Patent Application
20070131412
The invention relates to a mass isolation joint for electrically isolating a downhole tool from adjacent tools.
Downhole tools used in hydrocarbon exploration and production are typically made of metallic or conductive bodies. In logging operations, it is common to use these metallic bodies as measure electrodes. For example, a metallic tool body may be used to emit a current signal into a surrounding formation, where the rate at which the current flows from the tool body into the surrounding formation can be measured and related to the resistivity of the formation. In a tool string including several tools, it may be necessary to prevent current generated within one tool having a tool body used as an electrode from migrating to adjacent tools, where the adjacent tools may or may not be used as electrodes. Mass isolation joints are typically used for this electrical isolation. A mass isolation joint typically includes threads on adjacent joint sections and an insulating material between the threads. To be effective, the mass isolation joint must be able to maintain its integrity when subjected to shear and bending forces as the tools are conveyed inside a borehole.
Logging techniques known in the art include wireline logging, logging while drilling (LWD), measurement while drilling (MWD), and logging while tripping (LWT). Wireline logging involves lowering the instrument into the borehole at the end of an electrical cable to obtain the subsurface measurements as the instrument is moved along the borehole. LWD/MWD involves disposing the instrument in a drilling assembly for to obtain subsurface measurements while a borehole is drilled through subsurface formation. LWT involves disposing sources or sensors within the drill string to obtain measurements while the drill string is withdrawn from the borehole.
U.S. Pat. No. 6,116,337 discloses an articulated connector for connecting two adjacent logging sondes including a mass isolation joint to prevent electrical signals from migrating between the logging sondes. The mass isolation joint includes a first section and a second section arranged coaxially and coupled together by threaded engagement with a coaxial insulator. The first section, second section, and the insulator are generally cylindrical, but the insulator includes an enlarged diameter portion which extends between opposing ends faces of the first section and the second section, thereby electrically insulating the first section from the second section. An insulating sleeve is disposed over the first section and second section to protect the joint between the first and second section and the insulator from wellbore fluids. The insulating sleeve may be formed of non-conducting material such a fiberglass or epoxy composite.
There is an ongoing need for a robust mass isolation joint for use in electrically a downhole tool that can withstand shear and bending forces typical of downhole operations.
In one aspect, the invention relates to a mass joint for electrically isolating a downhole tool which comprises a first joint section having a distal end in which a first thread is formed, a second joint section, and an insulating composite structure coupling the first joint section to the second joint section, wherein at least one of the first and second joint sections is adapted for coupling to the downhole tool. The insulating composite structure comprises a first composite layer formed on the second joint section. The first composite layer has a second thread which engages the first thread on the distal end of the first joint section.
In another aspect, the invention relate to a tool string for use in a borehole penetrating a subsurface formation which comprises a plurality of downhole tools and a mass isolation joint, as described above, coupled to at least one of the downhole tools.
Other features and advantages of the invention will be apparent from the following description and the appended claims.
The accompanying drawings, described below, illustrate typical embodiments of the invention and are not to be considered limiting of the scope of the invention, for the invention may admit to other equally effective embodiments. The figures are not necessarily to scale, and certain features and certain view of the figures may be shown exaggerated in scale or in schematic in the interest of clarity and conciseness.
The invention will now be described in detail with reference to a few preferred embodiments, as illustrated in the accompanying drawings. In describing the preferred embodiments, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be apparent to one skilled in the art that the invention may be practiced without some or all of these specific details. In other instances, well-known features and/or process steps have not been described in detail so as not to unnecessarily obscure the invention. In addition, like or identical reference numerals are used to identify common or similar elements.
The insulating composite structure 106 includes an inner composite layer 112 formed on the outer surface 114 of the second joint section 104. The inner composite layer 112 also covers an end face 116 of the second joint section 104, that is, the end face opposing the first joint section 102. Forming the inner compost ire layer 112 on the second joint section 104 may include a suitable wrapping device such as a lathe machine. The inner composite layer 112 may include one or more wraps of a composite material. The outer surface 114 of the second joint section 104 may be textured to allow for increase bonding between the inner composite layer 112 and the second joint section 104. Texturing may be provided by sandblasting the outer surface 114 of the second joint section 104 and similar processes. The inner composite layer 112 may be made of any suitable composite material that can withstand the borehole environment. Preferably, the composite material can be machined to form features such as threads. In one example, the composite material is formed of a resin material such as epoxy or fiber-resin material. Useable composite materials include, but are not limited to, fiber-resin composite, polyaryletherketone, such as polyetheretherketone and polyetherketone, and filament wound glass.
One or more threads 118 are formed on the inner composite layer 112, e.g., by machining. The thread pitch is preferably low e.g., 3 to 4 threads per inch (2.54 cm), to allow more of the inner composite layer 112 to be used for bearing shearing loads. A distal end 120 of the first joint section 102 is provided with a recess 122. The inner diameter of the recess 122 is such that it can receive a distal end 115 of the second joint section 104 and the inner composite layer 112 formed thereon. One or more thread 124 are formed in the wall of the recess 122 at the distal end 120 of the first joint section 102. The thread(s) 118 on the inner composite layer 112 is used as a gauge for the thread(s) 124 on the first joint section 102 so that the first joint section 102 can engage the inner composite layer 112 via the thread 118, 124. A high temperature adhesive 126 may be injected or inserted between the first joint section 102 and the inner composite layer 112. The high temperature adhesive may be a curable material such as epoxy. The curable material is allowed to cure, thereby providing a bond between the first joint section 102 and the inner composite layer 112 that can withstand high temperature conditions. The inner composite layer 112 provides an insulation layer between the second joint section 104 and the first joint section 102 and thereby prevents migration of currents from the second joint section 104 to the first joint section 102.
The insulating composite structure 106 further includes a sealant layer 128 formed on the distal end 120 of the first joint section 102 and the inner composite layer 112 on the second joint section 104. An outer composite layer 130 is formed on the sealant layer 128. The sealant layer 128 and the outer composite layer 130 protect the joint between the first section 102 and the inner composite layer 112 from borehole fluids. The sealant layer 128 may be made of an elastomer or rubber material or other sealant material suitable for use in a borehole environment. Suitable material for the sealant layer include, but are not limited to, Neoprene (RTM), Viton (RTM), and Nitrile (RTM). The outer composite layer 130 may also be made of any suitable composite material. For example, the outer composite layer 130 could be made of a fiber-resin composite, fiberglass, or fabric impregnated with resin. Forming the outer composite layer 130 on the sealant layer 128 may include winding a composite material in tension about the sealant layer 128 manually or using a suitable wrapping device such as a lathe machine. The outer composite layer 130 may include one or more wraps of the composite material.
An outer shoulder 132 of the first joint section 102 that abuts the outer composite layer 130 and the sealant layer 128 may be slanted, as shown, or may be straight. A slanted shoulder provides an increased surface area for the seal. In general, the thickness of the insulating composite structure 106, or the individual layers in the insulating composite structure 106, is selected such that the insulating composite structure 106 is flush with the outer diameter of the first joint section 102.
The disclosed invention provides advantages over conventional structures, including reduced manufacturing costs, compatibility for smaller design circles, and lower failure rates during manufacture. While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein.
This application claims priority to U.S. Provisional Application No. 60/690,328, entitled “Composite Shelled Tools for Subsurface Measurements” filed on Jun. 14, 2005, which is hereby incorporated in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 60690328 | Jun 2005 | US |
