Means To Prevent Inward Leakage Across Seals In A Well Tool

Abstract

A means is provided for preventing leakage of drilling fluid into a housing of a logging-while-drilling tool around seals in said housing. As illustrated, the tool has at least one oil-filled compartment in which a shaft is journaled. The shaft extends outward from the housing and has a rotor of a turbinelike means attached to the end thereof. A seal surrounds the shaft where it exits the housing. A pressure-sensitive means is provided on the tool upstream of the rotor and is positioned so that the pressure of the mud at that point is applied to the external surface of the pressure-sensitive means. Since the interior surfaces of both the pressure-sensitive means and the seal are in fluid communication with each other through the oil-filled compartment, the pressure on the interior surface of the seal will be effectively the same as the upstream pressure of the drilling fluid. By construction, the drilling fluid has to pass through either the rotor or the stator of the turbinelike means before the fluid acts on the exterior of the seal. Since an inherent drop in pressure occurs in the drilling fluid across the rotor or stator, the pressure of the oil acting inside the seal will be greater than the pressure of the drilling fluid acting on the outside of the seal. Accordingly, any leakage around the seal will be that of oil leaking out and not drilling fluid leaking in.

Description

BACKGROUND OF THE INVENTION

The present invention provides a means for preventing fluid from leaking into a housing around a seal in said housing and more particularly relates to a logging-while-drilling tool having a means for preventing fluid from outside the tool leaking into the tool around seals in said tool.

The desirability of a system which is able to measure downhole drilling parameters and/or formation characteristics and transmit them to the surface while actual drilling of an earth well is being carried out has long been recognized. Several such systems have been proposed and are commonly referred to as "logging-while-drilling" systems. In logging-while-drilling systems, one of the major problems exists in finding a means for telemetering the information concerning the desired parameter from a downhole location to the surface and having it arrive in a meaningful condition.

In this regard, it has been proposed to telemeter the desired information by means of a pressure wave signal generated in and transmitted through the mud system normally associated with rotary drilling operations. The pressure wave signal which is representative of a particular parameter is generated in the mud near the bit by a generating means or tool and the wave travels up the hole through the mud to a signal detector at the surface. One logging-while-drilling system utilizing this technique of telemetry is disclosed in U.S. Pat. No. 3,309,656 to John K. Godbey, issued Mar. 14, 1967.

However, systems of this type require the signal generating tool to be positioned directly in the flowing mud stream. Since drilling mud is normally highly erosive and is under great pressure adjacent the tool, the flowing mud stream will readily attack the vulnerable areas of the tool and invade the interior thereof to seriously affect the operation of the tool unless some means are provided to prevent this from occurring. One of the most vulnerable of these areas in signal generating tools of this type is that of the seals which seal various openings through the housing of the tool. For example, the signal generating tool disclosed in U.S. Pat. No. 3,309,656 comprises a motor-actuated, rotating turbine type valve which periodically interrupts a portion of the mud stream in response to a measured downhole condition, thereby imparting a representative pressure wave to the mud stream. The motor, sophisticated gearing, and the necessary electronics are mounted in a protective housing but the shaft of said motor exits from said housing to drive the valve which is positioned in the mud stream. The seal means around the rotating shaft is directly exposed to the pressure and the erosive effects of the mud and it should be readily apparent that if this seal means wears to the point where mud can leak by the seal into the interior of the tool, severe or even fatal damage to the tool will result. The same situation exists where a turbine mounted on the tool is driven by the mud stream to rotate a generator in the tool to produce the electrical power required for operation of the tool.

SUMMARY OF THE INVENTION

The present invention provides a means for a logging-while-drilling tool of the above-mentioned type for partially balancing the pressures between the interior and the exterior of the tool and for preventing the leaking of mud into the housing of said tool around or through seals on said housing.

The logging-while-drilling tool used to illustrate the present invention comprises a housing which is divided into three compartments. The housing is adapted to be mounted in a drill collar which in turn is coupled into a drill string near the bit. Mud, used in the drilling, circulates down the drill string, through the drill collar and around the tool housing, out the bit, and back to the surface.

The electronic section of the tool is sealed in the central compartment of the housing. An electric motor used for driving a signal generating valve is mounted in the compartment at the upper end of the housing. The shaft from the motor exits from the upper end of the upper compartment and is connected to the rotor of the turbine type valve. A seal surrounds the shaft where it exits the housing to prevent mud from penetrating into the upper compartment.

A generator for supplying electricity for the tool's operation is mounted in the compartment at the lower end of the housing. A shaft from the generator exits from the lower end of the lower compartment and is attached to the rotor of a power turbine. The turbine is driven by the circulating mud stream to drive the generator. A seal surrounds the generator shaft where it exits the housing to prevent mud from penetrating into the lower compartment.

The present invention provides a means for preventing leakage around the above-mentioned seals in the tool. Structurally, the present invention comprises a pressure-sensitive element strategically located on the tool upstream of the seal with which said element is to cooperate. The pressure-sensitive element, in effect, seals an opening through the tool which fluidly communicates the outside of the tool with the interior of a respective compartment. The upper and lower compartments of the tool are both filled with noncompressible fluid, e.g., lubricating oil. Since the upstream pressure of the mud is applied to the outer surface of said pressure-sensitive element and hence is applied to the oil within the compartment, the pressure of the interior of the seal which is in contact with the oil will be substantially balanced with that of the mud where it contacts the outer surface of the pressure-sensitive element.

By construction of the tool, the mud has to pass through restrictions in the rotor of the valve or the stator of the power turbine before it contacts the exterior of the respective seal means of the upper and lower compartments. Due to the inherent pressure drop in the mud stream which occurs as it flows through the respective restrictions, the pressure of the oil acting on the internal surface of the seal means, which is effectively the upstream pressure of the mud, will be greater than the downstream pressure of the mud acting on the external surface of the seal means. If the seal means wear to the point where leakage takes place around the seal means, due to the pressure differential across the seal means, the leakage must be that of oil leaking out from the tool instead of mud leaking in. Therefore, the present invention protects the interior of the tool from the damaging effects of the erosive mud if undue wear of the seal means occurs.

BRIEF DESCRIPTION OF THE DRAWINGS

The actual construction, operation, and the apparent advantages of the invention will be better understood by referring to the drawings in which like numerals identify like parts and in which:

FIG. 1 is a schematic elevation of a rotary drilling apparatus including in vertical section a well containing a drill string in which the present invention is employed;

FIG. 2 is a schematic elevation, partly in section, of a portion of the drill string of FIG. 1 having a logging-while-drilling tool mounted therein which utilizes the present invention;

FIG. 3 is a detailed sectional view of the upper portion of FIG. 2;

FIG. 4 is a detailed sectional view of the lower portion of FIG. 2; and

FIG. 5 is a partial view of a modification of the upper portion of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring more particularly to the drawings, FIG. 1 discloses the present invention as used in a logging-while-drilling system which is incorporated in a rotary drilling apparatus. A derrick 21 is disposed over a well 22 being formed in the earth 23 by rotary drilling. A drill string 24 is suspended within the well and has a drill bit 27 at its lower end and a kelly 28 at its upper end. A rotary table 29 cooperates with kelly 28 to rotate string 24 and bit 27. A swivel 33 is attached to the upper end of kelly 28 which in turn is supported by hook 32 from a traveling block (not shown). This arrangement not only supports the drill string 24 in an operable position within well 22 but also forms a rotary connection between the source of circulating drilling fluid, such as mud, and the drill string 24. It should be understood that "mud" as used throughout this disclosure is intended to cover those fluids normally used in rotary drilling operations.

The pump 36 transfers drilling mud from a source such as pit 34 through desurger 37 into mudline 38. Desurger 37 is adapted to reduce the pulsating effect of pump 36 as is well known in the art. The mud flows through mudline 38, flexible hose 39, swivel 33, drill string 24, and exits through openings (not shown) in drill bit 27 to pass outwardly into well 22. The mud then circulates upward carrying drill cuttings with it through the annulus between the well and drill string 24 to the surface of the earth 23. At the surface, well head 41 is secured to casing 39 which is cemented in the well 22. Pipe 42 is connected to casing 39 for returning the mud to pit 34.

As schematically illustrated in FIGS. 1 and 2, a logging and signal generating means or tool 46 is located in drill collar 26 which is part of the lower end of drill string 24 near bit 27. Tool 46 is preferably of the general type fully disclosed and described in U.S. Pat. No. 3,309,656 to John K. Godbey. Although the details of the electronics of the tool do not form a part of the present invention, a brief description of entire means 46 will be set forth in order to fully understand and appreciate the present invention.

Transducer means, shown schematically at 47 (see FIG. 2), senses a downhole condition, e.g., a strain gauge which senses downhole weight on bit 27, and converts it to a corresponding electrical signal. This electrical signal in turn is applied to control circuitry sealed in compartment 48 of the tool which in turn allows current from electric power source (e.g., generator) 49, to drive variable speed, electric motor 50 at a speed determined by the value of the electrical signal. Motor 50 is coupled to rotary valve 52 through gear train 53 so valve 52 will rotate at a set speed determined by the speed of motor 50. Valve 52, which is comprised of stator 54 and rotor 55, will interrupt flow of mud therethrough in such a manner that a pressure wave signal representative of the sensed condition will be generated in the mud. This signal then travels up through the mud in drill string 24 (FIG. 1) and is detected at the surface by sensor 30 which in turn is connected to signal processing equipment 31. A power turbine 57 having a stator 58 and a rotor 59 is used to drive generator 49.

In the system described above, the signal generating tool 46 is continuously exposed to the flow of mud which passes down the interior of drill string 24 and through valve 52, annulus 70 between means 46 and collar 26, and out turbine 57. It should be obvious that the flowing mud, normally being highly erosive and under high pressure readily attacks vulnerable spots within tool 46. Some of the most vulnerable of these spots are those of the seals 60, 61, surrounding the rotating shaft 51 on valve 52 and rotating shaft 56 of turbine 57, respectively. As erosion of these seals occurs, mud would normally penetrate into the interior of tool 46 where it would quickly damage the internal components, e.g., bearings, gears, etc., of the tool. The present invention prevents such damage from occurring.

Briefly, the invention involves filling compartments 62, 63 of tool 46 in which the rotating shafts 51, 56, respectively, are journaled with a noncompressible fluid, e.g., lubricating oil. Pressure-sensitive means 64, 65 are provided at strategic locations within tool 46 so that the pressure inside an oil-filled compartment at the seal is greater than the pressure of the mud flowing on the outside of said compartment at the seal. Reference will be made to the more detailed structure disclosed in FIGS. 3 and 4 for a better understanding of the invention.

FIG. 3 discloses the upper part of tool 46 including the upper end of compartment 62, rotating shaft 51, sealing means 60, and pressure-sensitive means 64. More specifically, housing 46a is positioned and secured inside collar 26. Stator 54 of valve 52 is secured against movement on housing 46a by set screw 54a or the like. Stator 54 has a plurality of longitudinal slots therethrough, although not shown in FIG. 3. Shaft 51 is journaled in housing 46a by means of bearings 71. Rotor 55, having longitudinal slots 55a therethrough, is fixed to shaft 51 by means of tapered bushing 72, key 73, and nut 74. Pressure-responsive means 64 comprising a flexible bellows of suitable material, e.g., acrylo-nitrile rubber, is attached to an upstanding flange 75 of rotor 55 whereby it will rotate with said rotor.

Press-fitted or otherwise secured within annular recess 76 of rotor 55 is an annular seal block 60a of suitable material, e.g., tungsten carbide, which cooperates with annular seal block 60b which in turn is slidably mounted in recess 77 of housing 46a. Spring 78, positioned in spring retainer 79, normally biases block 60b outward into contact with block 60a to form the sealing surface of seal means 60. The internal diameters of blocks 60a and 60b and spring retainer 79 are all larger than that of adjacent shaft 51 so that a passageway 80 is formed between said elements and the shaft. Elongated passages 81 in rotor 55 communicate the interior of bellows 64, through passageway 80, into compartment 62. Alternate structure for communicating the interior of bellows 64 with compartment 62 is shown in FIG. 5. Passage 81a is provided through shaft 51a which opens at one end into bellows 64 and at the other end into compartment 62.

Operation of the above-described portion of the invention is as follows. Compartment 62 is filled with non-compressible fluid, e.g., lubricating oil or the like, through port 82 (FIG. 2) with plug 83 removed from vent passage 84 in bellows 64 (FIG. 3). Lubricating oil is preferred in that it also functions to lubricate bearing, gearing, seals, etc., and serves as a heat transfer meduim for the various elements. When compartment 62 and bellows 64 are filled, port 82 and vent passage 84 are closed. Protective cap 85 having openings 86 therethrough is secured over bellows 64 by screws 87. When signal generating tool 46 is in its operating position, drilling mud will flow down drill string 24 through collar 26, and around housing 46a. Mud will enter openings 86 in cap 85 and exert pressure P.sub.1 on the exterior of bellows 64. Due to the head of mud, its weight, etc., pressure P.sub.1 will be substantial. However, since the bellows and compartment 62 are filled with oil, the pressure P.sub.2 at the interior of seal 60 will be approximately the same as pressure P.sub.1, thereby balancing the pressures across the tool. The mud, as it continues to flow downward, will pass through slots 55a of rotor 55 which inherently causes a pressure drop in the mud stream across these points. Therefore, the pressure P.sub.3 which acts on the exterior of seal means 60 will be less than the pressure P.sub.2 which acts on the interior of seal 60. This pressure differential will cause any leakage which may occur across seal 60 to be that of oil leaking outward into the mud instead of mud leaking into the interior of means 46a.

FIG. 4 discloses a slightly different application of the present invention as it applies to the lower portion of tool 46. Housing 46a is secured in collar by spider 90 having longitudinal slots 90a therethrough. Rotating shaft 56 is journaled in housing 46a by means of bearings 92 and spacer 93. Rotor 59 of power turbine 57 is fixed to shaft 56 by key 94, nut 94a, cap 95, and screw 96 while stator 58 of turbine 57 is fixed to housing 46a by screws 97. Seal block 61a of suitable material, e.g., tungsten carbide, is pinned or otherwise secured to rotor 59 so it will rotate therewith. Sliding seal block 61b of suitable material, e.g., graphite, is slidably mounted in annular recess 98 in housing 46a and is normally biased outward into contact with block 61a by spring 99 to form the sealing surface of seal means 61.

Housing 46a has a recess 100 in the wall thereof which communicates by means of openings 101 with the interior of compartment 63. Clearances between spacer 93 and housing 46a and shaft 56, openings 102 through spacer 93, bearings 92, and clearance between spring retainer 103 and shaft 56 form a passageway from recess 100 to the interior of seal 61. A flexible diaphragm 65 is secured in recess 100 so that it overlies and seals openings 101 from the exterior of tool 46.

Operation of the lower portion of the invention is as follows. Compartment 63 is filled with lubricating oil or the like through port 107 (FIG. 2). When generating tool 46 is in its operating position, drilling mud will flow down drill string 24, through collar 26, and around housing 46a. Mud will enter recess 100 and exert pressure P.sub.4 on diaphragm 65. Since fluid communication exists between the interior of diaphragm 65 and the interior of seal 61 and compartment 63 is filled with noncompressible oil, the pressure P.sub.5 at the interior of seal 61 will be effectively the same as pressure P.sub.4. The downward flowing mud passes through slots 90a on spider 90 and through the slots (not shown) on stator 58. This inherently causes a pressure drop in the mud stream across these points. Therefore, P.sub.6 which acts on the exterior of seal 61 is less then P.sub.5 which acts on the interior of seal 61. This pressure differential causes any leakage which may occur across seal 61 to be that of oil leaking from inside compartment 63 and not that of mud leaking into tool 46.

Claims

What is claimed is:

1. A well tool adapted to be positioned in a circulating drilling fluid stream normally associated with a rotary drilling apparatus comprising:

a housing having a compartment in the upper end thereof, said compartment adapted to be filled with a noncompressible fluid;

a shaft journaled in said housing and extending upward through said housing from said compartment;

seal means surrounding said shaft to seal said housing where said shaft exits same;

a rotor attached to the upper end of said shaft and positioned in said drilling fluid stream, said rotor having openings therein to allow drilling fluid to pass therethrough;

a pressure-sensitive means attached to the upper portion of said rotor, the exterior of said pressure-sensitive means being exposed to said drilling fluid stream before said stream passes through said openings in said rotor; and

means forming a passage which fluidly communicates the interior of said pressure-sensitive means with the interior of said seal means within said compartment.

2. The well tool of claim 1 wherein said pressure-sensitive means comprises:

a flexible bellows.

3. A well tool adapted to be positioned in a circulating drilling fluid stream normally associated with a rotary drilling apparatus comprising:

a housing having a compartment in the lower end thereof, said compartment adapted to be filled with a noncompressible fluid;

a shaft journaled in said housing and extending downward through said housing from said compartment;

seal means surrounding said shaft to seal said housing where said shaft exits same;

a turbine comprising:

a rotor attached to the lower end of said shaft and positioned in said drilling fluid stream; and

a stator affixed to said housing above said rotor and having openings therein to allow drilling fluid to pass therethrough; and

a pressure-sensitive means on said tool upstream of said stator, the exterior of said pressure-sensitive means being exposed to said drilling fluid stream before said fluid passes through said openings in said stator and the interior of said pressure-sensitive means being in fluid communication with the interior of said seal means within said compartment, said pressure-sensitive means comprises a flexible diaphragm secured over at least one opening through said housing into said compartment.

4. A logging-while-drilling tool adapted to be positioned in a drill string of a rotary drilling apparatus whereby said tool will be in the path of drilling fluid circulating through the drill string, said tool comprising:

a housing having at least an upper and a lower compartment, said upper and said lower compartments adapted to be filled with a noncompressible fluid;

a first shaft journaled in said upper compartment and extending upward through said housing from said upper compartment;

a first seal means surrounding said first shaft to seal said housing where said first shaft exits same;

a first rotor attached to the upper end of said first shaft and positioned in said drilling fluid, said first rotor having openings therein to allow drilling fluid to pass therethrough;

a first pressure-sensitive means attached to the upper portion of said first rotor, the exterior of said first pressure-sensitive means being exposed to said drilling fluid before said fluid passes through said openings in said first rotor;

means forming a passage which fluidly communicates the interior of said first pressure-sensitive means with the interior of said first seal means within said upper compartment;

a second shaft journaled in said housing and extending downward through said housing from said lower compartment;

a second seal means surrounding said shaft to seal said housing where said shaft exits same;

a turbine comprising:

a second rotor attached to the lower end of said second shaft and positioned to be rotated by said drilling fluid, and

a stator affixed to said housing above said second rotor and having openings therein to allow drilling fluid to pass therethrough; and

a second pressure-sensitive means on said tool upstream of said stator, the exterior of said second pressure-sensitive means being exposed to said drilling fluid before said fluid passes through said openings in said stator and the interior of said second pressure-sensitive means being in fluid communication with the interior of said second seal means within said lower chamber.

5. The logging-while-drilling tool of claim 4 wherein said first pressure-sensitive means comprises:

a flexible bellows; and

said second pressure-sensitive means comprises:

a flexible diaphragm secured over at least one opening through said housing into said compartment.