AADE 01-NC-HO-24 - American Association of Drilling …24.pdf · casing failure. At the edges of...

AADE Houston ChapterMarch 2001 Conference

03/27/2001 1

Subsidence Remediation – Extending Well Life through the Use of SolidExpandable Casing Systems

AbstractLoss of wells and / or production due tosignificant casing damage caused byformation subsidence can be a costlyproblem, particularly in shallow high porosityreservoirs. Solid Expandable Tubular (SET)Cased-hole Liners (CHL) is one methodbeing utilized to overcome damage to casingdue to formation subsidence. Thetechniques developed for this remediationsolution could also be used to repair casingin a number of other environments.

Subsidence has been reported in manyfields throughout the world including theEkofisk field in the Norwegian sector of theNorth Sea, the northern Adriatic, theGroningen gas field in the Netherlands, LakeMaracaibo in Venezuela and in severalfields in both Long Beach and Bakersfield,California.1 Subsidence can have dramaticconsequences on production operations andeventually can completely shut down aproducing well.

Subsidence is expected within and above aproducing formation where the reservoirrock is weak and porous (Fig. 1). As thefluids are extracted from the reservoir therock is compacted, and in a shallowreservoir, this compaction can alter the over-

burden and may even be observed on thesurface (Fig. 2).

This paper discusses:

• Techniques developed to remediatewellbores that have been damaged dueto subsidence

• Wellbore preparation

• Installation procedure of a SolidExpandable Tubular Cased-hole LinerSystem

• Challenges solved while attempting toexpand the SET Cased-hole Linersdownhole once the wellbore wasprepared

• Final solutions customized to remediatethese subsidence challenges.

Introduction

The Lost Hills field consists of a massive (upto 1,000 ft thick), fairly soft, high porosity (upto 50%) diatomite in the shape of a plunginganticline (Fig. 1). This anticline is overlayedwith a series of sands, silts and shales.There is no surface indication of the anticlinein the Lost Hills field.

Production of oil and gas from this formationhas caused surface subsidence of the field

AADE 01-NC-HO-24Title: Subsidence Remediation – Extending Well Life Through the

Use of Solid Expandable Casing Systems

Company: Enventure Global Technology, LLC

Presenting Author: Gerry Cales/ Chevron USA, Inc.

Co-authors: David Shepherd , Brad Wiest/ Chevron USA, Inc.,

Pat York, Chan Daigle, Larry Rose / Enventure Global Technology, LLC;

and Mike Patterson / Jet Research Center


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of up to 20 feet in its center (Fig. 3). Thisprocess manifests itself as a bowl-shapedindentation dipping to the center of the field.Primary production is proportional toreservoir thickness; and as expected, water-flooding has greatly slowed, and in someareas arrested subsidence in Lost Hills.2

The mechanism that produced this "bowl"has caused two non-exclusive modes forcasing failure. At the edges of the bowl, theoverburden can slide on the soft claystoward the bowl center (Fig. 4a). This side-loading causes the casing to bend with theflow, thus creating a dogleg. Bending of thecasing can happen at various depths in thesame wellbore.

Near the center of the bowl (field), a differentproblem exists. The extensive compaction ofthe diatomite, over time, causes ashortening of the distance from the surfaceto the bottom of the well (Fig. 4b). Asexpected, the casing buckles, just as itwould if the same length of casing was runinto a shorter length hole.

The subsidence solution discussed here toremediate Lost Hills wells damaged bysubsidence, is an expandable cased-holeliner (CHL) system.

Although this remediation technique will notprevent further damage to the casing, it willlengthen the useful life and profitability of thewell. The refurbished wellbore is expected toproduce at least as long as the initialwellbore did and with sufficient waterfloodsupport, longer still.

Well Candidate SelectionThere were three wells selected for an initialpilot program at Lost Hills. Each wascapable of producing 35-40 bbls/day.However, the degree of wellbore damagecaused by subsidence had dictated that allthree wells be classified as “plug andabandon” candidates.

The wells selected for the pilot program willbe referred to as Well A, Well B and Well C.(Figure 5 depicts Wells A and C. Well B wasnot remediated.) The casing in Well A was7-inch 29 ppf, that in Well B was 7-inch 23ppf and the casing in Well C was 5-1/2 inch15.5 ppf. The dogleg had become so severe

in each of the wells that the effective insidediameter (ID) of the casing no longerallowed tubing and rods to operate in theboreholes. The three abandonment candi-dates would require replacement to recoverthe remaining reserves attributable to thatportion of the field.

Wellbore Preparation

The approach taken to remediate these LostHills candidates was to divide eachoperation into two phases. The first phaseentailed preparing the well for the CHLsystem — that is, opening the wellboreenough to run the system. The secondphase of the operation was to run and setthe expandable cased-hole liner.

Wellbore preparation is critical to thesuccess of using expandable CHL systemsto remediate subsidence-damaged wells.The casing immediately above and belowthe damaged wellbore section(s) must beround and within dimensional tolerance ofthe setting range for the CHL. Any debris inthe wellbore either must be removed and /or “ballooned out” through plasticdeformation. Therefore, damaged casingalso must be removed or "altered", and thewellbore properly cleaned using high-ratewellbore “sweeps", while circulating debrisand running wireline junk baskets.

For Phase One, wellbore preparation, twomethodologies were evaluated to removethe damaged wellbore casing and halt theencroaching formation so that CHL(s) couldbe installed.

Removal of Damaged Casing

The first wellbore preparation methodutilized a tri-blade mill developed specificallyfor the removal of subsidence damagedcasing. Once the casing was removed, a“lace" collar was run to ensure a straight,full-gauge hole. The second method ofremoving damaged casing employed theEngineered System for Casing Preparationwith Explosives (ESCaPE). This systemplastically deformed and explosivelyexpanded, or removed, the damaged casingand “pushed back” the subsided formationthat had encroached on the cased borehole.

Because this method was perceived to beuntried technology, the first two wells (Aand B), were prepared utilizing the tri-blade


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milling procedure. Well A was prepped, thenthe "best practices" learned during the tri-blade milling process on Well A wereapplied to preparing Well B. However,during milling operations on Well B, themilling assembly exited the milled sectionand the wellbore was lost.The ESCaPE system had been reserved forthe third well, Well C, whose wellbore hadbeen deemed beyond repair.

Subsidence Milling Solution

Severe doglegs created by the lateralshearing of layers in the formation andoverburden are extremely difficult to mill.This is due to the bending moment causedby lateral displacement of the mill as itattempts to follow the offset casing, creatinga cyclic loading that fatigues the metal veryquickly. Milling had to be conducted at aslow rate to avoid failures, resulting in a jobtime that was far too excessive to beeconomic.

Two different milling procedures wereattempted in Lost Hills - one using anarticulated reamer (Fig. 6) and the other witha tri-blade mill (Fig. 7a). The articulatedreamer comprised a tapered mill witharticulated collars hung below it to provideweight to pull the mill through the doglegwhile rotating, keeping the mill inside thecasing. The articulated reamer had beenused with moderate success on two wellswith mild doglegs (< 6 degrees) – however,milling time and resulting costs were toohigh to be economic.

Tri-blade theory and use. The tri-blademilling process proved to be the mostpromising (Fig. 7a). This mill is similar to asection mill with three blades that cut onboth the side and the bottom. Its overalllength is less than 6 feet, so lateral bendingis minimized. A 30-ft long stinger is runbelow the mill to ensure it remains inside thecasing as it cuts. Two "laced" collars (30 ftin length) [Fig. 7b] are then used to bring themilled section back to its original casingdiameter and to "smooth" the cuts madewith the tri-blade.

The tri-blade milling method also had beenused successfully in two wells but costswere high. The Tri-blade milled through thedogleg quickly while the "laced" collars weremuch slower - the primary cause for this was

thought to be the high wear on the Tri-bladeblades creating more work for the "laced"collars than their design could tolerate. Thetri-blade mill was successfully tested in 7-inch casing. The mill shifted the casing's fulldiameter within five feet, which is moresevere than the majority of well failures inLost Hills.

Engineered Explosive Solution

Explosives theory and use. The ESCaPEsystem utilizes specific engineeredexplosive material housed within a pliableflexible housing (Fig. 8). The system iscustomized by the type and length ofexplosive material used to create thespecific energy needed to either re-form orremove the casing damaged by formationsubsidence.

It was decided to use the ESCaPE systemto remove the damaged casing and to "pushback" the encroaching formation in the thirdLost Hills well, Well C.

There are several key criteria to consider indetermining the appropriate explosivesystem and charge design necessary toprovide the optimum impulse loading of thecasing steel:• cost• low debris• maximum assembly flexibility:

a) delivery system must be flexibleenough to pass through tightrestrictions and conform todeviations of the casing doglegs

b) wide variety of delivery housing ODsto adjust as necessary since true IDand deviation of dogleg is unknown

• maximum dogleg expansion – anexplosive that provides maximum plasticdeformation of steel and ensuressufficient re-sizing of casing in thedogleg

• minimize wireline assemby lengths.

Components of the explosive systeminclude:1. a range of flexible nylon/rubber hoses to

provide containment and durability todeliver explosive to target area

2. special blend of liquid explosive formaximum burn rate and detonationpressures to achieve maximum impulse-loading for given OD


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3. high output booster/initiation assemblyto maximize full yield of explosive

4. aluminum bull plug with special seal tocontain non-viscous explosive material

5. aluminum fill-neck to facilitate pouringliquid explosive at wellsite.

Casing removal process. In Well C, thecharge was run in on electric wireline, usingthe wireline depth meter and weightindicator to position the charge. Once inposition, an electrical impulse was used todetonate the charge.The first wireline run with the charge was notsuccessful. Several key lessons werelearned:• Initially the well was filled with water, as

the charge was designed to besuspended in well fluid. Although thewater tanker was pulled back to a safedistance, the well was taking fluid morerapidly than expected, causing thecharge to be unsupported in the wellwhile being filled. The additional weighton the bull plug seal may also havecaused a leakage of explosive liquidthrough the seals.

• With no “feel” for the weight of theassembly being run, the wireline speedwas too fast, which was thought to havecaused fluid loss through the top of thefiller tube. Being flexible, the assemblywould collapse when “set down” andfluid would flow from the top of the fillerneck.

• Fluid loss caused an unsuccessful initialdetonation.

Lessons learned. The followingmodifications were made in the runningprocedures during the second wireline run,and proved successful.

• A continuous water flow ensured thewell was kept full of fluid

• Lowering of the charge was kept under50 ft/min, "yo-yoing" was eliminated

• A special vented plug was used in thefiller-tube assembly to ensure noexplosive fluid was lost. Bull plug wasmodified to improve the bottom seal.

Remediation - Bridging DamagedCasingOnce the casing has been removed or “bal-looned” and the subsided formations either

removed or “impenged” (pushed back), theexpandable casing was positioned in theprepared wellbore and expanded across thedamaged casing, sealing it against the ID ofthe undamaged cased wellbore (Fig. 9).

Installing the CHLFigure 10 illustrates the steps required toinstall an expandable cased-hole linersystem. First the CHL launcher is run andthe system hung off in the slips. (The CHLlauncher contains the expansion cone andmandrel, as well as the casing that is to beexpanded.) The workstring is then run insidethe expandable CHL system and latchedonto the top of the expansion cone. Next,the entire assembly is run into the wellbore,supported by the workstring.

The CHL system is then positioned acrossthe prepared area of the wellbore damagedby subsidence. The surface pumping unitincreases hydraulic pressure down theworkstring, through the expansion cone andinto the pressure chamber area. When thepressure inside the pressure chamber(across the expansion-cone / expandable-casing interface) reaches the requiredmechanical force, the casing begins toextrude over the expansion cone.

Note: The mechanism that extrudes theexpandable casing downhole can becompared to that of tearing off the end of apaper-wrapping around a soda straw andthen blowing the paper off the straw…thepaper is being "extruded" off the straw asthe pipe is extruded over the expansioncone downhole.

The expandable casing moves over theexpansion cone and down the well until itexpands the first elastomer sealing element(about 1 foot). Once the sealing element iscompressed between the expandable casingand wellbore casing, a seal is made and theCHL is hydraulically and mechanicallysealed to the wellbore casing wall.3

When the expansion process nears the topof the CHL, another set of elastomer sealsare encountered and an additional hydraulicand mechanical seal is formed, cladding thetwo tubulars together. The elastomer servesa dual purpose. First, it fills the voidscaused by ovality problems or workstring


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wear. Secondly, the elastomer improves themechanical and hydraulic integrity of thedamaged casing. Typically, this seal forms amechanical connection with a pulloutstrength of 500,000 ppf of cladded pipe.

The CHL forms a “sealed bridge” across thedamaged area with expandable casing thathas physical properties similar to those ofL80 grade conventional casing. Becausethe ID of the remediated casing is onlyreduced by about two times the thickness ofthe expanded casing and the compressedelastomer (typically 0.125 in.), there isminimal inside diameter restriction throughthe remediated area. Also, since the repairhas been made using casing withmechanical properties similar to those ofconventional casing, the area of expandedcasing enhancement and below can be“worked through” without fear of damagingthe expanded casing.4

Lessons Learned During EngineeredExplosive Solutions• Each subsidence well presents unique

characteristics, and therefore requiresspecial adaptations based on thespecific well conditions observed.

• The explosive assemblies must becapable of being adjusted “on the spot”,be provided in a variety of lengths,outside diameters and explosive“loadings ” for various casing sizes.

• Ideally, using a minimum explosiveimpulse loading to achieve plasticdeformation that yields no separation inthe casing, more reliably ensures theworkstring remains inside the wellbore.

• Some well deformations may requiremore than one charge or type of chargeto remedy the dogleg severity.

Challenges Solved During ExpansionOperationsWhen casing was removed or extensivelyplastically-deformed, such as is done duringthe well preparation for subsidenceremediation, certain operational precautionsmust become part of the operationalprocesses.

One of these precautions necessitatedprotection of the expandable CHL in a wellwith potential protrusions or sharp edges, or

possibly in a well that requires significantmilling. If the casing is damaged while beingrun in-the-hole or during expansion, thepotential of splitting the casing duringexpansion exists. Protection could either beprovided in the form of "standoff" of theexpandable casing while running it in thewell, or of a protective coating placed on theOD of the expandable CHL.

In Well A, for instance, once the damagedcasing was milled out, a casing centralizerarm was partially exposed, protruding intothe wellbore. When the CHL was run in, thesharp end of the tempered steel centralizerarm severely damaged the expandablecasing connection. This reduced theexpansion pressure, halting the expansionprocess.

The casing was then cut just below thetransition face, above the damaged basecasing. The unexpanded casing and theexpansion face were removed from the well.After retrieving the upper portion of thecasing, the expansion cone was retrieved,allowing repair of the well to proceed. Thesecond CHL system was then run in andplaced on the top of the first CHL (Fig. 11).

Another enhancement to the CHL system isthe use of a standard float shoe (Fig. 12) onthe bottom of the launcher. The float shoeallows circulation and / or annular controlthrough the CHL while running in the holeand before removal of the debris and“flowing formation" from the backside of theliner, prior to expansion. When running thesecond cased-hole liner in Well B, thisaforementioned system enhancement wouldhave allowed the removal of a bridgecreated by the diatomite formation flowinginto the wellbore from the opening where thecasing had been removed. This formationbridge, formed between the CHL andwellbore casing, presented problems duringexpansion of the second system (Fig. 13a).

The unexpanded casing and the expansionface were removed from the well (Fig. 13b).Then both the upper section of the casingand the expansion assembly were retrieved,freeing the wellbore so the repair could befinished.


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The repair was completed with a third,specially-designed CHL that incorporated a6-in. diameter "mule shoe" extension belowthe CHL (Fig. 14). Once this "special" CHLwas installed, the mule shoe was insertedinto the second CHL installation, and the"special" CHL was expanded, bridgingacross the subsided area of the wellborethat had been removed. Figure 15 depictsthe CHL installation originally planned forWell A.

Results of the OperationsWell A was remediated using theexpandable cased-hole liner and put backon line. It is currently producing at the samelevel that it did before subsidence causedthe well to fail.

Well B was lost due to the mill exitingthrough the window that had been cut toremediate the well.

During the CHL installation in Well C, theliner was initially anchored below the casing“pushed back” with the ESCaPE explosive.However, the base casing was damaged /altered sufficiently so that the expandableliner did not hold and the liner was pulled upthe hole and set off-depth. The topelastomer seals on the CHL in Well C weremilled off and the system was “pushed”approximately 8 feet down the wellbore.However, about a 12-foot "gap" still remainsbetween the bottom of the expanded CHLand the top of the 5-1/2” base casing. Theremay be further attempts to push the CHLdown the wellbore in order to reconnect theCHL to the base casing below the removedcasing.

ConclusionsSuccessful implementation of SET Cased-hole Liner Systems can extend the life ofLost Hills wells. Economic production fromthe Lost Hills field depends upon very largehydraulic fractures (1.3 MM pounds), whichalso contribute to over half the cost of thewells. Repair of the wellbore allowscontinued access to this thin fracture

system. Many of the wells that fail in LostHills due to subsidence leave significantreserves undepleted. The current practice isto replace the failed wells.

The Engineered Explosive Assemblyappears to be a viable, more economicmethod of clearing a path through thedogleg for installation of a SET system. Theuse of mills, while successful, is slow andtherefore costly, calling into question theeconomics of well repair.

References1. "SINTEF project sheds light on

mechanics of reservoir subsidence",Offshore, April 2000, pp. 187-188.

2. Morris, C.W. and Mitzel, D.P,Schlumberger Wireline & Testing;Gwinn, R.L., Aera Energy; Rambow,F.H.K., Shell E&P Technology,"Ultrasonic measurements monitorcasing offset damage", World Oil, July1999.

3. Daigle, C., et al, "Expandable Tubulars:Field Examples of Application in WellConstruction and Remediation", SPE62958 at 2000 SPE Annual TechnicalConference, Dallas, 2-4 October.

4. Mack, R., Shell E&P Technology;McCoy, T., Halliburton Energy Services;Ring, L., Enventure Global Technology;"How in-situ expansion affects casingand tubing properties", World Oil, July1999,pp.69-71.

5. Addis, M.A., Choi, X and Gunning, J.(1998) "The influence of the reservoirstress-depletion response on the lifetimeconsiderations of well completiondesign", Eurock '98, Vol. 1, ProceedingsSPE/ISRM, Rock Mechanics inPetroleum Engineering, pp. 443-441.

6. Germanovich, L. N., Chanpura, R.A.and Ring, L.M., (1999) "Fault Slip andSeismicity Induced by Subsurface FluidWithdrawal", Proceedings of the 37th

U.S. Rock Mechanics Symposium, B.Amadei, et al (eds), Balkema,Rotterdam,pp.1145-1154.


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Figures:

Figure 1 - Lost Hills field Belridge diatomite structure

Figure 2 - Photo showing the results on the surface of compactionas fluids are extracted.


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.

Figure 3 - Diagrams of Lost Hills field illustrate: (left) production from the formation hascaused surface subsidence in the center up to 20 ft and (right) the variety of casingdamage caused by subsidence throughout the field

Figure 4a - Subsidence evidenced in well Figure 4b - Extensive compaction neardamage due to side-loading of casing "bowl" center causes shortening of the

distance from surface to bottom of thewell, buckling the pipe


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Figure 5 - Wellbore schematics of Well A and Well C

Figure 6 - Articulated reamer Figure 7a - Tri-blade mill Figure 7b - "Lace" collars


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Figure 8 - The ESCaPE system is pictured at far right. One of the key components is thepliable flexible housing, shown onsite.


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Figure 9 - Schematic of 5-1/2" X 7"Expandable Cased-Hole Liner System


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Figure 10 - Installation sequence for Expandable Cased-hole Liner System


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Figure 11 - Second CHL installation in Well A


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Figure 12 - Expandable CHLsystem using standard float shoe


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Figure 13a – Diatomite formation flow Figure 13b - Unexpanded casing andshown in Well A schematic expansion face removed from Well A


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Figure 14 - Customized CHL with mule Figure 15 - Originally planned CHLshoe installed in Well A installation for Well A

This paper was prepared for presentation at the 2001 National AADE Technical Conference heldat the Omni Hotel, Katy Freeway, Houston, Texas, March 27-29, 2001. The informationpresented in this paper does not reflect any position, claim, or endorsement made or implied bythe American Association of Drilling Engineers, their officers or members. Questions concerningthe content of this paper should be directed to the individuals listed as author/s of this work.

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