US3163218A - Method of consolidating a formation using a heater within a liner which is thereafter destroyed - Google Patents

Description

Dec. 29, 1964 T. o. ALLEN ETAL 3,163,218

METHOD OF' CONSOLIDATING A FORMATION USING A HEATER WITHIN A LINER WHICH IS THEREAFTER DESTROYED Filed March 14, 1960 4 Sheets-Sheet l la t: le I6 FIG.3

Thomas O. Allen John E. Ortloff Bertram T. Willman Inventors BY -ma...) t. Qui. Alorney Dec. 29, 1964 T. o. ALLEN ETAL.

METHOD OF CONSOLIDATING A FORMATION USING A HEATER WITHIN A LINER WHICH IS THEREAFTER DESTROYED 195o 4 Sheets-Sheet 2 Filed March 14.

FIG. 5

FIG. 4

Thomas O. Allen John E. Ortloff Bertram T. Willman Y Invenors` By e. (2....),

Attorney Dec. 29, 1964 T. o. ALLEN ETAL 3,163,218

`METHOD 0F CONSOLIDATING A FORMATION USING A HEATER WITHIN A LINER WHICH IS THEREAFTER DESTROYED Filed March 14. 1960 4 Sheets-Sheet 5 FIG.6

Thomas O. Allen John E. Orloff Bertram 'I'. Willman Inventors By 5 AOTney Dec. 29, 1964 T. o. ALLEN ETAL 3,163,218

METHOD OF cONsOLIOATINO A FORMATION usING A HEATER WITHIN A LINER wHIcH Is THEREAFTER OESIROYEO Filed March 14, 1960 4 Sheets-Sheet 4 FIG.7

Thomas O. Allen John E. Ortloff Bertram T. Willman ,Invenors By MH...) E. QLML Attorney oil in contact therewith.

nited States Patent O 3 163 218 Martino or coNsrLrnArrNG A Foniviarrcrl USING A HEATER WlTI-HN A LINER WHCH iS THEREAFER DESROYED f rhornas Allen and .lohn E. Grtlo, Tulsa, kla., and Bertram 'I'. Wilman, Union, NJ., assignors to Jersey Production Research Company, a corporation of Delaware Filed Mar. 14, 1960, Ser. No. 14,905 4 Claims. (Ci. 1661-25) The present invention relates to methods for consolidating subsurface reservoirs in the vicinity of oil wells, gas wells and similar boreholes and more particularly relates to an improved thermal consolidation process wherein heat is applied to a reservoir in order to coke ln stillV greater particularity, the invention relates to a thermal consolidation process wherein an expendable liner is positioned in the wellbore, heat is applied to the reservoir through the liner, and the liner is thereafter at least partially destroyed in order to restore communication with the reservoir.

Many subsurface oil and gas reservoirs are located in formations made up of unconsolidated or loosely consolidated sand particles. When a Well drilled into such a reservoir is placed on production, the uids entering the wellbore carry entrained sand particles with them. These particles vtend to settle in the wellbore and clog it, necessitating workover operations at frequent intervals. Particles which do not settle in the wellbore and instead are entrained in fluids pumped to the surface cause excessive wear and erosion of pumps, tubing and other apparatus. Erosion of sand from the formation by the producing fluids may lead to undermining about the wellbore and cause the subsidence of overlying strata. When this occurs, the tubing or casing may be bent or, in some cases, completely collapsed. This sometimes necessitates abandonment of the well, or makes it necessary to perform an expensive sidetracking and redrilling operation. Subsidence of the overlying strata may permit the entry of foreign uids into the producing reservoir or, particularly in the case of gas wells, permit substantial quantities ofthe reservoir iiuid to escape int higher reservoirs outsidefthe .producing zone.

A Vnumber of methods designed to prevent the inux of sand particles into wells completed in unconsolidated reservoirs and thus alleviate the difculties outlined above have been suggested in recent years. A particularly attractive method involves heating the-unconsolidated zone.

about the wellbore to temperatures -suiicientto coke oil in thev formation and cement the particles together. Experimental work and field test have shown that this method can result in a highlyV permeable, well-consolidated area about the wellbore. There are certain problemsV which must be overcome, however. The presence of gate into light ends which are carriedupwardly bythe convection currents and 'heavy' components which settle about the heating unit.V 'Ihe heavy constituents of theoil generallycoke'rnuch more rapidly than do'the lighter materials and hence a thick layer of coke tends to form about the heater near the base of the producing zone.

This may cause the heaterto become `stuck inthe wellbore.

thermal consolidation process which circumvents the difflculties set forth above. In accordance with the invention, it has now been found that the use of an expend- The present inventionproviders a new and improved "ice,

able liner in the wellbore opposite the zone to be con-`V solidated permits the application of heat to the' reservoir from within the liner without the establishment of convection currents in the wellbore and without dangerl ofV cementing the heater in place. The heat applied `to the. reservoir can be controlled to better advantage so that in most cases the time required for coking is greatly reduced. The use of'a liner which can at least in part be destroyed by chemical, thermal or other methods after coking has been completed, without injuring the consolidated structure, permits uids to be produced from the formation without` diiiiculty.

The liner employed in carrying out the process of the invention may be constructed of a variety of different metals having melting points in excess of the coking temperature. Metals which can readily be destroyed by treatment with chemical Vagents without damaging the consolidated formation surrounding the wellbore are generally preferred. Representative examples of such metals and chemical treating agents which rapidly attack them are shown in the following table.

Metal Chemical Agent Aluminum 1 N Sodium Hydroxide.

35% Hydrochloric Acid.

% Propionic Acid.

Mixed 50% Suliurie Nitric Acid.

15% Nitric Acid.

15% Hydrochloric Acid.

15% Sulfuric Acid.

55% Nitric Acid.

55% Nitric Acid.

15% Ammonium Hydroxide.

55% Nitric Acid.

40% Hydrochloric Acid.

15% Ammonium Hydroxide.

25% Phosphoric Acid.

Acid-50% Magnesium 25% Nickel-75% Iron Alloy Copper Brass Nickel Bronze 1t will be understood that the above metals and chemical agents are merely representative and that other metals, other agents and other concentrations may be e ployed in carrying out the invention.

In addition to metals which are subject to chemical attack, metals that melt at temperatures slightly higher than the coking temperature may be utilized for carrying out theV process of the invention., By rapidly increasing the wellbore temperature following completion of the coking operation, the -metallicliner can be meltedtoV complete the well. Suitable metals and their 'melting points include the following.

. Crudeoils can readily be coked at temperatures be- `tween about 600 F. and about 1500 F. The optimumYV coking temperature will depend somewhat upon the com?, position of the oil and the pressure conditions in the borehole. As indicated by the `above table,Y a variety; of metals andrmetal alloys melting at temperatures between about 1000 F. and about 1650 F.'areY available andfrnay be utilized in the practice of the invention. .The particular metal employed will, of course, dependupon the -coking A temperature utilized.'

The coniiguration of the liner used in carrying out the process of the invention will depend in part upon the metal employed and in part `upon the method, chemical or thermal, to be used to render the liner permeable v'following the coking operation. Because many metals other wise particularly suitable for purposes of the invention lose much of'their strength at temperatures in the coking range, it is generally preferred to'employ an inner perwith` an outer layer o r sheath of the metal to be chemically or thermally removed. In other cases, a liner containing one or more plugs lor sections of metal which may be removed by chemical or thermal means will beV preferred. In still other instances, however, ahornogeneous liner may be used. Q

In carrying out the process of the invention, a liner which can be totally or in part removed by chemical or thermal means is rst lowered into the wellbore opposite the unconsolidated formation. The wellbore may contain casing vwhich has been perforated opposite an unconsolidated producing zone or instead may be open opposite the unconsolidated zone.Y In a wellbore of the rst type, the liner will normally bev suspended at the lower end of a string of producing tubing and a heatresistant packer willV be'placed between the casing and 'tubing above the liner. YIn a wellbore open opposite the unconsolidated formation, the liner may be connected to and supported by the lower .end of the casing.` After the'liner has been set in place,f-a borehole heater of the."

chemical, electrical or combustiontype is lowered into ,the liner. Heat is then applied to thek reservoir through the linerY wall.` The lighterlconstituentsof `theoil sur.-

rounding the linerare vaporized by theheat and'for'cedY into the formation.V` The heaviercomponents which remain in the formation in the area adjacent the liner are converted into coke. The coking which thus occurs con- Y solidates the formation. 1After coking has been com-Y Y pleted, theliner is at least in part destroyed by Vrapidly increasing the wellbore temperature or by removing the heater and introducing a chemical agentinto theA liner.V

FIG. represents in vertical section a wellbore open opposite an unconsolidated producing zone wherein an Y expendable liner has been connected to the lower end .-forated liner of alloy steel or ceramic material provided Y l Y Yof the casing and cemented in place;

FIG. 2V is a vertical section through the wellbore of FIG. l after the cementing plugs have been removed and. the heater has been suspended inside the liner to start Vthe coking operation;

FIG. 3 depicts in verticalV section the wellbore shown in FIGS. 1 and 2 aftercoking has been completed and4 Y the liner has been destroyed.

forated Ywellbore containing an expendable liner and Y FIG. 4 is a vertical section through a cased and -perheater useful in the practice of the invention;

FIG. 5 is a partialview of the wellbore of FIG. 4 showing'an alternate method for closing olic the lower end of the liner employed in the Vpractice of the invention;

' FIG. 6 illustrates in vertical section a wellbore con?- taining a slottedliner ittedwith an yexpendable outer sleeve; and,

FIG. 7 is a vertical section through a wellbore containing la slotted liner provided with plugs of a lower` melting point metal more susceptible to attack by chendv cal agents than the base metal ofthe liner.

Turning now to FIG.,1, reference numeral 11 designates a wellbore drilled into an unconsolidated oil-pro'- ducing reservoirV beneath the earths surface. has been installed in the upper part of theA wellbore above unconsolidated zone 13. Collar 14,'attached to the lower end of theY casing before it is lowered into place, supports cementing plug 15 of brass, aluminum orY other drillable material and cementing basket 16 carried on the Voutside of the casing.V A cement basket of the type suitable for this purpose is shown on p. 2212 ofthe l 958-59`.CompositeV Catalog and can be furnished by Halliburton Oil Well Cementing; Company, Duncan, Oklahoma. Ports` If heat is used to meltthe liner,1the molten metal'will ilow` into the bottom of the wellbore and solidify after the heater has been removed.V Where a slotted 'liner containing fusible plugs is employed, Va gas or other fluid can often be injected into the Wellin Yorder to force the .metal out into the .formation after it has softened. If a Vchemical agent is usedfto dissolve at least part of the liner, it` may be pumped down the well casingor tubingv for instead maybe injected'Y through a corrosion-resistant hose or string` of. tubin'glow'ered intoY the.A lwell lforY that purpose. Many acids and bases Ysuitablejfor use inthe practicefof the invention have little or-norelect`upon alloy steel Well tubing and casing and do not require that particularV precautions be taken; It is frequently .advis-y able, however.. to inject a neutralizing'agent after/.the` liner has beenldissolved'in order to prevent corrosion of the well maycomeinto contact. Y i The process Vof. the invention is Yparticularly useful as a means for completing *wellsY Y drilled intof unconsolidated equipment' witlrwhich the initialfluids producedfrom oil-producing reservoirsbutmayalso beiutilized mires- Vshaped torincrea'se its'fresistance 'to external pressure. In Vlieu of a continuous linerhaving a rounded` bottom` as` shown in FIG.1,'a liner consisting of ametallic sleeve *i Vfitted with a suitable capk or` plug at its lower endjmay be utilized. The collar 14 may be an integral part of the ervoirs which contain little or no' oil'. YIt is sometimes de-Y 17 above the cementing'plug extend through thecasing wall to Vpermit the. passage of cement into the annular space between the casing and borehole wall above the basket. .Upper plug 18Y has been provided above the cement 19 within the casing to facilitate pumping of the cement downwardlytherein.` A plug of this type is also readily available from the Halliburton Oil Well Cementing Company in Duncan, Ok1homa, and is shown on page 2211 of the 1958-19'59 Composite catalog. As

shown'in FIG. 1, the cement has'beencirculated down` thezcasing and up the annular space and has been allowed to set.V Y l f Y Liner 20 of brass or a smilarmetalwhichcan be fused at temperatures somewhat above the'cokingY tem` per'ature'or dissolved with an acidicfor basic reagent is attached to the lower endf; of collar 14 below cementing plug 15. The liner `n1ayibe corrugated or otherwise liner if desired.

. After thecasing and liner 20 have been installed in the j wellbore as discussed in the preceding paragraph," the cementingplugs 15 and 18 and the ement remaining; therebetween are drilledr out inthe conventional manner. Anelectrical heaterV 21 supported by an varmoured cable 22 or other suitable heating-device is the'nlowered"into-V the liner as shown in FIG'. 2 of the drawing. Ihe'heater isturned onand heat is transmitted to the formation by conduct /ion' and radiation. Thermocouples, not shown, maybe installed on Hthe innerwallof thevline'r for pur- `poses of temperature control, if .i desired. Heat reaching oil in the wellbore outside the -liner and in the surround-` ing formation results in vaporization'of Vthe lighter con#` Vstituents ,of the toil. V'I he vaporized materials are forced finto the formation, leaving the heavier'components of the oil behind. These` areY convertedl'intocokeV 23'which Casing 12 'v animate` serves to bond together the particles making up the formation. The liner and the cement between the casing and formation wall prevent excessive heat losses, gravity segregation and other difliculties which might otherwise arise in the coking process. The time required for the formation of sufficient coke to consolidate the unconsolidated zone will depend largely upon the characteristics of Ithe oil in the reservoir and the coking temperature utilized. The coking rate under a particular set of conditions can readily be determined in advance by coking samples of the oil at the surface underV simulated wellbore conditions.

Upon completion of the 'coking operation as described above, the liner shown in FIGURES l and 2 is at least in pant destroyed by treating it With nitric acid or a similar reagent. A tube of Teon or other corrosion-resistant material may be inserted in the wellbore to convey the acid or other reagent into the lining in the event that a reagent highly corrosive to steel casing is used. The elevated temperature of the linerl following the coking operation accelerates reaction between the liner metal and the reagent and results in rapid destruction of the liner.

Tests have shown that petroleum coke formed in the wellbore in the manner described herein is relatively inert with respect to acids and bases and that permeability is not. appreciably alected during the destruction of the liner. A neutralizing reagent can be pumped down the wellbore after the liner has been destroyed in order to counteract any reagent which may have contacted the casing or may remain in the bottom of the well. 'I'he wellbore following destruction of the liner is shown in FIG. 3 of the drawing.

Reference is now made to FIG. 4 of the drawing which depicts a cased'and perforated .wellbore containing an expendable liner and an electrical-heater useful in the practice of the invention. Casing 26 extends below the unconsolidated producing zone 27 `and has been cemented in place in the conventionalmanner, the cement being designated by reference numeral 28. Perforations 29 penetrate the casingrandjcement opposite thev producing zone. In the practice of the invention'in such a wellbore, an expendable liner 30 of aluminum or a similar metal is lowered into the wellbore and held in place opposite the producing zone by means-of a conventional packer or other anchoring Vdevice 31. A typical liner hanger and packer assemblypis shown on page 4848 of the 1958-59 Composite Catalog and is available from the Texas Iron Works, Inc., of Houston, Texas. If a packer" is employed, it will preferably beconstructed of asbestos or otherheat resistant material. A conventional packer of rubber or the like positioned a suicient distance above the perforated section of thecasing to avoid damage due to high temperatures may be used in some cases, however. After the liner has been installed, and the hole bailed substantially dry, electrical heater 32 is lowered into'place opposite the unconsolidated formation and is used to coke oil present therein. Following they coking operation, the heater may be withdrawn and the liner iilled with a 'chemical agent to effect its destruction. The chemical agent can be spotted inthe liner by using a string of tubing extending from the bottom of the liner to the surface. The wellbore and tubing above the chemical agent can be lilled with oil or saltwater to maintain pressure control when communication between the formation and the wellbore is restored. Y

FIG. 5 of the drawing is a partial view of the wellbore of FIG. 4 showing an alternate method for closing olf the lower end of the liner employed in accordance with the invention. As indicated therein, the liner 30 may be simply a cylinder of suitablemetal open at the lower end. Cement 33 may be placed'in the bottom of the wellbore about the end of the liner in order to close it. The use of cement as shown anchors the liner and prevents it from moving upwardly in the borehole when the fluid level therein is reduced by swabbing,

. In4 FIG. 6 of the drawing is shown a liner assembly consisting of an inner slotted liner 34 of alloy steel, ceramic material or the like which is resistant to heat and chemical attack and an outer sleeve 35 of aluminum or a light metal whichcan be destroyed by chemical or thermal means. Thel slotted liner supports the outer sleeve against the formation pressure and thus permits the use of metals in the sleeve which would otherwise be unsuitable because of their low strength at elevated temperatures. The width of the slots in the inner liner will depend somewhatupon the particular metal employed in the sleeve. In general, slotsfrom about to about 1/2 inchin width will be satisfactory. .If the outer sleeve and the slotted liner are made of metals having similar coefficients of thermal expansion, they may be welded to one another as shown in the` drawing. In other cases, suitable collars and asbestos packing may be used to connect the two and accommodate different rates of thermal expansion.

Casing 36 has been set and cemented in place in the wellbore shown in FIG. 6 of the drawing. The cement is designated by reference numeral 377. Perforations 38 have been made opposite the unconsolidated formation` The liner assembly is connected to production tubing 39 by collar '4Q and is suspended adjacent the perforations. Packer 41 of asbestos or other heat-resistant material is positioned between the production tubing and casing above the liner assembly. The packer is not always essential, however, andin some cases can be dispensed with, particularly where the annular section of the wellbore is filled with gas and maintained under suliicient pressure to prevent the intlux of fluids from the reservoir.

Heater .42 is lowered through production tubing 39 into the liner assembly shown in FIG. 6 in order to consolidate the formation. Upon completion of the coking operation, thel outer sleeve of the assembly can be dissolved chemically'in the manner described heretofore, or it can be melted by raising the temperature above the melting point of the material in the outer sleeve. The inner liner of the assembly remains in the'borehole after the outer Vsleeve has been at least partially destroyed and, particularly in the case of the wells which are not cased opposite the producing zone, affords added protection against the influx of solids into the tubing with the producing uids should the consolidated zones about the wellbore` subsequently fail,

FIG. 4 of the drawingillustrates a further method of carrying out the processV of the invention wherein a liner containing plugs ofa `fusible or soluble metal is used. As shown in FIG. 7, liner 43 of steel or other high melting, corrosion-resistant material contains slots or openings iilled with plugs 44 of aluminum, magnesium, copper or other material which can be readily melted or dissolved with acid or a caustic solution. A convenient method of fabricating the liner is to drill holes in a steel pipe and plug them with rivets of aluminum or the like. A cap can be welded or threaded onto the lower end of the pipe. The liner is supported in the wellbore by a packer or similar anchoring means 45 which engages casing 46 above the unconsolidated producing zone. The cement behind the casing is designated by reference numeral 47. Heater 48gat the end of cable 49 is lowered into the liner in order to coke the formation and may be thereafter utilized to melt plugs 44 in the liner. An acid or base may instead beemployed to dissolve the plugs.

The invention is further illustrated by the results of tests carried outlto determine the electiveness of the process. In the first test, an 18 API gravity Bayou Choctaw crude oil was coked in unconsolidated sand packed around a 7-inch perforated cemented casing Vlor was filled withcrudeoil and then blocked olf above the perforations. An electrical heater 3 inches in diamter and 10.8 feet long was positionedinside the liner'opposite the perforations and energized. A period of about 41/2 hours was required to Vvaporizethe oil in the annular space and drive itthrough the perforations into the sand.

During this period the heater temperature, as Yindicated by thermocouples attached to its outer surface', gradually increased to about 15920" F. The power to theV heater was thereafter decreased at intervals to maintain Va constant temperature. Heating was continued for 24 Vhours formed.` It is therefore apparent that the processkof the invention providesan effective means for 'overcoming the diiculties encountered with unconsolidated sands in the n What is claimed is:` Y u 1. A process for consolidating an unconsolidated subterranean formation surrounding a borehole which com-- prises installing an impermeable liner in said `boreholej after the oil in the wellbore had been vaporized. The f heater was then turned off and the borehole was allowed to'cool forseveral hours.

' The heater, liner and cemented'casingwere raised from the borehole and examined; The sand surrounding the cemented liner had been coked for an average distance of about 11/2 inches away from the liner. Next tothe liner it was well consolidated. The coked sand was found to have an average permeability to oil of about 10,154-millidarcies and an averageperrneability to air of-about 16,123 millidarcies. the coked sand showed an average strengthiof about 456 pounds per square inch. f Y

, After the above test had Vdemonstrated that the use of an electrical heater inside a liner is an eiectivemeans `for coking oil in an unconsolidated formation, tests Were carried out to determine .the effectiveness of concentrated nitric acid for dissolving plugs of copper and brass 5/6 inch in diameter set in holes inV Vthe wall of steel tubing. The tubingv containing the plugs Vwasheated at 1200 F. for 24 hours and thereafter filled with the acid. It was found that the acid ate its wayV through the brass in about Y 20 minutes, while about 25 minutes was required to dissolve the copper. v

The effect of acids and bases on coke formed by heat- Measure of the compressive Ystrength of` to prevent uid communication between the borehole andV said unconsolidated formation, said'lin'er being `atleast tween saidbrehole and'sa'id formation.

, 2.V A process forrconsolidating an unconsolidated sub1 terranean4 formation surrounding a borehole which cornprises installing an impermeable -liner in said ,borehole Y to preventrtiuid communication between the borehole and n l-said unconsolidated formation, said liner being at leastj Y in part readily soluble in a selectedV chemical reagent; low`.

y ering a Wel'lboreheater `into said liner adjacent said'ft'n`r` mation; heating Voilirr said formation bymeans of saidV heater until sicient'coke to consolidate' said formation in the immediate vicinity said borehole has been"l formed; and thereafter introducing said selected chernit'tal'4 f i. reagent into said borehole. in contact with said liner to at ing crude oil inthe presence of unconsolidated sand wasY tested by soaking samples of the coke in 28%'Y hydroi chloric acid, concentrated sodium hydroxide and concentrated nitric acid for periods ranging from 23 days to 35 days. Neither the acids nor the caustic had any percep- Vtible effect `upon the coke. v

Therdata obtainedin the above-described' tests clearly demonstrate that unconsolidated sands surrounding a wellbore can kbe consolidated by utilizing a heater inside a liner within the Wellbore to coke'oil Vin contact with the sands, that chemical reagents canbe employedto dissolve copper and similar inserts in liners,VV 'and that the use of suchreagents doesY not adversely affect the coke thus least partially dissolve said liner and thereby restore fluid communication between said borehole and said formation.

3. A process as defined by claim 2 wherein said chemical reagentV is an acid.

4. A process as defined by Vclaim 2 wherein said chemical reagent is a base. Y

References Cited Yin thele of thisl patent Y Y UNITED STATES PATENTS v 2,335,578 Carter Nov. 30,: 1943 V2,491,035 Akeyson et al. May 28, 19.7463k Y 2,685,930 Aibaugh ...f f Aug. 10, 1954 2,906,340Y Herzog Sept. 29, :11959 2,914,309 sa10m0nSSqn- Nov. 24, 1959; Y 3,003,555 Y Freeman e V oet. 10, 1961V 3,072,188V Y

Claims (2)

1. A PROCESS FOR CONSOLIDATING AN UNCONSOLIDATED SUBTERRANEAN FORMATION SURROUNDING A BOREHOLE WHICH COMPRISES INSTALLING AN IMPERMEABLE LINER IN SAID BOREHOLE TO PREVENT FLUID COMMUNICATION BETWEEN THE BOREHOLD AND SAID UNCONSOLIDATED FORMATION, SAID LINER BEING AT LEAST IN PART READILY FUSIBLE AT A TEMPERATURE IN EXCESS OF A PREDETERMINED COKING TEMPERATURE; LOWERING A WELLBORE HEATER INTO SAID LINER ADJACENT SAID FORMATION; HEATING OIL IN SAID FORMATION TO SAID COKING TEMPERATURE BY MEANS OF SAID HEATER UNTIL SUFFICIENT COKE TO CONSOLIDATE SAID FORMATION IN THE IMMEDIATE VICINITY OF SAID BOREHOLE HAS BEEN FORMED; AND THEREAFTER INCREASING THE TEMPERATURE IN SAID BOREHOLE BY MEANS OF SAID HEATER TO AT LEAST PARTIALLY FUSE SAID LINER AND THEREBY RESTORE FLUID COMMUNICATION BETWEEN SAID BOREHOLE AND SAID FORMATION.

2. A PROCESS FOR CONSOLIDATING AN UNCONSOLIDATED SUBTERRANEAN FORMATION SURROUNDING A BOREHOLE WHICH COMPRISES INSTALLING AN IMPERMEABLE LINER IN SAID BOREHOLE TO PREVENT FLUID COMMUNICATION BETWEEN THE BOREHOLE AND SAID UNCONSOLIDATED FORMATION, SAID LINER BEING AT LEAST IN PART READILY SOLUBLE IN A SELECTED CHEMICAL REAGENT; LOWERING A WELLBORE HEATER INTO SAID LINER ADJACENT SAID FORMATION; HEATING OIL IN SAID FORMATION BY MEANS OF SAID HEATER UNTIL SUFFICIENT COKE TO CONSOLIDATE SAID FORMATION IN THE IMMEDIATE VICINITY OF SAID BOREHOLE HAS BEEN FORMED; AND THEREAFTER INTRODUCING SAID SELECTED CHEMICAL REAGENT INTO SAID BOREHOLE IN CONTACT WITH SAID LINER TO AT LEAST PARTIALLY DISSOLVE SAID LINER AND THEREBY RESTORE FLUID COMMUNICATION BETWEEN SAID BOREHOLE AND SAID FORMATION.

Images