WO2016019415A1

WO2016019415A1 - Drilling fluid additive

Info

Publication number: WO2016019415A1
Application number: PCT/AU2015/000463
Authority: WO
Inventors: Ryanto Husodo; Mohammad As'ad
Original assignee: Ryanto Husodo; As Ad Mohammad
Priority date: 2014-08-05
Filing date: 2015-08-05
Publication date: 2016-02-11
Also published as: AU2015299741A1; AU2019204667B2; AU2019204667A1

Abstract

The invention relates to methods for sealing pores and/or fractures in drilled formations by defining a seal in the fracture including a matrix of lost circulation material delivered through a pill of drilling fluid additive. The invention also relates to a drilling fluid additive comprising the lost circulation material that comprises fibres and acid-soluble flakes. In a particular arrangement, the fibres may comprise wood fibres such teakwood fiber. In an arrangement, the acid soluble flakes may comprise calcium carbonate flakes. Moreover, the invention also provides for a lost circulation pill, a drilling fluid and methods for treating a borehole that extends into a formation to define an impermeable layer that include a matrix of the lost circulation material.

Description

DRILLING FLUID ADDITIVE

FIELD OF THE INVENTION

[0001] The present invention relates generally to drilling fluid additives and, in particular, to drilling fluid additives that include lost circulation material and that are for use in sealing pores and/or fractures in drilled formations to prevent or at least limit lost circulation of drilling fluid.

[0002] Although the present invention will be described with particular reference to sealing pores and fractures inside boreholes for oil, gas, and geothermal wells, it will be appreciated that it may be used to seal pores and fractures in other types of wells.

BACKGROUND ART

[0003] Wells such as oil, gas, and geothermal wells are typically drilled to depths of thousands of metres below the Earth's surface. Such wells are drilled using a drill bit that is positioned at the bottom of the well borehole, and that is connected to a drill string that extends up to the surface. A drilling fluid such as drilling mud is pumped down the drill string, which comprises a plurality of pipes that are secured end to end, to the drill bit, and is then circulated back up an annulus between the borehole and the drill string so that drill cuttings produced by the cutting action of the drill bit on the drilled formation are carried up to the surface by the drilling fluid. At the surface, the drill cuttings are usually removed from the drilling fluid so that the fluid can be recirculated through the borehole.

[0004] Various problems can occur while drilling such wells. The problem of "lost circulation" occurs when drilling fluid escapes from the borehole through pores and fractures in the drilled formation instead of returning up the annulus between the borehole and the drill string. An undesirable increase in the amount of torque which is required to rotate the drill pipe can sometimes be experienced while the drill pipe is being rotated. Also, sometimes the drill pipe can be subjected to excessive drag while it is being moved up or down in the borehole. Other problems that are associated with unstable boreholes are sloughing of formation which can occur when drilling through formations such as coal and shale formations, and differential sticking where the drill pipe becomes stuck while drilling.

[0005] All of these problems are a common occurrence when drilling oil, gas, and geothermal wells. The occurrence of any of these problems can add millions of dollars to the cost of drilling a well. Furthermore, if there is a well blowout as a result of any of the aforementioned problems occurring, the blowout can be fatal to people who are located near the site of the blowout at the time that it occurs.

[0006] In the past, a common practice to combat these problems was to add ground coconut shell, ground-up Formica or other inorganic fibres to the drilling fluid to create a "pill" which is then pumped downhole. However, the use of these additives/supplements has been found to be unable to inherently solve the various drilling problems, especially the problem of lost circulation, and they can actually cause further damage if they are used in the producing zone of the drilled formation and if they plug the pores of the producing zone irreversibly. In particular, the addition to the drilling fluid of non-biodegradable particles/solids that can penetrate the formation may permanently obstruct the producing zone thus making the well non-productive.

[0007] Organic drilling fluid additive products that are biodegradable have been developed from rice husks, peanut shells, and softwood in an attempt to overcome the problem of permanent producing zone obstruction which is associated with non-biodegradable additives. However, these organic products have been found to have some disadvantages in their application as drilling fluid additives due to their natural properties.

[0008] A particular organic drilling fluid additive that has been found to be effective at sealing pores and fractures in formations and that is therefore able to prevent or limit lost circulation when drilling such formations is disclosed in published Australian Patent Application No. 200172159, the contents of which are incorporated herein by reference. The additive includes a blend of long teakwood fibres and short cotton fibres. It has been found that this drilling fluid additive is only effective in sealing pores and fractures in formations that have permeability in the range of 2000 - 5000 mD (milli Darcy). This is unfortunate, as it is known that severe lost circulation that occurs when drilling highly porous/fractured formations having permeability that is greater than 5000 mD costs oil companies US$2-3 billion per annum.

[0009] Our International patent application PCT/AU2011/001209, which was published on 29 March 2012 under International Publication Number WO/2012/037600, discloses a drilling fluid additive that combines the advantages of the drilling fluid additive disclosed in Australian Patent Application No. 200172159, and that is able to seal formations having a permeability that is greater than 5000 mD. The drilling fluid additive disclosed in WO/2012/037600 includes fibres and flakes. The fibres can include long fibres and/or short fibres. Also, the drilling fluid additive may include acid-soluble granules. Although the drilling fluid additive disclosed in Australian Patent Application No. 200172159 is effective at reducing lost circulation in formations that have a permeability in the range of 2000 - 5000 mD, and the drilling fluid additive disclosed in WO/2012/037600 is effective at reducing lost circulation in formations that have a permeability that is greater than 5000 mD, they are not as well-suited to stabilising and strengthening wellbores such as, for example, wellbores that extend through sand formations.

[0010] It is against this background that the present invention has been developed.

SUMMARY OF THE INVENTION

[001 1] It is an object of the present invention to overcome, or at least ameliorate, one or more of the deficiencies of the prior art mentioned above, or to provide the consumer with a useful or commercial choice.

[0012] Other objects and advantages of the present invention will become apparent from the following description, taken in connection with the accompanying drawings, wherein, by way of illustration and example, a preferred embodiment of the present invention is disclosed.

[0013] According to a first broad aspect of the present invention, there is provided a drilling fluid additive comprising lost circulation material that comprises fibres and acid-soluble flakes. [0014] Preferably, the fibres comprise wood fibres. It is particularly preferred that the wood fibres comprise teakwood fibres. It is also preferred that the fibres comprise ground and sized fibres.

[0015] Preferably, the fibres comprise fibres that range in size from 2 microns to 50 microns, and that comprise 1 % to 30% by weight of the lost circulation material.

[0016] Preferably, the fibres comprise fibres that range in size from 40 microns to 1 10 microns, and that comprise 1 % to 25% by weight of the lost circulation material.

[0017] Preferably, the fibres comprise fibres that range in size from 100 microns to 180 microns, and that comprise 1 % to 8% by weight of the lost circulation material.

[0018] Preferably, the fibres comprise fibres that range in size from 150 microns to 200 microns, and that comprise 1 % to 10% by weight of the lost circulation material.

[0019] Preferably, the fibres comprise fibres that range in size from 180 microns to 300 microns, and that comprise 1 % to 5% by weight of the lost circulation material.

[0020] Preferably, the fibres comprise fibres that range in size from 275 microns to 400 microns, and that comprise 1 % to 10% by weight of the lost circulation material.

[0021] Preferably, the flakes comprise calcium carbonate flakes. It is further preferred that the flakes comprise ground and sized flakes.

[0022] Preferably, the flakes comprise flakes that range in size from 2 microns to 30 microns, and that comprise 2% to 25% by weight of the lost circulation material.

[0023] Preferably, the flakes comprise flakes that range in size from 20 microns to 90 microns, and that comprise 5% to 25% by weight of the lost circulation material. [0024] Preferably, the flakes comprise flakes that range in size from 70 microns to 160 microns, and that comprise 1 % to 18% by weight of the lost circulation material.

[0025] Preferably, the flakes comprise flakes that range in size from 130 microns to 180 microns, and that comprise 1 % to 15% by weight of the lost circulation material.

[0026] Preferably, the flakes comprise flakes that range in size from 150 microns to 250 microns, and that comprise 1 % to 15% by weight of the lost circulation material.

[0027] Preferably, the flakes comprise flakes that range in size from 225 microns to 500 microns, and that comprise 1 % to 10% by weight of the lost circulation material.

[0028] Preferably, the flakes are derived from mini sea or river shells.

[0029] Preferably, the lost circulation material is a single sack lost circulation material, which means that no other lost circulation materials need to be added to it.

[0030] According to a second broad aspect of the present invention, there is provided a drilling fluid that includes a drilling fluid additive according to the first broad aspect of the present invention.

[0031] Preferably, the drilling fluid is a liquid drilling fluid. For example, the drilling fluid may be a water-based drilling fluid, an oil-based drilling fluid, or a synthetic-based drilling fluid. In a particular preferred form the drilling fluid is a water or oil-based drilling mud.

[0032] According to a third broad aspect of the present invention, there is provided a method of treating a borehole that extends into a formation, the method comprising the steps of:

providing a drilling fluid according to the second broad aspect of the present invention; and circulating the drilling fluid through the borehole so that a substantially impermeable layer that includes a matrix of the lost circulation material from the drilling fluid's additive forms on a wall surface of the borehole.

[0033] Preferably, the layer comprises a filter cake.

[0034] According to a fourth broad aspect of the present invention, there is provided a formation that includes a borehole through which a drilling fluid according to the second broad aspect of the present invention has been circulated, the borehole including a substantially impermeable layer on a wall surface of the borehole, the layer including a matrix of the lost circulation material from the drilling fluid's additive.

[0035] Preferably, the layer comprises a filter cake.

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order that the invention may be more fully understood and put into practice, a preferred embodiment thereof will now be described with reference to the accompanying drawings, in which:

Figure 1 depicts a barrel containing a drilling fluid that includes a drilling fluid additive;

Figure 2 is a cross-section of a borehole in a formation, a drill string that has a drill bit secured to a lower end thereof inserted into the borehole, and the drilling fluid circulating through the drill string and the borehole;

Figure 3 is a cross-section of a borehole in a sand formation, and a substantially impermeable layer of filter cake on a wall surface of the borehole;

Figure 4 depicts a section of the wall surface of the borehole covered by the layer of filter cake that includes a matrix of the lost circulation material;

Figure 5 depicts the matrix of the lost circulation material; and

Figure 6 is a flow chart of a method of treating the borehole with the drilling fluid. DESCRIPTION OF EMBODIMENTS

[0037] Referring to Figures land 5, a drilling fluid additive 10 comprises lost circulation material 1 1 that includes teakwood fibres 12 and calcium carbonate flakes 13. The circulation material 1 1 is a single sack lost circulation material, which means that no other lost circulation material need to be added to it.

[0038] Owing to the presence of the calcium carbonate flakes 13, the lost circulation material 1 1 is acid-soluble.

[0039] The lost circulation material 1 1 actually comprises a blend of ground and sized teakwood fibres 12 and ground and sized calcium carbonate flakes 13 that have a range of sizes. The teakwood fibres 12 comprise: teakwood fibres 12 that range in size from 2 microns to 50 microns, and that comprise 1 % to 30% by weight of the lost circulation material 1 1 ; teakwood fibres 12 that range in size from 40 microns to 1 10 microns, and that comprise 1 % to 25% by weight of the lost circulation material 1 1 ; teakwood fibres 12 that range in size from 100 microns to 180 microns, and that comprise 1 % to 8% by weight of the lost circulation material 11 ; teakwood fibres 12 that range in size from 150 microns to 200 microns, and that comprise 1 % to 10% by weight of the lost circulation material 1 1 ; teakwood fibres 12 that range in size from 180 microns to 300 microns, and that comprise 1 % to 5% by weight of the lost circulation material 1 1 ; and teakwood fibres 12 that range in size from 275 microns to 400 microns, and that comprise 1 % to 10% by weight of the lost circulation material 1 1 .

[0040] The calcium carbonate flakes 13 comprise: calcium carbonate flakes 13 that range in size from 2 microns to 30 microns, and that comprise 2% to 25% by weight of the lost circulation material 1 1 ; calcium carbonate flakes 13 that range in size from 20 microns to 90 microns, and that comprise 5% to 25% by weight of the lost circulation material 1 1 ; calcium carbonate flakes 13 that range in size from 70 microns to 160 microns, and that comprise 1 % to 18% by weight of the lost circulation material 11 ; calcium carbonate flakes 13 that range in size from 130 microns to 180 microns, and that comprise 1 % to 15% by weight of the lost circulation material 11 ; calcium carbonate flakes that range in size from 150 microns to 250 microns, and that comprise 1 % to 15% by weight of the lost circulation material 1 1 ; and calcium carbonate flakes that range in size from 225 microns to 500 microns, and that comprise 1 % to 10% by weight of the lost circulation material 1 1 . The calcium carbonate flakes 13 may be derived from mini sea or river shells.

[0041] The fibres 12 may all be produced using the same grinding and/or sizing equipment. For example, they may all be produced using the equipment and/or methods disclosed in published Australian Patent Application No. 200172159 whose contents have, as mentioned above, been incorporated herein by reference.

[0042] Referring to Figure 1 , the drilling fluid additive 10 is added to and mixed with a drilling fluid 30 such as, for example, a water or oil-based drilling mud 31.

[0043] With reference to Figure 2, in use, the drilling fluid 30 to which the drilling fluid additive 10 has been added is pumped down a well borehole 40 that extends through a formation. In particular, the drilling fluid 30 is pumped down the borehole 40 through a drill string 41 and a drill bit 42 that is attached to the drill string 41 , and is then circulated back up an annulus 43 between a wall 44 of the borehole 40 and the drill string 41 . In addition to the additive 10, the drilling fluid 30 which is circulated back up the annulus 43 also includes cuttings and other fine solid particles. The overbalance pressure (i.e. the extent to which the hydrostatic pressure of the drilling fluid 30 in the borehole 30 exceeds the pressure of the formation through which the borehole 30 is being drilled) of the drilling fluid 30 results in the fibres 12 and flakes 13 of the additive 10 combining with the cuttings and other fine solid particles in the drilling fluid 30 to form an impermeable layer 45 comprising a thin wall/filter cake 46 that lines the wall surface 47 of the borehole 40.

[0044] Figure 3 depicts the borehole/wellbore 40 passing through a sand formation 50. Drilling fluid 30 in the borehole 40 can be lost through the pores in the formation 50. Also, because the formation 50 is a sand formation, it is not as strong or as stable as rock formations. The impermeable layer 45 on the wall surface 47 inhibits the drilling fluid 30 in the borehole 40 from being lost in the porous formation 50. In addition, it strengthens and stabilises the borehole 40 to inhibit the wall 44 of the borehole 40 from collapsing. [0045] The fibres 12 and flakes 13 form an impermeable matrix 60 in the layer of wall filter cake 46. The flakes 13 combine with the fibres 12 to reduce the spaces between the fibres 12 in the matrix 60 so as to thereby enhance the matrix 60 in the wall cake 46. The cuttings and other fine solid colloidal particles in the drilling fluid 30 further enhance the matrix 60 by filling the spaces between the fibres 12 and flakes 13 and assist in making the wall cake 46 impermeable. The impermeable layer of wall cake 46 is able to substantially plug or seal the porous/fractured formation 50, and is thereby able to substantially prevent drilling fluid 30 in the borehole 40 from entering the formation 50 and being lost.

[0046] With reference to Figure 6, the above-described steps comprise a method 70 of treating a borehole that extends into a formation.

[0047] The inclusion of the ground and sized calcium carbonate flakes 13 in the lost circulation material 1 1 makes the drilling fluid additive 10 particularly suitable for use in sealing a producing formation such that severe lost circulation in the formation is eliminated or at least reduced.

[0048] The seal/plug formed by the matrix 60 of lost circulation material 11 can be removed/released without damaging the sealed formation zone by acidizing/adding acid to the material 1 1 so that the acid dissolves the calcium carbonate flakes 13. After the seal/plug has been removed/released in this way, the formation zone is able to produce an amount of oil or gas which is the same as or more than that which was originally intended.

[0049] The inclusion of calcium carbonate flakes 13 in the lost circulation material 1 1 results in an acid-soluble lost circulation material 1 1 that can be used to eliminate or at least reduce lost circulation in a producing formation. Importantly, modifying the lost circulation material 1 1 in this manner enables the material 11 to eliminate or at least reduce lost circulation without damaging the formation. This is in contrast to other acid-soluble lost circulation materials that are available and that are prone to damaging producing formations so that the amount of oil or gas that the formations are able to produce is consequently reduced. The drilling fluid additive can be used to pretreat drilling fluid such as drilling mud, so that as a borehole is drilled using the pretreated mud, an impermeable layer that includes a matrix of the lost circulation material 1 1 is formed on the surface of the borehole wall. As mentioned above, the impermeable layer improves the stability and the strength of the borehole. Moreover, it seals all microfractu res/fractures and/or any impermeable surface of the borehole so that no drilling fluid/mud will penetrate into the formation from the wellbore/borehole.

[0050] Whereas most other lost circulation materials are only able to effectively seal highly fractured formations with a maximum success rate in the low 30% range, it is anticipated that the lost circulation material 1 1 according to the present invention will be able to effectively seal such formations with a success rate of up to 50%.

[0051] It will be appreciated by those skilled in the art that variations and modifications to the invention described herein will be apparent without departing from the spirit and scope thereof. The variations and modifications as would be apparent to persons skilled in the art are deemed to fall within the broad scope and ambit of the invention as herein set forth.

[0052] Throughout the specification and claims, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

[0053] Throughout the specification and claims, unless the context requires otherwise, the term "substantially" or "about" will be understood to not be limited to the value for the range qualified by the terms.

[0054] Also, future patent applications may be filed in Australia or overseas on the basis of, or claiming priority from, the present application. It is to be understood that the following provisional claims are provided by way of example only, and are not intended to limit the scope of what may be claimed in any such future application. Features may be added to or omitted from the provisional claims at a later date so as to further define or re-define the invention or inventions. Moreover, additional claims may be added at a later date so as to claim other aspects of the invention. [0055] It will be clearly understood that, if a prior art publication is referred to herein, that reference does not constitute an admission that the publication forms part of the common general knowledge in the art in Australia or in any other country.

Claims

CLAIMS:

1. A drilling fluid additive comprising lost circulation material that comprises fibres and acid-soluble flakes.

2. The drilling fluid additive defined by Claim 1 , wherein the fibres comprise wood fibres.

3. The drilling fluid additive defined by Claim 2, wherein the wood fibres comprise teakwood fibres.

4. The drilling fluid additive defined by any one of Claims 1 to 3, wherein the fibres comprise ground and sized fibres.

5. The drilling fluid additive defined by Claim 4, wherein the fibres comprise fibres that range in size from 2 microns to 50 microns, and that comprise 1 % to 30% by weight of the lost circulation material.

6. The drilling fluid additive defined by any one of Claims 4 to 5, wherein the fibres comprise fibres that range in size from 40 microns to 1 10 microns, and that comprise 1 % to 25% by weight of the lost circulation material.

7. The drilling fluid additive defined by any one of Claims 4 to 6, wherein the fibres comprise fibres that range in size from 100 microns to 180 microns, and that comprise 1 % to 8% by weight of the lost circulation material.

8. The drilling fluid additive defined by any one of Claims 4 to 7, wherein the fibres comprise fibres that range in size from 150 microns to 200 microns, and that comprise 1 % to 10% by weight of the lost circulation material.

9. The drilling fluid additive defined by any one of Claims 4 to 8, wherein the fibres comprise fibres that range in size from 180 microns to 300 microns, and that comprise 1 % to 5% by weight of the lost circulation material.

10. The drilling fluid additive defined by any one of Claims 4 to 9, wherein the fibres comprise fibres that range in size from 275 microns to 400 microns, and that comprise 1 % to 10% by weight of the lost circulation material.

1 1 . The drilling fluid additive defined by any one of Claims 1 to 10, wherein the flakes comprise calcium carbonate flakes.

12. The drilling fluid additive defined by Claim 11 , wherein the flakes comprise ground and sized flakes.

13. The drilling fluid additive defined by Claim 12, wherein the flakes comprise flakes that range in size from 2 microns to 30 microns, and that comprise 2% to 25% by weight of the lost circulation material.

14. The drilling fluid additive defined by any one of Claims 12 to 13, wherein the flakes comprise flakes that range in size from 20 microns to 90 microns, and that comprise 5% to 25% by weight of the lost circulation material.

15. The drilling fluid additive defined by any one of Claims 12 to 14, wherein the flakes comprise flakes that range in size from 70 microns to 160 microns, and that comprise 1 % to 18% by weight of the lost circulation material.

16. The drilling fluid additive defined by any one of Claims 12 to 15, wherein the flakes comprise flakes that range in size from 130 microns to 180 microns, and that comprise 1 % to 15% by weight of the lost circulation material.

17. The drilling fluid additive defined by any one of Claims 12 to 16, wherein the flakes comprise flakes that range in size from 150 microns to 250 microns, and that comprise 1 % to 15% by weight of the lost circulation material.

18. The drilling fluid additive defined by any one of Claims 12 to 17, wherein the flakes comprise flakes that range in size from 225 microns to 500 microns, and that comprise 1 % to 10% by weight of the lost circulation material.

19. The drilling fluid additive defined by any one of Claims 12 to 18, wherein the flakes are derived from mini sea or river shells.

20. The drilling fluid additive defined by any one of Claims 1 to 19, wherein the lost circulation material is a single sack lost circulation material.

21 . A drilling fluid that includes a drilling fluid additive according to any one of Claims 1 to 20.

22. The drilling fluid defined by Claim 21 , wherein the drilling fluid is a liquid drilling fluid.

23. The drilling fluid defined by Claim 22, wherein the drilling fluid is selected from the group of drilling fluid comprising: a water-based drilling fluid; an oil-based drilling fluid; and a synthetic-based drilling fluid.

24. The drilling fluid defined by any one of Claims 22 to 23, wherein the drilling fluid is a drilling mud.

25. A method of treating a borehole that extends into a formation, the method comprising the steps of:

providing a drilling fluid according to any one of Claims 21 to 24; and circulating the drilling fluid through the borehole so that a substantially impermeable layer that includes a matrix of the lost circulation material from the drilling fluid's additive forms on a wall surface of the borehole.

26. The method defined by Claim 25, wherein the layer comprises a filter cake.

27. A formation that includes a borehole through which a drilling fluid according to any one of Claims 21 to 24 has been circulated, the borehole including a substantially impermeable layer on a wall surface of the borehole, the layer including a matrix of the lost circulation material from the drilling fluid's additive.

28. The formation defined by Claim 27, wherein the layer comprises a filter cake.

29. A drilling fluid additive substantially as hereinbefore described with reference to the drawings.

30. A drilling fluid substantially as hereinbefore described with reference to the drawings.

31 . A method of treating a borehole that extends into a formation, the method being substantially as hereinbefore described with reference to the drawings.

32. A formation substantially as hereinbefore described with reference to the drawings.