Abstract:
A method and apparatus for determining a parameter of a production fluid in a wellbore by providing an initially blocked isolated communication path between a sensor and an aperture formed in a sleeve. The isolated communication path is subsequently unblocked to allow measurements of the parameter of the production fluid.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    Embodiments of the present invention generally relate to apparatus and methods for determining parameters of a fluid in a wellbore and, more specifically, an apparatus and method for determining parameters in cemented multi-zone completions. 
         [0003]    2. Description of the Related Art 
         [0004]    In the hydrocarbon industry, there is considerable value associated with the ability to monitor the flow of hydrocarbon products in every zone of a production tube of a well in real time. For example, downhole parameters that may be important in producing from, or injecting into, subsurface reservoirs include pressure, temperature, porosity, permeability, density, mineral content, electrical conductivity, and bed thickness. Downhole parameters may be measured by a variety of sensing systems including acoustic, electrical, magnetic, electro-magnetic, strain, nuclear, and optical based devices. These sensing systems are intended for use between the zonal isolation areas of the production tubing in order to measure fluid parameters adjacent fracking ports. Fracking ports are apertures in a fracking sleeve portion of a production tube string that open and close to permit or restrict fluid flow into and out of the production tube. 
         [0005]    One challenge of monitoring the flow of hydrocarbon products arises where cement is used for the zonal isolation. In these instances, the annular area between the production tubing and the wellbore is filled with cement and then perforated by a fracking fluid. As a result, sensors located on an exterior surface of the tubing may not be in direct fluid communication with the fluid flowing into and out of the perforated cement locations. Another challenge arises where the sensor spacing is not customized to align with the zonal isolation areas for each drilling operation. For example, the sensing system may include an array of sensors interconnected by a sensing cable. The length of the sensing cable between any two sensors is set and not adjustable. Conversely, the distance between each zonal isolation area varies for each drilling operation. As a result, the sensing system&#39;s measurements may be inaccurate due to the sensor&#39;s location along the production tube. 
         [0006]    What is needed are apparatus and methods for improving the use of sensing systems with cemented zonal isolations. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention generally relates to a method for determining a parameter of a production fluid in a wellbore. First, a plurality of sensors is attached to a string of tubing equipped with a plurality of sleeves. An isolated communication path is then provided for fluid communication between the plurality of sensors and a plurality of apertures formed in the sleeves. The apertures are initially closed. Next, the string of tubing is inserted and cemented in the wellbore. The apertures in the sleeves are subsequently remotely opened and a fracking fluid is injected into a formation adjacent the wellbore via the apertures, thereby creating perforations in the cement. In one embodiment, the isolated communication path is initially blocked and then, after fracking the path is unblocked, and the parameter of the production fluid adjacent the apertures is measured. 
         [0008]    The present invention also relates to a tool string for determining a parameter of a production fluid in a wellbore having a tubing equipped with a sleeve, wherein at least one aperture is formed in the sleeve. The tool string contains a sensor on a sensing cable, wherein the sensor is spaced from the at least one aperture, and a sensor container, wherein the sensor is at least partially enclosed in the sensor container. The tool string includes an isolated communication path that spans a predetermined distance from the sensor container to the nearest aperture, wherein the isolated communication path includes a removable seal. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    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 to embodiments, some of which are illustrated 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, for the invention may admit to other equally effective embodiments. 
           [0010]      FIG. 1  illustrates a string of production tubing coupled with a string of sensing systems, according to one embodiment of the present invention; 
           [0011]      FIG. 2  shows the production tubing and sensing system strings of  FIG. 1  with cement injected into an annulus formed between the production tubing and a wellbore; 
           [0012]      FIG. 3  shows the production tubing and sensor system strings of  FIG. 2  after the cement has been perforated by a fracking fluid; 
           [0013]      FIG. 4  shows the wellbore with a mandrel, the production tubing, and a fracking sleeve; 
           [0014]      FIG. 5  shows a sensor container on the mandrel of  FIG. 4 ; 
           [0015]      FIG. 6  shows a cross section of a tube port; and 
           [0016]      FIG. 7  shows the sensor container. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    The present invention is a method and apparatus for sensing parameters in cemented multi-zone completions. 
         [0018]      FIG. 1  shows a string of production tubing  110  coupled with a string of sensing systems  101 , configured to implement one or more aspects of the present invention. As shown, a wellbore  102  includes a casing  106 , cement  108 , the production tubing  110  with a plurality of fracking sleeves  114 , and the sensing systems  101 . Each sensing system  101  includes a sensing cable  118 , a sensor  124 , and a communication path  126  between the sensor  124  and a location adjacent the fracking sleeve  114 . 
         [0019]    As shown, the wellbore  102  is lined with one or more strings of casing  106  to a predetermined depth. The casing  106  is strengthened by cement  108  injected between the casing  106  and the wellbore  102 . The production tubing  110  extends into a horizontal portion in the wellbore  102 , thereby creating an annulus  109 . The string of production tubing  110  includes at least one fracking zone  116 . Each fracking zone  116  includes production tubing  110  equipped with a fracking sleeve  114 . The fracking sleeve  114  includes a plurality of apertures that can be remotely opened or closed during the various phases of hydrocarbon production. In one example, the apertures are fracking ports  112  that remain closed during the injection of cement  108  and are later opened to permit the injection of fracking fluid into a formation  104 . 
         [0020]    The sensing systems  101  may be interconnected by the sensing cable  118 . The sensing cable  118  runs along the outer diameter of the production tubing  110  in the annulus  109 . In one example, the sensing cable  118  may be fed from a spool and attached to the production tubing  110  as the strings of the production tubing  110  are inserted into the wellbore  102 . The sensing cable  118  contains sensors  124 , which may include any of the various types of acoustic and/or pressure sensors known to those skilled in the art. In one example, the sensing system  101  may rely on fiber optic based seismic sensing where the sensors  124  include fiber optic-based sensors, such as fiber Bragg gratings in disclosed in U.S. Pat. No. 7,036,601 which is incorporated herein in its entirety. To determine fluid parameters at the fracking port  112 , the sensor  124  is coupled to the communication path  126 . The communication path  126  provides fluid communication between the sensor  124  and a fracking port  112 . In one example, the communication path  126  may be placed either adjacent the fracturing port  112  or a close distance from the fracking port  112 . The communication path  126  may be initially sealed. In one example, a removable plug  128  prevents fluids, up to some threshold pressure, from reaching the sensor  124  through the communication path  126 . 
         [0021]      FIG. 2  shows the production tubing  110  and sensing system  101  strings of  FIG. 1  with cement  108  injected into the annulus  109 . In one example, cement  108  is injected into the production tubing  110  and exits at a tube toe  202  to fill the annulus  109 . In  FIG. 2 , cement is shown filling annulus  109  upwards of the intersection between the production tubing and the casing  106 . However, it will be understood that a packer or similar device could isolate the annulus above the casing and the cement could terminate at a lower end of the casing. 
         [0022]      FIG. 3  shows the production tubing  110  and sensor system  101  strings of  FIG. 2  after the cement  108  has been perforated by the fracking fluid. To inject fracking fluid into the formation  104 , the fracking ports  112  of the fracking sleeve  114  are remotely opened. In one example, U.S. Pat. No. 8,245,788 discloses a ball used to actuate the fracking sleeve  114  and open the fracking port  112 . The &#39;788 patent is incorporated by reference herein in its entirety. The fracking fluid pressure creates perforations  302  in the cement  108  and fractures the adjacent formation  104 . Production fluid travels through the fractures in the adjacent formation  104  and into the production tubing  110  at the fracking ports  112  via the perforations  302  in the cement  108 . The injection of fracking fluid through the fracking port  112  may erode or dislodge the removable plug  128  on the communication path  126 . The removable plug  128  may also be dislodged by the actuation of the fracking sleeve  114 . The elimination of the removable plug  128  permits fluid to flow through the communication path  126  to the sensor  124  for an accurate reading of the fluid parameter at the fracking port  112 . The measurements at each sensor  124  are carried through the sensing cable  118  to provide information about the fluid characteristics in each fracking zone  116 . 
         [0023]      FIG. 4  shows the fracking zone  116  with a mandrel  402 , the production tubing  110 , and the fracking sleeve  114 . The mandrel  402  includes a sensor container  404  and couples the sensing system  101  ( FIG. 3 ) to the production tubing  110 . In one example, the mandrel  402  may be installed on the production tubing  110  at a location of the sensor  124  (not visible) on the sensing cable  118 . The sensor container  404  forms a seal around the sensor  124 , prevents contact with cement  108  during the cementing operation, and ensures that fluid is transmitted to the sensor  124  during the fracking and production operations. 
         [0024]    In another embodiment, the sensor container  404  is on a container carrier (not shown). The container carrier is coupled to the production tubing  110  and is independent of the mandrel  402 . Therefore, the container carrier provides the ability to attach the sensor container  404  to the production tubing  110  at locations not adjacent the mandrel  402  or the fracking sleeve  114 . The communication path  126  of sufficient length is provided to couple the sensor  124  to the mandrel  402 . 
         [0025]      FIG. 5  shows the sensor container  404  on the mandrel  402  of  FIG. 4 . The mandrel  402  protects the sensor container  404 , the communication path  126 , a sensor port  502 , and a tube port  504  from contact with the walls of the wellbore  102 . 
         [0026]    In the embodiment shown, the mandrel  402  includes a holding area  506 , which provides an enlarged area to seat the sensing system  101 . The position of the sensor container  404  in the holding area  506  determines the minimum length of the communication path  126 . In one example, the communication path  126  must be sufficient in length to couple the tube port  504  to the sensor port  502 . The tube port  504  supplies fluid from the inner diameter of the mandrel  402  directly to the communication path  126 . Fluid flows through the communication path  126  to the sensor port  502  on the sensor container  404 . 
         [0027]    The sensor container  404  is designed to easily attach to the holding area  506  on the mandrel  402 . In one example, the sensor container  404  and/or the sensing cable  118  may be fastened to the mandrel  402  by a clamping mechanism  508 . The clamping mechanism  508  restricts the sensor container  404  from shifting in the holding area  506 . To further provide a secure fit in the holding area  506 , a cable slot  510  may be machined into the mandrel  402  at each end of the holding area  506 . The mandrel  402  may include a mandrel cover (not shown) to cover the holding area  506  and further secure the sensing system  101 . 
         [0028]      FIG. 6  shows a cross section of the tube port  504 . The tube port  504  provides fluid communication between the communication path  126  and the mandrel  402  via a fluid channel  601  and a vertical drill hole  602 . In one example, the tube port  504  includes a removable seal, a disc plug  604 , a debris screen  606 , and a plug fastener  608 . The removable seal may be a burst disc  603 . 
         [0029]    The burst disc  603  is seated and sealed by the disc plug  604  in a tube slot  610 . The burst disc  603  prevents cement  108  from entering the communication path  126  during the cementing operation. However, the burst disc  603  may fail and allow fluid to enter the communication path  126  during the fracking operation. In one example, the burst disc  603  may be manufactured of a material set to fail above the pressure used in the cement operation, but below the pressure used in the fracking operation. After the burst disc  603  fails, a sample of fluid in the mandrel  402  flows through the vertical drill hole  602  and into the tube slot  610 . The debris screen  606 , which is seated in the tube slot  610  on the disc plug  604 , traps material from the burst disc  603  and prevents the communication path  126  from clogging. After the debris screen  606  filters the fluid, the fluid enters the communication path  126  by passing through the fluid channel  601  and a fitting  616 . The burst disc  603 , the disc plug  604 , and the debris screen  606  are held in the tube slot  610  by the plug fastener  608 , which sits in a plug slot  612 . 
         [0030]    In another embodiment, the tube port  504  includes the fluid channel  601  and the vertical drill hole  602  separated by a removable plug (not shown). The removable plug may be dislodged or eroded by fluid flowing through the mandrel  402 . After the removable plug is eliminated, a sample of fluid in the mandrel  402  flows into the communication path  126  for a parameter reading in the sensing container  404 . 
         [0031]      FIG. 7  shows the sensor container  404 . The sensor container  404  includes a container cover  702  and a container base  704 . In one example, at least one bolt  716  may be used to couple the container cover  702  to the container base  704 . The container cover  702  and the container base  704  are machined to align and fit around the sensor  124  and the sensing cable  118 . In one example, grooves  718  may be machined into the container cover  702  and the container base  704  to align the sensor  124  in a sensor compartment  706 . 
         [0032]    The sensor compartment  706  isolates the sensor  124  and ensures accurate sensor measurements by providing a seal. In one embodiment, the sensor compartment  706  may be located on the container base  704  and include a pair of side seals  710  and a pair of end seals  712 . The side seals  710  run parallel to the sensing cable  118  and the end seals  712  run over and around the sensing cable  118 . The side seals  710  and the end seals  712  may include a layer of seal material  713  that prevents fluid from contacting the sensor  124 . 
         [0033]    The sensor  124  determines the parameters of fluid in the production tubing  110 . In one example, the sensor  124  reads a pressure of the fluid at varying stages of the drilling operation. The sensor  124  may measure the pressure of the fracking fluid injected into the formation  104  during the fracking operation. The sensor  124  may also measure the pressure of the production fluid exiting the formation  104  during the production operation. The sensor  124  may be either completely or partially covered by the sensor container  404 . 
         [0034]    The sensor container  404  includes the sensor port  502 . The sensor port  502  couples the communication path  126  to the sensor compartment  706  by feeding fluid into the fluid channel  601 . In one example, the container cover  702  includes the sensor port  502  and a test port (not shown) opposite the sensor port  502 . The test port is substantially similar or identical to the sensor port  502  and tests the quality of the side and end seals  710 ,  712 . 
         [0035]    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.