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APPLICATION AND INTERPRETATION OF DRILL STEM TESTMerl in Anderson

Halliburton ServicesDuncan,Oklahoma

INTRODUCTION

Figure I

REMOTE CONTROLSAFETY VALVE

:\U~ifl1~~~ MANIFOLDFLOWLINE

HYDRAULICCONTROL LINE

'-----'-LT- 20 SWIVELPRESSURE BALANCEDSWIVEL

MASTER VALVENIPPLE

'--J""~ DRILL PIPE

Disconnect removed and the new portion instal led.

TWO TYPICAL SYSTEMS OF SURFACEEQUIPMENT FOR AN OPEN HOLE LAND TEST

SURFACE EQUIPMENT

TESTING ON LAND

The surface control head equipment providescontrol of the wei I at the surface during the test.Careful thought needs to be given to the selectionof this equipment to see that it adequately ful­fil Is the requirements of the test. Questionsthat need to be considered are: What surfacepressures are expected? Are multiple chokechanges requ ired? Wi I I high f low rates for exten­ded periods of time be encountered? Wi I I the for­mation be treated during the test? Wii I wire lineequipment be run through the string? Is a ki I II ine to be connected to the test tree? Can sourgas be expected? Will chemical injection be re'­quired? The integrity of the test tree should notbe compromised.

The Dril I Stem Test is an analysis tool forevaluating potentially productive formation. Aproperly conducted test can yield information asto production rate, transmissibil ity, flow capa­city, relative permeabi I ity, damage and possiblyindicate if a I imited reservoir has been encoun­tered. The Dri I I Stem Test provides this informa­tion at a time when the least expenditure has beenmade, i.e. before the wei 1 has been completed andoften before casing has been set. Knowledge ofthe original reservoir conditions can be impor­tant both in designing the wei I completion and inthe reservoir engineering work performed later inthe I ife of the wei I. Technology avai iable todayhas provided the tools and equipment to safelyevaluate almost any formation being encountered.

UNITEST TREE surface control eguipmentSYSTEM: The Unitest Tree surface control equip­ment System provides a series of components suchthat by proper selection, the control head can becustom bui It for the individual test requirements.A description of the components avai lable are des­cribed below. Figure I shows two possible testtree designs.

THE LIFT NIPPLE provides a means of latchingthe elevators to the control head to handle thestring of pipe at the surface. Often a joint ofdri I I pipe is used for this purpose.

THE QUICK DISCONNECT provides a means ofquickly altering the form of the control head. Itis located in the test tree at the place it is tobe changed. The portion of the test tree to beadded (a lubricator for example) is preassembledtoa top half of a Quick Disconnect. When it be­comes desirable to change the tree design, theMaster Valve is closed, the Quick Disconnect isknocked loose, the portion of the tree above the

THE BAR DROP SUB contains the brass bar thatis released at the end of the test, al lowed tofal I to bottom, break the pin in the Impact Rever­sing Sub, and permit ~he recovery to be reversed.The Bar Drop Sub al lows the bar to be instal led inthe control head, out of the flow stream, beforethe start of the test. The bar may be releasedwith pressure on the control head. It is alwaysrecommended that, for safety reasons, the recov­ery be reverse circulated.

THE FLOW-TEE provides ports for the produc­tion to exit from the test tree into the manifoldor the flow I ine. Dual ported Flow-Tee~s areavai lable when extreme flow rates for extendedperiods are expected. A plug is available whichwi I I close the bore at the top of the tool. Theplug can be removed if other equipment is to berun above or can be replaced with a back pressurevalve which wi I I permit fluid movement downthrou~h the Flow-Tee but prevent any fluid move­ment In the reverse direction.

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trol I ing this wing are opened and the two valvescontrol I ing the side containing the original chokeare closed, diverting the flow through the secondchoke. This process may be continued to flowthrough as many chokes as desired. The Manifoldis usuai Iy fastened directly to the Flow-Tee orRemote Control Safety Valve. However, it can beplaced on the rig floor with a high pressure steelhose connecting it to the Control Head.

THE REMOTE CONTROL SAFETY VALVE is run inplace of the Flow-Tee to provide an exit for theflow into the Manifold or flow I ine. As its nameimpl ies it provides additional safety by al lowingthe wei I to be shut in at the surface from a re­mote position. The remote Control Safety Valvecontains an internal spring loaded sleeve valve.The valve normally is in the closed position.Prior to the start of the test, pressure appl iedthrough a high pressure rubber hose (run from thevalve to a remote position) opens the valve. Aslong as the pressure is maintained, the valve wi I Istay open. If it should become desirable to closethe valve, al I that is required is to release thepressure from the I ine. The spring, aided by thewell head pressure, will close the valve. Thevalve may be reopened at any time by applyingenough pressure to overcome the valve spring plusthe wei I head pressure time a sma I I differentialarea. The remote control valve provides an easymethod of taking surface closures when the con­trol head is positioned some distance up in thederrick. Using the safety valve for surface clo­sures also prevents wear and possible damage tothe master valve maintaining its integrity foremergency situations. The remote control valve isvery desirable when testing offshore or in an areawhere hydrogen sulfide might be encountered.

A SWIVEL provides the abi I ity to rotate thepipe to operate down hole tools without having toclose the master valve and release the surfaceflow I ines. If the test is conducted with rota­tional tools and a swivel is not used, al I bottomhole closures wi I I be preceded by a surface clo­sure. This may be detrimental to the informationbe ing obta ined.

THE MASTER VALVE is the main valve in theControl Head System and provides a means of shut­ting the well in at the surface. If surface clo­sures are to be taken, it may be desirable to takethese with the Remote Control Safety Valve or themanifold valves. This prevents possible wear onthe Master Valve maintaining its integrity forpossible emergency situations. A second MasterValve can be added if redundancy is desired.

THE ACCESS VALVE provides a means of havingaccess into the flow stream at the Control Head.It may be necessary to inject chemicals into theflow stream to prevent a freezing action fromoccurring at the chokes or retard hydrate formingin the surface equipment. The Access Valve hasalso been used as a tap for measuring surfacepressures. The Access Valve may be opened orclosed by rotation of a sleeve located on thevalve.

OPEN HOLESINGLE PACKER TEST

RILL PIPE OR DRILL COLLARS

EVERSE CIRCULATION PORTS

YDROSPRING TESTER

T. PRESSURE RECORDERlAP TYPE)

XPAND SHOE PACKERASSEIIBLY

NCHOR PIPE SAFETY JOINT

LUSH JOINT ANCHOR

-+-HT 500 TEIIPERATURERECORDER

T. PRESSURE RECORDER(8LANKED OFF)

OPEN HOLESTRADDLE PACKER TEST

-HANDLING SUB a CHOKEASSE1l8LY

l-o-HYDROSPRING TESTER

'--'i...",.-BY-PASS PORTS

B. T. PRESSURE RECORDERlAP TYPE)

81G JOHN HYDRAULIC JAR

VR SAFETY JOINT

,--,..",...-BY- PASS PORTS--UPPER BOOY­

PRESSURE EQUALIZERPRESSURE EQUALIZERPORTSNR PACKER ASSEIIBLY

ANCHOR PIPE SAFETY JOINT

FLUSH JOINT ANCHOR

......-:o=r-EQUALIZING TU8E

8.1. PRESSURE RECORDERlBLANKED OFF)

NR PACKER ASSEIIBLY

FLUSH JOINT ANCHOR

BT PRESSURE RECORDER(BLANKED OFF)

THE MANIFOLD has the valve, chokes and pres­sure gauges necessary for monitoring the up streamflowing pressure and control I ing the flow rate.The double wing construction (two identical halvesconnected together) al lows the wei I to-be flowedthrough multiple choke sizes without ever havingto shut the wei I in. This is accompl ished by clo­sing two valves which isolate one half of themanifold and forces the flow through the choke onthe open wing. If it should become desirable toflow through a second choke size, this choke isplaced in the isolated wing. The two valves con-

Figure 2

ROTATIONALLY OPERATED TOOLS FOR OPEN HOLE TESTING

Figure 2 illustrates a typical string of openhole and open hole straddle testing tools.

THE IMPACT REVERSING SUB provides a means ofreverse circulating the recovery from the dri I Ipipe at the conclusion of the test. The sub has ahoi low brass pin that protrudes to the inside ofthe bore of the tool. The Inside of the hoi low

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o u : I;;

pin is exposed to the annulus. At the conclusionof the test a brass bar Is released from the sur­face and allowed to fall through the dri II pipe tothe revers ing sub, str i king the ho I Iowp in, brea k­ing it off and opening a port from the inside ofthe dri I I pipe to the outside. The recovery maythen be reverse circulated from the hole.

THE PUMP OUT SUB offers a means of reversecirculating the recovery from the dri I I pipe. Abrass disc seals the port leading from the bore ofthe tool to the annulus. At the conclusion ofthe test, an approximate 1200 psi differentialpressure app lied ins ide the sub wi I I shea r thedisc and al low the wei I to be reverse circulated.The disc is so constructed that it wil I withstand10,000 psi differential pressure from the annulus.

THE HANDLING SUB AND CHOKE ASSEMBLY providesa means of latching the elevators on the toolstr i ng at the surface fac II i tat i ng ma king up thetools for running in the wei I. There is a provi­sion for placing a choke inside the tool if a downhole choke is required. A metal screen is placedahead of the choke to help fi Iter out sol ids inthe flow stream which might tend to plug the choke.The tool is so constructed that if it should be­come desirable to pump fluids down through thetools, the choke and screen are by-passed removingthe restriction to flow in the reverse direction.

THE DUAL CIP VALVE provides bottom hole valvefor taking flow and closed in pressure periods.The Valve is initially in the open position sothat when the main tester valve (Hydrospring Test­er) opens, the test begins. After the desiredamount of time has been given to the initial flowperiod, the valve may be closed by rotating theDrill Pipe to the right. The flow, closed inpressure sequence, may be repeated by further righthand pipe rotation giving a total of two flow andclosed in pressure periods. After the Valve hasbeen rotated to the final closed in pressure posi­tion, continued rotation wit I open reversecircu­lation ports al lowing the recovery to reverse cir­culate during the final closed in pressure period.Reverse circulating through the Dual C. I .P. Valveis not normally attempted when testing open hole.

THE HYDROSPRING tester is the main valve inthe tool string and is run in the hole in theclosed position. A by-pass port located in thelower portion of the tool al lows the wei I borefluid to by-pass the packers through the inside ofthe tool string. This aids in reducing the pres­sure surges as the tools are lowered in the hole.When the tools are on bojtom and pipe weight isappl ied to expand the packer elements, the weightactivates a hydraul ic metering system which con­trols the opening of the tester valve. After atime delay of approximately 3-5 minutes, the me­tering system releases al lowing free fal I for thelast inch of valve travel. The free fal I closesthe by-pass port, opens the valve and provides asurface indication that the test has started. Atthe conclusion of the test, upward movement of thedrl I I pipe closes the tester valve and opens theby-pass placing annulus hydrostatic pressureacross the formation and terminating the test.

THE AP CASE is used to hold the flowstream

pressure recorder. The pressure recorder is posi­tioned in the center of the case with flow passageprovided around the outside of the gauge.

THE HYDRAULIC JARS are used to provide an up­ward flow to help release the tools if they shouldbecome stuck during the test. A hydraul ic meter­ing system in the jar prevents any relative travelin the jar so a pul I can be taken to stretch thedril I pipe. After a short time delay, the hydrau­I ic system releases al lowing rapid upward movementof the jar mandrel which del ivers an upward impactto help knock the tools loose. The jar does notmeter on the downward stroke so it can be recock­ed rapidly to permit the maximum number of blowsper unit time.

THE V.R. (VERTICAL-ROTATION) SAFETY JOINT pro­vides a place to back-off and release the toolsabove the packer if packer becomes stuck and is un­able to be jarred loose. This is accompl ished byraising the drill pipe, applying right hand torqueand lowering the pipe. This process is repeateda total of 39 times to release the safety joint.There is also a by-pass bui It in the Safety Jointto aid the wei I bore fluid in by-passing the pack­ers. A telescoping action closes the by-pass whenweight is appl ied to the packers.

THE OPEN HOLE PACKER affects a seal betweenthe tool string and the wal I of the hole isolatingthe formation to be tested from the fluid in theannulus. The packers are designed to al low themetal supports on either end and the packer ele­ments to be changed readi Iy so the 0.0. of thepacker can be sized to the diameter of the hole.A sma I I hard rubber element below the main packeris expa nded by contro I led trave I . It does not sea Ibut partially bridges the gap between the metalshoes and the hole reducing the clearance and pro­viding additional support for the main packer. AI Iexterior metal parts are locked to the inside man­drel preventing any free rotation if it shouldever become necessary to remove the packers with awash over tool.

THE DISTRIBUTOR VALVE al lows you to controlthe pressure in the annulus between two packerswhen more than one packer is run. When two pack­ers are set in tandem the annulus fluid trappedbetween the two packers is compressed creating apressure bui Id-up ranging from i200 psi to morethan 2000 psi. The pressure increase may be suf­ficient to break down a weak or naturally verti­cal fractured formation allowing the annulus hy­drostatic pressure to communicate through the for­mation to the tested interval. The DistributorValve permits the annulus pressure between the twopackers to be maintained at a preset valve. Thisprogressively drops the pressure differentialacross the packers subjecting the formation to theleast stress possible. The valve is designed suchthat if during the test the top packer should loseits seat dropping the total hydrostatic pressureon the bottom packer, the valve wi I I not reopen.If the bottom packer holds, the test can be comple­ted.

THE ANCHOR PIPE SAFETY JOINT is run below thebottom packer. This permits the string to be re­leased below the bottom packer If the anchor pipe

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becomes stuck and can not be jarred loose. It isimportant to back-off below the packers if possi­ble.

This leaves a relatively simple fishIng jobof just having to fish for the anchor and not hav­ing to cut over the packers. A very high percen­tage of the time it is the anchor that becomesstuck and not the packer.

THE ANCHOR PIPE is very heavy wall pipe witha multitude of sma I I holes through it to provideaccess for the wei I production to enter the dri I IpIpe. The length of the anchor is varied to spacethe packer(s) the proper distance above the bottomof the hole. The Anchor Pipe has to be of highstrength because the entire weight of the annuluscolumn of fluid is transferred through the anchorto the bottom of the hole.

THE BLANKED OFF RUNNING CASE carries theblanked-off pressure recorder in the hole. Thisgauge can not sense pressure in the flow stream.It only has access to pressure from the annulusin the tested interval.

STRADDLE TESTING

Sometimes it is desirable to test a formationthat had been previously penetrated and is abovethe bottom of the hole. Straddle Testing providesa means of isolating the formation to be testedfrom other potentially productive formations inthe we I I. The Pressure Equa liz i ng tube prov idesa means of maintaining annulus hydrostatic pres­sure below the bottom packer while preventing itfrom being placed across the tested interval. SeeFigure 2.

THE SIDE WALL ANCHOR provides a means of sup­porting the weight necessary to expand the packeron a straddle test when it is not practical torun anchor pipe to bottom. The tool consists oflarge sl ips which can be expanded against the boreof the hole to support the tools. The equal izingtube run when straddle testing maintains hydro­static pressure below the bottom packer el imina­ting the need for the side wal I anchor to supportthe annulus hydrostatic pressure. The drag springassembly which provides the resIstance required toexpand the sl ips wil I not rotate as the tools areremoved from the hole. This al lows the Drl I I Pipeto be rotated out without the drag springs dama­ging the filter cake.

RECIPROCAL TESTING

The Dri I I Stem Test tools can also be con­trol led by recIprocatIng the dri I I pipe. To con­duct the test with up and down pIpe movement, al Iof the previously described tools are used withthe exception of the Dual C. I .P. Valve. The toolsI isted below are added or modified as described.

THE MODIFIED HYDROSPRING TESTER Is a conven­tional hydrospring that has been modifIed to per­mit taking closed in pressures. The bypass is re­moved from the bottom of the tool and an indexIng'J' slot added at the top. The tool is run in theclosed position. When weight is set through theHydrospring tester to expand the packers, a hy-

draul ic meterIng system is activated in the tool.After a 3 to 5 minute time delay the Hydrospringtester opens starting the test. A free fal Itravel of approximately one inch at the time thetool opens, jars the dril I pipe, giving a surfaceindication that the test has started. When it be­comes desirable to close the Hydrospring testerfor a bottom hole closed In pressure, the dri IIpipe ispicked up until the Hydrospring testercloses. The 'J' slot at the top of the tool In­dexes al lowing weight to be reappl ied to the toolswithout the valve reopening. To open the valvefor subsequent flow, the dri I I pipe is again raisedto a neutral position and weight appl ied to thetool. The 'J' slot indexes and the Hydrospringtester opens after the 3-5 minute time delaycaused by the hydraul ic metering system. Thisprocess may be repeated to permit as many flow andclosed in pressure perIods as desired.

THE L.O.C. (LOCKED OPEN CLOSED) BY-PASS isrun in conjunction with the modified Hydrospringtester to provide the fluid by-pass that was re­moved from the bottom of the Hydrospring tester.The By-Pass is open goIng in the hole and does notclose unti I just before the Hydrospring opens.After the by-pass has closed, it remains ciosed un­til returned to the surface.

THE EXTENSION JOINT provides the free travelnecessary to close the Hydrospring tester withoutunseating the packer. After the Hydrospring test­er closes the additional upward travel of the Ex­tension Joint can be taken before the packer re­leases. Each Extension JoInt provides 30 inchesof free travel. As many Extension Joints as re­quired can be run to provide the free travel nec­essa ry to corduct the test.

TESTING INSIDE CASING

The tools required for testing inside casingare the same as described for open hole testingwith the exception that the open hole packers arereplaced with a casing hookwal I packer and theflush joint anchor is replaced with perforated tai Ipipe.

Additional tools for testing in casing are de­scribed in the section under Floating Vessel Test­I ng.

THE SAMPLER is a modification of the testervalve to al low it to catch a sample under finalflowing conditions. Samplers are avai lable forrotational or reciprocal testing. The size of thetrapped sample ranges from 2100 to 2750 cc depend­ing on the Sampler used. The sample from a dri I Istem test is taken at final flowing conditionswhere phase separation may have occurred andtherefore should not be considered a P.V.T. sample.The fol lowing information is avai lable from thesample: Recovery volumes, amounts of gas, oi I,water, mud, API gravity of the 01 I, specific grav­ity of the water, chloride content of the water,resistivity of the water, and the gas oi I ratioin the Sampler.

If there is water in the dri I I pipe recoveryand no water in the Sampler, then the final fluidsflowing contained no water and this is a good in-

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odicatlon that the water in the Dril I Pipe is in­filtrate loss and not formation production. Thisis an additional check in conjunction with thechlorides, and the resistivity as to where thewater came from.

If a larger sample is required, then one tothree dri I I col lars can be run between the DualC. I .P. Valve and the Hydrospring tester. A drainvalve is run above and below the col lars. A dropand seat, to prevent fluids in the sample fromdraining to bottom during the closed in pressureperiods, is run below the lower drain valve. Thesample wi II be trapped at final closed in pres­sure. The gas is removed from the sample chamberthrough top drain valve. The I iquids are thendrained from the lower drain valve.

MECHANICS OF TESTING

Preplanning and the use of proper procedureswi I I greatly aid in safely obtaining the objec­tives of the test. Selection of the equipmentwil I have to be based on the type of test to beconducted and the hole conditions that exist. Con­sideration should be given to the size and type oftools required, the pressure gauge range, lengthof the gauge clocks, bottom hole temperature,whether the wei I is being dri lied underbalanced,whether H2S is to be expected. AI I these factorswil I have an effect on the success of the test.

If it is to be open hole test, conditioningthe hole prior to the test wi I I do more to insurea mechanically successful test than any othersingle factor. More misruns are caused by anchorperforation and/or tool plugging than any otherreason.

As the tools are made up on location, theproper amount of flush joint anchor is placed inthe tail pipe to space the packer(s) the desireddistance from bottom. If the available flushjoint anchor, usually about 40 feet, does not pro­vide the desired length, then dril I col lars canbe added to achieve the proper interval. Whendril I col lars are run in the anchor, they are nor­mal Iy placed above the perforated anchor. Thisis because the 0.0. of the col lars is usually lar­ger than the perforated anchor and would, if runon bottom, expose an upward step at the transitionbetween the collars and the anchor. This stepwould be a good place for any sol ids settl ing outof the flow stream to bridge and possibly stickthe tail pipe. If the perforations are run onbottom, any smal I sol ids in the annulus would becarried through the anchor into the flowstream.Drill Pipe should never be used as tail pipe. Itdoes not have the strength to withstand the tre­mendous loads that can be appl ied to the anchorduring the test.

It is common to place dri I I col lars on top ofthe string of test tools to help provide the ri­gidity and weight required at the tools to set thepackers. In some areas "weight pipe" is used forthis purpose. Weight pipe is Dril I Pipe with asecond piece of pipe fitted lengthwise providingadditional weight and rigidity. Weight pipe cannot be distinguished from Dril I Pipe by outwardappearance. If weight pipe is used, it should be

made certain that the length and 1.0. is correctlyreported; otherwise, an erroneous I iquid productionrate calculation could result.

The hole should be ful I at the time the toolsare started. If water cushion is to be run, eitherfor protecting the dri I I pipe from col lapse pres­sure, or for placing a back pressure against theformation, a heavy gel should be mixed and pouredin the first few joints of pipe run on top of thetools. This wi II hold in suspension any scale,dried mud, etc., that may be washed out of thedri II pipe and prevent it from settl ing inside andplugging the tools.

Water cushion should be added approximatelyevery 10 stands. This wil I help prevent large airpockets from accumulating in the cushion.

The rise in the level of the mud pit shouldbe monitored as the dril I pipe is run. The in­crease should be equal to the volume of mud beingdisplaced by the pipe. If it is less than thevolume being displaced, then fluid is being lostin the hole. A formation may be taking fluid orthe dri II pipe may be leaking. If the increase isgreater than the volume being displaced, then someformation is producing into the well. If this isoccurring, the well is underbalanced and the threatof a kick is very real.

The dri I I pipe should not be run at an exceed­ingly high rate. The piston effect could createpressure surges great enough to exceed the frac­ture gradient of the formation. A rate of ap­proximately I foot per second is about right.Peri­odically, the dri II pipe should be checked forleaks. A very sl ight blow from the dri I I pipeshould not create concern, as this may be causedby expansion of air from the increase in tempera­ture. However, if a dri II pipe leak develops, itshould be discovered and corrected or a mis-runwi II result.

As the tools approach packer depth, the rateshould be siowed down to watch for bottom. If thepipe tally is in error, the tools could hit bottombefore expected and possibly damage the pipe ortool string. The Control Head equipment is madeup on the last joint and the pipe slowly worked upand down observing the indicator coming up and go­ing down. A 5 minute wait with the pipe hangingstationary prior to setting weight on the packershould yield a clean place on the charts for read­ing initial hydrostatic pressure.

After it has been observed that the hole isfull, the desired weight, usually 20-40,000 Ib, isplaced on the packer. The height of the ControlHead above the rotary table should be observed. Ifit is higher in the derrick than it should be,thisis an indication of fi I I on bottom. The cuttingsand cavings creating the false bottom wi I I usuallyexplode up around the tai I pipe when the testervalve opens causing the packers to start sl idingto bottom, picking up additional mud in the recov­ery, creating situations conducive to anchor per­foration plugging, and also possibly sticking theanchor pipe.

Someone should be assigned to observe the

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annulus from the time the tester valve opens unti Ithe packer is unseated. If the fluid in the annu­lus drops, the pipe should be picked up immediate­ly to close the tester valve and prevent the mudfrom u-tubing. A second attempt may be made toobtain a test by setting more weight on the pack­ers than was app lied in the first attempt. Ifthe packer does not seat after 2 or 3 tries, thetools should be removed and the hole conditionedor another packer seat selected.

The recommended testing procedures for ob­taining good reservoir information are discussedunder the chart interpretation section. However,it is felt the test should be conducted based onthe wei I 's performance and not restricted to somepreset inflexible plan.

If the test is being conducted inside casing,the dril I pipe recovery may be reverse circulatedduring the final closed in pressure. However, itis usually unacceptable to reverse in open holewhile the packers are stili seated.

At the conclusion of the final C. I .P., thepipe is raised to terminate the test.The by-pass opens placing hydrostatic pressureacross the tested interval and equal izing pres­sure around the packers. Continued upward move­ment unseats the packers. The packers should begiven a few minutes after releasing to give themtime to return to their original diameter. Ifthe pipe is started out of the hole immediately,the packers may not have returned to size andcause a problem in swabbing the wei I. After thepackers have been unseated and the tools free,one of the reverse circulating subs should be ac­tivated and the recovery reverse circulated fromthe dril I pipe. The constituents in the recoverycan be fairly accurately determined by observingthe returns, catching samples and counting thepump strokes. There wil I be a fluid sample belowthe reversing sub, and a sample between the DualC. I .P. valve and the Hydrospring tester. Also, asampler may be run if desired.

The trip out of the hole is probably the mostdangerous time during a dri I I stem test. This iswhen everyone feels the test is concluded and letstheir guard down. As the pipe is removed from thehole, the annulus should be fil led approximatelyevery 10 stands. The amount of mud required tofil I the annulus should be measured. If this isless than the volume of the pipe removed, thensome formation is feeding into the annulus. Thismay be caused by the packer swabbing the wei I. Therate the tools are being pul led should be reduced.If the amount to fil I the annulus continues to beless than the volume of the dril I pipe removed,consideration should be given to going back tobottom and conditioning the mud. If the trip outof the hole is continued with the formation comingin, the wei I may become underbalanced and thethreat of a blowout exists.

Another hazard is present when hydrocarbonshave been recovered and not reverse circulated.The pipe is pul led wet. The agitation of the re­covery as the pipe is removed often causes gas tocome out of solution resulting in a spray of oilblowing out the top of the pipe. Anytime the rig

is showered with oil, there is a threat of fire.The fire wi II not last long, but the toll in humanresources and equipment can be great. Wet plugs(plugs designed to blank off the top joint of astand of dri I I pipe to prevent the pipe from un­loading as it is raised in the derrick) are some­times used when pulling a set string. However,the tendency of the plug to get loose and fal Ifrom the elevators as they are lowered for thenext stand seems to present a greater threat tothe crew than the risk of fire. Both threats areremoved if the recovery is reverse circulated.

When the tools reach the surface, the pres­sure recordings should be inspected for a visualinterpretation of the test. This wi II indicateif the test is a mechanical test as wei I as givingan immediate indication of permeabi I ity (low,medium, high), wei I bore damage (none, low,medium,high), possibly depletion,etc. The first pres­sure recording recovered wi I I be from the flowstream gauge. A decision on the test should notbe based on analysis of this gauge alone. Theblanked off pressure recording should also be in­spected and compared to the flow stream gauge. Ifthey do not look al ike, an explanation as to whythey don't should be obtained.

TESTING FROM FLOATING VESSELS

Figure 3 illustrates a Dril I Stem Test beingconducted from a floating vessel (next page).

SURFACE EQUIPMENT

The Unitest Tree surface control equipmentsystem as described for land testing is appl icablefor the offshore testing. The componentized ap­proach al lows the control head to be configured inthe manner required for a particular test. Oftentwo master valves are run for redundancy. Amaster valve and flow-tee may be placed on top ofthe test tree to permit a ki II I ine to be install­ed throughout the test.

SUBSURFACE EQUIPMENT

THE SUB-SEA TEST TREE (SSTT) increases thesafety of an offshore test by providing an oceanfloor test tree. The SSTT is run as a part of thetest string and is spaced out such that it is land­ed in the blow-out preventer (BOP) stack when thetools are on bottom. The Test Tree is sized tothe stack so the pipe rams may be closed againstthe SSTT. Two bal I valves in the SSTT are in thenormally closed position. A dual conduit hydrau-I ic I ine is run from the SSTT, strapped to theside of pipe, to the surface. Pressure appl iedthrough the hydraul ic I ine to the SSTT rotates thebal I valves to the open position. The valves wi I Iremain open as long as the pressure is maintained.Anytime the pressure is released, either on pur­pose or through an accident such as the I ine beingsevered by the vessel being blown off location,thebal I valves automatically close shutting the wei Iin at the ocean floor. The valves may be reopenedby again applying pressure to the lines.

A quick disconnect al lows the pipe above theSSTT to be released from the SSTT if it should be­come desirable to do so. This is accompl ished

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0 u , <J .} ,,,)

.,.. ~., ; '. .) ..-'-;; ,)

either hydraul ical Iy applying pressure throughthe second conduit of I ine running to the surfaceor by rotation of the pipe. The geometry of manyof the BOP Stack wi I I permit the bl ind rams to beclosed above the SSTT after the pipe is released.The pipe from the surface can be run and re-en­gaged in the SSTT whenever desired.

OFF SHORE TEST 'SYSTEM

ll1Ilil"'lOl~----SUB SEA TEST TREE

1-+---- FUL-FLO SAFETY VALVE

;c:::§-I---- S LIP J 0 I N T S~~~--- DRILL COLLARS

b"i-+---- CIRCULATING VALVEISI

1'i'~n-!----(OPTIONALlWEIGHT OPERATED

TESTER

n-+---- APR-N TESTER

AUXILlARY TOOLS

Figure 3

THE FUL-FLO SAFETY VALVE TESTING TOOL is de­signed to provide additional safety by automat-lea I IY shutt Ing the we I lin if the pipe shou Idpart near the ocean floor but below the Sub-SeaTest Tree. The valve is placed in the string theappropriate distance above the upper sl ip joints.It consists of a bal I valve which is held open aslong as the valve is in tension. If the pipe partsthe fal I ing action of the pipe wi I I telescope thevalve to the closed position. A pressure build­up in the pipe below the valve wi I I not pump thevalve back to the open position.

The valve has also found an appl ication foropen hole tests in areas where Hydrogen Sulfidemay be encountered. It is run just high enoughin the string to remain in tension when the packer

is set. If the pipe should part during the test,the valve wi I I close shutting in the wei I andpossibly preventing a blowout.

THE SLIP JOINTS are free travel joints de­signed to counteract the effect of pipe movementwhile operating down hole tools and to provide ameans of accurately placing the desired weight onthe down hole packers. After the amount of weightto be placed on the down hole tools has been run,the SI ip Joints are inserted in the string. Whenthe packer is set and the pipe landed at the oceanfloor, the SI ip Joints wi I I be in the neutral posi­tion with the weight below resting on the tools.In areas where the vessel movement is minimal,these SI ip Joints are sometimes omitted from the~tring. Slip Joints are also used for free traveljoints below the weight operated tester valves toaid in their operation.

THE TYPE 'A' REVERSE CIRCULATING VALVE pro­vides a dependable means of reverse circulatingthe recovery from the pipe. The valve is set,prior to going in the hole, to open when the de­sired pressure is appl ied to the casing. Thispermits the recovery to be reverse circulated with­out any mechanical manipulation. Usually eitherthe pump out or impact reverse circulating sub(described in open hole testing) is run to provideredundancy.

THE ANNULUS PRESSURE RESPONSIVE-(APR) TESTERVALVE was designed to permit a test to be conduct­ed inside casing without any manipulation of thepipe. This greatly simpl ified testing from float­ing vessels where the constant motion of the rigmade the operation of the tool by pipe movementdifficult. The valve is control led by the appl i­cation and release of pressure appl ied to the cas­ing. After the packer has been set, the valve isopened by applying the appropriate pressure to thecasing. The valve Is closed by releasing the cas­ing pressure. The tester valve can be opened andclosed as many times as necessary. If the casingpressure should exceed a pre-determined amount,the valve automatically closes and can not be re­opened unti I it is returned to the surface. Thisis a safety feature which wi II shut the well in,if a leak should develop in the dri I I pipe, beforea dangerously high pressure could be appl ied to thecasing.

PROCEDURE FOR TESTING FROM FLOATING VESSELS

The testing tools are made up and run in thehole unti I the weight indicator shows the desiredamount of weight, usually about 25,000 Ib, to beabove the tools. The upper sl ip joints are in­stalled in the string and the pipe from the slipjoints to the ocean floor run. The Sub-Sea TestTree placed in the string and the remainder of thepipe' run. The su rface test tree is i nsta I Ied andpressure tested. If a ful I string of water cush­ion is run, the entire pipe string from the sur­face to the tester valve can be tested. The pack­er is then set and the pipe lowered untl I the Sub­Sea Test Tree is landed In the B.O.P. stack. Thisplaces the upper SI ip Joints in the neutral posi­tion with the pipe weight above supported by thefluted hanger. The weight below the SI ip Jointsis resting on the tools and packer.

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If the weight actuated tools are run, thetester valve wil I open after a short time delay.The remainder of the test is conducted by recip­rocating the pipe when it is desired to open orclose the tester valve.

If the Annulus Pressure Responsive tools arerun, the pipe rams are closed against the Sub-SeaTest Tree and the casing pressured to the predeter­mined amount. This opens the tester valve. Theremainder of the test is conducted by release andreapplication of the casing pressure. No pipemovement is required.

During the final bottom hole closure, orafter the packer has been unseated, one of the re­verse circulating valves is opened and the recov­ery is reverse circulated from the pipe. The toolsare then returned to the surface.

HIGH VOLUME TESTING

Some of the offshore wei Is being encounteredwere capable of producing at extremely high rates.These wei Is needed to be adequately defined duringthe test so the proper drl I I ing and producingplatforms could be designed. The extreme cost ofthese faci I ities left I ittle room for error. Therestricted bore through conventional tool did notpermit the highly prol ific wells to be drawn downsufficiently to al low the reservoir's character­istics to be accurately determined. To obtain theformation parameters from these wei Is, a ful Iopening string of test tools and related surfaceequipment was developed. These tools permit awei I to be flowed at high rates for extendedperiods of time. See Figure 3.

THE SURFACE CONTROL HEAD equipment was modi­fied to permit the flow to exit from both sides ofthe Remote Control Safety Valve. AI I right angleturns are replaced with large radius sweeps tohelp prevent fluid cutting. A bypass floor chokemanifold al lowed the flow to be diverted throughthe manifold when desired and bypass the manifoldthe remainder of the time.

THE TESTER VALVES, the Ful-Flo Hydrospringtester which is a weight actuated valve, and theful I opening APR tester valve were designed withfull openings to permit unrestricted flow.

THE BUNDLE CARRIER was designed to carry twopressure recorders and two temperature recorderswithout restricting the bore through the case. Therecorders are carried in pockets mi I led in the out­side of the case. The pressure gauges have portsleading from the bore of the case to the gauge.This al lows the gauges to be run above the packersas frow stream gauges or they may be run as blank­ed off gauges below the packers.

THE FULL OPENING TESTING TOOLS designed forhigh volume testing had several other advantageswhich became apparent. The ful I opening permittedthe formation to be perforated through the toolafter they were in place and the packer set. Thisal lows the wei I to be perforated in an underbal­anced condition (formation pressure greater thantUbing hydrostatic) helping prevent the wei I frombecoming damaged by producing back crushed forma-

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tion particles and debris frol\l shooting. If thebundle carrier is used, the gauges are ~Iready inplace, the perforating gun is removed and the teststarted. If the bundle carrier is not used, theperforating gun is removed and the gauges run inon wire I ine and landed in a seating nipple posi­tioned below the packer. The wire I ine is thenremoved and the test run.

The ful I opening tools also permit the forma­tion to be stimulated through the tools. Whenthe formation is to be treated during the test,the reverse circulating valves are often replacedwith tubing operated circulating valves. Thepumping equipment Is connected to the Test Treethrough a ki I I I ine. The wei I is tested in theconventional manner taking the desired flow andclosed in periods. The wei I can then be stimula­ted through the test tools. The top circulatingvalve is opened, the recovery reverse circulatedand the treating fluid circulated to bottom. Thetester valve is opened, and the formation treated.After the treatment, the formation is again test­ed to evaluate the treatment.

If difficulty Is encountered in breaking downthe formation, the test can be terminated or spe­cial procedures may be fol lowed. One procedurewould be to kil I the wei I through the circulatingvalve, pul I the test string and remove the Sub­Sea Test Tree. Install a back pressure valve andrun the string back down unti I the upper circula­ting valve is below the perforations. Acid isspotted across the perforations and the stringpul led to remove the back pressure valve. TheSub-Sea Test Tree is re i nsta I Ied and the teststring run back to the original packer depth. Theformation is broken down, treated and the testingresumed.

CHART INTERPRETATION

Figure 4

The Charts shown in Figure 4 are typicalBourdon Tube (BT) type pressure recordings of adual closed in dri I I stem test. The top chart isthe flow stream gauge and the bottom chart is theblanked off gauge. Time on a B.T. chart startsat the left and increases from left to right. Thetime represented in the time axis is dependentupon the clock being used in the gauge. Clocksof 12, 24, 48, 72 and 120 are available. Pressure

u

starts at the zero pressure line or "ba se line"and increases in the"down direction. The baseI ine is scribed on the chart by the gauge at thesurface prior to running in the wei I. The otherhorizontal I ine on the charts are placed on thechart at the time it is read. Each of these linesrepresent 1000 psi unless another value is writtenon the I ines. The vibrations at the start 4-aand at the end 4-k of the test represent vibrationof the stylus at the time the gauges are made upand removed from the running case. These vibra­tions should be on the charts and indicate thestylus assembly is free. The vibration excursionsshould be centered on the base I ine with approxi­mately one half above and one half below. Theline extending diagonally down is the recordingof the tools being run in the hole. The width ofthe I ine is actually drawn by vertical stylus mov~

ment caused by pressure surges due to the pistoneffect of the tools being lowered in the hole.

Visual observation of this line wil I indicatehole conditions and/or the speed the tools wererun in the hole. Running the tools at excessivespeeds can cause pressure surges sufficient topossibly break down a formation. The short hori­zontal I ine at 4-b represents the initial hydro­static pressure. At 4-c, the test valve has open­ed and the pressure dropped to the hydrostatichead above the gauges. When no water cushion isrun, the pressure wil I be close to zero. The por­tion of the chart from 4-c to 4-d represents theinitial flow period. The rise in pressure is dueto the increase in hydrostatic pressure from theformation flowing into the dri I I pipe. At point4-d, the tester valve is closed and the formational lowed to regenerate its pressure in the drawndown area, from 4-d to 4-e. The valve is againopened at point 4-e. The pressure at the start ofthe second flow period on a I iquid production testshould be close to the same as the pressure at theend of the initial flow period. This is becausethere should be the same hydrostatic head on thegauge at the start of the second flow as was therewhen the valve was closed for the initial C.I .P.If the pressure is less than the final of theinitial flow, then this indicates the dri I I pipeis unloading at the surface during the closed inpressure. If the second flow starts at a distincthigher pressure than the end of the initial flow,this is a strong indication of possible dri I I pipeleakage. The well is open to flow from 4-f to 4-g.At point 4-g, the valve is closed for the finalclosed in pressure. At point 4-h, the dri I I pipeIs raised opening the by-pass and dropping the hy­drostatic pressure across the formation. The firelhydrostatic pressure is read at 4-i. At 4-j, therate the tools are being pul led is slowed down.The recovery has been reached and the string ispul led wet. At 4-k, the gauge has been returnedto the surface.

When looking at a B.T. pressure chart, thefirst observation that should be made is if thebase I ine is good. Does the gauge start and endon the base I ine? If the gauge starts and ends onthe base I ine, then the information recorded canbe con s idered to be true. If it does not sta rtand/or end on the base I ine, a gauge problem maybe indicated. The flow stream gauge starts abovethe base line 4-1 and returns to the surface above

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the base line 4-n. The initial flow pressure alsoextends above the base line 4-m, indicating avacuum was drawn against the gauge. Of course,this did not occur. The base I ine on a B.T. charthas to be drawn with the gauge in the vert~cal

position. If the base I ine is drawn with thegauge laying down, the weight of the stylusassembly wil I cause the Bourdon Tube to rotateslightly causing the base line to be drawn inerror. When the gauge is returned to the verticalposition, the stylus assembly rotates back to thetrue zero. This is an example of an improperlydrawn base line.

Figure 5

Figure 5 is an example of a properly conductedtest. Two good flow periods are taken with onehalf of the total flow time given to each flow.Production calculation can be made from each flowperiod. Two good closed in pressures are record­ed both with sufficient closure for rei iableHorner extrapolation. The closed in pressureperiods are equal in duration to the flows. Thisis sufficient for a wei I with this permeabi I itybut is not necessari Iy the correct procedure forother wei Is. More wi I I be discussed on this later.With the abi I ity to make production calculationsfrom the flow periods and to extrapolate theclosed in pressures, the reservoir parameters maybe calculated from both bui Id-ups. The dril I pipewas not reverse circulated and the string waspu II ed wet.

Figure 6

The test in Figure 6 is a good test mechanic­ally. The gauge starts on the base line 6-a. Atpoint 6-b, the rate the tools are being run in thehole is increased. The reason for the slower rateto this point is that dri I I col lars are being rununti I this time. At 6-c, the tester valve isopened and the initial flow is started. At 6-d,the valve is closed for the initial closed inpressure. At 6-e, the valve is reopened for thefinal flow. At point 6-f, there is a direct an­gular break recorded in the flow period. It givesthe appearance of a sudden reduction in rate whensuch is not the case. It is caused by the transi­tion of production from the smal I capacity of thedri I I col lars into the large capacity of the dril Ipipe. At 6-g, the valve is closed and the finalclosed in pressure period taken until the test isterminated at point 6-h. The trip out of the holeis recorded unti I 6-1, at which the chart time ex­pired. It is not necessary for the ttip out ofthe hole to be on the chart. The vibration thatoccurs when the gauge is removed 6-j indicates thegauge did return to the base I ine. The obviousquestion that arises from this test is, is thewei I depleting? A comparison of the two closedin pressures gives a strong indication of reservoirpressure caused by the production during thesecond flow period. If that is the case, then thewei I should not be completed based on this zone.However, there is a second possible cause for thediscrepancy between the two closed in pressures:Super Charge. Super Charge is a term that is usedto describe the over pressured zone adjacent tothe wei I bore and caused by infi Itrate loss intothe formation. This is referred to as the flushzone or invaded zone on the logs. There is a prffi­sure gradient starting at hydrostatic pressure atthe wei I bore and extending to true reservoir prffi­sure some distance back in the formation. Thedepth of the pressure invasion is primari Iy afunction of permeabiJ ity. The lower the permeabil­ity, the deeper the invasion. If the well is notproduced for a sufficient length of time duringthe initial flow period to remove this invadedpressure, the initial bui Id up wil I reflect theinvad~d pressure and record a false closed inpressure. The problems involved in interpretingthis test would be removed if sufficient time topositively remove Super Charge had been given tothe initial flow. It is recommended that a mini­mum of 30 minutes and preferably half the totalflow time be given to the initial flow period. Ifthe possibil ity of Super Charge does exist, theone clue which can help determine if it is deple­tion or Super Charge is the second flow period.If the wei I is producing at a constant rate,approximately equal increases in flow pressure forincremental time, then the reservoir can not belosing energy. This test does indicate a relativeconstant rate of production from 6-f to 6-g;therefore depletion is not occurring and theinitial closed in pressure is Super Charged. Thetime spent during the initial C. J.P. 6-d to 6-eis actually a waste of rig time.

The test shown in Figure 7 is simi lar inappearance to the preceding test with a shortinitial and long final flow. The final closed inpressu re wi I I never reach the va Ive recorded onthe initial C.I.P. Again the question, is thisSuper Charge or is it depletion? Looking at the

Figure 7

second flow period, it can be seen that the produc­tion rate is continually decl ining from start tofinish. This is a very strong indication that de­pletion is occurring. If it is felt that this isnot conclusive enough evidence, then the wellshould be retested. On the second test sufficienttime should be given to the initial flow period topositively remove Super Charge forces. Again along second flow should be taken. A comparison ofthe two closed in pressures on this test with eachother and with the pressures recorded on the pre­vious test should give a conclusive answer.

There is one pther phenomena that causes adecl ining rate during the flow period back pres­sure. The back pressure due to the increase inhydrostatic head inside the dri I I pipewil I even­tual Iy cause a decl ine in .production rate. A'rule of thumb' from the observation of many testsis that the decl ining rate wi I I start to becomereadily apparent when the back pressure is approxi­mately equal to half of th~ formation pressure.

Figure 8

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l' u <j 9 0Figure 8 shows a tes~ with three flows and

closed in pressures. The reason usual Iygiven fortaking three flows and closed in pressures is tocheck for depletion. On this test the reservoirpressure is almost completely depleted at the con­clusion of the final flow. However, what we mostoften see with three flows and closed in pressuresis indicated in Figure 9. On this test, due tothe short first flow, the initial closed in pres­sure is sti I I under the influence of Super Chargeand wi I I extrapolate to a higher value than the

, second and third C.I.P. The second and thirdclosed in pressures are good. It is felt thatmany times two properly conducted flows andclosed in periods wi II yield better informationthan three or more. Often there is only a cer­tain amount of time permitted on bottom. If thistime is divided into three or more flow and closedin periods, there is not sufficient time i~any ofthe periods to obtain good information.

Figure 10

Figure 10 is a test where the surface reac­tion (very I ittle indicated production) is sayinglow permeabi I ity. If the formation has low per­meabi I ity, then it takes longer to get good re­servoir information. More time is required to re­move Super Charge and it wil I take longer for theclosed in pressures to develop. On this test theinitiafflow period mayor may not have been longenough to remove Super Charge. Insufficient timewas given the initial C. I .P. It does not haveenough closure for a rei iable Horner extrapolationand provides very I ittle information. The secondclosed in pressure was given enough time to devel­op a good bui Id up from which reservoir parametercan be determined. The initial C. I.P. could becon'sidered a waste of rig time.

Figure I I illustrates a test where again thereaction at the surface indicated low permeabi I ity.This suggested an extended time would be requiredto obtain good closed in pressures. However, thebui Idups developed very rapidly with short radiusof curvature and yielded two good closed in pres~

sures. The fast bui Id up is not compatible withlow permeabi I ity. The reason for ,the discrepancyis high wei I bore damage. The quick bui Idup re­sults because the formation is capable of produc­ing at a much greater rate than the restrictedpermeabi I ity at the wei I bore wi I I al low. Conse­quently there is I ittle draw down and when thetester valve is closed, the formation quickly re-

<c,J'.)

generate pressu~e. With a little practice,a visual rpretation will give an indicationof damage. 'he indicated permeabi I ity needs tobe weighed L ]ainst how rapidly the build up oc­curs,figure 12 shows a test 'indicating high per­meab iii ty and no damage. The v i sua I interpreta­tion of damage on gas wei Is can be a I ittle moredifficult.

Figure II

Figure 12

Figure 13

Figure 13 illustrates a gas producing wei I.

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There is one procedure difference b~ c.,"inga gas well and a liquid well. The pr,_ In rateon a I iqu id test can be gauged if it to thesurface or ca n be ca Icu Iated from the ~ dingpressure on the cha rt if it does not. ,,8 rate ona gas wei I has to be measured at the surface. Dueto the short duration of the initial flow periodon this test, the rate was not measured and there­fore no reservoir calculations can be made fromthe initial C. I .P. A near stabi I ized rate was ob­tained during the final flow period. The finalC. I .P. could be extrapolated and reservoir calcu­lations made.

Figure 14

Figure 14 illustrates a mechanically success­ful gas wei I test. The test starts and ends onthe base I ine. Stops were made at 14-a and 14-bto add water cushion. The tester valve was openedat 14-c for a short initial flow. At 14-d thetester valve was closed and a bui Id up recorded.At 14-e the tester valve was opened and the sur­face valve closed. The surface valve was openedat 14-f and the wei I flowed for a clean up periodto 14-g. At 14-g the wei I was placed on a smallchoke and produced against the sma I I choke unti I14-h. At 14-h the wei I was placed on a largerchoke. At 14-i the choke was changed to a stil Ilarger choke. At 14-j the final choke change wasmade. At 14-k the tester valve was closed and abottom hole closed in pressure taken. At 14-1 thebypass was opened and the hydrostatic pressuredropped across the format ion. If the we I I Is tobe flowed through a series of chokes, theproper sequence is to start with the sma I lestchoke and progressively change to larger ones.This extends the radius of investigation furtherinto the reservoir and increases the radius ofcurvature in the closed in pressures making themeasier to interpret. If the well is flowingagainst a smal I choke at the time it is closed in,the back pressure may be so great that the closedin pressure wi II bui Id so quickly that it is dif­ficult to obtain enough reading in the curved por­tion to make a Horner Plot.

Flowing the wei I against increasingly largerchoke sizes, however, can also create problems.If the wei I is not al lowed to stabil ize duringthe flow periods, it can be exceedingly difficultto obtain accurate information from the test. Onthis test the bottom hole charts indicate the

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sand face flowing pressure was never al lowed tostabi I ize durinq the test.

Figure 15

A decision on a test should not be made onthe basis of the flow stream gauge alone. Itshould always be compared to the blank-off gauge.Figure 15 shows the flow stream and blanked offgauge. The charts indicate severe hole conditionsexist near the bottom 15-a. The extreme shake ofthe opening line 15-b to 15-c is an indication ofthe tools sl iding to bottom. The height of thecontrol head above the rotary should have been aclue that the tools were resting on fi I I and noton bottom. The flow periods from the flow streamgauge 15-c to 15-d and 15-e to 15-f indicate lowpermeabi I ity. Close examination does show aI ittle roughness during the flows. The flowperiods on the blanked off gauge show a completelydifferent picture. Severe anchor perforationsplugging is occurring. When al I of the anchorperforations plug, it is the same as closing avalve on the blanked off gauge; and it starts apressure bui Idup. Then a perforation breaks freeand the pressure released. The continual plug­ging and releasing creates the appearance of theflow periods shown on the blanked off chart. Thebypass is opened at 15-g. The pressure surges atthe start of the trip out indicate the jars hadto be tripped to drive the tools out of the cut­tings and cavings on bottom. It should have beenexpected that plugging and possible sticking thetools would occur because of the difficulty inreaching bottom. The conditions encountered at15-a should have been sufficient cause to removethe tools and make a bit trip to clean the hole.This test was a complete waste of rig time.Plug­ging due to cuttings and cavings left on bottomare the single largest cause of misruns.

Figure 16 shows a test where the plugging ac­tion is shown on both the flow stream and the

oblanked off charts. This indicates the pluggingis occurring above the flow stream gauge, andtherefore it is the tools that are plugging.

Figure 16

Figure 17

Figure 17 illustrates a problem that can oc­cur when long intervals are tested. The trip inthe hole indicates stops were made periodically toadd water cushion. The tester valve was opened at17-a with the gauges recording the back pressureof the water cushion. After an extremely shortinitial flow period, the tester valve was closedand the initial shut in pressure taken. Observ.ingthe initial C. I.P. at i7-b, it can be seen that asecond bui Idup is imposed on the early bui Idup.The tester valve was opened at 17-c for a secondflow. The portion of the second flow from 17-cto17-d indicates a rise in hydrostatic due to pro­duction into the dri I I pipe. At 17-d the watercushion surfaces and the decline in flowing pres­sure for the remainder of the period is caused bythe water cushion being produced from the pipeand being replaced by a lighter oi I. At 17-e thetester valve is closed for the final closed inpressure. Again at 17-f a second buildup is impos­ed on the early bui Idup. At 17-g the bypass isopened and the test terminated. The bui Idup on abui Idupis an indication that two distinct zonesof different permeabi I Ity and pressure are open

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in the tested interval. This makes it very dif­ficult to arrive at the individual reservoir pro­perties. To evaluate these zones, they should beisolated and tested separately.

Figure 18

Figure 18 indicates a test where there was agauge malfunction. The chart shows the initialflow and closed in periods. The test appears tohave terminated at 18-a. However, the secondflow was longer than shown and there was a finalclosed in pressure taken. The clock in the pres­sure gauge stopped at 18-a and the remainder ofthe flow and,the C. I .P. was recorded as a verticalI ine. The clock remained stopped unti I the vibra­tion of the gauge on the trip out of the holestarted the clock running again at 18-b and therest of the trip from the hole was recorded.

Figure 19

Figure 19 shows a test which has one fiow andclosed in pressure. However, the operator at­tempted to close the valve at 19-a for an initialclosed in pressure. The valve was not successful­ly operated and remained open. At 19-b the opera­tor thinking the valve was closed attempted toopen it for a second flow. Again the valve re­mained open. At 19-c the operator·successful Iyclosed the valve and a closed in pressure was re­corded.

Figure 20 represents an unsuccessful test.The tester valve was opened at 20-a and an ini­tial flow period recorded from 20-a to 20-b. Thevalve was closed at 20-b for an initial closed in

pressure. The tester valve was leaking and noC. I.P. was recorded. The valve was again openedat 20-c and a second flow taken from 20-c to 20-d.The tester valve was closed at 20-d for the finalC.I.P. Again the tester valve was leaking and thepressure bui Idup was not recorded. At 20-e thebypass was opened ending the test.

Figure 21 shows a Dri I I Stem Test where theformation was tested, then treated through testtools and retested to evaluate the treatment.This test was conducted in the North Sea throughful I opening tools. The tester valve was openedand after 25 minutes the water cushion flowed tothe surface 21-a. At the end of the flow periodthe rate had stabi I ized at 1500 MCF/D with a sur­face pressure of 136 PSI. The tester valve wasclosed and an initial C. I .P. reached 4048 PSI,21-c. The physical appearance of this bUildup (arelatively low flowing back pressure fol lowed by avery rapid short radius bui Idup 21-b is an indica­tion of wei I bore damage. The damage ratio forthis buildup was calculated to be 9.3. The test­er valve was reopened 21-d and the well stimulatedwith acid 21-e. The wei I was then opened for asecond flow and produced at a rate in excess of7200 MCF/D at a surface pressure of 180 PSI. Thisis an increase of 4.8 fold over the initial rate.The valve was closed and a final closed in pres­sure of 3975 PSI recorded 21-g. The appearance ofthe final C.I.P. 21-f differs in appearance fromthe initial closed in pressure. The final C. I.P.has a more gradual rate of closure indicatingI ittle wei I bore damage and a greater radius ofinvestigation.

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CONCLUSION

Modern equipment and techniques offer theversati I ity to test a wei I in the manner bestsuited for that particular wei I. The test can beconducted by or without pipe movement. The ful Iopening test tools permit the extreme flow neces­sary to evaluate prol ific wei Is, al lows the forma­tion to be perforated with the tools already inplace and pErmitsthe formation to be tested,treated and retested al I on one trip in the hole.

There is a need to have real time pressureinformation available at the surface during thetest. This can be accompl ished currently withwire I ine run through the test string to bottom.However, the objections to the wire I ine havebeen sufficient that very few people have beenwil I ing to test in this manner. Telemetry (whichhas received considerable attention but no work­able solution for testing) would be extremelybeneficial on Dri I I Stem Test.