Modulation scheme for high speed mud pulse telemetry with reduced power requirements

Abstract

A method for transmitting data from a downhole location to a location at the surface of the earth includes: receiving data using a modulator disposed at the downhole location on a drill tubular in a borehole penetrating the earth and modulating the data using offset quadrature phase shift keying (OQPSK) and smooth transitions between phase shifts to produce a series of two-bit symbols having smooth transitions in transition intervals between phase shifts of both in-phase and quadrature-phase components of the OQPSK modulated data. The method further includes transmitting the series of two-bit symbols as an acoustic signal in drilling fluid disposed in the borehole using a mud-pulser, receiving the acoustic signal using a receiver disposed uphole from the downhole location; and demodulating the acoustic signal using a demodulator coupled to the receiver to provide demodulated data.

What is claimed is: 
     
         1 . A method for transmitting data from a downhole location to a location at the surface of the earth, the method comprising:
 receiving data using a modulator disposed at the downhole location on a drill tubular in a borehole penetrating the earth;   modulating, using the modulator, the data using offset quadrature phase shift keying (OQPSK) and smooth transitions between phase shifts to produce a series of two-bit symbols having smooth transitions in transition intervals between phase shifts of both in-phase and quadrature-phase components of the OQPSK modulated data;   transmitting the series of two-bit symbols as an acoustic signal in drilling fluid disposed in the borehole using a mud-pulser;   receiving the acoustic signal using a receiver disposed uphole from the downhole location; and   demodulating the acoustic signal using a demodulator coupled to the receiver to provide demodulated data.   
     
     
         2 . The method according to  claim 1 , wherein one or more of the smooth transitions is characterized by a continuous first derivative of amplitude with respect to time. 
     
     
         3 . The method according to  claim 1 , wherein a smooth transition comprises a change of instantaneous frequency of the acoustic signal. 
     
     
         4 . The method according to  claim 1 , wherein each of the transition intervals are of the same duration. 
     
     
         5 . The method according to  claim 1 , wherein at least two transition intervals have different time durations. 
     
     
         6 . The method according to  claim 1 , further comprising applying forward error correction encoding before modulating the data. 
     
     
         7 . The method according to  claim 6 , wherein the forward error correction encoding comprises turbo coding. 
     
     
         8 . The method according to  claim 6 , further comprising applying forward error correction decoding to the demodulated data uphole of the downhole location. 
     
     
         9 . The method according to  claim 1 , further comprising storing the demodulated data in memory or a storage medium. 
     
     
         10 . The method according to  claim 1 , further comprising sensing a downhole property using a downhole sensor and transmitting sensed data to the modulator. 
     
     
         11 . The method according to  claim 10 , wherein the downhole sensor is configured to sense at least one of temperature, pressure, radiation, optical reflectivity, optical transmissivity, acoustic energy, electrical current, electrical voltage and electromagnetic waves. 
     
     
         12 . The method according to  claim 10 , further comprising generating a two-dimensional image representation of the sensed data before transmitting the sensed data to the modulator. 
     
     
         13 . The method according to  claim 10 , further comprising extracting a sample of formation fluid using an extendable probe, sensing a property of the formation fluid using the downhole sensor to provide sensed formation fluid data, and transmitting the sensed formation fluid data to the modulator. 
     
     
         14 . An apparatus for transmitting data from a downhole location on a drill tubular to a location at the surface of the earth, the apparatus comprising:
 a drill tubular disposed in a borehole penetrating the earth and configured to convey drilling fluid;   a modulator configured to receive data from the downhole location and to modulate the data using offset quadrature phase shift keying (OQPSK) and smooth transitions between phase shifts to produce a series of two-bit symbols having a smooth transitions in a transition intervals between phase shifts of both in-phase and quadrature-phase components of the OQPSK modulated data;   a mud-pulser configured to transmit the series of two-bit symbols as an acoustic signal in drilling fluid disposed in the borehole;   a receiver disposed uphole from the downhole location and configured to receive the acoustic signal; and   a demodulator coupled to the receiver and configured to demodulate the acoustic signal received by the receiver to provide demodulated data.   
     
     
         15 . The apparatus according to  claim 14 , wherein the mud-pulser comprises a plunger configured to interface with the drilling fluid to transmit the acoustic signal. 
     
     
         16 . The apparatus according to  claim 14 , wherein the mud-pulser comprises a rotating or oscillating disc configured to interface with the drilling fluid to transmit the acoustic signal. 
     
     
         17 . The apparatus according to  claim 14 , further comprising a signal receiving device comprising one of a display or printer configured to display the demodulated data to a user. 
     
     
         18 . The apparatus according to  claim 14 , further comprising a signal receiving device comprising one of a storage medium or memory configured to store the demodulated data. 
     
     
         19 . The apparatus according to  claim 14 , further comprising an encoder configured to apply a forward error correcting code before the data is modulated by the modulator. 
     
     
         20 . The apparatus according to  claim 14 , further comprising a sensor disposed on the drill tubular and configured to sense a downhole property and transmit sensed property data to the modulator. 
     
     
         21 . The apparatus according to  claim 20 , wherein the sensed property comprises at least one of temperature, pressure, radiation, optical reflectivity, optical transmissivity, acoustic energy, electrical current, electrical voltage and electromagnetic waves. 
     
     
         22 . The apparatus according to  claim 21 , further comprising a formation fluid tester configured to extract and analyze a sample of formation fluid and to transmit formation fluid property data to the modulator.