CA1134257A

CA1134257A - System for measuring downhole drilling forces

Info

Publication number: CA1134257A
Application number: CA341,518A
Authority: CA
Inventors: Keith K. Millheim
Original assignee: Standard Oil Co
Current assignee: Standard Oil Co
Priority date: 1979-02-28
Filing date: 1979-12-10
Publication date: 1982-10-26
Also published as: NL8000761A; GB2043747A; NO800553L; GB2113275A; GB2043747B; BR8001157A; EG13909A; GB2113275B

Abstract

ABSTRACT OF THE DISCLOSURE
An apparatus is described whereby the side force on a drill bit can be measured during drilling operations and transmitted to the surface where it can be used in predicting trajectory of the hole and taking corrective action in the drilling operation. A downhole assembly using a downhole motor is modified to include means to detect the side thrust or force on a bit driven by the motor and the force on the deflection means of the down-hole motor. These measured forces are transmitted to the surface of the earth during drilling operations and are used in evaluating and controlling drilling operations.
Means are also provided to measure magnitude of the force on a downhole stabilizer.

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Description

SYSTEM FOR MEASURING DOWNHOLE DRILLING FORCES
BRIEF SUMMARY OF THE INVENTION
This invention concerns a system for drilling wells in the earth and in particular wells drilled for oil and gas with a trajectory having a horizontal component.
15 In one embodiment of many locations, and particularly in offshore locations where a large number of wells, e.g., 32, may be drilled from a single platform, the bottom of the individual wells may be located many thousands of feet horizontally from the position of the platform. In one

2~ embodiment of my invention, during drilling operations, I
measure the force on the drilling bit perpendicular to its a~is. An indication of this measured force is transmitted to the surface where it is used by the driller to control drilling operations so that the well takes the proper tra-~5 jectory. Unless the bit is pulled, the functions which can be changed include changing the weight applied the bit, the rate of rotating the bit, and the hydraulics, all of which influences the direction the bit will go during drilling operations.
My invention can be used either with a system using a downhole motor or a system in which the bit is rotated by rotating a string of drill pipe or a combina-tion thereof.
My invention can also be used with a method for 35 drilling a borehole in the earth in which a downhole motor having a rotating sub is provided with an orienting sub or cylinder connected to the downhole motor. The side thrust is measured during drilling operations on the rotating sub or bit and transmitted to the surface. I also measure the ~ ~ .

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~ ' ~ :. : ~ , ` , , :. . ~ . , ~39~25~7 force between the orienting sub and the borehole wall which force measurement is also transmitted to the sur-face. These transmitted force measurements are then used at the surface to determine any corrective action which 5 may be needed to the operation of the downhole motor and the orienting sub.
DRAWINGS
A better understanding of the invention can be had from the following description taken in conjunction 10 with the drawings in which:
Figure l illustrates a well being drilled in a controlled direction deviating from the vertical.
Figure 2 illustrates a downhole drilling assem-bly incorporating one embodiment of my invention for mea-15 suring downhole side force during drilling.
Figure 3 is a view taken along the line 3-3 of Figure 2.
Figure 4 illustrates a modification of the loca-tion of the strain gauges of the apparatus of Figure 2.
~0 Figure 5 is a view taken along the line 5-5 of Figure 4.
Figure 6 illustrates a modification of downhole stabilizers.
Figure 7 illustrates a modification of a down-~5 hole drill motor and associated deflection means modified to obtain measurements of the side forces at key posi-tions.
Figure 8 illustrates a modified downhole build-ing assembly.
Figure 9 illustrates a modified downhole drop-ping assembly.
Figure 10 illustrates an enlarged portion of the drill collars showing the addition of a strain ~auge or load cell.
DETAILED DESCRIPTION
Attention is directed to Figure l which illus-trates a drilling rig 10 used for drilling borehole 12 and from which is suspended drillpipe 14 having a bottomhole assembly at the lower end. The bottomhole assembly 16 . _ ,. . . .

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includes a bit 18 and suitable assessories such as stabi-lizers properly spaced. The borehole has three compo-nents, ~, Y, and Z. X is the direction, Y the inclina-tion, and Z is the axis of the borehole. Side thrust or 5 forces are measured on the bottomhole assembly 16 and bit 18 by detection means shown in the other figures of the drawings. These side force measurements are transmitted to the surface receiver 20 and then to data processor 22.
The information from surface receiver 20 will show the 1~ side force components X and Y. By knowing the side force components ~ and Y, one can determine the amount -the bit will cut sideways in the next footage of hole drilled, e.g., 10 feet. The actual measurement of the resultant side force interaction can show many things to the dril-15 ler. For example, if there is an exceedingly high sideforce on the bit, it shows that there is exceptionally high curvature to the hole at the point where it is being drilled. This may not be desirable and corrective action may need to be taken. An exceedingly high side force on 20 ehe bit can also indicate the possibility of a transition zone or the starting of a severe dogleg situation. An example of an exceedingly high side force on a bit would be above 2000 lbs. It is thus clear that a knowledge of the side force which is available during drilling is very ~; useful.
Also, if we know the resultant side force and direction, one can determine the amount the bit will cut sideways with a relatively high degree of accuracy. For a discussion of this, see Millheim, K. K. and Warren, T., 30 "Side Cutting Characteristics of Rock Bits and Stabilizers While Drilling", SPE preprint 7518, presented in the 1978 Annual Meeting of the SPE in Houston. That paper did not teach to measure the side force downhole nor how to do it but suggested a method of approximating or calculating the 35 side force. Once an indication is given of the amount or prediction of how far the bit will cut horizontally in a given vertical measurement, one can then decide what cor-rective action if any is needed. Corrective actions include adjusting the weight on the bit and adjusting the : i 257' rotary speed. For a discussion of how surface available adjustments can affect trajectory, see the article "Behav-ior of Multiple-Stabilizer Bottomhole Assemblies" by Keith Millheim, The Oil and Gas Journal, Jan. 1, 1979. Direc-5 tion of the side force can be determined by taking per-iodic measurements of the displacement of the bit in the inclination and direction planes (y and x). Systems by ~hich this can be accomplished are available; for example, see U.S. Patent 3,713,089, "Data-Signaling Apparatus for 10 Well Drilling Tools", Jackson R. Clacomb, inventor, Schlumberger Technology Corporation, assignee.
Attention is now directed to Figure 2 which illustrates a modification of a downhole drilling appara-tus for detecting and transmitting side force on a bit.
15 Shown thereon is a bit 18 connected to drill collars 26 which is connected to drillpipe 14 not shown in Figure 2.
As shown in Figures 2 and 3, there are three strain gauges 28 mounted about the legs of drill bit 18. These strain gauges should be equally spaced about the circumference of 20 the drill bit. As shown in Figure 3, if there are three strain gauges used, they should be approximately 120 apart. These strain gauges should be positioned to detect ~orce or displacement on the bit shank. Each strain gauge 28 is connected by appropriate conduits 30 to a signal 25 transmitter 32. The signal transmitter 32 is used to transmit the signal to surface receiver 20 as shown in Figure 1. One type signal transmitter is described in U.S. Patent 3,713,089, supra. It is apparent that by knowing the forces in three or more different parts of the 30 bit which are equally spaced that one can readily deter-mine the resultant side force on the bit. It is consid-ered simplest to transmit the measurement of each strain gauge 28 to the surface and make the calculation or deter-mination at the surface.
Attention is next directed at Figure 4 which shows a slightly different embodiment than that of F`ig-ure 2 for use in determining the side force on the bit.
Shown in Figures 4 and 5 are a plurality of strain gauges 34 which are positioned on bit sub 36. The measurements . . .
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~h3~7 from each strain gauge 34 is then transmitted to the sur-face through signal -transmitter 32, and this signal is used at the surface to aid in drilling the well as indi-cated above.
The most common method of drilling for oil and gas is by use of the rotary drilling method. As is well-known in that system a bit is suspended at the lower end of a string of tubing and the bit is rotated by rotating tubing or drill pipe at the surface. Another form of 10 drilling which is used quite frequently in directional drilling is the use of a downhole motor. The downhole motor is suspended at the lower end of a string of drill-pipe or tubular member. However, in this case a drillpipe is not usually rotated and the rotation of the bit is pro-15 vided by a hydraulic or electric motor. When this typesystem is used in directional drilling, there is also usu-ally provided an orienting sub or deflection barrel to apply lateral force to the side of the housing of the motor in order to aid in getting the bit to drill in the 20 desired direction and inclination. One such system is described in U.S. Patent 4,040,495, "Drilling Apparatus,"
Kellner, et al., inventors.
Attention is next directed to Figure 7 which illustrates a downhole assembly having a downhole motor 25 for rotating a drill bit that has been modified in accor-dance with my invention. Shown in Figure 7 is a downhole motor 50 attached to the lower end of a string of drill pipe or tubing 52. The motor 50 is connected to a rotat-ing sub 54 which has bit 56 which is used for drilling.
30 Also used with a motor 50 is an orienting sub 58.
Means are provided to detect the side force on the rotating sub 54 and on the orienting sub 58 of the downhole assembly of Figure 7. Strain gauges 60 are pro-vided in rotating sub 54 and can be positioned similarly 35 to that shown in Figure 5. A strain gauge or load cell 62 is provided to make a measure of the force exerted between the orienting sub 58 and the borehole wall. Each strain gauge 60 and load cell 62 is connected to transmitter 64 so that a reading of each such strain ga-uge can be :

~ ~ 3 transmitted to the surface for use. If the apparatus of Patent 4,040,495 were used, load cell 62 would be provided on deflection barrel 41. The point on which the orienting or deflecting sub 58 contacts the borehole wall 12 deter-5 mines to a large extent the direction in which bit 56 willgo in drilling. The circumferential position of this point of contact can be changed without pulling the tool from the hole. For example, in said Patent 4,040,495, deflector barrel 41 can be rotated to any desired circum-10 ferential position within the wellbore. Knowing the sideforce on the orienting sub 58 and on bit 56 assists the drilling in determining or predicting the trajectory in which the hole will be made. If the prediction is differ-ent from the desired trajectory of the hole, corrective 15 action can be taken prior to drilling that part of the hole. This permits corrective action to be taken before the hole is drilled rather than waiting until the hole is drilled and determining what action should have been taken when it is too late. It should be noted that the term ~0 deflection means when used in connection with the downhole assembly as described in this invention would include the bent or orienting sub as illustrated in Figure 7 or a deflection barrel or any other downhole means used with a rotating drilling bit to guide its trajectory.
~5 Most downhole assemblies used in drilling opera-tions contain or include what is known as a stabilier.
Shown in Figure 6 is one such stabilizer 70 having four equally spaced longitudinal blades 72. Stabilizers are well known and can take various forms. As shown in Fig-30 ure 6 on blade 72A, there are spaced longitudinally an upper strain gauge 74 and a lower strain gauge 76. They are each connected independently to transmitter 78. Sta-bilizer 70 is connected to a drill collar 80. Strain gauges 74 and 76 are aligned. This will give a measure of 35 the difference in side force at two longitudinally spaced points on the stabilizer. This is useful in determining hole trajectory.
Attention is next directed to Figure 8 which shows a downhole building assembly, e.g., one which would ~3~ 7 increase the angle of the hole from the vertical. This assembly includes bit 82, and stabilizers 83 and 84 and 86 mounted on a drill string section which may comprise drill collars. A load cell 88 is provided between stabilizers 5 83 and 84. The output from load cell 88 can be used to determine when that part of the drill pipe or drill col-lars between stabilizers 83 and 84 becomes tangent with the borehole wall. This would be a signal that no more weight should be applied to the drill bit . The principle 10 of my invention can also be applied to the embodiment of Fig. 9 which illustrates a downhole dropping assembly which includes a bit 90, a stabilizer 92 and a load cell 94 therebetween on the connecting drill collar or pipe 93.
Load cell 94 serves a purpose similar to that of load cell 15 88. As illustrated in Fig. 10, the measured values from the load cells is transmitted by transmitter 89 to the surface. For a discussion of the spacing of stabilizers in downhole assemblies see the article "Behavior of Multi-ple-Stablilzer Bottomhole Assemblies," supra.
While the above system has been described in detail, various modifications can be made thereto without departing to the spirit or scope of the invention.

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method of drilling a hole in the earth using a drill string and drill bit which comprises:
(a) measuring downhole during drilling operations the force on said bit perpendicular to its axis, (b) transmitting indication of the measured force to the surface.

2. The method of Claim 1 including the step of:
(c) using said transmitted indication to control drilling operations.

3. The method of Claim 1 wherein step (a) is accomplished by using a downhole motor having a rotating sub connected to a bit and a deflector means connected to the housing of said downhole motor, whereby the strain on said rotating sub is measured at at least three circumferentially spaced locations and the force between said deflector means and said wellbore wall is measured, and indications of the measurements are transmitted to the surface of the earth.

4. The method of Claim 3 wherein the effect of said force on said bit perpendicular to its axis and said force between said deflector means and said borehole wall are determined on the predicted trajectory hole and positioning said deflector means in accordance with such determination.

5. A downhole assembly for use in drilling a wellbore comprising:
a drill string section, a bit supported at the lower end of said section, a first stabilizer mounted on said section above said bit, and a load cell means positioned on the exterior of said section between said stabilizer and said bit.

6. A downhole assembly as in Claim 5 wherein said first stabilizer has at least one longitudinal blade and said blade provided with a strain gauge.

7. A downhole assembly as in Claim 5 wherein a second stabilizer is mounted on said section above said first stabilizer, and a load cell means is positioned on the exterior of said section between said first stabilizer and said second stabilizer.

8. A downhole assembly as in Claim 5 including means to measure the side force on said bit perpendicular to its axis.

9. A downhole assembly as in Claim 5 wherein said drill string section comprises a downhole motor having a rotating sub attached to said bit, said sub and said bit forming a rotating unit.

10. A downhole assembly as in Claim 9 wherein said first stabilizer is connected to said downhole motor, a gauge means is mounted on said first stabilizer for measuring the force between said first stabilizer and the wall of the wellbore.

11. A downhole assembly as in Claim 10 including means to transmit to the surface of the earth indications of signals from said load cell means on said rotating unit and gauge means on said stabilizer means.

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