Patent Publication Number: US-6705406-B2

Title: Replaceable electrical device for a downhole tool and method thereof

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates generally to a tool for use in an oilfield wellbore, and more specifically to an easily replaceable electrical device for use in such a tool. 
     2. Description of the Related Art 
     Tools requiring electrical power are often used for conducting various operations in a wellbore. This creates a need for portable electrical power, preferably power that can be mounted directly onto a downhole tool. One way of providing electrical power downhole is through the use of a battery pack. Typically, the battery pack is constructed of multiple cells mounted in rigid plastic, epoxy, fiberglass, or aluminum shells and is housed in a sonde or in an annular housing mounted in the bore of a downhole tool. One or more cells are typically contained within the battery pack. The cells can be electrically connected in various series or parallel configurations to provide the necessary voltage and current capacities required for the various loads. The cells generally are immobilized inside the battery pack by an epoxy. In order to change the battery pack in the downhole tool, the tool has to be disassembled. Disassembly of the tool makes replacing a battery pack time consuming and, in certain cases, is impossible at the job site. For quicker job turnaround, it is desirable that the battery be replaceable without requiring tool disassembly and without the use of specialized equipment typically not available at the job site. 
     The methods and apparatus of the present invention overcome the foregoing disadvantages of the prior art by providing an externally replaceable battery pack that does not require major tool disassembly. 
     SUMMARY OF THE INVENTION 
     In general, in one aspect of the present invention, a downhole tool for use in a wellbore, comprises a tubular member, such as a drill collar housing, in a drill string. The tubular member has at least one cavity formed on an external surface. A housing is adapted to insert in and extract from the cavity. The housing has at least one electrical device, such as a battery stack, disposed within the housing. 
     In another aspect of the present invention, sensors are disposed in the housing for measuring downhole parameters of interest including, but not limited to, annulus pressure and annulus temperature. 
     In another embodiment, a replaceable battery pack for a downhole tool in a wellbore, comprises a housing adapted to be insertable in and extractable from a cavity on an external surface of the downhole tool, and has at least one electrical power cell disposed in the housing. 
     In one aspect, a method of replacing an electrical device in a downhole tool, comprises removing a first housing containing the electrical device from a cavity on an external surface of the downhole tool, and installing a second housing containing a second electrical device in the cavity without disassembling the tool further. 
     In yet another embodiment, a method of replacing a battery pack in a downhole tool, comprises removing a first housing containing a plurality of electrical power cells from a cavity on an external surface of the downhole tool, and installing a second housing containing a second plurality of electrical power cells in the cavity without disassembling the tool further. 
     Examples of the more important features of the invention thus have been summarized rather broadly in order that the detailed description thereof that follows may be better understood, and in order that the contributions to the art may be appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will form the subject of the claims appended hereto. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For detailed understanding of the present invention, references should be made to the following detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, in which like elements have been given like numerals, wherein: 
     FIG. 1 is a schematic diagram of a drilling system according to one embodiment of the present invention; 
     FIG. 2 is a schematic of a downhole tool with a replaceable battery pack according to one embodiment of the present invention; 
     FIG. 3 is a schematic section of a downhole tool with a replaceable battery pack installed therein; and 
     FIG. 4 is an exploded schematic of a downhole battery pack according to one embodiment of the present invention. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1 shows a schematic diagram of a drilling system  10  having a downhole assembly containing a downhole sensor system and the surface devices according to one embodiment of present invention. As shown, the system  10  includes a conventional derrick  11  erected on a derrick floor  12  which supports a rotary table  14  that is rotated by a prime mover (not shown) at a desired rotational speed. A drill string  20  that includes a drill pipe section  22  extends downward from the rotary table  14  into a wellbore  26 . A drill bit  50  attached to the drill string downhole end disintegrates the geological formations when it is rotated. The drill string  20  is coupled to a drawworks  30  via a kelly joint  21 , swivel  28  and line  29  through a system of pulleys (not shown). During the drilling operations, the drawworks  30  is operated to control the weight on bit and the rate of penetration of the drill string  20  into the wellbore  26 . The operation of the drawworks is well known in the art and is thus not described in detail herein. 
     During drilling operations, a suitable drilling fluid (commonly referred to in the art as “mud”)  31  from a mud pit  32  is circulated under pressure through the drill string  20  by a mud pump  34 . The drilling fluid  31  passes from the mud pump  34  into the drill string  20  via a desurger  36 , fluid line  38  and the kelly joint  21 . The drilling fluid is discharged at the wellbore bottom  51  through an opening in the drill bit  50 . The drilling fluid circulates uphole through the annular space  27  between the drill string  20  and the wellbore  26  and is discharged into the mud pit  32  via a return line  35 . Preferably, a variety of sensors (not shown) are appropriately deployed on the surface according to known methods in the art to provide information about various drilling-related parameters, such as fluid flow rate, weight on bit, hook load, etc. 
     A surface control unit  40  receives signals from the downhole sensors and devices via a sensor  43  placed in the fluid line  38  and processes such signals according to programmed instructions provided to the surface control unit. The surface control unit displays desired drilling parameters and other information on a display/monitor  42  which information is utilized by an operator to control the drilling operations. The surface control unit  40  contains a computer, memory for storing data, data recorder and other peripherals. The surface control unit  40  also includes models and processes data according to programmed instructions and responds to user commands entered through a suitable means, such as a keyboard. The control unit  40  is preferably adapted to activate alarms  44  when certain unsafe or undesirable operating conditions occur. 
     In the preferred embodiment of the system of present invention, the downhole subassembly  59  (also referred to as the bottomhole assembly or “BHA”), which contains the various sensors and MWD devices to provide information about the formation and downhole drilling parameters, is coupled between the drill bit  50  and the drill pipe  22 . The downhole assembly  59  is modular in construction, in that the various devices are interconnected sections. 
     Referring to FIG. 1, the BHA  59  also preferably contains downhole sensors and devices in addition to the above-described surface sensors to measure downhole parameters of interest. Such devices include, but are not limited to, a device for measuring the formation resistivity near the drill bit, a gamma ray device for measuring the formation gamma ray intensity and devices for determining the inclination and azimuth of the drill string. The formation resistivity measuring device  64  provides signals from which resistivity of the formation near the drill bit  50  is determined. 
     The above-noted devices transmit data to the downhole telemetry system  72 , which in turn transmits the received data uphole to the surface control unit  40 . The present invention preferably utilizes a mud pulse telemetry technique to communicate data from downhole sensors and devices during drilling operations. A transducer  43  placed in the mud supply line  38  detects the mud pulses responsive to the data transmitted by the downhole telemetry  72 . Transducer  43  generates electrical signals in response to the mud pressure variations and transmits such signals via a conductor  45  to the surface control unit  40 . Other telemetry techniques such electromagnetic and acoustic techniques or any other suitable technique may be utilized for the purposes of this invention. 
     The sensors and telemetry devices can be powered by batteries, downhole alternators, or a combination of such devices. In conventional systems, the power sources are typically contained in the bore of the BHA  59  and require some time-consuming and difficult disassembly to change out batteries. In many instances, such a change-out is impractical at the rig site. 
     FIGS. 2-4 shows downhole tool  125  suitable for placement in a portion of a drill string such as BHA  59 . In a preferred embodiment, tool  125  comprises a tubular member  101  such as a drill collar. Tool  125  has a replaceable battery module  120 , also called a battery pack, inserted in a cavity  121  formed in an external surface of tubular member  101 . Downhole sensors and circuits as discussed above may be disposed in the tubular member  101 . The battery module  120  may provide power for such devices. 
     The battery module  120  comprises a housing  102  having a bore  115  adapted to receive a battery stack  108 . Battery stack  108  may be a combination of multiple cells (not shown) or a single cell. If multiple cells are used for battery stack  108 , they are typically encased in a plastic or metal cylinder. Such techniques are known in the art and are not discussed here further. Battery stack  108  is suitably wired to provide the required voltage and current properties for the particular application and has connection contacts  117  for engaging mating contacts  118  on connector  107 . Electrical connector  107  is fitted into the end of bore  115  and is connected to connector  112  by wires  116 . Battery stack  108  is inserted in bore  115  and is aligned by key  119  in stack  108  that aligns with a suitable groove (not shown) in housing  102 . The key  119  provides alignment to ensure proper mating of contact pins  117  in stack  108  with mating contacts  118  in connector  107 . Key  119  also prevents rotation of stack  108  during downhole drilling that might damage the connection between stack  108  and connector  107 . Stack  108  is held in place by spring  109  that is captured in a compressed state between stack  108  and cap  110 . The spring preload minimizes axial movement of the stack  108  during downhole drilling. Elastomeric seals  111  and  112  are used to seal out borehole fluids. Seal  112  resides in groove  105  and acts as a face type seal with surface  123  when module  120  is fastened to member  101  by mechanical fasteners  122  inserted though holes  103  and screwed into mating threaded holes (not shown) suitably arranged in cavity  121  in member  101 . As module  120  is inserted into cavity  121 , electrical connection is made between connector  106  in module  120  and connector  113  in member  101 . Wires (not shown) are connected between the connector  113  and sensors and circuits (not shown) disposed in member  101 . Such wiring techniques are known in the art and are not discussed here further. Any suitable mating connectors may be used for connectors  106  and  113  including but not limited to individual pin-to-socket connectors and coaxial connectors. 
     In another preferred embodiment, suitable circuitry (not shown) is included in module  120  to facilitate the use of inductive coupling techniques for transferring power between module  120  and circuits and sensors (not shown) in member  101 . 
     Grooves  104 , see FIG. 4, are adapted to receive an elastomeric seal  130  for use in providing a pressure lock to assist in holding the module  120  in cavity  121 . When the module  120  is installed in the cavity  121 , the seals  130  mate with the surface (not shown) in cavity  121 . The volume enclosed by the seal  130  is at atmospheric pressure. Effectively, the downhole pressure times the area enclosed by the seal generates a force holding the housing  102  against the surface of cavity  121 . At downhole pressures of several thousand pounds per square inch, even a small enclosed area results in a substantial holding force. 
     While the module  120  is described above as containing power cells, it is anticipated that such a module may contain other devices including but not limited to electronic circuits and sensors for measuring downhole parameters of interest. Such parameters include but are not limited to, annulus fluid pressure and annulus fluid temperature. 
     While only one module  120  is described as being attached to the tubular member  101 , several such modules can be disposed on the tubular member. Such modules can be disposed at multiple angular positions around the tubular member at the same axial location; at multiple axial locations; or a combination of these. 
     The foregoing description is directed to particular embodiments of the present invention for the purpose of illustration and explanation. It will be apparent, however, to one skilled in the art that many modifications and changes to the embodiment set forth above are possible without departing from the scope and the spirit of the invention. It is intended that the following claims be interpreted to embrace all such modifications and changes.