Patent Publication Number: US-9422801-B2

Title: Modulated opto-acoustic converter

Description:
TECHNICAL FIELD 
     The present disclosure relates generally to optically powered and controlled systems for use in a wellbore and, more particularly (although not necessarily exclusively), to downhole actuator devices for producing acoustic signals and being controlled by optical signals from surface devices. 
     BACKGROUND 
     Hydrocarbons can be produced from wellbores drilled from the surface through a variety of subsurface formations. A wellbore may be substantially vertical or may be deviated. Conditions and other parameters in the wellbore can be sensed using powered devices downhole. For example, many parameters, such as pressure, temperature, fluid density, and fluid flow rate, may be sensed downhole and their values reported to the surface. Powering these devices electrically can be challenging in view of, among other things, temperature limitations of complex electronic sensors. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional schematic view of a wellbore that includes an opto-acoustic subsystem according to one aspect. 
         FIG. 2  is a cross-sectional schematic view of a wellbore that includes an opto-acoustic subsystem according to another aspect. 
         FIG. 3  is a schematic view of an opto-acoustic subsystem according to one aspect. 
         FIG. 4  is a schematic view of an actuator device of an opto-acoustic subsystem according to one aspect. 
         FIG. 5  is a schematic view of an actuator device of an opto-acoustic subsystem according to another aspect. 
     
    
    
     DETAILED DESCRIPTION 
     Certain aspects and features relate to a controlled or modulated acoustic source that is downhole and that is optically powered by optical signals from the surface of a wellbore. Acoustical energy from the acoustic source can be detected and analyzed for determining downhole parameters or conditions. For example, the acoustic source may be in fluid or attached to a pipe or other tubular. Parameters of the fluid or pipe movement can be determined using a modulated acoustical signal from the acoustic source. 
     In some aspects, an acoustic source is a downhole actuator that can respond to a modulated optical signal received by optical fiber from an optical transmitter at the surface of the wellbore by outputting a modulated acoustical signal. For example, the downhole actuator can include a photodiode and a piezoelectric actuator. The photodiode can detect the modulated optical signal and transform it into a modulated electrical signal. The piezoelectric actuator can respond to the modulated electrical signal by outputting a modulated acoustical signal that can travel through the environment in the wellbore and be detected by a sensor in the wellbore. The sensed signal can be analyzed to determine downhole conditions or parameters. 
     An acoustic source according to some aspects can provide a modulated acoustical signal without requiring externally applied electric power or copper or other electrical conductors to be run from an electrical power source to the acoustic source. In some aspects, the acoustic source can be used as a component for optical downhole flow measurement, data transmission, and monitoring of the state of cure of cement, for example. 
     These illustrative aspects and examples are given to introduce the reader to the general subject matter discussed here and are not intended to limit the scope of the disclosed concepts. The following sections describe various additional features and examples with reference to the drawings in which like numerals indicate like elements, and directional descriptions are used to describe the illustrative aspects but, like the illustrative aspects, should not be used to limit the present disclosure. 
       FIG. 1  depicts an example of a wellbore system  10  that includes an acoustic source according to one aspect. The system  10  includes a wellbore  12  that penetrates a subterranean formation  14  for the purpose of recovering hydrocarbons, storing hydrocarbons, disposing of carbon dioxide, or pumping fluid into the well for stimulation (e.g., fracturing, acidizing, etc.) of producing zones or for storage or disposal. The wellbore  12  may be drilled into the subterranean formation  14  using any suitable drilling technique. While shown as extending vertically from the surface  16  in  FIG. 1 , in other examples the wellbore  12  may be deviated, horizontal, or curved over at least some portions of the wellbore  12 . The wellbore  12  may be cased, open hole, contain tubing, and may include a hole in the ground having a variety of shapes or geometries. 
     The wellbore system  10  includes a casing  18  extending through the wellbore  12  in the subterranean formation  14 . A tubular  20  extends from the surface  16  in an inner area defined by the casing  18 . The tubular  20  may be production tubing through which hydrocarbons or other fluid can enter and be produced. In other aspects, the tubular  20  is another type of tubing. 
     Some items that may be included in the wellbore system  10  have been omitted for simplification. For example, the wellbore system  10  may include a servicing rig, such as a drilling rig, a completion rig, a workover rig or other mast structure, or a combination of these. In some aspects, the servicing rig may include a derrick with a rig floor. Piers extending downwards to a seabed in some offshore implementations may support the servicing rig. Alternatively, the servicing rig may be supported by columns sitting on hulls or pontoons (or both) that are ballasted below the water surface, which may be referred to as a semi-submersible platform, rig, or drillship. In an off-shore location, a casing or riser may extend from the servicing rig to the sea floor to exclude sea water and contain drilling fluid returns. Other mechanical mechanisms that are not shown may control the run-in and withdrawal of a workstring in the wellbore  12 . Examples of these other mechanical mechanisms include a draw works coupled to a hoisting apparatus, a slickline unit or a wireline unit including a winching apparatus, another servicing vehicle, and a coiled tubing unit. 
     The wellbore system  10  includes an opto-acoustic subsystem that can output a modulated acoustical signal in the wellbore  12 . The opto-acoustic subsystem includes an optical transmitter  22  at the surface, an actuator device  24  in the wellbore  12 , and a cable  26  between the optical transmitter  22  and the actuator device  24 . The cable  26  can include one or more optical fibers. In other aspects, the cable  26  is one or more optical fibers. The cable  26  may also include other types of conductors, such as electrical conductors. The cable  26  is located exterior to the tubular  20 . The optical fibers may be single mode or multi-mode fiber, or multiple optical fibers can be run in parallel to supply higher optical power than may be supplied by a single optical fiber. The optical transmitter  22  can transmit a modulated optical signal through the optical fibers in the cable  26  to the actuator device  24 . The actuator device  24  can transform the modulated optical signal into a modulated electrical signal, and then output a modulated acoustical signal into an environment of the wellbore  12  using the modulated electrical signal. 
     The opto-acoustic subsystem can also include a receiver  30  and a line  32 . The line  32  may be exterior to the tubular  20 . The line  32  can include one or more sensors (not shown) that can detect the modulated acoustical signal after the modulated acoustical signal has traveled through the environment of the wellbore  12 . The detected acoustical signal can be provided to the receiver  30  by the line  32 . The receiver  30  can analyze the detected acoustical signal and determine a parameter or characteristics of the environment of the wellbore  12 . For example, the receiver  30  may detect a fluid flow rate or the density of a fluid flowing in the wellbore  12 , and the information may be used to control production in a zone of the wellbore  12 . The line  32  may be any type of suitable signal conveyance. Examples of the line  32  include an optical fiber, an electrical cable, or both. The line  32  itself may detect modulated acoustical signals or it can be coupled to devices in the wellbore  12  that can detect modulated acoustical signals. The devices may convert the detected modulated acoustical signals to electrical signals, optical signals, or both, prior to transmitting signals to the receiver  30 . The line  32  may contain an optical fiber, which may be itself the detector by being connected to a suitable receiver. For example, the line  32  may be connected to a receiver  30  which is a distributed acoustic sensor (DAS) unit. 
     In other aspects, the opto-acoustic subsystem does not include the separate line  32 . The cable  26  can be used to convey signals from the wellbore  12  to components at the surface  16 . Furthermore, the optical transmitter  22  and the receiver  30  can be connected to the same cable, such as to the same or different optical fibers or conductors in the cable. 
     Optical fibers and actuator devices according to other aspects can be positioned in wellbore locations other than the exterior of tubing.  FIG. 2  depicts a wellbore system  100  according to another aspect. The wellbore system  100  is similar to the wellbore system  10  in  FIG. 1 . It includes a wellbore  112  through a subterranean formation  114 . Extending from the surface  116  of the wellbore  112  is a casing  118  and tubular  120  in an inner area defined by the casing  118 . The opto-acoustic subsystem includes an optical transmitter  122  at the surface  116  and an actuator device  124  in the wellbore  112 . The actuator device  124  is communicatively coupled to the optical transmitter  122  by a cable  126 . The cable  126  can include one or more optical fibers. 
     The cable  126  and the actuator device  124  are in an inner area defined by the tubular  120 . In other aspects, the cable  126  may be hung inside the tubular  120  or spooled win and out with a winch. The opto-acoustic subsystem also includes a receiver  130  at the surface  116  and a line  132  in an inner area defined by the tubular  120 . The actuator device  124  in the inner area defined by the tubular  120  can output modulated acoustical signals according to modulated electrical signals created in the actuator device  124  from modulated optical signals received from the optical transmitter via the cable  126 . The line  132  may include one or more sensors that can detect the modulated acoustical signals after the modulated acoustical signals have traveled through part of a wellbore environment. The detected signals can be conveyed to the receiver  130  for analysis. 
     Actuator devices according to various aspects may be located in any position in a wellbore. For example, an actuator device may be integrated in tubing. In some aspects, a wellbore includes multiple actuator devices located in multiple production zones separated by packers or other wellbore components. 
       FIG. 3  is a schematic diagram of the optical transmitter  22  and the actuator device  24  of  FIG. 1  according to one aspect. The optical transmitter  22  is at a surface of the wellbore. The actuator device  24  is a downhole device in the wellbore. 
     The optical transmitter  22  includes a laser  202 , a power source  204 , a modulator  206 , and a signal source  208 . The power source  204  can provide electrical power to the laser  202 . Light from the laser  202  can be modulated by the modulator  206  according to a modulation signal from the signal source  208 . For example, the signal source  208  can provide a continuous wave signal and the modulator  206  can vary the output of the optical transmitter  22  according to the continuous wave signal. In other aspects, the power from the power source  204  is modulated. Any type of optical modulation technique can be used. The output of the optical transmitter  22  can be a modulated optical signal that is coupled to the cable  26 . The laser output may be modulated by varying the electrical power supplied to the laser  202 . Modulation may include turning power to the laser  202  on and off with a predetermined frequency or in a particular pattern such that modulator  206  may be omitted. The actuator device  24  includes a photodiode  210  and a piezoelectric actuator  212 . The photodiode  210  can receive the modulated optical signal from the cable  26 , which may be or include an optical fiber, and generate a modulated electrical signal from the modulated optical signal. The modulated electrical signal can cause the piezoelectric actuator  212  to generate a modulated acoustical signal in response to the modulated electrical signal that has been generated in response to the modulated optical signal received from the optical transmitter  22 . For example, the piezoelectric actuator  212  can expand and contract based on a frequency of the modulated electrical signal to create a sound that is a modulated acoustical signal. The frequency of the modulated acoustical signal can correspond to the frequency of the modulated optical signal from the optical transmitter  22 . In some aspects, the photodiode  210  is a stack of photodiodes and the piezoelectric actuator  212  is a stack of piezoelectric actuators, in one component. Examples of the component include a 6 volt or 12 volt photovoltaic power converter (i.e., PPC-6 or PPC-12) from JDS Uniphase Corporation. 
     An actuator device according to some aspects may include additional components.  FIG. 4  schematically depicts an actuator device  324  according to another aspect. The actuator device  324 , which can be positioned downhole in a wellbore, includes a photodiode  310 , a piezoelectric actuator  312 , and a blocking diode  314 . Photodiodes can be damaged by reverse bias and piezoelectric actuators can generate a voltage when deformed. The blocking diode  314  can prevent voltages, such as voltage spikes, that may be generated by the piezoelectric actuator  312  from damaging the photodiode  310 . 
       FIG. 5  schematically depicts an actuator device  424  according to another aspect. The actuator device  424 , which can be positioned downhole in a wellbore, includes a photodiode  410 , a piezoelectric actuator  412 , a blocking diode  414 , and a resistor  416 . The resistor  416  is in series with the piezoelectric actuator  412 . The resistor  416  can limit the amount of current that is provided to the piezoelectric actuator. In some aspects, an actuator device can include the current-limiting resistor  416  without including the blocking diode  414 . 
     The foregoing description of certain aspects, including illustrated aspects, has been presented only for the purpose of illustration and description and is not intended to be exhaustive or to limit the disclosure to the precise forms disclosed. Numerous modifications, adaptations, and uses thereof will be apparent to those skilled in the art without departing from the scope of the disclosure.