1. Field of the Invention
The present invention pertains to a downhole tool for insertion in a drill stem for earth drilling and having interchangeable cylindrical half sleeve tool sections which are supported on a body. The interchangeable tool sleeve sections may comprise drill stem stabilizers, reamers or hole enlarging tools, for example.
2. Background
In oil, and gas well and other types of earth drilling operations it is often necessary to provide downhole tools interposed at predetermined points in the drill stem, also commonly called the drill string, for performing functions such as stabilizing or centralizing the drill stem in the hole, reaming the hole or other structures in the hole and performing various other operations such as undercutting or enlarging the hole diameter at a predetermined depth. Downhole tools such as stabilizers, reamers and the like are subject to high rates of wear and require frequent replacement or repair. Typically, these tools are formed on a body or sub having conventional pin and box threaded ends and adapted to be interposed in the drill stem between any two of the end-to-end coupled drill pipe sections, or connected to the lower end of the drill stem. The replacement of worn or damaged tools of the aforementioned type can be expensive and time consuming if it is required to break one or both of the joints between the tool body and the drill stem in order to replace the tool itself. Moreover, with each drill stem joint makeup or breakout operation there are the ever present dangers associated with handling the pipe section above the joint and creating the possibility wherein the drill stem portion remaining in the hole may fall out of the slips or other supports on the drill rig floor and back into the drillhole. Accordingly, it is highly desirable to be able to replace downhole tools such as stabilizers, reamers and the like without decoupling the tool itself from the drill stem.
Another problem associated with replacing drill stem stabilizers, reamers and other downhole tools pertains to the condition that, with integral tool structures, the entire tool including the sub or body must be replaced or repaired if the tool wear surfaces become excessively worn or damaged. This is expensive and wasteful of a considerable portion of the tool structure and adds to the cost of drilling operations. Therefore it has been considered highly desirable to provide downhole tools which have replaceable tool inserts or sections wherein the tool components which are subject to wear or are likely to be damaged can be replaced without replacing the entire tool body.
In an effort to overcome the aforementioned problems downhole tools have been developed wherein the tool body is adapted to support a replaceable tubular sleeve having stabilizer wear surfaces or reamer cutting surfaces thereon. However, this type of replaceable downhole tool requires disconnecting at least one joint between the tool and the drill stem to replace the sleeve.
Other types of downhole tools have been developed wherein tool sections or inserts are secured to the tool body by threaded fasteners and other support parts which are separate from the tool body. This design approach is undesirable because of the risk of failure or loosening of the fasteners under the severe loading which downhole tools are subjected to while in the hole, or due to the possible loss of the fasteners and other support parts during tool replacement or servicing operations. This latter aspect of prior art replaceable downhole tools is particularly disadvantageous when working with such tools on the rig floor wherein there is considerable likelihood of loss of the fasteners or other relatively small parts down the drillhole. Such mishaps require expensive and time consuming fishing operations or can result in damage to the drill stem or bit by the presence of these objects in the drillhole when drilling operations are resumed. Moreover, replacement and servicing operations for these last mentioned type of tools are time consuming and usually require the use of special tools and procedures.
Accordingly, the problems related to the use of prior art downhole tools been somewhat vexatious to the art worker and there has been a continuing need to improve the types of downhole tools discussed herein. To this end the present invention provides several embodiments of an improved downhole tool having replaceable tool sections which can be interchanged quickly without disconnecting or removing the tool body from the drill stem and without the use of relatively small, weak and easily lost or damaged parts.