestone, marble, granite, clay, shale, ground salt, calcium carbonate, calcium oxide, dolomite, or mixtures of the aforesaid fillers. The resin and filler being can be mixed and delivered downhole in a fluid such that in use under the temperature and pressure conditions typically encountered downhole the resin cures in the composition, to form a fused flexible concretion.

Description

1 2431949 1 Improvements in materials for use in subterranean 2

formations 4 This invention relates to drilling operations conducted in oil-and gas-bearing formations, arid provides 6 improvements in materials for use in facilitating 7 drilling operations and mitigating problems often 8 encountered in drilling into formations which are S.....

9 unconsolidated or weakly pressured. S... S *

LJ **.. S...

11 Background to the Invention *,* :

13 Many oil and gas fields which have been producing for a 14 considerable time <mature assets) suffer pressure depletion in the rock structures to a considerable 16 degree. This can become so reduced that continued 17 drilling using the necessary density of drilling fluid 18 can cause induced fracturing which leads to serious loss 19 of drilling fluid. Furthermore, expansion of exploration has caused consideration to be given to naturally weak or 21 flawed formations which are inherently susceptible to 22 fractures.

1 The problems associated with weak formations often 2 manifest themselves as "lost circulation", for example 3 where the near weilbore rock structure is weakened to the 4 extent that it cannot contain the overpressure of the dynamically circulating drilling fluid, thus causing 6 induced fractures and mud losses. This problem is 7 described for example in outline in US 5,207282. The 8 formations into which the drilling fluid is lost are 9 often referred to as "lost circulation zones" or "thief zones".

12 The lost circulation encountered in the drilling of a 13 well can usually be attributed to a formation of 14 unusually high permeability, with crevices or otherwise S...

being highly susceptible to fractures to the extent that 16 it is simply not sufficiently competent to support the 17 hydrostatic pressure applied by the drilling fluid, and 18 the bore breaks down under this hydrostatic pressure and 19 allows the drilling fluid to flow away into the formation. US 5,207,282 proposes use of an additive to:::: 21 the circulation fluid in the form of a loss prevention 22 material selected from petroleum coke, gilsonite, calcium 23 carbonate, glass, ceramics, polymeric beads and nut 24 shells.

26 One of the limiting factors in drilling a particular 27 portion of a well is the mud weight (density of the 28 drilling fluid) that can be used. In many cases, wells 29 are drilled through weak or lost-circulation-prone zones prior to reaching a potential producing zone, requiring 31 use of a low mud weight and installation of sequential 32 casing strings to protect weaker zones above a potential 33 producing zone. However, use of casing strings is 1 disadvantageous and elimination of even one casing string 2 from a well provides important savings in time, material 3 and costs of drilling the well. Thus whilst it is known 4 in the art that problems of weak formations generally can be addressed by installing casings for completion and 6 production, introduction of such structures adds labour, 7 time and costs to the operation, and does not deal with 8 the immediate problem encountered in the initial drilling 9 operation.

11 Therefore, quite apart from the lost circulation fluid 12 standpoint, drilling operations in oil-and gas-bearing 13 formations can be otherwise hampered by the aforesaid 14 instability in the formation leading to fractures in the ***.

bore. In-fall of material can occur dramatically upon 16 the drill-string in weak zones of the formation, trapping 17 the drill-string and leading to downtime whilst recovery 18 and remedial steps are taken. Such potential problems 19 may become apparent during drilling into a weakly S..

consolidated formation, when excessive consumption of 21 drilling fluid due to losses into the formation is: 22 observed but the ability to counter the potential 23 collapse around the drill remains a problem to be solved 24 reliably.

26 An apparently simple approach to the problem of lost 27 circulation is to lower the density of the drilling fluid 28 but this is not satisfactory because this can exacerbate 29 the risk of collapse of the borehole around the drilipipe leading to trapping of the drill-pipe and significant 31 hold-up in drilling operations whilst recovery and 32 remedial steps are taken.

1 The induced fractures might possibly be sealed by pumping 2 down cement but the attendant downtime associated with 3 setting up and taking down the equipment for such an 4 operation leads to excessive cost burdens. For example, to pump down cement means a lot of expensive downtime 6 while setting up and taking down the equipment required.

7 This can be as much as a full day and at rig rates as 8 much as $500,000 per day this can be excessive.

9 Furthermore, the cement can be too dense and exacerbate the induced fracture and circulation fluid losses. The 11 density of cement can require a very large volume to be 12 pumped to address the fracture problems, and the length 13 of time required to cure the cement can be viewed as 14 unacceptable for the needs of the driller. *..S ***

16 Thus alternatives have been considered such as borehole 17 reinforcements, e.g. gravel packs which are also 18 expensive. Furthermore, in US 6,273,192 Bi, there is 19 described a proposal involving injection of aqueous gellable compositions including cross-linkable polymers *.S.

21 downhole in an effort to stabilise the weilbore and.. : 22 inhibit fractures. The aqueous composition described 23 there is used together with a non-gellable fluid, such as 24 diesel fuel for an oil-bearing formation, and a C6 or less hydrocarbon gas or an inert gas such as nitrogen for gas- 26 bearing formations. In use, the gellable composition and 27 non-gellable fluids are injected alternately, the 28 gellable composition intended to stabilise the near 29 weilbore area, whilst the non-gellable fluid is intended to maintain a clear production flow path in the borehole.

31 A method of reducing formation breakdown during a 32 drilling operation is also described in WO 2005/012 687, 33 where a circulating fluid including a fluid loss additive 1 and a solid particulate material is forced under pressure 2 into the weilbore, the intention being that fractures are 3 formed and bridged by the particulate material which also 4 facilitates the function of the usual fluid loss inhibitors which may precipitate upon the particulate 6 material or fill voids around them.

8 Despite these prior art proposals to address the

9 attendant problems of weak formation drilling, there remains to be found a reliable method of addressing them.

11 Accordingly, an object of the present invention is to 12 obviate or mitigate the problems associated with drilling 13 operations to be conducted in weakly consolidated 14 formations. * S S.

16 A further object of the invention is to provide a method 17 of stabilising boreholes in formations susceptible to 18 fractures during drilling. * S S...

A further object of the invention is to provide fluids 21 for use together for the purpose of stabilising boreholes 22 in formations susceptible to fractures during drilling.

24 A further object of at least one embodiment of the invention is to provide a method and composition capable 26 of strengthening the near weilbore in a weak or 27 unconsolidated formation.

29 A further object of at least one embodiment of the invention is to provide a method and composition for 31 providing reinforcement to a weak formation around a 32 weilbore, in the form of a fused, flexible concretion or 1 stress cage having a limited penetration into the 2 formation.

4 Summary of the Invention

6 According to the present invention the problems 7 associated with drilling in oil-, and gas-bearing 8 formations are addressed by providing at the welibore 9 surface susceptible to induced fractures a stabilising composition comprising physically interacting organic and 11 inorganic components, which together form a flexible 12 fused sealing composition in the induced fractures. This 13 is achievable by judicious selection of thermoplastic S...

14 polymerisable resin materials coupled with generally inert inorganic fillers, in particulate form sized for 16 convenient mixing and delivery in a fluid, pumpable 17 downhole generally in the same manner, and using the same 18 equipment as for a drilling fluid, circulation fluid, 19 completion fluid etc. The polymerisation is thermally S...

activated in the presence of a suitable initiator. It is 21 preferred to select components which will not require a 22 chemical reaction to provide an acceptable result, hence 23 the preference for thermoplastic resins and inorganic 24 filler, which in use as described herein are physically interacting organic and inorganic components.

27 A suitable composition comprises a polymerisable resin, 28 preferably a flexible resin, such as a low molecular 29 weight thermoplastic resin, preferably an olefinic resin, or copolymer resin provided in a particle size which 31 enables the resin to be suspended in an aqueous fluid, 32 the said resin being one which in use, in the presence of 33 an initiator, and under the temperature and pressure 1 conditions typically encountered downhole cures in the 2 composition, to form therefrom a fused flexible 3 concretion preferably with a degree of resilience which 4 assists in the retentive properties thereof in situ in an induced fracture.

7 Thermoplastic petroleum resins (a class of hydrocarbon 8 resins) obtained as a variable mixture of unsaturated 9 monomers as by-product from cracked and distilled petroleum streams are one group of resins useful for the 11 purposes of the invention. Such may contain indene, 12 which is co-polymerisable with other unsaturated monomers 13 including styrene, vinyl toluene, and methyl indene.

14 These have an aromatic character but an important feature thereof in relation to this invention is the presence of 16 an available vinyl group (unsaturated and reactive and 17 thus available for polymerisation of the resin in the 18 presence of an initiator under the elevated temperature **.* 19 and pressure conditions encountered downhole). Copolymer resins such as alkylaromatic/cycloaliphatiC resins, and * * 21 modified alkylaromatic/cycloaliphatiC resins are another 22 useful group. Hitherto these have been typically used in 23 printing inks and are obtainable from Neville Chemical 24 Europe.

26 A common feature of these resins is the ability to form a 27 thermoplastic resin mass by polymerisation between 28 unsaturated groups of the respective resin components 29 which may be the same or different, in the presence of a suitable initiator under elevated thermal conditions, 31 e.g. a free-radical generator to promote polymerisation.

32 The composition also contains a particulate inorganic 33 filler material, which may be sand, aggregate fines, or 1 other particulate matter or fibres which can be suspended 2 in water or an aqueous fluid such as would be suitable 3 for circulation downhole. The composition may optionally 4 include fluid formulation auxiliaries or other additives such as a bonding agent or setting additive or the like, 6 suspending agents, surfactants, solvents, viscosity 7 modifiers, or thickeners selected from those considered 8 to be compatible with the polymerisable thermoplastic 9 resin.

11 In use the inorganic filler is retained by the physical 12 form of the cured resin.

14 It is known in the art that borehole temperatures can vary over a wide range in temperature and pressures, 16 typically say from 50 -160 C (perhaps 30 -260 C /100 - 17 500 F in extremes) and ambient pressure to 20,000psi 18 (-137.9MFa). Therefore, it may be preferred to have a 19 selection of resins, same being selected to provide a group within which a resin may be selected to suit the 21 conditions at the drilling zone (depth). Thus one may 22 conveniently select and provide a group of resins, 23 respectively adapted to cure, yet remain sufficiently 24 flexible (soften slightly) to envelope and retain particulates, in the ranges of say, 50-90 C, 90-120 C, 26 120-140 C, arid 140-160 C or above. The fusible 27 compositions intended for use under different zone 28 conditions may vary in terms of the thermoplastic resin 29 which may be chemically modified, branched or differ in chain length or in degree of unsaturation, and in terms 31 of any associated auxiliaries utilised to obtain 32 appropriate performance of the resin in the respective 33 fusible composition.

2 The fusible compositions of this invention may comprise 3 hydrocarbon resins of low molecular weight (average 300 -4 1400) 6 Thus according to an aspect of the present invention 7 there is provided a fusible composition for use dowrxhole, 8 particularly for use prior to, or during a drilling 9 operation, comprising a polyinerisable thermoplastic resin, a polymerisation initiator and an inorganic 11 filler, the said resin being one which in use under the 12 temperature and pressure conditions typically encountered 13 downhole cures in the composition, to form therefrom a 14 fused flexible concretion. The thermoplastic resin, initiator, and inorganic filler and any other desired 16 additives or auxiliaries are provided in a form suitable 17 for incorporation in a fluid, which may be an aqueous 18 fluid, e.g. water or brine, for the purposes of delivery 19 dowrihole. A particulate, coxmninuted, or microbead form 0*** may be conveniently delivered in water, using if I...

21 necessary a viscosifying agent or surfactant or 22 emulsifier to provide a pumpable fluid. This is 23 conveniently prepared on site using standard mud-mixing 24 equipment on the rig.

26 The fusible thermoplastic resin may comprise a petroleum 27 fraction comprising unsaturated components of from eight 28 to twelve carbon atoms, preferably at least eight to ten 29 carbon atoms. Thus the resin may comprise at least one of the following polymerisable components: vinyltoluene, 31 indene, niethylindene, aipha-methyistyrene, styrene, a 32 cyclic conjugated diene such as an optionally alkyl- 1 substituted dicyclopentadiene, or a mixture of any of the 2 aforesaid components and analogues thereof.

4 An appropriate thermoplastic resin may comprise an aromatic mono-olef in, optionally an alkyl-substituted 6 aromatic mono-olef in such as a di(alkyl)- 7 dicyclopentadiene.

9 Where the resin comprises an optionally alkyl substituted molecule, the substituent may be a lower alkyl (C1-C4) 11 substituent, preferably a methyl group.

13 The fusible composition may comprise a resin which 14 comprises co-polymerisable components suitable for forming a copolymer alkylaromatic/cycloaliphatic resin.

16 The resin may comprise co-polymerisable components, at 17 least one of which comprises a hydroxyl group, or a 18 carboxyl group, for forming a functionalised (modified) 19 resin. * * * . .

21 The fusible composition may comprise, as the inorganic 22 filler, a particulate material selected from sand, 23 aggregate fines or other particulate matter or fibres 24 which can be suspended in water or an aqueous fluid such as would be suitable for circulation downhole.

27 The inorganic filler may comprise at least one of 28 limestone, marble, granite, clay, shale, ground salt, 29 calcium carbonate, calcium oxide, dolomite, or mixtures of the aforesaid fillers.

32 In the situation where the selected inorganic filler is a 33 water-soluble filler, it may be provided for mixing with 1 the thermoplastic resin component(s) as a saturated or 2 super-saturated solution, thick slurry, suspension or 3 paste.

The fusible composition may optionally comprise at least 6 one additive or auxiliary selected from a bonding agent 7 or setting additive or the like, suspending agents, 8 surfactants, solvents, viscosity modifiers, or thickeners 9 selected from those considered to be compatible with the thermoplastic resin.

12 The additive may comprise at least one surfactant 13 selected from anionic surfactants, non-ionic surfactants, 14 and ionic surfactants, and may include at least one phosphate surfactant. * * *.*.*

17 The properties of the composition are such that upon: **.. ** 18 introduction into the welibore at a predetermined zone, 19 the aqueous content of the composition seeps away or is *0* driven off under pressure, whilst the resin and 21 particulates become packed into the induced fractures, 22 and in the presence of an initiator, the resin cures and 23 provides a flexible fused compacted mass which does not 24 shrink like cementitious compositions of the prior art.

Such a fusible composition if sample-tested before use 26 may be found to be rigid and inflexible at topside 27 surface ambient conditions, but on account of the 28 thermoplastic nature of the resin selected for use in a 29 particular temperature zone, it is adequately flexible to achieve well strengthening under downhole conditions to 31 stabilise induced fractures arising during drilling 32 operations.

1 Appropriate selection of the temperature range of the 2 thermoplastic resin component enables the use of the 3 composition at a range of depths whilst ensuring that the 4 thermoplastic resin will at the intended zone become sufficiently pliable to envelope or bind with inorganic 6 filler components to form a stabilising concretion.

8 According to one aspect of the invention1 a method of 9 drilling in oil-, and gas-bearing formations wherein a welibore surface susceptible to induced fractures is 11 encountered, comprises providing a dry mix of 12 particulates comprising a thermoplastic resin and 13 inorganic materials in a predetermined ratio together 14 with a polymerisation initiator, introducing the dry mix to an aqueous fluid to form a liquid suspension, 16 introducing the liquid suspension under pressure into the 17 weilbore to contact a selected zone surface during a 18 drilling operation, whereby induced fractures are filled 19 with the suspension, and water is substantially driven S..

out depositing a fusible mass of resin and inorganic 21 materials in intimate contact, which in the presence of 22 the initiator under conditions of temperature and 23 pressure normally prevailing in the borehole, form a 24 fused flexible sealing composition in the induced fractures.

27 optionally, a separate liquid suspension of a particulate 28 inorganic material, such as sand, may be introduced 29 initially, as a first step, to pack the induced fractures with sand before the suspension of fusible mass of resin 31 and inorganic materials is introduced to the welibore.

32 According to an aspect of the invention, a kit for use in 33 drilling in oil-, and gas-bearing formations susceptible 1 to induced fractures comprises a plurality of dry-mix 2 containers, each containing a fusible mix of 3 thermoplastic resin and inorganic materials, together 4 with an appropriate polymerisation initiator, the resin in each being adapted to cure and remain flexible within 6 a predetermined range of temperatures, whereby the full 7 range of conditions to be anticipated during the drilling 8 operations can be accommodated by appropriate selection 9 amongst the plurality of dry-mix containers. The mix preferably is a ready to use" pre-mix of appropriately 11 sized particulates, and already including any 12 polymerisation initiator, bonding agent or setting 13 additive required, or other auxiliaries optionally 14 selected from surfactants, a natural or synthetic suspending agent, viscosity modifiers or thickeners, 16 selected from those compatible with the thermoplastic *...

17 resin. The particulate sizes are such as to permit 18 mixing of the materials using on-rig mud handling and 19 mixing equipment, and to be pumpable when mixed with S...

water using circulation fluid or mud pumps. These will 21 already be familiar to those in the art accustomed to use 22 of such equipment on the rigs.

24 Since the composition of the invention is not intended to react chemically, but rather interact physically when 26 deployed at depth during a drilling operation, it is 27 remarkably stable topside when made up in suspension in 28 water or an aqueous fluid with minimal need for 29 subsequent agitation, and so according to another aspect of the invention, a further kit including "ready for use" 31 suspensions is provided for use in drilling in oil-, and 32 gas-bearing formations susceptible to induced fractures, 33 said suspensions being provided respectively in a 1 plurality of containers, each containing an aqueous 2 suspension of a fusible mix of thermoplastic resin and 3 inorganic materials, the resin in each case being adapted 4 to cure and remain flexible within a predetermined range of temperatures (as hereinbefore described), whereby the 6 full range of conditions to be anticipated during the 7 drilling operations can be accommodated by appropriate 8 selection amongst the plurality of containers containing 9 ready-for-use suspensions.

11 Optionally, a separate liquid suspension of a particulate 12 inorganic material, such as sand, may be provided for use 13 prior to the use of the suspensions of fusible mass of *...

14 resin and inorganic materials. Such a separate liquid suspension serves as a pre-pack for the induced fractures 16 to facilitate the later fusing of thermoplastic resin and 17 inorganic particles in certain unconsolidated formations.

S.....

18 The use of inert inorganic materials in any aspect of 19 this invention may be augmented by or partially substituted by, the use of fibrous material of a size *: 21 which enables the fibres to be incorporated in the 22 suspensionS of fusible materials, and subsequent 23 operational use of the suspensions of fusible materials 24 in the intended purpose with improved bonding.

26 The invention will now be further explained by way of the 27 following examples which are intended to provide 28 illustrative embodiments of the invention to demonstrate 29 how performance of the invention may be put into practice.

1 Example 1

3 In a first embodiment of the invention, to be applied in 4 a drilling operation to be conducted in a formation anticipated as being poorly consolidated, e.g. containing 6 dolomitic limestone or the like readily fractured rock 7 structure, a kit of materials is provided for make-up on-8 site as required. The kit includes several dry pre-mixes 9 of materials in appropriate proportions intended to conform to a predetermined weilbore strengthening or 11 stabilisation composition suitable for particular 12 anticipated conditions in the welibore. The dry pre- 13 mixes are intended to be mixed into an aqueous fluid to a...

14 provide a pumpable suspension using the available on-site mud mixing equipment typically found on any rig. The ** 16 aqueous fluid may be water alone, or water including * *.*..

17 additives such as freezing point depressants provided *.....

18 that any such additive is verified as being compatible 19 with the dry pre-mix before mixing takes place. *::::

21 The dry pre-mixes will comprise a thermoplastic resin 22 selected on the basis of its ability to cure in the 23 presence of an initiator and retain flexibility within 24 the temperature and pressure conditions anticipated in the borehole during the drilling operation. Since the 26 conditions vary as drilling progresses, it is necessary 27 to have to hand more than one pre-rnix, so that an 28 appropriate one can be selected for make up as a 29 suspension adapted to suit the conditions encountered as drilling advances through the formation. The resin is 31 also selected on the basis of its ability to adhere to 32 inert particulate inorganic materials to form upon curing 1 under downhole conditions a fused flexible concretion 2 thereby strengthening the weilbore.

4 Thus the solution to the problem is based on the utilisation of the physical bonding properties of 6 selected thermoplastic solid hydrocarbon resins when 7 mixed in conjunction with inert aggregate material of a 8 specific and complimentary size range.

In practice of the invention, initial preparation steps 11 involve selection of the thermoplastic hydrocarbon resin, 12 which is first ground to a usable powder / particulate 13 form capable of being placed in suspension in an aqueous 14 fluid and typically dry mixed in the right proportions with an inert inorganic filler/aggregate material, of 16 correspondingly appropriate particle size, in the desired:.:.

17 ratio. Any necessary auxiliaries such as initiators, or 18 a bonding agent or setting additive, surfactants, S...

19 viscosity modifiers, or thickeners compatible with the *....

resin may be included here or added later. The mixed..

21 materials are intended to be supplied in the mixed form 22 in a suitable container, e.g. a bag or sack.

24 The dry mixed material of powdered thermoplastic resin and inert inorganic filler/aggregate, with bonding agent 26 or setting additive, initiator or other auxiliary as 27 required, is then mixed in water optionally using a 28 suitable viscosity controlling agent to give a pumpable 29 liquid suspension. This is done on site using the standard mud mixing equipment on any rig.

32 The suspension so obtained can then be selectively 33 introduced to a weak zone to be drilled in the same 1 manner as a circulation fluid (drilling mud). This 2 process leaves in place a solid, fused flexible 3 concretion that displays considerable compressive 4 strength whose overall effect is to sufficiently increase the strength of the near-weilbore formation thus allowing 6 continuation of safe drilling of the previously weak rock 7 formation without loss of drilling fluid.

9 Typically, a general working formulation would comprise (per barrel) Aqueous Fluid Carrier (water / brine): 1 barrel (-160 litres approx.) * * Fusible Thermoplastic Resin(s): 10-90 pounds per barrel (0.028 -0.256 kg/litre) ***** Aggregate Filler: 25-170 pounds per barrel (0.071 -0.485kg/litre) S..... S... * . S

Formulation Additives (surfactant etc.): 0.2-4 pounds per barrel (0.0005 -0.011kg/litre) Polymerisation initiator: trace amount 13 Suitable formulations for performing the invention are 14 given by way of example in the following Table, wherein "bbl" = 1 barrel (approx. 160 litres or 35 imperial 16 gallons) and "ppb" = pounds per barrel (1 pound per 17 barrel approximates to 0.002853 kg/litre).

Table

COMPONENT TEMPERATURERANGES O( -90 90 -120 120 -140 140 - WATER 50 --50 -80% 50 -80% 50 -80% 80% XANTHAN GUM 1-3 -3 1 -3 ppb 1 -3 ppb ppb ppb INORGANIC FILLER 100 -100 -100 -100 -* * S..

(Barite, CaCO3 3lOppb 3lOppb 3lOppb 3lOppb powder, silica sand:...:.

__________ ____________ * S *SSS.S

S

Copolymer or 40 -40 -40 -40 -petroleum resin l2Oppb l2Oppb l2Oppb l2Oppb

of suitable

softening point _________ Phosphate 0.5 -0.5 -0.5 -0.5 -surf actant 3ppb 3ppb 3ppb 3ppb AnioniC surfactant 0.1 -0.1 -0.1 -0.1 - 1.5ppb 1.Sppb 1.5ppb 1.5ppb Non ionic 0.1 -0.1 -0.1 -0.1 -surfactant 2.5ppb 2.Sppb 2.Sppb 2.Sppb

1 Example 2

3 In an alternative embodiment of the invention, the 4 general procedure described in Example 1, is followed but with the following modifications.

6 A liquid suspension of a particular size of sand is also 7 mixed in water in advance of requirement. This serves as 8 an optional fracture packing precursor for use in the 9 well before use of the resin/aggregate suspension. Both liquid suspension mixes can be prepared in advance and 11held for extended periods, indefinitely with minimal 12 agitation in fact, till needed. Thus, in practice of 13 this embodiment, when it is required to be used, firstly, 14 a sufficient quantity of the sand suspension is to be pumped down the well followed immediately by sufficient 16 volume of the fusible thermoplastic resin/inert aggregate 17 suspension. e

S

19 When the plugs of the respective suspensions reach the intended downhole site, namely the induced fracture, 21 first the sand is injected under pressure followed by the 22 fusible thermoplastic/inert aggregate. The water is 23 naturally filtered out at the head of the fracture 24 leaving the sand in a compacted state (in a similar fashion to what is known as gravel packing'). In turn 26 the suspended solids of thermoplastic/inert aggregate 27 particulate mixture are also filtered out on the sand.

28 As there is no filter control' material in either of 29 these liquid suspensions the water portion of each suspension is lost leaving behind the solids which become 31 compacted.

1 Once the thermoplastic resin and inert inorganic 2 aggregate and sand particles are in direct contact 3 downhole, under the prevailing pressure and temperature, 4 in the presence of an initiator, the resin particles fuse together around the inert inorganic particles and form a 6 strong adhesive bond. This process leaves in place a 7 solid, flexible fused concretion that displays 8 considerable compressive strength whose overall effect is 9 to sufficiently increase the strength of the near-welibore formation thus allowing continuation of safe 11 drilling of the previously weak rock formation without 12 loss of drilling fluid. S..

14 Example 3

LJ

16 In a variant of the invention, the particulate materials 17 to be made up into a suspension for introduction to an *.....

18 induced fracture zone are dosed and mixed together in the 19 correct ratios with a carrier fluid eg. water, on the rig and the resulting suspension of thermoplastic resin 21 and inert inorganic materials (sand and/or aggregate) 22 optionally comprising a suspension aid such as xanthan 23 gum, hydroxyethyl cellulose (HEC), or guar gum or the 24 like, and a bonding agent or setting additive or the like, are introduced without standing over, directly to 26 the well bore for strengthening thereof during a drilling 27 operation.

29 Example 4

31 In a further variant of the invention, inert durable 32 fibres are incorporated in the mixture, the dimensions of 33 the fibres being such as to permit suspension thereof in 1 a substantially homogeneous way without inducing any 2 significant detrimental effect on the suspension or 3 otherwise inhibiting the dispersion of the thermoplastic 4 resin and inert inorganic particles forming the fusible composition to be introduced to a zone of induced 6 fractures for well strengthening purposes.

8 The advantages of the invention described hereinbefore 9 include 1) The fact that the particulate thermoplastic 11 resinhinorgaflicS are mixable to prepare as a 12 suspension in any normal rig's mud mixing 13 plant/equipment; 14 2) Its use is compatible with both WBM (water-based mud) and OBM (oil based mud); 16 3) It displays sufficient compressive strength to:...:.

17 remain in place in the fracture without collapsing, :..:.

18 and maintains a degree of flexibility to facilitate 19 inhibition of ingress of unwanted fluids; 4) It is usable once it is in place downhole within an.. : 21 acceptable period of time, because it is heat- 22 activated in the presence of a suitable initiator, 23 and sets/cures more quickly than cement, and yet 24 avoids the potential problem that some curable two part systems may have namely the risk of being 26 flash' set while still in the drilipipe; 27 5) All the components contemplated here are currently 28 considered to be environmentally acceptable. i.e., 29 non-toxic, and non-hazardous to both the environment and humans.

Claims

1 Claims 3 1. A fusible composition for use downhole comprising a 4

polyrnerisable thermoplastic resin, and an inorganic filler, the said resin being one which in use in the 6 presence of an initiator under the temperature and 7 pressure conditions typically encountered downhole 8 cures in the composition, to form therefrom a fused 9 flexible concretion.

11
2. A composition according to claim 1, wherein the 12 resin comprises a low molecular weight thermoplastic 13 resin (say average 300 -1400). * *

3. A composition according to claim 1, wherein the 16 resin comprises an olefinic resin.

S

*5S*S* 18 4. A composition according to claim 1, wherein the S...

19 resin comprises an aromatic monoolef in, optionally S...

22 5. A composition according to claim 4, wherein the 23 resin comprises a petroleum fraction comprising 24 unsaturated components of from eight to twelve carbon atoms.

27 6. A composition according to claim 5, wherein the 28 resin comprises at least one of the following 29 polymerisable components: vinyltoluene, indene, methylindene, aipha-methyistyrene, styrene, a cyclic 31 conjugated diene such as an optionally alkyl- 32 substituted dicyclopentadiene, or a mixture of any 33 of the aforesaid components.

2 7. A composition according to claim 4, or claim 6, 3 wherein the alky? substitution is a lower alkyl (C1- 6 8. A composition according to claim 7, wherein the 9 9. A composition according to claim 1, wherein the resin comprises co-polyrnerisable components for a 11 copolymer alkylaromatic/cycloaliPhatiC resin.

13 10. A composition according to claim 1, wherein the S...

14 resin comprises co-polyrnerisable components, at S.. S least one of which comprises a hydroxyl group, or a 16 carboxyl group, for forming a functionalised S.....

17 (modified) resin.

S.....

19 11. A composition according to any one of claims 1.. . *5**

to 10, wherein the inorganic filler is a particulate 21 material selected from sand, aggregate fines or 22 other particulate matter or fibres which can be 23 suspended in water or an aqueous fluid such as would 24 be suitable for circulation downhole.

26 12. A composition according to claim 11, wherein the 27 inorganic filler is at least one of limestone, 28 marble, granite, clay, shale, ground salt, calcium 29 carbonate, calcium oxide, dolomite, or mixtures of the aforesaid fillers.

1 13. A composition according to claim 12, wherein the 2 inorganiC filler is a water-soluble filler, provided 3 as a saturated solution or suspension.

14. A composition according to any one of claims 1 6 to 11, comprising at least one additive or auxiliary 7 selected from a bonding agent or setting additive or 8 the like, suspending agents, surfactants, solvents, 9 viscosity modifiers, or thickeners, selected from those considered to be compatible with the ii thermoplastic resin.

13 15. A composition according to claim 14, wherein the S...

14 additive comprises at least one surfactant. SS* S IC. .

_I_3 S. 16 16. A composition according to claim 15, wherein at *5*I** 17 least one surfactant is a phosphate surfactant, S.....

18 whilst others are selected from anionic surfactants, 19 and non-ionic surfactants... S... * . S

21 17. A composition according to any one of claims 1 22 to 16, wherein the resin is selected from a range of 23 resins having properties adapted for use at 24 different depths of drilling, to operate at an ambient pressure of up to 20,000psi (-137.9MPa), and 26 respectively adapted to cure, yet remain 27 sufficiently flexible (soften slightly) to envelope 28 and retain particulates, in the temperature ranges, 29 50-90 C, 90-120 C, 120-140 C, and 140-160 C or above.

32 18. A composition according to claim 17, comprising 33 per barrel (-160 litres approx.) of water, fusible 1 thermoplastiC resin(s) in the range of 10-90 pounds 2 per barrel (-0.028 -0.256 kg/litre), aggregate 3 fillers in the range of 25-170 pounds per barrel 4 (-0.071 -0.485kg/litre) and formulation additives (surfactant etc.) in the range of 0.2-4 pounds per 6 barrel (-0.0005 -0.011kg/litre), and a sufficient 7 amount of polymerisation initiator.

9 19. A composition according to claim 17, wherein a copolymer resin and/or a petroleum resin is present 11 in an amount of from 40 -120 ppb (-0.11 -0.34 12 kg/litre), fillers consisting of barite, chalk 13 powder, and silica sand in an amount of from 100 - 14 310 ppb (-0.28 -0. 88 kg/litre), a phosphate surfactant in an amount of from 0.5 -3 ppb (0.001 -16 0.008 kg/litre) an anionic surfactant in an amount:...:.

17 of from 0.1 -1.5 ppb (0.0002 -0.004 kg/litre), and 18 a non-Ionic surfactant in an amount of from 0.1 - 19 2.5 ppb (0.0002 -0.007 kg/litre), and xanthan gum * **.

in an amount of from 1 -3 ppb (0.002 -.. : 21 0.008 kg/litre), the balance being water per barrel 22 (50-80%) and a sufficient amount of initiator.

24 20. A method of drilling in oil-, and gas-bearing formations wherein a weilbore surface susceptible to 26 induced fractures is encountered wherein the method 27 comprises providing a dry mix of particulates 28 comprising a thermoplastic polynierisable resin with 29 an initiator, and inorganic materials in a predetermined ratio, introducing the dry mix to an 31 aqueous fluid to form a liquid suspension, 32 introducing the liquid suspension under pressure 33 into the welibore to contact a selected zone surface 1. during a drilling operation, whereby induced 2 fractures are filled with the suspension, and water 3 is substantially driven out depositing a fusible 4 mass of resin and inorganic materials in intimate contact, which under conditions of temperature and 6 pressure normally prevailing in the borehole, form a 7 fused flexible sealing composition in the induced 8 fractures1 wherein the composition is a composition 9 as claimed in any one of claims 1 to 19.

11 21. A method according to claim 20, wherein a separate 12 liquid suspension of a particulate inorganic 13 material, is introduced initially to pack the 14 induced fractures before the suspension of fusible mass of resin and inorganic materials is introduced 16 to the welibore.

18 22. A kit for use in drilling in oil-, and gas-bearing 19 formations susceptible to induced fractures comprises a plurality of dry-mix containers, each *,, : 21 containing a fusible mix of thermoplastic 22 polymerisable resin, a polymerisation initiator, and 23 inorganic materials, the resin in each being adapted 24 to cure and remain flexible within a predetermined range of temperatures, whereby the full range of 26 conditions to be anticipated during the drilling 27 operations can be accommodated by appropriate 28 selection amongst the plurality of dry-mix 29 containers, wherein the fusible mix comprises a composition according to any one of claims 1 to 19.

32 23. A kit according to claim 22, wherein the mix is a 33 "ready to use" pre-mix of appropriately sized 1 particulates, including additive or other 2 auxiliaries required, wherein the particulate sizes 3 are such as to permit mixing of the materials using 4 on-rig mud handling and mixing equipment, and to be pumpable when mixed with water using circulation 6 fluid or mud pumps. . *1 I. *4S* * * S. P.S * S * 0S4 S... * . . I.. S