Abstract:
The present invention provides methods and apparatus for determining the location of an apparatus in a wellbore. The method includes lowering the apparatus with a conveying member and measuring a parameter associated with the conveying member. Thereafter, the measured parameter is used to determine the location of the apparatus as well as other conditions in the wellbore. The apparatus includes a conveying member operatively connected to an object released downhole. The apparatus may also include a dispensing apparatus coupled to one end of the conveying member. Preferably, the conveying member is a fiber optics line capable of transmitting optical signals. Other types of conveying members include a wire, a tube, and a cable. Additionally, a sensor may be disposed on the object and connected to the conveying member.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention generally relates to apparatus and methods for completing a well. Particularly, the present invention relates to apparatus and methods for cementing operations. More particularly, the present invention relates to apparatus and methods for locating a cementing apparatus in the wellbore. More particularly still, the present invention relates to apparatus and methods for determining the amount of cement displaced. 
   2. Description of the Related Art 
   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. After drilling a predetermined depth, the drill string and bit are removed and the wellbore is lined with a string of casing. An annular area is thus formed between the string of casing and the formation. A cementing operation is then conducted in order to fill the annular area with cement. The combination of cement and casing strengthens the wellbore and facilitates the isolation of certain areas of the formation behind the casing for the production of hydrocarbons. 
   It is common to employ more than one string of casing in a wellbore. In this respect, a first string of casing is set in the wellbore when the well is drilled to a first designated depth. The first string of casing is hung from the surface, and then cement is circulated into the annulus behind the casing. The well is then drilled to a second designated depth, and a second string of casing, or a liner, is run into the well. The second string is set at a depth such that the upper portion of the second string of casing overlaps the lower portion of the first string of casing. The second liner string is then fixed or “hung” off of the existing casing. Afterwards, the second casing string is also cemented. This process is typically 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 of an ever-decreasing diameter. 
   The process of cementing a liner into a wellbore typically involves the use of liner wiper plugs and drill-pipe darts. Plugs typically define an elongated elastomeric body used to separate fluids pumped into a wellbore. A liner wiper plug is typically located inside the top of a liner, and is lowered into the wellbore with the liner at the bottom of a working string. The liner wiper plug has radial wipers to contact and wipe the inside of the liner as the plug travels down the liner. The liner wiper plug has a cylindrical bore through it to allow passage of fluids. 
   Typically, the cementing operation requires the use of two plugs and darts. When the cement is ready to be dispensed, a first dart is released into the working string. The cement is pumped behind the dart, thereby moving the dart downhole. The dart acts as a barrier between the cement and the drilling fluid to minimize the contamination of the cement. As the dart travels downhole, it seats against a first liner wiper plug and closes off the internal bore through the first plug. Hydraulic pressure from the cement above the dart forces the dart and the plug to dislodge from the liner and to be pumped down the liner together. At the bottom, the first plug seats against a float valve, thereby closing off fluid flow through the float valve. The pressure builds above the first plug until it is sufficient to cause a membrane in the first plug to rupture. Thereafter, cement flows through the first plug and the float valve and up into the annular space between the wellbore and the liner. 
   After a sufficient volume of cement has been placed into the wellbore, a second dart is deployed. Drilling mud is pumped in behind the second dart to move the second dart down the working string. The second dart travels downhole and seats against a second liner wiper plug. Hydraulic pressure above the second dart forces the second dart and the second plug to dislodge from the liner and they are pumped down the liner together. This forces the cement ahead of the second plug to displace out of the liner and into the annulus. This displacement of the cement into the annulus continues until the second plug seats against the float valve. Thereafter, the cement is allowed to cure before the float valve is removed. 
   During the cementing operation, it is desirable to know the location of the second plug/dart in the wellbore. Generally, the position of the plug will indicate the amount of cement that has been displaced into the annulus. If insufficient cement is displaced (“underdisplacement”), cement will remain in the casing. If too much cement is displaced, (“overdisplacement”), portions of annulus will not be cemented. 
   One method of determining the plug location is by measuring the volume displaced after the second plug is released. Then, the volume displaced is compared to the calculated displacement volume based upon the dimensions of the casing or drill pipe. A second method is attaching an indication wire to indicate that a plug has been released. The indication wire is usually 2 to 3 feet in length. A third method is using mechanical flipper indicator. In this method, a lever is disposed below the plug container. A released plug will shift the lever when the plug travels by it. A fourth method is using electromagnetic or magnetic signals. Generally, an identification tag is attached to the plug or dart. A detector located below the cementing head picks up the signal when the plug passes to indicate that the plug has been launched. 
   There are drawbacks to using these methods to determine plug location. For instance, the displacement method is not very accurate and does not give a positive indication that the plug is moving at the same rate as the fluid being pumped behind the plug. Casing and drill pipe are generally manufactured to dimensional tolerances that could result in a substantial difference between the calculated displacement volume and the actual displacement volume. Further, fluids are subject to aeration and compression during the operation, thereby affecting measured volume. Indicator wires and mechanical flipper indicators only indicate that the plug has been released, not the location thereof. Finally, the signal detectors cannot track the plug for long distances and only indicate that the plug has moved past the detection device. 
   There is a need, therefore, for an apparatus for locating a plug in the wellbore. Further, there is a need for an apparatus for determining the amount of cement that has been displaced. The need also exists for a method for completing a cementing operation. 
   SUMMARY OF THE INVENTION 
   The present invention provides an apparatus for determining the location of an object in a wellbore. The apparatus includes a conveying member operatively connected to an object released downhole. The apparatus may also include a dispensing apparatus coupled to one end of the conveying member. Preferably, the conveying member is a fiber optics line capable of transmitting optical signals. Other types of conveying member include a wire, a tube, and a cable. Additionally, a sensor may be disposed on the object and connected to the conveying member. 
   In another aspect, the present invention provides a method for determining the location of an apparatus in a wellbore. The method includes lowering the apparatus with a conveying member and measuring a parameter associated with the conveying member. Thereafter, the measured parameter is used to determine the location of the apparatus. In one embodiment, the apparatus includes a cementing apparatus such a dart or a plug. 
   In another aspect, the method includes connecting one end of a fiber optics line to the apparatus and coupling the other end of the fiber optics line to a dispensing tool. Thereafter, the apparatus is placed in the wellbore and the length of fiber optics line is measured to determine the location of the apparatus in the wellbore. 
   In another aspect still, the present invention provides a method for determining a condition in a wellbore. The method includes connecting one end of a fiber optics line to an object to be lowered into the wellbore and coupling the other end of the fiber optics line to a dispensing tool. Additionally, one or more optical sensors are operatively coupled to the fiber optics line. Thereafter, the object is placed in the wellbore. Finally, one or more optical signals are sent along the fiber optics line to the one or more optical sensors and a change in the one or more optical signals is measured. 
   In another aspect still, the present invention provides a method for operating an apparatus in a wellbore. The method includes connecting a fiber optics line to the apparatus, connecting a signal source to the fiber optics line, and connecting a controller to the fiber optics line. Thereafter, an optical signal is sent along the fiber optics line to the controller to operate the apparatus. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     So that the manner in which the above recited features and advantages of the present invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof 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. 
       FIG. 1  is a schematic view of an apparatus according to one aspect of the present invention disposed in a partially cased wellbore. In this view, a dart is moving towards a plug. 
       FIG. 2  is a schematic view of a dispensing apparatus usable with the present invention. 
       FIG. 3  is a schematic view of the apparatus of  FIG. 1 . In this view, the dart and the plug has moved to a lower portion of the wellbore. 
       FIG. 4  is a schematic view of another aspect of the present invention. In this view, the optic fiber is provided with an optical sensor. 
       FIG. 5  is a schematic view of an apparatus according to another aspect of the present invention. 
       FIG. 6  is a schematic view of an apparatus according to another aspect of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1  is a schematic view of a partially cased wellbore  10 . In this view, an upper portion  20  of the wellbore  10  has been lined with casing  25 , and the annular area between the casing  25  and the wellbore  10  has been filled with cement  30 . Additionally, a lower portion  40  of the wellbore  10  is in the process of being lined with a tubular  50 . 
   The tubular  50  is a liner  50  disposed adjacent the lower portion  40  of the wellbore  10  and at least partially overlapping the existing casing  25 . The liner  50  is attached to a liner running tool  57 . As shown, a first plug  61  having a first dart (not shown) seated therein has traveled down the liner  50  and seated in a float valve  65  disposed at a lower portion of the liner  50 . Further, a membrane in the first plug  61  has ruptured, thereby allowing fluid communication between an interior of the liner  50  and the wellbore  10 . Disposed at an upper portion of the liner running tool  57  is a second plug  62 . The second plug  62  is selectively connected to the liner  50  until it is ready for release downhole. The second plug  62  contains an internal bore  66  for fluid flow and a seat for mating with a second dart  72 . 
   The second dart  72  is shown moving along the liner running string  55 . The second dart  72  is moved along the liner running string  55  by a wellbore fluid such as drilling mud that is pumped in behind the second dart  72 . The second dart  72  separates the cement from the drilling mud to minimize contamination of the cement. As the second dart  72  moves along the liner running string  55 , the cement in front of the second dart  72  is displaced into the wellbore  10 . 
   An optic fiber line  80  (or “fiber”) is attached to an upper portion of the second dart  72 . The other end of the fiber  80  is coupled to a dispensing apparatus  85  disposed at the surface as shown in  FIG. 2 . Preferably, a tension is maintained in the fiber  80  such that a fiber  80  remains substantially straight or taut as the fiber  80  is dispensed. As the second dart  72  moves downhole, a corresponding length of fiber  80  is dispensed from the dispensing apparatus  85 . In this manner, the location of the second dart  72  may be determined in real time. Although a dart or plug is used herein, the aspects of the present invention are equally applicable to determining the location of other objects downhole including, but not limited to, perforating guns, retrievable packer, and other objects as known by one of ordinary skill in the art. 
     FIG. 2  is an exemplary dispensing apparatus  85  usable with the present invention. The dispensing apparatus  85  is disposed inside a cementing head  90  along with the second dart  72 . In this view, the second dart  72  has not been released into the wellbore  10 . As shown, one end of the fiber  80  is attached to the second dart  72  and another end coupled to the dispensing apparatus  85 . The dispensing apparatus  85  contains a release mechanism designed to dispense a length of fiber  80  that corresponds to the distance traveled by the second dart  72 . In this respect, the amount of fiber  80  dispensed is a measurement of the linear displacement of the second dart  72 . Consequently, the location of the second dart  72  can be tracked by determining the amount of fiber  80  dispensed. In another embodiment, the dispensing apparatus  85  may be placed outside of the cementing head. It must be noted that other types of dispensing apparatus  85  may be used with the aspects of the present invention; for example, one such dispensing apparatus  85  is manufactured by Gas Technology Institute. 
   The fiber  80  may be provided with markings  84  to facilitate the reading of the length dispensed. Alternatively, one or more rollers  82  may be disposed below the dispensing apparatus. As the fiber is dispensed, it will cause the roller to rotate a respective distance. The length of the fiber dispensed may be calculated from the number of revolutions made by the roller. Other methods of measuring the length of fiber dispensed known to a person of ordinary skill in the art are contemplated within the scope of the present invention. 
   One advantage of using optic fiber line  80  is its size. Generally, the fiber  80  has a smaller outer diameter than other wire products such as a wireline. As such, any fiber  80  remaining in the wellbore  10  can easily be drilled out, thereby minimizing any problems associated with materials left in the wellbore  10 . Additionally, optic fiber lines  80  are tolerant of high temperatures and corrosive environments, and thus have broad application in the oil industry. Although an optic fiber line  80  is used herein, it must be noted that the present invention also contemplates the use of similar small diameter wire transmission lines. 
   In operation, after a desired amount of cement has been introduced into the wellbore  10 , the second dart  72 , with the optic fiber line  80  attached, is released behind the cement. Thereafter, drilling mud is pumped in behind the second dart  72  to move the second dart  72  downhole as shown in  FIG. 1 . As the second dart  72  travels down the wellbore  10 , cement in front of the second dart  72  is displaced out of the liner  50  and into the wellbore  10 . Additionally, more fiber  80  is dispensed as the second dart  72  travels lower. Preferably, the tension in the fiber  80  is sufficient to maintain the fiber  80  substantially straight or taut. Consequently, the location of the second dart  72  can be determined from the length of fiber  80  dispensed. 
   The second dart  72  continues to move down the wellbore  10  until it seats in the second plug  62 . This stops the second dart&#39;s  72  movement in the wellbore  10 , thereby causing the fluid pressure behind the second dart  72  and the second plug  62  to build. At a predetermined level, the fluid pressure causes the second plug  62  to disconnect from the liner  50  and move down the liner  50  together with the second dart  72  and the fiber  80 . 
     FIG. 3  shows the second plug  62  engaged with the first plug  61 , thereby blocking off fluid communication between the interior of the liner  50  and the wellbore  10 . In this view, all or substantially all of the cement have been displaced into the wellbore  10 . Additionally, cement is prevented from flowing back into the liner  50  through the float valve  65 . Once the second plug  62  is stationary, an operator at the surface can compare the approximate distance between the surface and the float valve  65  to the length of fiber  80  dispensed. In this manner, the operator is provided with a positive indication that the second plug  62  has successfully reached the bottom of the liner  50 . The operator may then discontinue supplying the drilling mud into the wellbore  10 . When the cement cures, the darts  72 , plugs  61 ,  62 , float valve  65 , and fiber  80  are drilled out. 
   Other applications of the present invention include attaching the fiber optic line to a dart that lands on a plug attached to a subsea casing hanger running tool. Additionally, if the cementing operation does not require the use of darts, the fiber optic line may be attached to one or more cementing plugs that are launched from the surface. It must be noted that aspects of the present invention are not limited to cementing operations, but are equally applicable to other types of wellbore operations requiring the release of an apparatus downhole. 
   In another aspect, the optic fiber line  80  may provide data regarding the wellbore  10  conditions. Generally, elastic properties inherent in the optic fiber  80  may complicate a reading of the length of fiber  80  dispensed. In operation, the fiber  80  may elongate or strain under the weight of the plug  62  or the drilling mud behind the plug  62 . Therefore, a true indication of the location of the plug  62  may not be achieved by reading the length of fiber  80  dispensed. Although a plug  62  is used herein, aspects of the present invention are equally applicable to determining locations or positions of other apparatus disposed downhole. 
   In one embodiment, the fiber optics line  80  may be equipped with one or more sensors  100  to provide a more accurate indication of the location of the dart  72 . As illustrated in  FIG. 4 , a single discrete sensor  100  may be disposed on the fiber  80  at a location near the dart  72 . The dart  72  is shown traveling in a running string  55  and coupled to a dispensing apparatus  85  disposed at the surface. In addition to the dispensing apparatus  85 , the fiber  80  may also be connected to an optical signal source  110  and a receiver  120 . An optical signal sent from the surface must travel the full distance along the fiber  80  to reach the sensor  100 . Typically, the distance can be determined by measuring the total time required for the signal to travel from the optical signal source  110  to the sensor  100  and then to the receiver  120 . Because the total length of fiber  80  and the amount of fiber  80  dispensed are known, any elongation of the fiber  80  due to strain may be adequately accounted for. As a result, the location of the dart  72  may be determined in real time. 
   Moreover, the sensor  100  may also provide a means for determining the movement of the dart  72 , namely, whether it&#39;s moving or stationary. As more fiber  80  is dispensed, the fiber  80  will continue to elongate due to strain on the fiber  80 . The length of the elongated portion of fiber  80  may be measured by the sensor  100 . Thus, if the length of the fiber  80  continues to change due to strain as measured by the sensor  100 , it may indicate that the dart  72  is moving along the wellbore. If no change in the length of the fiber  80  is measured, then it may indicate that the dart  72  has stopped moving in the wellbore. 
   In addition to measuring location and movement, the sensor  100  may be designed to provide real time data regarding other parameters such as pressure, temperature, strain, and/or other monitored parameters of the wellbore  10 . Generally, perturbations in these parameters induce a phase shift in the optical signal, which is transmitted by the sensor  120 . When the receiver  120  receives the signal, the phase shift is detected an intensity variation. The phase shift is converted into the intensity change using interferometric techniques such as Mach-Zehnder, Michelson, Fabry-Perot, and Sagnac. 
   In another embodiment, multiple optical sensors  100  may be arranged in a network or array configuration with individual sensors multiplexed using time division multiplexing or frequency division multiplexing. The network of sensors may provide an increased spatial resolution of temperature, pressure, strain, or flow data in the wellbore  10 . One form of sensor networks is known as distributed sensing. Distributed sensor schemes typically include Bragg grating sensors and optical time domain reflectometry (“OTDR”). For example, Bragg grating sensors may be formed in one or more positions along the length of the fiber  80 . These sensors provide real time data at each of these positions, which can be processed to give a clearer picture of the conditions along the length of the wellbore  10 . In another example, Raman OTDR may be used to collect temperature data to provide a temperature gradient inside the wellbore  10 . In another example still, Brillouin OTDR may be used to measure the strain of the fiber  80  and the temperature inside the wellbore  10 . It is contemplated that other schemes of optical sensors  100  may be used without departing from the aspects of the present invention. 
   The location of a dart  72  may be determined from the pressure or temperature surrounding dart  72  in wellbore. As the dart  72  descends in the wellbore, the pressure or temperature of the dart  72  changes relative to the depth of the wellbore. This change in pressure or temperature may be measured by the one or more sensors  100  attached to the dart  72 . Because pressure and temperature is related to depth, the depth of the dart  72  may be determined from the pressure and/or temperature measured by the one or more sensors  100 . 
   In another aspect, optic fibers  80  may be used to transmit signals to a downhole apparatus to effect the operation thereof. In one embodiment, a fiber optics line  80  may be disposed along a length of the wellbore  10 . Thereafter, signals may be transmitted through the fiber  80  to operate a flapper valve  200  as illustrated in  FIG. 5 .  FIG. 5  shows a flapper valve  200  disposed in a casing collar  210 . The fiber  80  is connected to a controller  220  that, in turn, is connected to a power supply  230  and an actuator  240  of the flapper valve  200 . A signal from the surface may be transmitted through the fiber  80  and processed by the controller  220 . Thereafter, the controller  220  may operate the actuator  240  as directed by the signal. In this manner, a downhole flapper valve  200  may be activated by the fiber  80 . In addition to the flapper valve  200 , other types of downhole valves may be activated in this manner, including plunger valves and other types of float valves. The controller  220 , as used herein, may be any computer or other programmable electronic device. It will be appreciated by those skilled in the art, however, that other types of controller may be used without departing from the scope of the present invention. 
   In another embodiment, fiber optics line  80  may be used to activate a sleeve  300 .  FIG. 6  shows a sleeve  300  disposed coaxially within a casing collar  310 . The sleeve  300  is movable between an open position and a closed position and includes one or more sleeve ports  320  formed therein. In the open position, the one or more sleeve ports  320  align with one or more casing ports  330  of the casing collar  310 , thereby allowing fluid communication between an interior of the casing collar  310  and an exterior of the casing collar  310 . In  FIG. 6 , the sleeve  300  is shown in the open position. In the closed position, the sleeve ports  320  are moved out of alignment with the casing ports  330 , thereby blocking fluid communication between the interior and the exterior of the casing collar  310 . One or more actuators  340  are used to move the sleeve  300  between the open and closed positions. The actuator  340  is connected to a power supply  350  and operated by a controller  360  connected to the fiber  80 . In this manner, signals may be transmitted through the fiber  80  to operate the sleeve  300 . 
   In another aspect (not shown), the casing in the wellbore may be equipped with one or more magnetic or radioactive tags. The tags may be placed at predetermined positions in the casing. The tags may be used in connection with a dart having a tag sensor and an optical sensor. When the dart moves past a tag, the tag sensor may send a signal to the optical sensor. Thereafter the optical sensor may send an optical signal back to the surface through the optical fiber to indicate that the dart has moved past a certain tag in the wellbore. 
   In addition to fiber optics cable, aspects of the present invention also contemplate using other types of transmission lines as the conveying member for the sensor. For example, a sensor connected to a wire may be disposed on an apparatus released downhole. The wire is spooled out from the surface by the apparatus, which may include cementing equipment such as a plug or dart, during its descent. As the apparatus travels downhole, the sensor may collect and transmit data regarding the wellbore. Further, the wire may transmit the signal by electrical or non-electrical means. The sensor may collect data regarding the wellbore such as pressure and temperature. The collected data may be used to determine the location of the apparatus downhole. 
   In another embodiment, the conveying member may include a tube. Preferably, a sensor attached to the tube is disposed on an apparatus released downhole. The tube may transmit information using hydraulic means supplied through the tube. Additionally, a cable may be used to convey the apparatus downhole. The length of the cable dispensed may be used to determine the location the apparatus downhole. 
   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.