Method of and apparatus for detecting an influx into a well while drilling

• US 5,275,040 A
• Filed: 06/11/1991
• Issued: 01/04/1994
• Est. Priority Date: 06/29/1990
• Status: Expired due to Term

• Current Assignee: Anadrill Incorporated
• Original Assignee: Anadrill Incorporated
• Inventors: Codazzi, Daniel
• Primary Examiner(s): Williams, Hezron E.
• Assistant Examiner(s): DOMBROSKE, GEORGE M
• Application Number:
  US07/714,103
• Time in Patent Office: 938 Days
• Field of Search: 73/151, 73/153, 73/155, 73/19.09, 73/579, 73/597, 73/602, 166/250, 175/48, 367/81, 367/83, 367/34
• US Class Current: 73/152.22
• CPC Class Codes: E21B 21/08 Controlling or monitoring pressure or flow of drilling fluid, e.g. automatic filling of boreholes, automatic control of bottom pressure valve arrangements therefor E21B21/10
• CPC Class Codes: E21B 47/107 using acoustic means
• CPC Class Codes: E21B 49/005 Testing the nature of borehole walls or the formation by using drilling mud or cutting data

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.

Claims

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, 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.

2. The apparatus of claim 1 wherein said means for determining said total transmit time T at any time t includes

means for evaluating the function

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:

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.

4. The method of claim 3 wherein said step for determining the transmit time T at any time t includes the step of evaluating the function:

space="preserve" listing-type="equation">T=(n-Φ

/2π

)/f

where

Φ

represents said phase difference,

f represents said particular oscillation frequency, and

n is an integer which is incremented or decremented until the rate of change of T with respect to frequency is approximately zero.

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:

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 f_o 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.

6. The method of claim 5 wherein

said characteristic frequency f_o of said S(ω

) spectrum is that frequency in the spectrum corresponding to the position of the maximum amplitude of said S(ω

) spectrum, and

said characteristic frequency f₀ '"'"' of said A(ω

) spectrum is that frequency in the spectrum corresponding to the position of the maximum amplitude of said A(ω

) spectrum.