US 4,208,906 AGranted

Mud gas ratio and mud flow velocity sensor

AssigneeInterstate Electronics Corporation

InventorLiona R. Roberts, Jr.

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Abstract

A remote sensor for the measurement of the amount of gas present in the drilling fluid or "mud" in an offshore well-drilling operation, for the purpose of giving prompt warning of geologic conditions conducive to the occurrence of a blow-out. An acoustic projector projects an acoustic wave of fixed wavelength through the mud returning upwardly from the borehole. The wave is received by a first array of acoustic receivers locked in a known phase relationship with the projector. Changes in the speed of sound due to changing relative amounts of mud and gas produce a shift in frequency of the acoustic wave which is proportional to the speed of sound in the mud/gas mixture. The change in frequency is electronically detected and scaled to yield the value of the speed of sound, from which the mud to gas mass ratio is calculated by means of a computer. A second array of acoustic receivers is arranged with the first array and the projector to form a phase-shift velocimeter which uses the value of the speed of sound obtained in conjunction with the mud/gas mass ratio measurement to calculate the velocity of the mud flow, which is used as a further indicator of potential blowout conditions.

Claims25

Dependent claims

A device for the sensing of drilling fluid properties in a well-drilling operation, comprising:

a riser through which said drilling fluid passes;
acoustic projector means mounted in said riser for projecting an acoustic wave through said drilling fluid, said acoustic wave having a predetermined wavelength .lambda. and a frequency f;
first acoustic receiver means mounted in said riser for receiving said acoustic wave, said first acoustic receiver means having a phase center which is spaced from said acoustic projector means by a distance equal to a predetermined number of said wavelengths .lambda.;
means for locking said first acoustic receiver means into a predetermined phase relationship with said acoustic projector means by changing said frequency f of said acoustic wave so as to maintain said predetermined number of said wavelengths .lambda. in said distance when the speed of sound c through said drilling fluid changes in response to a change in the amount of gas in said drilling fluid;
metering means electronically coupled to said phase-locking means for measuring said frequency f and producing a signal;
first electronic scaling means responsive to said signal from said metering means, for calculating said speed of sound c and producing a signal indicative of said speed of sound c;
computing means responsive to said signal from said first scaling means, for calculating a ratio .gamma. of drilling fluid mass to gas mass, using an equation ##EQU8## where c.sub.1 is the speed of sound in pure drilling fluid, c.sub.2 is the speed of sound in gas, .rho..sub.1 is the density of pure drilling fluid, and .rho..sub.2 is the density of gas;
second acoustic receiver means mounted in said riser for receiving said acoustic wave, said second receiver means having a phase shift with respect to said first receiver means due to a flow velocity of said drilling fluid, said phase shift being approximately proportional to said drilling fluid flow velocity and inversely proportional to said speed of sound c through said drilling fluid;
phase detector means electronically coupled to said first and second receiver means for measuring said phase shift and producing a signal;
and
second electronic scaling means, responsive to said signal from said phase detector means and said signal from said first scaling means, for calculating said drilling fluid flow velocity.

8 more elements

A device for measuring the amount of gas present in a drilling fluid used in drilling a well, comprising:

a riser through which said drilling fluid flows;
acoustic projector means mounted in said riser for projecting an acoustic wave through said drilling fluid, said acoustic wave having a pre-determined wavelength .lambda. with an associated frequency f, said wave being produced in response to an electrical input signal to said projector means;
acoustical receiver means mounted in said riser downstream from said projector means for receiving said acoustic wave and converting said wave into an electrical output signal, said receiver means having a phase center spaced from said projector means by a distance equal to a predetermined number of said wavelengths .lambda.;
means for locking said output signal into a predetermined phase relationship with said input signal by varying said input signal to change said frequency f of said projected acoustic wave so as to maintain said predetermined number of said wavelengths .lambda. in said distance when the speed of sound c through said drilling fluid changes in response to a change in the amount of gas in said drilling fluid;
metering means electronically coupled to said phase-locking means for measuring said frequency f and producing a signal;
electronic speed of sound scaling means responsive to said signal from said metering means for calculating said speed of sound c and producing a signal indicative of said speed of sound c;
and
computing means responsive to said signal from said scaling means, for calculating a ratio .gamma. of drilling fluid mass to gas mass, using an equation ##EQU9## where c.sub.1 is the speed of sound in pure drilling fluid, c.sub.2 is the speed of sound in gas, .rho..sub.1 is the density of pure drilling fluid, and .rho..sub.2 is the density of gas.

5 more elements

In a well-drilling operation in which drilling fluid is pumped up and out of a bore-hole through a riser, and in which said riser has mounted therein an acoustic projector, a first acoustic receiver downstream from said projector, and a second acoustic receiver upstream from said projector, a method of measuring the amount of gas mixed with said drilling fluid and the flow velocity of said drilling fluid, comprising the steps of:

projecting an acoustic wave through said drilling fluid and gas mixture from said projector in response to an electrical input signal to said projector, said wave having a wavelength .lambda., a predetermined number of which equals the distance from said projector to said first receiver, said wavelength .lambda. having an associated frequency f;
receiving said wave by said first and second receivers;
converting said wave into a first electrical output signal from said first receiver;
locking the phase of said first output signal into a predetermined phase relationship with the phase of said input signal by changing said frequency f of said acoustic wave so as to maintain said predetermined number of said wavelengths .lambda. in said distance when the speed of sound c in said drilling fluid changes in response to a change in the amount of gas in said drilling fluid and gas mixture;
measuring said frequency f which maintains said predetermined number of said wavelengths .lambda. in said distance;
calculating said speed of sound c by using a relationship f.lambda./c=1;
computing a ratio .gamma. of drilling fluid mass to gas mass in said mixture with an equation ##EQU11## where c.sub.1, c.sub.2, .rho..sub.1, and .rho..sub.2 are pre-determined values of the speed of sound in drilling fluid, speed of sound in gas, density of drilling fluid, and density of gas, respectively;
converting said acoustic wave into a second electrical output signal from said second receiver;
measuring the difference in phase between said first output signal and said second output signal, said difference in phase being approximately proportional to the flow velocity v of said drilling fluid through said riser and inversely proportional to said speed to cound c through said drilling fluid and gas mixture;
and
using the previously calculated value of the speed of sound c through the drilling fluid and gas mixture to calculate the value of said flow velocity v.

8 more elements

Dependencies are inferred from the claim text.