Patent Grant
7243536
1. Field of the Invention
This invention relates generally to formation fluid sampling, and more specifically to an improved reservoir fluid sampling module, the purpose of which is to bring high quality reservoir fluid samples to the surface for analysis.
2. The Related Art
The desirability of taking downhole formation fluid samples for chemical and physical analysis has long been recognized by oil companies, and such sampling has been performed by the assignee of the present invention, Schlumberger, for many years. Samples of formation fluid, also known as reservoir fluid, are typically collected as early as possible in the life of a reservoir for analysis at the surface and, more particularly, in specialized laboratories. The information that such analysis provides is vital in the planning and development of hydrocarbon reservoirs, as well as in the assessment of a reservoir's capacity and performance.
The process of wellbore sampling involves the lowering of a sampling tool, such as the MDT™ formation testing tool, owned and provided by Schlumberger, into the wellbore to collect a sample or multiple samples of formation fluid by engagement between a probe member of the sampling tool and the wall of the wellbore. The sampling tool creates a pressure differential across such engagement to induce formation fluid flow into one or more sample chambers within the sampling tool. This and similar processes are described in U.S. Pat. Nos. 4,860,581; 4,936,139 (both assigned to Schlumberger); U.S. Pat. Nos. 5,303,775; 5,377,755 (both assigned to Western Atlas); and U.S. Pat. No. 5,934,374 (assigned to Halliburton).
The desirability of housing at least one, and often a plurality, of such sample chambers, with associated valving and flow line connections, within “sample modules” is also known, and has been utilized to particular advantage in Schlumberger's MDT tool. Schlumberger currently has several types of such sample modules and sample chambers, each of which provide certain advantages for certain conditions. None of these sample module/chamber combinations, however, exhibit all the characteristics of: permitting a gas charge behind the collected sample for better pressure management of the sample; being heatable up to 400° F. at internal pressures up to 25,000 psi to promote the sample fluid components to go back into solution; being sized and certified for transportation directly from the well site to the laboratory without a need to transfer the collected sample; and being equipped to serve as a storage vessel. Nor do known sample chambers/modules sufficiently minimize the dead volume during sampling to reduce contamination of the sample by a pre-filling fluid, such as water.
To address these shortcomings, it is a principal object of the present invention to provide an apparatus and method for bringing a high quality formation fluid sample to the surface for analysis.
It is a further object of the present invention to provide a sample chamber that is safely heatable to at least 400° F. at internal pressures up to 25,000 psi at the surface.
It is a further object of the present invention to provide a sample chamber that is able to be pressurized to maintain a sample in “single phase,” meaning that as the sample cools down pressure must be maintained so that components such as gas and asphaltenes, which would normally separate out of the mixture during the pressure reduction caused by the cooling of the sample mixture, will remain in solution. Components that do not stay in solution by maintaining pressure while the sample cools, such as paraffins, can be recombined by applying heat to the chamber at the surface. It is a further object of the present invention to provide a sample chamber that is certified for transportation so that, if desired, the sample can be taken directly to a lab for analysis without the need for transferring the sample from the sample chamber at the wellsite.
It is a further object to provide a sample chamber that is adapted for use as a storage vessel, meaning the sample contents will not leak across the seals that contain the sample within the sample chamber.
It is a further object to provide a sample chamber having a volume that is adequate for proper PVT sampling, but not too large that the sample could not be transferred, if desired, into a separate transportable sample bottle, most of which are 600 cc or less in capacity.
It is a further object to provide an independent validation sample chamber, having a substantially smaller capacity than the sample chamber, that will be safer and easier to heat and recombine separated sample components on the surface for validating the quality of the sample at the well site.
The objects described above, as well as various other objects and advantages, are achieved by a sample module for use in a downhole tool to obtain fluid from a subsurface formation penetrated by a wellbore. The sample module includes a sample chamber carried by the module for collecting a sample of formation fluid obtained from the formation via the downhole tool, and a validation chamber carried by the module for collecting a substantially smaller sample of formation fluid compared to the sample chamber. The validation chamber is removable from the sample module at the surface without disturbing the sample chamber.
The sample chamber and the validation chamber may be placed in either parallel or serial fluid communication with a fluid flowline in the downhole tool such that the chambers may be filled either substantially simultaneously or consecutively as desired.
Preferably, the sample chamber is adapted for maintaining the sample stored therein in a single phase condition as the sample module is withdrawn with the downhole tool from the wellbore. The phrase “single phase” is used herein to mean that the pressure of the sample within a chamber is maintained or controlled to such an extent that sample constituents which are maintained in a solution through pressure only, such as gasses and asphaltenes, should not separate out of solution as the sample cools upon withdrawal from the wellbore. The sample may be reheated at the surface to recombine the constituents which have come out of solution due to cooling, such as paraffins. Alternatively, the validation chamber may also be adapted for maintaining the fluid sample stored therein in a single phase condition as the sample module is withdrawn from the wellbore.
It is also preferred that the sample chambers be capable of safely withstanding heating at the surface, following collection of samples and withdrawal of the sample module from the wellbore, to temperatures necessary to promote recombination of the sample components within the chambers that may have separated due to cooling upon withdrawal.
It is further preferred that the sample chamber be sufficiently equipped so as to be certified for transportation.
Still further, it is desirable that the sample chamber be adapted for storing the sample collected therein for an indefinite period without substantial degradation of the sample. One solution for achieving this goal is for the sample chamber to include metal-to-metal seals as the final shut-off seals for the sample collected therein.
In another aspect, the present invention provides an improved sample chamber for use in a downhole tool to obtain fluid from a subsurface formation penetrated by a wellbore. The improved sample chamber includes a substantially cylindrical body capable of safely withstanding heating at the surface, following collection of a formation fluid sample via the downhole tool and withdrawal of the sample chamber from the wellbore, to temperatures necessary to promote recombination of the sample components within the chambers. Additionally, the body is sufficiently equipped so as to be certified for transportation. At least one floating piston is slidably positioned within the body so as to define a fluid collection cavity and a pressurization cavity, whereby the pressurization cavity may be charged to control the pressure of the sample collected in the collection cavity. A second such piston may be provided to create a third cavity wherein a buffer fluid may be utilized during sample collection. Metal-to-metal seals act as the final shut-off seals for the sample collected in the collection cavity of the body.
In another aspect, the present invention provides an apparatus for obtaining fluid from a subsurface formation penetrated by a wellbore. The apparatus includes a probe assembly for establishing fluid communication between the apparatus and the formation when the apparatus is positioned in the wellbore, and a pump assembly for drawing fluid from the formation into the apparatus. A sample chamber is provided for collecting a sample of the formation fluid drawn from the formation by the pumping assembly, and a validation chamber is provided for collecting a substantially smaller sample of the formation fluid than the sample chamber. The validation chamber is removable from the apparatus at the surface without disturbing the sample chamber or its contents.
It is preferred that the sample chamber be adapted for maintaining the sample stored therein in a single phase condition as the apparatus is withdrawn from the wellbore. In this regard, the sample chamber may include at least one floating piston slidably positioned within the sample chamber so as to define a fluid collection cavity and a pressurization cavity. A flow line in the apparatus establishes fluid communication between the probe assembly, the pump assembly, and the fluid collection cavity of the sample chamber. A pressurization system in the apparatus charges the pressurization cavity to control the pressure of the collected sample fluid within the collection cavity via the floating piston. The pressurization system preferably includes a valve positioned for fluid communication with the pressurization cavity of the sample chamber, the valve being movable between positions closing the pressurization cavity and opening the pressurization cavity to a source of fluid at a greater pressure than the pressure of the formation fluid delivered to the collection cavity.
The pressurization system controls the pressure of the collected sample fluid within the collection cavity during either collection of the sample from the formation, or retrieval of the apparatus from the wellbore to the surface, or both. For the former purpose, the source of fluid at a greater pressure than the pressure of the collected sample fluid may be wellbore fluid. For the latter purpose, the source of fluid at a greater pressure than the pressure of the collected sample fluid may be a source of inert gas, such as Nitrogen, carried by the apparatus.
The apparatus may be a wireline-conveyed formation testing tool, but is not necessarily so limited.
In another aspect, the present invention contemplates a method for obtaining fluid from a subsurface formation penetrated by a wellbore, and includes the steps of positioning an apparatus within the wellbore, establishing fluid communication between the apparatus and the formation, and inducing movement of fluid from the formation into the apparatus. A sample of the formation fluid moved into the apparatus is delivered to a sample chamber for collection therein, and a substantially smaller sample of the formation fluid moved into the apparatus is delivered to a validation chamber for collection therein. This permits the smaller sample to be evaluated independently of the sample stored in the sample chamber following withdrawal of the apparatus from the wellbore to recover the collected samples.
The manner in which the present invention attains the above recited features, advantages, and objects can be understood in detail by reference to the preferred embodiments thereof which are illustrated in the accompanying drawings.
It should be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
In the drawings:
Turning first to prior art
As shown in
The hydraulic power module C includes pump 16, reservoir 18, and motor 20 to control the operation of the pump. Low oil switch 22 also forms part of the control system and is used in regulating the operation of pump 16. It should be noted that the operation of the pump can be controlled by pneumatic or hydraulic means.
Hydraulic fluid line 24 is connected to the discharge of pump 16 and runs through hydraulic power module C and into adjacent modules for use as a hydraulic power source. In the embodiment shown in
The pump-out module M, seen in
Bi-directional piston pump 92, energized by hydraulic fluid from pump 91, can be aligned to draw from flow line 54 and dispose of the unwanted sample though flow line 95 or may be aligned to pump fluid from the borehole (via flow line 95) to flow line 54. The pump out module M has the necessary control devices to regulate pump 92 and align fluid line 54 with fluid line 95 to accomplish the pump out procedure. It should be noted here that pump 92 can be used to pump samples into sample chamber module(s) S, including overpressuring such samples as desired, as well as to pump samples out of sample chamber module(s) S using pump-out module M. Pump-out module M may also be used to accomplish constant pressure or constant rate injection if necessary. With sufficient power, the pump out module may be used to inject fluid at high enough rates so as to enable creation of microfractures for stress measurement of the formation.
Alternatively, straddle packers 28 and 30 shown in
As also shown in
Having inflated packers 28 and 30 and/or set probe 46 and/or probes 12 and 14, the fluid withdrawal testing of the formation can begin. Sample flow line 54 extends from probe 46 in probe module E down to the outer periphery 32 at a point between packers 28 and 30 through adjacent modules and into the sample modules S. Vertical probe 46 and sink probes 12 and 14 thus allow entry of formation fluids into sample flow line 54 via one or more of a resistivity measurement cell 56, a pressure measurement device 58, and a pretest mechanism 59, according to the desired configuration. When using module E, or multiple modules E and F, isolation valve 62 is mounted downstream of resistivity sensor 56. In the closed position, isolation valve 62 limits the internal flow line volume, improving the accuracy of dynamic measurements made by pressure gauge 58. After initial pressure tests are made, isolation valve 62 can be opened to allow flow into other modules.
When taking initial samples, there is a high prospect that the formation fluid initially obtained is contaminated with mud cake and filtrate. It is desirable to purge such contaminants from the sample flow stream prior to collecting sample(s). Accordingly, the pump-out module M is used to initially purge from the apparatus A specimens of formation fluid taken through inlet 64 of straddle packers 28, 30, or vertical probe 46, or sink probes 12 or 14 into flow line 54.
Fluid analysis module D included optical fluid analyzer 99 which is particularly suited for the purpose of indicating where the fluid in flow line 54 is acceptable for collecting a high quality sample. Optical fluid analyzer 99 is equipped to discriminate between various oils, gas, and water. U.S. Pat. Nos. 4,994,671; 5,166,747; 5,939,717; and 5,956,132, as well as other known patents, all assigned to Schlumberger, describe analyzer 99 in detail, and such description will not be repeated herein, but is incorporated by reference in its entirety.
While flushing out the contaminants from apparatus A, formation fluid can continue to flow through sample flow line 54 which extends through adjacent modules such as precision pressure module B, fluid analysis module D, pump out module M (FIG. 2), flow control module N, and any number of sample chamber modules S that may be attached. Those skilled in the art will appreciate that by having a sample flow line 54 running the length of various modules, multiple sample chamber modules S can be stacked without necessarily increasing the overall diameter of the tool. Alternatively, as explained below, a single sample module S may be equipped with a plurality of small diameter sample chambers, for example by locating such chambers side by side and equidistant from the axis of the sample module (See FIG. 6C). The tool can therefore take more samples before having to be pulled to the surface and can be used in smaller bores.
Referring again to
Sample chamber module S can then be employed to collect a sample of the fluid delivered via flow line 54 where the piston motion is controlled via the buffer fluid from the non-sample side of the piston being regulated by flow control module N, which is beneficial but not necessary for fluid sampling. With reference first to upper sample chamber module S in
It should also be noted that buffer fluid in the form of full-pressure wellbore fluid may be applied to the backsides of the pistons in chambers 84 and 90 to further control the pressure of the formation fluid being delivered to sample modules S. For this purpose, valves 81 and 83 are opened, and pump 92 of pump-out module M must pump the fluid in flow line 54 to a pressure exceeding wellbore pressure. It has been discovered that this action has the effect of dampening or reducing the pressure pulse or “shock” experienced during drawdown. This low shock sampling method has been used to particular advantage in obtaining fluid samples from unconsolidated formations.
It is known that various configurations of the apparatus A can be employed depending upon the objective to be accomplished. For basic sampling, the hydraulic power module C can be used in combination with the electric power module L, probe module E and multiple sample chamber modules S. For reservoir pressure determination, the hydraulic power module C can be used with the electric power module L, probe module E and precision pressure module B. For uncontaminated sampling at reservoir conditions, hydraulic power module C can be used with the electric power module L, probe module E in conjunction with fluid analysis module D, pump-out module M and multiple sample chamber modules S. A simulated Drill Stem Test (DST) test can be run by combining the electric power module L with packer module P, and precision pressure module B and sample chamber modules S. Other configurations are also possible and the makeup of such configurations also depends upon the objectives to be accomplished with the tool. The tool can be of unitary construction a well as modular, however, the modular construction allows greater flexibility and lower cost, to users not requiring all attributes.
As mentioned above, sample flow line 54 also extends through a precision pressure module B. Precision gauge 98 of module B should preferably be mounted as close to probes 12, 14 or 46 as possible to reduce internal flow line length which, due to fluid compressibility, may affect pressure measurement responsiveness. Precision gauge 98 is more sensitive than the strain gauge 58 for more accurate pressure measurements with respect to time. Gauge 98 is preferably a quartz pressure gauge that performs the pressure measurement through the temperature and pressure dependent frequency characteristics of a quartz crystal, which is known to be more accurate than the comparatively simple strain measurement that a strain gauge employs. Suitable valving of the control mechanisms can also be employed to stagger the operation of gauge 98 and gauge 58 to take advantage of their difference in sensitivities and abilities to tolerate pressure differentials.
The individual modules of apparatus A are constructed so that they quickly connect to each other. Preferably, flush connections between the modules are used in lieu of male/female connections to avoid points where contaminants, common in a wellsite environment, may be trapped.
Flow control during sample collection allows different flow rates to be used. Flow control is useful in getting meaningful formation fluid samples as quickly as possible which minimizes the chance of binding the wireline and/or the tool because of mud oozing into the formation in high permeability situations. In low permeability situations, flow control is very helpful to prevent drawing formation fluid sample pressure below its bubble point or asphaltene precipitation point.
More particularly, the “low shock sampling” method described above is useful for reducing to a minimum the pressure drop in the formation fluid during drawdown so as to minimize the “shock” on the formation. By sampling at the smallest achievable pressure drop, the likelihood of keeping the formation fluid pressure above asphaltene precipitation point pressure as well as above bubble point pressure is also increased. In one method of achieving the objective of a minimum pressure drop, the sample chamber is maintained at wellbore hydrostatic pressure as described above, and the rate of drawing connate fluid into the tool is controlled by monitoring the tool's inlet flow line pressure via gauge 58 and adjusting the formation fluid flowrate via pump 92 and/or flow control module N to induce only the minimum drop in the monitored pressure that produces fluid flow from the formation. In this manner, the pressure drop is minimized through regulation of the formation fluid flowrate.
Turning now to
Sample chamber 110, which is shown more particularly in
Additionally, the sample chamber body 110b should be sufficiently equipped so as to be certified for transportation. Essentially, this requires that the sample volume be limited to 600 cc, and that a minimum ten percent gas cap exists inside the chamber body that protects the potentially volatile hydrocarbon contents collected therein in the event of impact to the body. The use of such gas cap charging is described further below.
Still further, it is desirable for sample chamber 110 to be equipped to store the sample collected therein for an indefinite period without substantial degradation of the sample. One solution for achieving this goal is for the sample chamber to include metal-to-metal seals 110s therein as the final shut-off seals for the sample collected therein, as mentioned previously. Thus, the use of metal-to-metal seals instead of elastomeric seals provides several advantages to sample chamber 110.
Referring again to
The smaller validation sample is taken downhole along with the larger “PVT” sample either sequentially or in parallel, and also may be displaced from the full size sample as well as taken separately from the full size sample. It is important, however, that the validation sample be taken at substantially the same time as the PVT sample to minimize variation between the two samples. In addition to being safer and easier to reheat than the much larger full-sized PVT sample, the validation sample is also much easier to promote recombination of its components through such heating on the surface. Typically, validation at the surface does not entail a full PVT analysis because the primary concern is contamination discovery. Because of this, the validation sample can either be maintained in single phase (again, meaning pressure compensated) or not.
Those skilled in the art will appreciate sample module SM can be combined to advantage with downhole tools, such as formation tester A, to improve the fluid sampling capabilities that such tools provide. In that regard, the present invention contemplates an improved downhole tool for obtaining reliable, high quality formation fluid samples that includes a probe assembly (see the description of probe modules E, F above, for example) for establishing fluid communication between the apparatus and a subsurface formation, and a pump assembly (see, for example, the description of pump-out module M above) for drawing fluid from the formation into the apparatus, in combination with improved sample module SM.
There are several different methods for achieving a high (PVT) quality sample and a validation sample. The most crucial attribute is that of maintaining a single phase sample from the time when the sample is taken (at least the PVT sample) to when it is analyzed. This is preferably accomplished by charging the sample with an inert gas which, by nature, loses much less pressure when the sample temperature drops during withdrawal of the sample chamber from the wellbore. The gas charging system can be contained in either the sample chamber itself or can be contained in the sample module, and preferably utilizes Nitrogen gas for charging purposes.
The gas charge configuration can be rearranged in several different ways, two more of which are illustrated in
There are other methods for maintaining pressure on a sample such as an electromechanical system which senses the pressure via a pressure gauge (not shown) sensing the pressure of cavity 124 and acts to maintain the pressure above a set limit. Such methods are contemplated by and within the scope of the present invention, but are not described further herein.
In order to allow wiring and fluid flow lines to pass through the sample module, there are certain design constraints on the sample chambers. There are two basic methods of designing the sample module. One module, referred to as SMa, can be thought of as a canoe style module and the other module, referred to as SMb, can be considered an annular style module. The two basic concepts are shown respectively in
Canoe style module SMb is equipped with a U-shaped channel for receiving the elongated cylindrical sample chamber 110b, and permits sample chamber 110b to be much simpler in design (essentially a tubular pressure vessel), allowing the sample chamber to be a more cost effective transport and storage vessel. However, the canoe style module makes a more complicated carrier due to the routing of the power/control/communication wiring passage 154b and flowline 54b as seen in FIG. 6B.
The annular style module SMa, on the other hand, makes the routing of wiring and fluid passages 154a and 54a simpler, but complicates the sample chamber 110a as shown by the tube within a tube within a tube design of FIG. 6A. In this embodiment, sample fluid is collected in annulus cavity 124a.
As mentioned above, sample chamber 110 must be transportable, meaning it must meet the design requirements of transportation regulating agencies such as the U.S. Department of Transportation and Transport Canada, as well as others having jurisdiction over the region(s) wherein the tool is used. The sample chamber is also designed to serve as an acceptable storage container. To achieve these goals, no elastomeric seals are used to maintain sample pressure after the chamber is shut in by an operator when the tool reaches the surface. Thus, the present invention entails minimizing or eliminating any elastomeric seals which hold the pressurized sample. The final shut-in seals that are actuated either downhole or on the surface after the sample is taken should all be metal-to-metal so that gases do not migrate across the seals thereby disrupting the actual sample components. Minimizing elastomeric seals will also make the container safer for heating because elastomeric seals are not adequate for long heating/pressure cycles, although the use of elastomeric seals that are pressure balanced, such as by buffer fluid, in contact with the sample is permitted.
Along with being transportable and storable, sample chamber 110 must be heatable to reservoir conditions and, as such, the design safety factors must allow for safe heating of the vessel to temperatures up to 400° F. at pressures up to 25,000 psi). A pressure relief system (see, for example, the relief valve shown in
The sample chamber also allows a formation fluid sample to be taken at a minimum pressure drop just below reservoir pressure, and then raised to a pressure at or above reservoir pressure, in some cases substantially above reservoir pressure and even above wellbore pressure. The latter requirement entails that there is a buffer fluid at or above reservoir pressure against which the sample must be pumped, as described above in regard to formation testing tool A. The sample chamber may also need to allow the buffer fluid to be channeled to a device that can control the fluid flow so that the rate of the sample being taken can be controlled and therefore the buffer fluid must be routed back into the flow line.
“Dead volume” refers to the volume of fluid or gas which is contained in the fluid flow lines and the sample chambers which does not get extracted when the sample is taken. In other words, it is superfluous volume that is trapped in communication with the sample during sample collection. This dead volume fluid or gas is therefore mixed in with the sample fluid and contaminates the sample. In the described design, some dead volume is practically unavoidable, but it is desirable to minimize this volume to ensure a PVT quality sample.
The sample module and sample chamber of the present invention also minimize “dead volume” and prevent the loss of gas when shut in. Dead volume fluid typically consists of air or some other fluid such as water, which is generally used to prefill the flow lines in sample module SM. Dead volume is primarily minimized by limiting the length of flow line between isolating valves and the sample and validation chambers, as well as by minimizing the flow line length between these chambers.
While sampling, it is usually desirable to take at least two if not three PVT quality samples in the same zone at the same time. Therefore, sample module SM should allow multiple sample chambers 110 to be filled at the same sampling depth. It is preferable that the sample module include at least two PVT sample chambers 110 for filling with formation fluid at each sampling point. The chambers can be filled either in series (one after the other) or in parallel. The distance between their entrance ports shall be minimized in order to ensure the similarity of the fluid entering each chamber, and to minimize dead volume.
Several possible combinations of PVT sample chambers and validation sample chambers are shown in
In
In practice, parallel filling arrangements will most likely result in one chamber filling before the other due to differences in friction. Therefore, this method could technically be considered sequential, but the order of chamber filling is not forced like in the pure sequential modes shown in
Most sample chamber designs utilize at least one piston for several reasons, including minimizing the dead volume, controlling the pressure drop on the sample, easing extraction the sample for analysis, and for simplifying the design.
In
Once piston 123 is moved upwardly to its full extent within sample chamber 110, seal valve 151 is set to direct fluid in flow line 54 to bypass validation chamber 112 and sample chamber 110. This action, shown in
It will also be appreciated that
In
In
Referring now to
In
In
It should be further noted that all of the sample chambers, PVT and validation, will have a mechanism which promotes agitation of the fluid in order to facilitate recombination of the sample components at the surface. This mechanism may be as simple as a solid slug or dense non-miscible liquid inside the sample chamber which will, when shaken or inverted, fall through the sample to promote mixing. This mechanism may also be a stirring mechanism attached to the chamber, or a magnetic stirring system. If an external system is developed which can agitate without contacting the sample, such as ultrasonic, the mechanism in the sample chamber may be left out of the design.
In view of the foregoing it is evident that the present invention is well adapted to attain all of the objects and features hereinabove set forth, together with other objects and features which are inherent in the apparatus disclosed herein.
Existing sampling tools do not satisfactorily address all of the issues involved in bringing a high quality reservoir sample to the surface. This new module will be superior to existing modules in this area. This module can be run in either open or cased holes with no dependence on the means of conveyance.
As will be readily apparent to those skilled in the art, the present invention may easily be produced in other specific forms without departing from its spirit or essential characteristics. The present embodiment is, therefore, to be considered as merely illustrative and not restrictive. The scope of the invention is indicated by the claims that follow rather than the foregoing description, and all changes which come within the meaning and range of equivalence of the claims are therefore intended to be embraced therein.
This application is a continuation-in-part of U.S. Provisional Patent Application Ser. No. 60/126,088 filed on Mar. 25, 1999, and a continuation of U.S. patent application Ser. No. 09/511,183 filed Feb. 22, 2000, now U.S. Pat. No. 6,688,390.
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|---|---|---|---|
| 4434653 | Montgomery | Mar 1984 | A |
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| 4936139 | Zimmerman et al. | Jun 1990 | A |
| 4940088 | Goldschild | Jul 1990 | A |
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| Number | Date | Country |
|---|---|---|
| 2 288 618 | Oct 1995 | GB |
| 2288618 | Oct 1995 | GB |
| Number | Date | Country | |
|---|---|---|---|
| 20040129070 A1 | Jul 2004 | US |
| Number | Date | Country | |
|---|---|---|---|
| 60126088 | Mar 1999 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 09511183 | Feb 2000 | US |
| Child | 10738241 | US |
