Acoustic sensing system for downhole seismic applications utilizing an array of fiber optic sensors

A hydrophone for sensing acoustic signals in a harsh environment, comprising:

• an input optical fiber that receives an input optical signal from an optical source;
• an input hydrophone coupler that couples the input optical signal to a reference fiber and to a sensing fiber;
• a reference mandrel onto which the reference fiber is wound, the reference mandrel being substantially insensitive to the acoustic signals to reduce the effect of the acoustic signals on the reference fiber;
• at least one sensing mandrel onto which the sensing fiber is wound, the sensing mandrel being responsive to the acoustic signals and coupling the acoustic signals to the sensing fiber by causing the sensing fiber to change in length in response to the acoustic signals, the sensing mandrel comprising a material selected to withstand a pressure of at least 8,000 pounds per square inch and a temperature of at least 110 degrees Celsius;
• an output hydrophone coupler that receives an optical signal from the reference fiber and receives an optical signal from the sensing fiber, the output hydrophone coupler producing an output signal to the output optical fiber;
• and
• a protective layer around the reference mandrel and the sensing mandrel to protect the reference mandrel and the sensing mandrel from a corrosive environment.

A hydrophone for sensing acoustic signals, comprising:

• an input optical fiber that receives an input optical signal from an optical source;
• an input hydrophone coupler that couples the input optical signal to a reference fiber and to a sensing fiber;
• a reference mandrel onto which the reference fiber is wound, the reference mandrel being substantially insensitive to the acoustic signals to reduce the effect of the acoustic signals on the reference fiber;
• at least one sensing mandrel onto which the sensing fiber is wound, the sensing mandrel being responsive to the acoustic signals and coupling the acoustic signals to the sensing fiber by causing the sensing fiber to change in length in response to the acoustic signals;
• and
• an output hydrophone coupler that receives an optical signal from the reference fiber and receives an optical signal from the sensing fiber, the output hydrophone coupler producing an output signal to the output optical fiber;
• wherein the reference mandrel and the sensing mandrel are arranged in an end-to-end configuration to reduce the profile of the hydrophone and a flexible interlink is located between the reference mandrel and the sensing mandrel, said flexible interlink being designed to receive the sensing fiber and to protect the sensing fiber from damage.

A hydrophone for sensing acoustic signals, comprising:

• an input optical fiber that receives an input optical signal from an optical source;
• an input hydrophone coupler that couples the input optical signal to a reference fiber and to a sensing fiber;
• a reference mandrel onto which the reference fiber is wound, the reference mandrel being substantially insensitive to the acoustic signals to reduce the effect of the acoustic signals on the reference fiber;
• at least one sensing mandrel onto which the sensing fiber is wound, the sensing mandrel being responsive to the acoustic signals and coupling the acoustic signals to the sensing fiber by causing the sensing fiber to change in length in response to the acoustic signals;
• an output hydrophone coupler that receives an optical signal from the reference fiber and receives an optical signal from the sensing fiber, the output hydrophone coupler producing an output signal to the output optical fiber;
• and
• a flexible interlink for receiving one of the fibers, the interlink joining the reference mandrel and the sensing mandrel.

A hydrophone for sensing acoustic signals in a harsh environment, comprising:

• an input optical fiber that receives an input optical signal from an optical source;
• an input hydrophone coupler that couples the input optical signal to a reference fiber and to a sensing fiber;
• a reference mandrel onto which the reference fiber is wound, the reference mandrel being substantially insensitive to the acoustic signals to reduce the effect of the acoustic signals on the reference fiber;
• at least one sensing mandrel onto which the sensing fiber is wound, the sensing mandrel being responsive to the acoustic signals and coupling the acoustic signals to the sensing fiber by causing the sensing fiber to change in length in response to the acoustic signals;
• and
• an output hydrophone coupler that receives an optical signal from the reference fiber and receives an optical signal from the sensing fiber, the output hydrophone coupler producing an output signal to the output optical fiber;
• wherein at least one of the mandrels has at least one convex-shaped endcap that withstands a pressure of at least 4,000 pounds per square inch.

A hydrophone for sensing acoustic signals in a harsh environment, comprising:

• an input optical fiber that receives an input optical signal from an optical source;
• an input hydrophone coupler that couples the input optical signal to a reference fiber and to a sensing fiber;
• a reference mandrel onto which the reference fiber is wound, the reference mandrel being substantially insensitive to the acoustic signals to reduce the effect of the acoustic signals on the reference fiber;
• at least one sensing mandrel onto which the sensing fiber is wound, the sensing mandrel being responsive to the acoustic signals and coupling the acoustic signals to the sensing fiber by causing the sensing fiber to change in length in response to the acoustic signals;
• and
• an output hydrophone coupler that receives an optical signal from the reference fiber and receives an optical signal from the sensing fiber, the output hydrophone coupler producing an output signal to the output optical fiber;
• wherein the hydrophone comprises a material selected to withstand a pressure of at least 5,000 pounds per square inch and a temperature of at least 180 degrees Celsius.

A hydrophone for sensing acoustic signals in a harsh environment, comprising:

• an optical fiber that receives an input optical signal from an optical source;
• at least one sensing mandrel onto which a sensing fiber is wound, the sensing mandrel being responsive to the acoustic signals and coupling the acoustic signals to the sensing fiber by causing the sensing fiber to change in length in response to the acoustic signals, the sensing mandrel comprising a material selected to withstand a pressure of at least 5,000 pounds per square inch and a temperature of at least 130 degrees Celsius;
• a hydrophone coupler that couples the input optical signal to the sensing fiber and that receives an optical signal from the sensing fiber, the hydrophone coupler producing an output signal to the output optical fiber;
• and
• a protective layer around the sensing mandrel to protect the sensing mandrel from a corrosive environment.