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	England and Wales High Court (Chancery Division) Decisions
You are here: BAILII >> Databases >> England and Wales High Court (Chancery Division) Decisions >> Smith International Inc v Specialised Petroleum Services Group Ltd [2005] EWHC 686 (Ch) (21 April 2005) URL: http://www.bailii.org/ew/cases/EWHC/Ch/2005/686.html Cite as: [2005] EWHC 686 (Ch)

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IN THE HIGH COURT OF JUSTICE
CHANCERY DIVISION
PATENTS COURT

		Royal Courts of Justice Strand, London, WC2A 2LL
		21st April 2005

Mr. Justice Lewison:

Introduction

1. This is an appeal and cross-appeal from a decision of M P Hayward, Divisional Director of the Patents Office, acting on behalf of the Comptroller, and dated 1 December 2004.
2. The invention described in the patent is intended to be useful in the oil and gas drilling industry. When you drill for oil or gas you use a drill bit attached to a hollow series of pipes (the drill string) with a central bore. You pump well fluid down the hollow core and through the drill bit to remove rock cuttings from the hole. The drill string must be smaller than the well in which it is set in order for the well fluid to be brought to the surface. The well is typically lined with concrete to stop it collapsing on itself. The circular space between the outside of the drill string and the inside of the well lining is called an annulus. The well fluid passes down the drill string and up through the annulus. It is desirable for the interior of the lining to be clean. Typically, dedicated well cleaning apparatus is run in order to clean the liner before the well is completed. This kind of equipment can remove lumps of cement, rocks, congealed mud and so on. However, one potential problem is that in cleaning the inside of the lining, or more especially in removing the cleaning tool, the cleaning tool may itself dislodge additional debris, particularly if the cleaning tool relies on pressure against the lining to perform its function. One further problem is that tools designed to clean the linings are not generally suited to clean the well fluid itself. The result may be that debris dislodged from the lining may not be removed by circulating the well fluid but may remain suspended in the well fluid down-hole, causing problems in later stages of oil production. The invention, which is called "Apparatus for catching debris in a well bore" is designed to overcome or mitigate this problem.

Procedural history

3. The patent in suit (GB 2335687 B) was filed on 25 March 1999 and granted to Specialised Petroleum Services Group Ltd ("SPS") on 20 February 2002. On 31 January 2003 Smith International Inc ("Smith") applied to the Comptroller of Patents under section 72 (1) of the Patents Act 1977 on the ground that the invention claimed was not patentable on the ground that it was not novel and/or did not involve an inventive step.
4. In the light of the prior art relied on by Smith, SPS amended its claims. It was the amended claims that came before Mr Hayward for determination. He decided that:

i) Claim 1 in the patent was not novel; but was anticipated by prior art;

ii) If, contrary to his conclusion on novelty, claim 1 was novel, it was not obvious;

iii) Claim 8 was novel and was not anticipated by the prior art;

iv) Claims 13 and 14 were not obvious;

v) Claims 15 and 17 were novel and were not anticipated by the prior art;

vi) A proposed amendment to include claim 16 was invalid on the ground that it disclosed matter additional to that which was disclosed in the patent, as filed ("added matter");

vii) A proposed amendment to include claim 17 was not objectionable on the ground of added matter or lack of clarity;

viii) Claim 23 (which was a method claim rather than a product claim) was novel, and was not obvious.

5. Under section 97 of the Patents Act 1977 an appeal from a decision of the Comptroller lies to the Patents Court. Permission to appeal is not needed. SPS appeals against Mr Hayward's decision on claim 1. Smith cross-appeals on Mr Hayward's decisions on claims 8, 13, 14, 15, 17 and 23. However, CPR Part 52 applies to such an appeal. It follows, therefore that the appeal is limited to a review of Mr Hayward's decision and that (absent a serious irregularity in the proceedings below, which is not suggested) I can allow the appeal only if Mr Hayward's decision was wrong. In matters of discretion or judgment, a decision can only be categorised as "wrong" if it is outside the generous ambit within which a reasonable disagreement is possible.
6. Mr Guy Burkill QC appeared for SPS and Mr Richard Miller QC appeared for Smith.

How the invention works

7. The patent describes the invention in general terms:

"The present invention relates to apparatus for cleaning the interior bore of well bore tubulars, such as is found in the oil and gas production industries. A distinctive feature of the invention lies in its provision of a means for filtering or screening well fluid while down-hole."

8. Mr Hayward summarised the way the invention worked:


"The patent is entitled "Apparatus for catching debris in a well bore" and relates to cleaning the fluid and walls of a well bore, such as is found in the oil and gas production industries. This is done using a tool [comprising] a filter through which the well fluid is circulated to remove debris from the fluid. Debris dislodged from the sidewall of the well bore by a wiper is also trapped by the filter.

8. Figure 1 shows the first embodiment described in the patent specification. The tool has an internal bore 3 which communicates with a fluid circulation path, a cylindrical fluid filter screen 6 for trapping debris particles in an annular chamber 9, and a resilient cylindrical cup 5 for wiping debris particles off the sidewall 2 of the well bore and also for diverting fluid flowing in a downward direction relative to the tool into the chamber 9. There is also a ball valve mechanism 10-14 which opens when fluid flows in an upward direction relative to the tool so that the fluid bypasses the filter screen 6.

9. No filtering occurs when the tool is inserted into the well bore, because the fluid is then flowing in an upward direction relative to the tool. The well fluid simply passes through the open ball valve into the chamber 9 and through the bores 8 into the space between the cup 5 and the mandrel 4. When the tool is withdrawn from the well bore, well fluid travels between the cup and the mandrel 4 into the chamber 9 where, because the ball valve is sealed by the pressure of the well fluid, it passes through the filter screen 6. Debris particles are therefore left behind, trapped in the chamber 9. The description says that the well fluid may also be filtered by holding the tool stationary and pumping the fluid down the annulus between the well string and the well wall."

9. Mr Burkill amplified this description as follows:

i) The tool is intended for well clean up and may be run down to the bottom of the well and back up again in a matter of hours;

ii) It is necessary to be able to pump well fluid while the tool is running (whether it is moving down the hole or back up again) and to be able to move the drill string up or down while the tool is in operation;

iii) When the tool is running down the well, and the well fluid is flowing up the well, there is a relatively unrestricted flow, and any particles suspended in the well fluid are carried up above the tool. In this situation the flow path of the fluid begins at the inlet (11), passes the open ball valve (12), flows through the chamber (9) and passes out of the tool at the top (7). Particles that are too big to enter the tool at all will, of course, not pass through it;

iv) When the tool is extracted from the well (i.e. pulled up) or the well fluid is pumped in a reverse direction, the fluid passes through the filter in the tool, and suspended particles are strained out. In this situation the flow path of the fluid begins at the top inlet (7) and enters the chamber (9). But because the ball valve (12) is now closed, the fluid is forced through the filter (6);

v) Thus when the tool is run down the well, suspended particles will pass through the tool and remain suspended in the well fluid above the tool. When the tool is removed from the well, it will carry the suspended particles with it, trapped by the filter, thus removing them from the well fluid. This is done by diverting the debris-laden fluid to one side of the tool and then straining it out through the filter (6). As Mr Hayward put it in his decision: "in one direction the fluid is filtered and in the opposite it is not";

vi) The essence of the invention lies in its ability to filter the well fluid in one direction only, and to remove from the well the particles that have thus been filtered;

vii) The invention is to be contrasted with a junk catcher or sand trap; which is a seal that allows debris and sand to settle on top of the seal, so as to protect pumps and other equipment from malfunction; and which may remain in position for months or years, before being removed from the well.

Approach to construction

10. SPS say that Mr Hayward either failed to construe claim 1 at all or, to the extent that he construed it, misconstrued it. They say that he rolled up the question of construction with that of anticipation; and should have first construed the claim. I will begin by attempting to construe the claim.
11. The starting point for the construction of a patent is section 125 of the Patents Act 1977. That says that the scope of an invention is "that specified in a claim of the specification of the application or patent, as the case may be, as interpreted by the description and any drawings contained in that specification". Section 125 (3) applies the Protocol on the Interpretation of the European Patent Convention to the interpretation of section 125.
12. The correct approach is now authoritatively laid down by the House of Lords in Kirin-Amgen Inc v. Hoechst Marion Roussel Ltd [2005] RPC 9. In the course of his speech Lord Hoffmann said:

"The question is always what the person skilled in the art would have understood the patentee to be using the language of the claim to mean. And for this purpose, the language he has chosen is usually of critical importance. The conventions of word meaning and syntax enable us to express our meanings with great accuracy and subtlety and the skilled man will ordinarily assume that the patentee has chosen his language accordingly. As a number of judges have pointed out, the specification is a unilateral document in words of the patentee's own choosing. Furthermore, the words will usually have been chosen upon skilled advice. The specification is not a document inter rusticos for which broad allowances must be made. On the other hand, it must be recognised that the patentee is trying to describe something which, at any rate in his opinion, is new; which has not existed before and of which there may be no generally accepted definition. There will be occasions upon which it will be obvious to the skilled man that the patentee must in some respect have departed from conventional use of language or included in his description of the invention some element which he did not mean to be essential. But one would not expect that to happen very often."

13. Mr Burkill also relied on the principle of construction that a patent should not be construed with an eye on prior material, in order to avoid its effect: Glaverbel S.A v. British Coal [1995] RPC 255, 270 per Staughton LJ. The purport of this somewhat gnomic statement was explained by Jacob J in Beloit v. Valmet (No 2) [1995] RPC 705, 720 as follows:

"I believe Article 69 of the EPC does not legitimately allow courts to construe claims using the prior art either to widen them or narrow them. There is normally no reason to suppose the patentee when he set the limits of his monopoly knew of a particular piece of prior art which is therefore irrelevant in deciding what those limits are. Of course the position is different if the prior art is specifically acknowledged in the patent. The purposive construction would lead to a construction of a claim which did not cover that acknowledged prior art: it can hardly have been the inventor's purpose to cover that which he expressly recognises was old."

The specification

14. The following parts of the specification were relied on in support of the arguments on construction:

"The present invention relates to apparatus for cleaning the interior bore of well bore tubulars, such as is found in the oil and gas production industries. A distinctive aspect of the invention lies in its provision of a means for filtering and screening well fluid while down-hole." (page 1 lines 3-7)

"[Well cleaning] equipment is used to free the well tubing from debris particles such as, cement lumps, rocks, congealed mud, and so on." (page 1 lines 14-16)

"Indeed well clean-up apparatus is used in an attempt to clean the casing or other well tubing of even smaller debris particles such as oxidation lumps, metal debris, scale, slivers, shavings and burrs for example." (page 1 lines 18-21)

"However, in the present invention it is recognised that during the extraction of known cleanup tools from the well, additional debris can be dislodged, such as from the wall of the casing, thereby negating much of the cleaning work already performed. In fact, the dislodgment of debris or particles during the extraction of the tool can render futile the process of filtering and fine-screening that may have gone before. This problem is particularly prevalent as such cleanup tools, known to the art, typically have their cleaning members biased outwardly to ensure adequate pressure of the cleaning members on the walls of the casing or liner. While this is of assistance during the cleaning process, it has been a disadvantage during the extraction of the tool from the well.

It is also recognised in the present invention that tools suited to the cleaning of well tubulars are not generally also equipped to clean the well fluid. It is usual therefore that debris dislodged from the casing or liner walls is not then fully removed from the well by circulation. Rather the debris may remain suspended in well fluid down-hole, having detrimental effects during subsequent production stages.

An object of the present invention is to obviate or at least mitigate this problem associated with known clean up tools and their use.

A further object of the present invention is to provide apparatus suitable for providing a means of trapping and collecting debris in a well bore.

In the art there are tools commonly referred to as junk catchers. … A notable aspect of such tools, however, is that while they invariably provide a cage or some other catchment area for collecting debris or the like down-hole, they are not adapted to filter properly the well fluid. More particularly, junk catchers or junk subs known in the art have not been arranged to encourage the circulation of well fluid through a filter in a manner that is pro-actively designed to screen debris or other particles out of the fluid.

According to the present invention there is provided a down-hole tool for collecting loose debris particles in a well bore, the toll comprising a body connectable in a work string, diversion means for diverting well fluid passing the tool through the tool body, and a filtration means for filtering debris particles from at least some of the well fluid." (page 2 line 7 – page 3 line 25)

"It should be understood that the diversion means may be formed wholly or partly integral with the tool body. Preferably the diversion means comprises a barrier having an outer diameter that corresponds with the internal diameter of an adjacent tubular in the well bore to the extent that there is negligible fluid by-pass outside the tool body, and one or more flow paths that direct fluid passing through the tool body to the filtration means." (page 3 line 30 – page 4 line 3)

"The filtration means may be a wire screen sized to prevent particles of a predetermined size from passing therethrough. It will be appreciated however that many different types of filtration apparatus may be used, including permeable textiles, holed tubes or cages, and so on." (page 4 lines 20-25)

"The tool requires the relative movement of the well fluid in order to perform its function as a filter." (page 6 lines 24-25)

"The profile of the cup 5 also serves as a diversion means by diverting well fluid travelling in a relative down-hold direction into opening 7 and down through one or more flow paths." (page 10 lines 21-24)

"The filter 6 is shown as a wire wrap filter, although gauze or any other suitable filtration medium known to persons skilled in the art may be employed." (page 10 lines 32-34)

Claim 1

15. Claim 1, in the amended form in which Mr Hayward considered it, is as follows:

"A down-hole tool for collecting debris particles in a well bore, the tool comprising:

a body connectable in a work string having an internal bore running axially there-through which communicates with a circulation path in the work string;

a filter in the tool for filtering debris particles from at least some well fluid; and

diversion means for diverting said well fluid passing the tool through a flow path in the tool, distinct from the internal bore, which bypasses the filter when fluid flow is in a first direction relative to the tool and through the filter when fluid flow is in the reverse direction relative to the tool."

16. The two components (or integers) of the claim that have given rise to the dispute about the construction of the claim are the second and third. More particularly, the two main questions that arise are:

i) What does the claim mean when it speaks of a "filter for filtering debris particles" and

ii) What does the claim mean when it speaks of a diversion means for bypassing the filter in one direction and forcing the fluid through the filter in the other direction?

Filter

17. It is common ground that a "filter for filtering debris particles" means a filter suitable for filtering debris particles, rather than a filter designed or intended for filtering debris particles.
18. Mr Miller points out that the teaching of the patent reveals the following features:

i) It speaks of debris of all sizes: both large (cement lumps and rock) and small (slivers, shavings and burrs);

ii) The invention does not claim to eliminate all suspended debris: it claims to obviate or at least mitigate the problem of suspended debris. Thus some debris may remain in the well fluid even after filtration;

iii) The filtration means may be small gauge (wire screen or permeable textile) or larger gauge (holed tubes or cages);

iv) The claim itself refers only to filtering debris particles from at least some of the well fluid, not from all of it.

19. Mr Burkill on the other hand says that:

i) The invention does more than merely catch debris. Part of the deficiency that it identifies is that junk catchers offer only a catchment area (which by definition catches debris); and do not filter (or filter properly) the well fluid;

ii) Following on from this, the patent acknowledges the prior art of the junk catchers, and distinguishes it. So the filter contemplated by the patent must be more than a mere junk catcher;

iii) The distinctive feature of the invention is that it provides a means for filtering the well fluid;

iv) This means that after passing the filter, the fluid must be cleaner than it was before it passed through the filter.

20. The basic idea of a filter is that it is a porous substance or device which retains solid particles (or solid particles greater than a pre-determined size) suspended in a fluid, but which allows the fluid (and solid particles smaller than the pre-determined size) to pass through it.
21. I agree with Mr Miller that the invention described in the patent in suit is not limited to any particular size of debris. The filter may be of any gauge, large or small. But it must, nevertheless, be a filter.
22. The porous nature of a filter is important. An impermeable device such as a tube of a certain diameter will not allow particles larger than the internal diameter of the tube to pass through it, but no one would call that a filter. Equally an impermeable device that prevents any fluid from passing through it (such a plug in a sink) cannot be described as a filter. However, it is not necessary for the entirety of the filter to be porous. A device may properly be called a filter even it is made of impermeable material, provided that the device as a whole allows the passage of fluid, while retaining the suspended solids. Mr Burkill's analogy of a cafetière (which he accepted was a filter) is typically made of metal. The coffee grounds are retained by the wire mesh. The porosity of the filter is provided by holes in the mesh. Equally a tea strainer (which I would also regard as a filter) is a metal device with holes in it. Conversely, a hole is not itself a filter, because it is not porous. It may be part of a filter, but it is not the whole filter. The filter is made up by the collocation of the permeable and impermeable parts of the whole. A filter must both retain particles and allow the passage of fluid. Unless it does both, it cannot, in my judgment, be properly called a filter.
23. What, then, is the filter in the invention described in the patent in suit? The filter must be that part of the tool which both allows the passage of fluid and at the same time retains the particles. In my judgment a device cannot be described as a filter unless the particles are retained within it. In the case of the patent in suit the filter is clearly described as the wire wrap (6), although a different porous textile, or even a cage, could be substituted.
24. The essential idea of a junk catcher is that it is a seal or plug. It is inserted into a well in order to prevent debris and sand from falling on and fouling pumps and other machinery working below. If that is all it is, then I agree with Mr Burkill that a junk catcher is not within the claim. Although the patent discloses that the patentee was aware of junk catchers in general; it does not disclose that the patentee was aware of the particular piece of prior art on which Smith rely. So I see no reason why something which is principally designed as a junk catcher cannot also be a filter, if it functions in that way as well. It all depends on what kind of junk catcher you are talking about. The mere fact that something is designed as (and is properly called) a junk catcher does not necessarily mean that it falls outside the claim.

Diversion means for bypassing the filter

25. The clever thing about the invention described in the patent in suit is that as it moves in one direction the well fluid by-passes the filter (so large particles go straight through the tool) and in the other direction the well fluid goes through the filter (so that particles are retained in the tool and can be brought to the surface of the well). This is described in the second integer of claim 1.
26. It reads:

"diversion means for diverting said well fluid passing the tool through a flow path in the tool, distinct from the internal bore, which bypasses the filter when fluid flow is in a first direction relative to the tool and through the filter when fluid flow is in the reverse direction relative to the tool"

27. There is some difficulty in parsing this integer; but it does not matter for present purposes.
28. The patent identifies the "diversion means" as the cup (5). This is the means by which fluid is forced to travel through the tool. However, in the embodiments, the cup (5) does not itself determine which flow path within the tool the fluid takes. That is done by the ball valve (12). However, I do not think that this matters. It is implicit in the claim that the diversion means is not itself the filter, or part of the filter, because the diversion means operates in whichever direction the fluid flows (i.e. whether it bypasses the filter in the first direction or flows through the filter in the second direction).
29. Following on from this it is clear from the claim that in one direction the fluid does not go through the filter at all, but bypasses it. The fluid does not, therefore, pass through the wire wrap (6) in one direction, but does go through it in the other.

Novelty

30. Section 1 of the Patents Act 1977 says that a patent may be granted only for an invention that (among other things) is "new". Section 2 (1) says that an invention is taken to be new "if it does not form part of the state of the art". Section 2 (2) says that the state of the art comprises all matter which has at any time before the priority date of that invention been made available to the public. It does not matter how or where the matter has been made available to the public. If an invention described in a patent is not new, in this sense, it is said to have been "anticipated".
31. The law about anticipation is summarised in the judgment of the Court of Appeal in General Tire & Rubber Company v. Firestone Tyre & Rubber Company Ltd [1972] RPC 457, 485 as follows:

"If the prior inventor's publication contains a clear description of, or clear instructions to do or make, something that would infringe the patentee's claim is carried out after the grant of the patentee's patent, the patentee's claim will have been shown to lack the necessary novelty, that is to say, it will have been anticipated. The prior inventor, however, and the patentee may have approached the same device from different starting points and may for this reason, or it may be for other reasons, have so described their devices that it cannot be immediately discerned from a reading of the language which they have respectively used that they have discovered in truth the same device; but if carrying out the directions contained in the prior inventor's publication will inevitably result in something being made or done which, if the patentee's patent were valid, would constitute an infringement of the patentee's claim, this circumstance demonstrates that the patentee's claim has in fact been anticipated.

If, on the other hand, the prior publication contains a direction which is capable of being carried out in a manner which would infringe the patentee's claim, but would be at least as likely to be carried out in a way which would not do so, the patentee's claim will not have been anticipated, although it may fail on the ground of obviousness. To anticipate the patentee's claim the prior publication must contain clear and unmistakable directions to do what the patentee claims to have invented …A signpost, however clear, upon the road to the patentee's invention will not suffice. The prior inventor must be clearly shown to have planted his flag at the precise destination before the patentees."

32. Smith says that the invention described in claim 1 of the patent in suit is not new, but has been anticipated. This ground of objection was upheld by Mr Hayward. Any anticipating device must fall within all the integers of claim 1.
33. One particular question of construction arises in connection with the question of anticipation. Something may fall within the first of the two integers in dispute ("filter for filtering debris particles") if it is suitable for filtering debris particles, even if it was not expressly designed for that purpose. But it must, nevertheless, be capable, without misuse of language, of being described as a filter. And in deciding that question the purpose of the design is of some significance. Mr Burkill relied on the observations of Graham J in Hickman v. Andrews [1983] RPC 147, 168:

"The fact, however, that there is an overlap between the uses to which two articles can be put does not of itself to my mind make one an anticipation of another. Any article can be used for a purpose for which it was not intended."

The prior art

34. The prior art on which Smith rely as having anticipated the patent is a design for a junk catcher or sand trap. That invention is disclosed by US Patent 3,316,971 published on 2 May 1967. It has been referred to as D6. Mr Hayward described the invention disclosed by this patent as follows:


"Referring to figure 2 of D6, the apparatus comprises a tubular mandrel 10, a springloaded positioning sleeve 11 slidably mounted on the mandrel, and an upwardly facing cup-type catcher element 12 slidably mounted on the mandrel above the positioning sleeve. When the apparatus is stationary within the well, the catcher element 12 settles in a position slightly higher than that shown in figure 2, with the portion 25 of the catcher element aligned with the portion 29 of the mandrel. In this position the catcher element forms a seal between the mandrel and the well bore wall, so any sand or debris settling from above will be trapped by the catcher element. When removing the apparatus from the well, the mandrel and positioning sleeve are forced downwards by fluid pressure into the position shown in figure 2. Well fluid now flows downwards (relative to the apparatus) through the passage formed by the catcher element, lower grooves 28 in the mandrel, and slots 36 in the positioning sleeve. The slots in the positioning sleeve are said to be dimensioned to prevent the passage of larger fragments of debris which might prevent the release of the tool, although smaller debris, for example, very fine sand, may pass through the slots."

35. It is clear that the invention described in this patent is intended to be a junk catcher. The improvements to previous junk catchers that it made were improvements aimed at making it easier to remove the tool from the well once its work was done. However, Smith say that in removing the tool from the well it operates in the same way as the invention described in the patent in suit. Thus although it was not intended to be a filter, in fact it is one.
36. So the two questions that arise are:

i) Does this invention (D6) include a filter and, if so, what is it; and

ii) Does the well fluid bypass the filter in D6 in one direction and pass through it in the other?

37. Mr Hayward dealt with the first question as follows:

"I have looked very carefully at the disclosure in D6 relating to the slots 36 in the sleeve 11. The drawings show the slots as having a similar width to the grooves 28 in the mandrel, but if they did indeed have the same width, the slots would not in use block the passage of anything because any debris larger than the slots would never reach them - it would be blocked by the grooves 28. Mr Burkill relied on this to argue that slots 36 could not be a filter because anything that actually reached them would be small enough to pass through them. However, there is clear teaching in the description that the top portion of the slotted sleeve blocks the passage of larger fragments whilst allowing the passage of fluid, and that is not consistent with Mr Burkill's interpretation. I must conclude that the skilled person would regard the drawings as merely schematic and would understand that slots 36 must be narrower than the grooves 28 and should be sufficiently narrow to achieve the required degree of blocking. On that basis, I have no doubt in my mind that the slots 36 can properly be described as a filter. It is of no matter that finer particles can pass through the slots, because all filters only block particles above a certain size. The key point is that the slots are capable of blocking some particles."

38. Mr Miller supported this reasoning. He argued that the filter in this tool (D6) consists of the slots. The slots are dimensioned to allow fluid and some particles (fine sand) to pass through, while not permitting the passage of larger particles. I cannot agree that the slots alone constitute a filter. The essence of a filter is that it both lets fluid through and retains particles. The perforations in a filter may be part of a filter, but they are not the whole of it. Accordingly, I do not consider that Mr Hayward's identification of the filter as consisting of the slots (36) can be correct. The mere fact that the slots are capable of blocking some particles does not make them a filter. Any aperture of a given size is capable of blocking some particles. Moreover, the slots do not in fact block anything. On the contrary the slots allow particles through. It is it what defines the slots that does the blocking. Mr Miller was inclined to accept this; and said that describing the slots as the filter was merely shorthand. The filter, he said, consisted of the slots and that which defined the slots, namely the sleeve of D6 (11). There are three slots, all in the same horizontal plane, disposed equidistantly around the sleeve. When the tool is lifted from the well, well fluid passes through the sleeve and slots, but particles larger than fine sand cannot pass through the slots, and so are retained within the sleeve. That, he said, means that this tool contains a filter. Moreover Mr Miller submitted that as the tool is pulled up the well to the surface it will carry with it any debris and particles that it encounters along the way greater than the slots, while allowing well fluid and smaller particles through the slots. In that sense, too, it operates as a filter.
39. I do not accept these submissions. It is not always easy to articulate one's reasons why a given artefact does not fall within the meaning of an ordinary English noun; but I will do my best to explain:

i) When D6 catches debris in its working position, it catches everything. It catches large rocks and also fine sand. There is no selective retention of particles. Everything is retained in the catcher. At this stage of its operation, it is impermeable; and cannot be described as a filter.

ii) When the tool is removed from the well, it is necessary to release the fluid; otherwise the tool could not be readily extracted from the well, because of a "syringe effect". D6 achieves this by opening up what the patent calls "by-pass passages" through which the fluid will pass. Although the slots will prevent some of the already retained particles from passing through the passages, they will not prevent the passage of fine sand. This is immaterial to the efficient operation of D6, because the fine sand will not prevent the removal of the tool. At this stage, the purpose of the by-pass passages is to release fluid and fine sand; not to retain large particles which have already been caught in the catcher. Thus at this stage the tool is not performing the twin functions inherent in a filter.

iii) In addition, at this stage any debris that has been caught by the catcher will have settled within it. A filter typically filters particles suspended in a fluid. By the time that D6 is removed from the well, any debris that it has caught will no longer be suspended. Thus what is raised with the tool is debris that is no longer in suspension; and particles released through the by-pass passage are put into suspension, when immediately before the release they were not. Putting particles into suspension, rather than removing them from suspension, is the converse of a filter.

iv) It is true that as the tool is raised to the surface it will carry with it particles greater than a certain size. As Mr Hayward noted, the drawings disclosed in the patent show the slots and grooves as being the same size. He felt able to infer that the slots (36) must be smaller than the grooves (28). However, it is not necessary for the efficient operation of the tool that they should be. It would be equally easy to remove it from the well if the groove (28) were the same size as the slot (36). It is a matter of indifference to the designer of the tool (D6) whether particles are trapped within the catcher at the level of the groove or at the level of the slot. What matters is that fluid passes through the tool. Although it would be possible to make the tool (D6) with slots that are smaller than the groove it is not necessary to do so. It is true that the patent speaks of the slots (rather than the groove) preventing the passage of larger particles; but the drawings (which are engineering drawings) do not show the slot as being smaller than the groove. At best, therefore, there is ambiguity. There is, therefore, no clear instruction to manufacture a tool that will infringe the patent in suit; and no inevitability that a tool manufactured according to the specification of D6 will do so.

v) Any catchment area, if removed from the well, will bring up with it what it has caught. It is no different from a fishing net. The patent in suit expressly distinguishes a catchment area from its own inventive concept. Thus whatever meaning "filter" may bear in other contexts, in the context of the patent in suit it excludes a catchment area.

vi) One of the characteristics of a filter is that it is porous. It is stretching the meaning of porous beyond breaking point to describe an impermeable device with three slots in it as porous. Although one must not be tempted to answer questions like "how many grains make a heap of sand", a tool with only three slots does not immediately strike me as a filter. There are usually many more flow paths in a filter than that.

40. I conclude therefore that D6 does not contain a filter at all, and that therefore it does not anticipate the first disputed integer in claim 1.
41. If I am wrong, then I must proceed to identify what the "filter" in D6 might be. Mr Burkill argued that if there is a filter in D6 it consists of the slots (36), the sleeve (11) and the lower lip of the catcher (12). Mr Hayward rejected this argument in the following terms:

"I have carefully considered Mr Burkill's argument that there is no bypassing because the catcher must be regarded as part of the filter, but I do not accept it. Any filter requires some sort of fluid-channelling arrangement to ensure the fluid goes through the filter and not around it, and that is all the catcher is doing when in the figure 2 position."

42. Although Mr Miller accepted that the filter was more than merely the slots; it must in my judgment be more than the slots (36) and the sleeve (11). If the slots and the sleeve alone are considered, the slots will not form a hole. Fluid and particles may simply pass over the lip of the sleeve without passing through the slots at all. The full circumference of the hole, sufficient to make it an effective perforation, is completed by the lower lip of the catcher. Accordingly, I accept Mr Burkill's argument under this head; and respectfully disagree with Mr Hayward. The error which I consider that he has made is that he has considered only part of the filter and not the filter as a whole.

Does the fluid bypass the filter in one direction, but not in the other?

43. If I am right in including the lower lip of the catcher as being part of the "filter" in the tool (D6), assuming that it has one, it inevitably follows that the fluid does not bypass the filter in either direction. All the flow paths of the fluid (when the tool is in motion) pass through the catcher.
44. It follows that the tool (D6) does not anticipate the second disputed integer in claim 1.

Obviousness

45. Smith's next attack on claim 1 is to say that it is an obvious modification of the prior art; specifically the tool in D6. This objection failed before Mr Hayward; but was raised by Respondent's Notice. Mr Hayward set out his understanding of the law about obviousness, in terms which Mr Miller accepts are correct. He continued as follows:

"43 D6 teaches that the slots in the sleeve should be dimensioned so as to prevent the passage of fragments which might prevent the release of the tool string. Mr Miller contended that it would be obvious to place a mesh or a piece of wire across the slots so as to filter finer fragments from the well fluid using the apparatus. He supported this reasoning using two arguments: one relying on a common sense, prima facie, obviousness argument ("it would be an obvious thing to do"), the other relying on Mr McGarian's evidence.

44 I will consider the common sense argument first. There may be circumstances in which appealing to common sense will be sufficient, but this approach needs to be exercised with care because it is all too easy to jump to the wrong conclusion by not looking at things properly through the eyes of the skilled person, as required by the fourth Windsurfing step. What may seem obvious to a lay person may not be obvious to the skilled person because the latter is aware of potential snags. Conversely, what may seem very clever to the lay person may seem perfectly obvious to the skilled person.

45 D6 teaches that the slots are dimensioned in accordance with the size of the fragments of debris to be trapped. If the notional unimaginative skilled person had reason to trap finer particles, this teaching would lead him or her to use narrower slots. Choosing not to narrow the slots and instead add a separate mesh or extra wire is a diversion from the path suggested by D6. It is not merely a diversion, but a diversion down a more complicated route, since it means adding an extra component and finding a way of doing so that is robust-enough to withstand the rigours of a downhole environment. I am at a loss to see why that is a prima facie obvious step to take. From a "common sense" viewpoint, this is a step that needs a motive, and I cannot see one because, on the face of it, the skilled person can achieve all they need by narrowing the slots. Accordingly, even if the "common sense" approach is a valid one, I do not consider it demonstrates that claim 1 is obvious.

46 I turn now to the evidence of Mr McGarian. He says in his first witness statement that:

"The slots 36 in the sleeve 11 of the tool in D6 are merely defined to be dimensioned to prevent the passage of larger fragments of debris. It is, however, obvious to me that the slots 36 could be replaced or augmented by wire screen or (sic) appropriate size, or indeed, a series of wire screens of different permeabilities to enable debris of different sizes to be collected at different points in the trap"

I have already expressed my reservations about Mr McGarian's evidence. However, for the moment I will assume that to Mr McGarian this step really is obvious (or, to be strictly accurate, would have been obvious at the relevant time). That, of course, doesn't immediately kill claim 1, because the test is whether it is obvious to the notional unimaginative skilled addressee, not whether it is obvious to any one particular expert."

46. Having referred to authority, Mr Hayward continued:

"48 As Mr Burkill rightly said, Mr McGarian fails to give any reasons to back up his assertion that it would be obvious to him to add a wire mesh filter to the slots or trap of the D6 tool. That makes his assertion valueless. Because of this, even ignoring my concerns about the weight I can safely attach to his evidence (and also ignoring the fact that he has failed to say whether it would have been obvious to him in 1998), I do not consider that the evidence provided by Mr McGarian is sufficient to establish that the step of adding a filter is obvious.

49 Hence, claim 1, if novel, is not obvious."

47. Mr Miller did not argue with any great enthusiasm that Mr Hayward was wrong not to rely on Mr McGarian's evidence. In my judgment he was plainly right not to do so. Mr McGarian is clearly a very experienced person; and he heads a team of designers. What is obvious to him is neither here nor there. He gave no reasons for his view that the modification of D6 was obvious; so Mr Hayward was entitled to find his assertion was valueless. That left Mr Hayward with no reliable evidence to support the obviousness attack. What Mr Miller argued was that Mr Hayward had made the mistake of assuming that there was only one obvious step to take, whereas there could be more than one. However, there was evidence before Mr Hayward that to place a mesh over the slots in D6 would make it a less efficient tool; and that is clearly what he had in mind in referring to snags obvious to skilled persons. I do not consider that, having correctly set out the law, Mr Hayward made the egregious mistake that Mr Miller attributed to him. He was considering whether a particular modification on which Smith relied was or was not obvious.
48. Whether a modification is obvious or not has been described as a "jury question". On an appellate review, such as the one I am conducting, the only question for me is whether Mr Hayward was entitled to take the view that he did. I have no doubt that he was.

The big picture

49. Mr Burkill had a more general argument which he called "the big picture argument". In essence it was that it is all very well to deconstruct and dissect the integers of a patent claim; but in the end the claim must be read as a whole. The really clever thing about the invention described in the patent in suit is that the well fluid is filtered in one direction, but not in the other.
50. If that is compared with the tool (D6), this feature is not achieved. For each possible fluid flow direction, the flow path narrows in exactly the same way. Both times there is a constriction formed by the combination of a groove (27) or a groove or slot (28/36) and the lower lip of the catcher (12). If particles were stopped going down, they would be stopped going up and vice versa. Thus D6 does not disclose a device which filters fluid in one direction but not in the other.
51. I accept this submission.

Conclusion on claim 1

52. It follows that I will allow SPS' appeal on claim 1 and set aside Mr Hayward's decision.

Claim 17

53. Claim 17 is:

"A tool as claimed in any one of the preceding claims wherein the filter is elongate and vertically disposed, parallel to the internal bore."

54. Smith maintain their objection to this claim whatever the result on claim 1. The objection is based on two grounds:

i) It is not clear and

ii) It discloses added matter.

55. Mr Hayward did not expressly deal with the objection based on lack of clarity. Mr Miller argued that words such as "elongate" "vertically disposed" and "parallel to the internal bore" are all very well when the filter is of the type shown in the figures in the patent. But it is not difficult to conceive of examples of filters in which it is uncertain whether they possess these characteristics.
56. This is a difficulty inherent in the use of language itself. Most of the words we use have a central core of meaning which is clear in conventional usage, and problem areas the further away one moves from that central core. Most words are, so to speak, "fuzzy" at the edges. It is, of course possible to draft a patent specification with mathematical precision and precise dimensions, but that is an invitation to the world to take the essence of the invention and avoid infringement. That is why the rule is that the words of the patent must be as clear as the nature of the subject-matter admits. Mr Burkill drew my attention to cases in which words of imprecision or degree ("large", "thin", "flexible") are found in valid patent claims. The mere fact that one can think of cases where the answer may not be clear does not mean that the specification lacks clarity. I reject the objection based on this ground.
57. So far as added matter is concerned, Mr Miller argued that claim 17 had taken certain features of the invention found principally in the figures, and had imported them into the claim, without explaining why they were of any inventive significance; and, more importantly, without including all the features of the figures which made up what might be thought to be their inventive significance. Any advantage which a filter of this description might possess derived not from the filter alone; but from the radial flow of fluid through the filter, caused by the presence of an annular chamber within it. What the patentee had done was not to take the "whole package" but to select only some of the features of it. He said that this was an impermissible "intermediate generalisation": see Palmaz's Patents [1999] RPC 47.
58. Mr Hayward rejected this argument as follows:

"Claim 17 is not an intermediate generalisation that falls foul of Palmaz because the provision of the filter is the key part of the inventive concept, and the geometrical advantages of having an elongate vertically disposed cylindrical configuration in an elongate tubular well-bore leap out even to the non-expert and are clearly disclosed by the patent. Those advantages are not dependant on further features such as the trap, so the amended claim 17 does not include any features taken out of context. I consider that the specified features of claim 17 narrow the claimed subject matter down to a subclass. The claim is therefore acceptable so far as added matter is concerned."

59. I agree with Mr Burkill that an elongate vertical filter is disclosed by the patent. I agree also that Mr Hayward was entitled to take the view that the advantages of such a filter would be apparent to the skilled addressee: namely that it could be used to make a large filter and a trap behind it. Accordingly this ground of objection fails; and I uphold Mr Hayward's decision.

Claim 23

60. Claim 23 is a method claim. Mr Hayward rejected the attack upon it based on anticipation by D6. It is common ground that if claim 1 is valid (as I have held that it is) then claim 23 is also valid. I can therefore deal with this shortly.
61. Mr Hayward dealt with this as follows:

"Claim 23 is not claiming an apparatus which must be suitable for certain purposes. It is claiming a method of doing something, specifically a "method of cleaning a down-hole environment while running a tool on a work string". The novelty of a method claim like this is only destroyed by a disclosure of such a method, and I can find no disclosure in D6 of cleaning or filtering the fluid whilst running the tool. What D6 tells us is that in the rest position during well-bore operations, debris settles on the catcher. When the tool is pulled out, filter 11 holds all but the smallest debris (eg sand), but there is no disclosure of any cleaning taking place during this operation. Indeed, the presumption is that all the debris will have settled, so there is nothing left to clean. Accordingly I find that D6 does not anticipate claim 23."

62. Smith accept that D6 does not explicitly refer to cleaning. But Mr Miller argues that the very fact that in its rest position D6 prevents debris from settling on apparatus below the seal that it forms, and then removes that debris from the well when the tool is raised, amounts to cleaning. To prevent debris from settling on apparatus cannot, in my judgment, amount to cleaning, any more than placing a dust sheet over a sofa can be said to be cleaning the sofa. The fact that most of the trapped debris is removed when the tool is removed does not, in my judgment, amount to cleaning. It is merely incidental to the removal of the tool. In my judgment, Mr Hayward was right on this question.

Subsidiary claims

63. Claims 2 to 5. It is common ground that these stand or fall with claim 1.
64. Claims 6 and 7. These were not attacked and therefore stand.
65. Claim 8. It is common ground that if claim 1 is valid, so is claim 8. I can therefore deal with it shortly. This claim requires the barrier to be connectable to the body of the tool so as to permit relative rotation between the barrier and the tool. It is said that this feature is anticipated by D6. Mr Hayward disagreed; and so do I. There is nothing in D6 to suggest that the catcher is capable of rotation. It is true that there is nothing in D6 to suggest that it cannot rotate. But silence is not enough to amount to a clear instruction. I would indeed go further and say that the description of the catcher as "slidably" connected suggests (at least to me) that it does not rotate but moves in one plane only. The objection to this claim fails.
66. Claims 9 to 11. These claims are not attacked and stand as dependent claims.
67. Claims 13 and 14. These claims are attacked on the ground of obviousness. The objection is essentially the same as the objection to claim 1 based on obviousness, which I have rejected; and fails for the same reasons.
68. Claim 15. This requires the filter to be a "holed tube". The objection to this integer is based on anticipation. The claim is that D6 has a "holed tube". I would not say that a hole must be circular, but I agree with Mr Hayward that an open ended slot is not a hole. I therefore uphold his decision on this claim.
69. Claim 18. This claim requires a plurality of filters. The attack is based on the proposition that D6 already discloses one filter; and that it would be an obvious modification to affix another. Mr Hayward rejected this objection for the same reasons as he rejected the objection to claim 1; and I agree with him.
70. Claims 19 to 22. These claims are not attacked and therefore stand.
71. Claims 24 to 31. It is common ground that these claims stand or fall with claim 23. Since claim 23 stands, these claims also stand.

Further amendment

72. Mr Miller submitted to Mr Hayward that SPS should not be allowed to make "claim-validating" amendments to the claims once the determination had been made. He submitted that except in special circumstances, which he said were not suggested to exist, no "claim-validating" amendment should be allowed after what was, effectively, a trial. Mr Hayward considered a number of authorities and concluded that they did not lay down a rule that "claim-validating" amendments should never be allowed after trial, at least in revocation proceedings. It is necessary to consider the circumstances in each case.
73. However, because he was not asked for permission to make any particular amendment, he made no decision allowing or disallowing amendments. He merely said that if SPS wanted to ask for permission to amend, they should do so within a stipulated time limit; and he would consider the application on its merits.
74. Mr Miller accepted that there was no formal decision on amendment against which he could appeal, but said that Mr Hayward's approach was wrong; and that I should give guidance to the Patent Office about what approach should be followed. He made very interesting submissions on the practice of the court and the Patent Office in allowing or disallowing amendments, which I found very educational.
75. I do not wish to sound prissy about this; but it is not my function to give gratuitous advice to the Patent Office even if, as a newcomer to this field, I were confident enough to do so. Whether an amendment should or should not be allowed will have to await an actual ruling on a formulated amendment.

Result

76. The appeal is allowed and the cross-appeal is dismissed.