CA2039406A1 - Video system and method for determining and monitoring the depth of a bottomhole assembly within a borehole - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

Video systems and methods for determining the length of objects to be inserted in a wellbore, and for summing the lengths to obtain an accurate determination of the depth at which a bottomhole assembly is located at any given time. The video systems and methods of the present invention are also used in conjunction with hookload and traveling block location information to determine bottomhole assembly depth while drilling, or tripping-in or tripping out of a well. Also disclosed is a method of accurately determining the transition a drillstring undergoes and its associated movement when passing from in-slips to out-of-slips.

Description

203940~
3~30 SYE~EM AND MEIH~D FQR ~El}~f-YnNG AND ~CIIl~oRIN:
IffE DEPIH OF A ECn~YHOLE ASSEMBLY wo~nEnN A W~3~3~gE

TECHNIC~L FIELD
~he present invention relates to systems and mY*~hods for ~ and mcnitoring the db~h at whidh a dr~lling rig is operating, and more particularly relates to systems and n~bods for detlsll~ning and mLnitor m g the db~h at whidh a kc~ hola assembly is located within a wellhnre. The pres2nt invention further relates to systems and methcds for accurately dbelo~Linlng the leng~h of an ob~ect bafore it i8 pla oe d in a well.

EAf~Z~olND OF THE INVENTI~N
In comm~n rokary d~illing method~ and system6 used in d~illing o~l field b~rehales, power rotating nYxL~g d~livers torque to a drill pipe, a plurality of whidh forms a d~ill string, via a kelly and a rotary table. The drill string in turn rckate~ a bit located at its lowermL6t end that drills a borehole th~x~h the sLbrsurfa oe formation. The drill string i8 supported for up and dbwn mcvement by a dr~lling mast located at the earth's surf~ oe. A
drill lin~ or cable Fs~xrbad by tha drilling ~ast and coupled to the drill string i8 used in condunction w~ith a rokating drum to facilitate the up and down ~ t. The drill line i~ anL~x~n3d at c ~ end called the dead line anLhor, whidh i3 typically located ad~aoent to cne leg of the drilling mast.
The drill line e~ xds ~nom the anchor upwzLdly to a crcwn block formed of a plurality of .~atable ~h~#nu~s at the tcp o~ the mast. The Idrill lins is rE#n~3d a mloYd the sheaves in the cxcwn block and ext2nds db~}n~rdly b~tween the crown block sheaves and rot~ting sheaves in a traveling block. lhe drill line then extends from the cnown block db4~n~Lnd to a mtating drum or draw~

2 Q '~
works that ~ the crcwn block up and dbwn by reeling the drill line in or out.

As will be appreciated by thDse skilled in the art, dedl~ILhnina and mcnitoring the depkh at which a c~x~ent of the ~ ole assembly (BH~) is located at any given t;~P in a wellbore is important for many reasons. Fbr example, the drilling rig operator needs to know the depth at which the kx~x~u hole a~ly is located during trips in and out of the well so that he can be cautious when passing thra~h sensitive zones ~h as bridge~, ledges, or key seats. In addition, ~y ccrrelating inf~mation gathered frall offset wells, a driller needs aca~rate d~h ~sureent inf~atio,n while drilling slibsurfaçe fo~matior~ to anticipate trcuble zones, e.g., higih gas~ sus~ gas zones, in o~der to talce aE~ri~te precautionary mea~s. Also, aca~te d~h in~o~matian ~8 extre~y valuable when performing directional or horizorltal drilling operations.

In rece~t years, many develoED~Its have ~een made $n the area of gathering kcnn~hole data whilo the dr~lling operation i8 being ccndu{Ced. These services, whiclh ar~ ccmmcnly referred to a~ selu~Dre e~t-while~drllling ~WD), logging-while~drilling (IWD), and formation evaluatian whlle drilling (FEWD), t~pi~ y inla~lxlrate vari sensing devices into th~ bottomhole assembly to ~ather information relat4d to, for exa~ple, for~atlon lith~p~hy, dow~hole erwr n~ nent, and tool cperatlng pY~ncDrber . The raw or pe~x~3ss3d data gathered by such devioes are typir~lly either transmitted to the sur~ace in "real i~P~ by using, for example, a mud pulse telemetry ~ygtem, or stored in a memory devioe lo~a~ed in the dbwnhole tcol for later retrieNal when th~e BHA
is br~ught back to the earth~8 surfaoe, or simLltaneously transmitted in raal ~3~4~
time and stored dcwnhole. For much of this inform~tion to be of significant value, particularly lit~ phy data, it must ~e ccrrelat~d to the parti~lar depth at which the information was ob~2L~n3d. Acs~xnlingly, it is extremely important for MWD or IWD service prcviders to haNe an accurate dbpkh neRfw~o~ent system and apparatus.

~resent day d~pth systems and methods typi~lly includs a cc~bination of keepmg a tally indicating the length of eacih drill pipe ins~ted into the bor~hole, and m~Rl~ing the lr~al leng~h of ths laRt drill pipe be~ng lowered into ths borehole durir~ ths drilling or trippir~T operation by m~nitoring t!he mavement of ths travelir~ blo~k. Traveling blodk m~t is c~nly deto~ci~ by monitoring ths D~tion of ths dr~lling lir~ as it i8 fed fram th~ ~rk~, e.g., with a ser~or calpled to the r~tating dn~ or one of the sheav~ in ths cra~ blo~k. Ihis gen~al type of sy~tem, ha~ever, cltain~ many ~a~es of ~rs and ln~acie~. ~ example, ths ler~t~ of a particular pipe section i~ 8i~ply inaca~rately D~ed or noted errcr~Lsly, or added to the dr~ tring in an order differ~t fmm that noted in t)~e tally. In additil, with respect to monitc~ the DY~tion of the drilling line thr~gh dn~m rotation to recc~ ths leng~h of the la~t pipe, since the drill line cable stre~ over ti~ ar~l because the cable is wa~d in layers ar~und ths r~tating drum, the r~tation of t~B drum itself does not accurately correlate to the leng~h of ths last drill pipe baing lowered.

Further ln~ccurac$es w$th prior mekhods typically oocur during the pr~crdure when pipe $8 added or 8ubtracted to the drill string eitber WhilQ aonducting the drilling cperatian or while tripping in or out of the well. F~r example, when the rig's travel$ng block ha~ reached its maximum downward mcvement 2a~4~
dur m g a drilling cperation and a new ~ ion of pipe mLst be added, the traveling block and ccrr~x:~o~ drill string are first raised a short distanoe by reeling in the drill line cable, followed by placing slips in the rotary table. A~er the slips are inY~ 3d, the travEling blo~k is lcwered a ghort distanoe such that the slips support ths drill string, which allows the kelly to be unscrewed. ~n the prooess, cable i5 reeled cut while the EH~ remains StatiQnary. $hB disparity in mcvement is due to the release of tensian in the cable since the cable is no longer supporting the ~eight of the drill string.
~n the ckher end of the proccdure when the kelly i swung c~er to the pipe and the new pipe is attached cnto the kelly, and the kelly and new pipe are sw~ng baick and attached to the drill string, the traveling block first moves upward to a poin~ whers the slips can be remcved. When the slips ars removed, aga~n locations reaardlng drumi rotatian and traveling block movement with respect to the drlll string movement are made with resulting de$thi deeerclnation inaccuracies. Thesie small errcrs at each transitian can translate into an aocumulated error of several feet during the ccurse of drilling a well.

An addiiticnal prbblem witlh tracking EH~ po~ition basedi on traveling block altitude is that su~h systems, for a variety of reasons, ofben loo~e track of th2 block pocition. Systems that d~ter~nc block pc~iition based on enLoders oconected ta tbe drawworks loose block poaitiani accuracy, for ~x~Tple, bscause of r~ble ~ i over tlme and changes in the way the cable Wr3ipEi on the drumw~rk's rotating drumi. SyYtemsi that pla oe encoders on the fast sheave in the crown block typically 1006e block pc6ition accuracy, for example, because of cable slippage and cable stretch. Eokh of these general types of systems ~9~0;~
typically lack a raliable way of ri#uJ~:Lng blo~k position that does n~L affect or interfere with the drilling operation.

In order to overoome some of the inaccuracies inherent in mLst prior art depth techniques, several different n~xods and aFparatus have been proposed. For example, in U.S. Patent No. 4,114,435 to Fatton et al, it is prqpuc~ to nY~ re different traveling block reference points that relate to when the cable o,n the draww~rk drum rea~hes different layers of ~i~g, and then to d-t~e the location of t~e traveling block via an eq~ation, the reference points, the rotation of ~he dNm, etc. qSe Patton et al sy~tem, hawever, still pr~vides ina~uracies because it fail~ to aoca~t for t~e d~namic nature of th~ cable layering pmoess. ~er, an accaunt for ~e cable tret~ng ov~r ti~e is not ~vided fcxr.

U.S. Patent No. 4,787,244 to MilcDla~yk pr~oces to autaoatically deter=Lne the drill bit depth ~y t ~ cing the ma ~ t of the cable. Mbv ~ ts of the cable are o~ly tracked when the weight carried by the traveling block ~xneç~c a oertain minlmum threshold as deeernlned by a tensiometer on a cable.
However, this prior technique fa~l3 to account prcperly for mLuererts of the cable during th~ slip6-in and slips-out pzocadure when the transition is made thrcugh th~ threshold. S~ ar typ#s of errGrs are believed to be inherent in the syYtem prcposed ~n U.S. Patent No. 4,616,321 to Chan.

U.S. Patent No. 4,610,005 to Utasi prqposQs a videD system that D~nitorg the po~tion and mLvement o~ the traveling block to de*ersine borehole depth. In uta~i's sys~em, a video oamera i~ positioned to track th~ vertical mcvement of th~ traNeling block. Hbwever, Utasi's systems seems to be fairly impractical 2~33~J

and inaccurate ~ecause of the remote dis~Y~e that the camera mLst be p æ itioned to view the entire rig. In ad~ition, the dis~LY~e be*~3En the camera an~ the rig rendbrs the system wF~r~ptible to interference ~LU~ the rig stl~x~bur3, lighting changes, eqyipment Dr~nent, ekc.

}n light of the above, a principal ck~ect of the present invention is to prcvide a system for and DY~hod of accurately deter=lnln~ and mcnitoring the depth at which a koktomhole assembly is located with~n a welIbore.

A further ob~ect of the pres~nt invention to provide a system for and DY~hod of accurately mPa~rring and recordinq the length of an cb~ect h~fore it is inserted into a well.

Ancther cb~ct of the present invention is to provi~e a means for verifying and reo ttlng a d~pth deter~1natian to ~ubstanelally reduce accumulated errors.

A further ob~ect of the pxesent invenkicn i5 to pravide a system for and method of accurately DYasuring and recordlng the depkh at whidh a bcttcmhole assembly is located while 5ubEtane1a1ly not affecting or interfering with the normal operation of a drilling rig and its crew.

SUMM~RY OF TffE INVENTIoN
The present inYention provides system~ ~or and me*hods of accurat~ y deter dndng ~he leng~h of an ob~ect k~fore it is lnserted in a welIbore, and aocurately deeer~lring the depkh at which a bottol~ole assembly is located w~itbin a wellbore. In a preferred a~hn~mpnt of the present ~nvention, a . 2 video camera i~ positioned near the rig flcor and focused above the mLuse hole. The camera i8 associated with a video display having Dr~#ible cursors super~mp~G~ th~#an by a DE#~Lring devi oe . A~ r ths ~P~nring devi oe associated with 'Ihe camera and vidbD display has ~een calibrated to build a table of p;x~l dist~noe between cursor position versus leng~h within a computer, the length of an object placed with~n thhe mLuse hole, e.g., a section of drill pipe, is d~termLned by D ~ ing the cursors on the video display adjacent to the i~age of the pcrtlon of the object p m trudin~ from the mcuse hole, and equating the pixel distance bekween thhe cursors to a leng~h based upon the pixel dlJtarLe/le~g~h table. ~h~ length i8 addbd to thhe previously-deterI1ned leng~h that pipes extend below the rig n oor into the mouse hole to bbkain the ob~ect's overall leng~h. The comput~r is progra3~ed to ~um ~p t'he tokal leng~h of pipes added to the drillYL~-ing via ~he D ~ ole during either drilling or tripping operaticns.

~n another preferred e~bcdi~ent of the present invention, tw~ cameras are pcsitioned an a rig to measure the length of ~oints ~usperded within the rig's mast as they are added to or ~ub*laceed from a drill~LLing. Eokh caleras and thQ ~gpa displayed thereby an a video display and the ~eouurin~ devioe associated therewith are calibrated to generate a pixel distance versus length Wle whidh is ufied in detec ining thP length of added or subkr~cted joints, whidh are su~ned by the ca~ter in dsbe~inln3 depth.

In ather preferr~d e~lin~nts of ~ present i~til, t~veling bloc k K~ and posi~:iqn infomlation ar~l hocldoad infon~atian are l.c~l to deten~ d~th with tho ~rideo ~ being u~ed isl a~cciatien therewith to ~ 6 3~
verify the accuracy thÆreof and prcvide the basis far nE~c~ng resets and offsets when nf~Y#~=sry.

BRIEF DE~:K~PTICN OF TffE DR~WINGS
While the specification concludes with cl~;~s parti~llarly printing out and distinctly claiming the subject matter ~ d as f ~ the present invention, it is believed that the inNentian will be be~#r urlb~ >od and appreciated from the following detailed description and drZ~llg8 in whi d: -Figure 1 is a s dematic side view of a typical drilling rig and borehole whichillustrates the general env1ror ent~1 in whi d the present invention finds particular utility;

Figure 2 is a sche~atic block di~pnsm of the main c~DçlY~etts of one preferred sy~ m of the present invention;

Figure 3 is a schematic side view of a mouse hole having a drill pipe sectian ins~ 3d therein and shcwing the lengths to be dldl~3nlned in one ea!xxl~aent ofthe FI~##~nt inNention;

Figure 4 is a Frhem~tic 8ide view of the top portion of a drill pipe section q out of a msuse hole above a rig floor and the inage thereof recorded on a display;

Figure 5 is a schematic side view of a drill pipe joint suspendcd in a rig and ima3es th~n30f re~x~n3ed on two displays;

,~3~

Figure 6 is a s ~ tic side view of a drill pipa joint Dusl~3l1 d in a rig and showing the lengths to be dbdlDnLinc9 by a preferred o~hrd~ment of a system and nY~xod of the present invention;

Figure 7 is a schematic sid,e view of a drill pipe joint s~s}~3l~3d in a rig andshowing images of the upper and lower ends tkf~neof as reoorded on tw~
~1~rlays;

Figure 8 is a sdhematic side view of a drill string eonlsYlLng dcwn into a borehole and showing the lengths thereof to be d{*l~m~ed by a preferred e~bcxl~Dent of a system and nY~hcd of the present inwention;

Figure 9 is a sdhematic view of an i~age appearing on a display shch~ng a side view of the t~p portion of a drillstring being grasped by a rig's elevators;

Figu~e 10 is a schematic view of an image appearing on a display showing a side view of a rig's rotary table and the kelly extendlng through the rotary bushing;

Figure 11 is a graFh of hockload and traveling block altitude versus time ~uring a typical slip6 transition;

Figure 12 is a graph of hcckload and traveling block altit~e versus ti~e sh~ ng only the in-slip6 to out-of-slips transition with Table 1 illustrating a sFecific example of the out-of-slips lo~k bacX (06LB) calibration process of the pres~ ~tian;

_ g _ Fig~re 13A is a schematic view of an image refx~nlsd on a display shxx~ng a side view of the tcp portion of a drillstring e#cl3lling abcve a rig floor;

Figure 13B is a schematic side view of a joint having ~een added to the tcp por~ion of the drillstring appearing on the d ~ lay of Figure 13A;

Figure 13C is a schematic side view of the joint of Figure 13B after a scb~d;LJt1al pcrtion thereof has been lch~n3d into the welIbore:

Figure 13D is a C~hpm~tic view of an ima~e reoorded on a d ~ lay shcwing the joint of Figure 13C extendlng abcve the rig floor;

Figure 14 is a schematic side view of the joint of Figures 13A-13D and the lengths to be db*er~ln d by the systems and meth~ds of thQ present inventicn;

Figure l~A i8 a cr~om~tic view of an i~age reoorded on a di~play showing a side view of the tqp porticn of a dr111string extendinq above a rig floor;

Figure 15B i8 a schematic side view of the tap portion of the drillstrm g appearing on the display of Figure 15A

Figure 15C i~ a schematic side view of a joint having been pulled cut of a wellbore;

Figure 15D 1 a schÆmatic view of an ima~e reoorded an a display of the top porticn of a drillstring after the joint of Figure lSC has been removed ~efr~; ar~

3 ~5 ~

Figure 16 i~ a s ~ tic side view of the joint of Figures 15~-15D and the 1 ~ s to be dee~ Lnel by the systems and methn~ of a preferred ~hr~ime~t of the Fl~##ent ~ ion.

DE~iLLED DE5caIpqIoN OF THE INVENTIoN
Ihe dÆ~h dfd/~n~ling and mcnitoring ~ s and methcds of ths present invention may bs used and practioed in association with a wide v riety of dlrilling rig~ that ars commorly used in the industry, for example, on-shore, off-shor~, float~ng platforms, rokary tabls drives, tcp drives, mud mokor drives, ~tc. In addition, the systems and methods of the present invention may be used to det c~in and ~um the lengths of any ob~ect3 as they are plaoed with~n a welIbore, e.g., drill pipe, drill collars, MWD sub3, tubing, casing, etc. With reference to the Figures in which the same nLmeral is used to indicate ~all~n apparatus and a~pli~ation corpcn nta, Figure 1 schematically illustrates a t~pi~Pl drilling rig generally indicated as 10 that is repre~entative o~ most rigs commcnly used in the art. In Figure 1, rig 10 includes a vertic 1 derrick cr mast 12 having a crcwn block 14 at its ~ r end and a horizcntol rig flccL 16 at it~ lcwer end. Drill line 18 is fixed to ~ ine anchor 20, whiclh i8 ecu~dy prcvided w~i~h hook load sensor 21, and e ~ s upwardly to crown block 14 having a plur lity of sheaves (not shown).
From block 14, drill line 18 ex*ends dowrhardly to travellng block 22 that 8imilarly include~ a plurali~y of aheaves (not shown). ~rlll line 18 extends back and ~orth ~tween th~ sheaves of crcwn block 14 and th~ sheavas of travsling blodk 22, then extends dowrwardly ~rcm crown block 14 to drawworh~
24 having rckatlng drum 26 upon which drill line 18 ~3 wrapped in layer~. qhe mkatlon of dru~ 26 causes drill line 18 to ke taken in or ouk, which ralses or lowers traNeling b~ock 22 a3 required. Drawwork~ 24 may bs provided with 4 ~ ~

sensor 27 whi~h n~itors the rotatian of drum 26. Sensor 27 m~y be, fcr example, a qyadrablre i~al en~:oder that }~c~oes ~lses as dn~m 26 ~tates as is well kn~ in ~ art. Al~ernatively, se~ 27 may be located in crawn bloc~lc 14 ~ D~nitor the r~tatian of cne or re of t~e sheav~
therein.

Hkxik 28 and elevators 30 are attached to traveling block 22. Hbok 28 is used to attach kelly 32 to traveling block 22 during drilling operaticns, and elevators 30 are used to attach drlll str$ng 34 to traveling block 22 during tripping cperaticns. Drill stxing 34 is made up of a plurality of individual pip~ DY~ars, a group~ng of which are typically stored within mast 12 as ~oints 35 (~ingles, dcubles, clr trlples) in a pipe ra~k. Drill string 34 e~ Yds down into wellbore 36 and terminates at it~ lcwer end wit'h bottom hole ~CcP~hly (EH~) 37 that typically includes a drill bit, several heavy drilling collar~, and instl~sn~ntltion deNices CCDlh~y rsferred to as DeRUCIo3J3nt-while-drilling ~MWD) or logging-while ~ ing (IWD) tcols. Mbuse ,hole 38, which typically has spring 39 at the bottom thÆreof, extends thux~h and below rig ~loor 16 ar~ ~erves th~ purpo6e o~ st~ir~ next pipe 40 to be atta~ to dr~ll strir~ 34.

D~rir~ a drilling ~peration, pa~ rotati~ means (not shawn) rokates a mtary table (m~t sha~n~ h~ rotary ~shi~ 42 releas~ly atta~ ~eto locat~
cn rig ~loor 16. ~ lly 32, ~ ich passe~ thra ~ rotary } ~ hing 42 and is free to mLve ~etically thu~ln, is rokated by tha rotary table and rctates drill strin~ 34 and BHR 37 a~tached thereto.

During the drilling cperation, after kelly 32 has reached its lowest point commLnly referred to as the 'qhelly down" position, new pipe 40 in mouse hole 38 is added to drill string 34 by reeling in drill line 18 cnto rotating drum 26 until traveling block 22 raises kelly 32 and the tcp portion of drill string 34 above rig floor 16. Slips 44, which may be manual or hydraulic, are placed arxlDYl the tcp portion of drill string 34 and into the rokary table su~h that a slight lowering of trav~ling block 22 ca~cP~ slip8 44 to ~e r~rmly wedged between drill string 34 and the rotary table. At this time, drill string 34 is "in-slips" ~inoe its weight is supported thereby as oFpo6ed to when the wei~ht is 0uFport ~ by travaling block 22, cr "out-o~-slip6".

once drill ~-L-ing 34 is in-slips, kelly 32 is d1sconneceed from string 34 and moved over to and secured to new pip9 40 in mouse hole 38. New pipe 40 is then hoisted out of mouse hole 38 by raising travelling blodk 22, and attached to drill string 34. Iraveling blo~k 22 i3 then sllghtly raised whldh allows s1ip~ 44 to be removed from the rokary table. Traveling blodk 22 is thQn lowened and drilling r ~ .

'~ripping-out" i~ the process where ~ome or All of drill string 34 is removed fram wellborQ 36. In a trip-out, kally 32 ~a dL oQnnected fL~ drill ~tLing 34, set aside, and dekached from hook 28. Elevators 30 are then lcwered and to gra6p the uFpescl st pipe of drill ~tring 34 eYtendlny abova rig flcor 16. Dcawworks 24 reel in drill line 18 whidh hoist~ drill string 34 urtll the section o~ drill string 34 (usu21ly a '~triple") to be remcved i~ 5u6pendel above rig flo~r 16. String 34 i8 then placed lnr81ip5, and the section removed and stored in t~e pipe racX. '~rripping-in" is the process where scme 2~394~
or all of drill string 34 is replaced in wellh~re 36 and i h~cically the oppocite of tripping out.

In some drilling rig_, rotating the drill string ic acccmplished by a devi oe commLnly referred to as a '~qp drive" (nok shown). This devi oe is fixed to hook 28 and replar~s kelly 32, rctary bushing 42, and the rctary table. Pipe added to drill string 34 ~ cr~r~#:b3d to the bottam of the t~p drive. A~ with rotary table drive-c~ additional pipe ~ay either come fm m mcuse hole 38 in singles, or frcm the pipe racks as singles, dbublec, or triples.

Th~ dep~h of a c~n}xY nt of thQ EH~, whekher the bit or an MWD device for exa~ple, during the drilling operatian at any i d nt in tim~ is the sum of the d~E~ oe be~ween the lower edge of the lowermost pipe of drillstring 34 to the EH~ crn}rment, t~e total lenq~h of drill ~tring 34, and the length of the portion of kelly 32 ~dlQx1Ln~ bel~w rig floor 16, whi~h ia typically the reference point or "zero" for ~1l dep~h dh*l~nlin~tions- The dbpth of a ct~}x=lent of the BH~ while tripping ~n or out of a well is the total of the d~ noe between the lower edge Or the lowermcst pip~ of dr~llstring 34 to the ~H~ cccpcnent, plu~ tha tckal l~ngth of drill string 34, minu~ the portion of the u}~Y~rna~t pipe e~dislllng above rig floor 16. The dep~h de*lqmln~tian and m~ni~oring system~ and ~*~Yods of the E~ nt invention aocurately deter~Lne the depth of a ~H~ ccrlsJ~elt during drilling or wh~le tripping in or out of w~U~x~n3 36.

In one preferred e~bcdirent of the present invention and still referring to Figure 1, lower camera 50 i~ positioned within the lower pcrtion of ~ast 12 of rig 10 on or near rig floor 16 su~h tha~ its field of vi~w ls directed to the 2~39~3~

m*~L~y table and the tcp of drill string 34 e~nl3rLIng above the rotary table when present. ~he field of view of lower camera 50 is also preferably di~ ted to the upper portiQn of next pipe 40 stored within mLuse hole 38 that extends above drilling floor 16. On some drilling rigs, it might not be possible or practical to position lower camera 50 such that its field of view is di~ 3d to both the rokary table and the mouse hole. In such 1n6tdrcrs, two lower camera units are preferably used. In anr~ler preferred embcYI~bent of the present invention to be described in greater dbtail later herein, ~ r camera 52 is located in t~e upper portion of mast 12 and pcsitioned such that its field of view is directed to ~here t;he top edge of a ~oint 35 would be located during a tripping operation.

Figure 2 schemati~ally illustra~c the main c~xYnent6 of the video depth c~b~r=ina~iQn systems of t'he present inwention. Camera 54 repQi#3ent6 any one of t~he cameras used in ~he present invention and located on the rig, ~hÆther it be lower rotary table/~x~lse hole camera 50, upper camera 52, or a seFarate rckary table camera amd a ~Luse hole c~mera. Camera 54 may be of any standard video for~t, blac~ and white ar oolor, sudh as mcdel No. Wnn~L202 available from EblY~onic. Camera 54 aoquires an i~age of t'he abject to be n~#~ured and supplies a oorre~FYYILLna vidbo signal to ~a~rrlllg devi oe 56 such as that available from ~oeckeler InEt~ ents, Inc., model number VIA 100. M~ uring dÆvi oe 56 displays the image reoeived rr~ camera 54 on video screen or display 58 such as DXX~el No. VM4509 available fro~ Sanyo, an~ ~p~ri ~
Dr~ible curscrs 60 and 62 t ~ . Ihe location of cursors 60 and 62 ~n video ~isrlay 58 i8 irl b}X~YICqtly oontrolled by an input signal to measuring devi oe 56 frcm oontrol ccnsole 63. The dls~ncs between cursor~ 60 and 62 appearing on video display 58 is nf~Ln3d in pixels by measuring devi oe 56 and 2~3~ 3 s~lied to ~r 64, ~i~h m~y be a~y ~Futing de~ioe capable of aco~ptir~ data fr~ mea~ri~ de~ioe 56 ar~ making t~ re~ir~ ~aticns.
C~ 64 may be any c~ter, mi~, mi~ ~sor, mic ~ r¢roller, etc. su~h as an N286 available f m ~ Aa~ Inc. of H ~ stcn, Texas US~. In an Alternate e~txXL~nene, measuring devi oe 56 superi~po6Fs only one m ~ le cuu~r on disply 58, which in operation is ~ ionally ivalent to t~e two a~rsor G ~ i ~ nt sh ~ n in Figure 2.

In m ~ depkh dfdl~n 1~ations with a particularly preferred elbcXlonelt of the 6ystems and D#~iuols of the F2~##Ent invention to be described he~eLlY{Hber in greater detail, the pasition and Dr~n~ment of traveling block 22 and h~x~hwei~ht or hcckioad are preferably cbkaired and iDçlr~3d into computer 64. Hkx~cwei~ht rEYYnrreaents are made by hcckload sensor 21 located, for example, in con~unction with dbadline anchor 20 as shown in Figure 1 ~lthou~h as those akilled in the art will appreciate, hcokload D~y be nEasured at any one of D~ny locations su~h as at hxxik 28, in crown block 14, on drill line 18 etc.
Ihe F~6ition and D~m3ment of traveling blodk 22 ~ay be obtained from traveling block senscr 27 such as a dl~nh~arXs sensor that mLnitc~s the rctation of drum 26 as drill l~ne 18 i8 reeled in and cut of drzn~orks 24. Traweling block sensor 27 may be, fcr exa~ple, an encoder direckly c,r indir ctly attached to ths rotating shaft of rotating drum 26 as iB pre9ertly known in the art.
Alternatively, blodk pcsition and mLvement may be deeA~Lln d by a sensor locat~d in crown blodk 14 that monitors th~ rotation of one or mcre of the sheaves th~n~in, or monitcrs the Dr~3bEnt of drill line 18 as it passes t~ h th~ crown blo~k 14 or nEar drawworks 26. As noted previ~ly herein, de*}cn=ining depkh based uFon travel$ng block location by monitoring mLvement of drill line 18 and mLnitoring hcokioad alone as presertly dbne in the art ~c 2Q33~J
replete with curoes of errcr t~at individually or ~l~l]atively result in inaccurate depkh ~Y#:RDn3ments. Ek~nuer, the video depkh systems an~ me*hods of the present inNention are eqyipped with ~eans for df*l#l:Lng and substantially eliminating these errors as will be hY~ a~ber explained in greater detall.

~en detemllning d~h while drilling or tripping, it is i~portant to aca~rately measure the length of a pipe being ad~ed to or s~tracted fr~ the drillstring and keeping an aca~rate record of the length of ea~h of these pipe ~ectians. Figure~ 3 and 4 illustrate the pm~3are of a preferred e~t of the pre~ent inv~tion that ~cP~ lower caD~ra 50 for ~ring the ler~ of ne~ct pipe section 40 located within ~s~hole 38 to be ad~ed to drillstring 34, or that was re~ved fr~ drillstring 34. E~riefly, the p~e incl~3es a calibra~ien ~ and an acbual mea~rir~ step. 1~ calibration p~
prod ~es the le ~ h that pipe~ ~ct~ d belaw rig floor 16 and into ~ se hole 38 when a pipe iB plaoe d therein that loads spring 39 (if present), and a t~ble of coefficients used to measure t~e sectian of the pipe extending abcve ths rig floor. Ihe total length of pipe 40 in mLuse hole 38 is then obkalned by ad~ g the two lengths together.

First referring to Figure 3, face,to-face length "A" of any pipe placed within ~cuse hole 38 is equal to length "B" of th~ pip~ extardlng below rig floor 16 exLlud~ng th~ length of m~le tko~#xl3 41', plus lenqth ~cn that ths pipe exbends akove rig floor 16. Slnce th~ leng~h of male threads or "pin" 41' of all pipes to be DYY~med is fairly cr~Y~mt and held to a tolerance set by the AEI, th$s length is ig¢x~n3d. In the first step o~ the ~libration pQXY~3tlne, tok21 face-to-fac~ leng~h A o~ referenoe ar calibration pipe 41 i8 accurately ~ ~ 3 ~

D~asl~red before it i~ plaoed in D~usehole 38 with a steel tape, for example, arYl entered into c~ter 64. ~en pipe 41 is plaoed within ~s*~le 38, the weight thereof loads ar~l ~esses spring 39, and since spring 39 is very rigid, all sul~t pipes plaoed within ~sehole 38 will ca~ress .,~ir~ 39 a~a ely the sa~e an~nt. Ihen, with refer~ to Figure 4, after refere~e pipe 41 is plaoed in ~s~hole 38, calibration md 70 havir~ a plurality of calibration ~arks 72 thereon is plaoed ad~aoent to the u~er portion of pipe 41 e~ctc ~ir~ above rig floor 16, bokh pipe 41 ar~ m d 70 preferably being aç~ Li=ately the sa~e d~ noe away fro~ lower camera 50.
In a preferred tcX1bnent, marXs 72 on rod 70 are spaoe d an equal distance from one another, e.g., 0.5 feet (15.25 cm), the nLmber and s ~ ing of marks 72 dlE~#YlLna on the degree of accuracy desired to overcome the apparent displa oe ment of ncE~#3uidistant bbjects associated with camera 50.

IhQ iuage recx~3b1 by ca~era 50 is displayed on display 58 which has superi ~ d thereon referenee cursor 62 and reYf~nn30ent eursor 60 by nYY~xring device 56 as shown in Figure 4. Fron oontrol ccnsole 63, referenoe eursor 62 is Dxm3d and plaeed where calibration rod 70 eontaet~ rig floor 16 and remain~ in t ~ 8 poeitlon d~xing bcth the calibration and length rYyc3ure~ent Fl~xaY~mes. }q##~lreeLnt cursor 60 is then first placed over or adjacent to the ne~t mark 72 an rod 70 up from rig floor 16. W~n so placed, an entry i~ made on CX~,tLV1 corsole 63 whiclh sends a sigral to c ~ er 64 tkux~u~h mP~Tring db~ 3 56 to det~Dlne the number of pixels be~3En cursors 60 and 62 and to ~ate that rder to th~ kna,~n di~ betwe~ the bo~t~
and fir~ marks 72 an md 70. ~as~nt a~rsar 60 i~ then maved up thr~
ea::h ~:cessive m~rk 72 on rod 70 ar~ Bigrlal8 a~ ~t to ca~ 64 at ea~h poi~t. ~oe all marks 72 cn md 70 have been reco~ded in th$s fashion (or as y marks ~ accuracy requires and tire and cl~ Y;tances permit), cco~lr~Yr 64 has ~yiled a table of pixel dis~ oe ~#*~3En cursors 62 and 60 versus length, or actual height ~ e rig floor 16 in this case. In an alternate form of the present invention, display 58 has only cne mLveable cursor superimposed thereon by ~e2suring devioe 56, which functlonally is the s a as the two cursor e~bcrl~ent just described by the one cursor serving as both a reference cursor in one mcde and as a =ecsur-ment cursor in the okher mode.

In the final calibration step, sea3wrement cursor 60 is placed ad~acent to the tcp edge of pipe 41 as shown on display 58 in Figure 4. Eased on imput from mP~lring device 56, ~ ter 64 then equates the pixel distance be*ween reference cursor 62 and measure~ert cursor 60, which correspcnds ~o length C
(Fig. 3) of pipe 41 extendinq above rig floor 16, to a length (f~et or meters and fractions thereof) by using the earlier-generated pixPl distance versus length table. A linear interpolation, a curve fitting algu~-ithm, or any sinilar algorithm known to those skilled in the art can be used to solve for poin~s that fall between the calibratiQn points. In t ~ manner, length C
(Figure 3~ i~ c ~ , ~hich i8 5ub*raoted frc~ earlier~dnteecined tctal length A o~ pipe 41 to cetJrnlne length B of tbe pipe e~cfrYlnq below rig floor 16. Lenqth B i~ stored in cocputer 64 for future use.

The video ~ygte~ of the present invention illustrated in Figur~ 4 i8 then fully ~librated an~ ready to accurately measura and autcmati~lly tally the length of eadh new pipe 40 of u ~ 1~ ~ U~ before it i~ added to drillstring 34, c~ after it is removed therefrcm, via mLuse hole 38. In the re#sLre=ent pcocedure, af~er a pip~ ~ placed in mcuse hole 38, rea3wreme~t c~rsor 60 ~
lined up with ~hQ very tcp edge of the pipe with reference cursor 62 re=alning -- 19 ~

w~u~ne it was plaoed during the calibration p~slY3hDre, and an entry i8 made in oontrol oonsole 64. From the pixel distance v~sus length table generated during the ~alibration Fc~xY~ure and stored in ccnç~l~er 64, ccnçlr~er 64 equates the distance k~ sen cursors 62 and 60 into a length, and then adds the previously-deter~nel and stored length B of mous~hole extension thereto, whiclh giv,es the tokal faoe-to-fa oe lengtih of the pipe about to ~e added to drillstring 34. Eaclh ti~e the leng~h of a new pipe is r~a urel in this fashion and the pipe is added to drillstring 34, an entry is made on oontrol console 64 which thru~gh ~P~lring devioe 56, updates a summation program in oamputer 64 to add the new length to a running tokal leng~h. Alternatively, ea~h tlme a pip~ is removed fram drillstring 34 and the length there~f detcr~lned as just described, an entry i5 made on oontrol oonsole 64 whic;h throu~h _ ~lring device 56, updates a aubtr~ctian program in ca~puter 64 to subtract the length of the remLved pipe fram the running total length. In a preferred ~br~mPnt, the tokal leng~h of all pipes making up drillstring 34 is displayed on ~play 58, and also reoorded on ta~e for playtack if desired.

In an alternate version of the e~bcdlment of the present invention justdescr~bQ~, reasure~ nt devi oe 56 i8 replaced with a video digitizer equipped with digitization software 8uch as a I~RG~ M8 available fram Dawson and Associates of Hbuston, Texas USA. In this alternate ~mbcd1~ent, the video digitizer i8 resident on the co~puter 64 bus, for exa~ple, or as a corponent separate from oomputer 64 as with measuring devioe 56. Ihe i~age recorded by the camera i~ digitized, written to thQ co~puter's videol en~ry, and displayed on the display or screen associated wi~h the computer along with cursors also genera~ed ~y the digitization software. ~e software mavas the a~r~ors ~pan cperat~r crarxl and dete~ir~s the pixel distance betwe~ the a~rsor~ as was done in the ~urement devioe d~ent.

qhe calibratian and ~I#fwao3nelt EI~xa#hrnes from an operator viewpoint are basir~lly the same.

Arx*~her implementatian of th~ alternate }xxLI/3nt automates the ~YYu~1DCn~=t pr~x~hlre with ~ r 64 n~c~ng the ~#~cn3Dent with little or no cperator input. Specifir~lly, a map, for example, reçno~Y4~ting the approximate shapes of calibration rod 70 and the objects to be DEY~nsd are stored in coEputer 64. During the calibratian E~lx~edbn#, calibratian rod 70 is placed the same as previously described. Co~puter 64 recognizes its basic shape as well as each c libration marking 72 therean and stores the pixel location of each ~rk 72 in its memary. C~n~lrter 64 then uses the pixÆl dis~Y~e between each ~rk 72 along with its pr~vious knowled~e of the diE~noe between each m~rking to generate a pixel ~ e versus length table as previously dÆscribed.

Reference pipe 41 is placed in Dxl~sehole 38 and its total length entered into computer 64. I'he computer th~n examines and reoognizes the section of pipe 41 exterc~ng above rig floor 16 and u~P~ th~ inage in de~ nlng the length thereof with the pixel di ~ versus length table, and solves for le ~ B
of Figure 4. ISYolesY;er, computer 64 throu~h i~age recognition dete~L~Ies the leng~h of any pipe in ~r~ehole 38 as previously described. In inst3nces where a ccnfusing bacX~px~md miyht ~rrbq~!Ln3 or interfere with the ability of ccE~ er 64 to recognize shapes and cutlines of ob~ect, a ccnY~mt shade bac~n~p or bacxlight i3 preferably used.

~n an~*~u~r preferred eabcXl~Dsnt of ~he FI~x~nt invention, the lenqth of singl~, dkAible, or triple ~oints 35 sbQred in the pipe racXs of rig 12 may be accurately n~#E~Dn3d and tallied a~ they are added to or subtrac~ed frcm ~ ~ 3 9 ~ ~ `
drillstring 34 either while tripping with a rctary table drive rig, or when addin~ pipe during drilling or tripping with a tcp drive rig. Referring briefly to Figurs 1, upper camera 52 is positioned in the upper portian of m2st 12 and is used in conjunction with lower camera 50 to make the required length ~e#~l~n3melts. AS with the previous elbcxl~ent used to measure the length of a pipe in Drl~ehole 38, the pipe rack emtKxL~ent of the present inNention includes first a ralibratiQn step followed by the actual n~##RuDccent steps, either in digitized or non-digitized format.

Figure 5 illustrates the calibration F3~x~#!ure used fcr the two camera e~bcdl=ent of the F~#~ent invE~tion, which will generate two separate tables of pixæl distanoe v~sls length in ccmputer 64, one fcr each camera. In calibrating thQ system, uFper camera 52 i8 focused an the uFper portion of reference pipe 80, which may be a single, dcuble, or triple, that has been previously measured by any accurate tedhnique such as by hand with a steel tape, or with ~he previcusly-descr;hc~ mousehole eDb~XL~ne~t as reference pipe 80 is assembled and attached to t ~ portion of drillstring 34 c~tendina abcve rig fl 16. Calibration rod 82, which i~ e~ ertlally identical to previ~cly~described rod 70 and includes a plurality of DYU~C~ngB 83 t ~ , is pc~iticned ad~acent to the uFper portion of reference pipe 80 such that bokh the tcp portion of pipe 80 an~ rcd 82 ar~ within the field of view of upper ca~era 52 and preferably being ~çpQ~IcL=ately the same distanoe away fm m camera 52. ~h~ view recorded by uç~r camera 52 i di~played on display 9o h2n~ng referenoe cm ~r 84 and ~LYI~ro3ne~t cursor 85 ~lr~rimposed thfu~3~n altku~h as noked earlier h#~ n, cne cursor may be used that i~ functionally equivzlent to curso~s 84 and 85. Similarly, lower camera 50 i~ poeiticned ~uch that its field of view is directed to the lower portion of referenoe pipe - 2~ -~3~
80 an~ sec2nd calibration rod 88 having a plurality of markings 89 thereon held ad~acent to pipe 80. The view from lower camera 50 is displayed on display 58 having reference cursor 92 and =ee#D~o3Jent cursor 93 superi ~
th~n#xn. Lower camera 50 and display 58 may be the same as thoee used in DY~ ring the length of pipe located in nrlEi~hole 38 as just described, or may be a seFarate third camera if it is desired to leave the mous~hole camera urr~f~lD~bed in order, for example, to preserve the mousehole calibratian. ~n an alternate e~bcXl~nent, both the view frcn upper camexa 52 and the view f D
lower camera 50 may be displayed on a single ~crlay in a split screen format, or alternately on the sa~e display an command.

~n r~librating first upper OE era 52, re~erence cursor 84 is placed on or adjacent to the lowest D~u~king 83 on upper calibration rod 82 as shown in Figure 5. Sinoe refer~a: cursor 84 will remain in th~ C po6itian for all s~}Y~x;oent ~E~:~D~3nenes, c re should be taken that th~ po6itian of reference cursor 84 will be below the tcp end o~ ea~h ~oint that is planned to be nY~sured when it i8 added to drillstring 34. Next, nY#~u~3~ent cursor 85 is placed cn ~ next mar3cir~g 83 ~p fm~ the lc~t marking. ~n entry is then made irrto ca~ter 64 via c~l c~ole 63 ~nd ~uri~ device 56 ~at recor~ tho pi.Yel di~tance b~n cur~ors 84 ar~l 85, ar~ also the lengt~ that t~liS piYPl distance ~ eg!ual to, e.g., 0.5 feet (15.25 cm). A~ter th~s en~cry has been ~Dade, ~Y#I~no3Dent a~rsor 85 i~ D~ved up ala ~ ea ~ ~ ~ ive markir.g 83 on u~ r calikraticn rod 82 wi~h an entry being made into cc~çl~er 64 fcr each D2u~c~ng such that a pixæl ~ e ~ sws length table 1~ g~nerated and sbored inside computer 64. In th~ f$nal cali~ratian step, ~EY~lrerent cursor 85 is plaoed ad~acent to th~ tcp edge of reference pipe 80 as sho~n in Figure S. ~a~ed on th~ p~Fl d~s~nce v~n3us length tahle stored in conlrjer 64, the 203940~
p~v~l dis~LY~e bed~3en reference cursor 84 and DYY~RLn3/3nt cursor 85 is cxrw~crt3a into length with this 1 ~ h "P' as indicated on display 9o be m g stored in ~ r 64 for future use A~ will be hf21~1Yleber explained.

The cal~bration of lower camera SO is done in essontLally the same manner as with upper camera 52 by using lower calibratian rod 88, reference cursor 92, and nf#~laoa~ent cursor 93 exoept that the final calibration step records the pixæl distanoe be ~ n reference cursor 92 and DEysLre=ent c~rsor 93 when the later is placed ad~acent to the lower edge of reference pipe 80 as shcwn an d~splay 58 in Flgure 5. ~h~ p;YP~ distance is ccowertoa into a length based on the pixQl distanoe versus length table generated for lower camera 50 and stored in ccmputer 64. ~h1~ lengkh "G" as indicated on ~play 58 is stored in cocputer 64 for future use as will be hereinafter explained.

Figure 6 ~llustrates how length l-Dn H n lowest marking 89 on lower ~alibration rod 88 (which corresponds to referenoe cursor 92), and lowest marking 83 on upper calibraticn rod 82 (which oorrespcnds to reference cursor 84), is d t r~lned, length D being needed to ~ e the length of a new joint being added to ar ~ubtract d from drillstring 34 during the r~#~wrim ht pr~oe~ur . AS noted previcusly, tokal lenqth '~" of referenoe pipe 80 was previcusly measured by u ing any accurate technique and ~ d into computer 64. Iength F ketween lowermc6t marking 83 on rod 82 (where referen oe cursor 84 i~ fiY~ ) and the top edge of r~ference pipe 80 was measured and r during the calikration prcoedur an~ is therefore ~150 known. S~ arly, length G bekween lowermo6t markin~ 89 on rod 88 (where refe!rence cursor 92 is fixed) and the low~r edge of reference pipe 80 wa~ also measured and raoorded during the calibratlon prccodure an~ is therefors also kncwn. Length D

therefore is ~lAl to length E plus length G ~ length F. anoe length D is dbdlon~ed in this fashion and stored in cc~çlr~er 64, the length of any new pipe joint added to or subkracted form drillstring 34 can be dE*Y~ined from the equation: ulX~x~n pipe length = length D (known) - length G (to be deter=ined) + leng~h F (to be determined), lengths G and F being dE~e Dined in the following manner.

After the ralibratian F~IlY~huDe of upper ca~era 52 and lower camera 50 is ccmplete, th~ video system of the present inwEntion is ready to dEdY~nLne and reoor~ the leng~h of any joint being ad~ed to or subtracted from drillstring 34, t'his E~rxa#dure being illustrated in Figure 7. In Figure 7, lower camera 50 records the lower portian of ur~x~wn pipe 100 and displays this view an display 58. Hee:wuncnent cursor 93 is placed adjacent to the lowermost edge of unkncwn pipe 100 (lllp~rmoFt edge of drillstring 34) with referenoe cursor 92 re~eLnLng w~u~ne it was placed and fixed during the ~rlie~ #;cribed r~l ibraticm prcx~xhIre. An entry is made in control console 63 which ir~*~nx ts ccF~ er 64 via measuring devi oe 56 to ccmpute leng~h G based on ~he pixel dis~ oe versus length table generated and stored in coFputer 64 during the calibration Felxxl~Lre. Similarly, witlh the view of the upper section of ur~x}~n joint 100 displayed by upper camera 52 on display 90 (or on display 58 in a split-sK3~3en format), Dt#~rrement cursor 85 is plaoed adjacent to the UpÇe~.uJ~t edge of uc~bx~wn pipe 100 with referenoe cursor 84 re=alning where itwas plao~d and fixed during the calibration p:~xsa~lre. An entry is made into cx~nsl console 63 which LnYt~5'D computer 64 via measuring devi oe 56 to cx~ te length F ~ased on the p~xel di~mce versus length table generated and stored in ccn~llter 64 during the calibration pn~lY3~une- Qnoe lengths F and G
are dete~lL~3d in this fashion, computer 64 ccQ~rtes the lenq~h of unXnown ~39~
pipe 100 aocording to the eguation: unXncwn length = D - G + F. ~hic known length is t~en stored in computer 64 and used in adding or sukractlng the lengths of all pipes that have been added to or subtracted from drillstring 34 either while the drilling operatian is being cxrYhx:t d, or while tripping in or out of the well. In an alternate emtxXlu~ent, the ralibration and D~Y~D~ement prcY~s~1res may be performod in a digitlzed format as was described earlier in canjunction w~ith the mousehole e~t~xl~ent.

In particularly preferred cabcxl~nents, the videD systems and methsds of the Fr~#~Ent invention find particular use in c~d~nllnlng and verifying the depkh at whidh a ccmqK~ e~t of a BH~, e.g., ths drill bit ar a particular sensar of an IWD sub, is looated at any given moment in a wellbore in onder to, for exa~ple, reset BH~ position, re~et traveling block position, db*}~=~in D2ud~lm bit p#ne*ration, and measure lncre neal bit penetration. Referring to Figure 8, thera is shcwn in si~plifled form drillstring 34 e~dlrYIing below rig floor 16 and into borehole 36. Drill~LLing 34 includes EH~ 37 at its lower end and portion 102 of the last measurad pipe added tD drillstring 34 exterdlng abcve rig floor 16. Camera 50 i~ po6itioned sudh that it~ field of view is d~#~ted to th~ portion 102 of drlllstring 34 eYtYslLLn~ above rig floDr 16. camera 50 may be th~ sase camera a3 that used to ~easure th~ length of a piFe placed withln the ~Lusehole as described earlier herein in oonjunction ~with Figureæ 3 and 4, or ans~Er camera if it is not po6sible to focue in on koth the Dx~ bDle and immediately above the rotary table. In the alternative, camera 50 may be the sa~e as lcw~r camera 50 used in denf~L~Iing the length of a joint added to drillstring 34 as describe1 lier hf~ n in con~unctlon with Figures 5 - 7. In whatever case, a pixel distance v~nsus length table (hf/~u=~eter referred to as the "r2tary table calibraticn table") i~ generated ~t ~ O ~J
and stored in computer 64 by following the calibration Fr~x~32~re ~ des~r;hcd earlier ~ n, and the table is ~-CP~ in dbt~onL~nin~ the depth of 2H~ 37 at any given time in the following manner.

In Figure 8, depkh '~r' of 2H~ 37 at any given ~ in borehole 36 is simply the summation of length "I" (the overall 1 ~ h of drillstring 34) minus length "J" (the length of sectian 102 eYtlclLlng abcve rig floor 16). ~ h I
is dç1l~n~inel by following the calibratian, reeu~ mcmeat, and summatian F~x~hYres described earlier herein by using the cre!c~L r~ technique of measuring the length of a pipe when it i9 in the mLusehole before being crisY#:bed to drlllstring 34, or the t~rcZLDera te~tDn~Iu of ~fasuring the length of a ~oint while it i8 r~lsperL~x2 in mast 12. Iength J of portion 102 of drillstrin~ 34 exterLlng above rig fleor 16 i~ detf~ d by following the 8ame kasic calibratiQn and rYY~=Ioenent technique used for measuring length C
of pipe 40 çodbxndlng QUt of Dr~ hol~ 38, which wa8 described P~ lier herein in can~unctiQn with Figures 3 and 4 and there~ore believed unL~#Y##=ary to be repeated. cnce length J i~ deeer~ined by c ~ r 64 thrsu~h the use of the m~L~y t3ble r~1ibratiQn table, c ~ r 64 d eernlnes the dbpth H at which EH~ 37 i~ pc~itloned ~y subtII~ tlng length J fron the summatiQn of all lengths, or length I.

Ihe ability to accurately denlLo~ine tbe depth of EH~ 37 at any given D~ln~tlt in ~ a~ shown in Figure 8 is particularly useful in verifying and res~tLn;
block positicn and dbpth as r~cor~ed by a block positi~n sensor/hocXload sensDr type of depkh system used in associatian wi~h the video systems o~ the E~YuEnt inNention. For exa~ple, if drill6tring 34 is placed "inrsliR6" AC
shcw.n in Figur~ 8 w*u~her during a drilling or tripping operatiQn, the vi~n sy~3m of the El~##~nt invontion can dbdl3~:lne depkh H as just described and cro~x~ne that depth with that indicated by the traweling block Drh~3n~nt sensor 27 and hookload sensor 21. In a parti~larly preferred ~trY~nent of tho F~#~nt i ~ ion as shcwn in Figur_ 2, signals from traveling block movement sensor 27 and hcckload sensor 21 are s_nt to ccnçlr~er 64, which ccrn~ cusly cc~çar_s the dep~h indicated by sensors 27 and 21 with that dete~=lino~ by th_ procedure indicated in Figure 8. If a d~5cDo$xmcy exists, ccmput_r 64 au~natically or an command res_ts the positian of t]he traveling blc~k as indicated by sensors 27 and 21, ~hic~ as noked earlier her_in, is a major shslllx~nln7 of prior systems in that re#~d~:lng block position is a slow and disrupkivo proces3.

Figure 9 illustrates hcw one cm~nd~mont of the E~#i~nt video system can bs used in res~d~:Lng block position in an alternate meun~er. In Figure 9, lower camera 50 (Figure 8) display~ an imags on display 58 of the tcp portion of dr~llstring 34 b~ing grasped by elevator3 30 with reference cursor 92 and E#~rneme~t cursor 93 superimposed on this ~mage by measuring dQvi oe 56.
Re~erence cursor 92 is fixed in the samo position it was placed ~ n the rokary table calibration table was generated, and reY#~Ynanent cursor 93 is placed adjaoent to the lowermost edge of elevators 30, which i5 the preferred referenca point. Eased on the rctary table r~librat~on table, co0puter 64 oorn~rts the pixel d~ be~h*3en cursors 92 and 93 to an actual length.
di~tance ~n the la~st point of elevatcrs 30 and rig ~116 is the s~me a~ (or ~ ~ahn d~tano~ f~) ~e traveling block altitu~3e. If this newly = d distanoe varie~ fr~ that indicated by travelir~ bloc~k position sensor 27, c~ter 64 either on ~1 or aut~atically r~ts block po~itlcn.

4 ~ i `
Figure 10 illustrates a method of an embcrl~3ent of the present invention that i9 used in m~ ing ~ncreaentdl bit ~Lvement and in dedf~=L~aing D2~C~Im bit penetratian. In figure 10, incremental bit DYnnement is DEY~m3d by placing rYz~Dlcnent cursor 93 ad~a oe nt to a mark 110 on kelly 32 with reference cursor92 re~ LI~Lng in its calibration position (i.e., on rig floor 16). The length correY~xI~ling to the pixæl dis~ ce between cursors 92 and 93 i9 nY~Lred by ccmpu~er 64 with the rotary table calibration table. After a period of drilling time, kelly 32 will have move dchn~lrd, for example, to where mark 110 on kelly 32 is shcwn in pbankam. At that time, reYuRnreDent cursor 93 (shown in pb2ntam) is moved aldja oe nt to mark 110 on kelly 32 and the distancebekween cursors ~2 and 93 is again DY~aSUred. The difference between thP two r/Y#D m3~ents is thQ a~ount of bit penetratian, which is recorded as su~h by computer 64. In a preferred e lxXL~nDnt, the bit penetration is ad~ed to the previcusly - DY#~med and d~tl~min l sum of the lengths of all the pipe in the bore~ole to give EH~ dpkh at any given Dxl~Ent in ti~a. In a particularly preferred embcdl~ent~ oomputer 64 is prcvided with a clock or timing circuitry means which records bit penetration versus time to yield rate! of penetration, which ig a v luable FYulGDeaer to the cperator of the drill~ng rig.

Ih~ systems and D~x~ds o~ the El~##ent invention can be further used inoonjunLtion with block pceitiQn ~ensor 27 and hocXload sens~r 21 in accurately dftfqJ~lnlng depth ~hilo dk~lling, tripp~ng-in, or tri~ping-aut, all as shown cperaticnally in Figure 2. Hbckload i5 monitored to di*Y~o~ln when traveling block ~ t, a8 ~on~tored by txaveling block positicn sensQr 27, can be eguat2d to drillstring ar EH~ n~wn~3~nt. In gereral, a high hccXioad indicates that the drillst~-ing i8 suFported by the traveling block, i.e., th~ string i8 cut-of-61ips, and therefoxe ~x~3bent of the traveling blodk can ccn~ic~nkly be c~

equated to drillstL-ing Drnn~nent. A low hockload indicates that the drillstring ~ supported by the dip8, i.e., the string is in-slips, and therefore nr~3~ent of the traveling block shculd not be equated to drillstring movement.

HcoXload sensors are typically bydraulic or load ~ell driven and are commonly pla oe d on or near the dP~dline anchor. Uhfortunately, using hncXload sensors in df*~ nln7 the slips-in versus slips-out transition is somewhat inaccurate with Dlost of th~ 1nacouracies arising because of delays i~posed on the hsoXload sensor signal. For example, delays are i~x~#3d by the D~hanics of the h~draulie system or the eleetronies of th~ load cell, and the mechanies of the cable as it stret~hes and oontraots. Ihere are also delays induced by eleetrical and eleetrenie oxa~ elts of the data aequisition circuitry, b~th intentienal and p2rasitie. ~hess delays and their DYKplitude, whic'h typically vary f,~ sensor to sensor and rig to rig, adversely affect hcckload mLY~*me~ents because they D~#~k the 81ips transition point, i.e., the exact point at ~hic~h the drillstring and 8H~ start mLving ~hen taken aut-of-slip6.
~ R prbblem i8 Dade DYXne acut~ at 81ip8 transition points kecause bo~h traNeling blodk position and hcckload are typic lly changing rapidly.

Hkokloal =e#UWln3D217t9 can Al SO vary appreciably because the drill~tL-ing is typically Wf~X~Yi d at the end of 2cre than a t ~ d feet of cable. This cable Etl}dI~h3~ and act~ liXe a ~u-ing w~YEver the drawworXs plays out or take~ in c 'bl~, which ~uc~c ~ blry c~ dh~Jt~ and urc-el~hooe~ an the hscXload signal tha~ ar~ more a function o~ driller or rlg ackion than string ~ ~ 3 Friction of tbe string a ~ t the f~n~tion, especi~lly in a deviated well, can also cause c~oodho~ts and ueL~a~ ooes in hookloæd dho~l~g Drn~3nEnt, dfçYoYilng on w~ her tbe str m g is going in out of the hole. These false drcp~ and rises during nY~ament can also occur in a well that has both high mLd weight an~ a bit with small ~ets. False hookload sY#~Dn~ l~ne- can also ocalr in a string that is statianary because sane of the string weight can be t~rted by the formatian w 1l in the case of a deviated well, and,/or by the formatian itself when the bit is an-botta~. In ~tian, the accuracy of ho~kload sensors, especially l~raull~lly driven ones, are s~ptible to te~gperature cha~ s~h as thcse caused ~y changes in ~nlig,ht patterns or precipitation.

TS~aveling block D~vement sensors are t~Ct~lly up/dbwn ca~ters and are cc~ly placed on t}~e drawworks or the fast sheave in th~ c~awn bloclc. There are also cable D ~ nt sensors, also ma~nted in tl~ cn ~ block or near tl~e do~n~works, that can be used to de*}o~ne block Dr~aY~nt and positian. When plac~d an the drawwcrks, they a~tually function as a drawwork pcc$tian sensor. ~n all ~CPq, a rqlibralt$an rL~t be performed to relate draN~orks mcvement or cable mov~lY~lt to traveling block nr~J~nt ar pccition. This i~ typically d~ne by positianing the traweling block at it~ lowest point and setting t~e draww2rk~
posit$an ln a computer. A series of periodic 8_ of block heig'ht and oorrl#~x}oding dIls**~rks pccitian a~e then ~ade at certain prescribed intervals a~ th~ dlan* mrk~ turns, th~n~y taking in cabl~ and ra~ing the traveling block. W~n the block iB at its highest positian, the calibration posxa#hlr~
i~ complete and these draww~rks-position/block-~eight coe~ficients make up a table that is us~d to relate drawwarXs pcsition to block height. When t~e traveling block sens3r 18 plaoed on the fast sheave in the crown block, a conversion is preformed based on sheave diameter so that sheave rotation can be equated to drawwcrk~ ~cvement. Sinoe sheave diameter is constant, only initi~l block pccition needs to be entered and then traveling block position can be tracked.

The drawworks cable is subject to bokh elastic and plastic stretch when under tensian. Elastic stretch i8 temporary, i.e. the cable return~ to its previous leng~h when tension is remaved. Since the cable wraps over the draww~rks drum in sevaral layers, the relaticnship between drawwarks position and block altitude is neither cxrY~b~nt ncr linear. Ihese layers are ~plied at different times under different hockloads (different tension) and therefore the cable does not always change layers at the same Dvact place with respect to block po6ition. The effects of plastic stretch, which typi~lly nrcur with a new c~ble or when a cable is s~b~ected to a higher ~hen nLrmal stresc, are nDt reIYnned with a reduotion in tension. ~herefore, drawworks ~li'brationc shoLld be preformed whenever th~e c~ble i8 replaced, after new cable haB been '~dorked in", and wt~ ner the cable h~R been s~b~ected ~o e-rY~cive loadc su~h as after the freeing o~ a ~tuck drill 8tring-A rctation sensor Drl~r~3d on the dead 5 ~ e can be used to detect cablestret~h because the ~d sheave only moves an a~x~3T~ prcportional to cible stretch. X~h~n~er, a c~ble stretch 6e~nsor adds a third sen80r to the oost of the SyE~3~, dbes not address the cable 81ipçagæ problem, i3 s~bject to fculing, and is difficult to install and ~e~J~lin because it is located at the tcp of the derrick.

~g~

Cable mLNement sensors can also be used to d{*ernine block mcvement. These sensors typi~lly detect cable mcvement by sensing the s ~ s on tbe rible t ~ hall effect sensors or some other means. Ihey basir~lly preform the same as, and have the sa~e drawbacks as, sheave sensors. That is, they are expensive, diffi~lt to install and mainkain, and are subject bo fculing.

rn using the present video system and methods in oanjunctian with a o~ticnal h~oa~Vblock position dep~ system, tw~ hco~clcad thr~;holds are preferably used to pr~vide hysteresis in the slips transitian deten;in~tion algorith~ pn~ra=~ within ca~ter 64. An in-slips threshold is ~lec~ed lcw enough su~h that whenever h~klcad is belcw the threshold, it may be ocnfidently assumed that the ~tring i~ definitely in-slip~. An alt-of-slip thre~ld is ~lected high enough such that wh~ hffldcad is abave the threshold, it may be cr~fidently A~ that the string is definitely c~t-of-slips. E~lclcad must pass thm~h both thre~lds befare a slips trar~ition can be said bo have oc red.

Figure 11 illustrabes the cF#rati~n of a hcoklcad niboring me*hcd used in oanjunction w~ith the video systems of the present inNenticn that e~plcys hysteresis. The bqp graph of Figure 11 illustrabes hccXload 112 versus time w~ile the lower gra~h ill~Lrdtes traveling block position or traveling block ~ltitude (TB~) 115. rn Figure 11 in conjunctian with Figure 2, oomputer 64 scans the hocklo3d 8ign21 11~ imputed to oomputer 64 from hcoXload sensor 21 at a rate sufficient to ensure the recessary accuracy and resolutian.
Ccæputer 64 saves ~a~h hcokload mYasLreaent as well as the correspond~n~ block pcsition ~YasoreIent 115 frcm block position sensor 27 in a buffer. qhis buffer pre~erably contains a sufficient nu~ber of samples so that when a slips 4 ~ ~

transitian occurs, ~ r 64 is able to scan back through the buffer and find tbe block pOSitiQn oorle#~x~llLng to the hccXload value at the previous thL~#shold.

During an in-slips transitian, hcckload 112 can be seen to fall thox~h the out-of-slip~ t ~ ld at point 113 and then t ~ the inrslips tbreshold at point 114 at which time drillaL~ing 34 is firmly in-slips. Elock positian 115 also falls during this time since the traveling block is being lcwered as drillstrinq 34 is being plac~d in-slip~. Ce~ ter 64 scans the hcckload sample~3 stor~d wit~in the buffer back fra~ point 114 until it finds point 113, ~hidh is abave the out-of~lips trar#ition t~ld. At point 113, o~er 64 t~ the ~d~g bloc~k po~iticn at point 116 as the point ~e the drill~ inq st~ed D~vinq.

~e ~ramic~ of an out-of-slip~ transitica~ is different fmm thcoe of an in-slips transition because the bit does rx~t start ~ving ur~til the hockload $8 above the out-of-slips thre~old. C~ 64 ~tors hcc3clo~d 112 as it ri~es aba~ thQ in~lipB thr~hold at point 117 and then to out-of~lips th~#~hold at point 118. At thi~ time, o ~ 64 A ects blodk po~tion 115 at point 119, ~hi~h csllo#~D}n3~ to point 118 of hcokioad 112 as thQ point the bit stau~i3d mLYinq. c~D~Ir~er 64 then uses inrslip6 block po6ition 116 subtracted from out-of-saips block po6ition 119 and equates thls the leng~h of the pips iust added to or ou}~ cbed from drillstring 34.

Inc31~3nt31 depkh DY~Y~UyaDere~ while the drillstring is out-of-slip are usually quite accurate in a Eux~perly functioninq hLokload/cable Drn~3nent type sys~em Errors ~ ly oocur durinq slipc transitions, and these errors are ~ ly smPll. Uhortunately, these errors a ~ mnulate and cver a period of ~mP can ~x~ne significant, well over several feet in a trip-in or trip-out operation. The seoond source of inaccuracy typir~lly occurs in measuring the length of pipe added to or subtracted from the drillstring by the hooJcloadJ'draww~rks Yaso~ routine. Since the prim~y purpose of these pipe s~asur~ts is a chec~c of t'he driller's manual tally, this che~c should be more aocurate and reliable than tha oasur~ it is being used to veri~y.

A particularly preferred Pnit~d~m~lt of th~ preser~t inverrtion significantly i~mves the dept lh ~R:re~ algorith~ns with tha additil of a rig calibration algorithm. It also has a video llea~eent capability to provide fr~ent d~th resets that eli~ninate the acam~latil of d~ errors. This video based lleaQ~e is Ir~k of cc~ventianal sensors, and does not int ~ r ~ t or affect the normal drilling ~ eraticn of the rig or its crew.

Th~ Rig r~libration Algorithm of the present invention uses the same hcckloadytraveling block position pair3 saved by the ~ust dPcrribed s#asw~e~ent algorithm and ~dds two offsets called the InrSlip6 ILok 2ack (TCrR) and tha Out-of~Slip6 Look Eack (OSLB). These offsets are llePd by the hooXloadVT~A ~ea3wre3enk algorit~m to calibrate ~he hLbkloadVblock position ~t-In calibratlng a rlg, a referehoe pipe being added to tha drillstring is f~rstacrurately measured with ~ tape or with tha video systems and methods ribed earlier herein. Thi~ pipe b#ccmes a referenoe for use by the rig calibration algorithm. The referenoe pipe ~.~ subGeqoently added to the drillstring and the length ~ of nY#~Ln3d by the hccklcad4~3~ =ee~Ln~3aent algorith~. If the le ~ of the reference pipe as nE~E~n3d by the =IY~R~n33Cnt algcrith~ is nok the same as that actually nY#~Dn3d nanL21ly or by video, the cperator can select a ISLB offset and/or an 06LB offset so that length of the pipe is indeed accurately df~l~ncLn3~ by the DYY-ollc~ent algorith~. Ihis same offset is then applied to all su}Y#YIoerst Y2k=Dn~nants autcmatically.

Figure 12 and accxE~x~lying lable 1 illustrate an ex2mple of the ralibration proQess where cnly an cut-of-slips lcck back i8 used, t~e inrslips look back being esscntlally identical in principle and therefore b~lieved nck ne~Y#L=Lry to b~ also d ~ i~ed in detail. Sa~ples taken by ths software are nL~bered Qn the graph of hcokload 112 versus time and shown in Table 1 along with cc~J#~xlldin7 travaling block altitudes (TE~s). In the e~2mple, a reference pipQ i~ nYY~Ined as 30.00 feet (9.14D~) and an in-slips T9A o~ 4S.92 feet (14.00m) is recorded. TCT~ and OS~B ara both initlally set at zero. Ihe cut-of-slips ~ old (OST) is set at 90 RIbe (40.8KXG).

At sa~ple #6, h~bklcad i~ 91 Xlbs (41.3XKG) ~hich i8 above the OST threshold of 90 Xlks (40.8XKG). The ~trin~ i9 now out-of-slip~ and the ~Y#f~rrcme~t algorithm looks bYu~k in time at eadh sample urtll it finds one at or h~low the 05T of 90 Xlbs. Sample 5 is, 89 lbs (40.4X~G), which i~ below ths 06T. At this point, the out-o~-slip6 TEA is 74.98 feet (22.8$m).

The in~lips TEA wa~ n##~m3d during thQ previcue transition and w 45.00 feet (13.72m) and therefore the leng~h of the pipe ls out-of-slips T~A (75.98 ft. (23.1~m)) minus in, d ips T~A (45.92 fee~ (14.0Qm)) or 30.06 ft (9.16m), whi~h ls O.06 ft longer than tbe reference pipe actually is. The operator ~&3~iJ

therefore adjusts the OSLB to ccnl#~D~n~ to sa~ple # 3 which has an out-of-slips TBA of 75.92 (23.14m). After m ~ this OSLB adjuE~DEnt, the length of the pipe as cxn~lted by the ~yu#~Ln3~ nt algorithm is the out-of-slips TBA as OSLB adjus~ed (75.92 ft/23.14m), m m us the in-slips TE~
(45.92 ft/14.00m) 8 30.00 feet (9.14m~. Now every time the D~ Drcment software steps back th~x~h the tra oe buffer it will lock back an extra three ti~eB (the out-of-slips look back OS~B) to cbtain the out-of-slips TE~.

In a partic~larly preferred e~txXl~ ~t of the present invention, the video DYY~Dre~t allow8 bit positic,n to be chfx~u3d and reset at frequent intervals, thereby plewlrrc1ng the a ~ nnllatic,n of dep~h errors. Bit po6iticm can be reset w!hen drillstring 34 is in-slips and a particin of the string, called the stem, extends akcve the rig flcor. Bit positicn can also be reset while dr~lling and ~he kelly is fully e~fYK3ed into the hole.

The video ~ystem also measures pipe lndfp~ 3~t of th0 hockicad/blcck po6ition sensors. ~his video DYY~oDn33e~t can be used to resolve d1e~Dnq~ancies bekwe~n the driller's and the hcckloadVblock poBition 8~ ~YYU~=n~nent. Aa90, 8ince all pip8 ig preferably ~d~#r-tapel while going ~nto the hole, the tape can be reviewed at a later t~m~ to ct~ mct a complete depkh-versus-ti~e log or to resolve speci~ic db~h anLmalies. Ihe video 8~ can al80 be ~P~ to reset th~ traveling block position should it get out of calibration. Blodk poeition st be known at all ti~es because it is the basis o~ both inL3e-~3lta1 bit pccition and hcokloadVblock pc6iticn ~YYU~ mc33nts.

Figure~ 13~-13D illustrate a DE*~bod o~ a preferred erlxXLI~cnt of ths pres~nt inventicn that uses ~he previously-described video rig flcor cali,braticn and o ~

~ o3~cnt pQ~XY3~ mes in oonj ~ ian with block ~ t sensor 27 and hookload sensor 21 (shown in Figures 1 and 2) to d~elslline depth while tripping in. In Figure 13A, the trip-in Fs~x~#lurc b ~ by mE#~Iring the height '~' of portian 120 of drillstring 34 e~nf3Yling above rig floor 16 as shcwn an display 58 having cursors g2 and 93 superi~çx~#3d ~ n. All of the video DY#~a5~3~enk3 are made while the string is in-slips to ensure ths string is motionl~Qc. In Figure 13B, new joint 122, either a single, ~ le, or triple, is added to drillstring 34, and string 34 is t~ken out of slips. Ihe out-of-slips block altitude "L" as indicated in Figure 13B is measured by block movement sensar 27. Height L is shcwn referenoed to the lower edge of box 124 of ~oint 122 ~ecause this is the point the elevators oontact the st~ing. Actual block hQight as reoorded ~y block nLn~3nent sensor 27 may not be t'his eY~t point but will always be a oonsta~t distanoe from ~hi~ point.
Eex~mse of that ocnstant d~s~nce relationship, block heig,ht distance dif~erences cancel out.

Referring to Figure 13C, drillstring 34 is placed in-slips once new ~oint 122 has been lowered into tho we~L~x~re and th6 inrslip block hel~ht M i5 measured ky block po6ition sen~or 27. ~n Figure 13D, ca~era 50 displays the tcp portion of ~oint 122 on display 58. N~#:;~o3~ent cursor 93 iB placed at the tcp edge o~ ~oint 122 with reference cursor 92 in its referenoe po6ition.
CXn~lrter 64 ~lculates height '~r', the length of the p~rtion of ~oint 122 ebdl~lLLng above rig floor 16, using the rig floor cal~bration table. I~e length of addbd pipe 1~2 is th~ out-of-slipfi block height L m~n~s the start heiqht K plus the end height N ~nus the inrslips block height M.

4 ~ ~
Figure 14 illustrates a c~osite of the abave ~s s~ rig floor 16 befc~e pipe 122 i~ ad~, ar~ rig floor 16 (~n in p~ant~) after th~
pipe ~ added. qhe ler~ "O" of joint 122 is eqaal to th~ alt-of slips blo~c height L ~ the video-mea~ stæt height K plus ~ video-measured erxl height N m~s the in-slips block height M.

Figures 15~-15D illustrates ths methad of a Ex~eferred ~llnPrlt of the present irn~tion that ~ the rig floor video ~nt syst~ in conjunction wi~h bloc~k pc6itian sen~or 27 ar~ haikload ser~or 21 to measure joints ~ile triE~ir~ c~t. In Figure 15A, the trip-aut ~a~r~r¢ ~xh:re begins ~y n~ the height "P" of pc~tian 130 of drillstring 34 a~i~
abave rig fl 16 a~ ~cor~ed ~y ca~ra 50 ar~ ~-~lay~ on di~lay 58. All o~ th~ video 1l_ ar~ pr~erably mads ~ile the ~trir~ 34 ~ in~lips to ensure the string is motianless.

Referrir~ to Figure 15B, the alt-of-slips blo~k altitu~e "Q" is mea~ b~the block positian 6er~or 27 and haikload sensor 21 when strir~ 34 is placed out of ~lips an~ ~ust befGre string 34 is raised from ths borehDle. m is height Q is shcwn referenoed bo ths botkom edge of box 132 because this is the point the ele~ator~ cGntact string 34. Actu21 block height as reoorded by block pc6ition sensor 27 may not be this exact point but will always be a constant d~E~nce from thi~ point. Eecause of that cxrYn~mt ~ e relationship, these block height diff ~ g cancel.

Referring to ~igure 15C, drillstring 34 ls shown raised such that ~oint 134 to be r~ved :~w drill~;trir~ 34 e~ above rig fl 16. Str~ng 34 is placed ir~lips ar~ th~ ir~slip6 block height "R" is ~asured by block -- 3g --pcsiticn sensor 27. In Figure 15D, camera 50 reoords the tcp portion of drillstring 34 eYtl3Yling above rig floor 16. ~e2!~rn3b~nt cursor 93 is placed at the top edge of drillstring 34 (which c~ 3~pDn~e to the lower edge of removed joint 134) and computer 64 calculates height "S" of the porticn of drillstring 34 e#*(sYlLnl above rig floor 16 using the rig floor calibration table. The length of re~Y~ned joint 134 is the in-slips block height R minus the videc-nY#~Ln3d end height S plus the video-DY#~Dnbd start height P ~unus the out-of-slips block height Q.

Figure 16 shows a oomposite of the above ne4~RI~a] nte showing rig floor 16 be~vLG ~oint 134 is re~Lved fL~ drillstring 34, and rig floor 16 (shown in ph2u~om) after ~oint 134 is remcved. Again, leng~h ~rn of ~oint 134 is equal to the vid20-rlnsure* start height P D~113 the out vf-slip block hei~ht Q
pl w the in-slips blo~k hei~ht R DLLnug the video measured end height S.

qhe previou~ly-described video dep~h determlnativn ~ s and methLds are particularly suited for accua ~ly deterc1ning dep~h in con~unoti~n with pr~viding servioe 8 su~h a~3 nYYu~r~33ente~whlle-drilling ~WD), logging-while ~ ~ng (rWD), and formation ~valuatian whlle drilling (FEWD).
In prcviding such 8ervioe~ downhole EYU~cYeter sensing tools typically eithPr telenY*~r i~nformation to the surfa oe ~n Ureal time," and~or reoord dc~rhole information in a nY~x~y devi oe in an i,nfuL~tion V~5~3 time log for later rc h ieval and evaluation at 6urfa oe . In the case of realtime telenY~n3d data, ~HA depkh as DY#~Ired and recorded v~n~1s time with the systems and m~n~xods of the Fr~##~nt inve~tion is r~y~dhronlzed with dcwnhole information asit is received at the surfa oe . In the case of reoorded data, the dcwnhole reoorded information v~ w3 time log is retrieved ~rom the IWD tool when it is blxl~ht back to surfa oe and synoh~onized with the depth V~ lS time log reoorded by tbe systems and D~xxds of the ~ t invention to generate a downhole information ~ 3lg depth log.

Sy~1Ems and nEn~xxd3 for accurately det~2IL~Iing depkh are t~c provided. ~he systems described and illustrated herein have been scmewhat si~plified so that a person skilled in the art n~y readily uu~lonsband the present inNention and incorporate it into any application by making a number of ~r~fications and additions tkf~nEto, none of ~hich entailing a deFxulbur3 frcm the spirit and sccpe of the present invention. ALcxldlngly, thQ following d ~imc are intended to embrace su~h modifications.

Claims (10)

1. A method of determining the depth at which a component of a bottomhole assembly is located within a wellbore, said bottomhole assembly being attached to the lower end of a plurality of objects interconnected to one another, said method characterized by the steps of:
a) displaying an image of at least one of said objects onto a display before said object is inserted into said wellbore, said display having at least one moveable cursor superimposed thereon;
b) generating a table of cursor position on said display versus length;
c) moving said cursor superimposed on said video display to points corresponding to the length of said at least one object;
d) determining the distance between said points;
e) equating said distance between said points to a length from said table, thereby determining the length of said at least one object; and f) summing the lengths of said plurality of objects as they are inserted into said wellbore, thereby determining the depth of said component of said bottomhole assembly.

2. The method recited in claim 1 wherein said table of cursor position versus length is generated by the steps of placing calibration means adjacent to where said at least one object will be when said length thereof is determined, said calibration means having a plurality of markings thereon spaced a predetermined length from one another; moving said cursors on said display to points corresponding to said markings on said calibration means;
and equating said marking points to said predetermined length between said markings, thereby generating said table.

3. The method recited in claim 1 wherein said object is suspended within a drilling rig mast, and wherein an image is displayed of the top portion and the bottom portion of said object on said display, and wherein step a) through step e) is performed for said top and said bottom portion images.

4. The method recited in claim 3 further characterized by the step of:
g) simultaneously with step f), recording the time at which said objects are inserted into said wellbore, thereby generating a depth versus time recording.

5. The method recited in claim 4 wherein said bottomhole assembly includes at least one logging while drilling sensor, and wherein said method further comprises the steps of measuring downhole parameters with said sensor; recording the time at which said measurements were made, and correlating said depth versus time recording with said downhole parameter measurements versus time recording, thereby producing a downhole parameter measurement versus depth recording.

6. The method recited in claim 1 wherein said plurality of objects are inserted into said wellbore with a moveable traveling block suspended from the mast of a drilling rig with the aid of a moveable cable, and wherein means are provided for determining the movement of and load on said cable, said method further characterized by the steps of:
g) determining the movement of and load on said cable, h) equating movement of said cable to movement of said component of said bottomhole assembly when said load on said cable exceeds a predetermined amount;
i) in response to equating movement of said cable to movement of said bottom hole assembly component, determining the depth of said bottom hole assembly component in said wellbore;
and j) comparing said depth determined in step (i) to said depth determined in step (f) and resetting the depth determined in step (i) to correspond to the depth determined in step (f).

7. An apparatus for determining the depth at which a component of a bottomhole assembly is located within a wellbore according to the method recited in claim 1, said apparatus characterized by:
a) means for displaying an image of at least one of said objects onto a display before said object is inserted into said wellbore, said display having at least one moveable cursor superimposed thereon;

b) means for generating a table of cursor position on said display versus length;
c) means for moving said cursor superimposed on said video display to points corresponding to the length of said at least one object;
d) means for determining the distance between said points;
e) means for equating said distance between said points to a length from said table, thereby determining the length of said at least one object; and f) means for summing the lengths of said plurality of objects as they are inserted into said wellbore, thereby determining the depth of said component of said bottomhole assembly.

8. The apparatus recited in claim 7 wherein said means for generating said table includes calibration means having a plurality of markings thereon spaced a predetermined distance from one another.

9. The apparatus recited in claim 7 further characterized by:
g) means for recording the time at which said objects are inserted into said wellbore, thereby generating a depth versus time recording.

10. The apparatus recited in claim 7 wherein said plurality of objects are inserted into said wellbore with a moveable traveling block suspended from the mast of a drilling rig with the aid of a moveable cable, said objects placing a load on said cable, said apparatus further characterized by:
g) means for monitoring movement of said cable;
h) means for monitoring said load on said cable; and i) means for equating movement of said cable to movement of said bottomhole assembly component when said load on said cable exceeds a predetermined value.