Patent Publication Number: US-2007114032-A1

Title: Methods of consolidating unconsolidated particulates in subterranean formations

Description:
BACKGROUND  
      The present invention relates to the treatment of subterranean formations. More particularly, the present invention relates to methods for stabilizing portions of a subterranean formation that comprise unconsolidated particulates.  
      Hydrocarbon wells are often located in subterranean formations that contain unconsolidated particulates (e.g., sand, gravel, proppant, fines, etc.) that may migrate out of the subterranean formation into a well bore and/or may be produced with the oil, gas, water, and/or other fluids produced by the well. The presence of such particulates, in produced fluids is undesirable in that the particulates may abrade pumping and other producing equipment and/or reduce the production of desired fluids from the well. Moreover, particulates that have migrated into a well bore (e.g., inside the casing and/or perforations in a cased hole), among other things, may clog portions of the well bore, hindering the production of desired fluids from the well. The term “unconsolidated particulates,” and derivatives thereof, is defined herein to include loose particulates and particulates bonded with insufficient bond strength to withstand the forces created by the production of fluids through the formation. Unconsolidated particulates may comprise, among other things, sand, gravel, fines and/or proppant particulates in the subterranean formation, for example, proppant particulates placed in the subterranean formation in the course of a fracturing or gravel-packing operation. The terms “unconsolidated subterranean formations,” “unconsolidated portions of a subterranean formation,” and derivatives thereof are defined herein to include any formations that contain unconsolidated particulates, as that term is defined herein. “Unconsolidated subterranean formations,” and “unconsolidated portions of a subterranean formation,” as those terms are used herein, include subterranean fractures wherein unconsolidated particulates reside within the open space of the fracture (e.g., forming a proppant pack within the fracture).  
      One method of controlling unconsolidated particulates in subterranean formations involves placing a filtration bed containing gravel (e.g., a “gravel pack”) near the well bore to present a physical barrier to the transport of unconsolidated particulates with the production of desired fluids. Typically, such “gravel-packing operations” involve the pumping and placement of a quantity of certain particulate, into the unconsolidated subterranean formation in an area adjacent to a well bore. One common type of gravel-packing operation involves placing a screen in the well bore and packing the surrounding annulus between the screen and the well bore with gravel of a specific size designed to prevent the passage of formation sand. The screen is generally a filter assembly used to retain the gravel placed during the gravel-pack operation. A wide range of sizes and screen configurations are available to suit the characteristics of the gravel-pack sand used. Similarly, a wide range of sizes of gravel is available to suit the characteristics of the unconsolidated particulates in the subterranean formation. To install the gravel pack, the gravel is carried to the formation in the form of a slurry by mixing the gravel with a fluid, which is usually viscosified. Once the gravel is placed in the well bore, the viscosity of the treatment fluid may be reduced, and it is returned to the surface. The resulting structure presents a barrier to migrating sand from the formation while still permitting fluid flow.  
      However, the use of such gravel-packing methods may be problematic. For example, gravel packs may be time consuming and expensive to install. Due to the time and expense needed, it is sometimes desirable to place a screen without the gravel. Even in circumstances in which it is practical to place a screen without gravel, it is often difficult to determine an appropriate screen size to use as formation sands tend to have a wide distribution of grain sizes. When small quantities of sand are allowed to flow through a screen, formation erosion becomes a significant concern. As a result, the placement of gravel as well as the screen is often necessary to assure that the formation sands are controlled. Expandable sand screens have been developed and implemented in recent years. As part of the installation, an expandable sand screen may be expanded against the well bore, cased hole, or open hole for sand control purposes without the need for gravel packing. However, expandable screens may still exhibit such problems as screen erosion and screen plugging.  
      Another method used to control unconsolidated particulates in subterranean formations involves consolidating unconsolidated particulates into stable, permeable masses by applying a consolidating agent (e.g., a resin or tackifying agent) to the subterranean formation. However, it may be desirable in some cases to preferentially place a consolidating agent in a particular region of a subterranean formation (e.g., an unconsolidated portion) penetrated by a well bore. To place the consolidating agent in a specific region of a subterranean formation, certain types of isolation tools, such as “pack off” devices, packers, gel plugs, mechanical plugs, bridge plugs, ball sealers, and the like, have been used in the art to isolate certain intervals of a subterranean formation and place a consolidating agent in a region of the subterranean formation in that interval. However, the use of these isolation tools may be problematic. First, in applications where it is desirable to treat multiple regions of a subterranean formation in multiple different intervals, the isolation tools used must be removed and repositioned to isolate subsequently treated intervals, a process which may, among other things, risk damage to the subterranean formation and/or the well bore, and increase the cost, complexity, and duration of the operation. Moreover, in methods employing these isolation tools, some amount of the consolidating agent and/or associated treatment fluid(s) introduced into the subterranean formation usually “leak” into regions of the subterranean formation outside of the isolated interval, and thus those methods generally require larger amounts of consolidating agent (and/or the treatment fluid carrying the consolidating agent) to ensure that the isolated interval of the subterranean formation is completely treated.  
     SUMMARY  
      The present invention relates to the treatment of subterranean formations. More particularly, the present invention relates to methods for stabilizing portions of a subterranean formation that comprise unconsolidated particulates.  
      In one embodiment, the present invention provides a method comprising: providing a consolidating agent; introducing the consolidating agent into an unconsolidated portion of a subterranean formation through a dynamic diversion tool; and allowing the consolidating agent to at least partially consolidate the unconsolidated portion of the subterranean formation.  
      In another embodiment, the present invention provides a method comprising: providing a consolidating agent; introducing the consolidating agent into an unconsolidated portion of a subterranean formation through a dynamic diversion tool, wherein a plurality of unconsolidated proppant particulates reside within the subterranean formation; and allowing the consolidating agent to at least partially consolidate the unconsolidated proppant particulates within the unconsolidated portion of the subterranean formation.  
      In another embodiment, the present invention provides a method comprising: providing a consolidating agent; introducing the consolidating agent into an unconsolidated portion of a subterranean formation through a dynamic diversion tool, wherein a plurality of unconsolidated formation particulates reside within the subterranean formation; and allowing the consolidating agent to at least partially consolidate the unconsolidated formation particulates within the subterranean formation.  
      The features and advantages of the present invention will be apparent to those skilled in the art. While numerous changes may be made by those skilled in the art, such changes are within the spirit of the invention.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      These drawings illustrate certain aspects of some of the embodiments of the present invention, and should not be used to limit or define the invention.  
       FIG. 1  illustrates a side view of a subterranean formation that may be treated in certain embodiments of the present invention.  
       FIG. 2  illustrates a side view of a subterranean formation being treated during the course of one embodiment of the present invention.  
       FIG. 3  illustrates a side view of a subterranean formation being treated during the course of one embodiment of the present invention.  
       FIG. 4  illustrates a side view of a subterranean formation being treated during the course of one embodiment of the present invention.  
       FIG. 5  illustrates a side view of a subterranean formation being treated during the course of one embodiment of the present invention.  
       FIG. 6  illustrates a side view of a subterranean formation being treated during the course of one embodiment of the present invention.  
       FIG. 7  illustrates a side view of a subterranean formation that has been treated in the course of one embodiment of the present invention.  
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
      The present invention relates to the treatment of subterranean formations. More particularly, the present invention relates to methods for stabilizing portions of a subterranean formation that comprise unconsolidated particulates.  
     I. METHODS OF THE PRESENT INVENTION  
      The methods of the present invention generally comprise: providing a consolidating agent; introducing the consolidating agent into an unconsolidated portion of a subterranean formation through a dynamic diversion tool; and allowing the consolidating agent to at least partially consolidate the unconsolidated portion of the subterranean formation. The consolidating agent may be provided and/or introduced into the subterranean formation as a component of one or more treatment fluids introduced into the subterranean formation. The term “consolidating agent,” is defined herein to include any substance that may stabilize a portion of the subterranean formation, which may, at least in part, stabilize unconsolidated particulates such that they are prevented from shifting or migrating. The term “dynamic diversion tool” is defined herein to include any device that is capable of modifying (e.g., increasing) the velocity of a fluid into a subterranean formation from the velocity of that fluid in a well bore. The methods of the present invention may be used to at least partially consolidate a selected interval in an unconsolidated portion of a subterranean formation without the need for isolation tools used heretofore in the art.  
      The subterranean formations treated in the methods of the present invention may be any subterranean formation wherein at least a plurality of unconsolidated particulates resides in the formation. An example of such a subterranean formation is illustrated in  FIG. 1 . A well bore  110  penetrates several different intervals of the subterranean formation depicted therein; several of the intervals comprise consolidated portions  121 ,  122 ,  123 ,  124 , and  125 , while several intervals comprise unconsolidated portions  131 ,  132 ,  133 , and  134 , which comprise at least a plurality of unconsolidated particulates. These unconsolidated particulates may comprise, among other things, sand, gravel, fines and/or proppant particulates within the open space of one or more fractures in the subterranean formation (e.g., unconsolidated proppant particulates that form a proppant pack within the fracture). Proppant particulates may be comprised of any material suitable for use in subterranean operations. Examples include, but are not limited to, sand, bauxite, ceramic materials, glass materials (e.g., glass beads), polymer materials, Teflon® materials, nut shell pieces, seed shell pieces, cured resinous particulates comprising nut shell pieces, cured resinous particulates comprising seed shell pieces, fruit pit pieces, cured resinous particulates comprising fruit pit pieces, wood, composite particulates, and combinations thereof. Composite particulates also may be used, wherein suitable composite materials may comprise a binder and a filler material wherein suitable filler materials include silica, alumina, fumed carbon, carbon black, graphite, mica, titanium dioxide, meta-silicate, calcium silicate, kaolin, talc, zirconia, boron, fly ash, hollow glass microspheres, solid glass, ground nut/seed shells or husks, saw dust, ground cellulose fiber, and combinations thereof. Typically, the particulates have a size in the range of from about 2 to about 400 mesh, U.S. Sieve Series. In particular embodiments, particulates size distribution ranges are one or more of 6/12 mesh, 8/16, 12/20, 16/30, 20/40, 30/50, 40/60, 40/70, or 50/70 mesh. It should be understood that the term “particulate,” as used in this disclosure, includes all known shapes of materials including substantially spherical materials, fibrous materials, polygonal materials (such as cubic materials) and mixtures thereof. Moreover, fibrous materials that may be used, inter alia, to bear the pressure of a closed fracture, are often included. In some embodiments, the proppant particulates may be coated with any suitable resin or tackifying agent known to those of ordinary skill in the art.  
      The subterranean formations treated in the methods of the present invention may be penetrated by a well bore through which the consolidating agent and/or other treatment fluids may be introduced, for example, as shown by well bore  110  in  FIG. 1 . A well bore penetrating the subterranean formation being treated may contain one or more pipes or casing strings (e.g., a “cased” or “partially cased” well bore), as shown by casing  140  in well bore  110  in  FIG. 1 . In certain embodiments, the well bore may be uncased. In certain embodiments, a well bore penetrating the subterranean formation may contain one or more screens and/or gravel-packs, among other purposes, to decrease the migration of formation sands into the well bore. In other embodiments, the well bore may contain no such screens or gravel-packs (e.g., an “unscreened” well bore).  
      In those embodiments where the portion of the well bore penetrating the portion of the subterranean formation being treated is cased or partially cased, the dynamic diversion tool may introduce fluids and/or the consolidating agent into the subterranean formation by directing the through perforations or holes in the casing that allow fluid communication between the interior of the casing and the annulus (i.e., the space between the walls of the well bore and the outer surface of the casing). Referring now to  FIG. 1 , one or more perforations  150  may be created in the casing  140  that is set in the well bore  110  to allow fluid communication between the interior of the casing and an unconsolidated portion  134  of the subterranean formation. In certain embodiments, the dynamic diversion tool may be used to create those perforations or holes in the casing, for example, by propelling a fluid comprising abrasive materials (e.g., particulate materials such as sand, gravel, degradable particulates, and the like) at the interior surface of the casing and/or propelling a fluid at a sufficiently high pressure at the interior surface of the casing to create the perforations or holes in the casing. In other embodiments, the perforations or holes may be created using some other method or apparatus prior to or during the course of conducting a method of the present invention. In certain embodiments, particulates residing in the perforations or holes in the casing may be displaced by the consolidating agent (or the fluid comprising the consolidating agent), which may, inter alia, enhance or restore the flow of fluid through those perforations or holes in the casing.  
      Referring now to  FIG. 2 , the dynamic diversion tool  210  may be placed in the well bore with a pipe string comprising  220  coiled tubing or jointed pipe. The dynamic diversion tool  210  is placed in a portion of the well bore adjacent to an unconsolidated portion  134  of the subterranean formation. Referring now to  FIG. 3 , the consolidating agent may be introduced through the coiled tubing or jointed pipe  220  to the dynamic diversion tool  210 , where the tool may direct the consolidating agent  320  into the unconsolidated portion  134  of the subterranean formation.  
      In certain embodiments, it may not be desirable to use certain types of dynamic diversion tools that are capable of propelling fluid at a pressure sufficient to erode and/or fracture a portion of the subterranean formation. However, in certain embodiments, it may be desirable to use certain types of dynamic diversion tools that are capable of propelling fluid at a pressure to sufficient to penetrate through a gravel-pack and/or screen residing in the well bore. One of ordinary skill in the art, with the benefit of this disclosure, will recognize when certain types of dynamic diversion tools are suitable or unsuitable for a particular application of the methods of the present invention, depending upon a variety of factors, including the rate and/or pressure of fluid flow desired, the structure and/or composition of the subterranean formation, the length of the interval in the subterranean formation being treated, and the like. Examples of dynamic diversion tools that may be suitable for the methods of the present invention are described in Section II. below.  
      The methods of the present invention may optionally include providing and introducing one or more preflush fluids into the subterranean formation at any point prior to, during, or subsequent to performing the methods of the present invention. Typically, injection of a preflush fluid may occur at any time before the consolidating agent is introduced into the subterranean formation. In certain embodiments, a preflush fluid may be applied to the subterranean formation, among other purposes, to clean out undesirable substances (e.g., oil, residue, or debris) from the pore spaces in the matrix of the subterranean formation, to clean out such undesirable substances residing in perforations or holes in a casing string, and/or to prepare the subterranean formation for later placement of the consolidating agent. For example, an acidic preflush fluid may be introduced into at least a portion of the subterranean formation that may, inter alia, dissolve undesirable substances in the subterranean formation. The preflush fluid may be introduced into the subterranean formation through the dynamic diversion tool, pumped directly into the annular space between the walls of a well bore and a casing string penetrating the subterranean formation, or introduced into the subterranean formation by any other suitable means. Generally, the volume of the preflush fluid introduced into the formation is between 0.1 times to 50 times the volume of the consolidating agent. Examples of preflush fluids suitable for use with the present invention are described in more detail in Section III.A. below.  
      The methods of the present invention optionally may comprise placing a static diverting agent within a portion of the subterranean formation. As used herein, the term “static diverting agent” is defined to include any static diverting agent or tool (e.g., chemicals, fluids, particulates or equipment) that is capable of diverting the flow of fluid away from a particular portion of a subterranean formation to another portion of the subterranean formation. Among other things, the static diverting agent may aid in controlling the placement of the consolidating agent in the desired area. Examples of suitable static diverting agents include, but are not limited to fluids (e.g., aqueous-base and/or non-aqueous-base fluids), emulsions, gels, foams, degradable materials (e.g., polyesters, orthoesters, poly(orthoesters), polyanhydrides, dehydrated organic and/or inorganic compounds), particulates, packers (e.g., pinpoint packers and selective injection packers), ball sealers, pack-off devices, particulates, sand plugs, bridge plugs and the like. A person skilled in the art, with the benefit of this disclosure will recognize when a static diverting agent should be used in a method of the present invention, as well as the appropriate type of placement of the static diverting agent.  
      The methods of the present invention may be used to consolidate a single interval in an unconsolidated portion of a subterranean formation, or may be repeated to consolidate several different intervals in a subterranean formation. Referring now to  FIG. 3 , for example, the dynamic diversion tool  210  initially may be positioned within a well bore so as to introduce the consolidating agent  320  into a particular interval  134  in a portion of a subterranean formation. As shown in  FIG. 4 , after introducing the consolidating agent  320  into that particular interval  134 , the dynamic diversion tool  210  may be repositioned so as to introduce the consolidating agent  420  into another interval  133  in the subterranean formation (e.g., an interval closer to the surface than the first interval treated). As shown in  FIG. 5 , this process may be repeated for any number of other intervals comprising unconsolidated portions  132  and  131  of a subterranean formation, introducing the consolidating agent  520  into those portions of the subterranean formation. In embodiments where several different intervals are treated, the several intervals may be penetrated by a single well bore, different contiguous well bores, or different well bores that are not contiguous. After the treatment of one or more intervals, the dynamic diversion tool  210  then may be relocated to the bottom of the well bore  110 , as shown in  FIG. 5 .  
      The methods of the present invention may optionally include providing and applying one or more afterflush fluids into the subterranean formation at any stage of the treatment process. Typically, injection of an afterflush fluid may occur at any time after the consolidating agent is introduced into the subterranean formation. When used, the afterflush fluid is preferably placed into the subterranean formation while the consolidating agent is still in a flowing state. For example, an afterflush fluid may be placed into the formation prior to a shut-in period. In certain embodiments, an afterflush fluid may be applied to the subterranean formation, among other purposes, to activate the consolidating agent, and/or to restore the permeability of a portion of the subterranean formation by displacing at least a portion of the consolidating agent from the pore channels therein or forcing the displaced portion of the consolidating agent further into the subterranean formation where it may have negligible impact on subsequent hydrocarbon production. The afterflush fluid may be introduced into the subterranean formation through the dynamic diversion tool, pumped directly into the annular space between the walls of a well bore and a casing string penetrating the subterranean formation, or introduced into the subterranean formation by any other suitable means. As shown in  FIG. 6 , the dynamic diversion tool  210  may be repositioned in the well bore  110  and used to circulate an afterflush fluid  660  in the well bore to restore fluid circulation in the portion of the well bore  611  and  612  adjacent to a region  133  and  134  of the subterranean formation that was consolidated in the methods of the present invention. As shown in  FIG. 7 , this process may be repeated for each interval until fluid circulation is restored to the entire length of the well bore  711 , and the dynamic diversion tool then may be removed from the well bore. Generally, the volume of afterflush fluid introduced into the subterranean formation ranges from about 0.1 times to about 50 times the volume of the consolidating agent. In some embodiments of the present invention, the volume of afterflush fluid introduced into the subterranean formation ranges from about 0.1 times to about 5 times the volume of the consolidating agent. Examples of afterflush fluids suitable for use with the present invention are described in more detail in Section III.A. below.  
      The methods of the present invention may be used prior to, in combination with, or after any type of subterranean operation being performed in the subterranean formation, including but not limited to fracturing operations, gravel-packing operations, frac-packing operations (i.e., combination of fracturing and gravel-packing operations), and the like. For example, the methods of the present invention may be used at some time after a fracturing operation, wherein the methods of the present invention are used to at least partially consolidate proppant particulates placed within one or more fractures created or enhanced during the fracturing operation. In certain embodiments, the methods of the present invention optionally may comprise introducing other additives and treatment fluids, such as relative permeability modifiers, proppant, surfactants, gases, biocides, acids, or any other suitable additives or treatment fluids, into the subterranean formation through the dynamic diversion tool and/or by any other means suitable for introducing those additives or treatment fluids into the subterranean formation.  
     II. DYNAMIC DIVERSION TOOLS  
      The methods of the present invention utilize a dynamic diversion tool to introduce the treatment fluids into the subterranean formation. Suitable dynamic diversion tools for use in the present invention may comprise any assembly that is capable of modifying (e.g., increasing) the velocity of a fluid into a subterranean formation from the velocity of that fluid in a well bore. In certain embodiments, the dynamic diversion tool may comprise a pipe string (e.g., coiled tubing, drill pipe, etc.) with at least one port (e.g., nozzle or jet) thereon that is capable of directing the flow of fluid from within the pipe string into a subterranean formation in a desired direction. Examples of suitable dynamic diversion tools include, but are not limited to, ported subassemblies, hydroblast tools and hydrajetting tools, including those described in the following U.S. patents and patent applications, the relevant disclosures of which are incorporated herein by reference: U.S. Pat. No. 5,765,642; U.S. Pat. No. 5,249,628; U.S. Pat. No. 5,325,923; U.S. Pat. No. 5,499,678; U.S. Pat. No. 5,396,957; U.S. patent application Ser. No. 11/004,441 by East, Jr. et al. In certain embodiments, the dynamic diversion tool may comprise an acoustical tool or a pulsonic tool (e.g., a tool capable of applying a pressure pulse having a given amplitude and frequency to a fluid). Examples of suitable acoustical and pulsonic tools include, but are not limited to, fluidic oscillators, and those devices described in U.S. patent application Ser. No. 10/863,706 by Nguyen, et al., the relevant disclosure of which is incorporated herein by reference. In embodiments where the dynamic diversion tool comprises a pulsonic tool, the acoustical energy generated by the pulsonic tool may, inter alia, further stabilize the unconsolidated particulates in the subterranean formation, in conjunction with the consolidating agent used. In certain embodiments, the dynamic diversion tool may comprise an uncemented liner having jets on the outer surface of the liner.  
      The selection of a suitable dynamic diversion tool for a particular application of the present invention may depend upon a variety of factors, including the rate and/or pressure of fluid flow desired, the structure and/or composition of the subterranean formation, the length of the interval in the subterranean formation being treated, the particular composition of the fluid being introduced into the subterranean formation, and the like. For example, in certain embodiments, it may or may not be desirable to use certain types of dynamic diversion tools that are capable of propelling fluid at a pressure sufficient to erode and/or fracture a portion of the subterranean formation. One of ordinary skill in the art, with the benefit of this disclosure, will be able to recognize which types of dynamic diversion tools are suitable for a particular application of the methods of the present invention.  
     III. FLUIDS  
      In certain embodiments, the consolidating agent may be provided and/or introduced into the subterranean formation as a component of one or more treatment fluids introduced into the subterranean formation. These treatment fluids may include any fluid that does not adversely interact with the other components used in accordance with this invention or with the subterranean formation. Such treatment fluids may be aqueous-based or non-aqueous-based. Aqueous-based treatment fluids may comprise fresh water, salt water, brine, seawater, or a combination thereof. Non-aqueous-based treatment fluids may comprise one or more organic liquids, such as hydrocarbons (e.g., kerosene, xylene, toluene, or diesel), oils (e.g., mineral oils or synthetic oils), esters, and the like.  
      The preflush and afterflush fluids utilized in certain embodiments of the present invention may include any fluid that does not adversely interact with the other components used in accordance with this invention or with the subterranean formation. For example, the preflush or afterflush fluid may be an aqueous-based fluid, a hydrocarbon-based fluid (e.g., kerosene, xylene, toluene, diesel, oils, etc.), or a gas (e.g., nitrogen or carbon dioxide). Aqueous-based fluids may comprise fresh water, salt water, brine, or seawater, or any other aqueous fluid that does not adversely react with the other components used in accordance with this invention or with the subterranean formation. In certain embodiments, an aqueous-based preflush or afterflush fluid may comprise a surfactant. Any surfactant compatible with later-used treatments (e.g., the consolidating agent) may be used in the present invention, for example, to aid a consolidating agent in flowing to the contact points between adjacent particulates in the formation. Such surfactants include, but are not limited to, ethoxylated nonyl phenol phosphate esters, mixtures of one or more cationic surfactants, one or more non-ionic surfactants, and an alkyl phosphonate surfactant. Suitable mixtures of one or more cationic and nonionic surfactants are described in U.S. Pat. No. 6,311,773, the relevant disclosure of which is incorporated herein by reference. A C 12 -C 22  alkyl phosphonate surfactant is preferred. The surfactant or surfactants used may be included in the preflush or afterflush fluid in an amount sufficient to prepare the subterranean formation to receive a treatment of a consolidating agent. In some embodiments of the present invention, the surfactant is present in the preflush or afterflush fluid in an amount in the range of from about 0.1% to about 3% by weight of the aqueous fluid.  
      The treatment fluids, preflush fluids, and/or afterflush fluids utilized in methods of the present invention may comprise any number of additional additives, including, but not limited to, salts, surfactants, acids, fluid loss control additives, gas, foamers, corrosion inhibitors, scale inhibitors, catalysts, clay control agents, biocides, friction reducers, antifoam agents, bridging agents, dispersants, flocculants, H 2 S scavengers, CO 2  scavengers, oxygen scavengers, lubricants, viscosifiers, breakers, weighting agents, relative permeability modifiers, particulate materials (e.g., proppant particulates) and the like. In certain embodiments the treatment fluids, preflush fluids, and/or afterflush fluids may comprise an activator or catalyst which may be used inter alia, to activate the polymerization of the consolidating agent. A person skilled in the art, with the benefit of this disclosure, will recognize the types of additives that may be included in the treatment fluids, preflush fluids, and/or afterflush fluids for a particular application.  
     IV. CONSOLIDATING AGENTS  
      Suitable consolidating agents for the methods at the present invention include any composition that may stabilize a portion of the subterranean formation, which may, at least in part, stabilize unconsolidated particulates such that they are prevented from shifting or migrating. Examples of suitable consolidating agents include resins, tackifying agents, and gelable liquid compositions.  
      A. Resins  
      Resins suitable for use as the consolidating agents in the methods of the present invention include any suitable resin that is capable of forming a hardened, consolidated mass. The term “resin” as used herein includes any of numerous physically similar polymerized synthetics or chemically modified natural resins, including but not limited to thermoplastic materials and thermosetting materials. Many such resins are commonly used in subterranean consolidation operations, and some suitable resins include two component epoxy based resins, novolak resins, polyepoxide resins, phenol-aldehyde resins, urea-aldehyde resins, urethane resins, phenolic resins, furan resins, furan/furfuryl alcohol resins, phenolic/latex resins, phenol formaldehyde resins, polyester resins and hybrids and copolymers thereof, polyurethane resins and hybrids and copolymers thereof, acrylate resins, and mixtures thereof. Some suitable resins, such as epoxy resins, may be cured with an internal catalyst or activator so that when pumped downhole, they may be cured using only time and temperature. Other suitable resins, such as furan resins, may be formulated to cure at a delayed rate, or require a time-delayed catalyst or an external catalyst to help activate the polymerization of the resins if the cure temperature is low (i.e., less than 250° F.) but will cure under the effect of time and temperature if the formation temperature is above about 250° F., preferably above about 300° F. Such external catalysts may be introduced into the subterranean formation through the dynamic diversion tool (e.g., as a component of a treatment fluid) and/or by some other means (e.g., pumped into the annulus from the surface). It is within the ability of one skilled in the art, with the benefit of this disclosure, to select a suitable resin for use in embodiments of the present invention and to determine whether a catalyst is required to trigger curing.  
      Selection of a suitable resin may be affected by the temperature of the subterranean formation to which the fluid will be introduced. By way of example, for subterranean formations having a bottom hole static temperature (“BHST”) ranging from about 60° F. to about 250° F., two-component epoxy-based resins comprising a hardenable resin component and a hardening agent component containing specific hardening agents may be preferred. For subterranean formations having a BHST ranging from about 300° F. to about 600° F., a furan-based resin may be preferred. For subterranean formations having a BHST ranging from about 200° F. to about 400° F., either a phenolic-based resin or a one-component HT epoxy-based resin may be suitable. For subterranean formations having a BHST of at least about 175° F., a phenol/phenol formaldehyde/furfuryl alcohol resin may also be suitable.  
      Any solvent that is compatible with the chosen resin and achieves the desired viscosity effect is suitable for use in the present invention. Some preferred solvents are those having high flash points (e.g., about 125° F.) because of, among other things, environmental and safety concerns; such solvents include butyl lactate, butylglycidyl ether, dipropylene glycol methyl ether, dipropylene glycol dimethyl ether, dimethyl form amide, diethyleneglycol methyl ether, ethyleneglycol butyl ether, diethyleneglycol butyl ether, propylene carbonate, methanol, butyl alcohol, d-limonene, fatty acid methyl esters, and combinations thereof. Other preferred solvents include aqueous dissolvable solvents such as, methanol, isopropanol, butanol, glycol ether solvents, and combinations thereof. Suitable glycol ether solvents include, but are not limited to, diethylene glycol methyl ether, dipropylene glycol methyl ether, 2-butoxy ethanol, ethers of a C 2  to C 6  dihydric alkanol containing at least one C 1  to C 6  alkyl group, mono ethers of dihydric alkanols, methoxypropanol, butoxyethanol, hexoxyethanol, and isomers thereof. Selection of an appropriate solvent is dependent on the resin chosen and is within the ability of one skilled in the art with the benefit of this disclosure.  
      B. Tackifying Agents  
      Tackifying agents suitable for use in the methods of the present invention exhibit a sticky character and, thus, impart a degree of consolidation to unconsolidated particulates in the subterranean formation. The term “tackifying agent” is defined herein to include any composition having a nature such that it is (or may be activated to become) somewhat sticky to the touch. In certain embodiments, the tackifying agent may be formulated such that it is “activated” at a delayed rate, by contact with a catalyst or activator, or at certain conditions (e.g., temperature). Examples of suitable tackifying agents suitable for use in the present invention include non-aqueous tackifying agents, aqueous tackifying agents, and silyl-modified polyamides.  
      One type of tackifying agent suitable for use in the present invention is a non-aqueous tackifying agent. An example of a suitable tackifying agent may comprise polyamides that are liquids or in solution at the temperature of the subterranean formation such that they are, by themselves, non-hardening when introduced into the subterranean formation. One example of such a tackifying agent comprises a condensation reaction product comprised of commercially available polyacids and a polyamine. Suitable commercial products include compounds such as mixtures of C 36  dibasic acids containing some trimer and higher oligomers and also small amounts of monomer acids that are reacted with polyamines. Other polyacids include trimer acids, synthetic acids produced from fatty acids, maleic anhydride, acrylic acid, and the like. Such acid compounds are commercially available from companies such as Witco Corporation, Union Camp, Chemtall, and Emery Industries. The reaction products are available from, for example, Champion Technologies, Inc. and Witco Corporation. Additional compounds which may be used as non-aqueous tackifying agents include liquids and solutions of, for example, polyesters, polycarbonates and polycarbamates, natural resins such as shellac and the like. Other suitable non-aqueous tackifying agents are described in U.S. Pat. Nos. 5,853,048 and 5,833,000, the relevant disclosures of which are herein incorporated by reference.  
      Non-aqueous tackifying agents suitable for use in the present invention may be either used such that they form non-hardening coating, or they may be combined with a multifunctional material capable of reacting with the non-aqueous tackifying agent to form a hardened coating. A “hardened coating,” as used herein, means that the reaction of the tackifying agent with the multifunctional material will result in a substantially non-flowable reaction product that exhibits a higher compressive strength in a consolidated agglomerate than the tackifying agent alone with the particulates. In this instance, the non-aqueous tackifying agent may function similarly to a hardenable resin. Multifunctional materials suitable for use in the present invention include, but are not limited to, aldehydes such as formaldehyde, dialdehydes such as glutaraldehyde, hemiacetals or aldehyde releasing compounds, diacid halides, dihalides such as dichlorides and dibromides, polyacid anhydrides such as citric acid, epoxides, furfuraldehyde, glutaraldehyde or aldehyde condensates and the like, and combinations thereof. In some embodiments of the present invention, the multifunctional material may be mixed with the tackifying agent in an amount of from about 0.01 to about 50 percent by weight of the tackifying agent to effect formation of the reaction product. In some preferable embodiments, the multifunctional material is present in an amount of from about 0.5 to about 1 percent by weight of the tackifying compound. Suitable multifunctional materials are described in U.S. Pat. No. 5,839,510, the relevant disclosure of which is herein incorporated by reference.  
      Solvents suitable for use with non-aqueous tackifying agents include any solvent that is compatible with the non-aqueous tackifying agent and achieves the desired viscosity effect. The solvents that can be used in the present invention preferably include those having high flash points (most preferably above about 125° F.). Examples of solvents suitable for use in the present invention include, but are not limited to, butylglycidyl ether, dipropylene glycol methyl ether, butyl bottom alcohol, dipropylene glycol dimethyl ether, diethyleneglycol methyl ether, ethyleneglycol butyl ether, methanol, butyl alcohol, isopropyl alcohol, diethyleneglycol butyl ether, propylene carbonate, d-limonene, 2-butoxy ethanol, butyl acetate, furfuryl acetate, butyl lactate, dimethyl sulfoxide, dimethyl formamide, fatty acid methyl esters, and combinations thereof. It is within the ability of one skilled in the art, with the benefit of this disclosure, to determine whether a solvent is needed to achieve a viscosity suitable to the subterranean conditions and, if so, how much.  
      Aqueous tackifying agents suitable for use in the present invention are not significantly tacky when placed onto a particulate, but are capable of being “activated” (that is, destabilized, coalesced, and/or reacted) to transform the compound into a sticky, tackifying compound at a desirable time. Such activation may occur before, during, or after the aqueous tackifier agent is placed in the subterranean formation. In some embodiments, a pretreatment may be first contacted with the surface of a particulate to prepare it to be coated with an aqueous tackifying agent. Suitable aqueous tackifying agents are generally charged polymers that comprise compounds that, when in an aqueous solvent or solution, will form a non-hardening coating (by itself or with an activator and/or catalyst) and, when placed on a particulate, will increase the continuous critical resuspension velocity of the particulate when contacted by a stream of water. The aqueous tackifying agent may enhance the grain-to-grain contact between the individual particulates within the formation (be they proppant particulates, formation fines, or other particulates), helping bring about the consolidation of the particulates into a cohesive, flexible, and permeable mass. When used, the activator and/or catalyst may be a component of a treatment fluid comprising the aqueous tackifying agent, or may be introduced into the subterranean formation separately through the dynamic diversion tool (e.g., as a component of a treatment fluid) or by some other means (e.g., pumped into the annulus from the surface).  
      Examples of aqueous tackifying agents suitable for use in the present invention include, but are not limited to, acrylic acid polymers, acrylic acid ester polymers, acrylic acid derivative polymers, acrylic acid homopolymers, acrylic acid ester homopolymers (such as poly(methyl acrylate), poly(butyl acrylate), and poly(2-ethylhexyl acrylate)), acrylic acid ester co-polymers, methacrylic acid derivative polymers, methacrylic acid homopolymers, methacrylic acid ester homopolymers (such as poly(methyl methacrylate), poly(butyl methacrylate), and poly(2-ethylhexyl methacryate)), acrylamido-methyl-propane sulfonate polymers, acrylamido-methyl-propane sulfonate derivative polymers, acrylamido-methyl-propane sulfonate co-polymers, and acrylic acid/acrylamido-methyl-propane sulfonate co-polymers, and combinations thereof. The term “derivative” is defined herein to include any compound that is made from one of the listed compounds, for example, by replacing one atom in one of the listed compounds with another atom or group of atoms, ionizing one of the listed compounds, or creating a salt of one of the listed compounds. Methods of determining suitable aqueous tackifying agents and additional disclosure on aqueous tackifying agents can be found in U.S. patent application Ser. No. 10/864,061, filed Jun. 9, 2004, and U.S. patent application Ser. No. 10/864,618, filed Jun. 9, 2004, the relevant disclosures of which are hereby incorporated by reference.  
      Silyl-modified polyamide compounds suitable for use in the tackifying agents in the methods of the present invention may be described as substantially self-hardening compositions that are capable of at least partially adhering to particulates in the unhardened state, and that are further capable of self-hardening themselves to a substantially non-tacky state to which individual particulates such as formation fines will not adhere to, for example, in formation or proppant pack pore throats. Such silyl-modified polyamides may be based, for example, on the reaction product of a silating compound with a polyamide or a mixture of polyamides. The polyamide or mixture of polyamides may be one or more polyamide intermediate compounds obtained, for example, from the reaction of a polyacid (e.g., diacid or higher) with a polyamine (e.g., diamine or higher) to form a polyamide polymer with the elimination of water. Other suitable silyl-modified polyamides and methods of making such compounds are described in U.S. Pat. No. 6,439,309, the relevant disclosure of which is herein incorporated by reference.  
      Some suitable tackifying agents are described in U.S. Pat. No. 5,249,627 by Harms, et al., the relevant disclosure of which is incorporated by reference. Harms discloses aqueous tackifying agents that comprise at least one member selected from the group consisting of benzyl coco di-(hydroxyethyl) quaternary amine, p-T-amyl-phenol condensed with formaldehyde, and a copolymer comprising from about 80% to about 100% C 1-30  alkylmethacrylate monomers and from about 0% to about 20% hydrophilic monomers. In some embodiments, the aqueous tackifying agent may comprise a copolymer that comprises from about 90% to about 99.5% 2-ethylhexylacrylate and from about 0.5% to about 10% acrylic acid. Suitable hydrophilic monomers may be any monomer that will provide polar oxygen-containing or nitrogen-containing groups. Suitable hydrophilic monomers include dialkyl amino alkyl (meth) acrylates and their quaternary addition and acid salts, acrylamide, N-(dialkyl amino alkyl) acrylamide, methacrylamides and their quaternary addition and acid salts, hydroxy alkyl (meth)acrylates, unsaturated carboxylic acids such as methacrylic acid or preferably acrylic acid, hydroxyethyl acrylate, acrylamide, and the like. These copolymers can be made by any suitable emulsion polymerization technique. Methods of producing these copolymers are disclosed, for example, in U.S. Pat. No. 4,670,501, the relevant disclosure of which is incorporated herein by reference.  
      C. Gelable Liquid Compositions  
      Gelable liquid compositions suitable for use in the methods of the present invention may comprise any gelable liquid composition capable of converting into a gelled substance capable of substantially plugging the permeability of the formation while allowing the formation to remain flexible. That is, the gelled substance should negatively impact the ability of the formation to produce desirable fluids such as hydrocarbons. As discussed above, the permeability of the formation may be restored through use of an afterflush fluid or by fracturing through the consolidated portion. As referred to herein, the term “flexible” refers to a state wherein the treated formation or material is relatively malleable and elastic and able to withstand substantial pressure cycling without substantial breakdown. Thus, the resultant gelled substance should be a semi-solid, immovable, gel-like substance, which, among other things, stabilizes the treated portion of the formation while allowing the formation to absorb the stresses created during pressure cycling. As a result, the gelled substance may aid in preventing breakdown of the formation both by stabilizing and by adding flexibility to the formation sands. Examples of suitable gelable liquid compositions include, but are not limited to, resin compositions that cure to form flexible gels, gelable aqueous silicate compositions, crosslinkable aqueous polymer compositions, and polymerizable organic monomer compositions.  
      Certain embodiments of the gelable liquid compositions comprise curable resin compositions. Curable resin compositions are well known to those skilled in the art and have been used to consolidate portions of unconsolidated formations and to consolidate proppant materials into hard, permeable masses. While the curable resin compositions used in accordance with the present invention may be similar to those previously used to consolidate sand and proppant into hard, permeable masses, they are distinct in that resins suitable for use with the present invention do not cure into hard, permeable masses; rather they cure into flexible, gelled substances. That is, suitable curable resin compositions form resilient gelled substances between the particulates of the treated portion of the unconsolidated formation and thus allow that portion of the formation to remain flexible and to resist breakdown. It is not necessary or desirable for the cured resin composition to solidify and harden to provide high consolidation strength to the treated portion of the formation. On the contrary, upon being cured, the curable resin compositions useful in accordance with this invention form semi-solid, immovable, gelled substances.  
      Generally, the curable resin compositions useful in accordance with the present invention may comprise a curable resin, a diluent, and a resin curing agent. When certain resin curing agents, such as polyamides, are used in the curable resin compositions, the compositions form the semi-solid, immovable, gelled substances described above. Where the resin curing agent used may cause the organic resin compositions to form hard, brittle material rather than a desired gelled substance, the curable resin compositions may further comprise one or more “flexibilizer additives” (described in more detail below) to provide flexibility to the cured compositions.  
      Examples of curable resins that can be used in the curable resin compositions of the present invention include, but are not limited to, organic resins such as polyepoxide resins (e.g., bisphenol A-epichlorihydrin resins), polyester resins, urea-aldehyde resins, furan resins, urethane resins, and mixtures thereof. Of these, polyepoxide resins are preferred.  
      Any diluent that is compatible with the curable resin and achieves the desired viscosity effect is suitable for use in the present invention. Examples of diluents that may be used in the curable resin compositions of the present invention include, but are not limited to, phenols; formaldehydes; furfuryl alcohols; furfurals; alcohols; ethers such as butyl glycidyl ether and cresyl glycidyl etherphenyl glycidyl ether; and mixtures thereof. In some embodiments of the present invention, the diluent comprises butyl lactate. The diluent may be used to reduce the viscosity of the curable resin composition to from about 3 to about 3,000 centipoises (“cP”) at 80° F. Among other things, the diluent acts to provide flexibility to the cured composition. The diluent may be included in the curable resin composition in an amount sufficient to provide the desired viscosity effect. Generally, the diluent used is included in the curable resin composition in amount in the range of from about 5% to about 75% by weight of the curable resin.  
      Generally, any resin curing agent that may be used to cure an organic resin is suitable for use in the present invention. When the resin curing agent chosen is an amide or a polyamide, generally no flexibilizer additive will be required because, inter alia, such curing agents cause the curable resin composition to convert into a semi-solid, immovable, gelled substance. Other suitable resin curing agents (such as an amine, a polyamine, methylene dianiline, and other curing agents known in the art) will tend to cure into a hard, brittle material and will thus benefit from the addition of a flexibilizer additive. Generally, the resin curing agent used is included in the curable resin composition, whether a flexibilizer additive is included or not, in an amount in the range of from about 5% to about 75% by weight of the curable resin. In some embodiments of the present invention, the resin curing agent used is included in the curable resin composition in an amount in the range of from about 20% to about 75% by weight of the curable resin.  
      As noted above, flexibilizer additives may be used, inter alia, to provide flexibility to the gelled substances formed from the curable resin compositions. The term “flexibilizer additive” is defined herein to include any substance that is capable of imparting properties of flexibility (e.g., malleability, elasticity) to the gelled substances formed from the curable resin compositions. Flexibilizer additives should be used where the resin curing agent chosen would cause the organic resin composition to cure into a hard and brittle material instead of desired gelled substances described herein. For example, flexibilizer additives may be used where the resin curing agent chosen is not an amide or polyamide. Examples of suitable flexibilizer additives include, but are not limited to, an organic ester, an oxygenated organic solvent, an aromatic solvent, and combinations thereof. Of these, ethers, such as dibutyl phthalate, are preferred. Where used, the flexibilizer additive may be included in the curable resin composition in an amount in the range of from about 5% to about 80% by weight of the curable resin. In some embodiments of the present invention, the flexibilizer additive may be included in the curable resin composition in an amount in the range of from about 20% to about 45% by weight of the curable resin.  
      In other embodiments, the gelable liquid compositions may comprise a gelable aqueous silicate composition. Generally, the gelable aqueous silicate compositions that are useful in accordance with the present invention generally comprise an aqueous alkali metal silicate solution and a temperature activated catalyst for gelling the aqueous alkali metal silicate solution.  
      The aqueous alkali metal silicate solution component of the gelable aqueous silicate compositions generally comprises an aqueous liquid and an alkali metal silicate. The aqueous liquid component of the aqueous alkali metal silicate solution generally may be fresh water, salt water (e.g., water containing one or more salts dissolved therein), brine (e.g., saturated salt water), seawater, or any other aqueous liquid that does not adversely react with the other components used in accordance with this invention or with the subterranean formation. Examples of suitable alkali metal silicates include, but are not limited to, one or more of sodium silicate, potassium silicate, lithium silicate, rubidium silicate, or cesium silicate. Of these, sodium silicate is preferred. While sodium silicate exists in many forms, the sodium silicate used in the aqueous alkali metal silicate solution preferably has a Na 2 O-to-SiO 2  weight ratio in the range of from about 1:2 to about 1:4. Most preferably, the sodium silicate used has a Na 2 O-to-SiO 2  weight ratio in the range of about 1:3.2. Generally, the alkali metal silicate is present in the aqueous alkali metal silicate solution component in an amount in the range of from about 0.1% to about 10% by weight of the aqueous alkali metal silicate solution component.  
      The temperature-activated catalyst component of the gelable aqueous silicate compositions is used, inter alia, to convert the gelable aqueous silicate compositions into the desired semi-solid, immovable, gelled substance described above. Selection of a temperature activated catalyst is related, at least in part, to the temperature of the subterranean formation to which the gelable aqueous silicate composition will be introduced. The temperature activated catalysts which can be used in the gelable aqueous silicate compositions of the present invention include, but are not limited to, ammonium sulfate, which is most suitable in the range of from about 60° F. to about 240° F.; sodium acid pyrophosphate, which is most suitable in the range of from about 60° F. to about 240° F.; citric acid, which is most suitable in the range of from about 60° F. to about 120° F.; and ethyl acetate, which is most suitable in the range of from about 60° F. to about 120° F. Generally, the temperature activated catalyst is present in the range of from about 0.1% to about 5% by weight of the gelable aqueous silicate composition. When used, the temperature activated catalyst may be a component of a treatment fluid comprising the gelable aqueous silicate composition, or may be introduced into the subterranean formation separately through the dynamic diversion tool (e.g., as a component of a treatment fluid) or by some other means (e.g., pumped into the annulus from the surface).  
      In other embodiments, the gelable liquid compositions may comprise crosslinkable aqueous polymer compositions. Generally, suitable crosslinkable aqueous polymer compositions may comprise an aqueous solvent, a crosslinkable polymer, and a crosslinking agent.  
      The aqueous solvent may be any aqueous solvent in which the crosslinkable composition and the crosslinking agent may be dissolved, mixed, suspended, or dispersed therein to facilitate gel formation. For example, the aqueous solvent used may be fresh water, salt water, brine, seawater, or any other aqueous liquid that does not adversely react with the other components used in accordance with this invention or with the subterranean formation.  
      Examples of crosslinkable polymers that can be used in the crosslinkable aqueous polymer compositions include, but are not limited to, carboxylate-containing polymers and acrylamide-containing polymers. Preferred acrylamide-containing polymers include polyacrylamide, partially hydrolyzed polyacrylamide, copolymers of acrylamide and acrylate, and carboxylate-containing terpolymers and tetrapolymers of acrylate. Additional examples of suitable crosslinkable polymers include hydratable polymers comprising polysaccharides and derivatives thereof and that contain one or more of the monosaccharide units galactose, mannose, glucoside, glucose, xylose, arabinose, fructose, glucuronic acid, or pyranosyl sulfate. Suitable natural hydratable polymers include, but are not limited to, guar gum, locust bean gum, tara, konjak, tamarind, starch, cellulose, karaya, xanthan, tragacanth, and carrageenan, and derivatives of all of the above. Suitable hydratable synthetic polymers and copolymers that may be used in the crosslinkable aqueous polymer compositions include, but are not limited to, polyacrylates, polymethacrylates, polyacrylamides, maleic anhydride, methylvinyl ether polymers, polyvinyl alcohols, and polyvinylpyrrolidone. The crosslinkable polymer used should be included in the crosslinkable aqueous polymer composition in an amount sufficient to form the desired gelled substance in the subterranean formation. In some embodiments of the present invention, the crosslinkable polymer is included in the crosslinkable aqueous polymer composition in an amount in the range of from about 1% to about 30% by weight of the aqueous solvent. In another embodiment of the present invention, the crosslinkable polymer is included in the crosslinkable aqueous polymer composition in an amount in the range of from about 1% to about 20% by weight of the aqueous solvent.  
      The crosslinkable aqueous polymer compositions of the present invention may further comprise a crosslinking agent for crosslinking the crosslinkable polymers to form the desired gelled substance. In some embodiments, the crosslinking agent may be a molecule or complex containing a reactive transition metal cation. A most preferred crosslinking agent comprises trivalent chromium cations complexed or bonded to anions, atomic oxygen, or water. Examples of suitable crosslinking agents include, but are not limited to, compounds or complexes containing chromic acetate and/or chromic chloride. Other suitable transition metal cations include chromium VI within a redox system, aluminum III, iron II, iron III, and zirconium IV.  
      The crosslinking agent should be present in the crosslinkable aqueous polymer compositions of the present invention in an amount sufficient to provide, inter alia, the desired degree of crosslinking. In some embodiments of the present invention, the crosslinking agent is present in the crosslinkable aqueous polymer compositions of the present invention in an amount in the range of from 0.01% to about 5% by weight of the crosslinkable aqueous polymer composition. The exact type and amount of crosslinking agent or agents used depends upon the specific crosslinkable polymer to be crosslinked, formation temperature conditions, and other factors known to those individuals skilled in the art.  
      Optionally, the crosslinkable aqueous polymer compositions may further comprise a crosslinking delaying agent, such as a polysaccharide crosslinking delaying agents derived from guar, guar derivatives, or cellulose derivatives. The crosslinking delaying agent may be included in the crosslinkable aqueous polymer compositions, inter alia, to delay crosslinking of the crosslinkable aqueous polymer compositions until desired. One of ordinary skill in the art, with the benefit of this disclosure, will know the appropriate amount of the crosslinking delaying agent to include in the crosslinkable aqueous polymer compositions for a desired application.  
      In other embodiments, the gelled liquid compositions may comprise polymerizable organic monomer compositions. Generally, suitable polymerizable organic monomer compositions may comprise an aqueous-base fluid, a water-soluble polymerizable organic monomer, an oxygen scavenger, and a primary initiator.  
      The aqueous-base fluid component of the polymerizable organic monomer composition generally may be fresh water, salt water, brine, seawater, or any other aqueous liquid that does not adversely react with the other components used in accordance with this invention or with the subterranean formation.  
      A variety of monomers are suitable for use as the water-soluble polymerizable organic monomers in the present invention. Examples of suitable monomers include, but are not limited to, acrylic acid, methacrylic acid, acrylamide, methacrylamide, 2-methacrylamino-2-methylpropane sulfonic acid, 2-dimethylacrylamide, vinyl sulfonic acid, N,N-dimethylaminoethylmethacrylate, 2-triethylammoniumethylmethacrylate chloride, N,N-dimethyl-aminopropylmethacryl-amide, methacrylamidepropyltriethylammonium chloride, N-vinyl pyrrolidone, vinyl-phosphonic acid, and methacryloyloxyethyl trimethylammonium sulfate, and mixtures thereof. Preferably, the water-soluble polyrnerizable organic monomer should be self crosslinking. Examples of suitable monomers which are self crosslinking include, but are not limited to, hydroxyethylacrylate, hydroxymethylacrylate, hydroxyethylmethacrylate, N-hydroxymethylacrylamide, N-hydroxymethyl-methacrylamide, polyethylene glycol acrylate, polyethylene glycol methacrylate, polypropylene glycol acrylate, polypropylene glycol methacrylate, and mixtures thereof. Of these, hydroxyethylacrylate is preferred. An example of a particularly preferable monomer is hydroxyethylcellulose-vinyl phosphoric acid.  
      The water-soluble polymerizable organic monomer (or monomers where a mixture thereof is used) should be included in the polymerizable organic monomer composition in an amount sufficient to form the desired gelled substance after placement of the polymerizable organic monomer composition into the subterranean formation. In some embodiments of the present invention, the water-soluble polymerizable organic monomer(s) are included in the polymerizable organic monomer composition in an amount in the range of from about 1% to about 30% by weight of the aqueous-base fluid. In another embodiment of the present invention, the water-soluble polymerizable organic monomer(s) are included in the polymerizable organic monomer composition in an amount in the range of from about 1% to about 20% by weight of the aqueous-base fluid.  
      The presence of oxygen in the polymerizable organic monomer composition may inhibit the polymerization process of the water-soluble polymerizable organic monomer or monomers. Therefore, an oxygen scavenger, such as stannous chloride, may be included in the polymerizable monomer composition. In order to improve the solubility of stannous chloride so that it may be readily combined with the polymerizable organic monomer composition on the fly, the stannous chloride may be pre-dissolved in a hydrochloric acid solution. For example, the stannous chloride may be dissolved in a 0.1% by weight aqueous hydrochloric acid solution in an amount of about 10% by weight of the resulting solution. The resulting stannous chloride-hydrochloric acid solution may be included in the polymerizable organic monomer composition in an amount in the range of from about 0.1% to about 10% by weight of the polymerizable organic monomer composition. Generally, the stannous chloride may be included in the polymerizable organic monomer composition of the present invention in an amount in the range of from about 0.005% to about 0.1% by weight of the polymerizable organic monomer composition.  
      The primary initiator is used, inter alia, to initiate polymerization of the water-soluble polymerizable organic monomer(s) used in the present invention. Any compound or compounds which form free radicals in aqueous solution may be used as the primary initiator. The free radicals act, inter alia, to initiate polymerization of the water-soluble polymerizable organic monomer(s) present in the polymerizable organic monomer composition. Compounds suitable for use as the primary initiator include, but are not limited to, alkali metal persulfates; peroxides; oxidation-reduction systems employing reducing agents, such as sulfites in combination with oxidizers; and azo polymerization initiators. Preferred azo polymerization initiators include 2,2′-azobis(2-imidazole-2-hydroxyethyl) propane, 2,2′-azobis(2-aminopropane), 4,4′-azobis(4-cyanovaleric acid), and 2,2′-azobis(2-methyl-N-(2-hydroxyethyl) propionamide. Generally, the primary initiator should be present in the polymerizable organic monomer composition in an amount sufficient to initiate polymerization of the water-soluble polymerizable organic monomer(s). In certain embodiments of the present invention, the primary initiator is present in the polymerizable organic monomer composition in an amount in the range of from about 0.1% to about 5% by weight of the water-soluble polymerizable organic monomer(s).  
      Optionally, the polymerizable organic monomer compositions further may comprise a secondary initiator. A secondary initiator may be used, for example, where the immature aqueous gel is placed into a subterranean formation that is relatively cool as compared to the surface mixing, such as when placed below the mud line in offshore operations. The secondary initiator may be any suitable water-soluble compound or compounds that may react with the primary initiator to provide free radicals at a lower temperature. An example of a suitable secondary initiator is triethanolamine. In some embodiments of the present invention, the secondary initiator is present in the polymerizable organic monomer composition in an amount in the range of from about 0.1% to about 5% by weight of the water-soluble polymerizable organic monomer(s).  
      Optionally, the polymerizable organic monomer compositions of the present invention further may comprise a crosslinking agent for crosslinking the polymerizable organic monomer compositions in the desired gelled substance. In some embodiments, the crosslinking agent is a molecule or complex containing a reactive transition metal cation. A most preferred crosslinking agent comprises trivalent chromium cations complexed or bonded to anions, atomic oxygen, or water. Examples of suitable crosslinking agents include, but are not limited to, compounds or complexes containing chromic acetate and/or chromic chloride. Other suitable transition metal cations include chromium VI within a redox system, aluminum III, iron II, iron III, and zirconium IV. Generally, the crosslinking agent may be present in polymerizable organic monomer compositions in an amount in the range of from 0.01% to about 5% by weight of the polymerizable organic monomer composition.  
      Therefore, the present invention is well adapted to attain the ends and advantages mentioned as well as those that are inherent therein. The particular embodiments disclosed above are illustrative only, as the present invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. While numerous changes may be made by those skilled in the art, such changes are encompassed within the spirit of this invention as defined by the appended claims. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular illustrative embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the present invention. In particular, every range of values (e.g., “from about a to about b,” or, equivalently, “from approximately a to b,” or, equivalently, “from approximately a-b”) disclosed herein is to be understood as referring to the power set (the set of all subsets) of the respective range of values. The terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee.