GEDDRILLING THREE

=is zinc:ecanic uesin wa:er wecri inc:caoe:oo cri incBy P. K.

CRUSE'HE

AVERAGE mechanically inclined per-son may be taught in a matter of weeksto operate a standard water well drillingrig and to produce a borehole Severalyears would elapse before he would becapable of drilling with the minimum risk oftrouble. Yet further years would pass before he could w'ith confidence and effici-ency deal with difficult fishing situations.

This Paperl examines some of thecauses of "lost" tools, the range of equip-ment usual'ly available to undertake fishingoperations, special problems calling for"one-off" approaches, and the techniqueof fishing.

The accent 'is on cable-tool (percus-sion) equipment and although much of thePaper applies in general terms to all drill-ing, the author intentionally refrains fromdetailed discussion of small diamond workand oil well practice, as neither of thesefields falls within the brief for the Paper.

introductionFishing is defined in the dictionary as

'the action, and/or practice of catchingfish'. A worried and frustrated drillerwould use less bland terms to describehis task. And yet it is an art based uponsound instruction, common sense andconsiderable experience.

In well drilling terminology the word'fishing's applied to operations carriedout with the aim of locating, grasping andremoving any object found to be uninten-tionally in the well, and may range froma set of false teeth to several tons ofdrilling tools.

Under ideal conditions few if any fish-ing operations should be necessary, How-ever, human error, the vagaries of natureand the failings of meehan'ical devices cancontribute or combine in a set of eventswhich lead to the inevitable problem. In-

deed, a large drilling contractor will con-sider himself fortunate if he experiencesa few weeks without fishing operations,especially in hard-ground areas.

Fishing is non-productive, time-consum-ing and costly, It is also somewhat uniquein that as a civil/mechanical engineeringexercise it cannot be programmed on atime scale. Some operations literally takeminutes to attain success whilst on somesites several weeks might pass before thefish is recovered.

Although worrying for those persons car-rying the responsibility, there is no doubtthat fishing offers a challenge to the in-

genu'ity, patience and skill of the driller—perhaps even providing spice! Be thatas it may, the sight of the hitherto losttool safely lying on the site is a rewardingexperience —whic'h may be quickly ex-tinguished by a review of the cost! Fail-

ure to bring the fishing operation to a

successful conclusion, on the other hand,may result in abandonment of the hole, alost fish or even a lost set of recoverytools. Should such a situation occur on aremote overseas site it may not be pos-sible to arrange rapid replacement of thetools, especially where only one rig isemployed —which would rule out thepossi'bility of borrowing from an adjacentoutfit.

In view of the above it is very import-ant to be aware of the causes of fishingjobs and to guard against their occurrence.

Causes of fishing jobsTools becoming fast in the hole

Some common causes are:(a) Infall occuring which jams between

the shoulder of the bit (chisel) and thewall of the borehole.

(b) The tools cease to rotate due tothe mandrel becoming stuck in the ropesocket; this causes a 'keyhole'o be drill-ed into which the bit eventually jams,

(c) A new or dressed bit is run tooqu'ickly into a hard rock hole which maybe tapered by the diminishing 'gauge'fthe previous bit, and

(d) Tools may become fast in fissuredand cavernous formation such as somelimestones and volcanic areas.Cable breakage

This can occur due to:(a) Drilling with a worn cable, a condi-

tion wh'ich might be aggravated by localabrasion against a crooked borehole,

(b) Drilling in an extremely hard for-mation where footage is slow and con-sequently the cable spends an abnormallylong period of time flexing over the crownwheel at the top of the mast,

Wire rope

Recovery grooves

Steel wire rope

Rope socketBailer

Sand pump

'Window"for

emptying

Mandrel

iH ~i

Spanner flats

Q Recovery grooves

Hinged door

Piston

Coupling threadDnlf stemior sinker barf ~

ior keys)

Taper ffireadHinged door

Stop

(c) A cable damaged at its exit pointfrom the rope socket, caused by loweringthe tool string to a horizontal positionwithout fitting a 'rope-saver'o the ropesocket,

(d) Insufficient attention to the spool-ing of the cable on the bull reel result-ing in crushing of the cable, and

(e) General misuse such as overloadingand absence of lubrication.Tool joints becoming unscrewed

A properly made-up API cable tool jointgives very little trou'ble. However, fromtime to time a lost tool is reported to haveoccurred due to the unscrewing of a jointduring drilling. There is rarely a valid ex-cuse for this as it is normal practice fora driller to punch a pair of matching markseither side of the joint each time a jointis made up (but not so close to the jointsuch as to burr or swell the joint faces)and these marks are examined every timethe tools are inserted into the boreholein order to see if the joint is sound or ifcreep is taking place. Incidentally, to avoidconfusion with a previous mark, whichmay lie alongside, it is B good habit toobliterate any surplus marks with a ballpein hammer. Also, if any joint is causingconcern, the use of a spec!al mark assiststhe identification of that particular joint,

Accidental unscrewing may be due to:(a) Oil or grease having been applied

to the joint rather than clean water,(b) Dirt in the threaded portions,(c) Damaged threads due to careless

handling of the separate tools on site, e.g.absence of thread protectors,

(d) Incorrectly machined joints, Theseshould be observed by the driller wheninitially assembling the tools, and

vcontracts Engineer, George Stow ffr Co. Ltd.,Henley on Thames.

fJThis Paper is based on information presented bythe author at a seminar on fishing techniquesarranged by the British Drilling Association andheld last year at Seaton Burn, Newcastle uponTyne.

Jack

Fig, 1. Percussion drilling tools

January, 1980 37

(e) Insufficient torque having been ap-plied when making up the jroint. One manusing a proper Barrett-jack, circle andstop, with matching keys or wrenches, orusing claw-ended wrenches with chain-and-lever tightener, is quite adequate a'I-

though it may take two men to'break'he

joint following drilling in a,hard for-mation.Broken tools

When drilling tools have been used fora long period the risk of fatigue failureswill increase, especially when drilling inhard ground. Sma! I diameter boreholesare less prone to trouble, even with re-latively heavy tool weights, as there ismore lateral guidance provided and conse-quently less swing On the other hand, alarger borehole permits. a greater deviationwhich periodically allows the chisel tostrike the bottom of the hole at an angle.The shock of impact is thus transformedfrom an acceptable straight line to a bend-ing moment that will eventually cause the'pin'f the tool joint to fail.

A similar condition arises when drillingin dipping formation where alternate banksof hard and soft strata occur. Particularcare should be taken under these circum-stances as the driller often adds a fur-ther drill stem/sinker bar to increase dir-ectional stability in order to control ver-ticality. A change to a shorter dri'llingstroke wil'I relieve the situation to a de-gree.

Apart from pin breakage it is not un-common for tools to fail at a change ofsection in their length and one should payparticular attention if a manufacturer hasomitted a smooth transitional radius at apoint of change, especially if the tool hasbeen long in service.

One 'on site'ethod of testing forcracks 'is to leave paraffin soaked rags oin

the tool, then clean off and'ry the sur-

face thoroughly and apply chalk. Anycrack will show up when the paraffinweeps back into the chalk. This systemis used to check steam locomotive mainframes where these are still in serviceoverseas.

The most reliable testing is carried outemploying ultrasonic equipment.

Conventional recovery toolsThere is a range of fishing/recovery

tools for cable-tool (percussion) drillingwork, covering most of the standard situ-ations; these are discussed 'in the follow-ing paragraphs and illustrated in Figs. 2-8.

Most of the tools are fitted below a fish-ing string consisting of a rope socket,short drill stem and fishing jars. These fish-ing jars are of long stroke and allow apowerful jarring blow to be deliveredeither Upwards or downwards as needed;the drill rig stroke must, of course, be setto give a shorter stroke than the jars soas to prevent both up and down blowsbeing delivered during one rotation of thespudding gear. This latter facility is onlybrought into use as a last resort when try-ing to break free from a fishing holdfollowing an unsuccessful recoveryattempt.Jar bumper

This tool (Fig. 2a) consists of a heavycylindrical bar which is vertically slottedin order to permit it ta be fitted acrossthe centre line of the drilling line. It issecured by two pins which allow freevertical movement.

The bumper is run into the borehole onthe sandline and two or three 'passes'fincreasing depth made before finally com-ing to rest on the rope socket neck. Th'isprocedure is recommended in order toavoid the entanglement of the sandlinewith the drilling line.

The jar 'bumper is used to free a string

of stuck tools by raising it 2 —3m abovethe rope socket and allowing it to fall.Sufficient tension is maintained on thedrilling line to (a) prevent slack line frombeing trapped between the bumper andthe rope socket face, and (b) keep thedrilling jars (if fitted) open.

The effect of the downward blow onthe tools is to momentarily cause the jarsto partially close. However, due to thetension in the drilling line the jars arerapidly snapped (ypen again and the re-sultant upward shock helps to free thetools. This procedure is sometimes con-tinued for an hour or more before thetool string becomes free.

In situations where the driller has notfitted drilling jars a jar bumper may stillbe used but with less effect. It is usualto apply a heavier blow —perhaps a fallof 4m or more —but it should be bornein mind that excessive work with the jarbumper will eventually spread the top ofthe rope socket neck thereby renderingit unsuitable for the application of a com-bination socket should this become neces-sary.Rope knife

Should jarring with a bumper be un-successful it will be necessary to cut thedrilling line in order to leave a clear pathfor the application of alternative fishingtools. Sometimes the line can be cut byallowing a little slack in the drilling lineand applying the jar bumper. This causesthe line to be trapped between the baseof the bumper and the face of the ropesocket neck during each blow and des-troys the line. However, this is an un-tidy and inefficient method and it is pre-ferable to use a proper rope knife (Fig.2c) .

A rope knife 'consists of a body rathersimilar to a jar bumper but incorporatinginclined planes in which a pair of hard-

w—Sand-line

() (suspending jar bumper )t '} and drilling line

Drilling line

Short stem~Fishing lars

Drilling line(held taut)

Short dnllstem

Fishing jars w

~Short stem~Fishing jars

/t) Secunng pin

~~ r—Jar bumper

~--.()IIb

---*Drilling jars

0

t

Hard steel cutters

Stone trappedabove shoulder

Cover plate

e e

0 0

0 e

r

r

r

r

'I

Cutawayview~

Wooden spacer ~~Two-pronged rope

grab (single speartype also available)

Alternative jaws~or slips

~Broken drilling

line "birdsnested"

Spring

Taper

w Guide bell

(a)

~SauationSruck rools unableto pull outNew or dressed bitjammed in taperedborehole

(c)

SituationDulling )me attachedbut tools will col

bump or l sr out

(a)

Recoveryteeth

—Rope socket

(b)

~Dnlling larsor dnll stem

Fig. 2 (a) Jar bumper; (b) Drilling jars; (c) Wire line cutter orrope knife

38 Ground Engineering

Fig. 3 (a) Rope grab/spear; (b) Combination socket

GEODRILLING SEVEN

Cutawayvrew

'Wooden spacer

Spnng

Long arms of skps

~ r—Latch tack

Wrench orspanner flats

I I

t~ v—Hard steer body

i

~Taperedheavy-wallpipe

b

Screw threadto suit vanousdnll pipe orsold rod

Ciprevent deepentry

r—Internal slow rape

Corrugations

' —Taperrrv I.~ I( ~Two full arete slips

—~—SituationBroken pin

Ra

~ v—Slot (a)

(b)

(c)

(d)

(a) (b)

Fig. 5 (a) Frictionsocket; (b) Corru-gated socket; (c)Horn socket; (d)Crows foot

toothed cutters slide. An API tool jointconnection is provided so that jars, stemand rope socket may be fitted above it.

The knife is first assembled without thecutters and carefully measured down theborehole to the rope socket face. Thisprocedure is necessary in case a kink in

the drilling line or an obstruction in theborehole prevents full insertion of the tool,the removal of which would otherwiseengage the cutters at the wrong depth.

Having established a clear path the toolis re-erecte'd with the cutters and run onthe sandline down to the rope socketface. A firm tension is applied to thedrilling line and upward blows deliveredto the rope knife by the jars and stemabove it. This causes the cutters to slidedown their planes, engage the wire ropeand cut through it.Rope grab or spear

In the event of a drilling line or sandlinebreakage leaving a length of wire rope in

the borehole this situation is usually dealtwith by the use of a rope grab or spear,However, some drillers achieve successusing a hook on the end of a column ofpipes which are rotated alongside thebroken line with the aim of winding a

loop to establish a 'hold'.The rope grab (illustrated in Fig. 3a) is

run down the borehole on the drilling line

below jars and a short stem until it en-tangles with the broken line. At this pointit should be mentioned that opinions dif-

fer over the exact procedure for obtaininga hold. There are strong adherents to theview that one should first 'birdsnest'herope by pushing it down the borehole with

a blunt object, whilst others subscribe tothe practice of running straight in with thegrab to secure a hold.

If the tools were free at the time ofrope failure it may only be necessary topull the complete tool string and ropeout of the hole; however, should the ropehave broken due to the tools becoming

fast, it might require jarring action to freethem. It is also possible that the brokenline will have to be removed in severallengths leaving a short piece protrudingfrom the rope socket, in which case amilling bit would have to be spudded onto the rope socket in order to disposeof this piece.

Having taken hold and drawn the ropeand/or tools to the surface it is advis-able to bind any loose loops or ends thatemerge as it is likely that the confiningaction of the borehole is contributing tothe security of the hold, and this maybe lost if the rope springs apart aboveground.Combination socket

This tool is a precision made deviceincorporating a set of spring-loaded slipsin a tapered seat (Fig. 3b). It is used togrip the neck of the rope socket. An alter-native set of slips matches the pin threadof an API tool joint.

A combination socket should be runinto the borehole without the slips andmeasured carefully down to the fish, Asmall piece of wood is inserted just in-side the body of the tool to indicatewhether or not the fish entered. Alterna-tively, quick drying cellulose paint maybe applied round the entrance to the tooland any scratch marks noted.

Having marked the drilling line the toolis removed, examined, the slips fitted, andre-inserted down to the fish. It may benecessary to apply one or two blows tothe assembly to ensure full entry, thenupward jarring is commenced and con-tinued until the lost tools are free tobe lifted out of the borehole.

In the event of this method being un-successful the combination socket isbroken free by jarring loosely both upand down. This severe treatment destroysthe recovery teeth or threads on the fishand allows the grip to be broken. It mayperhaps spoil the slips, but this is a com-

Fig. 4 (a) Full circle slip socket; (b) Latch jack

paratively small price to pay for the re-covery of the string of fishing tools.Full circle slip socket

If a tool joint pin breaks, a suitablefishing tool is the full circle slip socketillustrated in Fig. 4a. The operation ofthis tool is very similar to that of thecombination socket except that provisionis made for a deeper entry of the fish in

order to engage the body of the tools.Also the tool is slimmer to allow opera-tion within a 150mm (6in) dia. boreholeand yet swallow the full diameter of tools.

It is not normally used to recover bitsbecause if the pin breaks the bit usuallycomes to rest at an angle to the bore-hole, especially if it is of large diameter.Latch jack

This is a standard fishing tool used tofish a lost bailer out of the borehole. Asmay be seen in Fig. 4b, it consists of atwo-pronged fork, one prong of whichcarries a hinged latch which rests hori-zontally in a slotted seat in the otherprong.

The tool is measured into the boreholeand gently lowered past the bail or loopat the top of the bailer with the objectof positioning a prong either side of thebail. The latch is lifted up by the bailand falls back into its slot. The entrappedbailer is then drawn out of the borehole.

Should the bailer have been lost due tojamming in the borehole it may be nec-essary to arrange some jarring action. Thelatch jack carries a standard API pin.Friction socket, corrugated frictionsocket, horn socket

These similar tools are simple tubulardevices which rely upon friction to holdand remove drilling tools which have un-screwed or broken in the borehole. Theywill not usually remove tools which arestuck.

The friction socket (Fig. Sa) consists ofa hard steel open body incorporating aslow internal taper. It is fitted below jarsand a short stem which are used to jarthe socket over the lost tools to obtaina friction hold.

The corrugated type (Fig, Sb) has aparallel internal bore but corrugationsare formed into the body to cause an'interference fit'ver the lost tools, there-

January, 1980 41

GEODRILLING EIGHT

~Ad)ustment forspnng pressure

Broken jarreins

~Spring))~Slips in inclined

si pway

A -—- —A

Section A—A

~I~!~ee e!

Ia!n~5

s r mr

—Slops io preventfunher entry oflong object

SifuafioiiSmall oblecr such asslip wrench sferfgci anirnp.

(a) ifrojiped Iii role (b)

SifuaiioiiDirllng larsbroken acres* sins

Situati onTools surrounded byinlall or cuttingswhich require agitatingto loosen them

Thicker secbonto provideclearance

8»——-—8

SituationTools leaning againstwall ol borehole, suchthat conventionalhshing tools will notlocate over lish

by facilitating a grip.A horn socket, as seen in Fig. 5c, has

a long body of heavy-wall pipe formedinto a slow taper. A vertical slot runsfor most of its length. It is driven overthe lost tools and the slot permits de-formation to accommodate the fish.Crows foot

Made of round, square or rectangularbar, a crows foot (Fig. 5d) is a most use-ful tool for removing lost bits.

Consisting of a strong hook arrangedhorizontally and with a 'clockwise entry',it is welded to a short vertical rod whichin turn is screwed to suit small drill pipeor solid Whitworth rods or similar.

A crows foot is selected which is smallenough to pass down the borehole andyet large enough to sweep round the neckof the 'bit. It is attached to the above-mentioned rods and lowered to a levelcalculated to be opposite t'e key orwrench flats of the lost bit. Preferably itshould be painted, which will give someindication of attempted contact and entryif a grasp is difficult. The rods are rotatedvery slowly and slight depth adjustmentsmade until a hold is obtained.

Great care must be taken when break-ing the drill rod joints to ensure that thecrows foot is not snatched anti-clockwiseas this may dislocate the fish.Steel hand or devils hand

It is not always drilling tools which arethe object of a fishing operation. Smallitems such as a hammer, wrench or slipoccasionally find their way to the bottomof a borehole and lie in such a positionthat insufficient area is presented to afishing magnet. This situation calls forthe application of a steel hand (alsoknown as a devils hand), illustrated in

Fig. 6a.This fishing tool carries three or four

long spring steel arms to the bottom ofwhich are attached hard steel fingers. Theupper length of th arms taper in beforeentering the tubular body of the toolwhere a spring keeps them extended. Inthis position the fingers are some 120mmapart.

Upon lowering the tool to the bottomof the hole the arms will at first encir-cle the fish. Gentle use of the jars will

42 Ground Eingineering

Fig. 6 (a) Steelhand; (b) Reinsocket

(a) Hardened tip

Fig. 7 (a) Spud; (b) Wa/I hook

tools leaning across the borehole, thetool made expressly for this purpose iscalled a wall hook. Shown in Fig. 7b, thistool is worked down alongside the losttools and slowly drawn up to the topof them. This action tends to bring themin to alignment and they may 'be held inthis position by dropping into the bore-hole a few pieces of slack coal or similarsoft material before drawing the wall hookaway from the tools.Casing spear-trip type

Casing spears are tools designed toenter the bore of casing or pipe droppedin the borehole where a hold is made forrecovery to surface. They may also beused to remove a 'drop-set'f screen orcasing during borehole reconstructionworks. The normal diameter range is from100mm (4in) to 300mm (12 in) and theyare either of the standard type where thehold cannot be disengaged once taken, orof the trip type (see Fig, Sa) which issafer and more convenient.

A solid steel body carries two extern-ally mounted slips running on inclinedplanes. When pushed up the planes theslips reduce to a d'iameter less than thatof the casing to be engaged, but gravityholds them down to rest on a settingcollar in which position they increase to alight interference fit in the casing.

The setting collar is pulled downagainst a powerful spring by an indepen-dent loading device and retained by asmall spring-leaded peg. There are nor-mally several positions for this pin inorder to provide adjustment for variationin the nominal bore of casing.

In operation the casing spear is rundown the borehole and brought to restwithin the lost casing —preferably justbelow a joint. Initially the slips are push-ed up the slides by the interference ele-ment, this allowing entry for the tool. Ifan upward pull is now taken the slipswill catch against the bore of the casingand be forced to expand as they traveldown their inclined planes. Assuming that

then overcome the spring pressure anddrive the body of the tool down over thetaper of the arms forcing them to closearound the encircled fish. The completeassern'bly is then drawn to the surface.Rein socket

Drilling and fishing jars are robust toolsdesigned to do a tough job, but afterprolonged usage, especially if worn, thelinks or reins as they are known may frac-ture, leaving two smooth bars facing upthe borehole.

There is a tool called a rein socket(Fig. 6b) which is specially made to copewith this situation. It consists of a solidcylindrical body on either side of whichis formed a long rectangular slot slightlywider than the standard rein.

Using care, and relying to a certainextent on good fortune, this tool is gentlyworked over the protuding reins so thatthey enter the two slots. On one side-face of each slot a pair of serrated slipsare located and are pushed up an in-clined plane on the entry of the reins.However, upon raising the rein socket thebroken reins are jammed by the slipsdescending in their diminishing sl'pway,and drawn out of the borehole.Spud

There will be occasions when drill cut-tings or infall pack round the lost toolssuch as to make withdrawal difficult. Inthis case a spud is used to disturb andloosen the material. This tool, seen inFig. 7a, takes the form of a forged steelblade which may be up to gm long, ofsemi-circular section, and offset to en-able it to operate in the annular spacebetween the borehole wall and the stringof lost tools or bit. It is slowly spuddedusing a somewhat slack line and bothstrokes of the jars.

This tool may also be used to try tostraighten a string of inclined tools which,being out of centre, defy the engagementof a fishing socket.Wall hook

Further to the subject of straightening

GEODRILLING TEN

the spear has been correctly set, the footof the slips will now be pressing downagainst the setting collar thus relieving thespring strain on its retaining peg —whichitself being lightly spring loaded, will dis-engage.

There now exists a situation where theupward pulling or jarring keeps the slipsin a firm grip inside the casing whilst asecondary force, provided by the mainspring, is standing by to propel the slipsup into their retracted position.

Pulling and/or jarring should eventuallyrecover the casing, but if this operationis unsuccessful the casing spear is re-leased by a downward blow of the jarsand stem, which allows-the freed slips tospring back into retraction,Latch tool

This tool is used for the same dutiesas a casing spear, but it covers the largerdiameters from, say, 375mm upwards. Theprinciple of taking hold also differs,

Basically the latch consists of a strongdisc slightly smaller than the casing intowhich it is required to run. Two or moreflaps with hardened bevelled outer edgesare hinged near the centre of the uppersurface of the disc. The outer radius ofthe flaps approximates to the inside dia-meter of the casing but when they lie flaton the disc they are in fact a little larger.

The disc is welded to a short stemwhich is screwed to suit drill pipe or solidrods. Each flap has a small eye on topto which is shackled light steel wire ropepassing (eventually) up the borehole. Theunderside of the disc carries guide websto facilitate its entry into the lost casing.

To take a hold in the casing the tool islowered down tho borehole. The guidenose and main disc enter freely. However,the flaps in their horizontal position willnot pass inside until pushed up to anangle of some 20'. If an upward pull isnow taken it will be seen that the beveledges will bite into the bore of the casingin their endeavour to assume a flat atti-tude, and in so doing will take hold.

Should it be found impossible to pullthe casing, the tool is lowered off a littleand sufficient lift taken on the wire ropeto raise the flaps on their hinge". Thisretracts them whilst the tool is broughtback to the surface.

and a positive mark made at surface level,From one to five hours, depending on thetool and borehole and severity of the grip,should be allowed for the desired effectto take place. Quantities of acid requiredvary from 20 to 250 litres. Note that healthand safety regulations must be compliedwith.Fishing magnet

Powerful permanent magnets are avail-able with either screwed connections ora lifting eye, These are very effective iiit is possible to locate them on to a fairlyflat surface of the fish.

Frequently some sediment may coverthe fish, in which case a sand-pumpshould be used, taking care to lower itgently upon the fish.

Magnets are supplied with a keep plate,and potential operators should be warnedagainst trapping their fingers between themagnet and the plate vthen replacing thelatter.

Another point is that if a magnet isbeing air-freighted, the carrier should benotified as the instrumentation of somesmaller aircraft may be affected. Packingthe magnet in lead wool may reduce thishazard.M.'scellatteous

It is not always possible to bring afishing job to a successful conclusion, inwhich case it may be worth consideringdrilling alongside and by-passing the fish.

This is usually achieved by the insertionof a device called a whipstock which islowered into the borehole below a columnof tubes. The whipstock may be 10m longand takes the form of a 'shoe horn'nsection. It presents a full circle to thedrilling tools where they first enter but asdepth increases an angled deflector causesthe new set of drilling tools to travel offcentre until at 10m (at the foot of thewhipstock) they are in entirely new

(concluded on page 50)

Fishing larsattached here

length of drill pipe; it is then lowered intothe borehole and given one bump (only)on to the fish. In the event of contactuncertainty a second attempt at an im-pression should not be made unless thetool is first brought to the surface forexamination otherwise a "double image"may confuse the observer.Double-door bailer

Where the borehole is of large size andthe lost tools are known to be standingfree in the hole it is sometimes a quickoperation to run a double-door bailer (orscow) down over them.

This operation may take only a few min-utes to achieve success, but before em-barking on it due consideration must begiven to safety in view of the weightsinvolved and the use of the sandlineequipment.

In hard dipping rock or cavernous form-ation where the risk of tool failure is in-creased it may be advantageous to weldrecovery lugs on to the tools, These pro-vide additional opportunity for the bailerto take hold. Sometimes the bailer doorsare shaped by gas cutting to suit a spe-cific task.

For larger diameter work some heavyscows or bailers have been extensivelymodified to incorporate a long window orslot in the side. These are used to lowerover tools leaning in the borehole Uponraising the fishing tool, the short heavydoors grip the lost tools part way down,the upper part of which then swings intoa vertical attitude through the upperwindow.Acid treatment

Commercizl grade hydrochloric acid isfrequently used in calcareous ground tofree stuck tools when more conventionalmethods have failed.

The acid is slowly fed through suitableplastic pipes to a point just above thestuck tool. Tension is applied to the tool

Special operationsImpression tool

There will be occasions when conven-tioinal fishing tools fail to recover the fishand some doubt exists as to the truesituation down the hole. In these circum-stances it may well prove enlightening torun an impression tool.

Such a tool, illustrated in Fig. Sb, isusually made up for the particular problemand takes the form of a wooden discslightly smaller than the borehole diam-eter at the fish depth. The disc is providedwith a number of thin nails driven par-tially into the underside at random and alayer of plasticine, beeswax, clay or sim-ilar material is pressed across the surface.The nails help to retain the layer whichmay be of 15-20mm thickness.

An alternative method is to glue a sheetof polystyrene to the disc.

It is essential that two vertical holesare provided through the disc and plasticto allow displaced water to pass whenra sing the tool, otherwise the edge of theimpress ion mate ria I may be swept off.

The tool is attached to the dart of adart valve bailer or may be fitted to a

44 Ground Engineering

Inclined planes

Hardened steelslips

Setting collar

Perhaps attached todan valve bailer orSingle length of dnll pipe

Setting peg

Strong releasespriiig

SiluationCasing or screen

pipe ro be recovered

(a)

Setsng stirrup

Guide noses s a

Pins to secureplasbc matenal

Air holes loallow displacement

(b)

Fig. 8 (a) Trip casing spear; (b) Impression tool

Wooden disc

~ Plastisanebees'ax.polystyreneor clay

Fish

GEODRILLING SIXTEEN

ment to the notice of all employees. Thisobligation arose on April 1, 1975,

i became a criminal offence

provideor any substantial employer t f 'Io ai to

Polic stasuch a policy statem

's atements should consist of

ent.

statements on general safetn an arrangements, and should b

made available te to all employees as shouldou e

e ealth 8(any subsequent revisions. Th H

or aniy Commission suggest th t h

g isation and arrangementa w ere the

plex it ma be r

ements are com-ay e preferable to have two d

uments: a concise statement of polic,wo oc-

organisation and arrangempo Icy,

e-

I

~ including manuals ofru es and procedures, kept centrall orposted where it could be s

I

p 'lar requirement of theUnder this articuAct the British Drillin A

I'

dc u e as part of the introduction

statement of the olice o e of Safe Drillin

e policy of the Associa-

It is the policy of all members:

(1) To provide for all employees wor'

p e tendr an p ant, tools, e ui mw ic provide and maintain Conclusion

From the foregoing the imb d h

'p rations conformine t at fishin o e

e procedures and thatchosen path

a to follow a

tunatel thiwill ensure suuccess, Unfor-

y t is is not the case and it isquently necessary t

n it is fre-

devices wh'' h hy o resort t

specific problem.ic ave to be de

'tools and

esigned for a

Blank pin billets are availabl'b Id d

it to be connected to thee e any suitable tool,

ec e to the standard string

Electric welding and as-' 'ia items oif e ui

rd dnlling plantion with stan dars. t is also useful toof th e nearest scrap metal ard!

t must be accepted thatf'h' b 'll p'g a es place but th sev

r'roblemcan be held to a

a o drilling or fishing tool ~

i serted into th bexists a sketch showin t

e orch o!e un le

(b) The driller should at all times

t th d of a hift

fi

c No decision should b'shing procedure until o thor

e taken a

I f 11the in ormation has taken I

few moie mlnut finutes of initial discvera wasted days later on.

if at all suspect. If inin doubt, leave it out.en to stop fishing? The ski.lsd

dril,'wever,

thowe, here comes a time whthe cost of continued fishin g e cee s t

s and work so fart e lost tools aie out; it is then time t

abandonment.ime to consid r

In th'is Paper the author has set

is ing in percussion-drilled borehole .

a t ese are of minor importance.

il'he

highest standards of safety andfreedom from health risk. ec niques

(2) To ensure the rovi'

provision and mainten-(continued from page 44)

ance of standards, systems and r-an pro-ic protect people other

Two choices may now be o en

than employees at work.dow alo 'd

3 Tlost tools ma

ngsi e and sli htl'g y below the

( ) o ensure that each em lomay have relieved them suffi '-

emp oyee is in- ently for them to too, recognises and takes steps hole, whereu on fi

h

bl for the or rill in cane;

e latter course is takenr peop e who may be affected necessary to lace

'

y his activities or omissioions at work, e y-Passed tools ty o place cement in the area fa o

(4l Toaeo s to ensure a safe pass-

g o q eqpd

n, instruction,i ment.

p rvision necessary to I

permissible verticalit

ensure, insofar as 'ts it is reasonably Sho Id I bso e considered.

practical, the health and fsa et of allometimes a lost bit ''

I b

employees at work.y can be driven oiut of the w

'in c ay ased sto t e way using heavy

(5) To ensure tha

s an a flat bottomed reamer.

re at all requirements of the charge of blasting d namivanou e corn- tional char

Safetny at W

d t A

too s. his a icapp ication is more commonosen ast

s ry ct, Water Resouices A D-posit of Pois

s ct, e-

ControlW A 1972 is inserted dow th b

n'

co.'umn of ca

'egulationsmade th d, the

n e orehole

ereun er and allis . uick settin c

and driven

other relevant legislat'h Id'

conditions as laid d

in t e bottom, a d9 fic' I t th

P gether with h f'casin is 'a

er a ings, local auth-i te ish.

orities and clients.

50 Grouound Engineering