Ultrasonic measurement apparatus - Patent Review 5130950

What is claimed is:

1. Bore hole measurement apparatus comprising,

a tool adapted for connection in a drill string in said borehole through earth formations, said tool having a cylindrical body which when disposed in said borehole defines an annulus between a borehole wall and said body, said annulus having drilling fluid with entrained drilling cuttings disposed therein, the distance between said borehole wall and said cylindrical body defining standoff distance,

ultra-sonic transmitter means disposed in said cylindrical body for emitting an ultra-sonic transmitter pulse in said drilling fluid toward said borehole wall, said ultra-sonic pulse being reflected from said borehole wall as a borehole echo adn from said drilling cuttings toward said cylindrical body as a cuttings echo,

ultra-sonic transducer means disposed in said cylinrical body for generating a borehole echo signal representative of said borehole echo and a cuttings echo signal representative of said cuttings echo, and

logic means for distinguishing said borehole echo signal and its time delay from said cuttings echo signal, and means for generating a standoff signal representative of said standoff distance which is inversely related to said borehole echo time delay, wherein said ultra-sonic transmitter means and said ultra-sonic transducer means includes a single transceiver in which one sensor element serves first as a sonic transmitter and later as a sonic receiver,

wherein said transceiver is disposed in said cylindrical body so that said sensor element faces laterally outwardly from said cylindrical body whereby said ultra-sonic pulses and echoes travel essentially perpendicularly between said borehole wall and said cylindrical body in said annulus, and

wherein said logic means includes

circuit means for storing echoes where each echo is defined as the approximate maximum amplitude and associated delay time of each pulse received by said sensor element after said ultra-sonic transmitted pulse has terminated.

2. The apparatus of claim 1 wherein

said drill string is rotating in said borehole, said drilling fluid with entrained drilling cuttings disposed therein is flowing in said annulus, and

wherein said apparatus further includes processing means for generating said standoff signal a plurality of times each second for a predetermined time interval and for generating from said plurality of standoff signals an average standoff signal for said time interval.

3. The apparatus of claim 2 further including

memory means for storing a tool diameter signal representative of a diameter of said cylindrical body of said tool, and

processing means for generating a hole diameter signal representative of a diameter of said borehole by adding said diameter signal to a signal equal to twice said average standoff signal.

4. The apparatus of claim 3 further including

clock means for generating a time signal, and

memory means for storing said diameter signal as a function of said time signal.

5. The apparatus of claim 3 further including

communication means for transmitting said diameter signal to surface instrumentation.

6. The apparatus of claim 1 wherein said single transceiver includes a delay line between said sensor element and said annulus, and wherein a delay-line echo is received by said sensor element as a result of said ultra-sonic pulse being reflected from an interface of said delay- line and said drilling fluid in said annulus.

7. The apparatus of claim 1 wherein said logic means includes

delay line echo elimination logic means for eliminating stored echoes having a delay time shorter than a predetermined delay time after said transmitter pulse.

8. The apparatus of claim 1 wherein said logic means includes

noise rejection echo elimination logic means for eliminating stored echoes which are noise artifacts of previous echoes rather than reflection from said borehole or said cuttings.

9. The apparatus of claim 8 wherein said noise rejection echo elimination logic means includes

a minimum echo amplitude function stored as a function of delay time from said transmitter pulse,

comparison means for identifying stored echoes having amplitudes less than said minimum echo amplitude at its associated delay time, and

means for eliminating said identified echoes from said stored echoes.

10. The apparatus of claim 1 wherein said logic means includes

decreasing echo amplitude logic means for eliminating a stored echo, A.sub.M, T.sub.M, when the amplitude A.sub.M+1 of the next in time echo, A.sub.M+1, T.sub.M+1, is larger than A.sub.M.

11. The apparatus of claim 1 wherein said logic means includes,

time separation logic means for eliminating a stored echo, A.sub.M, T.sub.M, when the time separation T.sub.M -T.sub.M-1 between such stored echo and a preceding stored echo, A.sub.M-1, T.sub.M-1 is less than a predetermined minimum time T.sub.MIN.

12. The apparatus of claim 1 wherein said logic means includes,

noise rejection echo elimination logic means for eliminating stored echoes which result from noise rather than reflection from said borehole or said cutting, decreasing echo amplitude logic means for eliminating a stored echo, A.sub.M, T.sub.M, when the amplitude A.sub.M+1 of the next in time echo, A.sub.M+1, T.sub.M+1, is larger than A.sub.M,

time separation logic means for eliminating a stored echo, A.sub.M, T.sub.M, when the time separation T.sub.M -T.sub.M-1 between such stored echo and a preceding stored echo, A.sub.M-1, T.sub.M-1 is less than a predetermined minimum time T.sub.MIN,

temporary formation echo selection logic means for selecting a final echo, A.sub.N, T.sub.N of said remaining stored echoes as a temporary formation echo, and

double echo elimination logic means for identifying said temporary formation echo as a double echo if said delay time T.sub.N of said temporary formation echo is equal to approximately twice the delay time of a previous stored echo, and it such temporary formation echo is so identified, eliminating said final echo from said stored echoes, whereby a penultimate echo, A.sub.N-1, T.sub.N-1, becomes said temporary formation echo.

13. The apparatus of claim 12 wherein said logic means further includes

echo induced sensor noise elimination logic means for comparing said temporary formation echo A.sub.N, T.sub.N, with an immediately preceding echo A.sub.N-1, T.sub.N-1, to identify such echo A.sub.N, T.sub.N as a formation echo signal if A.sub.N >K*A.sub.N-1, where K is a predetermined minimum ratio of successive amplitudes of echoes above which an echo is unlikely to be an echo induced noise pulse.

14. The apparatus of claim 13 further including control means for generating and storing said formation echo signal A.sub.N, T.sub.N, a plurality of times each second for a predetermined time interval and for generating from said plurality of standoff signals an average standoff signal for said time interval.

15. The apparatus of claim 14 further including

memory means for storing a diameter signal representation of a diameter of said cylindrical body of said tool, and

processing means for generating a hole diameter signal representative of a diameter of said borehole by adding said diameter signal to a signal equal to twice said average standoff signal.

16. Borehole measurement apparatus comprising,

a tool adapted for connection in a drill string in said borehole through earth formations, said tool having a cylindrical body which when disposed in said borehole defines an annulus between said borehole wall and said body, said annulus having drilling fluid with entrained drilling cuttings disposed therein,

first and second ultra-sonic transmitter means disposed diametrically opposed from each other in said cylindrical body for emitting first and second ultra-sonic transmitter pulses in said drilling fluid toward said borehole wall, the distance between said borehole wall and said cylindrical body at said first ultra-sonic transmitter means defining a first standoff distance, the distance between said borehole wall and said cylindrical body at said second ultra-sonic transmitting means defining a second standoff distance, said ultra-sonic pulses being reflected from said borehole wall as first and second borehole echoes and from said drilling cuttings toward said cylindrical body as first and second cutting echoes,

first and second ultra-sonic transducer means disposed in said cylindrical body for generating first and second borehole echo signals representative of said first and second borehole echo signals representative of said first and second borehole echo amplitudes and time delays, and first and second cuttings echo signals representative of said cuttings echoes, and

logic means for distinguishing said first borehole echo signal and its time delay in the presence of said first cuttings echo signal and for generating a first standoff signal representative of said first standoff distance which is inversely proportional to said time delay of said first borehole echo signal from said emitting of said first ultra-sonic transmitter pulse and for distinguishing said second borehole echo signal and its time delay in the presence of said second cuttings echo signal and for generating a second standoff signal representative of said second standoff distance which is inversely proportional to said time delay of said second borehole echo signal from said launching of said second ultra-sonic transmitter pulse,

wherein said first and second transmitter means emit said first and second ultra-sonic transmitter pulses alternately in time with said logic means identifying said first borehole echo signal after said first ultra-sonic transmitter pulse is emitted and said logic means identifying said second borehole echo signal after said second ultra-sonic transmitter pulse is emitted, and

processing means for generating a first standoff signal proportional to said time delay of said first borehole echo signal and for generating a second standoff signal proportional to said time delay of said second borehole echo signal,

processing means for generating said first and second standoff signals a plurality of times each second for a predetermined time interval, and for generating from said plurality of standoff signals an average first standoff signal and an average second standoff signal for said time interval,

memory means for storing a diameter signal representative of a diameter of said cylindrical body of said tool, and

processing means for generating a hole diameter signal representative of a diameter of said borehole by adding said diameter signal to a said average first standoff signal and to said average second standoff signal.

17. The apparatus of claim 16 further including

clock means for generating a time signal, and memory means for storing said diameter signal as a function of said time signal.

18. The apparatus of claim 16 further including

communication means for transmitting said diameter signal to surface instrumentation.

19. The apparatus of claim 16 wherein said first ultra-sonic transmitter means and said first ultra-sonic transducer means and said second ultra-sonic transmitter means and said second ultra-sonic transducer means are each a single transceiver in which one sensor element serves as a sonic transmitter and as a sonic receiver.

20. Borehole measurement apparatus for identifying large gas bubble influxes into a borehole comprising

a tool adapted for connection in a drill string in said borehole through each formation, said tool having a cylindrical body defining an annulus between said borehole wall and said body, said annulus having drilling fluid disposed therein,

ultra-sonic transceiver means disposed in said cylindrical body for emitting an ultra-sonic pulse in said drilling fluid toward said borehole wall and for receiving ultra-sonic echo pulses reflected from said borehole wall, and

a phase detector for detecting the phase of said pulses and for generating a signal indicating that an echo has high frequency oscillations which are approximately 180.degree. out of phase from the echo pulse, such signal indicative of the sensing of a large gas bubble.

Description Submit all comments and votes

TECHNICAL FIELD

This invention relates generally to the ultra-sonic measurement of borehole characteristics. More particularly this invention relates to, apparatus and methods of ultra-sonic measuring of borehole characteristics while a well is being drilled. Still more particularly the invention relates to measurement of borehole diameter and gas influx of a borehole while it is being drilled. The invention relates also to a particular ultra-sonic sensor incorporated in the apparatus for measuring such characteristics.

BACKGROUND OF THE INVENTION

The apparatus and methods of this invention provide for the measurement of borehole diameter and for the detection of gas influx while a well is being drilled.

Borehole Caliper Measurement

Knowledge of a borehole's diameter while it is being drilled is important to the driller because remedial action may be taken by the driller in real time, preventing the delay inherent in tripping the drill string and conducting open-hole logging activities. If the diameter of the borehole is over-gauge, such fact may indicate that there is inappropriate mud flow, or an improper mud chemical characteristic or that the well hydrostatic pressure is too low, or that there is some other source of well-bore instability. If the diameter of the borehole is below gauge or nominal size, such fact may indicate that the bit is worn and should be replaced so as to obviate the need for later well reaming activities.

Well bore diameter instability increases the risk that the drilling string may become stuck downhole. Stuck pipe implies an expensive and time consuming fishing job to recover the string or deviation of the hole after the loss of the bottom of the drilling string. Well bore diameter variation information is important to the driller in real time so that remedial action may be taken.

Well bore diameter as a function of depth is also important information for a driller where the borehole must be kept open for an extended portion of time. Monitoring of well bore diameter when the drill string is tripped out of the borehole provides information to the driller regarding proper drilling fluid characteristics as they relate to formation properties.

Knowledge of borehole diameter also aids the driller when deviated holes are being drilled. When a borehole is out of gauge, directional drilling is difficult because the drill-string, bottom-hole assembly, and collar stabilizers do not contact the borehole walls as predicted by the driller. Real time knowledge of borehole diameter provides information on which to base directional drilling decisions. Such decisions may eliminate the need for tripping the string so as to modify the bottom-hole assembly to correct a hole curvature deviation problem.

Real time knowledge of well bore diameter is important in logging while drilling (LWD) operations. Certain measurements, especially nuclear measurements of the formation, are sensitive to borehole diameter. Knowledge of the well bore diameter under certain circumstances can be critical for validating or correcting such measurements.

U.S. Pat. No. 4,665,511 describes a system for measuring the diameter of a well while it is being drilled. Such system provides ultra-sonic transducers on diametrically opposed sides of a drilling sub. It relies on the reception of echoes of emitted pulses from the borehole walls, but such reception is often confused by the presence of drill cuttings in the drilling fluid. Measurement of the diameter of a borehole using the apparatus of this patent may also be inaccurate where the sub is not centralized with the axis of the borehole. Such inaccuracy may occur where the drilling sub is adjacent the borehole wall and the diameter of the sub is smaller than the diameter of the borehole. Under such conditions, the "diameter" sensed by the drilling sub is in reality a chord of the borehole which is smaller than the actual borehole diameter.

Identification of objects of the invention with respect to borehole caliper measurement aspects of the invention are described below after other aspects of the invention are described.

Borehole Gas Influx Detection

Gas influx, or a "kick" into the borehole, is a serious hazard in the drilling art since kicks, if uncontrolled, can cause well blowouts. Well blowouts may result in loss of life, damage to expensive drilling equipment, waste of natural resources, and damage to the environment.

Prior art kick detection while drilling has typically involved observation of the mud flow rate and/or mud pit volume. Accordingly, almost every rig which uses drilling fluid or mud to control the pressure in the borehole has some form of pit-level indicating device that indicates a gain or loss of mud. A mud pit-level indicating and recording device, such as a chart, is usually located in a position so that the driller can see the chart while drilling is occurring. When a kick occurs, the surface pressure required to contain it largely depends upon closing well-head BOPs quickly and retaining as much mud as possible in the well.

Flow meters showing relative changes in return mud flow have also been used as a kick warning device, because mud hold-up in solids control devices, degassers, and mixing equipment affects average pit-level. Such fluctuations in pit-level due to such factors recur periodically during drilling and may occur simultaneously with a kick. When such conditions are present, a return flow rate may be the first indication of a kick.

To determine kicks as early as possible while drilling, the driller typically uses instantaneous charts of average volume of the mud pit, mud gained or lost from the pit, and return flow rate. Preferably, the pit volume and return flow rate is displayed (and possibly recorded by means of a graph) on the drilling floor so that trends can be observed. As soon as an unexpected change in the trends occurs, a driller checks for a kick condition.

These prior art kick detection techniques for land drilling operations typically require ten to twenty minutes of delay from the time a gas influx occurs at the bottom of the well until pit volume or return mud flow rate is sufficiently affected to be detected. For offshore operations such delay may be twice that for land operations.

Because a kick can lead to a blowout with possible disastrous results, prior attempts have been made to obtain information as to gas influx into the borehole before such influx affects pit mud volume or return flow rate. U.S. Pat. No. 4,571,603 discloses apparatus for measuring characteristics of drilling mud with a probe adapted for inclusion in a drill string member. Such probe includes an ultra-sonic transducer which serves to emit sonic pulses and receive echo signals. A gap in the path of the ultra-sonic pulses is provided so that drilling fluid may enter the gap. Reflections from a near surface of the gap and from a far surface of the gap are analyzed. Such analysis is said to permit determination of the speed of sound of the drilling fluid, sonic attenuation, the product of fluid density and compressibility, viscosity etc.

Such patent does not describe a practical system in a down-hole measuring-while-drilling environment, because the probe gap may quickly become caked or filled with mud particulate. Such caking of the gap renders the probe inoperable for determining characteristics of downhole drilling fluid. The apparatus and method also ignores the presence of cuttings in the drilling fluid which affect reflections received by an ultra-sonic transducer.

Identification of objects of the invention with respect to gas influx or kick detection measurements of the invention are described below.

Ultra-sonic Sensor for a Measurement While Drilling Environment

The drilling environment in which an ultra-sonic sensor must function, if it is to measure borehole and drilling fluid characteristics while drilling, is truly daunting. Shocks and vibrations up to 650 G's/mSec of the drill string render prior art ultra-sonic sensor assemblies useless. Measurement while drilling sensors must survive for several days, unlike wireline logging sensors, because drilling continues for such time length. Noise created by high speed drilling fluid through drilling tools and by tools impacting rock formations must be eliminated in signal processing. In addition, the sensors must be capable of withstanding pressures up to 20,000 psi and temperatures up to 150.degree. C. as well as mechanical abrasion and direct hits on the sensor face.

Identification of objects of the invention with respect to the ultra-sonic sensor aspects of the invention are described below.

IDENTIFICATION OF OBJECTS OF THE INVENTION

Borehole Caliper Measurement

It is a primary object of the invention to measure-while-drilling the borehole diameter and tool standoff by pulse-echo techniques by recognizing and eliminating reflections from cuttings in the drilling fluid returning to the surface between the tool and the borehole wall.

It is another object of the invention to measure-while-drilling borehole diameter and tool standoff by pulse echo techniques and to statistically process such measurements downhole to significantly improve the accuracy of such measurements.

It is still another object of the invention to mount a pulse echo sensor on or near a stabilizer of a drilling tool to minimize inaccuracies caused by such tool not being centralized with the axis of the borehole.

It is still another object of the invention to measure while drilling borehole diameter and tool standoff by pulse echo techniques and to transmit a signal representative of same to the surface.

Borehole Gas Influx Detection

Another primary object of the invention is to provide a practical and reliable method and apparatus for measuring gas influx into a well while it is being drilling and telemetering a signal representative of that measurement to the surface.

Another object of the invention is to provide a method and apparatus for detecting gas influx into a borehole even though drill cuttings are entrained within the borehole fluid.

Another object of the invention is to provide a method and tool for assessing gas influx into a borehole by pulse-echo measurement of flowing drilling fluid as it returns to the surface in the annulus between the tool and the borehole.

Another object of the invention is to provide alternative techniques for assessing gas influx into a borehole and using such techniques as redundant indicators of gas influx.

Another object of the invention is to provide apparatus and method for measuring the sonic impedance of drilling fluid in a borehole by assessing echoes from the interface between a delay line and such drilling fluid.

Another object of the invention is to provide apparatus and method for measuring sonic attenuation of drilling fluid in the borehole by assessing echoes from the borehole wall.

Another object of the invention is to provide apparatus and method for detection of large bubbles in the borehole drilling fluid.

Ultra-sonic Sensor for a Measuring-while-drilling Environment

Another primary object of the invention is to provide an ultra-sonic sensor and associated electronics and tool in which it is placed which can survive extremely harsh forces, temperatures, pressures and noise present in a borehole while it is being drilled.

Another object of the invention is to provide a tool structure and ultra-sonic sensor which are not subject to mud caking while measuring characteristics of drilling fluid as it flows past the sensor.

Another object of the invention is to provide a sensor assembly which includes a delay line including a structure for focusing ultra-sonic pulses toward the borehole.

Another object of the invention is to provide a sensor assembly which creates a smooth outside profile with a downhole drilling tool to prevent caking of drilling fluid particulate in the path of ultra-sonic pulses and echoes.

Another object of the invention is to provide a mounting structure for a pulse echo sensor assembly in a downhole drilling tool to protect the assembly from extremely high shock forces.

Another object of the invention is to provide a pulse echo sensor assembly to accommodate thermal expansion of components due to extremely high downhole temperatures.

Another object of the invention is to provide a pulse echo sensor assembly which prevents fluid invasion into sensor components even under extremely high pressures of a borehole environment.

Another object of the invention is to provide mechanical noise rejection structures to reduce noise generated by high velocity mud flow through the drilling tool, thereby allowing a large range of signal detection after attenuation.

Still another object of the invention is to provide electronic control and processing circuits for emitting and receiving ultra-sonic pulses and echoes and for processing echo data to generate caliper and gas influx signals.

SUMMARY OF THE INVENTION

The objects identified above, as well as other advantages and features of the invention, are preferably incorporated in an ultra-sonic system disposed within a measuring-while-drilling (MWD) or logging-while-drilling (LWD) apparatus to perform hole caliper monitoring and/or gas influx detection.

The system includes an ultra-sonic transceiver installed in a drill collar. Such drill collar functions in the drilling process to put weight on the bit, etc. In other words, it functions as an ordinary drill collar independent of the MWD measuring apparatus described here. A second identical transceiver is preferably installed at the azimuthal opposed position of the first transceiver in the same collar, and at the same axial position. This second transceiver improves the reliability of gas detection and the caliper accuracy.

The transceiver is designed to generate an ultrasonic pulse in the mud in the direction perpendicular to the face of the collar. The wave pulse travels through the mud, reflects from the formation surface and comes back to the same transceiver which, after the ultra-sonic pulse has been emitted, acts as a receiver. The travel time of the pulse in the mud is proportional to the standoff distance of the tool from the borehole wall.

The transceiver includes a solid "delay-line" between a ceramic sensor and the drilling fluid. Such "delay-line" reflects a portion of the emitted sonic pulse back to the sensor from the interface of the delay line and the mud. The amplitude of such pulse is related to the sonic impedance of the mud. Such sonic impedance depends directly on the amount of gas in the mud, i.e., it depends on the density of the mud. Accordingly, the sonic impedance of the mud is an important parameter for down-hole gas influx detection.

Providing a delay-line in front of the sonic sensor advantageously allows echo detection where the tool is close to the borehole. Furthermore, such delay-line provides focusing, protection of the sensor, and other mechanical functions as described below.

In addition to the transceiver, the drill string collar includes electronic circuits, a microprocessor, and memory circuits to control the sensor and to receive echo signals and process them. Processed signals may be stored in down-hole memory (caliper for example), or may be transmitted to the surface by a standard measuring-while-drilling mud pulse device and method. Both methods (storage and transmission) can be used simultaneously. Alternatively, the caliper signals may be stored and the gas influx signals transmitted to the surface in real time.

Borehole Caliper Measurement

The apparatus of the invention provides a tool standoff measurement to determine the hole diameter when the tool is rotating (which is the normal case during drilling), or when the tool is stationary. When the tool is rotating, the transceiver sends the sonic pulse through the mud gap distance between the tool and borehole wall. Such gap varies with the tool rotation. The measured standoffs are accumulated for statistical processing, and the average hole diameter is calculated after several turns. Several standoff measurements are preferably evaluated each second. Because the typical drill string rotation speed is between about 50 to 200 RPM, an average accumulation time from about 10 to about 60 seconds creates enough data for accurate averaging.

Providing a second transceiver diametrically opposed from the first improves the diameter measurement when the tool axis moves from side to side in the well-bore during drilling. One transceiver measures the standoff on its side. Then immediately thereafter the other transceiver measures the standoff on the other side of the tool. An instantaneous firing of both transceivers is not required as long as tool movement in the time between the two transceiver measurements is small.

The hole diameter is determined by adding the tool diameter to the standoffs measured on successive firings. A number of borehole diameter determinations are accumulated and averaged to produce a borehole measurement. Additional processing according to the invention relates to processing for rejection of false echoes. Such processing identifies formation echoes which occur after echoes from drilling cuttings in the