Early Kick Detection in an Oil and Gas Well

Abstract

An acoustic transducer on a downhole tool sends an acoustic wave through a sensor plate in contact with drilling fluid. Vibrations of the sensor plate are indicative of the impedance of the borehole plate that may be associated with gas influx. A processor analyzes the vibrations and uses an estimated Q of the vibrations to determine gas influx. It is emphasized that this abstract is provided to comply with the rules requiring an abstract which will allow a searcher or other reader to quickly ascertain the subject matter of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. 37 CFR 1.72(b).

1 . An apparatus for detection of gas influx in a borehole fluid during drilling operations, the apparatus comprising:
 (a) a bottomhole assembly (BHA) configured to be conveyed in the borehole;   (b) at least one transducer assembly on the BHA including:
 (A) a sensor plate in contact with the borehole fluid, and 
 (B) a cavity disposed between a transducer and the sensor plate, the transducer configured to generate acoustic vibrations in the sensor plate; and 
   (c) a processor configured:
 (C) to estimate from a signal indicative of the acoustic vibrations an impedance of the borehole fluid, and 
 (D) to use the estimated fluid impedance to provide an indication of the gas influx. 
   
   
   
       2 . The apparatus of  claim 1  wherein the cavity includes a fluid having a known density and compressional velocity. 
   
   
       3 . The apparatus of  claim 1  wherein the signal indicative of the acoustic vibrations is provided by at least one of: (i) the transducer, and (ii) a receiver. 
   
   
       4 . The apparatus of  claim 1  wherein the sensor plate has an acoustic impedance selected to match an expected impedance of the borehole fluid. 
   
   
       5 . The apparatus of  claim 1  wherein the processor is configured to estimate the impedance of the borehole fluid by determining a quality factor (Q) of the acoustic vibrations. 
   
   
       6 . The apparatus of  claim 1  wherein the processor is configured to provide the indication of gas influx using a table lookup. 
   
   
       7 . The apparatus of  claim 1  further comprising a device configured to measure a P-wave velocity in the borehole fluid and wherein the processor is configured to provide the indication of gas influx using a density derived from the estimated fluid impedance and the measured P-wave velocity. 
   
   
       8 . The apparatus of  claim 1  wherein the sensor plate is made of a material selected from: (i) a polyamide, (ii) a polymethylpentene, (iii) pyrolitic graphite, (iv) titanium, and (v) aluminum. 
   
   
       9 . The apparatus of  claim 1  further comprising an absorptive backing on a back side of the transducer having an impedance substantially equal to that of the transducer. 
   
   
       10 . The apparatus of  claim 1  wherein the at least one transducer assembly further comprises a plurality of transducer assemblies in electrical communication. 
   
   
       11 . The apparatus of  claim 1  wherein the transducer is configured to provide the indication of gas influx by providing an alarm signal when the estimated fluid impedance changes by more than a specified threshold value relative to the estimated fluid impedance in an earlier interval. 
   
   
       12 . A method of detecting gas influx in a borehole fluid during drilling operations, the method comprising:
 (a) conveying a bottomhole assembly (BHA) including at least one transducer assembly into the borehole;   (b) using a transducer on a first side of a cavity in the transducer assembly to generate acoustic vibrations in a sensor plate on a second side of the cavity, the sensor plate being in contact with the borehole fluid;   (c) estimating from a signal indicative of the acoustic vibrations an impedance of the borehole fluid, and (d) using the estimated fluid impedance to provide an indication of the gas influx.   
   
   
       13 . The method of  claim 12  further comprising having a fluid having with a known density and a known compressional velocity in the cavity. 
   
   
       14 . The method of  claim 12  further comprising providing the signal indicative of the acoustic vibrations using at least one of: (i) the transducer, and (ii) a receiver. 
   
   
       15 . The method of  claim 12  further comprising selecting a material for the sensor plate that has an acoustic impedance which matches an expected impedance of the borehole fluid. 
   
   
       16 . The method of  claim 12  wherein estimating the impedance of the borehole fluid further comprises determining a quality factor (Q) of the acoustic vibrations. 
   
   
       17 . The method of  claim 12  wherein the providing the indication of gas influx further comprises using a table lookup. 
   
   
       18 . The method of  claim 12  further comprising measuring a P-wave velocity in the borehole fluid and wherein the providing the indication of gas influx further comprises using a density derived from the estimated fluid impedance and the measured P-wave velocity. 
   
   
       19 . The method of  claim 12  further comprising selecting a material for the sensor plate from: (i) a polyamide, (ii) a polymethylpentene, (iii) pyrolitic graphite, (iv) titanium, and (v) aluminum. 
   
   
       20 . The method of  claim 12  further comprising providing an absorptive backing on a back side of the transducer to reduce reflections therefrom. 
   
   
       21 . The method of  claim 12  further comprising using, for the at least one transducer assembly, a plurality of transducer assemblies in electrical communication. 
   
   
       22 . The method of  claim 12  wherein providing the indication of gas influx further comprises providing an alarm signal when the estimated fluid impedance changes by more than a specified threshold value relative to the estimated fluid impedance in an earlier interval. 
   
   
       23 . A computer readable medium for use with an apparatus for detection of gas influx in a borehole fluid during drilling operations, the apparatus comprising:
 (a) a bottomhole assembly (BHA) configured to be conveyed in the borehole;   (b) at least one transducer assembly on the BHA including:
 (A) a sensor plate in contact with the borehole fluid, and 
 (B) a cavity disposed between a transducer and the sensor plate, the transducer configured to generate acoustic vibrations in the sensor plate; 
   the medium comprising instructions that enable a processor to:   (c) estimate from a signal indicative of the acoustic vibrations an impedance of the borehole fluid, and   (d) use the estimated fluid impedance to provide an indication of the gas influx.   
   
   
       24 . The computer readable medium of  claim 23  further comprising at least one of:
 (i) a ROM, (ii) an EPROM, (iii) an EAROM, (iv) a flash memory, and (v) an optical disk.