US3857281A

US3857281A - Method and apparatus for detecting potentially dangerous conditions in a well bore during trips of the well string in and out of the well bore

Info

Publication number: US3857281A
Application number: US00343787A
Authority: US
Inventors: E Dower
Original assignee: Warren Automatic Tool Co
Current assignee: Warren Automatic Tool Co; MI Drilling Fluids Co
Priority date: 1973-03-22
Filing date: 1973-03-22
Publication date: 1974-12-31
Anticipated expiration: 1991-12-31

Abstract

A method and apparatus for detecting potentially dangerous conditions in a well bore which is being drilled by the use of a drill string suspended in the well bore and with a drilling mud system. The method and apparatus is arranged for detecting losses of drilling mud to the well bore formation and the incursion of well fluids into the well bore during times when the drill string is being run into and taken out of the well bore. The apparatus includes means for sensing the weight of the drill string suspended in the well bore during running in and coming out as an indication of the volume of space in the well bore occupied by the suspended drill string. Signal means are connected to the weight sensing means for generating a first signal representative of the drill string volume. Means are also provided for sensing the volume of drilling mud in the drilling mud system outside of the well bore during running in and coming out of operations. Signal means are also connected to the mud volume sensing means for generating a second signal representative of the aforesaid mud volume outside the well bore, and variations therein. Readout means, which may include a two-pen chart or the like, are connected to receive the first and second signals and for reading out variations between the two signals as either a loss of drilling mud to the formation or the incursion of fluid from the formation into the well bore.

Description

United States Patent 1 Dower Dec. 31, 1974 METHOD AND APPARATUS FOR DETECTING POTENTIALLY DANGEROUS CONDITIONS IN A WELL BORE DURING TRIPS OF THE WELL STRING IN AND OUT OF THE WELL BORE Ethell J. Dower, Houston, Tex.

[73] Assignee: Warren Automatic Tool Company,

Houston, Tex.

[22] Filed: Mar. 22, 1973 [21] Appl. No.: 343,787

[75] Inventor:

Primary Examiner-Jerry W. Myracle Attorney, Agent, or FirmLee R. Larkin [57] ABSTRACT A method and apparatus for detecting potentially dan- L/NE TENS/ON TRANSMITTER BIAS RELAY SUPPL Y DEAD LINE CABLE 72 MUD LEV BIAS RELAY TRANSMITTER 42 33 40 SUPPLY 30 MUD TANK ADJUSTABLE GAIN RELAY Z7 SUPPLY gerous conditions in a well bore which is being drilled by the use of a drill string suspended in the well bore and with a drilling mud system. The method and apparatus is arranged for detecting losses of drilling mud to the well bore formation and the incursion of well fluids into the well bore during times when the drill string is being run into and taken out of the well bore. The apparatus includes means for sensing the weight of the drill string suspended in the well bore during running in and coming out as an indication of the volume of space in the well bore occupied by the suspended drill string. Signal means are connected to the weight sensing means for generating a first signal representative of the drill string volume. Means are also provided for sensing the volume of drilling mud in the drilling mud system outside of the well bore during running in and coming out of operations. Signal means are also connected to the mud volume sensing means for generating a second signal representative of the aforesaid mud volume outside the well bore, and variations therein. Readout means, which may include a two-pen chart or the like, are connected to receive the first and second signals and for reading out variations between the two signals as either a loss of drilling mud to the formation or the incursion of fluid from the formation into the well bore.

10 Claims, 1 Drawing Figure CAPACITY TANK SUPPLY 20 BLEED OFF TWO PEN RECORDER MUD ADJUSTABL VOLUME 44 ERELAY SIGNAL METHOD AND APPARATUS FOR DETECTING POTENTIALLY DANGEROUS CONDITIONS IN A WELL BORE DURING TRIPS OF THE WELL STRING IN AND OUT OF THE WELL BORE BACKGROUND OF THE INVENTION a. Field of the Invention This invention relates to an apparatus and-method for detecting potentially dangerous conditions, such as potential blow-out conditions, which might arise during times when the drill string is either being run into or removed from a well bore, as for example, an oil well being drilled.

b. Description of the Prior Art As is common knowledge to those familiar with the oil industry, fluid pressure in subterranean formations generally increases with depth. If the fluid pressures are not properly controlled, then a potential blow-out condition may arise. This potentialblow-out condition is generally countered by the use of a drilling mud of the desired specific gravity, such that the hydrostatic pressure of the column'of drilling mud opposes the pressure of the formation fluid. In the event that the pressure of the hydrostatic column of fluid is too little, then formation fluids such as gas, or the like, may incur into the well bore and rise to the top, thereby creating a blowout condition, with its known destructive propensities. Alternatively, if the weight of the column of mud is too great, then there is likely to be loss of the drilling mud to the formation, which likewise can result in undesirable and potentially dangerous conditions, as is well known to those skilled in the art.

During normal drilling operations, that is to say, when the drill string is bottomed on the bottom of the well bore and is being rotated, and drilling fluid is being circulated through the drill pipe, apparatus have been developed for sensing any changes in the volume of drilling mud in the drilling mud system, as indication of the potential blow-out conditions. One such device is marketed under the brand name BARREL-O-GRAF by Warren Automatic Tool Company of Houston, Texas. However, this system has limited usefulness for detecting the aforesaid potentially dangerous blow-out condition during times when the drill string is either being run into or removed from the well bore. As is well known to those skilled in the art, during times when the drill string is being run into the well bore, drilling mud is displaced from the well bore and, conversely, when the drill string is being removed from the well bore, the level of drilling mud in the well bore declines, and thus additional mudmust be pumped thereinto in order to maintain the proper hydrostatic pressure. Because of this dynamic situation, there is need for some apparatus and method which will be useful for detecting any potentially dangerout conditions that may arise during the aforesaid tripping operations.

In the past, it has been common practice for the drilling crew to pull one or more stands of drill pipe, and thereafter fill up the well bore by actuating the mud pump and counting the number of pump strokes required to fill up the well bore. The number of strokes of the pump is used to calculate the volume of mud used to fill up the well bore, which figure is then mentally compared with the theoretical or calculated required displacement of the number of stands of drill pipe removed from the well bore. However, this system is very inaccurate and subject to operational error. Many drill strings contain two or more sizes of drill pipe, in addition to the large drill collars, and such a system is subject to several sources of human and measurement error.

It is therefore an object of this invention to provide an improved apparatus and method for detecting losses of drilling mud to the well bore formation and the incursions of formation fluid into the well bore during times when the drill string is being either run into or taken out of the well bore.

SUMMARY OF THE INVENTION Briefly stated, the method of this invention is arranged for detecting potentially dangerous conditions in a well bore which is being drilled by the use of a drill string suspended in the well bore and with a drilling mud system. The method is arranged for detecting losses of drilling mud to the well bore formation and the incursion of formation fluids into the well bore during times when the drill string is being run into and taken out of the well bore. The method includes the steps of sensing the weight of the drill string suspended in the well bore during the running in and coming out operation as an indication of the volume of space in the well bore occupied by the drill string. A first signal is generated which is representative of the suspended drill string volume. The method also includes sensing the volume of the drilling mud in the drilling mud system outside of the well bore during the running in and coming out operation. A second signal is generated representative of the mud volume change outside of the well bore.- The method includes monitoring variations in the difference between the first and second signals as indications of loss of drilling mud to the formation and the incursion of fluids from the formation. Preferably, the well bore and the drill string are maintained full of drilling mud during the sensing and monitoring steps. It is to be understood that this maintaining of the well bore full of mud can be done either continuously or periodically. It is to be also understood that the mud system can be either the usual mud system, or it can be a special fill up mud tank specially adapted for that purpose and which is connected to a pump which continuously pumps drilling fluid to the well bore, from which it returns through an overflow pipe, such that the well bore can continuously be maintained in a full condition.

The apparatus in this invention includes means for sensing the weight of the drill string suspended in the well bore during the running in and coming out operation as an indication of the volume of space in the well bore occupied by the drill string. Means are connected to the weight sensing means for generating a first signal representative of the drill string volume. Means are also provided for sensing the volume of the drilling mud in the drilling mud system outside the well bore during the running in and coming out operations. Means are also provided for sensing changes in the volume of the drilling mud in the drilling mud system outside the well bore during the running in and coming out operations. Means are connected to the mud volume sensing means for generating a second signal representative of the mud volume outside the well bore. Read-out means are connected to receive the first and second signals for reading out variations therebetween as indications of loss of drilling mud to the formation or the incursion of drilling fluid from the formation into the well bore.

Preferably, calibration means are provided for setting the signals to comparable volume scales. The read-out means may include recording means for displaying the signals on a chart, or the like, or may include means for generating a third signal which can actuate some alarm system, or the like.

BRIEF DESCRIPTION OF THE DRAWINGS The Drawing is a schematic block diagram generally showing the arrangement of one form of the apparatus of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT It is to be understood that the apparatus and. method of this invention are adaptable for use when drilling a well bore such as an oil well utilizing a drill string such may be equipped with a pump 31 which is arranged to continuously draw mud from mud tank 30 and deliver it through fill-up line 32, which terminates at the casing head, which connection will be normally below the northe well bore full of mud. As the drill string is withas a rotary drill string suspended in a well bore and with i the drill string having a drill bit on the lower end thereof. It is also contemplated that the drilling system will include a mud system which includes means for circulating a drilling mud through the drill pipe and across the bottom of the well bore to flush out cuttings and the like and to maintain the desired hydrostatic pressure on the formation fluid.

The apparatus of this invention includes means for sensing the weight of the drill string suspended in the well bore during the running in and coming out of the drill string as an indication of the volume of space in the well bore occupied by the drill string. One convenient'means for detecting the weight of the suspended drill string is to attach a conventional line tension transmitter such as pneumatic transmitter 11 to the dead line cable 12, which is connected to the travelling block as is well known to those skilled in the art. Hence, the greater the weight of the suspended drill string, the greater will be the tension on dead line cable 12, and hence the signal produced by transmitter 11 on signal line '13 is proportional to the weight of the suspended drill string. Because of the known density of the drill string, it is therefore'known that the volume of mud displaced by the drill string is generally directly proportional to such weight. The pneumatic signal along signal line 13 is applied to a bias relay 14 through snubber 15, which dampens out undesirable fluctuations in the signal. The output of bias relay 14 is applied to an adjustable pneumatic relay 16, which in turn applies a pneumatic signal on signal line 17, which is connected through check valve 18 to one pen of a two-pen recorder 20, or, alternatively, other appropriate read-out means.

Signal line l7,'downstream of check valve 18, may have attached thereto acapacity tank 21 and a bleedoff valve 22 for manipulating operation of the: system. Hence, the foregoing system generally provides the pipe volume signal to recorder 20. By manipulation of bias relay [4' and adjustable relay 16, the appropriate pen of recorder can be calibrated to record over the desired volume range.

The means for sensing the volume of drilling mud in the drilling mud system outside the well bore during running in and coming out of the drill pipe, may be the conventional drilling mud tanks or may be a special fillup mud tank such as fill-up mud tank 30. Preferably mud tank 30 is a separate fill-up tank of a known capacity such as 100 barrels and is used to maintain the well bore full as the drill pipe is pulled. Hence, tank 30 drawn, the volume of mud in fill-up tank 30 will decrease. Likewise, during such coming out operation, the weight of the drill string and hence the volume of the drill string suspended in the well bore decreases. Under usual circumstances, when there is no loss of drilling fluid to the formation or incursion of formation fluid into the well bore, then changes of pipe volume suspended in the well bore will be proportional to the I changes of mud volume in mud tank 30.

Hence, means are provided for sensing the volume of the drilling mud in the drilling mud system outside the well bore which can conveniently take the form of mud level pneumatic transmitter 40, which is arranged to sense the level of mud in mud tank 30 and transmit a signal on signal line 41 which is representative of the volume of mud in mud tank 30. Line 41 is connected to an appropriate pneumatic bias relay 42. The output of bias relay 42 is applied to adjustable relay 44 which likewise applies a pneumatic ou'tputon mud volume signal line 45, which connects to the other pen of twopen recorder 20. By adjusting bias relay 42 and adjustment relay 44, the signal on signal line 45 can be adjusted such that the appropriate pen of two-pen recorder 20 can be adjusted to substantially the same volume scale as the other pen connected to receive the pipe volume signal. It is to be understood that recorder 20 may be a circular time chart, for example, having pens which are connected as aforesaid and which provide a visible readout of the two signals.

As stated before, the two signals, when properly calibrated and during the running in and coming out opera- 7 tions, will be recording approximately the same volume changes. In the event that there are any variations between the two signals above the normal level, then this would be indicative of a potentially dangerous condition. An increase of drilling fluid relative to pipe voltime which would indicate an incursion of drilling fluid into the formation. Conversely, in the event that the volume of mud relative to the volume of pipe suspended in the well bore decreased, then this would indicate a loss of drilling fluid to the formation. Either one of these conditions can cause a potential blow-out condition, and the well driller needs to be aware of such conditions so that corrective actions can be taken.

It is to be understood that other types of weight sensing means can be used for sensing the weight of the suspended drill pipe, as for example a load cell supported under the rotary table to measure the weight of the pipe when it is set'in the slips in the rotary table when the stand is removed, or before the stand is added. It is to be understood that the signals generated may be either electrical or pneumatic, but the operation thereof would be thesame. Other readout means can be used than a recorder. For example, the pipe volume signal and the mud volume signal may be used to generate a third signal which is connected to an appropriate alarm system, for example, either audio or visual.

It is also to be understood that rather than using a special fill-up mud tank such as mud tank 30, the signal on line 31 can be taken from the conventional mud still have drilling fluid therein, a slug'of heavier mud may be introduced into the top of the drill pipe prior to pulling the same, or trip mud of slightly lower density than drilling mud, may be used. It is to be understood that the trip mud should be of the same type as the drilling mud but slightly cut back with water.

It will thus be observed that this invention provides a method and apparatus for detecting potential blowout conditions which might arise during times when making trips with the drill stem either into or out of the well bore and eliminates the mental calculations heretofore utilized in some instances and gives a positive readout at all times.-

As previously stated, the well bore may be maintained full of drilling mud during the sensing and monitoring steps, which maintaining may be done periodically or continuously. However, it is preferable that the well bore be full when the monitoring step is performed to provide accurate measurements of mud volume.

Moreover, it is preferable to have the signals calibrated so that they may be more easily compared in terms of volume. By recording the signals, a permanent record may be made which may be useful in analyzing well conditions at a subsequent time. Alternatively, the two generated signals may be used to generate a third signal, which in turn may be used to operate a single pen of a recorder or an audible alarm signal, or the like.

Further modification and alternative embodiments of the apparatus and method of this invention will be apparent to those skilled in the art in view of this description. Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the manner of carrying out the invention. It is to be understood that the forms of the invention herewith shown and described is to be taken as the presently preferred embodiment. Various changes may be made in the shape, size and arrangement of parts. For example, equivalent elements or materials may be substituted for those illustrated and described herein, parts may be reversed, and certain features of the invention maybe utilized independently of the use of other features, all as would be apparent to one skilled in the art after having the benefit of this description of the invention.

What is claimed is:

1. In a method of detecting potentially dangerous conditions in a well bore which is being drilled by the use of a drill string suspended in said well bore and with a drilling mud system, which method is arranged for detecting losses of drilling mud to the well bore formation and the incursion of fluid into the well bore from the formation during times when the drill string is being run into and taken out of the well bore, the combination of steps comprising:

sensing the weight of the drill string suspended in said well bore during said running in and coming out as an indication of the volume of space in said well bore occupied by said drill string;

generating a first signal representative of said suspended drill string volume;

sensing the volume of drilling mud in said drilling mud system outside of said well bore during said running in and coming out operations;

generating a second signal representative of said mud volume outside said well bore;

and monitoring variations in the difference between said first and second signals as indications of loss of drilling mud to the formation and the incursion of fluid from the formation.

2. The invention as claimed in claim 1 including:

maintaining said well bore and said drill string full of drilling mud during said sensing and monitoring steps.

3. The invention as claimed in claim 1 including:

calibrating said first and second signals to comparable volume scales.

4. The invention as claimed in claim 3 wherein:

said monitoring step includes recording said signals on a common display chart.

5. The invention as claimed in claim 3 wherein:

said monitoring step includes generating a third signal representative of said differences between said first and second signals.

6. ln apparatus for detecting losses of drilling mud to the well bore formation and the incursions of fluid into the well bore from the formation which is being drilled by the use of a drill string suspended in said well bore and with a drilling mud system, which apparatus is arranged for such detecting during times when the drill string is being run into and taken out of the well bore, the combination comprising:

means for sensing the weight of the drill string suspended in said well bore during said running in and coming out as an indication of the volume of space in said well bore occupied by said drill string;

means connected to said weight sensing means for generating a first signal representative of said drill string volume;

means for sensing the change of volume of drilling mud in said drilling mud system outside said well bore during said running in and coming out operations; I

means connected to said mud volume sensing means for generating a second signal representative of said mud volume;

' and readout means connected to receive said first and second signals for reading out variations therebetween as indications of 'loss of drilling mud to the formation and the incursion of fluid from the formation into saidwell bore.

7. The invention-as claimed in claim 6 including:

means for filling said well bore full of drilling fluid at determined times. a

8. The invention as claimedin claim 6 including:

calibration means for adjusting said signals to comparable volume scales.

9. The invention as claimed in claim 6 wherein:

saidreadout means includes means for recording said tween said first and second signals;

signals on a display chart. and means connected to said third signal generating 10. The invention as claimed in'claim 6 wherein: means for producing an alarm signal when said 1 said readout means includes means for generating a third signal increased beyond a determined level.

third signal representative of said differences be- 5 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION P n 3,857,281 Dated December 31, 1974 Inventor(s) Ethell J. Dower It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On the title page "METHOD AND APPARATUS FOR DETECTING POTENTIALLY DANGEROUS CONDITIONS IN A WELL BORE DURING TRIPS OF THE WELL STRING IN AND OUT OF THE WELL BORE" should read METHOD AND APPARATUS FOR DETECTING POTENTIALLY DANGEROUS CONDITIONS IN A WELL BORE DURING TRIPS OF THE DRILL STRING IN AND OUT OF THE WELL BORE-- In column 1, line 3, "WELL" second occurrence should read DRILL Signed and sealed this 6th day of May 1.975.

(SEAL) Attest:

C. MARSHALL DANN RUTH C. MASON Commissioner of Patents Attesting Officer and Trademarks ORM PO-105O (10-69) USCOMM-DC 60378-1 69 i U.S. GOVERNMENT PRINTING OFFICE I908 Q-S66-33l.

Claims

1. In a method of detecting potentially dangerous conditions in a well bore which is being drilled by the use of a drill string suspended in said well bore and with a drilling mud system, which method is arranged for detecting losses of drilling mud to the well bore formation and the incursion of fluid into the well bore from the formation during times when the drill string is being run into and taken out of the well bore, the combination of steps comprising: sensing the weight of the drill string suspended in said well bore during said running in and coming out as an indication of the volume of space in said well bore occupied by said drill string; generating a first signal representative of said suspended drill string volume; sensing the volume of drilling mud in said drilling mud system outside of said well bore during said running in and coming out operations; generating a second signal representative of said mud volume outside said well bore; and monitoring variations in the difference between said first and second signals as indications of loss of drilling mud to the formation and the incursion of fluid from the formation.

2. The invention as claimed in claim 1 including: maintaining said well bore anD said drill string full of drilling mud during said sensing and monitoring steps.

3. The invention as claimed in claim 1 including: calibrating said first and second signals to comparable volume scales.

4. The invention as claimed in claim 3 wherein: said monitoring step includes recording said signals on a common display chart.

5. The invention as claimed in claim 3 wherein: said monitoring step includes generating a third signal representative of said differences between said first and second signals.

6. In apparatus for detecting losses of drilling mud to the well bore formation and the incursions of fluid into the well bore from the formation which is being drilled by the use of a drill string suspended in said well bore and with a drilling mud system, which apparatus is arranged for such detecting during times when the drill string is being run into and taken out of the well bore, the combination comprising: means for sensing the weight of the drill string suspended in said well bore during said running in and coming out as an indication of the volume of space in said well bore occupied by said drill string; means connected to said weight sensing means for generating a first signal representative of said drill string volume; means for sensing the change of volume of drilling mud in said drilling mud system outside said well bore during said running in and coming out operations; means connected to said mud volume sensing means for generating a second signal representative of said mud volume; and readout means connected to receive said first and second signals for reading out variations therebetween as indications of loss of drilling mud to the formation and the incursion of fluid from the formation into said well bore.

7. The invention as claimed in claim 6 including: means for filling said well bore full of drilling fluid at determined times.

8. The invention as claimed in claim 6 including: calibration means for adjusting said signals to comparable volume scales.

9. The invention as claimed in claim 6 wherein: said readout means includes means for recording said signals on a display chart.

10. The invention as claimed in claim 6 wherein: said readout means includes means for generating a third signal representative of said differences between said first and second signals; and means connected to said third signal generating means for producing an alarm signal when said third signal increased beyond a determined level.