Implements or apparatus for applying pushing or pulling force – Method or apparatus for placement of conductive wire
Reexamination Certificate
1998-08-21
2001-01-30
Scherbel, David A. (Department: 3723)
Implements or apparatus for applying pushing or pulling force
Method or apparatus for placement of conductive wire
C254S134400
Reexamination Certificate
active
06179269
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to devices and techniques for installing cable, such as power cable, into coiled tubing such as for use in delivering electrical power to submerged machinery in a petroleum well. More particularly, the invention relates to a novel technique for installing lengths of cable in coiled tubing by at least partially placing the cable or cable shielding under compressive loading at an entry end of the coiled tubing.
2. Description of the Related Art
A number of applications exist wherein power or data signals must be supplied to remote subsea or subterranean locations, such as to drive or control underground equipment. For example, in the field of petroleum extraction and exploitation, it is commonplace to form a wellbore that penetrates a number of subterranean zones, including one or more zones of interest. The zones of interest commonly include geological horizons bearing minerals, such as petroleum, gas, paraffin, and so forth. The minerals flow into the wellbore and are removed by pumping systems either situated at the earth's surface or submerged within the wellbore. In either case, it is often necessary to transmit electrical power or control signals to equipment situated in the wellbore to power or control operation of the downhole equipment.
In one class of equipment used in petroleum and similar wells, a submersible electric motor is coupled to one or more pumps. The electric motor is powered by cables extending from a power supply at the earth's surface. As the electric motor is driven, the pumps displace wellbore fluids, transmitting fluids of interest to a location above the earth's surface for collection and further processing. Certain systems of this type also include ancillary equipment such as fluid separators, injection pumps, and so forth, adding to the complexity and flexibility of the overall system.
In heretofore known devices, several techniques have been employed for transmitting power and control signals to downhole equipment in wells. For example, various types of shielded cable are known and are currently available for transmitting significant levels of electrical power to submerged pumping systems of the type described above. The cables may include multiple conductors, such as for three-phase operation, and are commonly shielded by a flexible, durable metallic casing or armor designed to reduce the risk of damage to the power conductors during deployment and use of the equipment. Control signals may be superimposed on power signals in certain applications, or may be transmitted via separate cables, radio telemetry, or other signal transmission techniques.
In an increasing number of applications, it is useful to dispose cables and signal conductors in extended lengths of conduit extending between the earth's surface and a submerged pumping system, particularly in petroleum and other production wells. One particular type of conduit presently employed in such systems is coiled tubing, which is available in extended lengths capable of being wound around a storage spool. The tubing may be deployed in the well by unwinding it from the storage spool. Lengths of tubing may be spliced together, as required by the depth at which the submerged equipment is deployed. A difficulty arises, however, in insertion of the cable conductors in the tubing or conduit. In many applications it is preferable to pre-install the cable in lengths of conduit to facilitate proper attachment of the cable to the submerged equipment prior to deployment. Presently, power cable is installed in coiled tubing by tensioning the cable during the installation process and drawing the cable through extended lengths of tubing, often several thousand feet long.
Significant disadvantages have been encountered in tensioning techniques for deploying cables in conduit such as coiled tubing. For example, high tension tensile forces are required to draw the cable into the tubing, owing to the weight of the cable and to frictional forces between the interior of the conduit and the exterior of the cable shielding. Such forces can result in damage to the cable during installation process. Moreover, excessive tension in the cable can lead to stretching of the cable during installation. Residual strain resulting from such tension may then be stored along the cable, which remains unrelaxed prior to connection to the powered equipment. During subsequent operation, the residual strain can be relieved, leading to contraction of the cable and, in certain cases, interruption of electrical power between the submerged equipment and wellhead equipment.
There is a need, therefore, for an improved technique for installing conductive cabling, such as power cable into a conduit. In particular, there is a need for a technique for positioning power cable in coiled tubing and the like over considerable lengths that addresses or avoids the drawbacks of prior art techniques, such as damage to the cable or conduit, and storage of residual strain within the cable.
SUMMARY OF THE INVENTION
The present invention provides a novel technique for installing power cables and similar conductors in conduits designed to respond to these needs. The technique applies a compressive loading to a portion of the cable to urge the cable into an entry end of the conduit. The compressive forces are sufficient for installing the cable into the conduit over relatively shorter lengths. For longer lengths of cable and conduit, the compressive insertion approach can be used in combination with cable tensioning. The combined use of compression and tension permits extended lengths of cable to be installed in conduit without damage to the cable or conduit. The inventive technique also significantly limits or reduces the tendency of the cable to store residual stain.
In accordance with a first aspect of the invention, an apparatus is provided for installing a cable in an elongated conduit. The conduit has a substantially closed side wall extending between first and second open ends. The apparatus includes a compression station and a tension station. The compression station is disposed adjacent to the first end of the conduit and contacts the cable to exert compressive forces on the cable to urge the cable into the conduit via the first end. The tension station is disposed adjacent to the second end and contacts the cable to exert tensile forces on the cable to draw the cable toward the second end. The compression station advantageously includes a drive unit in which mutually opposed drive members receive the cable therebetween and urge the cable toward the first end of the conduit. The drive members preferably include an endless belt which contacts the cable over a predetermined length thereof.
In accordance with another aspect of the invention, a method is provided for installing a cable, such as a power cable into an elongated conduit, such as coiled tubing for use with a submersible pumping system. The method includes the steps of exerting longitudinal compressive forces on the cable to urge the cable into the conduit via a first end thereof, and exerting tensile forces on the cable to draw the cable through the conduit towards a second end thereof. The step of exerting the compressive forces on the cable is advantageously accomplished by drawing the cable through a compression station, the compression station contacting the cable to exert radial compressive forces on the cable to drive the cable into the conduit. The compression station preferably exerts the radial compressive forces against an external shielding layer provided on the cable. In a preferred arrangement, frictional forces between the cable and internal surfaces of the conduit are opposed primarily by the longitudinal compressive forces during a first phase of installation, and primarily by the tensile forces during a second phase of installation.
In accordance with a further aspect of the invention, a method is provided for installing a submersible pumping system in a well. T
Camco International Inc.
Fletcher Yoder & Van Someren
Scherbel David A.
Shanley Daniel
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