CA2004204A1 - Acoustic data transmission through a drill string - Google Patents
Acoustic data transmission through a drill stringInfo
- Publication number
- CA2004204A1 CA2004204A1 CA 2004204 CA2004204A CA2004204A1 CA 2004204 A1 CA2004204 A1 CA 2004204A1 CA 2004204 CA2004204 CA 2004204 CA 2004204 A CA2004204 A CA 2004204A CA 2004204 A1 CA2004204 A1 CA 2004204A1
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- drill string
- noise
- acoustical
- signal
- data
- Prior art date
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Abstract
ABSTRACT OF THE DISCLOSURE
Acoustical signals arc transmitted through a drill string by canceling upward mov-ing acoustical noise and by preconditioning the data in recognition of the comb filter impedance characteristics of the drill string.
Acoustical signals arc transmitted through a drill string by canceling upward mov-ing acoustical noise and by preconditioning the data in recognition of the comb filter impedance characteristics of the drill string.
Description
2~)04Z04 s-66,6 ACOUSTIC DATA TR.ANSMISSION
THROUGH A DRILL STRING
The United Stntes Go~ernment has rights in this invention pursuant to Contract ~o.
DE-.~Co~-lGDPools~ between the Department of Energ~, and AT~T Technologies, Inc.
BACI;GROIJND OF THE I~-VEl.\TIO~
Tllis in~ csltion rclntes gcnerall~- to a s~ stem for transmitting data along a drill string, S an~ morc particulall~ ~o a s~ stem for transmitting data throu8;h a drill string b~ mod-ulation of i~ltermcdiatc-frcquenc~ acoustic carrier u a~ es.
D~p ttcll:; of tllc t~pe commonlt used for petroleum or ~eothermal exploration are t~l~inllt Icss than 30 cm (1'~ inches) in diameter and on the order of ~ };m (1.5 miles) Ir-llg. Thcse ~clls arc drilled using drill strings assembled from relati~el~ Iight sections 10 (citllcr 30 or ~3 feet long) of drill pipe that are connccted end-to-end by tool joints, ad~litional scctions bcillg a-lded to the uphole end as the hole deepens. The downhole cnd of thc drill string t~picall~ includes a drill collar, a tcad weight assembled from Jectiolls oi rclati~cl,t hcn~ Iengths of uniform diameter collar pipe ha~ing an oterall length oll the ordcr of 300 metcrs (1000 fect). A drill bit is attached to the downllole 1~ end of lhc drill collar, tllc weight of the collar causing thc bit to bite into the earth as tlle ~Irill string is rotated from the surface. Somctimcs, do~nhole mud motors or turI~incs are uscd to turn thc bit. Drilling mud or air is pumped from the surface to the drill hit througll an axial hole in the drill strin6. This fluid rem~es the cuttings from thc holc, pro~id-s a h~drostatic hcad ~hicll controls the form;~tion gases, and ~0 somctimcs pro~ idcs cooling for thc bit.
Communication bctwccn do~nhole sensors of paramctcrs such as pressure or tem~
pcraturc and thc surfacc has long bcen desirable. Various mcthods that ha~ e becn tried for this c-)m~nullication include electromagnctic radiation through thc ground forma~
tion, clcctrical transmission through an insulatcd con(luctor, pressurc pulse propagatio '' ~
. : . . . :. . .
200a~204 S-66,6"7 ~ ~ ~
througll the drilling mud, and acoustic u ave propagation through the metal drill string.
Each of thesc methods has disad antages associated with signal attenuation, ambient noise, high tempcratures, and compatibility with standard drilling procedures. ~ ~`
The most commerci~lly successful of these methods has been the trar~smission of ; ~ `
infor~nation b~ prcssure pulse ;n the trilling mut. However, attenuation mechanisms ~`
in tlle mu~l limit the transmission rate to about 2 to 4 bits per second. -This ini ention is directed towards the acoustical transmission of data through the mct711 drill string. The history of such efforts is recorded in columns 2 - 4 of UT.S. Patcllt ~o. 4,~3,93G, issucd Oct. 6, 1981, of Cox and Chanc~. As reported therein, the first :`
efforts ~crc in thc late 1~0 s b! Sun Oil Compan-, ~hich organization concluded there ~ u too mucll ~ttenl1ation in the drill string for the technolog~ at that time. Another ~ - -compan~- cam~ to thc sarnc conclusion during this period.
I,.S. ratent ~'o. 3,~S'~,2'~S, issued ~Iav 24, lDG¢, of E. Hi~;on concluded thnt thc length of the drill pipes and joints had an effect on the transmission of energ up the 13 drill string. Hix-)n determinet that the ~sa~elength of the transmitted data should be at least t~icc tl~c Icngth of a section of pipc. ;
In 19~S Sun Oil tried again, using repcaters spaced along the drill string and trans-mittin6 in thc bcst frcquenc~ range, one uith attenuation of onl~ 10 dB/1000 feet. A ;
paI)cr b~ Th-)mas Bnrncs et al., UPassbands for Acoustic Transmission in an Ideali%ed ~0 Drill Stringn, Journal of Acoustical Society of Amcrica, ~!ol. 51, ~o. S, 19~'>, pagcs 1û06-1¢08, ~AS consultc(l for an explanAtion of the field-test results, which werc not totall~ consistcnt wi.th the theory. Eventually, Sun went bacl; to r~ndom searching for the best frequcncies for transmission, an unsucccssful procedurc.
The aforcmentioned Cox and Chaney patent concluded from their interpretation of the measured data obtained from a field test in a pctrolcum well that the Barnes model must be in crror, bccause the ccnter of tlle passbands measured b~ Cox and Cllane~
did not agree with the prcdicted passbands of Barnes et al. The patent uses acoustic rcpcaters alon~ the drill string to ensurc transmission of a particular frequency for A
particu];~r length of drill pipe to the surface. ~ ~
'"' 2 ~
,.. , .: . .. , . ~ . , , . . . . - , . , . : . . -:
. :~ . ~ :
ZOO~x04 S-66,6 U. S. Patent No. 4,314,3~5, issued February '~,1982, of C. Petersen et al. discloses a s~stem similar to Hixon for transmitting acoustic ~requencies between 290 Hz and 400 Hz down a drill string.
U. S. Patcnt ~o. 4,390,9l5, issue` June '78, 1983, of E. Shawhan, noted that ring~
o ing in thc drill string could cause a binary "zero" to be mistaken a~ a "one". This patent transmitted data, and then a delay, to allow the transients to ring down before transmitting subsequent data.
U. S. Patent 1\70. 4,~6'~ 9, ijs~led December 31, 19~5, of H. E. Sharp et al., unco~
ere~ the cxistcnce of "fine structure" uithin thc passbands; e.g., Usuch fine structure 10 is in thc natnre of a comb with transmission voids or gaps occurring bet~een tectl rcprescnting transmission bands, both within the ovcrall passbands." Sha~p attributed this structure to Udi~erences in pipe length, conditions of tool joints, and the like." The patent proposcd a complicated phase shiftcd u~a~e with a broader frequency spectrum to bridge thesc gaps.
The prescnt in~ ention is based upon a morc thorou~h consideration of the underlying thcory of acoustical transmission through a drill string. For the first time, the ~ork of Bnrncs ct al. has been anal~zed as a banded structure of thc t~pe discussed by L. Brillouin, Wavc Propagation in Pcriodic Structurc~, ~cGraw-Hill Book Co., NewYorl;, 19~6. The thcoretical results have also becn correlated to extensive laboratory ~n e.xpcrimcnts on scale models of the drill string, and the original data tape obtained from Cox and Chane~ 's field-test has been reanalyzed. This anal~sis shows that Cox and ChaneS's measurcments contain data which is in excellent agreement ~ith thc thcorctical prcdictions; that Sharp misinterpreted the cause of the fine structure; and that the rinsing and the frequency limitations cited b~ Sha- han and Hixon are easil~
'~ o~crcome by signal processing.
Figure 1 shows some of the rcsults of the new analysis of the data recorded by Cox and Chanc~. This figure is a plot of the po- er amplitude versus frequenc~ of thc transmitted signal. The theoretical boundarics bet~cen the passbands and thestopbands are sho~vn by the v ertical dotted lines. If this figure is compared to Figure 1 '' -.... ,`, ' . . ' ' . .. ' ' . , ' ' , . ,, . . . , . 1 .. , .. :. ~,, ' , ,, , ' ...... ', , ," ' . , ' .
20t)420~ S-66,6~7 ~ ~ ~
in Cox and Cllaney's patent, significant and obvious differences can be noted. These are attributable to error in Cox and Chaney's analysis.
Furthermore, this Figure 1 also shows the "fine structure" of Sharp et al. From the new analysis we now kno~ that this fine structure is caused by echos bounc;ng between 5 oppo~ite ends of the drill string, the number of peaks being correlated to the number of sections of drill pipe. A theoretical calculation of this field test was used to produce Figure ~. All of the phenomena important to the transmission of data in the drill string is represented in this calculation. The~e theoretical results accurately predict the location of thc passbands and the fine structure produced by the echo phenomena.
SI~ R~' OF THE IN~'E~\TTIO~
10 It is an object of this invcntion to pro~-ide appAratus and method for transmitting data along a drill string by use of a modulated continuous acoustical carrier wave (wa~es) ~hich is (asc) ccntered within one (scveral) of the passbands of the drill string.
It is a further object of this invention to pro ide a method for transmission at carrier fscqucncies ~ hich ase on the order of several hundreds to se-eral thousands of Hertz 13 in ordcr to minimize thc interference by the noise which i9 generated by the trilling ;
procc~
It is an additional object of this invcntion to pro~ide a system for suppressing the 1 tsansmission of noise within the transmission band or bands.
It is another object of this invention to pro idc a systcm for suppressing echos from ~ ;
~0 thc cnds of the drill string. ~ -It is still another object of this in~ention to pro-ide a system for preconditioning acoustical data for transmission through a passband ha~in~ characteristics determined ~-by the pasamcters of the drill string. ~ , Adtitional objects, atvantages, ant novel fcatures of the invention wjll become ~3 apparent to those skilled in the art upon examination of the following tescription or may be learned by practice of the invention. Thc objccts and ad~ antages of the inven-~æ -.
,. . ~, . ..
200~204 S-66,6 tion ma~ be realized and attained by means of the instrumentalities and combinations `~
. .. - - .
particularly pointed out in the appended claims. -;
To achie~ e the foregoing and other objects, aIld in accordance with the purpose of the present in ention, as embodied arid broadly described herein, the present int ention may comprise transrnitt;ng means for coupling data to a drill string near a first end of said drill string for acoustical transmission to a second end of said drill string; anti~
noise mearis near the first end of said drill string for preventing acoustical noise from the first end from being transmitted through the drill stnng to the second end; and recei-ing means near the second end for recei-ing the acoustically transmitted data. ~ -In addition, the in~ention mav further comprise a method comprising the steps of preconditioning the data to counteract distortions caused by the drill string, the distortions corresponding to the effects of multiple passbands and stopbands ha-ing charactcristics depcndent upon the properties of the drill string; applying the precon- .
ditioncd data to a first end of the drill string; and detecting the data at a second end of the drill string.
~. , BRIEF DESCRIPTION OF THE DR~ INGS
. . -Thc accompnnying drawin6s, which nre incorporated in and form part of the spec-i~Scation, illustrate an embodiment of the present in~ention and, to6ether with thc description, ser-c to e~cplain the principles of the in~ention. -~
Fig. 1 shows the measured frequency response within two passbands of the Cox-and-Chaney dr;ll string.
Fig. 2 shows the calculated ~rcquency response uithin tr~o passbands of the Cox~
and-Chancy drill string.
Fig. 3 shows a drill string.
Fig. 4 sho~s dispersion cur~cs for a uniform string (dashed line) and a typical drill string (solid line).
..''''' Z00a~204 S-66,62 Fig. 5 shows the transrmission arrangement at a first end of a drill string.
DETAILED DESCRIPTION
As shou n in Figure 3, this invention involves the transmission of acoustical tata along a drill string 10 which consists of a plurality of lengths of constant diameter drill pipe lS fastened end-to-end at thicker diameter joint portions 18 by means of screw threads 5 a~ is well kno~n in this art. Lower end 12 of drill string 10 may include a length of constant diameter drill collar to provide downward force to drill bit 22. A constant diamctcr mud channel 2g extends axiall~ through each component of drill string 10 to pro~ide a path for drilling mud to be pumped from the surface at upper end 14through holes in drill bit 22 as is well known in this art. The upper end 14 of drill 10 string 10 is terminated in contentional structure such as a derrick, rotary pinion, and kelly, represented by box 25, to permit additional lengths of drill pipe to be added to the string, and the string to be rotated for drilling. Details of this con~ entional string structure ma~ be fount in the aforementionet patent of E. Hixon.
Although the disclosure is tirected towards transmitting data from the lower end1~ to tlle upper cnd, it is to be understood that the teachings of this invention apply to data transmission in either direction.
The th-or~ upon ~hich this in ention is based bcgins ~ith the deri-~tion the fol~
lowing E~luation 1, which equation is in the form of a classical wa e equation:
~2F 2~2F (1) where impedance 2 = pac, and total axial force F(:~,t) =--c:~ where p is density, ~O a is area, and c is speed of sound over a cross-section of a slender, elastic, rod, u is the displacemcnt, 1: is the position, m is the Lagrangian mass coordinate, and t is the time.
The existcncc of frequency bands which block propagation of acoustic energy is dcmonstratcd for an idealized drill string where each piece of drill pipe consists of a . :. . ,: , .
- . . .
200420~ S-66,6' tube of length dl, mass density p" cross-sectional area al, speed of sound cl, and mass rl; and a tool joint of length d2, mass density P2. cross-sectional area a2, speed of sound c2, and mass r2. A procedure demonstrated at page 180 of Brillouin has been used with ~ `~
the Floquet theorem to generate the following eigenvalue problem:
zl Z2 Z2 Al/z 1 -1 1 --1 Bl/zl = (2) zle~r~ 21e~ z2e-a2r2 .~,2e~~2~ --Al~ 2 o elrl _e/~rl e-a2r~ _e_/3~r~ --B~ 2 o erc z~ = p~a~c~ (3) .
a~ = i (kd/r--1;~,) (4) i (kd/r + ~
Here k is thc w a~ e number, i = ~ , r = rl + r2~ d = dl + d2, ~ = '),. f, Iir = w/;~, and f is the frequency being transmittet. This equation is seen to be similar to Equation lS of Barncs et al., except the present examination shous Barnes' UW" to be kd.
Brillouh sho~vs that frequencies which ~ield real solutions for k are banded andseparated by frequcncy barlds which ~ield complex solutions for k. He calls these `
t~vo types of regions passbands and stopbands. The attenuation in the stopbands is gencrally quite large. W;thin each of the passbands the alue of the phase ~elocity ` ~
w/k depcnds upon the ~ralue of . Thc drill string functions AS an acoustic comb filter, "; ~ -1~ and îrcquencics which propagate in the passb?nds are dispersed. Thus, signals which have broad fre(luency spectra are se-erel~ distorted b~ passage through a drill string.
Ho~vever, signal processing tcchniques can be used to remo e this distortion. ~ ~ ;
It is to lx understood that the Ucomb filter~ re*renced above refers to the gross structure in the frcquency spectrum which is produced b~ the stopbands and the pass- -. . .. .
7 ~ ~ ;
,:. ......
.
20()~2C)4 S-66,6'77 bands, where each tooth of the comb is an individual passband. In contrast, Sharp's reference to a comb refers to a fine structure which exists within each passband.
Figure 4 shows a plot of the characteristic determinate of Equation ~ using values for p~, a~, c~, and d,~ representati~e of actual drill pipe parameters. The straight dotted ;~ line repre~ents the solution for a uni~orm drill Jtring, e.g., one where the tiameter of the joints is equal to the diameter of the pipe. The velocity of propagation for a gi-en frequency is represented by the phase velocity. For the uniform drill string, this ratio is constant and equal to the bar velocitv of steel. When wa~es containing multiple frequcncy components tra~rel through a uniform drill str;ng (or drill collar 20), they to 10 not distort as all frequency components remain in the same relati~e position.A different result occurs ~ hcn the plot of Fig. 4 is cur~e~l, as each ~requenc~ then tra~ els at a different speed. The solid lines of Fig. 4 reprcscnt the solution to Equation '~
for a rcalistic drill string where the area of the drill pipe ;s 24;)0 mm2 (4 in2) and the area of a tool joint is 1~,900 mm2 (20 in2). In this situation, the phase ~relocity ~ithin 13each passband i~ curred, meaning that distortion exists. ~ ~ -Furtl~ermore, the gaps represent stopbants. This analysis predicts the same values -for the boundaries betwecn the stopbands and the passbands as that of Barnes et -al.; ho~ever, ;t also shows the characteristics of ware propagation within each of the passbands. BArnes et al. did not predict the distortion resulting from the effects of the '~0 passbands.
Calculations using a smaller diameter tool joint, representati~re of the reduction in diameter tllat occurs from wear, shows the stopbands to be narrower. This change is to be expected, because the worn joints bring the string geometry closer to the uniform gcometry that produced the straight, dotted, line of Fig. 4.
2~Further calcul,ltions show that strings comprised of random length pipes will ha~ e significantly narrowed passbands. This result corresponds with, and for the first time explains, obserrations made bs others.
Since thc transmission of acoustical data through the drill string in~ol~es sending ~vares with complcx transient shapes through strings of finite length, transient ware ~ ~
8 ~.
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~ .
,. .... .. .. . . .. . ... . . . ..
. . ,. ... . ... . ~ . , . ~ .
.; . : .~
. ' . . ~, .
200A;~04 S-6G,6~
analysis has been used to predict the perforrnance of the drill string. Fig. 2 shows the third and fourth passbands of a fast Fourier transform of the ~haveform which results from a signal which represents, to a rough approximation, the hammer blow used in the Cox and Chaney fidd test. This signal has a relati~ely narrow frequency content 5 which only stimulates the third ant fourth passband of the drill string. Ten sections of drill pipe were used in this field test, and the ends of the trill string produced nearly perfect reflection of the acoustic waYes which resulted from the hammer blows.
This figure sho~s the Ufine structure" of Sharp et al. to be caused by standing uar,e resonanccs within the drill string. The number of spil;es in each passband correlates 10 ~itll thc number of sections of pipe in the dri~l string, as explained in greater detail in the ~ppendix.
The anal~ sis suggests the following technique for processing data signals and com-pensating ~or the effects of the stopbands and dispersion. First, transmit inforrmation continuousl~ (as opposed to a broad-band pulse mode) and only within the passbands 13 and awa~ from thc edges of the stopbands. Second, compensate for dispersion b~ mul-tipl~ing each frequency component by exp(-ikL), whcre L is the transmission length in the drill pipe scction 18 of the drill string. Where a large arnount of acoustical noise i8 prcscnt, such as would be caused b~ a drill bit or drill mud, it is preferable to transform the data signal before transmission, resulting in an undispersed signal at the ')O recei~ cr position.
The foregoin6 analgsis ;J based on the assumption that echos are suppre~sed at each cnd of the clrill string. This is necessary to eliminate the spil;es or fine structure within each of thc pass~ands. It is common kno~vledge that signal processing is efEecti~ e ~ hen echo strength is "0 dB below the the signal level. Each time the acoustic uave interacts '~o with the interscction of the drill pipe and the drill collar 80, the signal weal;ens by 6 dB. Also, from the analysis of Cox and Chane~ 's field test, the signal attenuates about " dB/1000 feet. Therefore, an echo ~vhich is generated b~ a reflection of the data signal at thc top of the drill string 1~ will lose 6 + 4L dB as it tra~els back down the drill string to 80 and then returns to the recei~rer. Thus, if the drill pipe section has a length . . ., - . -- : . . .
. : . ~ , . . ..
X004204 S-66,6"l of 3500 feet or more, the echos ~om the receiving end of the string will be naturally attenuated to an acceptable level.
For shorter drill strings, additional echo suppression will be required. This can be accomplished with i device called a terminating tra~sducer. This te~ice has an 5 acoustical impedance which matches the acoustical impetance of the drill string and an acoustical 10s9 factor which is sufficient to make up the required 20 dB of echo suppression.
Because attenuation in the drill string is low, the energy velocity and group velocity are appro~;imately equal. Thercfore, the characteristic impedance of the drill string is 10 the orce F di~idcd by velocity ~. This alue is the eigen~alue part of Equation 2, a complex number with a real part called the viscous component and an imaginar~
part called the elastic component. Ideall--, the terminating transducers must ha~e a stiffness equal to the elastic component and a damping coefflcient equal to the viscous compone3t. PracticallS, tbe response need only make up the difference between ~0 tB
15 and the natural attenuation of the drill string.
The charactcristic imp~edance is a function of frequenc~ and position, the position dependence being periodic in accordance with the period of the drill string. Calculations sho~ that tool joints are not a good location for a tersnination because the impedance is a sensitive function of position. For the fourth passband, a location 1/3 or '~/3 ~long ~0 the pipe is bcttcr.
The design of tcrmination transducers is a con~ entional problem to those of ordinan sk;ll in that art pro~idet with the impedance data from Equation 2. This device, for example, could consist of a ring of polarized PZT ceramic elements and an electronic circuit ~ hose reacti-e and resisti-e components are adjusted to tune the transducer to '~ the characteristic impcdance of the drill string and pro~ ide the necessary acoustic loss factor.
Echo suppression is a more critical problem at the downhole end of the drill string ~vherc echos travel freely up and down the drill collar section and confuse the transmis-sion of data. At this location, it is useful to use noise cancellation techniques both to ' ~
, ,, ~ - - :: . :
'~ ' . '. ' . , . . ~ ;.:;
200~204 S-6~,6'7 l suppress echos and to prevent the noise of the drill bit or drilling mud from interfering with the desired data signal uphole. A noise cancellation technique for use with this invention is disclosed hereinafter.
Fig. 5 shows a section 30 of drill collar 20 located relatively close to downhole end 12 of drill string 10 and containing apparatus for transmitting a data signal towards ~-the other end of the drill string while suppressing the transmissiori of acoustical noise up the drill string. In particular, this apparatus includes a transmitter 40 for transrnitting data uphole, but not downhole, a sensor 50 for detecting acoustical noise from do~t nhole and appl~-ing it to transmitter 40 to cancel the uphole transmission of the noise, and a sensor 60 for pro~iding adaptive control to transmitter 40 and sensor 50 to minimize uphole transn~ission of noise. ~ ~ -Transmitter 40 includes a pair of spaced transducers 42, 44 for conterting an clcctrical input signal into aco~lstical energy in drill collar 30. Each transducer ma~
bc a m~gnetostricti~ c ring element with a winding of insulated conducting wire. These ; ~;
13 tranJduccrs are spaced ~part a distance b equal to one quarter wa~elength of the center frequency of the passband selected for transmission. A data signal from source 28 is applied tirectly to uphole transducer 44, preferably through a summing circuit 4G.
Tbe data signal is also applied to transducer 42 through a dela~ circuit 47 and an in~ertin,g circuit 48. Delay circuit 47 ha~ a dela~ alue equal to distance ~ di~ided b~
'~0 the speed of sound in drill collar 30 at transmitter 40. ~ ~ -The operation of this transrnitter may be understood from the following explanation.
Each of transducers 42, 44 provide an acoustical signal F~, F4 that tra ~els Soth uphole and do~nhole. Accortlingl~ the resulting upward and downward wa~es from both transducers are:
~U(t~ ~) = F2(t - ~/C) + F4(t ~ b)/c)) where ~ > b (6) ¢~d(t,~) = F2(t+~:/c)+ F4(t+(r--b)/c)) where ~<O
~5 wherc ~: is the uphole distance from transducer 42 and c is the speed of sound. For 11 ,. , ~, S-60,62 no downward wa~re, ~d(t, 2) = O, or ;
F2(t) =--F4(t--b/c) (7) ;~
and ;~;
¢~u(t, ~) =--F2(t--(~ + b)/c) + F2(t--(~--b)/c) (c') If the acoustical signal F2 has the form A cos(wt), then Equation 8 sol~es to ~u(r) =--2-4sin(~b/c)sin(~r) (9) w here r = (t--~/c).
THROUGH A DRILL STRING
The United Stntes Go~ernment has rights in this invention pursuant to Contract ~o.
DE-.~Co~-lGDPools~ between the Department of Energ~, and AT~T Technologies, Inc.
BACI;GROIJND OF THE I~-VEl.\TIO~
Tllis in~ csltion rclntes gcnerall~- to a s~ stem for transmitting data along a drill string, S an~ morc particulall~ ~o a s~ stem for transmitting data throu8;h a drill string b~ mod-ulation of i~ltermcdiatc-frcquenc~ acoustic carrier u a~ es.
D~p ttcll:; of tllc t~pe commonlt used for petroleum or ~eothermal exploration are t~l~inllt Icss than 30 cm (1'~ inches) in diameter and on the order of ~ };m (1.5 miles) Ir-llg. Thcse ~clls arc drilled using drill strings assembled from relati~el~ Iight sections 10 (citllcr 30 or ~3 feet long) of drill pipe that are connccted end-to-end by tool joints, ad~litional scctions bcillg a-lded to the uphole end as the hole deepens. The downhole cnd of thc drill string t~picall~ includes a drill collar, a tcad weight assembled from Jectiolls oi rclati~cl,t hcn~ Iengths of uniform diameter collar pipe ha~ing an oterall length oll the ordcr of 300 metcrs (1000 fect). A drill bit is attached to the downllole 1~ end of lhc drill collar, tllc weight of the collar causing thc bit to bite into the earth as tlle ~Irill string is rotated from the surface. Somctimcs, do~nhole mud motors or turI~incs are uscd to turn thc bit. Drilling mud or air is pumped from the surface to the drill hit througll an axial hole in the drill strin6. This fluid rem~es the cuttings from thc holc, pro~id-s a h~drostatic hcad ~hicll controls the form;~tion gases, and ~0 somctimcs pro~ idcs cooling for thc bit.
Communication bctwccn do~nhole sensors of paramctcrs such as pressure or tem~
pcraturc and thc surfacc has long bcen desirable. Various mcthods that ha~ e becn tried for this c-)m~nullication include electromagnctic radiation through thc ground forma~
tion, clcctrical transmission through an insulatcd con(luctor, pressurc pulse propagatio '' ~
. : . . . :. . .
200a~204 S-66,6"7 ~ ~ ~
througll the drilling mud, and acoustic u ave propagation through the metal drill string.
Each of thesc methods has disad antages associated with signal attenuation, ambient noise, high tempcratures, and compatibility with standard drilling procedures. ~ ~`
The most commerci~lly successful of these methods has been the trar~smission of ; ~ `
infor~nation b~ prcssure pulse ;n the trilling mut. However, attenuation mechanisms ~`
in tlle mu~l limit the transmission rate to about 2 to 4 bits per second. -This ini ention is directed towards the acoustical transmission of data through the mct711 drill string. The history of such efforts is recorded in columns 2 - 4 of UT.S. Patcllt ~o. 4,~3,93G, issucd Oct. 6, 1981, of Cox and Chanc~. As reported therein, the first :`
efforts ~crc in thc late 1~0 s b! Sun Oil Compan-, ~hich organization concluded there ~ u too mucll ~ttenl1ation in the drill string for the technolog~ at that time. Another ~ - -compan~- cam~ to thc sarnc conclusion during this period.
I,.S. ratent ~'o. 3,~S'~,2'~S, issued ~Iav 24, lDG¢, of E. Hi~;on concluded thnt thc length of the drill pipes and joints had an effect on the transmission of energ up the 13 drill string. Hix-)n determinet that the ~sa~elength of the transmitted data should be at least t~icc tl~c Icngth of a section of pipc. ;
In 19~S Sun Oil tried again, using repcaters spaced along the drill string and trans-mittin6 in thc bcst frcquenc~ range, one uith attenuation of onl~ 10 dB/1000 feet. A ;
paI)cr b~ Th-)mas Bnrncs et al., UPassbands for Acoustic Transmission in an Ideali%ed ~0 Drill Stringn, Journal of Acoustical Society of Amcrica, ~!ol. 51, ~o. S, 19~'>, pagcs 1û06-1¢08, ~AS consultc(l for an explanAtion of the field-test results, which werc not totall~ consistcnt wi.th the theory. Eventually, Sun went bacl; to r~ndom searching for the best frequcncies for transmission, an unsucccssful procedurc.
The aforcmentioned Cox and Chaney patent concluded from their interpretation of the measured data obtained from a field test in a pctrolcum well that the Barnes model must be in crror, bccause the ccnter of tlle passbands measured b~ Cox and Cllane~
did not agree with the prcdicted passbands of Barnes et al. The patent uses acoustic rcpcaters alon~ the drill string to ensurc transmission of a particular frequency for A
particu];~r length of drill pipe to the surface. ~ ~
'"' 2 ~
,.. , .: . .. , . ~ . , , . . . . - , . , . : . . -:
. :~ . ~ :
ZOO~x04 S-66,6 U. S. Patent No. 4,314,3~5, issued February '~,1982, of C. Petersen et al. discloses a s~stem similar to Hixon for transmitting acoustic ~requencies between 290 Hz and 400 Hz down a drill string.
U. S. Patcnt ~o. 4,390,9l5, issue` June '78, 1983, of E. Shawhan, noted that ring~
o ing in thc drill string could cause a binary "zero" to be mistaken a~ a "one". This patent transmitted data, and then a delay, to allow the transients to ring down before transmitting subsequent data.
U. S. Patent 1\70. 4,~6'~ 9, ijs~led December 31, 19~5, of H. E. Sharp et al., unco~
ere~ the cxistcnce of "fine structure" uithin thc passbands; e.g., Usuch fine structure 10 is in thc natnre of a comb with transmission voids or gaps occurring bet~een tectl rcprescnting transmission bands, both within the ovcrall passbands." Sha~p attributed this structure to Udi~erences in pipe length, conditions of tool joints, and the like." The patent proposcd a complicated phase shiftcd u~a~e with a broader frequency spectrum to bridge thesc gaps.
The prescnt in~ ention is based upon a morc thorou~h consideration of the underlying thcory of acoustical transmission through a drill string. For the first time, the ~ork of Bnrncs ct al. has been anal~zed as a banded structure of thc t~pe discussed by L. Brillouin, Wavc Propagation in Pcriodic Structurc~, ~cGraw-Hill Book Co., NewYorl;, 19~6. The thcoretical results have also becn correlated to extensive laboratory ~n e.xpcrimcnts on scale models of the drill string, and the original data tape obtained from Cox and Chane~ 's field-test has been reanalyzed. This anal~sis shows that Cox and ChaneS's measurcments contain data which is in excellent agreement ~ith thc thcorctical prcdictions; that Sharp misinterpreted the cause of the fine structure; and that the rinsing and the frequency limitations cited b~ Sha- han and Hixon are easil~
'~ o~crcome by signal processing.
Figure 1 shows some of the rcsults of the new analysis of the data recorded by Cox and Chanc~. This figure is a plot of the po- er amplitude versus frequenc~ of thc transmitted signal. The theoretical boundarics bet~cen the passbands and thestopbands are sho~vn by the v ertical dotted lines. If this figure is compared to Figure 1 '' -.... ,`, ' . . ' ' . .. ' ' . , ' ' , . ,, . . . , . 1 .. , .. :. ~,, ' , ,, , ' ...... ', , ," ' . , ' .
20t)420~ S-66,6~7 ~ ~ ~
in Cox and Cllaney's patent, significant and obvious differences can be noted. These are attributable to error in Cox and Chaney's analysis.
Furthermore, this Figure 1 also shows the "fine structure" of Sharp et al. From the new analysis we now kno~ that this fine structure is caused by echos bounc;ng between 5 oppo~ite ends of the drill string, the number of peaks being correlated to the number of sections of drill pipe. A theoretical calculation of this field test was used to produce Figure ~. All of the phenomena important to the transmission of data in the drill string is represented in this calculation. The~e theoretical results accurately predict the location of thc passbands and the fine structure produced by the echo phenomena.
SI~ R~' OF THE IN~'E~\TTIO~
10 It is an object of this invcntion to pro~-ide appAratus and method for transmitting data along a drill string by use of a modulated continuous acoustical carrier wave (wa~es) ~hich is (asc) ccntered within one (scveral) of the passbands of the drill string.
It is a further object of this invention to pro ide a method for transmission at carrier fscqucncies ~ hich ase on the order of several hundreds to se-eral thousands of Hertz 13 in ordcr to minimize thc interference by the noise which i9 generated by the trilling ;
procc~
It is an additional object of this invcntion to pro~ide a system for suppressing the 1 tsansmission of noise within the transmission band or bands.
It is another object of this invention to pro idc a systcm for suppressing echos from ~ ;
~0 thc cnds of the drill string. ~ -It is still another object of this in~ention to pro-ide a system for preconditioning acoustical data for transmission through a passband ha~in~ characteristics determined ~-by the pasamcters of the drill string. ~ , Adtitional objects, atvantages, ant novel fcatures of the invention wjll become ~3 apparent to those skilled in the art upon examination of the following tescription or may be learned by practice of the invention. Thc objccts and ad~ antages of the inven-~æ -.
,. . ~, . ..
200~204 S-66,6 tion ma~ be realized and attained by means of the instrumentalities and combinations `~
. .. - - .
particularly pointed out in the appended claims. -;
To achie~ e the foregoing and other objects, aIld in accordance with the purpose of the present in ention, as embodied arid broadly described herein, the present int ention may comprise transrnitt;ng means for coupling data to a drill string near a first end of said drill string for acoustical transmission to a second end of said drill string; anti~
noise mearis near the first end of said drill string for preventing acoustical noise from the first end from being transmitted through the drill stnng to the second end; and recei-ing means near the second end for recei-ing the acoustically transmitted data. ~ -In addition, the in~ention mav further comprise a method comprising the steps of preconditioning the data to counteract distortions caused by the drill string, the distortions corresponding to the effects of multiple passbands and stopbands ha-ing charactcristics depcndent upon the properties of the drill string; applying the precon- .
ditioncd data to a first end of the drill string; and detecting the data at a second end of the drill string.
~. , BRIEF DESCRIPTION OF THE DR~ INGS
. . -Thc accompnnying drawin6s, which nre incorporated in and form part of the spec-i~Scation, illustrate an embodiment of the present in~ention and, to6ether with thc description, ser-c to e~cplain the principles of the in~ention. -~
Fig. 1 shows the measured frequency response within two passbands of the Cox-and-Chaney dr;ll string.
Fig. 2 shows the calculated ~rcquency response uithin tr~o passbands of the Cox~
and-Chancy drill string.
Fig. 3 shows a drill string.
Fig. 4 sho~s dispersion cur~cs for a uniform string (dashed line) and a typical drill string (solid line).
..''''' Z00a~204 S-66,62 Fig. 5 shows the transrmission arrangement at a first end of a drill string.
DETAILED DESCRIPTION
As shou n in Figure 3, this invention involves the transmission of acoustical tata along a drill string 10 which consists of a plurality of lengths of constant diameter drill pipe lS fastened end-to-end at thicker diameter joint portions 18 by means of screw threads 5 a~ is well kno~n in this art. Lower end 12 of drill string 10 may include a length of constant diameter drill collar to provide downward force to drill bit 22. A constant diamctcr mud channel 2g extends axiall~ through each component of drill string 10 to pro~ide a path for drilling mud to be pumped from the surface at upper end 14through holes in drill bit 22 as is well known in this art. The upper end 14 of drill 10 string 10 is terminated in contentional structure such as a derrick, rotary pinion, and kelly, represented by box 25, to permit additional lengths of drill pipe to be added to the string, and the string to be rotated for drilling. Details of this con~ entional string structure ma~ be fount in the aforementionet patent of E. Hixon.
Although the disclosure is tirected towards transmitting data from the lower end1~ to tlle upper cnd, it is to be understood that the teachings of this invention apply to data transmission in either direction.
The th-or~ upon ~hich this in ention is based bcgins ~ith the deri-~tion the fol~
lowing E~luation 1, which equation is in the form of a classical wa e equation:
~2F 2~2F (1) where impedance 2 = pac, and total axial force F(:~,t) =--c:~ where p is density, ~O a is area, and c is speed of sound over a cross-section of a slender, elastic, rod, u is the displacemcnt, 1: is the position, m is the Lagrangian mass coordinate, and t is the time.
The existcncc of frequency bands which block propagation of acoustic energy is dcmonstratcd for an idealized drill string where each piece of drill pipe consists of a . :. . ,: , .
- . . .
200420~ S-66,6' tube of length dl, mass density p" cross-sectional area al, speed of sound cl, and mass rl; and a tool joint of length d2, mass density P2. cross-sectional area a2, speed of sound c2, and mass r2. A procedure demonstrated at page 180 of Brillouin has been used with ~ `~
the Floquet theorem to generate the following eigenvalue problem:
zl Z2 Z2 Al/z 1 -1 1 --1 Bl/zl = (2) zle~r~ 21e~ z2e-a2r2 .~,2e~~2~ --Al~ 2 o elrl _e/~rl e-a2r~ _e_/3~r~ --B~ 2 o erc z~ = p~a~c~ (3) .
a~ = i (kd/r--1;~,) (4) i (kd/r + ~
Here k is thc w a~ e number, i = ~ , r = rl + r2~ d = dl + d2, ~ = '),. f, Iir = w/;~, and f is the frequency being transmittet. This equation is seen to be similar to Equation lS of Barncs et al., except the present examination shous Barnes' UW" to be kd.
Brillouh sho~vs that frequencies which ~ield real solutions for k are banded andseparated by frequcncy barlds which ~ield complex solutions for k. He calls these `
t~vo types of regions passbands and stopbands. The attenuation in the stopbands is gencrally quite large. W;thin each of the passbands the alue of the phase ~elocity ` ~
w/k depcnds upon the ~ralue of . Thc drill string functions AS an acoustic comb filter, "; ~ -1~ and îrcquencics which propagate in the passb?nds are dispersed. Thus, signals which have broad fre(luency spectra are se-erel~ distorted b~ passage through a drill string.
Ho~vever, signal processing tcchniques can be used to remo e this distortion. ~ ~ ;
It is to lx understood that the Ucomb filter~ re*renced above refers to the gross structure in the frcquency spectrum which is produced b~ the stopbands and the pass- -. . .. .
7 ~ ~ ;
,:. ......
.
20()~2C)4 S-66,6'77 bands, where each tooth of the comb is an individual passband. In contrast, Sharp's reference to a comb refers to a fine structure which exists within each passband.
Figure 4 shows a plot of the characteristic determinate of Equation ~ using values for p~, a~, c~, and d,~ representati~e of actual drill pipe parameters. The straight dotted ;~ line repre~ents the solution for a uni~orm drill Jtring, e.g., one where the tiameter of the joints is equal to the diameter of the pipe. The velocity of propagation for a gi-en frequency is represented by the phase velocity. For the uniform drill string, this ratio is constant and equal to the bar velocitv of steel. When wa~es containing multiple frequcncy components tra~rel through a uniform drill str;ng (or drill collar 20), they to 10 not distort as all frequency components remain in the same relati~e position.A different result occurs ~ hcn the plot of Fig. 4 is cur~e~l, as each ~requenc~ then tra~ els at a different speed. The solid lines of Fig. 4 reprcscnt the solution to Equation '~
for a rcalistic drill string where the area of the drill pipe ;s 24;)0 mm2 (4 in2) and the area of a tool joint is 1~,900 mm2 (20 in2). In this situation, the phase ~relocity ~ithin 13each passband i~ curred, meaning that distortion exists. ~ ~ -Furtl~ermore, the gaps represent stopbants. This analysis predicts the same values -for the boundaries betwecn the stopbands and the passbands as that of Barnes et -al.; ho~ever, ;t also shows the characteristics of ware propagation within each of the passbands. BArnes et al. did not predict the distortion resulting from the effects of the '~0 passbands.
Calculations using a smaller diameter tool joint, representati~re of the reduction in diameter tllat occurs from wear, shows the stopbands to be narrower. This change is to be expected, because the worn joints bring the string geometry closer to the uniform gcometry that produced the straight, dotted, line of Fig. 4.
2~Further calcul,ltions show that strings comprised of random length pipes will ha~ e significantly narrowed passbands. This result corresponds with, and for the first time explains, obserrations made bs others.
Since thc transmission of acoustical data through the drill string in~ol~es sending ~vares with complcx transient shapes through strings of finite length, transient ware ~ ~
8 ~.
. . .
~ .
,. .... .. .. . . .. . ... . . . ..
. . ,. ... . ... . ~ . , . ~ .
.; . : .~
. ' . . ~, .
200A;~04 S-6G,6~
analysis has been used to predict the perforrnance of the drill string. Fig. 2 shows the third and fourth passbands of a fast Fourier transform of the ~haveform which results from a signal which represents, to a rough approximation, the hammer blow used in the Cox and Chaney fidd test. This signal has a relati~ely narrow frequency content 5 which only stimulates the third ant fourth passband of the drill string. Ten sections of drill pipe were used in this field test, and the ends of the trill string produced nearly perfect reflection of the acoustic waYes which resulted from the hammer blows.
This figure sho~s the Ufine structure" of Sharp et al. to be caused by standing uar,e resonanccs within the drill string. The number of spil;es in each passband correlates 10 ~itll thc number of sections of pipe in the dri~l string, as explained in greater detail in the ~ppendix.
The anal~ sis suggests the following technique for processing data signals and com-pensating ~or the effects of the stopbands and dispersion. First, transmit inforrmation continuousl~ (as opposed to a broad-band pulse mode) and only within the passbands 13 and awa~ from thc edges of the stopbands. Second, compensate for dispersion b~ mul-tipl~ing each frequency component by exp(-ikL), whcre L is the transmission length in the drill pipe scction 18 of the drill string. Where a large arnount of acoustical noise i8 prcscnt, such as would be caused b~ a drill bit or drill mud, it is preferable to transform the data signal before transmission, resulting in an undispersed signal at the ')O recei~ cr position.
The foregoin6 analgsis ;J based on the assumption that echos are suppre~sed at each cnd of the clrill string. This is necessary to eliminate the spil;es or fine structure within each of thc pass~ands. It is common kno~vledge that signal processing is efEecti~ e ~ hen echo strength is "0 dB below the the signal level. Each time the acoustic uave interacts '~o with the interscction of the drill pipe and the drill collar 80, the signal weal;ens by 6 dB. Also, from the analysis of Cox and Chane~ 's field test, the signal attenuates about " dB/1000 feet. Therefore, an echo ~vhich is generated b~ a reflection of the data signal at thc top of the drill string 1~ will lose 6 + 4L dB as it tra~els back down the drill string to 80 and then returns to the recei~rer. Thus, if the drill pipe section has a length . . ., - . -- : . . .
. : . ~ , . . ..
X004204 S-66,6"l of 3500 feet or more, the echos ~om the receiving end of the string will be naturally attenuated to an acceptable level.
For shorter drill strings, additional echo suppression will be required. This can be accomplished with i device called a terminating tra~sducer. This te~ice has an 5 acoustical impedance which matches the acoustical impetance of the drill string and an acoustical 10s9 factor which is sufficient to make up the required 20 dB of echo suppression.
Because attenuation in the drill string is low, the energy velocity and group velocity are appro~;imately equal. Thercfore, the characteristic impedance of the drill string is 10 the orce F di~idcd by velocity ~. This alue is the eigen~alue part of Equation 2, a complex number with a real part called the viscous component and an imaginar~
part called the elastic component. Ideall--, the terminating transducers must ha~e a stiffness equal to the elastic component and a damping coefflcient equal to the viscous compone3t. PracticallS, tbe response need only make up the difference between ~0 tB
15 and the natural attenuation of the drill string.
The charactcristic imp~edance is a function of frequenc~ and position, the position dependence being periodic in accordance with the period of the drill string. Calculations sho~ that tool joints are not a good location for a tersnination because the impedance is a sensitive function of position. For the fourth passband, a location 1/3 or '~/3 ~long ~0 the pipe is bcttcr.
The design of tcrmination transducers is a con~ entional problem to those of ordinan sk;ll in that art pro~idet with the impedance data from Equation 2. This device, for example, could consist of a ring of polarized PZT ceramic elements and an electronic circuit ~ hose reacti-e and resisti-e components are adjusted to tune the transducer to '~ the characteristic impcdance of the drill string and pro~ ide the necessary acoustic loss factor.
Echo suppression is a more critical problem at the downhole end of the drill string ~vherc echos travel freely up and down the drill collar section and confuse the transmis-sion of data. At this location, it is useful to use noise cancellation techniques both to ' ~
, ,, ~ - - :: . :
'~ ' . '. ' . , . . ~ ;.:;
200~204 S-6~,6'7 l suppress echos and to prevent the noise of the drill bit or drilling mud from interfering with the desired data signal uphole. A noise cancellation technique for use with this invention is disclosed hereinafter.
Fig. 5 shows a section 30 of drill collar 20 located relatively close to downhole end 12 of drill string 10 and containing apparatus for transmitting a data signal towards ~-the other end of the drill string while suppressing the transmissiori of acoustical noise up the drill string. In particular, this apparatus includes a transmitter 40 for transrnitting data uphole, but not downhole, a sensor 50 for detecting acoustical noise from do~t nhole and appl~-ing it to transmitter 40 to cancel the uphole transmission of the noise, and a sensor 60 for pro~iding adaptive control to transmitter 40 and sensor 50 to minimize uphole transn~ission of noise. ~ ~ -Transmitter 40 includes a pair of spaced transducers 42, 44 for conterting an clcctrical input signal into aco~lstical energy in drill collar 30. Each transducer ma~
bc a m~gnetostricti~ c ring element with a winding of insulated conducting wire. These ; ~;
13 tranJduccrs are spaced ~part a distance b equal to one quarter wa~elength of the center frequency of the passband selected for transmission. A data signal from source 28 is applied tirectly to uphole transducer 44, preferably through a summing circuit 4G.
Tbe data signal is also applied to transducer 42 through a dela~ circuit 47 and an in~ertin,g circuit 48. Delay circuit 47 ha~ a dela~ alue equal to distance ~ di~ided b~
'~0 the speed of sound in drill collar 30 at transmitter 40. ~ ~ -The operation of this transrnitter may be understood from the following explanation.
Each of transducers 42, 44 provide an acoustical signal F~, F4 that tra ~els Soth uphole and do~nhole. Accortlingl~ the resulting upward and downward wa~es from both transducers are:
~U(t~ ~) = F2(t - ~/C) + F4(t ~ b)/c)) where ~ > b (6) ¢~d(t,~) = F2(t+~:/c)+ F4(t+(r--b)/c)) where ~<O
~5 wherc ~: is the uphole distance from transducer 42 and c is the speed of sound. For 11 ,. , ~, S-60,62 no downward wa~re, ~d(t, 2) = O, or ;
F2(t) =--F4(t--b/c) (7) ;~
and ;~;
¢~u(t, ~) =--F2(t--(~ + b)/c) + F2(t--(~--b)/c) (c') If the acoustical signal F2 has the form A cos(wt), then Equation 8 sol~es to ~u(r) =--2-4sin(~b/c)sin(~r) (9) w here r = (t--~/c).
3 Accordingly, with a quarter wa~ elength spac;ng for ~ a~ es at the center of the trans-mission passband, transmitter 40 transmits an uphole signal ha~ing approximatelyt~ice thc amplitute A of the applied signal, ant no downhole signal.
Noise scnsor 50 includes a pair of spaced sensors 52, 54 which operate in a similar ~ . ~
manner to provite an indication of acoustic energy moting uphole, and no indication of enorlcy mo~ing downhole. The output of sensor 52, which sensor may be an accelerom-cter or strain gauge, is an electrical signal that is summed ;n summing circuit 56 with the output of similar sensor 54, ~ hich output is delayed by delay circuit 57 and and inverted by in~erting circuit 58. If the delay of circuit 57 is equal to the spacing di~ited by the speed of sound c, downward moYing energy is first detected by sensor 54 ant dela~ed, and later detected bS dounhole sensor 52. The in~erted electrical signal from 54 arrives at summing circuit 56 at the same time as the output of sensor ~ . ~. . .
52, pro~iding a net output of zero for downward mo~ing noise. Upward moving noise of the form A sin~(t - ~lc) yields an output from surnming circuit 56 of ~
~(t) = 2Asi~(7rf/2fo)cos! (t--b/c) (10):.--: :. ` i - .::. .~' .'.''''.",'"
1" ,. -,:
, ., ,'....,~.,, 200~Z0(1 S-66,627 where fO i~ the center frequency of the passband.
In the description which follows it is to be understood that all electrical signals are filtered so that the frequency content is limited to the passband or bands which are used for data transmission. Sensor 50 is spaced from transsnitter 40 by distance a.
5Accordingly, noise that is sensed at sensor 50 a~sives at transrnitter 40 a tisne a/c later.
If the output of sensors 50 is delayed by delay circuit 59 for an inter~al of a/c and appliet to transsnitter 40 tnrough summing circuit 4~, She output of transrnitter 40 can be shown o cancel the upward moving noise to within an error e =--(sin(~b/c))~ + 1 For a bandwidth-to-center frequency ratio of 150 Hz/650 Hz, the error is zero at the 10center of the transmission band and is only .03 at the band edges, a result showing 30 db noise cancellation.
~urther control of upward moving noise is provided by adaptive control 70, a con~
ventional control circuit that has an input from a secont pair of sensors ~2, ~4. The~e sensor~, identical to sensors 52, 54, also have corresponding delay circuit ~7 and in-15verter ~8 to provide an output indicative of an upward moving wave and no output in response to a downwart moving wave. The upward moving wave at control sensors~0 is a mixture of the noise and data that passet transsnitter 40. Accortingly, by telaying the tata signal in delay circuit 72 and adding the result to the output of sensors ~0 with surnming circuit 74, an error signal is produced which indicates the 20effectiveness of noise cancelation. This signal is fed into an adaptive control circuit 70 which controls conventional circuitry 75 to adjust voltage amplitudes or phas~ of the dgnals being appUed to any of sensors 52 and 62 or transmitters 42, 44 to minimize the amount of noise being transmittet upward towards the surface.
For a conventional steel drill collar, the spacing ~ between sensors or transmitters 25in the third passband would be about 30 cm (78 inches) or about 21 cm (53 inches) in the fourth passband.
., . :., The operation of the invention is as follows: The circuitry of Fig. 5 is mounted on a drill collar, including suitable circuitry 28 for generating data representative of a do vn-hole parameter. Power supplies, such as batterieg or mud-driven electrical generators, 13 ;
.: .- .
zoo4;~0~ S-66,6 ~7 and other supportive circuitry known to those of ordinary skill in the art, would also be incorporated into drill collar 30. The drill bit and mud create acoustic noise that travels in both directions through drill string 10. Downward noise is not sensed by the sensors; however, upward noise, including echos from the bottom of the drill collar, are o sensed by sensor circuit 50 a~d appl;ed to transmitter circuit 40, yielding a greatly reduced upward noise component. Primarily the data travels to the cormection 80 (Fig. 3) bctween drill collar 30 and the lowest drill joint 18, where a significant re~qec-tion of the data occurs because of the mismatch in acoustic impedance between these elements. Further echos occur at the tool joints 18 between each section of drill pipe 10 15. Thcse echos move downward through drill collar 30 where they pass the circuitr~
of Fig. S undetected, and become noise that is canceled out uhen they echo off the bottom of the drill collar. The signal that reaches the top is detected by a receiver such as an accelerometer. If necessary because of low attenuation within the drill string, an acoustically impedance matched transducer 80 may be used to terminate the signal15 and provide an accurate representation of the data transmitted from below.
As stated above, the data from circuit 28 ma~ be precompensated by multiplying cach frequency component of the signal by exp(--ikL) to adjust for the distortion caused b~ thc passbands of the drill string. Such compensation ma~ be accomplished b~ ~ny manner kno~n to those of ortinary skill in the art with a device such as an ~0 analog-to-digital signal proccssing circuit.
This in~ention recognizes and solves the problems noted by man~ previous workersin the ficld of transmitting data along a drill string. As a result, quality transmission on continuous acoustic carrier wa~es without extensive downhole circuitry, and without the use of impractical repeater circuits and transducers along the drill string, is possible at ~5 fre~uencies on the order of several hundred to several thousand Hertz. These frequencies are high in rdation to the ambient drilling noise ~about 1 to 10 Hz), and therefore allow ~ ~ -transmission relatively free of this noise. Also the bandwidths of the passbands allow ;~
data rates far in excess of present mut pulse systems. Also it is recognized that this ~ -method will work in drilling situations where air is used instead of mud. - ~ ~
14 - ~ ~ -,~''.,.,',"'-..''.,',',.',''.
Z004Z04 S-6G,6'~7 The particular sizes and equipment discussed above are cited merely to illustrate a particular embodiment of this invention. It is contemplated that the use of the invention may involve components hating different sizes and shapes as long as the principle set forth in the claims is followed. It is i~Itended that the scope of the invention be defined 5 by the claims appended hereto. A more detailed explanation of the calculations behind this ;nvention, and results of scale model te t~ and evaluations of field data, are protided in the Appendix attached to this disclosure.
, ;,~':,.
: -'~ ~ `'`'~'' -~ ;'~ ''''`~'``' ~: , .: ~:
`':: `~' ' . . .
~' ~ ' " '' . :' ' .:;: '. ,: .:
" " , . .:
: ~. . - ., :, , .
G ~
Noise scnsor 50 includes a pair of spaced sensors 52, 54 which operate in a similar ~ . ~
manner to provite an indication of acoustic energy moting uphole, and no indication of enorlcy mo~ing downhole. The output of sensor 52, which sensor may be an accelerom-cter or strain gauge, is an electrical signal that is summed ;n summing circuit 56 with the output of similar sensor 54, ~ hich output is delayed by delay circuit 57 and and inverted by in~erting circuit 58. If the delay of circuit 57 is equal to the spacing di~ited by the speed of sound c, downward moYing energy is first detected by sensor 54 ant dela~ed, and later detected bS dounhole sensor 52. The in~erted electrical signal from 54 arrives at summing circuit 56 at the same time as the output of sensor ~ . ~. . .
52, pro~iding a net output of zero for downward mo~ing noise. Upward moving noise of the form A sin~(t - ~lc) yields an output from surnming circuit 56 of ~
~(t) = 2Asi~(7rf/2fo)cos! (t--b/c) (10):.--: :. ` i - .::. .~' .'.''''.",'"
1" ,. -,:
, ., ,'....,~.,, 200~Z0(1 S-66,627 where fO i~ the center frequency of the passband.
In the description which follows it is to be understood that all electrical signals are filtered so that the frequency content is limited to the passband or bands which are used for data transmission. Sensor 50 is spaced from transsnitter 40 by distance a.
5Accordingly, noise that is sensed at sensor 50 a~sives at transrnitter 40 a tisne a/c later.
If the output of sensors 50 is delayed by delay circuit 59 for an inter~al of a/c and appliet to transsnitter 40 tnrough summing circuit 4~, She output of transrnitter 40 can be shown o cancel the upward moving noise to within an error e =--(sin(~b/c))~ + 1 For a bandwidth-to-center frequency ratio of 150 Hz/650 Hz, the error is zero at the 10center of the transmission band and is only .03 at the band edges, a result showing 30 db noise cancellation.
~urther control of upward moving noise is provided by adaptive control 70, a con~
ventional control circuit that has an input from a secont pair of sensors ~2, ~4. The~e sensor~, identical to sensors 52, 54, also have corresponding delay circuit ~7 and in-15verter ~8 to provide an output indicative of an upward moving wave and no output in response to a downwart moving wave. The upward moving wave at control sensors~0 is a mixture of the noise and data that passet transsnitter 40. Accortingly, by telaying the tata signal in delay circuit 72 and adding the result to the output of sensors ~0 with surnming circuit 74, an error signal is produced which indicates the 20effectiveness of noise cancelation. This signal is fed into an adaptive control circuit 70 which controls conventional circuitry 75 to adjust voltage amplitudes or phas~ of the dgnals being appUed to any of sensors 52 and 62 or transmitters 42, 44 to minimize the amount of noise being transmittet upward towards the surface.
For a conventional steel drill collar, the spacing ~ between sensors or transmitters 25in the third passband would be about 30 cm (78 inches) or about 21 cm (53 inches) in the fourth passband.
., . :., The operation of the invention is as follows: The circuitry of Fig. 5 is mounted on a drill collar, including suitable circuitry 28 for generating data representative of a do vn-hole parameter. Power supplies, such as batterieg or mud-driven electrical generators, 13 ;
.: .- .
zoo4;~0~ S-66,6 ~7 and other supportive circuitry known to those of ordinary skill in the art, would also be incorporated into drill collar 30. The drill bit and mud create acoustic noise that travels in both directions through drill string 10. Downward noise is not sensed by the sensors; however, upward noise, including echos from the bottom of the drill collar, are o sensed by sensor circuit 50 a~d appl;ed to transmitter circuit 40, yielding a greatly reduced upward noise component. Primarily the data travels to the cormection 80 (Fig. 3) bctween drill collar 30 and the lowest drill joint 18, where a significant re~qec-tion of the data occurs because of the mismatch in acoustic impedance between these elements. Further echos occur at the tool joints 18 between each section of drill pipe 10 15. Thcse echos move downward through drill collar 30 where they pass the circuitr~
of Fig. S undetected, and become noise that is canceled out uhen they echo off the bottom of the drill collar. The signal that reaches the top is detected by a receiver such as an accelerometer. If necessary because of low attenuation within the drill string, an acoustically impedance matched transducer 80 may be used to terminate the signal15 and provide an accurate representation of the data transmitted from below.
As stated above, the data from circuit 28 ma~ be precompensated by multiplying cach frequency component of the signal by exp(--ikL) to adjust for the distortion caused b~ thc passbands of the drill string. Such compensation ma~ be accomplished b~ ~ny manner kno~n to those of ortinary skill in the art with a device such as an ~0 analog-to-digital signal proccssing circuit.
This in~ention recognizes and solves the problems noted by man~ previous workersin the ficld of transmitting data along a drill string. As a result, quality transmission on continuous acoustic carrier wa~es without extensive downhole circuitry, and without the use of impractical repeater circuits and transducers along the drill string, is possible at ~5 fre~uencies on the order of several hundred to several thousand Hertz. These frequencies are high in rdation to the ambient drilling noise ~about 1 to 10 Hz), and therefore allow ~ ~ -transmission relatively free of this noise. Also the bandwidths of the passbands allow ;~
data rates far in excess of present mut pulse systems. Also it is recognized that this ~ -method will work in drilling situations where air is used instead of mud. - ~ ~
14 - ~ ~ -,~''.,.,',"'-..''.,',',.',''.
Z004Z04 S-6G,6'~7 The particular sizes and equipment discussed above are cited merely to illustrate a particular embodiment of this invention. It is contemplated that the use of the invention may involve components hating different sizes and shapes as long as the principle set forth in the claims is followed. It is i~Itended that the scope of the invention be defined 5 by the claims appended hereto. A more detailed explanation of the calculations behind this ;nvention, and results of scale model te t~ and evaluations of field data, are protided in the Appendix attached to this disclosure.
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Claims (18)
1. A method for transmitting data through a drill string comprising the steps of ? preconditioning said data to counteract distortions caused by said drill string, said distortions corresponding to the effects of a comb filter having charac-teristics dependent upon the properties of said drill string;
? applying said preconditioned data to a first end of said drill string; and ? detecting said data at a second end of said drill string.
? applying said preconditioned data to a first end of said drill string; and ? detecting said data at a second end of said drill string.
2. The method of claim 1 wherein said preconditioned data is a first electrical signal, said method further comprising:
? converting said first electrical signal to a first acoustical signal for application to said first end of said drill string; and ? converting said detected acoustical data to a detected electrical signal at said second end of said drill string.
? converting said first electrical signal to a first acoustical signal for application to said first end of said drill string; and ? converting said detected acoustical data to a detected electrical signal at said second end of said drill string.
3. The method of claim 2 wherein said drill string has low attenuation passbandsand high attenuation stopbands of acoustical signals, the frequencies of said first acoustical signal being in the passbands of said drill string.
4. The method of claim 3 wherein said preconditioning comprises multiplying eachfrequency component of said first electrical signal by exp(-ikL) where L is the transmission length of said drill string and k is the wave number in said drill string at the frequency of each component.
5. The method of claim 1 further comprising the step of suppressing acoustical echos from each end of said drill string.
6. The method of claim 5 wherein said step of suppressing acoustical echos at the receiver comprises matching the acoustical impedance of said transducers to the acoustical impedance of said drill string and providing a sufficient loss factor to terminate the signal
7. The method of claim 5 wherein said step of suppressing acoustical echos at the transmitter comprises applying echo-cancellation energy to said drill string in a position adjacent to said transducers.
8. The method of claim 5 wherein said step of apply energy comprises:
? providing an output indicative of acoustical noise traveling from said first end towards the location on said drill string where said data is applied, and providing no indication of acoustical noise traveling from said location towards said first end; and ? applying a delayed output to said drill string to cancel noise traveling from said location towards said second end.
? providing an output indicative of acoustical noise traveling from said first end towards the location on said drill string where said data is applied, and providing no indication of acoustical noise traveling from said location towards said first end; and ? applying a delayed output to said drill string to cancel noise traveling from said location towards said second end.
9. Apparatus for transmitting data on a continuous carrier wave through a drill string comprising a plurality of drill pipe sections connected end-to-end by tool joints, the length and cross-sectional area of the pipe sections being different from the length ant cross-sectional area of the tool joints, said apparatus comprising:
? transmitting means for coupling data to said drill string near a first end of said drill string for acoustical transmission to a second end of said drill string;
? anti-noise means near said first end of said drill string for preventing acousti-cal noise from said first end from being transmitted through said drill string to said second end; and ? receiving means near said second end for receiving said acoustically trans-mitted data.
? transmitting means for coupling data to said drill string near a first end of said drill string for acoustical transmission to a second end of said drill string;
? anti-noise means near said first end of said drill string for preventing acousti-cal noise from said first end from being transmitted through said drill string to said second end; and ? receiving means near said second end for receiving said acoustically trans-mitted data.
10. The apparatus of claim 9 wherein said anti-noise means comprises:
? first noise-receiving means for providing a first output indicative of acoustical noise traveling from said first end toward said transmitter means, and for providing no indication of acoustical noise traveling from said transmitter means towards said first end; and ? noise-cancelling means for applying a delayed output from said noise-receivingmeans to said transmitting means to cancel noise traveling from said trans-mitting means towards said second end of said drill string.
? first noise-receiving means for providing a first output indicative of acoustical noise traveling from said first end toward said transmitter means, and for providing no indication of acoustical noise traveling from said transmitter means towards said first end; and ? noise-cancelling means for applying a delayed output from said noise-receivingmeans to said transmitting means to cancel noise traveling from said trans-mitting means towards said second end of said drill string.
11. The apparatus of claim 10 wherein said anti-noise means further comprises:
? second noise-receiving means for providing a second output indicative of acoustical noise and data traveling from said transmitter means towards said second end, and for providing no indication of acoustical noise traveling from said second end towards said transmitter means; and ? adaptive control means for comparing said second output with said data, and adjusting at least one of said first and second outputs or said transmitted data to minimize the transmission of noise towards said second end.
? second noise-receiving means for providing a second output indicative of acoustical noise and data traveling from said transmitter means towards said second end, and for providing no indication of acoustical noise traveling from said second end towards said transmitter means; and ? adaptive control means for comparing said second output with said data, and adjusting at least one of said first and second outputs or said transmitted data to minimize the transmission of noise towards said second end.
12. The apparatus of claim 9 wherein said transmitting means comprises:
? a first and a second acoustical transmitter spaced along said drill string a distance equal to an odd multiple of a quarter wavelength of said carrier wave, said first transmitter being closer to said first end than said second transmitter;
? second signal applying means for applying said data signal to said second transmitter; and ? first signal applying means for applying a delayed, inverted, data signal to said first transmitter, the delay being equal to the transmission time of the transmitted signal from said first transmitter to said second transmitter, whereby said data signal is transmitted only toward said second end.
? a first and a second acoustical transmitter spaced along said drill string a distance equal to an odd multiple of a quarter wavelength of said carrier wave, said first transmitter being closer to said first end than said second transmitter;
? second signal applying means for applying said data signal to said second transmitter; and ? first signal applying means for applying a delayed, inverted, data signal to said first transmitter, the delay being equal to the transmission time of the transmitted signal from said first transmitter to said second transmitter, whereby said data signal is transmitted only toward said second end.
13. The apparatus of claim 9 wherein said first noise-receiving means comprises ? a first and a second acoustical receiver spaced along said drill string a dis-tance equal to an odd multiple of a quarter wavelength of the carrier wave, said first receiver being between said first end and said second receiver, said second receiver being between said first receiver and said transmitting means;
? means for summing a noise signal from said first receiver and a delayed, inverted noise signal from said second receiver to produce a noise-cancelling signal, the delay being equla to the transmission time of the received noise signal from said first receiver to said second receiver; and ? the delay of said noise-cancelling means being equal to the transmission time of said noise from said second receiver to said transmitting means.
? means for summing a noise signal from said first receiver and a delayed, inverted noise signal from said second receiver to produce a noise-cancelling signal, the delay being equla to the transmission time of the received noise signal from said first receiver to said second receiver; and ? the delay of said noise-cancelling means being equal to the transmission time of said noise from said second receiver to said transmitting means.
14. The apparatus of claim 11 wherein said second noise-receiving means comprises ? third and fourth acoustical receivers spaced along said drill string a distance equal to an odd multiple of a quarter wavelenght of said carrier wave, said receivers being between said transmitter means and said second end, said third receiver being between said fourth receiver and said transmitter means;
? means for summing a signal from said first receiver and a delayed, inverted noise signal from said second receiver to produce a noise-cancelling signal, the delay being equal to the transmission time of the received noise signal from said first receiver to said second receiver.
? means for summing a signal from said first receiver and a delayed, inverted noise signal from said second receiver to produce a noise-cancelling signal, the delay being equal to the transmission time of the received noise signal from said first receiver to said second receiver.
15. The apparatus of claim 12 wherein each of said acoustical transmitters comprise ? a transducer for converting an electrical signal into an acoustical signal for application to said drill string; and ? said receiving means comprises output transducer means for converting said received acoustical data to a detected electrical signal at said second end of said drill string.
16. The apparatus of claim 9 wherein said drill string further comprises a drill collar at said first end of said drill string, said transmitting means and anti-noise means being affixed to said drill collar.
17. The apparatus of claim 9 further including means for preconditioning said data to counteract distortions caused by said drill string, said distortions corresponding to the effects of a comb filter having characteristics dependent upon the properties of said drill string.
18. The apparatus of claim 9 wherein the acoustical impedance of said receiving means is matched to the acoustical impedance of said drill string at said secondend, thereby preventing the generation of echos from said second end towards said first end of said drill string.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2004204 CA2004204A1 (en) | 1989-11-29 | 1989-11-29 | Acoustic data transmission through a drill string |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2004204 CA2004204A1 (en) | 1989-11-29 | 1989-11-29 | Acoustic data transmission through a drill string |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2004204A1 true CA2004204A1 (en) | 1991-05-29 |
Family
ID=4143662
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2004204 Abandoned CA2004204A1 (en) | 1989-11-29 | 1989-11-29 | Acoustic data transmission through a drill string |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2004204A1 (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5850369A (en) * | 1991-06-14 | 1998-12-15 | Baker Hughes Incorporated | Method and apparatus for communicating data in a wellbore and for detecting the influx of gas |
| US6310829B1 (en) | 1995-10-20 | 2001-10-30 | Baker Hughes Incorporated | Method and apparatus for improved communication in a wellbore utilizing acoustic signals |
-
1989
- 1989-11-29 CA CA 2004204 patent/CA2004204A1/en not_active Abandoned
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5850369A (en) * | 1991-06-14 | 1998-12-15 | Baker Hughes Incorporated | Method and apparatus for communicating data in a wellbore and for detecting the influx of gas |
| US6310829B1 (en) | 1995-10-20 | 2001-10-30 | Baker Hughes Incorporated | Method and apparatus for improved communication in a wellbore utilizing acoustic signals |
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