CA2024664A1 - Method for selective plugging of a zone in a well - Google Patents

Abstract

METHOD FOR SELECTIVE PLUGGING OF A ZONE IN A WELL
Abstract of the Disclosure A mixture of a liquid epoxy material and a hardener is selec-tively placed in a well traversing a subterranean formation adjacent to a zone in said formation which is to be plugged. The mixture is dis-placed into the zone and allowed to harden, thereby plugging the zone.
The process is particularly applicable to sealing off water production in a gravel-packed well. A positive displacement bailer may be effect-ively used to deliver the mixture to the zone. The epoxy material used is immiscible with and is heavier than the fluid in the well. The epoxy material is further characterized as being essentially free of solids and having a low viscosity at downhole conditions of temperature and pressure. The hardener has an activation temperature which is lower than the downhole formation temperature.

Description

~ ~ 2 ~
~CR 80~0 M~THOD ~OR SELECTIVE PLUGGING OF A ZONE IN A W~LL
Back~round oi the Invantion Two basic factors which are especially prevalent in typical producing oil and gas wells in the Gulf of Mexico and the surrounding coastal regions have created the need for a new plugging technique.
First, the majority of oil and gas wells in the Gulf Coast region produce from reservoirs which are commonly classified as water-drive type reservoirs. In a water-drive reservoir, the predominant mechanism which forces the movement of oil or gas in the res~arvoir toward the wellbore is the advancement of a formation water aquifer. The formation water phase is found beneath the oil or gas phase in a "bottom-water"
reservoir or on the outer flanks of the oil or gas column in an "edge-water" reservoir. In either case, water moves into the rock pore spaces which were once filled with hydrocarbon fluids in response to continued production of oil or gas. Over time, this natural water encroachment leads to the advancement of water into the producing interval, and the well eventually begins to produce quantities of formation water. As the influx of water continues in the reservoir, the percentage of produced water, as compared to total fluid production, increases with time.
The ever increasing production rate of formation water is undesirable in both oil and gas wells. In the case of an oi.l well, the energy required and correspondinely the cost required to artiflclally lift a given volume of oil from a well must b~ proportionatcly :Lncreased if formatlon water is being produced toge~her with the oi.l. 'rherefore, the reduction or elimination of water production Erom an oil well ls economically advantageous since~ ~a) lifting costs to produce the oil are reduced, and (b) costs associated with the treatmen~ and proper disposal of the produced waste water are lowered.
In the case of a gas well, the production of even relatively low quantities of formation water can be detrimental to the productivity of the well. When formation water and natural gas enter the wellbore, each fluid phase begins to travel upward toward an environment of reduced pressure at the surface of the well. As pressure decreases ~i ~ 2, ~
toward the surface, gas contained in the well' 5 tubulars expands, and the velocity of the gas increases accordingly. As a result, the ex-panding gas acts as a carrying mechanism to continually remove the formation water from the well. However, as reservoir pressure decreases in response to eontinued gas production and/or water volumes entering the wellbore continue to increase, the ability oE the gas to carry and remove formation water from the well is greatly reduced. As this phenomenon begins to oceur, the relatively dense formation water begins to "fall baek" into the well. ~ventually this water will fill the well's tubing to the point that the hydrostatie pressure created by the water column approaches the prevailing reservoir pressure, and the productivity of the well is significantly redueed. Inereasing water en-croachment and/or eontinued pressure declination results in the eventual cessation of production The second basic factor, which is typical of Gulf Coast oil and gas production, is the common occurrence of unconsolidated sandstone reservoir rock formations. In this type formation, sand grains (which make up the sandstone rock) do not contain adequate intergranular cementation or rock strength to ensure rock stability during the pro-duction of oil and gas. As a result, the rock, in its natural state, often fails when subjected to the stresses imposed on it during the production mode. Small rock fragments are then produced into the wellbore. Once accumulated in the wellbore or well tubulars, this fine grain material possesses a permeability that approaches zero, and well productivity is greatly redueed.
Various techniques to increase the stabLlLty of the salldcl~one reservo:Lr rock (or methods oE "sand eontrol") have been ~mployed through the years. One common method oP s~md control which was employed exten sively during the nineteen sixties and early seventies was the pumping Of a compound through the formation pore spaces that, once cured, would coat the sand grains and add "artificial" grain-to-grain cementation Thus, the overall rock strength was increased in the treatment area.
This method of sand control had a positive effect on dealing with the previously mentioned problem of natural water encroachment into a well's producing interval. The completion interval utilizing this method of sand control remains essentiall.y free of downhole mechanical equipment.

Therefore, at the point in tlme when watcr moves in~o tha compl~tlon interval, an attempt can easily be made to l'plug-~ack" the lower port~on oi the well. This is accomplished by lowering, on electrlcal wirellne equipment, an expandable plug through the ~ell's productivn tubing and into the cased region of the well. The plug is positioned immediately beneath the completion interval, and the plug is expanded ~o contact and affix itself to the casing wall. Once in place, the plug acts as a "bottom" such that contmonly used oilfield cement can be placed on top of the plug to the desired height in the well. The placement o~ cement up to or above the oil- or gas-water contact in the res0rvoir, if success-ful, has a limiting e~fect on water production.
~ ith ~hs advancement of alternate sand control techniques, there came into use a new and pre~erred me~hod of sand control commonly referred to as "gravel packing." The widespread use of this technique occurred in the nineteen sevanties and is presently the sand control method of choice in most areas of the world. Gravel packing is a system in which uniformly sized and shaped sand grains are placed in a well's perforations and in the annular volume between the well's production casing and a slotted or perforated pipe, which is externally wrapped with wire. The sand grains, or "gravel," are slightly larger than the formation sand particles, and since they are tightly "packed" together, they prevent the collapse of the perforation ttmnels and act as a filter to prevent the migration of formation sand into the wellbore. The wire wrapped or slotted "screen" is normally placed between two packers and contains the sand ln an area adJacent to the perforated interval and prevents the movement of the gravel into the productLon tubing.
In the event that Eormation watar moves into the completion interval, the "plug-back" method previously described ig lneffective in reducing wa~.er production. The reAson ~or this is that particulates in the common oilfield-type cement "plate out" and bridge ofE at the gravel pack sand face. Only the liquid (usually-water) flltrate of the cement effectively permeates the gravel pack sand, and the cement dehydrates and cures as a plug inside the screen and slotted or perforated blank pipe. Even if the cement plug is spotted properly in the water-bearing portion of the producing interval, the formation water will simply flow vertically upward in the annular gravel-packed area surrounding the ~ '" 7 .i,1 plug; and, if this distance is not sufficient in length, the cement plug will havc very little efEect on reducing water production.
For similar reasons, the placem~nt of a mechanical plug inside the slotted or perforated blank pipe yields similar results. In this case, formation water enters the wellbors below the plug (which is set at a depth ~ust above the oil- or gas-water contact) and ~ravels "around" the plug, utilizing the high flow capacity annular area between slotted or perforated pipe and the screen. The l-lmited sffect of both of the a~ove-mentioned methods to reduce wat~r production from ~he lower portion of a gravel-packed well has led to the method of this invention.
Prior Art U.S. Patent No. 4,0~2,031 to Knapp discloses a method for plugging formations with epoxy emulsions containing fine solld particles. A du~p bail~r is used for selectively placing the slurry into the lower perforations.
U.S. Patent ~o. 4,034,311 to Sparlin et al. discloses a method for sealing permeable formations. The me~hod comprises: (1) introduc-ing sand to the wellbore to a level below the zone to be sealed, (2) adding gravel to the annular space between the ~ellbore and the slotted liner, (3) adding polymeriziable material and acidic catalyst to the wellbore at the zone to be sealed and allowing polymerization to take place, and (4) removing polymerized material and catalyst from the slotted liner.
U.S. Patent No. 3,709,296 to Glenn, Jr., discloses a method and apparatus for plugging a wellbore zone. The apparatus compr:Lses a bailer and a gamma ray logging tool. The method comprises lowerlng the bailer containing n catalyst and a polymerLz:Lable material into the wellbore to the zone to be plugg0d and displacing ~he mixture into the zone where it hardens.
U.S. Patent No. 3,933,204 to Almquist discloses a method for plugging a permeable formation by in~ecting into the formation an aqueous emulsion containing epoxy and carboxy polymers w~ich harden to form a plug.
Summary of the Invention According to this invention, a mixture of a liquid epoxy material and a hardener for the epoxy material are del.ivered to a zone - 5 - c.- r' ~ s fl ~n ~

in a well which Ls to be plugged. The mixture is thereafter displaced into said zone where it is allowed to harden and plug off said zone.
The mixture of liquid epoxy material and hardener is characterlzed in that: 1. The epoxy material has a density greater than the denslty of thewell fluids.

2. The epoxy material has a low viscosity at the downhole conditions of temperature and pressure.

3. The epoxy material is immiscible with the well fluid.

4. The epoxy material is essentlally free of solids.

5. The hardener has an activation temperature lower than the formation temperature at the zone to be plugged.

6. The set time of the epoxy materlal is of short duration at downhole conditions of temperature and pressure.
In one aspect of the invention, the mixture of epoxy material and hardener is introduced to a gravel-packed zone to seal off the production of water.
In another aspect of the inventlon, the mixture of epoxy material and hardener is delivered to the zone to be plugged with a bailer.
Brief description of the Drawings Figure l ls a sectional view of a typical wellbore containing gravel packing.
Figure 2 is a sectional view of the same wellbore after treatment in accordance with the process of the invention.
Figure 3 is a sectional view of a wellbore u~ Lzed 1n con~unction with a f:leld test procedure.
~3~ n~ s-l~lR~ of the_Inventio~
In carrying out the process of the invention, a mixture of an epoxy material and a hardener for the epoxy material are delivered ad~acent to a zone in a well which is to be plugged and the mixture is thereafter dlsplaced into the zone and allowed to harden. The process is particularly applicable to oil and gas wells containing gravel packs where water encroachment has led to advancement of water into the producing interval so that the well produces excessive quantities of water over a period of time. By plugging off the water zone, it ~ J ~ J!g 1 is possible to reduce or even eliminate the fl~w of water, ~hus restor-ing the desired production of oil and/or gas from the well.
The process of plugglng off a water formation in such a well may be described by refer~nce to the drawings. Referring to Figure 1, there is disclosed a subterranean oil or gas zone and a water zone at (18) and (20), respectively. Although these are shown as ssparate zones, they are not distinct and ssparate from each other but tend to merge one zone into the other. Traversing these zones is a producing well having an outer production casing (8) and inner production tubing (2). A portion of the well adJacent zones (18) and (20) is isolated from the remainder of the well by upper packer (12), which is placed between tubing (2) and casing (8) and lower packer (12) between slotted tubing (4) and production casing (8). Contained in this isolated area is a slottet tubing (4), which ls somawha~ larger in diameter than lS production tubing (2). Around the outside of slotted tubing (4) is a wire-wrapped screen (6), which is supported and spaced from the slotted casing by vertical rods (not shown). The isola~ed section of casing (8), which surrounds slotted tubing (4) and wirescreen (6) is Eilled with gravel (10). This gravel fills not only the casing but also the perforations (16) extending from the casing through the prlmary cement (14) around the casing and into zones (18) and (20).
It is desirable that the well remain dormant during the operation of the process. If the well does not remain dormnnt, downhole fluid movement, or "cross-flow," between sand beds wl~hln the completlon interval may cause the epoxy to be dispersed in~o portlons o~ the well which do not requlre plugging, Also, the epoxy plug can bocome "honeycombed" if ~ormation Pluld continues to ~.rickle into thc wellbore before the epo~y i8 completely hardened. If the well is not dormant, that i9 lf there is fluid flow, the flow may be ellminated or minimi~ed by filling the well with fluid and maintaining a positive pressure;
e,g,, from about 300 to about 500 psi at the surface of the well, The fluid used may be fresh water, formation brine, seawater, or any other formation-compatible material When format~on fluid naturally exists in the bottom of the well or when fluid has been placed in the well, the near wellbore area becomes sufficiently saturated ~hat the mlgration of oil or gas into the wellbore is minimized, The first step of the process, therefore, is to ensure that ~he well remains essentially dormant, 7 - 2~

In the next step of the proces3, liquid epoxy and hardener are mixed together to form a liquid mixture and ar~ introduced into the well and placed at a point adJacent to the gravel-packed zone (10). The hardener which is mixed with the epoxy matarlal has an activation temperature which is somewhat less than the ormation temperature in ~he area of the gravel-packed zone. The activation temperature is the temperature at which the hardener initiates reaction of the epoxy material. Since the tempersture in the well gradually increases ~rom the top of the well down to the formation to be plugged, it is desirable to place the mixture o~ epoxy material and hardener at the point of use as quickly as possible, thus ensuring that the epoxy material does not begin to harden until it ls placed in the area of the zone which ls to be plugged.
One method for moving the mixture of epoxy material and hardener to the desired location is to use a positive displacement dump bailer. Thls is a mechanical dsvice cylindrical in shape, which is filled with the mixture of epoxy material and hardener and lowered into the well on a cable. The bailer is positioned at the desired depth and when activated, releases a metal bar in the top of the device. I'he bar falls downward inside the device and impacts the top of ~he fluid creating a downward~moving shock wave which travels throu~h the fluid column contained by the baller. The shock wave causes the shearing of metal pins in the bottom of the baller and subsequent downward moveMent of a small piston which uncovers ports to allow ~he r~lease of the contained material, The metal bar contlnueff to fall throu~h the ball~r as fluid is released through the ports. The welght of the metal bar effcctively adds ~o the weight of the ~luid colwnn being dumped. As the bnr ~alls to the botkom of the bailer, the cylindrical bailer tube is wipod clean o~ the epoxy material/hardener mixture.
Other types of positive dlsplacement dump bailers, which operate in a simllar manner, may also be used. It is also possible to deliver the mixture of epoxy material and hardener in an open bailer, This $s a bailer which is open at the top and closed at the bottom.
When activated, the bottom cover, which is held by metal pins, is f; rJ ~ ~L ~
sheared by an explosive or by o~her means thereby opening the bottom and allowing the mixture o~ epoxy material and h~rden~r to ~low by gravlty from the bottom of the bsiLer and into the forma~lon.
A coiled tubing may also be ~sed to place the mixture at the deslred point in the well. The coiled tubing is a l-inch or other small pipe which is wound on a spool at the surface of ~he well. Ths mlxture of epoxy material and hardener is placed in the end of the tubing and held in place by wiper balls at the top and at the bottom of the mixture. The tubing 1s then uncoiled and lowered into the well to the desired location, after which the mixture of epoxy material and hardener is pressured through the tubing and released at the selected location.
Referring again to Figure 1, whatever apparatus is used for the purpose, the mixture of epoxy material and hardener is placed in the apparatus and is delive~ed as quickly as possible to a point sllghtly above water ~one (20). The apparatus is then activated to release the epoxy material/hardener mixture which flows into slotted tube (4) and from there into the gravel pack (10) and perforations (16). At this point, a small amount of liquid may ba pumped slowly into production tubing (2) to "squeeze~ the epoxy material into the pore spaces of the formation rock or any voids in the primary cement (14) nround the production casing. At the existing downhole ~emperature, the hardener is activated and the epoxy material begins to react. Flgure 2 shows the same well ater the epoxy material has hardened to Eorm a solld plug (22) ad~acent water ~one (20). This plug ~ills ~he slottsd plpe, the screen, the gravel, and may even entor khe perforatlons (16) to effectively plug of~ productlon of water ~rom zone (20~.
The epoxy m~terlals used in cnrrying out the lnventlon have denai~les greater than the welL ~luid, which ns prevlously pointed out, may be ~resh water, formation water, or other water contalning salts.
The epoxy materiaLs are also essentially immiscible wl~h the wel.l fluid.
These two properties assure that the epoxy/hardener mixture will not tend to rlse through the formation fluid, nor will the mixture be diluted in any way by the formation fluid so as to prevent the epoxy from performlng its proper function. Preferably, the epoxy will have a density of at least about 1 to about l 1/2 pounds per gallon greater than the wellbore fluid.

~t/ ~;J l~L ~

The epoxy ma~erials used will ~urther ha~e a relativel~ low viscosity at downhole conditions of temperature and pressure. Thus, the fluidity of the epoxy materlal and ~he density di~Perence between the epoxy material and the wellbore 1uid will facilltate the almost com-plete displacement of th~ wellbore ~luid, saturating the gravel-pack in the zone to be treated. The v~scosity of the epoxy material is usually between about 500 and about l centipoise at downhole temperatures of between about 75 and about 220 degrees Fahrenheit. The epoxy materials used are also essentially free of solids and, thereiore, contain no materials to plate out on the gravel-packed sand face as does cement.
The epoxy material goes through several physical stages in the process of the invention. In the first s~age, it is a flowable llquid of relatively low viscosity, particularly at higher temperatures. When the temperature of the epoxy material reaches the activation temperature oi the hardener, it begins to react and increase in viscosity.
Eventually the epoxy material hardens sufficiently that it ceases to flow. The point at which this occurs is called the "set point." ~ith additional time, the epoxy material continues to react and harden until it becomes a solid.
At this point, the epoxy is considered to be "hardened." The time required after the set point for the epoxy material to become hardened is normally of very short duration--usually from be-tween abou~
2 to about 20 minutes. With still additional time, the epoxy material becomes completely reacted and hardened and is considered to be cured.
As with concrete, thi~ ~inal curing ~tag~ may take as much as several days, depending on the part~cular epoxy material/hardener system.
The set tim0 of the epoxy material/hardener mi~ture should bo of short duration, Ideally, the epoxy material would begln to harden immediately ai'ter the mixture of epoxy material and hardener have had a chance to completely displace the wellbore fluid in the area to be treated. Delayed hardening is undesirable for two reasons. First, if the well does not remain entirely dormant from the time the epoxy material is placed until i~ is hardened, downhole iluid movement or cross-flow between sand beds within the treated area may cause the epoxy material to disperse into lower or upper portions of the well.
Secondly, if the epoxy material remains in an unhardened state, or if the reaction requires an extended period of time to complete, the integrity of the plug can be reduced if formation fluid contlnues ~o trickle lnto the wellbora beiore the cpoxy material is hardened. By proper selection of the epoxy material and hardener, set tlmes for the 5 epoxy material c~n be predetermined. The set time of the epoxy material will be between about 1 and about 180 minutes and preferably between about 10 and about 60 minutes.
The amount of epoxy material used to plug off a gra~el-packed intarval depends on the si~e of tha gra~el packing and th0 portion of the gravel pack which it is desirad to plug. Usually an amount of epoxy material between about 0.5 and about 2.0 gallons per foot of plugged interval is sufficient. Since the amount of epoxy material which a bailer or coiled tubing can deliver in a single operation is limlted, it may be necessary to carry out the delivery process in two or more stages.
The hardener materlals used in the process are those which are compatible with the epoxy matarlal ln that once the two are mixed, they form a llquid mixture which ls substantially free from sollds. The hardener material will have an activation temperature, that i3 the temperature at which the hardener acti~ates reaction of the epoxy material, which is below the temperature existing at the ~ona which is to be plugged o~f. The activation temperature of the hardener should not be too much below thc downhole temperature, slnce the initlatlon of reaction of the epoxy material should not occur until the epoxy material/hardener mlxture has had the time to substantlally dl.spl~cb wellbore fluid from the ~ormation to be plugged, The amount o~ hardener used is suf~icient to eE~ect complete reaction of the epoxy ma~erial ln a reasonabla perlod of tlme and is between about 1 and 15 parts per 100 parts of the epoxy mfltsrial, more usually between about 2 and about 6 parts per 100, Any epoxy material whlch meats the criteria previously set forth may be used in carrying out the process of the invention. A
widely used class of polyepoxides from which the epoxy ma~arial may be selected are the resinous epoxy polyethers obtaincd by reacting an epihalohydrin, such as epichlorohydrin, epibromohydrin, epliodilydrln, and the like wlth either a polyhydric phenol or polyhydrlc alcohol. The - 11 - G:~ f, ~

resulting resinous products may contaln free terminal hydxoxyl groups or t~rminal hydroxy groups and terminal apoxy groups.
Another class oi polymeric polyepoxides from ~hlch the epoxy material may be selected are the polyepoxy polyhydroxy polyethers obtained by re~cting a polyhydric phenol, such as bisphenol A, re-corcinol, catechol, and the like, or a polyhydric alcohol such as glycenol, sorbi~ol, pentaerythritol, and the like with a polyepoxlds such as bis(2,3-epo~ypropyl) ether, bis(2,3-epoxy-2-methylpropyl) ether, 1,2-epoxy-4,5 epoxypentane, and the like.
Another class of epoxides are the no~olac resins obtained by reacting, in the presence of a baslc catalyst, an epihalohydrin, such as epichlorohydrin, with the resinous condensate of an aldehyde; e.g., formaldehyde, and either a monohydric phenol; e.g., phenol itself, or a polyhydric phenol; e.g., bisphenol A.
Still another class of epoxides are the homopolymers and copolymers of epoxy containing monomers which also contain at least one double bond. Among such ethylenically unsaturated epoxy-containing monomers are vinyl 2,3-glycidyl ether, allyl 2,3-glycidyl ether, gly-cidyl acrylate, 2,3-epoxypropyl crotonate, glycidyl-oxystyrene, and the like. Suitable comonomers ior copolymrization with these ethylenically unsaturated epoxy-containing monomers include styrene, acrylonitrile, methyl acrylate, vinyl chloride, vinyl acetate, diallyl phthalate, and the like.
Yet another class of epoxides are the di- and tri-epoxides, such as 3,4-epoxycyclohe$ylmethyl, 3,4-opoxy-cyclohexene-carboxylate, 3,4-epoxy-6-methylcyclohexylme~hyl~3,4-epoxy-6-mel:hyl cyc:Lohexnne car-boxylate, bis(3,4-epoxy-cycloh~xylmethyl) maleate, bls(3,4-epoxy-6-methylcylohoxyl) methyl-s~ccinate, ethylene glycol bis(3,4-epoxycy-clohexane) carboxylate, 2 ethyl-1,3-hexanediol bis(3,4-epoxy-6-methy-lcyclohexane carboxylate, and the like.
Another type of epo~ides are the glycidyl ethers of alcoholsand phenols, including such compounds as the diglycidyl or triglycidyl ethers of trimethyl propane, the diglicidyl ethers of 1,4 butanediol, 1,6 hexanediol, neopentylglycol, resorcinol, hydroquinone, catechol, bis (hydroxyphenyl) methane, and the like.

Other monomeric polyepoxides whlch may be used lnclude dlc-yclopentadiene dioxide, epoxidized triglycerides such as epoY.idized glycerol trloleate, epoxidized glycerol ~rilinoleate, the diacetate of epoxidized glycerol trilinoleate and the like, 1,3-bis(2,3-epoxypro-poxy)octane, 1,4-bis(2,3-spoxypropoxy) cyclohe~ane, 1,4-bls(3,4-epoxy-butoxy)-2-chlorocy-clohexane, 1,3-bls(2,3-epoxypropoxy)benzene, 1,4-bis (2,3-epoxypropoxy)benzene, 1,3-bis(2-hydroxy-3,4-epoxybutoxy)benzene, 1,3-bis(4,5-epoxypentoxy)-5-chlorobenzene, 4,4'-bis(2,3 epoxypropoxy) diphenyl ether, and epoxy e~hers oi poly'basic acids such as diglycldyl succinate, diglycidyl adipate, diglycidyl maleate, diglycidyl phthalate, diglycidyl hexachloroendomethylenetetrahydrophthalate, and diglycidyl 4,4'-isopropylidenedibenzoate.
It will be appreciated by those skilled in the art that the epoxides used in carrying out the inventlon are not limited to those selected from the above-described materials, but that said epoxides are merely representative of the class of epoxides as a whole.
The hardeners which are used in carrying out the process of the inven~ion may be either liquids or solids. If present ln the solid state, they may be melted and combined with the liquid epoxy material or ~ they may be converted to fine solids; e.8., by grinding, and than combined with the epoxy. In any event, the inal mixture of epoxy material and hardener is a liquld and is characterized as being substantially free o~ solids.
Any hardener which hus an ac~i~a~ioll temperature lowor ~han the ~ormation t~mperatur~ at tho zona to bo plugged may bu used.
Rxamples o~ hardening a~ents are aliphatic and aromatic polyamlnes, acld nnhydrides, the hydrazides der:Lved ~rom polycarboxyllc acids, lmidazole derivatives, dicyanodiamide, guanidine derivatives, and biguan:Ldf ne deriva~ives. Typical examples o~ those hardeners are dlaminodicylo-methane, bis(4-amino-3-methylcyclohexyl) methane, diaminodiphenyl-methane, diaminodiphenyl-sulfone, 4,4'diamino-3,3'-dichlorodihexyl-methane, phthalic anlydride, chlorendic acid, and the like.
Hardeners which may be used also include primary and secondary polaymines, such as diethylene triamine, trie~hylene tetramine, tetra-ethylene pentamine, aminoethyl ethanolamine, hydrazine, ehtylenediamine, 1,3-propanediamine, 1,4-butane diamine, 1,6-hexane-diamine, 6~7~ ' fi ~Sr~ ~¦

3,3'-imino-blspropylamine, 1,2-propane dlamine, 1,5-pen~ane diamlne, phenylene diamine, and tertiary amines characterized by the formula.

N-R' I

R"

~1herein R, R', and R" are the same or di~ferent organic radicals such as dlmethylethanolamine, dimethylpropylamine, dimethylbutylamlne, dim-ethyloctylamine, dimethylethylamine, mono-methyl-diethylamine, die-thylethanolamine, dimethyl decyl amine, monomethyl ethyl butyl amine, monomethyl dibutyl amine, monomethyl dlprophyl amine, NN-dimethyl amino lS butyl amine, ~N-dimethyl-amino hexyl amine, NN-diethyl amino butylamine, tetramethyl ethylene diamine, tri-methyl ethylene diamine, tetramethyl propylene dlamine, tetraethyl ethylene diamine, triethyl ethylene diamine, tetraethyl propylene diamine, NN-diethylamino athylamine, dimethylamino-propylamine, diethylamino-propylamine, dimethylamino-methyl phenol, and tri-(dimethyl-aminome~hyl) phenol.
Other hardeners which may be used, some of which fall under the above classes of materials, are dicyanamide, ~hloameline, sodium phenylcyanamide, dithiobiurel, ethylenethiourea, diallcylmelamine, ace-toguanamine, melamine, guarylurea, benzoguan~mine, benzoyldicyandiamide, guanazole, 3-aminio-1,2,4,triazole, monomethyloldicyand:Lamide, khlo~e-micarbaæide, adipamide, adipyl dihydrazide, isophthalyl diamide, lso-ph~halyl dihydrazido, triAminomel.amine, tetraminoditolylmethane, diami-oacridino, phenylbiguanide, semicarbazide, 2-oxoimidazoline-4,5-diacar-boxamide, oxaldilmidic acid dyhydrazid, oxamidedloxlme, diaminomaleoni-trile, 2,3-diamino-5,6-dicyanopyrazine, stearic hydrazide, succiminide, and cyanoacetimide.
Still other hardeners include such ma~erlals as boron trifluoride-organic amine adduc~s; e.g., boron trifluoride-amine complex, con~aining p-chloromiline and triethylene glycol.
The foregoing ma~erials are not limiting; any hardener may be used which meets ~he previously described general requirements.

- 14 - 2 ~

The following examples illust~ates the results obtained ~n carrying out the inventlon:
Example 1 The well shown schematically in Figure 3 is producing through perfora-~ions (19) a~ 10,234 ieet to 10,288 ~eet. The well has a bot~om-hole temperature of 200F and a bottom-hole pressure 4,918 psi. The last tes~ on the well showed a gas production of 2,428 mcfd, an oil condensate production of 36 barrels per day, and a water produc~lon oi 1,336 barrels per day. Referring to the drawing, 3 1/2-inch production lo tubing (1) is connected in the bo~tom o~ the well to a slotted tubing (15) which is covered with 64 feet of 3 1/2-inch, 8-gauge screen (21).
A 7 5/8-inch production casing (3) is filled with gravel (17) which surrounds the lower portion of production tubing (1) and the screened slotted tubing (15). The e~tent of the gravel pack is defined by an upper packer (13~ around the production tubing and a bull plug with centralizer (11), which seals off the bottom of tha screened slotted tubing and the production casing and ~hich rests on a bottom packer (9`
which had been previously placed in the well.
To seal off the water producing zone, which is in the lower portion of the production interval, the ~ollowing procedure ~as followed:
l. The production tubing (1) was ~illed wlth salt water and pressured to provide a top pressure of approximately 515 psi. It was lmportant that the well remain iull therefore, the ttlbing and casing pressures were monitored before the treatmen~ wa.q c~rrled out to ensure that the well remained relntively s~at:Lc ~o~ at leas-~
four hours.
2. A 72-~oot positive displacement bniler WBS lowered in~o the well and loaded Erom the top with five gallons of Heloxy-69 epoxy material containing 3.94 parts o~ Ancamine K-61 B hardener per 100 parts of epoxy material. Heloxy-69 is a resorcinol diglycidyl ether marketed by Wilmington Chemical Corporation of Wilmington, Delaware. The Ancamine K-61-B hardener, which has an activation temperature o~ 170F to 180F, is a modified tertiary amine mar-keted by Pacific Anchor Chemical Company of Lo~ Angelos, Cali-fornia.

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3. The dump bailer containing the mixture of epoxy materlal and hardener was run lnto the hole quickly to a position 20 feet above the lowest perioration. The dump bailer was then actuated to displace the epoxy material/hardener mixture. 4, After the epoxy material/hardener mixture has had time to completely dump, the bailer was held stationary for se~eral mlnutes and then pulled very slowly from the well. In order to keep the production tubing liquid ~ull, additional liquid was added while the bailer was being removed to replace the volume occupied by the llne attached to the bailer.
5. The epoxy material was allowed to harden for approxlmately four hours.
6. After cleaning, the bailer was filled with 9 1/2 gallons of epoxy material containing the same amoùnt of hardaner which have been thoroughly mixed.
7. The bailer was again run into th0 well quickly to a depth of about feet abo~e ths lowest perforation snd dumped again. Af~er allowing time for the bailer to completely dump, one barrel of salt water was slowly pumped into the well. 0 8. The bailer was again slowly removed from the well with the well being maintained liquid-fluid full by replacing fluid displaced by the line connected to the bailer.
9. The epoxy material was agaln allowed to harden ior appro~lmately four hours. 5 10. The well was subsequen~ly return~d to productlon, fln~ u test wn3 carried out to det0rmine production rates. As a result of the epoxy mat~rlal trentment, the gns production was 1011 mcfd, the oil production was 132 bpd, and the water productlon was reduced to 928 bpd.

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EXAMF~ 2 .
Tho well shown schematically in Figure ~ had produced gas intermittently since mid-July 1988 because of the combination of reduced reservoir pressurs, water production, and high pipeline pressure. The 5production data showed that when the pipeline pressure exceeded 1,000 psi, gas production stopped completely because excess-produced water from a strong natural water drive loaded up the production tubing.
Sporadic attempts to flow the well during the period from August to November were unsuccessful. Production figures for this time period are 10shown in Figure 5.
Referring to Figure 4, tha well contains 2 3/8-inch production tubings (26) and (28) disposed within a 7 5/8-inch production casing (24). Production tubing (28), which terminates at a depth of 3,662 feet, is spaced from production casing (26) by a dual packer (30), which 15is located at a depth of 3,647 feet. After passing production tubing (28), production tubing (26~ makes a bend and continues down the center of the production casing to a depth beyond packer (38), which is placed at 3,967 feet. ~xtending downwardly from packer (34) at 3,794 feet to a packer (46) at a depth of 5,549 feet is a 3 1/4-inch 20tubing (32) which surrounds production tubing (26). At a depth of 3,924 to 3,968 feet, the 3 1/4-inch tubing is slotted and is surrounded by 8-gauge screen (56), which is spaced from the tubing with ver~ical rods (not shown). The space around the screened tubing, defined by packers (34) and (38), is filled with a gravel pack (3~ nother packer (39) 25is provided between tublng (26) and tubing ~32) at the same depth ~IS
packer (38). T~e wcll is belng produced through perfora~ions (40) a~
3,930 to 3,962 feet. The well wa0 previously produced through perforations (50) at 5,524 to 5,542 feet ~rom a gravel pack (48) surrounding a similar screen-slotted tubing (42). This gravel pack was 30defined by packers (44) and (46). The lower completion was plugged off previously by placing a packer (52) below production tubing (26) and cementing this tubing and the surrounding tubing (32). The top of the cement extended upwardly into tubing (26) to (54) a level of 3,918 feet.
To solve the water problem, it was originally proposed to 35treat the well by peri~orating productlon tublng (26) above the top level of the cement (54) and thereafter introduce the mixture of epoxy 17 ~J 2 ~ i ~ 3 J~

material and hardener through such perforations into gravel pack (36) to seal off the lower 10 ieet of perforations (~0) When a preliminary test was made with a bailer, it was found the bottom of the tool could not go below 3,897 feet because of an obstruction in tubing (26). Also, when the bailer was pulled to the surface, it was iound that the material contained therein was a highly viscous brine loaded with cement fines. Because of the difficulty encountered in trying to reach the cement plug at 3,918 feet and the contaminated fluids in the wellbore, it was concluded to treat the well through production tubing (28). It was decided to plug the gravel pack t36) from the packer (38) lnto the perforated interval (40) at 3,952 ~eet. This would eifectively isolate the bottom 10 feet of perforations (40). Since the bottom of the bailer could not pass beyond packer (34), it would be necessary to release the mixture of epoxy material and hardener at this point, a distance of 158 feet above packer (38).
In November, it was decided to commence treatment oi the well.
At the time of the treatment, the temperature at perforations (40) was 125F. The shut-in tubing pressure of the well was 1,250 psi, and the gas/water contact was located at 3,100 feet. In the flrst step of the treatment, a 51-foot bailer, having a capacity of 3.43 gallons, was loaded with a mixture of Heloxy 69 epoxy material containing 3.0 parts per hundred part oi epoxy and hardene~ Ancamine 1110, a modified tertiary amine marketed by Pacific Anchor ~hemical Company oE Los Angeles, California. The bailer was then lowere~ into production ~ubin~
(28) until it reached packer ~34), At this tlme, the bailer was activated ~o releAse the mixture t)f epoxy material and hardener. Ten minutes after firing, the bailer was slowly pulled out of the tublng.
The pick-up rate was increased after the gns/water level in the tubing was reached. On each of the next two days, the process was repeated so that a total of 9 88 gallons of epoxy material was placed at the desired location.
The following day, the well was placed back in production.
During the next several months, the well averaged a water production of about 60 barrels per day and a gas production of about 550 MSCF per day.
It is noted from Figure 5 that the water production was substantially reduced by the epoxy treatment. In the immediate period prlor to the treatment, the waLer production averaged over 100 barrels per day.

18 - f 1~;J ~

~hile the gas production after trcatmcnt did not reach the le~el previously attained before the well encountered water problems, the treatment did make it possible to obtain substantial gas production;
whereas, beiore treatment, no gas could be produced at the existing pipeline pressure of 1,000 psi or hlgher. It ls noted that all of the data illustra~ed in Figure 5 was obtained at a pipeline pressure at or exceeding 1,000 psl.
The example illustrates that it is possible to carry out the treating process oi the invention even though the epoxy/hardener mixture cannot be released in close proxlmity to the zone or area which is to be plugged. As noted in the example, the mlxture of epoxy and hardener was released 158 reet above the desired delivery point.
While the invention has been described in its specific appli-cation to a gravel-packed well, it is not limited to such use. The precise placement method disclosed herein may be used to plug any type of zone or formation in a well. Ordinarily, a single epoxy material is used in the process. However, it is w~thin the scope of the invention to use mixtures of difierent epoxys, particularly as this may be advantageous in obtaining the desired density difference between the epoxy material and the well fluid. Many of the epoxy materials are vlscous at well surface temperatures. To facilitate mixing with the hardener and introducing the mix~urc into the bailer, it may be de-sirable to heat the epoxy materlal to a ~emperature above ambient, usually, however, not higher than 110F to 120F.
While certain embodiments and details have benn shown for t:hc purpose o~ illustrating the present lnvelltion, it will be apparent to thosc skillcd in ~hc art, that various changes and modifications may be made herein without departing ~rom the ~pirit or scope of the invention.
WE CLAIM:

Claims (19)

1. A process for plugging a zone in a subterranean formation comprising:
(a) mixing an epoxy material and a hardener for the epoxy material to form a liquid mixture, the mixture being characterized in that:
(1) the epoxy material has a density greater than the density of the well fluid;
(2) the epoxy material has a low viscosity at downhole conditions of temperature and pressure;
(3) the epoxy material is immiscible with the well fluid;
(4) the epoxy material is essentially free of solids;
(5) the hardener has an activation temperature lower than the formation temperature of at the zone to be plugged;
(6) the curing or hardening time of the epoxy material is of short duration at downhole conditions of temperature and pressure;
(b) introducing the mixture into a well traversing a subterranean formation at a point adjacent a zone in such formation which is to be plugged; and (c) allowing the mixture to harden and plug said zone.

2. The process of Claim 1 in which said zone to be plugged is in a gravel-packed well.

3. The process of Claim 2 in which the mixture is delivered to the point adjacent to the zone which is to be plugged in a bailer.

4. The process of Claim 3 in which the epoxy material is a resorcinol diglycidyl ether epoxy.

5. The process of Claim 4 in which the hardener is a tertiary amine.

6. The process of Claim 4 in which the hardener is an imidazole compound.

7. The process of Claim 3 in which the amount of hardener used is between about 1 and about 15 parts per 100 parts of epoxy material.

8. The process of Claim 7 in which the amount of epoxy material used is between about 0.5 and about 2.0 gallons per foot of plugged interval.

9. The process of Claim 8 in which the viscosity of the epoxy material is between about 500 and about 1 cp at formation temperature.

10. The process of Claim 3 in which the set time of the mixture of epoxy material and hardener is between about 1 and about 180 minutes.

11. A method for selective plugging of a gravel-packed well which comprises:
(a) taking necessary steps to assure that the well remains dormant during the process;
(b) maintaining a constant pressure at the surface of the well;
(c) mixing an epoxy material and a hardener for the epoxy material to form a liquid mixture, the mixture being characterized in that:
(1) the epoxy material has a density greater than the density of the well fluid;
(2) the epoxy material has a low viscosity at downhole conditions of temperature and pressure;
(3) the epoxy material is immiscible with the well fluid;
(4) the epoxy material is essentially free of solids;
(5) the hardener has an activation temperature lower than the formation temperature of the zone to be plugged; and (6) the curing or hardening time of the epoxy material is of short duration at downhole conditions of temperature and pressure;
(d) immediately introducing the mixture of epoxy material and hardener into a positive displacement bailer;

(e) lowering the bailer into the well and positioning the bottom of the bailer above the zone in the gravel packing to be plugged;
(f) dumping and removing the bailer;
(g) pumping a small amount of liquid into the well to squeeze the epoxy material/hardener mixture into the gravel and adjacent formation;
(h) allowing time for the epoxy material to harden; and (i) returning said well to production.

12. The process of Claim 11 in which the epoxy material is a resorcinol diglycidyl ether epoxy.

13. The process of Claim 12 in which the hardener is a tertiary amine.

14. The process of Claim 12 in which the hardener Is an imidazole compound.

15. The process of Claim 11 in which the amount of hardener used is between about 1 and about 15 parts per 100 parts of epoxy material.

16. The process of Claim 15 in which the amount of epoxy material used is between about 0.5 and about 2,0 gallons per foot of plugged interval.

17. The process of Claim 16 in which the viscosity of the epoxy material is between about 500 and about 1 cp at formation temperature.

18. The process of Claim 11 in which the set time of the mixture of epoxy material and hardener is between about 1 and about 180 minutes,

19. The process of Claim 11 in which steps (c) through (h) are repeated at least once prior to returning said well to production.

August 25, 1989 A:RWC3.34