High-speed transmission of annulus pressure-while-drilling by data compression
A method for transmitting data from a downhole tool to a surface location includes running a downhole tool into a wellbore. The downhole tool includes a pressure sensor. An annulus pressure in the wellbore is measured at a first time, using the pressure sensor, to produce a first pressure measurement. The first pressure measurement is compressed to produce a reference sample. The reference sample is transmitted to the surface location. The annulus pressure in the wellbore is measured at a second time, using the pressure sensor, to produce a second pressure measurement. A difference between the first pressure measurement and the second pressure measurement is determined to produce a first delta pressure measurement. The first delta pressure measurement is compressed to produce a first compressed delta pressure measurement. The first compressed delta pressure measurement is transmitted to the surface location.
1. A method for transmitting data from a downhole tool to a surface location, comprising:
running a downhole tool into a wellbore, wherein the downhole tool comprises a pressure sensor;
measuring an annulus pressure in the wellbore at a first time, using the pressure sensor, to produce a first pressure measurement;
compressing the first pressure measurement to produce a reference sample;
transmitting the reference sample to the surface location;
measuring the annulus pressure in the wellbore at a second time, using the pressure sensor, to produce a second pressure measurement;
determining a difference between the first pressure measurement and the second pressure measurement to produce a first delta pressure measurement;
compressing the first delta pressure measurement to produce a first compressed delta pressure measurement; and
transmitting the first compressed delta pressure measurement to the surface location.
2. The method of claim 1 , further comprising:
measuring the annulus pressure in the wellbore at a third time, using the pressure sensor, to produce a third pressure measurement;
determining a difference between the first pressure measurement and the third pressure measurement to produce a second delta pressure measurement;
compressing the second delta pressure measurement to produce a second compressed delta pressure measurement; and
transmitting the second compressed delta pressure measurement to the surface location.
3. The method of claim 1 , further comprising:
demodulating the reference sample and the first compressed delta pressure measurement at the surface location; and
decompressing the reference sample and the first compressed delta pressure measurement at the surface location.
4. The method of claim 1 , wherein the reference sample and the first compressed delta pressure measurement are transmitted using mud pulses.
5. The method of claim 1 , wherein the reference sample is represented using more bits than the first compressed delta pressure measurement.
6. The method of claim 1 , wherein compressing the first pressure measurement to produce the reference sample comprises confining the first pressure measurement to a predetermined data range.
7. The method of claim 6 , wherein confining the first pressure measurement to the predetermined data range comprises truncating a portion of the first pressure measurement that is outside the predetermined data range.
8. The method of claim 6 , wherein compressing the first pressure measurement to produce the reference sample further comprises quantizing the first pressure measurement.
9. The method of claim 8 , wherein quantizing the first pressure measurement comprises:
selecting a step size corresponding to a predetermined pressure range; and
producing an integer having a predetermined number of bits.
10. The method of claim 1 , further comprising varying a weight of a drilling mud that is pumped into the wellbore from the surface location or varying a rate that the drilling mud is pumped into the wellbore from the surface location in response to transmitting the first compressed delta pressure measurement to the surface location.