Abstract:
The present invention involves a method and apparatus for communicating from within a wellbore to the surface of the wellbore, as well as communicating from the surface of the wellbore to downhole within the wellbore. More specifically, the present invention involves a method and apparatus for protecting and controlling cables or lines which connect surface equipment to downhole equipment. A spacer sub comprising a tubular body with a helical groove therearound is used to house one or more downhole cables. In one aspect, the spacer sub has a recess within the helical groove for housing one or more cable connectors. In another aspect, multiple helical grooves are disposed around the spacer sub to protect and house cables of different length.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates generally to oilfield operations. More particularly, the present invention pertains to apparatus and methods for monitoring downhole conditions in hydrocarbon wellbores, including fluid characteristics and formation parameters, using fiber optic gauges and other instrumentation. Moreover, the present invention pertains to apparatus and methods for controlling downhole equipment or instrumentation from the surface of the wellbore.  
           [0003]    2. Description of the Related Art  
           [0004]    In the drilling of oil and gas wells, a wellbore is formed using a drill bit that is urged downwardly at a lower end of a drill string. When the well is drilled to a first designated depth, a first string of casing is run into the wellbore. The first string of casing is hung from the surface, and then cement is circulated into the annulus behind the casing. Typically, the well is drilled to a second designated depth after the first string of casing is set in the wellbore. A second string of casing, or liner, is run into the wellbore to the second designated depth. This process may be repeated with additional liner strings until the well has been drilled to total depth. In this manner, wells are typically formed with two or more strings of casing having an ever-decreasing diameter.  
           [0005]    After a well has been drilled, it is desirable to provide a flow path for hydrocarbons from the surrounding formation into the newly formed wellbore. To accomplish this, perforations are shot through a wall of the liner string at a depth which equates to the anticipated depth of hydrocarbons. Alternatively, a liner having pre-formed slots may be run into the hole as the lowest joint or joints of casing. Alternatively still, a lower portion of the wellbore may remain uncased so that the formation and fluids residing therein remain exposed to the wellbore. Hydrocarbon production is accomplished when hydrocarbons flow from the surrounding formation, into the wellbore, and up to the surface.  
           [0006]    In modern well completions, downhole tools or instruments are often employed. These downhole tools or instruments include, but are not limited to, sliding sleeves, submersible electrical pumps, downhole chokes, and various sensing devices. These devices are controlled from the surface via hydraulic control lines, electrical control lines, mechanical control lines, fiber optics, and/or a combination thereof. The cables or lines extend from the surface of the wellbore to connect surface equipment to the downhole tools or instruments.  
           [0007]    Additionally, during the life of a producing hydrocarbon well, it is sometimes desirable to monitor conditions in situ. Recently, technology has enabled well operators to monitor conditions within a hydrocarbon wellbore by installing permanent monitoring equipment downhole. The monitoring equipment permits the operator to monitor downhole fluid flow, as well as pressure, temperature, and other downhole parameters. Downhole measurements of pressure, temperature, and fluid flow play an important role in managing oil and gas reservoirs.  
           [0008]    Historically, permanent monitoring systems have used electronic components to provide real-time feedback as to downhole conditions, including pressure, temperature, flow rate, and water fraction. These monitoring systems employ temperature gauges, pressure gauges, acoustic sensors, and other instruments, or “sondes,” disposed within the wellbore. Such instruments are either battery operated, or are powered by electrical cables or lines deployed from the surface.  
           [0009]    Recently, fiber optic sensors have been developed. Fiber optic sensors communicate readings from the wellbore to optical signal processing equipment located at the surface. The fiber optic sensors may be variably located within the wellbore. For example, optical sensors may be positioned to be in fluid communication with the housing of a submersible electrical pump. Such an arrangement is taught in U.S. Pat. No. 5,892,860, issued to Maron, et al., in 1999. The &#39;860 patent is incorporated herein in its entirety, by reference. Sensors may also be disposed along the production tubing within the wellbore. In either instance, a cable is run from the surface to the sensing apparatus downhole. The cable transmits optical signals to a signal-processing unit at the surface of the wellbore.  
           [0010]    In order to connect downhole sensors with signal processing equipment at the surface, fiber optic and electrical cables and lines must be connected through downhole production equipment such as packers and/or annular safety valves. This downhole production equipment represents a barrier through which downhole cables must travel to reach the downhole equipment to which the cable is to be connected. To minimize time spent feeding cable through the barriers at the production site, segments of cable are often placed through these barriers prior to reaching the production site. Cable connectors are then placed on the segments of cable so that the segments may be connected at the production site to the cable run into the wellbore from the surface equipment.  
           [0011]    When downhole cables are used to connect downhole equipment to surface equipment, the cables are typically wrapped around the working string to take up the slack in the length of the cable. The cables and cable connectors are thus left unprotected from the harsh and turbulent environment present in the wellbore. Consequently, fluid flow around the production string below the tubing-casing packer threatens the integrity of the cables and cable connectors. Of even greater concern is trauma inflicted on cables during initial run-in. In this respect, it is understood that many wellbores are drilled at deviated and highly deviated angles, meaning that cables external to the production string are subject to abrasion against the liner strings and any open hole wellbore portion. Wear and tear on the cables and cable connectors may force replacement of the cables or cable connectors, resulting in increased operating expense and lost production time.  
           [0012]    Additional problems also arise from the placement of cable along production tubing. When fixed lengths of cable are used, the operator often attempts to space out the required length of cable along the existing length of the production string or other tubing disposed within the wellbore. This task is often impossible due to the different lengths of cable that are used in wellbore operations. In order to take up slack in the cable, the operator must wind the cable around the production string. In some instances, the operator must wrap the cable multiple times around the tubing to take up the slack, even crossing the cable over itself or with other cables. Crossing the cable is disadvantageous because the cable juts outward radially from the tubing, thus becoming more easily damaged due to increased exposure to the wellbore fluids over time and due to contact with the wellbore during run-in.  
           [0013]    Thus, there is a need for an apparatus which protects ordinarily exposed cables and cable connectors from damage due to downhole conditions. There is a further need for an apparatus which allows cable to be wrapped in an orderly fashion around the tubing within the wellbore, thus controlling the location of the cable within the wellbore and preventing damage due to the crossing of cables and attempts to take up slack in a cable line.  
         SUMMARY OF THE INVENTION  
         [0014]    Hereinafter, when the term “cables” is used, the term shall include electrical lines, hydraulic lines, data acquisition lines, communication lines, fiber optics, and mechanical lines. “Surface equipment” includes processing equipment such as signal processors and central processing units, as well as equipment used to operate downhole tools or instruments. “Downhole equipment” includes downhole production tools or instruments such as sliding sleeves, submersible electrical pumps, and downhole chokes, as well as downhole monitoring equipment such as sensing devices and control instrumentation.  
           [0015]    The present invention generally provides a downhole spacer sub for housing and protecting cables, which connect downhole equipment to surface equipment. The spacer sub is configured to be threadedly connected to a working string, such as a string of production tubing or an injection tubing. The spacer sub has a tubular-shaped body with a bore therethrough. The wall of the spacer sub is preferably thicker than the wall of the working string so that the outer diameter of the spacer sub is larger than the outer diameter of the working string. The larger outer diameter of the spacer sub relative to the working string allows the spacer sub to serve as a flow coupling.  
           [0016]    The spacer sub of the present invention comprises at least one cable groove formed in the outer diameter of the spacer sub. The cable groove defines a spiral recess along the outer surface of the spacer sub. A cable is directed through the cable groove so that the cable wraps around the spacer sub. Optional countersunk keeper plates hold the cable in place within the cable groove. The spacer sub may have multiple cable grooves for housing multiple lengths of cable and multiple keeper plates along each of the cable grooves. Also, the spacer sub may further comprise at least one connector groove, which is larger than the cable groove to house and protect any cable connectors, which connect portions of the cable.  
           [0017]    The spacer sub of the present invention is advantageous because the cable groove allows the length of the cable to spiral around the outside of the spacer sub, thus taking up any slack in the length of the cable. When multiple cable grooves of various spiral angles around the spacer sub are formed to receive various lengths of cable, cables of different lengths can be wrapped around the spacer sub within the cable grooves. Housing the cable within the cable groove takes up the slack in the cable length without damaging the cable. Moreover, housing the cable within the cable groove protects the cable from suffering damage during tubing run-in, and due to fluid flow outside the spacer sub during wellbore operations. In this respect, the cable is flush with the spacer sub and protected from turbulent fluid flow. Furthermore, when multiple cables used to connect multiple downhole devices to the surface are placed within the cable groove, the cables are positioned within the cable grooves in an orderly fashion. The orderly manner in which the cables are positioned within the cable grooves minimizes damage to the cables due to the exposure to damaging fluid caused by the crossing of multiple cables and the increased outer diameter of the spacer sub due to this crossing of the cables.  
           [0018]    A further advantage of the present invention is that the cable connector groove on the spacer sub protects the cable connector from trauma during run-in and from erosion due to fluid flow in wellbore operations. Additionally, the spacer sub can serve as a flow coupling when used in conjunction with annular safety valves and packers, so that the additional wall thickness of the spacer sub prevents failures due to erosion in areas of turbulent fluid flow. Most advantageously, the spacer sub of the present invention performs the three desired functions of flow coupling, protecting downhole cables, and wrapping downhole cables all at once. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope.  
         [0020]    [0020]FIG. 1 presents a cross-sectional view of one embodiment of the spacer sub of the present invention. The spacer sub is disposed in a wellbore, and has a cable housed therein to connect downhole equipment to equipment at the surface.  
         [0021]    [0021]FIG. 2 provides a sectional side view of a groove on the spacer sub of FIG. 1. In this view, the spacer sub has a countersunk keeper plate located within the groove.  
         [0022]    [0022]FIG. 3 is a perspective of the countersunk keeper plate of FIG. 2.  
         [0023]    [0023]FIG. 4 shows a sectional view of a housing for a cable connector for use with the spacer sub of FIG. 1.  
         [0024]    [0024]FIG. 5 presents a cross-sectional view of an alternate embodiment of the spacer sub of the present invention. The spacer sub is again disposed in a wellbore, and has a cable residing therein to connect downhole equipment to equipment at the surface. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0025]    [0025]FIG. 1 presents a cross-sectional view of a wellbore  50 , which has been completed for the production of hydrocarbons. The wellbore  50  extends downward into a formation  55 , sometimes referred to in the industry as the pay zone, the area of interest, or the production depth. The wellbore  50  has a string of casing  15  disposed therein. The casing  15  has been cemented into place along the formation  55  by a column of cement  20 . The casing  15  is a tubular-shaped body with a bore therethrough. The lower end of the casing  15  is perforated. Perforations  35  provide fluid communication between the formation  55  and the internal bore of the casing  15 . It is understood, however, that the present invention may also be used in an open hole wellbore or any other type of completion.  
         [0026]    A working string  30 , which is hung from a surface production assembly (not shown), is disposed within the casing  15  and extends from the surface of the wellbore  50  to the production depth. The working string  30  defines an elongated tubular body having a bore therethrough. A packer  40  is seen disposed around the outer diameter of the working string  30  to seal off an annular space  5  between the casing  15  and the working string  30 . Production fluids, which enter the wellbore  50  through the perforations  35 , are forced by the packer  40  upward through the working string  30  and to the surface of the wellbore  50 . While wellbore  50  is presented as a producing well having string  30  as a production tubing, it is understood that the wellbore  50  may be an injection well, and working string  30  may be an injection string.  
         [0027]    A spacer sub  10  is located within the wellbore  50 . In the arrangement of FIG. 1, the spacer sub  10  is threadedly connected to the working string  30  below the packer  40 . The spacer sub  10  is a tubular-shaped body with a bore therethrough which is preferably 6 to 10 feet in length. The spacer sub  10  preferably has thicker walls than the working string  30  and therefore has a larger outer diameter than the working string  30 . The thick-walled spacer sub  10  can serve as a flow coupling to prevent failures caused by erosion of various completion components such as landing nipples (not shown) in turbulent fluid flow areas in the annular space  5 . When used as a flow coupling, the spacer sub  10  preferably is constructed with 2⅞-inch to 7-inch tubing.  
         [0028]    Also seen in the wellbore  50  of FIG. 1 is an item of downhole equipment. The downhole equipment is shown schematically at  100 , located below the spacer sub  10 . The downhole equipment  100  is utilized to monitor conditions downhole, including but not limited to pressure, temperature, acoustics, and flow rate of hydrocarbons. In the alternative, the downhole equipment  100  may include downhole production equipment or instruments. The downhole equipment  100  may include one or more sensors which may define pressure gauges, temperature gauges, acoustic sensors, or other sondes. In one aspect of the present invention, the downhole equipment  100  is designed to operate through one or more fiber optic sensors.  
         [0029]    The downhole equipment  100  is connected to the lower end of a cable  12 . The cable  12  ultimately connects at its upper end to surface equipment  132  located at the surface of the wellbore  50 . In one aspect, the cable  12  sends information collected by the downhole equipment  100  to the surface equipment  132 . The surface equipment  132  may include signal processing equipment such as a central processing unit which analyzes the information gathered from the downhole equipment  100 . The surface equipment  132  may also send signals such as excitation light to the downhole equipment  100 . Moreover, the surface equipment  132  may send signals to operate downhole production equipment or instruments.  
         [0030]    Preferably, the cable  12  is designed to withstand high temperatures and pressures within the wellbore  50 . The cable  12  includes but is not limited to a fiber optic cable, hydraulic cable, or electrical cable. When the cable  12  is a fiber optic cable, it includes an internal optical fiber which is protected from mechanical and environmental damage by a surrounding capillary tube. The capillary tube is made of high strength, rigid walled, corrosion-resistant material, such as stainless steel. The tube is attached to the downhole equipment  100  by appropriate means, such as threads, a weld, or other suitable method. The optical fiber contains a light guiding core which guides light along the fiber. The core preferably includes one or more sensor elements such as Bragg gratings to act as a resonant cavity, and to also interact with the downhole equipment  100 .  
         [0031]    In the arrangement of FIG. 1, the cable  12  is run from the surface equipment  132  downward, and then through a port  45  located within the packer  40 . From there, the cable  12  runs through a port  42  located within an annular safety valve  41 . The cable  12  then reaches the spacer sub  10  below the packer  40 . When the cable  12  reaches the spacer sub  10 , the cable  12  is run through a cable groove  200  located along the outer diameter of the spacer sub  10 . The cable groove  200  defines a spiral-shaped recess or indentation in the spacer sub  10  disposed around the outer surface of the spacer sub  10 . In the particular embodiment of FIG. 1, the cable  12  is housed within the cable groove  200  to helically surround the spacer sub  10 . The length of the cable groove  200  is calculated to house an anticipated surplus length of cable  12 .  
         [0032]    [0032]FIG. 2 shows a cross-sectional side view of a portion of the spacer sub  10 . Visible in this view is a cable groove  200  disposed in the sub  10 . The cable groove  200  is shaped deep and wide enough to substantially house the cable  12 . The cable groove  200  is preferably wide enough to accommodate various different cables used in the production of hydrocarbons as well as to house multiple cables at the same time. Located above the cable groove  200  in the view of FIG. 2, and radially outward from the cable groove  200  in the view of FIG. 1, is a keeper plate groove  90 . The keeper plate groove  90  is dimensioned to be wider than the cable groove  200  so that a keeper plate  95  or other retaining member maintains the cable  12  in place along the cable groove  200 . The keeper plate groove  90  is shaped deep and wide enough to accommodate the keeper plate  95 .  
         [0033]    A perspective view of the keeper plate  95  is shown in FIG. 3. The keeper plate  95  may be rectangular in shape, as shown in FIG. 3, or any other shape which will perform the purpose of holding the cable  12  in place within the cable groove  200 . The keeper plate  95  is preferably 2 mm to 3 mm thick and may have defined or rounded edges. The keeper plate  95  preferably has two holes  75  therethrough for receiving screws  70 , as shown in FIG. 2. Although two screws  70  are illustrated in FIGS. 2 and 3, any number or type of fasteners  70  may be utilized with the present invention. Referring again to FIG. 2, the screws  70  are placed through the holes  75  in the keeper plate  95  and through a portion of the spacer sub  10  so that the keeper plate  95  is secured to the spacer sub  10  and housed in the keeper plate groove  90 .  
         [0034]    As seen in FIG. 2, the keeper plate  95  is countersunk into the spacer sub  10  so that even the outermost portion of the keeper plate  95  is located within the outer diameter of the spacer sub  10 . Countersinking the keeper plate  95  prevents the interruption of fluid flow within the wellbore  50 . In this respect, if the keeper plate  95  protrudes radially outward past the outer diameter of the spacer sub  10 , unwanted turbulence could be created as fluid flows over the keeper plate  95 . Numerous keeper plates  95  may be disposed within the keeper plate groove  90 . The keeper plates  95  are placed within the keeper plate grove  90  at intervals needed to prevent the cable  12  from protruding out of the cable groove  200 .  
         [0035]    Optionally, a cable connector  150  may be protected at the top of the spacer sub  10  as shown in FIG. 4. The cable connector  150  is used to connect portions of the cable  12  to one another, and is especially useful when the spacer sub  10  is used in conjunction with the packer  40  and the annular safety valve  41 . An exemplary cable connector  150  is a dry mate connector used with fiber optics. The cable connector  150  is ordinarily approximately 0.9 inches thick. A connector groove  155  may be formed in the spacer sub  10  to house the cable connector  150  securely, thus protecting the cable connector  150  from damage caused by fluid flow through the annular space  5  and further preventing interruption of fluid flow by a protruding cable connector. The connector groove  155  defines a recess in the sub  10  which is preferably wider than the cable groove  200  and impressed deeper into the spacer sub  10  than the cable groove  200  so as to accommodate the larger diameter of the cable connector  150  relative to the cable  12 . The connector groove  155  is designed to essentially conform to the outer diameter of the cable connector  150 , so that the cable connector  150  is closely held within the spacer sub  10 . While only one connector groove  155  is shown in FIG. 4, multiple connector grooves  155  may be provided along the spacer sub  10  to house multiple cable connectors  150  along the cable  12 , as needed.  
         [0036]    An alternate embodiment of the spacer sub  10  of the present invention is shown in FIG. 5. The parts which are the same as in FIGS. 1-4 are labeled with the same numbers. The difference in this embodiment lies in the spacer sub  10 . The spacer sub  10  has three cable grooves  200 A,  200 B, and  200 C. The cable grooves  200 A,  200 B, and  200 C are spiral grooves within the spacer sub  10  which are placed at different helical angles along the spacer sub  10  to house various lengths of cable  12 . The spacer sub  10  may either have multiple entries for the cable  12  which are different for each cable groove  200 A,  200 B, or  200 C, or one entry point may be utilized into the spacer sub  10 . From there, the cable grooves  200 A,  200 B, and  200 C may branch from the one entry point to house varying lengths of cable  12  along three different routes. The cable grooves  200 A,  200 B, and  200 C allow for different lengths of cable  12  to be safely housed within the spiral grooves, and allows for slack in cables  12  of different lengths to be taken up. Furthermore, more than one cable  12  may be housed within the different cable grooves  200 A,  200 B, and  200 C at the same time. When using multiple entry points for different lengths of cable, the entry points may be marked to designate the length of cable  12  the cable groove  200 A,  200 B, or  200 C has the ability to accommodate, for example, different designations for 2-foot cable, 3-foot cable, and 4-foot cable.  
         [0037]    Although FIG. 5 shows three different cable grooves  200 A,  200 B, and  200 C, any number of cable grooves  200  can be used with the present invention. Any number of keeper plates (shown in FIG. 3) as described above may be utilized in each cable groove  200 A,  200 B, and  200 C in the embodiment shown in FIG. 5. Furthermore, one or more cable connectors (shown in FIG. 4) may be protected in any number of connector grooves (not shown), in the embodiment of FIG. 5.  
         [0038]    While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.