Apparatus and method for excluding gas from a liquid

Abstract

The present invention is directed to an apparatus and method for preventing diffusion of a gas under high pressure into the bulk of a liquid filling a substantially closed chamber. This apparatus and method is particularly useful in connection with test devices for testing fluid characteristics under harsh conditions of extremely high pressure and high temperature. These devices typically pressurize the liquid by placing the liquid in pressure and fluid communication with a high pressure inert gas. The apparatus and method of the present invention prevent diffusion of the pressurizing gas into the bulk of the test liquid by decreasing the chamber volume at a rate sufficient to maintain the bulk of the liquid free of absorbed or dissolved gas by expelling that portion of the liquid which is contaminated by the pressurizing gas.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to an apparatus and method for preventing diffusion of a first fluid into the bulk of a second fluid filling a substantially closed chamber. The present invention is particularly useful in preventing diffusion of a gas under high pressure into the bulk of a liquid filling a substantially closed chamber. This system is particularly useful in test devices where the liquid is being pressurized to extremely high pressures by the gas and where test instruments extend through the liquid/gas interface to immerse sensors in the test liquid.

2. Description of the Background

It is often desirable to pressurize a liquid to extremely high pressures to perform a variety of tests on that liquid. For example, drilling fluids manufactured for use in deep drilling operations are often subjected in use to temperatures in excess of 450.degree. F. and pressures in excess of 10,000 psi. Accordingly, it is desirable to test these fluids under conditions simulating this harsh borehole environment.

It is possible to test these fluids simply by pumping them to the downhole location where the fluids are subjected to the downhole environment. A variety of tests are then conducted on the fluids after they are returned to the surface. However, because these tests are not conducted in the actual harsh conditions and the results may not reflect the characteristics of the fluid in the borehole environment, this testing method is unsatisfactory. These tests really only reflect changes which have occurred in the fluids as a result of the harsh borehole conditions.

It is desirable to test drilling fluids while they are actually in an environment simulating the harsh borehole conditions. Accordingly, it is desirable to be able to test these fluids at temperatures in excess of 450.degree. F. and at pressures in excess of 10,000 psi. These conditions are simulated by placing the fluid in a container including the test devices and sensors and subjecting the entirety to the simulated environment. Those skilled in the art will appreciate that this harsh environment is readily produced by placing the test equipment in a device which is heated to the test temperature by an appropriate autoclave and which is pressurized to the test pressure by the introduction of nitrogen or another inert gas. Because the inert gas is employed to pressurize the fluid, it must be in pressure communication therewith. Further, test sensors and devices extend into the liquid while various control equipment is typically maintained outside the liquid-containing vessel.

Because diffusion of the pressurizing gas into the test liquid results in changes in the physical characteristics of the liquid and, accordingly, alters the test results, it is desirable to exclude the pressurizing gas from the test liquid. However, the harsh conditions, extremely high pressure and high temperature, under which these tests are performed have made exclusion of the pressurizing gas from the test liquid a continuing problem. Conventional sealing means have not proved satisfactory. Accordingly, there has been a long felt but unfulfilled need within the industry for an apparatus and method for preventing diffusion of the pressurizing gas into the bulk of the test liquid.

SUMMARY OF THE INVENTION

The present invention provides a new and improved apparatus and method for preventing diffusion of a first fluid into the bulk of a second fluid filling a substantially closed chamber. The apparatus and method of the present invention are particularly useful for preventing diffusion of a pressurizing gas into the bulk of a test liquid filling a substantially closed chamber. This apparatus and method are particularly useful in devices for testing the characteristics of a liquid in a simulated high-pressure, high-temperature environment.

An apparatus in accord with the present invention comprises a means for substantially enclosing a fluid, preferably a liquid, within a chamber having a volume of variable size. The volume of the chamber is variable to maintain the chamber substantially filled with a fluid substantially free from an absorbed or dissolved second fluid. In a presently preferred embodiment, this apparatus comprises a vessel having a port therein of sufficient size to permit the insertion of means for testing one or more characteristics of the fluid and a diffusion shield for cooperation with the vessel for substantially closing the port to define the chamber of variable volume. Further, the apparatus includes means for communicating pressure, and preferably fluid, from the exterior to the interior of the chamber. Further, the apparatus includes means for maintaining a fluid, preferably a gas, substantially exterior of the chamber and in communciation with the pressure and fluid communication means. Finally, the device includes means for decreasing the volume of the chamber at a rate sufficient to prevent diffusion of the gas into the bulk of the liquid in the chamber. In a presently preferred embodiment, relative movement is imparted to the diffusion shield and vessel.

In an alternative embodiment, the apparatus further includes means for determining the diffusion rate of the gas into the liquid and means for variably decreasing the volume in response to this determination in order to maintain the rate of discharge of the liquid from the chamber at a rate at least as great as the rate of diffusion of the gas into the liquid.

The method of the present invention comprises maintaining a fluid, preferably a liquid, in a substantially closed chamber capable of enclosing a variable volume and having an open surface area comprising only a small portion of the total surface area. Further, the method comprises maintaining another fluid, preferably a gas, substantially exterior of the chamber while contacting the fluids at the open area. Finally, the method comprises decreasing the volume of the container at a rate sufficient to prevent diffusion of the gas into the bulk of the liquid in the chamber. In a presently preferred embodiment, the volume of the container is decreased by imparting relative movement to the vessel and diffusion shield comprising the chamber. In an alternative embodiment, the volume is decreased at variable rates and is conveniently adjusted in response to the diffusion rate obtained by measuring or determining the diffusion rate of the gas into the liqiud in the chamber.

The apparatus and method of the present invention solve the longfelt but unfulfilled need for an effective system for preventing diffusion of the pressurizing gas into the test liquid in test devices which pressurize liquids to extremely high pressures by pressure or fluid contact with a pressurizing gas. These systems are particularly useful in test devices for simulating the high pressure, high temperature conditions encountered in deep drilling and borehole operations. The apparatus and method of the present invention permits insertion of test sensors and instruments into the liquid through the liquid/gas interface and solves the problems associated with attempts to apply conventional sealing technology at these interfaces. These and other meritorious features and advantages of the present invention will be more fully appreciated from the following detailed description and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and intended advantages of the present invention will be more readily apparent by the references to the following detailed description in connection with the accompanying drawings wherein:

FIG. 1 is an illustration in partial cross section of an apparatus in accord with the present invention incorporated into a testing device suitable for conducting high pressure, high temperature tests on liquids;

FIG. 2A is a cross-sectional representation of a device in accord with the present invention illustrating the portion of the device at the liquid/gas interface prior to pressurization; and

FIG. 2B is a cross-sectional representation of a device in accord with the present invention illustrating the portion of the device at the liquid/gas interface after pressurization and a reduction in the volume of the liquid-containing chamber.

While the invention will be described in connection with a presently preferred embodiment, it will be understood that it is not intended to limit the invention to this embodiment. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included in the spirit of the invention as defined in the appended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 of the drawings illustrates a diffusion prevention device 10 in accord with the present invention incorporated within a testing device 100 useful for testing the characteristics of liquids at high pressure and high temperature.

A fluid test device incorporating a diffusion prevention apparatus 10, together with appropriate test and control devices, is disposed within a chamber 26 in a longitudinal bore 72 in a steel containment cylinder 70 of sufficient strength to withstand the high pressures developed in the tests. In the illustrated embodiment, the bore 72 extends longitudinally through the entire length of a cylinder 70 and is sealed at its lower end by a cooperating steel plug 86 and O-ring 84. The test apparatus is affixed to the lower end of a steel plug 76 for sealing cooperation with the bore 72 as by O-rings 84. It will be appreciated by those skilled in the art that the O-rings 84 are merely illustrative and that any conventional sealing means capable of withstanding the expected pressures and temperatures may be employed in this device. The plug 76 is conveniently configured to include a shoulder 78 for cooperation with a shoulder 74 on the bore 72 to prevent the test apparatus and plug from inadvertently entering the chamber 26 beyond a desired location. Finally, the containment cylinder 70 is characterized by means for firmly engaging plugs 76, 86 to withstand the high pressures developed during testing. This means is conveniently provided by steel pin 82 inserted through a cooperating bore 80 in containment wall 70 and plug 76. A similar engagement means is employed with plug 86. The plug 76 further includes conventional means (not illustrated) for engagement of a lifting device to raise and lower the plug and attached test devices from and into operating position in the containment cylinder 70.

The test device 100 further includes means for producing the desired environmental conditions, e.g., temperature and pressure, in the fluid 40 within the vessel 20 and the fluid 50 surrounding the vessel 20 and contained within the chamber 26 defined by the sealed portion of the bore 72 between the top and bottom plugs 76, 86 and seal means 84. Those skilled in the art will be capable of pressurizing the chamber 26 by employing many conventional means for pressurizing a chamber. For example, in one embodiment, the chamber 26 is placed in fluid communication with conventional pressurizing equipment exterior of the test device 100 as through appropriate lines inserted through plug 76 and conduit 24. Further, the device includes coils 96 within insulation 98 located about the lower periphery of the bore 72 to raise or lower the temperature of the chamber 26 as desired.

The device further includes test control equipment disposed within a protective assembly 90 and affixed to the lower side of the plug 76. Because it is desirable to shield these control and recording devices from the extremely high temperatures often developed during testing, the assembly 90 is protected by a thermal shield 92 on its lower surface and by cooling coils 94 about its periphery.

A presently preferred diffusion prevention apparatus 10 in accord with the present invention comprises a cylindrical vessel 20 for holding a fluid, preferably liquid, 40. The vessel 20 is disposed within the chamber 26 on a plurality of supports 28. The apparatus 10 further comprises a diffusion shield 30 having an exterior configuration 32 for cooperation with the interior configuration 22 of the vessel 20 for substantially closing the vessel 20 to form a chamber 48 of variable volume. Although the diffusion shield 30 substantially closes the opening in the vessel 20, it is not in sealing relation and it permits both pressure and fluid communication between the gas 50 above the shield 30 and the fluid 40 below. The chamber is defined by the interior walls 22 of the vessel 20 and by the lower surface 36 of the diffusion shield 30. The diffusion shield 30 is suspended by movable supports 38 engaged by a motor 52 or other appropriate device within the control equipment assembly 90 capable of intermittently applying constant or variable motion to the diffusion shield 30. This motion as illustrated in FIGS. 2A and 2B typically will slowly drive the diffusion shield 30 further into the vessel 20 to slowly decrease the volume of chamber 48.

The diffusion shield 30 is typically characterized by a plurality of ports 34 therethrough for insertion of a plurality of support conduits or rods 60. These conduits 60 provide support for a variety of fluid testing sensors or devices 64 and provide shielded conduits for electrical connections between the sensors or devices 64 and control and data storage devices within the control assembly 90. Further, an agitator 62 typically is also suspended through the diffusion shield 30 in order to aid the maintenance of uniform fluid conditions in the liquid 50 within the chamber 48. The vessel 20 further includes conventional heating coils 68 useful in achieving the high temperatures at which typical tests are conducted.

In an alternative embodiment of the present invention, a device 66 useful for determining the diffusion rate of the gas 50 into the liquid 40, e.g., by determination of the fluid density near the liquid/gas interface, is suspended directly below the lower surface 36 of the diffusion shield 30. This device permits the rate of movement of the diffusion shield 30 and thus the rate of decrease in the volume of the chamber 48 to be constantly adjusted in response to the actual measured diffusion rates in order to prevent the diffusion of the gas 50 into the bulk of the liquid 40. The diffusion rate monitor 66 and an associated microcomputer means 54 disposed within control assembly 90 is capable of automatically determining the diffusion rate of the gas 50 into the liquid 40 just below the diffusion shield 30, establishing the minimum rate at which the volume of the chamber 48 must be decreased and variably decreasing the volume at a rate at least as great as the established minimum rate by adjusting the motor 52.

FIGS. 2A and 2B illustrate the operation of a simple diffusion shield in accord with the present invention. FIG. 2A illustrates the device prior to pressurization by the gas 50 above the liquid 40. The diffusion shield 30 is moved into contact with the surface of the liquid 40 in the vessel 20. It is desirable that the diffusion of the gas 50 into the bulk of the liquid 40 be prevented. For example, the gas 50 will diffuse into the liquid 40 at the liquid/gas interface and will diffuse to a level 42 which is chosen to be at or near the lower surface 36 of the diffusion shield 30. Thus, the fluid 44 represents liquid 40 having dissolved therein gas 50. As the test progresses, the gas 50 would typically diffuse to greater depths within the liquid 40, eventually affecting the composition and characteristics of the entire test liquid. However, the apparatus and method of the present invention provide that the volume of the chamber 48 be slowly decreased, expelling a small quantity of fluid 40 from the chamber 48 as illustrated in FIG. 2B. In the presently preferred embodiment the diffusion shield 30 is moved at a rate sufficient to decrease the volume of the chamber 48 by expelling fluid containing absorbed or dissolved gas 50 at a rate sufficient to maintain level 42 approximately constant relative to the diffusion shield 30.

The method of the present invention comprises maintaining a fluid in a substantially closed chamber of variable volume while maintaining another fluid substantially exterior of the chamber, maintaining pressure, and preferably fluid, communication between the fluids and decreasing the volume of the chamber at a rate sufficient to prevent diffusion of the fluid exterior of the chamber into the bulk of the fluid within the chamber. This method is conveniently and easily performed employing a device in accord with the present invention, e.g., the device described above. It is believed that the description of the above preferred embodiment of the present invention clearly conveys the method of the present invention in a manner appreciated by those skilled in the art. However, in summary, the method of the present invention is conveniently performed by maintaining a liquid 40 within a chamber 48 of variable volume defined by the interior walls 22 of a vessel 20 and the lower surface 36 of a diffusion shield 30. A pressurizing gas 50 is maintained exterior of the chamber 48 within the chamber 26. Pressure and fluid communication is maintained between the fluid 40 and the gas 50 at a liquid/gas interface 46 near the diffusion shield 30. The volume of the chamber 48 is decreased by moving the diffusion shield 30 into the vessel 20 using the motor 52. The volume of the chamber 48 is decreased at variable rates by adjusting the speed of the motor 52. In an alternative embodiment of the present invention the diffusion rate of the gas 50 into the liquid 40 near the diffusion shield 30 is determined by a sensor 66 and a microcomputer 54. Further, the microcomputer 54 adjustably controls the motor 52 to adjust the rate at which the volume of the chamber 48 is decreased to a rate sufficient to maintain the rate of discharge of the liquid 40 from the chamber 48 at least as great as the rate of diffusion of the gas 50 into the liquid 40. Accordingly, the diffusion of the gas 50 into the liquid 40 is maintained above a level 42 so that the bulk of the liquid 40 below the level 42 remains free of the gas 50.

The foregoing description of the invention has been directed in primary part to a particular preferred embodiment and method in accord with the requirements of the patent statutes and for purposes of explanation and illustration. It will be apparent, however, to those skilled in the art, that many modifications and changes in the specifically described apparatus and method may be made without departing from the scope and spirit of the invention. For example, in an alternative embodiment, the vessel 20 is moved slowly toward a stationery diffusion shield 30 in order to decrease the volume of the chamber 48. Accordingly, those skilled in the art will appreciate that any means for decreasing the volume of the chamber 48 at the required rate may be substituted for the presently preferred illustrated means. Therefore, the invention is not restricted to the particular form of construction illustrated and described, but covers all modifications which may fall within the scope of the following claims.

It is Applicant's intention in the following claims to cover such modifications and variations as fall within the true spirit and scope of the invention.

Claims

1. An apparatus for preventing diffusion of a gas under high pressure into the bulk of a liquid filling a substantially closed chamber, comprising:

a vessel for holding said liquid;

a port through the surface of said vessel, said port of sufficient size to permit the insertion into said vessel of means for testing one or more characteristics of said liquid;

a diffusion shield for cooperation with said vessel for substantially closing said port to define a liquid containing chamber;

means for maintaining a gas under high pressure exterior of said chamber and in fluid communication with said port; and

means for decreasing the volume of said chamber at a rate sufficient to prevent diffusion of said gas into the bulk of said liquid occupying said volume by moving one of said vessel or said diffusion shield.

2. The apparatus of claim 1 wherein said means for decreasing said volume comprises:

means for determining the diffusion rate of said gas into said liquid at said port;

means for establishing the minimum rate at which said volume must be decreased based on said determined diffusion rate; and

means for variably decreasing said volume at a rate at least as great as said established minimum rate.

3. The apparatus of claim 2 wherein said means for determining said diffusion rate, said means for establishing said minimum rate of decrease and said means for varying the rate of decrease comprises computer means.

4. An apparatus for preventing diffusion of a first fluid into the bulk of a second fluid filling a substantially closed chamber, comprising:

means for substantially enclosing said second fluid within a chamber of variable size to maintain said chamber substantially filled with said second fluid;

means for communicating pressure from the exterior to the interior of said chamber;

means for maintaining said first fluid substantially exterior of said chamber and in communication with said pressure communication means; and

means for decreasing the volume of said chamber at a rate sufficient to prevent diffusion of said first fluid into the bulk of said second fluid in said chamber.

5. The apparatus of claim 4 wherein said pressure communication means comprises fluid communication means.

6. The apparatus of claim 5 comprising means for variably decreasing said volume.

7. The apparatus of claim 6 further comprising means for determining the diffusion rate of said first fluid into said second fluid.

8. The apparatus of claim 7 comprising means for decreasing said volume at a rate sufficient to maintain the rate of discharge of said second fluid from said chamber at said fluid communication means at least as great as the rate of diffusion of said first fluid into said second fluid at said communication means.

9. The apparatus of claim 8 comprising means for decreasing said volume at a rate sufficient to maintain said rate of discharge equal to said rate of diffusion.

10. The apparatus of claim 7 comprising computer means for controlling the rate of decrease of said volume in response to said diffusion rate.

11. The apparatus of claim 5 wherein said means for enclosing comprises a vessel and cooperating diffusion shield.

12. The apparatus of claim 11 comprising means for moving at least one of said vessel or said diffusion shield to decrease said volume.

13. The apparatus of claim 12 comprising means for variably decreasing said volume.

14. A method for preventing diffusion of a first fluid into the bulk of a second fluid filling a substantially closed chamber, comprising:

maintaining said second fluid in a substantially closed chamber, said chamber substantially enclosing a variable volume but including pressure communication means between the interior and exterior of said chamber;

maintaining said first fluid substantially exterior to said chamber;

communicating the pressure of said first fluid with said second fluid at said pressure communication means; and

decreasing said volume of said chamber at a rate sufficient to prevent diffusion of said first fluid into the bulk of said second fluid in said chamber.

15. The method of claim 14 comprising contacting said first fluid with said second fluid at a fluid communication means.

16. The method of claim 15 comprising decreasing the volume of said chamber at variable rates.

17. The method of claim 16 comprising determining the diffusion rate of said first fluid into said second fluid and adjusting the rate at which the volume of said chamber is decreased.

18. The method of claim 15 wherein said chamber comprises a fluid containing vessel having an opening therein and a diffusion shield incompletely closing said opening and comprising decreasing the volume of said chamber by moving at least one of said vessel or said diffusion shield.

19. The method of claim 15 comprising decreasing the volume of said chamber at a rate sufficient to maintain the rate of discharge of said second fluid from said chamber at said fluid communication means at least as great as the rate of diffusion of said first fluid into said second fluid at said fluid communication means.

20. The method of claim 19 comprising decreasing the volume of said chamber at a rate sufficient to maintain said rate of discharge equal to said rate of diffusion.