Method of and apparatus for detecting an influx into a well while drilling
First Claim
1. In a borehole drilling system including a drill string terminated by a drill bit with said drill string defining an annulus between the outer diameter of said drill string and said borehole, said system including a drilling fluid pump for pumping drilling fluid downwardly through a standpipe and said drill string and upwardly through said annulus to the surface, apparatus for detecting fluid influx into the borehole comprising:
- a) pressure detecting means near the surface of said system for generating an annulus pressure signal as a function of time which is representative of pressure oscillation of said drilling fluid in said annulus caused by steady state oscillations of said drilling fluid pump;
b) pressure detecting means near the surface of said system for generating a standpipe pressure signal as a function of time which is representative of pressure oscillation of said drilling fluid in said standpipe caused by said steady state oscillation of said drilling fluid pump;
c) means for determining phase difference as a function of time between said annulus pressure signal and said standpipe pressure at a particular oscillation frequency of said steady state oscillation of said drilling fluid caused by said drilling fluid pump;
d) means for periodically determining total transit time of a drilling fluid pressure wave along a path defined from said standpipe downwardly along said drill string and upwardly along said annulus to the surface as a function of said phase difference and said particular oscillation frequency;
e) means for determining time rate of change of said total transit time, andf) means for comparing said time rate of change of said total transit time with a predetermined limit to generate a kick alarm signal if such limit is exceeded.
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Accused Products
Abstract
Gas influx into a wellbore, which is commonly referred to as a "kick", is detected during active drilling of the borehole. In a preferred embodiment of the invention a determination of mud pump noise round trip transit time T by evaluating a function T=(n-Φ/2π)f where Φ is the phase between standpipe and annulus signals and f is the frequency of a drill fluid oscillation caused by a mud pump and n is an integer which is incremented or decremented until the rate of change of T with respect to frequency is zero. An alarm signal is generated when the rate of change of T with respect to time exceeds a predetermined threshold. In another embodiment of the invention a determination of the Doppler frequency shift of a mud pump signal expressed as a ratio signal, Δf/f0 where Δf is the change in frequency measured at the annulus from the frequency f0 of the mud pump signal measured at the standpipe. The ratio is compared with a threshold signal to determine whether or not gas influx has entered the annulus.
64 Citations
6 Claims
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1. In a borehole drilling system including a drill string terminated by a drill bit with said drill string defining an annulus between the outer diameter of said drill string and said borehole, said system including a drilling fluid pump for pumping drilling fluid downwardly through a standpipe and said drill string and upwardly through said annulus to the surface, apparatus for detecting fluid influx into the borehole comprising:
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a) pressure detecting means near the surface of said system for generating an annulus pressure signal as a function of time which is representative of pressure oscillation of said drilling fluid in said annulus caused by steady state oscillations of said drilling fluid pump; b) pressure detecting means near the surface of said system for generating a standpipe pressure signal as a function of time which is representative of pressure oscillation of said drilling fluid in said standpipe caused by said steady state oscillation of said drilling fluid pump; c) means for determining phase difference as a function of time between said annulus pressure signal and said standpipe pressure at a particular oscillation frequency of said steady state oscillation of said drilling fluid caused by said drilling fluid pump; d) means for periodically determining total transit time of a drilling fluid pressure wave along a path defined from said standpipe downwardly along said drill string and upwardly along said annulus to the surface as a function of said phase difference and said particular oscillation frequency; e) means for determining time rate of change of said total transit time, and f) means for comparing said time rate of change of said total transit time with a predetermined limit to generate a kick alarm signal if such limit is exceeded. - View Dependent Claims (2)
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3. In a borehole drilling system including a drill string terminated by a drill bit with said drill string defining an annulus between the outer diameter of said drill string and said borehole, said system including a drilling fluid pump for pumping drilling fluid downwardly through a standpipe and said drill string and upwardly through said annulus to the surface, a method for detecting fluid influx into the borehole comprising the steps of:
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a) detecting near the surface of said system an annulus pressure signal as a function of time which is representative of pressure oscillation of said drilling fluid in said annulus caused by steady state oscillations of said drilling fluid pump; b) detecting means near the surface of said system a standpipe pressure signal as a function of time which is representative of pressure oscillation of said drilling fluid in said standpipe caused by said steady state oscillations by said drilling fluid pump; c) determining the phase difference as a function of time between said annulus pressure signal and said standpipe pressure signal at a particular oscillation frequency of said drilling fluid caused by said steady state oscillation of said drilling fluid pump; d) determining total transit time as a function of time of a drilling fluid pressure wave along a path defined from said standpipe downwardly along said drill string and upwardly along said annulus to the surface as a function of said phase difference and said particular oscillation frequency; e) determining time rate of change of said total transit time, and f) comparing said time rate of change of said total transit time with a predetermined limit to generate a kick alarm signal if such limit is exceeded. - View Dependent Claims (4)
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5. In a borehole drilling system including a drill string terminated by a drill bit with said drill string defining an annulus between the outer diameter of said drill string and said borehole, said system including a drilling fluid pump for pumping drilling fluid downwardly through a standpipe and said drill string and upwardly through said annulus to the surface, a method for detecting fluid influx into the borehole comprising the steps of:
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a) detecting near the surface of said system an annulus pressure signal as a function of time which is representative of pressure oscillation of said drilling fluid pump; b) detecting near the surface of said system a standpipe pressure signal as a function of time which is representative of pressure oscillation of said drilling fluid in said standpipe caused by said drilling fluid pump; c) determining the power spectrum S(ω
) of said standpipe pressure signal;d) determining the power spectrum A(ω
) of said annuls pressure signal;e) determining a characteristic frequency fo of said S(ω
) spectrum;f) determining a characteristic frequency f0 '"'"' of said A(ω
) spectrum;g) determining the difference in frequency Delta f between said characteristic frequency f0 '"'"' of said A(ω
) spectrum and said characteristic frequency f0 of said S(ω
) spectrum;h) comparing a signal proportional to the ratio of Delta f/f0 with a predetermined threshold signal; and i) generating an alarm signal if Delta f/f0 exceeds said threshold signal. - View Dependent Claims (6)
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Specification