Title:
Modular weight bar
Kind Code:
A1


Abstract:
A modular weight bar usable in conjunction with downhole tools disposed within a pressurized wellbore. The modular weight bar adds mass to the downhole tool so it can be suspended and lowered within the pressurized wellbore on wireline. The modular weight bar is separatable from the downhole tool at a selected depth within the wellbore thereby allowing the downhole tool to be further lowered within the wellbore without being accompanied by the weight bar.



Inventors:
Wills, Philip (Aberdeenshire, GB)
Application Number:
10/442694
Publication Date:
03/31/2005
Filing Date:
05/21/2003
Assignee:
BAKER HUGHES, INCORPORATED
Primary Class:
Other Classes:
166/332.4
International Classes:
E21B23/02; E21B23/04; E21B23/14; E21B47/01; (IPC1-7): E21B23/00
View Patent Images:



Primary Examiner:
STEPHENSON, DANIEL P
Attorney, Agent or Firm:
Darryl M. Springs (Houston, TX, US)
Claims:
1. A modular weight bar for use with a downhole tool comprising: a body formed for insertion within a wellbore; an engagement system formed to selectively engage the modular weight bar with the wellbore; and a deployment system formed to releasably secure said modular weight bar to the downhole tool, wherein included with the wellbore is at least one protrusion formed on the inner circumference of the wellbore.

2. The modular weight bar of claim 1, wherein said body is configured to house and protect the downhole tool.

3. The modular weight bar of claim 1, wherein said body encompasses the downhole tool and contains within said body hazardous material associated with the downhole tool.

4. The modular weight bar of claim 1, wherein the weight of said modular weight bar is substantially equal to the weight of a length of wireline that suspends the modular weight bar and down hole tool at a selected depth within the wellbore.

5. The modular weight bar of claim 1, where said deployment system comprises a rod disposed on the downhole tool having ridges formed on the outer surface of said rod, and corresponding ridges formed within an aperture formed on said body, where said aperture is situated substantially coaxial on said body.

6. The modular weight bar of claim 1, wherein said engagement system comprises at least one latch tab formed on the outer surface of said body formed to contact said at least one protrusion formed on the inner circumference of the wellbore.

7. The modular weight bar of claim 1, wherein said deployment system separates the wireline tool from said modular weight bar at a selected depth within the wellbore, thereby enabling the wireline tool to be deployed to a depth greater than the selected depth within the wellbore.

8. The modular weight bar of claim 1 further comprising at least one slip disposed on said body; and a sliding sleeve moveable along said body to deploy said at least one slip into a securing position.

9. The sliding sleeve of claim 8 further comprising at least one latch tab secured to said sliding sleeve, said latch tab being formed to matingly contact said at least one protrusion formed on the inner circumference of the wellbore such that the sliding sleeve is moved along said body upon contact of said latch tab.

10. The modular weight bar of claim 8 wherein said slips are remotely activatable.

11. The modular weight bar of claim 10 wherein said slips are remotely activatable from a signal transmitted via a wireline connected to the wireline tool.

12. The modular weight bar of claim 8 wherein said slips are activated by hydraulic pressure.

13. The modular weight bar of claim 12 further comprising at least one rupture disk formed to rupture at a hydraulic pressure corresponding to a selected depth within the wellbore thereby securing and suspending said modular weight bar to the wellbore at the selected depth.

14. The modular weight bar of claim 12 further comprising a pressure chamber proximate to said sliding sleeve, whereby when the modular weight bar is disposed at the selected depth the hydrostatic pressure within the wellbore is sufficiently greater than the pressure within the pressure chamber to move the sliding sleeve into the pressure chamber thereby securing and suspending said modular weight bar to the wellbore at the selected depth.

15. The modular weight bar of claim 8 further comprising a tapered edge provided on said sliding sleeve, said tapered edge formed for insertion between said at least one slip and said body as said sliding sleeve is upwardly urged, thereby outwardly extending said at least one slip into engaging contact with the wellbore.

16. The modular weight bar of claim 1, wherein said engagement system engages said modular weight bar within the wellbore and suspends said modular weight bar within the wellbore, thereby enabling the wireline tool to be deployed to a depth greater than the selected depth within the wellbore.

17. The modular weight bar of claim 1 where said engagement system comprises gravitationally resting said modular weight bar atop the downhole tool.

18. The modular weight bar of claim 1 further comprising a coaxial annular opening allowing for passage of a wireline therethrough.

19. A method of deploying a modular weight bar for use with a downhole tool within a wellbore comprising the steps of: disposing a downhole tool combined with a modular weight bar onto a wireline; inserting said modular weight bar and the downhole tool within a wellbore opening; lowering the combination within the wellbore to a depth within the wellbore; separating the modular weight bar from the downhole tool and suspending the modular weight bar within the wellbore; and lowering the downhole tool into the wellbore past the selected depth.

20. The method of claim 19 further comprising determining a selected depth within the wellbore such that the depth within the wellbore where said modular weight bar is separated from the downhole tool is substantially equal to the selected depth.

21. The method of claim 20 further comprising, forming at least one protrusion within the wellbore at approximately the selected depth.

22. The method of claim 21 further comprising adding at least one latch tab on said modular weight bar formed to mate with the at least one protrusion and secure and suspend the modular weight bar within the wellbore.

23. The method of claim 20 further comprising providing at least one slip to said modular weight bar, where the slip is activatable to secure and suspend the modular weight bar within the wellbore at approximately the selected depth.

24. The method of claim 19 further comprising raising the downhole tool from below the selected depth upward until the downhole tool recontacts the modular weight bar to reform a combination.

25. The method of claim 19 further comprising determining the total mass of the combination that is required to overcome wellbore pressure and providing sufficient mass to said modular weight bar so the mass of the combination is at least as great as the mass required to overcome wellbore pressure.

Description:

RELATED APPLICATIONS

This application claims priority from co-pending U.S. Provisional Application No. 60/441,007, filed Jan. 17, 2003, the full disclosure of which is hereby incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to the field of exploration and production of hydrocarbons from wellbores. More specifically, the present invention relates to a method and apparatus to operate wireline tools within a pressurized wellbore with increased effectiveness and at a greater wellbore depth. Yet even more specifically, the present invention relates to a method and apparatus to operate wireline tools within a pressurized wellbore having a releasably attached weight bar that is selectively removable at a specified depth within the wellbore.

2. Description of Related Art

Often the pressure within a wellbore exceeds the ambient pressure at the surface of the wellbore. Thus, when objects such as downhole tools are being inserted into a pressurized wellbore, a pressure differential will exist across the object between the wellbore and the surface. Downhole tools include perforating guns, logging devices, tool fishing devices, and any other apparatus inserted within a wellbore associated with hydrocarbon exploration/production or other wellbore operations.

When the object being inserted into a pressurized wellbore is attached to and conveyed by a rigid connector, such as a tubing string, the pressure differential across the object and tubing can often be overcome by supplying downward force onto the tubing. However, when conveying objects by wireline, a force applied from above the wireline cannot urge the objects downhole since wireline is generally flexible and has no compressive strength to push the objects downward into the wellbore to overcome the pressure differential. Although the pressure differential across a downhole tool or other object being inserted into a wellbore is equalized once the tool is fully within the wellbore, an upward force will still be exerted onto the wireline that is a function of its cross sectional area and the pressure in the wellbore. In fact, a pressure differential of less than 6.9×105 Pa (100 pounds per square inch) is a sufficient pressure differential to prevent an object that is suspended by a wireline from being lowered into a wellbore due to the pressure differential across the cross sectional area of the wireline.

Current wireline operations within pressurized wellbores sometimes use a weight bar attached to the downhole tool so that the combined weight of the weight bar and of the downhole tool exceeds the upward force exerted onto the downhole tool and wireline by the wellbore pressure. However, use of the weight bar in conjunction with a downhole tool to overcome wellbore pressure differentials presents many problems and has many limitations. Some of the problems with weight bars are that addition of a weight bar to a downhole tool reduces the depth at which a downhole tool can be lowered into a wellbore, weight bars cannot be used on all oilrigs due to height restrictions, and the presence of weight bars proximate to logging tools can diminish the accuracy of logging data.

In situations where the downhole tool is being lowered deep into a wellbore, such as in excess of a few thousand feet, the mass of wireline within the wellbore adds to the overall weight of what is being supported by the wireline. While the total weight of the wireline in the wellbore has little effect on the segment of wireline proximate to the downhole tool, the segment of wireline proximate to the surface is greatly affected, since the tool and all associated wireline is supported by the wireline proximate to the surface. While the strength of the wireline can be increased by using thicker wireline this does not help the weight issue since thicker wireline also has an increased mass per unit length. Further, thicker wireline also results in a need for more added weight since increasing the cross sectional area of the wireline increases the pressure differential across the wireline. As such, the maximum depth that a downhole tool can be lowered into a wellbore is reduced by the addition of the weight bar mass.

Space limitations are also a problem with some currently developed weight bars. Adding currently developed weight bars to a downhole tool results in an overall length that can be twice the length of the downhole tool itself. In some instances the oilrig platform at the wellbore surface has limited vertical space and cannot accommodate such a long length. Therefore restrictions of vertical height at some wellbores exist regarding the use and implementation of currently developed weight bars.

Addition of a weight bar also causes problems when using downhole tools in deviated wellbores. As a downhole tool is passed through deviated sections (non-vertical) of a wellbore, the tool will drag on the side of the wellbore. If the wireline is heavily loaded due to an added weight bar, the wireline loading is more likely to be close to the yield point of the wireline. When this is the case, the added loading caused by dragging the downhole tool along the borehole can take the wireline to its yield point and stretch the wireline that results in a jerky motion of the wireline tool up the wellbore instead of a smooth controlled ascent. This is especially a problem when the downhole tool is a well logging device because the jerking motion results in poor logging results since the well logging requires a steady constant ascent to obtain proper readings. Further, many downhole tools require that they be situated in the center of the wellbore. Even though many are equipped with centralizers, the added mass of a weight bar can temporarily deform the centralizers and eccentrically position the downhole tool within the wellbore. Downhole tools such as logging devices, perforating guns, or collar locators, may not perform their intended function if they are not centrally situated within the wellbore.

Certain dangers exist with many downhole tools that pose hazards to the downhole tool, the personnel handling the tool, or both. For example, production logging tools are susceptible to structural damage, especially when deployed in difficult or deviated wells. Even when extra care is taken to protect these tools, these tools can be damaged if they strike the inner surface of the wellbore or the production string. Some downhole tools contain radioactive sources that are potentially harmful to the workers employing the tool, thus radioactive monitoring is necessary in order to use these types of tools. Other downhole tools vulnerable to damage during use are perforating guns. Perforating guns can also be mechanically damaged during insertion into the wellbore, especially when they are in close contact with valves at the wellbore surface such as well control valves, master valves, swab valves, and sub-sea safety valves.

Another downhole tool that poses a risk is a chemical cutter. Chemical cutters, while typically sealed, can still leak flammable chemicals that will combust when exposed to an ignition source. Leakage can most likely occur when the cutter is being pressure tested or just after opening up the well. Ignition of the chemicals from a chemical cutter at this time can likely result in serious personal injury or death. Another hazard to wellbore personnel is from some wells that contain hazardous chemicals within the wellbore that will contact and coat the downhole tool. Consequently when the downhole tool is removed from the wellbore the personnel stationed at the wellbore surface are at risk of being contaminated or injured by the hazardous substance.

Therefore, there exists a need for disposing and lowering devices within wellbores that can allow the tools to be lowered in spite of pressure within the wellbore and does not limit use and application of the devices once inside of the wellbore. Additionally, a need exists for protecting a downhole tool from damage while also protecting personnel using the downhole tool from the dangers encountered during use of the downhole tool.

BRIEF SUMMARY OF THE INVENTION

The present invention includes a modular weight bar for use with a downhole tool comprising a body formed for insertion within a wellbore, an engagement system formed to selectively engage the modular weight bar with the wellbore, and a deployment system formed to releasably secure the modular weight bar to the downhole tool. Included with the wellbore is at least one protrusion formed on the inner circumference of the wellbore. The body of the modular weight bar can be configured to house and protect the downhole tool. The body of the modular weight bar can encompass the downhole tool and contain within the body hazardous material associated with the downhole tool. The weight of the modular weight bar can be substantially equal to the weight of a length of wireline that suspends the modular weight bar and downhole tool at a selected depth within the wellbore.

One embodiment of the deployment system of the present invention comprises a rod disposed on the downhole tool having ridges formed on the outer surface of the rod. Corresponding ridges are formed within an aperture formed on the body, where the aperture is situated substantially coaxial on the body. The deployment system of the present invention separates the wireline tool from the modular weight bar at a selected depth within the wellbore. This enables the wireline tool to be deployed to a depth greater than the selected depth within the wellbore.

One embodiment of the engagement system of the present invention comprises at least one latch tab formed on the outer surface of the body formed to contact said at least one protrusion formed on the inner circumference of the wellbore. An alternative embodiment of the engagement system of the present invention comprises at least one slip disposed on the body and a sliding sleeve moveable along the body to deploy the at least one slip into a securing position. The modular weight bar of claim 8 wherein said slips are remotely activatable. The slips can be remotely activatable from a signal transmitted via a wireline connected to the wireline tool. Another alternative is that the slips can be activated by hydraulic pressure. The engagement system of the present invention can also comprise gravitationally resting the modular weight bar atop the downhole tool.

Yet further alternatively, the sliding sleeve can also comprise at least one latch tab secured to the sliding sleeve where the latch tab is formed to matingly contact the at least one protrusion formed on the inner circumference of the wellbore. Contact between the latch tab and the at least one protrusion causes the sliding sleeve to be moved along the body upon contact of the latch tab.

Optionally combined with the sliding sleeve further comprising at least one rupture disk formed to rupture at a hydraulic pressure corresponding to a selected depth within the wellbore thereby securing and suspending said modular weight bar to the wellbore at the selected depth. The modular weight bar can further comprise a pressure chamber proximate to the sliding sleeve such that when the modular weight bar is disposed at the selected depth, the hydrostatic pressure within the wellbore is sufficiently greater than the pressure within the pressure chamber to move the sliding sleeve into the pressure chamber thus securing and suspending the modular weight bar to the wellbore at the selected depth.

A tapered edge can be provided on the sliding sleeve and formed for insertion between the at least one slip and the body as the sliding sleeve is upwardly urged, this action outwardly extends the at least one slip into engaging contact with the wellbore. Further, the engagement system of the modular weight bar engages the modular weight bar within the wellbore and suspends the it within the wellbore, thereby enabling the wireline tool to be deployed to a depth greater than the selected depth within the wellbore. The modular weight bar can further comprise a coaxial annular opening allowing for passage of a wireline therethrough.

The present invention can also include a method of deploying a modular weight bar for use with a downhole tool within a wellbore. One embodiment of the method of the present invention comprises disposing a downhole tool combined with a modular weight bar onto a wireline then inserting the modular weight bar and the downhole tool within a wellbore opening. The method also considers lowering the combination within the wellbore to a depth within the wellbore and then separating the modular weight bar from the downhole tool. After suspending the modular weight bar within the wellbore the downhole tool is lowered deeper into the wellbore.

The method of the present invention further comprises determining a selected depth within the wellbore such that the depth within the wellbore where the modular weight bar is separated from the downhole tool is substantially equal to the selected depth. The method also considers forming at least one protrusion within the wellbore at approximately the selected depth, adding at least one latch tab on the modular weight bar formed to mate with the at least one protrusion, and securing and suspending the modular weight bar within the wellbore.

A yet further alternative of the method of the present invention comprises providing at least one slip with the modular weight bar, where the slip is activatable to secure and suspend the modular weight bar within the wellbore at approximately the selected depth. The method of the present invention also considers raising the downhole tool from below the selected depth upward until the downhole tool recontacts the modular weight bar to reform a combination.

The method of the present invention can include determining the total mass of the combination that is required to overcome wellbore pressure and providing sufficient mass to the modular weight bar so the mass of the combination is at least as great as the mass required to overcome wellbore pressure.

Accordingly, one of the advantages provided by the present invention is the ability to operate a downhole tool within a pressurized wellbore, where the downhole tools can be lowered into the pressurized wellbore by adding weight to the downhole tool. Further, an additional advantage provided by the present invention is the ability to selectively separate and deploy the added weight from the downhole tool within the wellbore, and lower the downhole tool into the wellbore at deeper depths than if the weight were still combined with the downhole tool.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 depicts the prior art method of deploying wireline tools into a wellbore.

FIG. 2 illustrates on embodiment of the present invention within a wellbore.

FIG. 3 depicts a schematic representation of one embodiment of the present invention in use within a wellbore.

FIG. 4 illustrates a cross sectional view of one embodiment of the present invention.

FIG. 5 illustrates a cross sectional view of one embodiment of the present invention.

FIG. 6 illustrates a cross sectional view of one embodiment of the present invention.

FIG. 7 depicts one embodiment of the present invention including a fishing neck.

FIG. 8 illustrates a cross sectional view of a tool catcher included with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

With reference to the drawing herein, one embodiment of a modular weight bar 30 for use with a downhole tool 20 is shown in FIG. 2. This embodiment of the modular weight bar 30 comprises a body 31 formed to receive a downhole tool 20 within the body 31 and a deployment system that provides for releaseable attachment of the modular weight bar 30 to the downhole tool 20. In the embodiment of FIG. 2, the modular weight bar 30 provides added mass to the downhole tool 20 so the combination downhole tool 20 and modular weight bar 30 can be lowered into a pressurized wellbore on a wireline 10. To accommodate the wireline 10 the modular weight bar 30 should incorporate an opening 44 at its top that is substantially coaxial to the body of the modular weight bar 30. The modular weight bar 30 also works to house and protect the downhole tool 20 with its sleevelike configuration. Formed on the outer surface of the body 31 is at least one latch tab 34 situated to contact at least one protrusion such as a nipple profile 32 (or profiles) or a device commonly known as a “No-Go,” formed on the inner surface of the wellbore 5. The shape and material of the latch tab 34 is not critical to the invention, however the latch tab 34 must be able to withstand the harsh downhole environment and still possess sufficient structural integrity to secure the modular weight bar 30 within the wellbore 5 and suspend it where it contacts the nipple profiles 32.

In operation, the modular weight bar 30 is secured around the downhole tool 20 prior to inserting the combination of the downhole tool 20 and the modular weight bar 30 into the wellbore 5. Combining the modular weight bar 30 with the downhole tool 20 forms a sufficient mass to overcome the upward force exerted onto the downhole tool 20 and the wireline 10 by pressure in the wellbore 5. The mass can come from the configuration of the modular weight bar 30, or from the addition of weights (not shown) onto the modular weight bar 30. Having overcome the pressure resistance within the wellbore 5, the combination modular weight bar 30 and downhole tool 20 can be lowered within the wellbore 5.

One of the novel features of the present invention is that the modular weight bar 30 can be separated from the downhole tool 20 within the wellbore 5. It is preferred that separation of the modular weight bar 30 from the downhole tool 20 take place at a selected depth 4 within the wellbore 5. While the selected depth 4 can be determined in any one of a number of alternative methods, the preferred method is to calculate the depth within the wellbore 5 at which the mass of the wireline 10 deployed within the wellbore 5 is approximately equal to the mass of the modular weight bar 30. When these masses are approximately equal, the added weight of the modular weight bar 30 is no longer necessary to overcome the resistance to downward movement due to the pressure differential across the wireline 10 and can thus be separated from the downhole tool 20.

FIG. 3 provides an illustration of how the wireline tool 20 is further lowered into the wellbore 5 after it has been deployed from the modular weight bar 30. The specific manner of separating the modular weight bar 30 from the downhole tool 20 is not critical to the present invention, but instead can be accomplished in many different ways, including but not limited to the use of wellbore profiles, force activated slips, and pressure activated slips, to name but a few.

As is well known, a nipple profile 32 (or profiles) generally is installed within tubing or casing within a wellbore 5 for various reasons while the well is being completed. FIGS. 2 and 3 illustrate one embodiment of the present invention utilizing an existing nipple profile 32 (or detent) as a support on which to suspend the modular weight bar 30. Thus as long as a nipple profile 32 exists within the wellbore 5 that is at or below the selected depth 4, the latch tab(s) 34 on the body 31 can be mated with the nipple profile 32 to support and suspend the modular weight bar 30 within the wellbore 5 after the modular weight bar 30 has been separated from the downhole tool 20. It is appreciated that it is within the capabilities of one skilled in the art to identify a nipple profile 32 within a wellbore 5 and mate it with the latch tab(s) 34 of the present invention.

The embodiment of the present invention depicted in FIG. 4 can also work in combination with a nipple profile 32, some other protrusion positioned within the inner surface of a wellbore 5, or be remotely activated (such as from the surface of the wellbore 5) in the absence of any protrusions. The latch tab(s) 34 of FIG. 4 are formed onto a sliding sleeve 35 such that when the combination downhole tool 20 and modular weight bar 30 are lowered into a wellbore 5 and the latch tab(s) 34 contact a stationary obstruction, such as a nipple profile 32, the sliding sleeve 35 will be urged upward toward slips 36. The sliding sleeve 35 has a tapered edge 35a such that the thickness of the sliding sleeve 35 is smallest at the tapered edge 35a and increases in thickness along the length of the sliding sleeve 35 away from the tapered edge 35a. As the sliding sleeve 35 is moved upward and the tapered edge 35a slides between the slips 36 and the body 31a, the slips 36 are urged outward and press against the inner surface of the wellbore 5. The slips 36 are urged outward with sufficient force to put them into a securing position that results in locking engagement of the modular weight bar 30 with the inner surface of the wellbore 5. Engaging the slips 36 with the wellbore inner surface consequently secures and suspends the modular weight bar 30 within the wellbore 5 which allows the downhole tool 20 to be further deployed deeper within the wellbore 5.

FIG. 5 illustrates yet another embodiment of the present invention, here hydraulic pressure is used to secure the modular weight bar 30 to the wellbore 5 inner surface. In this embodiment the reservoir 38 is a pressurized chamber in which the hydraulic sleeve 37 can be inserted. As the combination downhole tool 20 and modular weight bar 30 is lowered into the wellbore 5, as is well known, the hydrostatic pressure within the wellbore 5 increases with depth as the combination is lowered into the wellbore 5. Ultimately the pressure impinging upon the lower surface 37a of the hydraulic sliding sleeve 37 overcomes the force exerted on the hydraulic sliding sleeve 37 by the pressure within the reservoir 38. When the pressure within the wellbore 5 exceeds the pressure of the reservoir 38 the sliding sleeve 35 moves upward that outwardly extends the slips 36 and thereby secures the modular weight bar 30 to the wellbore inner surface in the manner above described.

The hydraulic pressure mode of operation of the present invention can be made more precise by segmenting the reservoir 38 into a first zone 38a and a second zone 38b where the first zone 38a and the second zone 38b are separated by a rupture disk 39. As the modular weight bar 30 is disposed lower into the wellbore 5 the hydrostatic pressure of the wellbore 5 increases. The increasing hydrostatic pressure within the wellbore 5 pushes on the bottom of the hydraulic sliding sleeve 37 and urges it into the second zone 38b, which in turn raises the pressure within the second zone 38b. While the fluid (gas, air, hydraulic fluid, or other fluid) within the second zone 38b increases in pressure as the hydraulic sliding sleeve 37 is pushed into it, it should provide sufficient resistance to prevent the tapered edge 35a of the sliding sleeve 35 from contacting the slips 36. When the pressure differential between the first zone 38a and the second zone 38b exceeds the burst pressure of the rupture disk 39, the rupture disk 39 will burst and allow the hydraulic sliding sleeve 37 to freely move into the second zone 38b. One skilled in the art can determine the hydrostatic pressure at the selected depth 4 and thus design and implement a rupture disk 39 that will burst at that hydrostatic pressure thereby securing and suspending the modular weight bar 30 approximately at the selected depth 4.

As is well known, rupture disks can be accurately formed to burst within a relatively finite pressure range. Methods and manners of securing and suspending the modular weight bar 30 within the wellbore 5 exist other than those already discussed, such as initiating a securing device by an electrical motor, an electrical relay, an electrical/hydraulic solenoid, by either electrical transmission down an electric line, optical transmissions by fiber optics, hydraulic transmissions down fluid columns, or any combination of these. Furthermore, it is not necessary that the downhole tool 20 be released from the modular weight bar 30 at the same time the modular weight bar 30 is set instead these can be initiated separately if required.

Moreover, the activation of the slips 36 can be initiated from the surface by any one of a number of now known or later developed techniques, electrically such as by an electrical connection, hydraulically for example by a fluid column, a combination of electrical and hydraulic initiation, and optically by fiber optic transmission. Remote activation is especially useful in the absence of a protrusion at a depth suitably close to a selected depth 4. The slips 36 can be propelled into engaging contact with the wellbore by an electrical device, such as a motor, hydraulically propelled by hydraulic pressure, or by a pyro/ballistic device.

Although the preferred arrangement of the present invention is a modular weight bar 30 that encompasses and circumscribes the downhole tool 20, other arrangements exist as well. For example, the modular weight bar 30 could be wholly disposed atop or below the downhole tool 20, and therefore not encompassing the downhole tool 20. In one such embodiment of the present invention where the modular weight bar 30 resides above the downhole tool 20 (FIG. 6), the modular weight bar 30 is not secured to the downhole tool 20 but instead mates with the downhole tool 20 by resting on its top. In this embodiment latches 34a are formed on the outer surface of the modular weight bar 30 and catch on nipple profiles 32 at the selected depth 4 within the wellbore 5. An annulus 30a formed within the modular weight bar 30 provides for unrestricted passage of the wireline 10 through the modular weight bar 30.

A preferred manner of releasably mating the modular weight bar 30 to the downhole tool 20 involves implementing a tool catcher 44 onto the modular weight bar 30 and a corresponding fishing neck 42 onto the cablehead attached above the downhole tool 20. As is well known, the tool catcher 44 includes ridges formed on its inner circumference, such as a series of collets 45. As is also well known, the fishing neck 42 is a rod with ridges 43 formed thereon. The collets 45 are designed to grapple the corresponding ridges 43 formed on the outer surface of the fishing neck 42 and yet still be selectively releasable from the ridges 43 when a sufficient amount of force is applied. The design of the collets 45 and the fishing neck 42 should be such that the modular weight bar 30 can be secured to the downhole tool 20 and yet be easily detached and reattached. Since downhole operations often use such collet based mechanical systems for latching and unlatching fishing necks and as such are well suited for use with the present invention. It is appreciated that it is well within the capabilities of those skilled in the art to fabricate a tool catcher and fishing neck for use with the present invention without undue experimentation. Further, it is also preferred that the modular weight bar 30 be able to be recombined with the downhole tool 20 when the downhole tool 20 is raised up from below the selected depth 4.

It is preferred that a fishing neck (not shown) be included at the top of the modular weight bar. Inclusion of a fishing neck provides an alternative method to ensure the slip anchor mechanisms can be released when the modular weight bar is latched and then fished from above. It is appreciated that those skilled in the art can fabricate fishing equipment and slip anchor assemblies that allow slips to be released by application of a suitable mechanical force or impact.

Separating the modular weight bar 30 from the downhole tool 20 at a selected depth within the wellbore 5 provides many advantages to wellbore operators such as the ability to perform wellbore operations at a deeper depth, more accurate well logging results, and the opportunity to run heavier downhole tools within a wellbore 5. Removing the mass of a needed weight bar within the wellbore 5 relieves tension from the wireline 10 and enables the downhole tool 20 to be extended deeper within the wellbore 5. Well logging results taken from deviated wellbores are more accurate with the present invention since the reduced tension within the wireline 10 can eliminate the elastic effect experienced by tensioned wirelines. Additional advantages of the present invention are realized within deviated wellbores since many downhole tools, such as perforating guns and well logging devices, which are designed to be centrally located within the wellbore in order to provide accurate results. Eliminating the weight bar that can sometimes produce eccentric loading greatly improves the results of downhole tools. Further, in many instances height restrictions exist on an oilrig platform that limit the length of what can be inserted into a wellbore. Coaxially combining the present invention with a downhole tool reduces the overall length of a downhole tool and weight bar combination, thus allowing the present invention to be implemented in applications too restricted by height limitations to allow the current weight bar and downhole tool combinations.

Another advantage realized by application of the present invention to a downhole tool 20 is the elimination of certain hazards associated with use of the downhole tool 20. When the downhole tool 20 is either a production logging tool or a perforating gun, the modular weight bar 30 can be formed as a skirt that encompasses the entire tool thereby shielding the downhole tool 20 from mechanical damage caused by striking the downhole tool 20 against other solid objects, such as portions of the wellbore, valves, or production string. Further, the use of the modular weight bar 30 can provide protection to personnel using the downhole tool 20. In instances when the downhole tool 20 contains radioactive material or hazardous materials are present within the wellbore 5, the modular weight bar 30 can be formed to extend along the entire length of the downhole tool 20. When the modular weight bar 30 fully encompasses the downhole tool 20, it can protect associated personnel by absorbing or reflecting radioactive waves away from the personnel as well as preventing hazardous material from leaking from the downhole tool 20 and contaminating the personnel before the downhole tool 20 can be isolated and decontaminated.

The present invention described herein, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned, as well as others inherent therein. While a presently preferred embodiment of the invention has been given for purposes of disclosure, numerous changes exist in the details of procedures for accomplishing the desired results. These and other similar modifications will readily suggest themselves to those skilled in the art, and are intended to be encompassed within the spirit of the present invention disclosed herein and the scope of the appended claims.