Lost circulation additive, lost circulation treatment fluid made therefrom, and method of minimizing lost circulation in a subterranean formation

Abstract

For lost circulation treatment for decreasing fluid loss from a borehole into a subterranean formation, a lost circulation additive including water soluble crosslinkable polymer, a crosslinking agent, a filter aid that is preferably diatomaceous earth, and optionally a reinforcing material. The method of forming a lost circulation fluid includes contacting the additive with water or an aqueous solution, with a method of lost circulation treatment of the formation further including the step of injecting the fluid into the formation thereby decreasing fluid loss from the borehole into the subterranean formation.

Description

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to lost circulation additives and to methods of making such additives, to lost circulation treatment fluids made therefrom and methods of making such fluids, to methods of modifying a well fluid using such additives and/or fluids, to methods of operating a well using such additives and/or fluids, and to methods of minimizing lost circulation in a well using such additives and/or fluids. In another aspect, the present invention relates to lost circulation additives comprising polymer, crosslinking agent, and filter aid and to methods of making such additives, to lost circulation treatment fluids made therefrom and methods of making such fluids, to methods of modifying a well fluid using such additives and/or fluids, to methods of operating a well using such additives and/or fluids, and to methods of minimizing lost circulation in a well using such additives and/or fluids. In even another aspect, the present invention relates to lost circulation additives comprising a dry mixture of polymer, crosslinking agent, and filter aid and to methods of making such additives, to lost circulation treatment fluids made therefrom and methods of making such fluids, to methods of modifying a well fluid using such additives and/or fluids, and to methods of minimizing lost circulation in a well using such additives and/or fluids. In still another aspect, the present invention relates to lost circulation additives comprising polymer, crosslinking agent, and diatomaceous earth (“DE”), to lost circulation treatment fluids made therefrom, to methods of minimizing lost circulation in a well using such fluids.

[0003] 2. Description of the Related Art

[0004] Subterranean wells are utilized to reach desirable oil and/or gas bearing formations, and are generally drilled utilizing rotary drilling techniques. In such rotary drilling of wells for oil and gas, drilling fluids (“muds”) are circulated into the well through hollow tubular drill pipe, past the teeth of the cutter head to sweep away the cuttings from the cutter head, and returned to the surface along with the cuttings through the annulus surrounding the drill pipe. The drilling fluid is generally circulated in such a manner as to remove drill cuttings to prevent clogging of the cutter and to support the walls of the well hole. Such drill cuttings are entrained in the drilling fluid and brought to the surface with the fluid and then screened out and discarded. In addition to removing drill cuttings and supporting the walls of the well hole, the drilling fluid also serves to cool and lubricate the drill bit and, in the case of systems employing downhole drill motors, it functions as a power fluid for the drill motor.

[0005] Typically, drilling fluids may be water-base, employing a base of fresh water, salt water, or an oil-in-water emulsion in which water forms the continuous phase, or oil-base, employing a relatively pure oil such as crude petroleum oil or diesel oil, or in may be an “invert” emulsion, a water-in-oil emulsion in which oil forms the continuous phase or a synthetic base employing a polymer.

[0006] Drilling fluids normally contain clays and/or other dispersed solids which are employed to impart desired Theological properties to the drilling fluid. Not only do these clays and/or other suspended solids impart desirable thixotropic properties to the drilling fluid, they also serve to coat the walls of the well with a relatively impermeable sheath, commonly termed a filter cake, which retards the flow of fluid from the well into the surrounding subterranean formations.

[0007] In addition to clays and/or other suspended particles, a drilling fluid may also contain one or more weighting agents which function to increase the density of the fluid to a level which will offset high pressures encountered during the drilling operation. Non-limiting examples of suitable weighting agents which may be used in either water base or oil base drilling fluids include heavy minerals such as barite and gelena.

[0008] One problem very commonly encountered during rotary drilling operations is the problem of lost circulation in which part or all of the drilling fluid is not returned to the surface. This problem may manifest itself anywhere from moderate losses of the drilling fluid, to substantial or even total losses of the drilling fluid such that little or none of it is returned to the surface. Where a formation zone is identified in which unacceptably large amounts of drilling fluid is lost, such formation zone is commonly termed a “loss zone” or a loss circulation zone.” While there are many causes for loss circulation, non-limiting examples include those situations when the well encounters a formation of unusually high permeability or one which has naturally occurring horizontal or vertical fractures or fissures. Also, the formation may be fractured accidentally by the hydrostatic pressure exerted by the drilling mud, particularly when a change over to a relatively heavy mud is made in order to control high formation pressures.

[0009] As can be expected, over the years numerous techniques have been developed to prevent or reduce loss circulation. One common technique where the loss circulation is not so severe is to add various fluid loss agents which function to change the rheological properties of the drilling mud in order to increase its resistence to flow from the well bore into the formation. Such fluid loss agents include synthetic polymeric thickening agents such as partially hydrolyzed polyacrylamide, polyelectrolite such as an ionic polysaccharide, various gums such as locust bean gum and guar gum, various starches, and carboxymethylcellulose (CMC) or carboxyethylcellulose (CEC).

[0010] Where the loss circulation is more severe, it is a normal practice to incorporate into the drilling mud various bulk materials which function to combat or prevent loss circulation. It has been common in the past to add any number of materials to the drilling fluid which act to reduce or prevent flow of the drilling fluid from the well hole to the formation. These materials are commonly referred to as “loss (or lost) circulation additives”. Such prior art loss circulation materials include fibrous, flake (or laminated), and granular materials. A nonexhaustive list of such loss circulation includes nut and seed shells or hulls (peanut almond, walnut, peach, brazil, coconut, peanut, sunflower, flax, cocoa bean, cottonseed, rice, linseed) ; crude pectate pulp; feathers; citrus pulp; beet pulp; peat moss fibers; jute; flax; mohair; lechuguilla fibers; cotton; cotton linters; wool; paper; wet-strength paper; sugar cane; bagasse; bamboo; corn stalks; sawdust; straw; wood fiber; cedar fiber; bark chips; cork; popped popcorn; dehydrated vegetable matter (suitably dehydrated carbohydrates such as citrus pulp, oatmeal, tapioca, rice grains, potatoes, carrots, beets, and various grain sorghams); the ground woody ring portion of corn cobs; whole ground corn cobs; hydrophobic, organophilic, water-wettable fibrous materials such as treated cotton, dried bagasse, and dried peat fibers; and specific mixtures of these materials. Many assorted inorganic materials have also been utilized as loss circulation materials.

[0011] Seepage losses can occur to any type of loss zone and in any type of formation when the particles in the drilling fluid are not fine enough to complete the seal. It has been established that the maximum allowable drilling fluid loss is on the order of 1 bbl/hr (0.16m3/h), as measured in the mud pit at the surface.

[0012] There are numerous examples of patents teaching the use of various types of materials for use as lost circulation additives in drill fluids. The following are not an exhaustive sampling.

[0013] U.S. Pat. No. 2,610,149, issued Sep. 9, 1952, to Van Dyke, discloses the use of corn stalks, wood shavings, flake cellophane and chopped up paper in drilling fluids.

[0014] U.S. Pat. No. 2,779,417, issued Jan. 29, 1957, to Clark et al., discloses the use of cellophane, rice hulls and shredded paper as bridging agents in a well fluid.

[0015] U.S. Pat. No. 4,247,403, issued Jan. 27, 1981, to Foley et al., discloses the use of whole corncobs or the woody ring portion of corncobs as loss circulation additives for drilling fluids.

[0016] U.S. Pat. No. 4,474,665, issued Oct. 2, 1984 to Green, discloses a lost circulation material useful in drilling fluids formed from cocoa bean shell material having a particle size distribution from 2 to 100 mesh.

[0017] U.S. Pat. No. 4,579,668, issued Apr. 1, 1986 to Messenger, discloses for use as drilling fluid bridging agents, ground walnut shells, cellophane and shredded wood.

[0018] U.S. Pat. No. 5,004,553, issued Apr. 2, 1991, and U.S. Pat. No. 5,071,575, issued Dec. 10, 1991, both to House et al., disclose a well working composition containing oat hulls and optionally including one or more of ground corn cobs, cotton, citrus pulp, and ground cotton burrs.

[0019] U.S. Pat. No. 5,076,944, issued Dec. 31, 1991 to Cowan et al., discloses a seepage loss additive comprising ground cotton burrs in combination with one or more of ground oat hulls, ground corn cobs, cotton, ground citrus pulp, ground peanut shells, ground rice hulls, and ground nut shells.

[0020] U.S. Pat. No. 5,118,664, issued Jun. 2, 1992, and U.S. Pat. No. 5,599,776, issued Feb. 4, 1997, both to Burts, Jr., disclose the use of various comminuted plant materials as lost circulation materials.

[0021] U.S. Pat. No. 4,957,166, issued Sep. 18, 1990 to Sydansk, discloses the use of a water soluble carboxylate crosslinking polymer along with a chromic carboxylate complex crosslinking agent as a lost circulation material. Sydansk further teaches that the performance requirements of conformance improvement treatment polymers are different from those of lost circulation polymers. Thus, while U.S. Pat. No. 5,377,760, issued Jan. 3, 1995 to Merrill discloses addition of fibers to an aqueous solution of partially hydrolyzed polyacrylamide polymer, with subsequent injection into the subterranean to improve conformance, Sydansk teaches that such would not necessarily work for lost circulation treatment.

[0022] Additionally, Merrill's conformance treatment method of mixing the fibers with the polymer solution followed by injection, requires a multiplicity of storage and mixing tanks, and a metering system which must be operated during the operation of the well. Specifically, a first tank will store a water and polymer solution, a second tank will store a water and cross-linking solution, and a third tank will be used to mix fibers with polymer solution from the first tank to create a polymer/fiber slurry. This polymer/fiber slurry is then metered from the third tank and combined with cross-linking solution metered from the second tank to the well bore.

[0023] As an advance over the above prior art, U.S. Pat. No. 6,016,879, issued Jan. 25, 2000, to Boyce D. Burts, Jr., for “Lost circulation additive, lost circulation treatment fluid made therefrom, and method of minimizing lost circulation in a subterranean formation,” discloses an additive including a “dry mixture” of water soluble crosslinkable polymer, a crosslinking agent, and a reinforcing material of fibers and/or comminuted plant materials. The method of forming a fluid includes contacting the additive with water or an aqueous solution, with a method of treating the formation further including the step of injecting the fluid into the formation.

[0024] While not believed to be related prior art because they relate to different types of well operations, for completeness, attention is directed to five other similar “dry mixture” patents by Boyce D. Burts, Jr., which were filed on the same day (Oct. 31, 1997) as the '879 Patent: U.S. Pat. No. 6,218,343, issued Apr. 17, 2001, for “Additive for, treatment fluid for, and method of plugging a tubing/casing annulus in a well bore,” U.S. Pat. No. 6,102,121, issued Aug. 15, 2000, for “Conformance improvement additive, conformance treatment fluid made therefrom, method of improving conformance in a subterranean formation,” U.S. Pat. No. 6,098,712, issued Aug. 8, 2000, for “Method of plugging a well,” U.S. Pat. No. 6,016,871, issued Jan. 25, 2000, for “Hydraulic fracturing additive, hydraulic fracturing treatment fluid made therefrom, and method of hydraulically fracturing a subterranean formation,” and U.S. Pat. No. 6,016,869, issued Jan. 25, 2000, for “Well kill additive, well kill treatment fluid made therefrom, and method of killing a well.”

[0025] A number of patents discuss the use of diatomaceous earth (“DE”) in a well operation.

[0026] U.S. Pat. No. 3,380,542, issued Apr. 30, 1968 to Clear, for restoring lost circulation discloses a oil-based drilling fluid, containing a slurry of diatomite and asbestos, used to restore lost circulation during well drilling operations.

[0027] U.S. Pat. No. 4,369,844, issued Jan. 25, 1983 to Clear, discloses that various formation sealing agents have been used in the art to form formation seals and/or filter cakes on the wall of a well bore, including diatomaceous earth.

[0028] U.S. Pat. No. 4,110,225, issued Aug. 29, 1978 to Cagle, discloses that zones of lost circulation and other undesired fluid communication channels into a wellbore are sealed by isolating a volume in the well including such a zone and applying greater than formation pressure to a novel slurry spotted in the zone until it hardens into a solid, drillable seal. The slurry contains per barrel from 5-50 pounds diatomaceous mix, from about 35 to about 350 pounds of oil well cement, and at a minimum about 5 to 6 pounds of a flake type lost-circulation agent. This '225 patent cites a number of patents that disclose cement/diatomaceous earth compositions, including U.S. Pat. Nos. 2,585,336; 2,793,957; 2,961,044; 3,467,198; and 3,558,335.

[0029] Regarding these patents, the '225 patent notes the following:

[0030] Regarding U.S. Pat. No. 2,585,336, the '225 patent notes, “a mixture is made using from 2% to 100% diatomaceous earth, compared to the content of the cement in the slurry. The aim of the inventors was to prevent perlite from settling and to produce a lightweight cement. The diatomaceous earth-cement described in the disclosure is a mixture of Portland cement, perlite and diatomaceous earth, lime, and asbestos fibers.”

[0031] Regarding U.S. Pat. No. 2,793,957, the '225 patent notes, “refers to a highly permeable cement formed by use of the same basic mixtures of diatomaceous earth with Portland cement, the diatomaceous earth present being from five to seven times the proportion of the Portland cement in the slurry. The aim of the inventors was to produce a light highly permeable cement, entirely opposite to the purpose of my invention.”

[0032] Regarding U.S. Pat. No. 2,961,044, the '225 patent notes, “discusses and claims a cement composition which has diatomaceous earth in the amounts of from 30% to 70% of the Portland cement. The reason for using the diatomaceous earth was to prevent the strength retrogression of a salt-saturated cement. Thus, while Shell wishes (among other uses) to employ his mixture for squeeze cementing, he produces a relatively high-strength cement plug. There is a real tendency when redrilling such a plug for the bit to be deflected or sidetracked so that the new hole is beside rather than through the bore and the seal is ineffective. This is completely different from my invention which minimizes such tendency by producing a plug at least as drillable as the formation in which it is set. Also, Shell is directed to operations using salt-saturated cement slurries, while I prefer using a fresh or brackish water slurry. I employ lost-circulation agents; he makes no teaching of using such additives. Accordingly, his teaching is quite far from mine.”

[0033] Regarding both U.S. Pat. Nos. 3,467,198 and 3,558,335, the '225 patent notes, “describe cement compositions having diatomaceous mix present in the amounts from 0.5% to 10% of the amount of Portland cement present to prevent solids-settling.”

[0034] U.S. Pat. No. 4,369,844, issued Jan. 25, 1983 to Clear, discloses slurries to seal permeable earth formations encountered in the drilling of wells, comprising finely divided paper, diatomaceous earth, and in a further embodiment, lime. A slug of the slurry is spotted at the locus of the permeable formation and defluidized to form a formation seal on which a mud sheath is then deposited.

[0035] U.S. Pat. No. 4,505,751, issued Mar. 19, 1985, discloses a silicate/silica cement in oil field applications, including diatomaceous earth as a species of silica compound.

[0036] While not believed to be analogous prior art because it relates to earthen pits (for example a ditch) and not to subterrean wellbores nor well operations, U.S. Pat. No. 5,947,644, issued Sep. 7, 1999 to Gibbons et al., is included herein for completeness because it discloses a gelable slurry of aqueous solvent, a crosslinkable polymer, a crosslinking agent, and unconsolidated solids such as diatomaceous earth. This gelable slurry is placed in an earthen pit and allowed to form into a fluid impermeable barrier wall in the earthen pit. The polymer serves to bind the unconsolidated solids to convert the gelable slurry to a nondeformable gelled continuum of consolidated solids, which forms the barrier wall in the earthen pit. As disclosed in the '644 Patent in the Summary of the Invention section, at col. 1, lines 57-67, this gelable slurry is prepared by first forming a liquid gelation solution of the polymer and crosslinking agent, to which is subsequently mixed with the unconsolidated solids, or alternatively, by sequentially mixing the aqueous solvent, crosslinkable polymer, and polymer crosslinking agent with the unconsolidated solids.

[0037] Thus, in spite of the advancements in the prior art, there still need for further innovation in the lost circulation art.

[0038] There is need for further innovation for lost circulation art utilizing a water soluble polymer.

[0039] There is another need for lost circulation technology which would allow for simplification of the mixing equipment.

[0040] These and other needs in the art will become apparent to those of skill in the art upon review of this specification, including its drawings and claims.

SUMMARY OF THE INVENTION

[0041] It is an object of the present invention to provide for further innovation in the lost circulation art.

[0042] It is an another object of the present invention to provide for further innovation for lost circulation art utilizing a water soluble polymer.

[0043] It is even another object of the present invention to provide for lost circulation art which would allow for simplification of the mixing equipment.

[0044] These and other objects of the present invention will become apparent to those of skill in the art upon review of this specification, including its drawings and claims.

[0045] According to one embodiment of the present invention, there is provided a lost circulation additive comprising a water soluble crosslinkable polymer, a crosslinking agent, and a filter aid. In a further embodiment of this embodiment, the additive is a dry mixture.

[0046] According to another embodiment of the present invention, there is provided a well fluid comprising a lost circulation fluid, water soluble crosslinkable polymer, a crosslinking agent, and a filter aid.

[0047] According to even another embodiment of the present invention, there is provided a method of modifying a lost circulation fluid. The method generally includes providing a lost circulation additive comprising a mixture of water soluble crosslinkable polymer, a crosslinking agent, and a filter aid. While this additive may be in any form, it is preferably a dry mixture. The method also includes contacting the lost circulation fluid with the lost circulation additive to form a modified lost circulation fluid.

[0048] According to still another embodiment of the present invention, there is provided a method for plugging an opening in a subterranean formation. The method includes providing a lost circulation fluid comprising water or an aqueous solution, water soluble crosslinkable polymer, a crosslinking agent, and a filter aid. The method also includes injecting the lost circulation fluid into the formation and into the opening to be plugged. The method also includes dewatering the lost circulation fluid to force the polymer and crosslinking agent through the opening and into the formation, and to form the filter aid into a plug in the opening.

[0049] According to yet another embodiment of the present invention, there is provided a method for plugging an opening in a subterranean formation. The method includes providing a lost circulation fluid comprising water or an aqueous solution, water soluble crosslinkable polymer, a crosslinking agent, and a filter aid. The method also includes injecting the lost circulation fluid into the formation and into the opening to be plugged. The method also includes applying pressure to dewater the lost circulation fluid to force the polymer and crosslinking agent through the opening and into the formation, and to form the filter aid into a plug in the opening.

[0050] According to even yet another embodiment of the present invention, there is provided a method of circulating a fluid in a welbore penetrating a subterranean formation. The method includes providing a lost circulation fluid comprising water or an aqueous solution, water soluble crosslinkable polymer, a crosslinking agent, and a filter aid. The method also includes circulating the lost circulation fluid in the wellbore.

[0051] According to even yet another embodiment of the present invention, there is provided a method of modifying a lost circulation fluid circulating in a wellbore penetrating a subterranean formation. The method includes introducing a water soluble crosslinkable polymer, crosslinking agent, and filter aid to the circulating lost circulation fluid.

[0052] Various further embodiments of any or all of the above embodiments include any or all of the following in any combination: the filter aid is selected from the group consisting of diatomaceous earth, perlite, glass beads, magnesium silicate, solid thermoplastic or thermoset polymer beads, talc, and calcium silicate; or the polymer is an a carboxylate-containing polymer, and the crosslinking agent is selected from the group consisting of chromium (III) carboxylate complexes, aldehydes, dialdehydes, formaldehydes, glutaraldehyde, dichromates, titanium chelates, phenols, substituted phenols, ethers, aluminum citrate, and aluminates; the filter aid comprises at least one of diatomaceous earth or pearlite; the polymer comprises a low molecular weight polymer having a molecular weight less than 500,000, and a high molecular weight polymer having a molecular weight of at least 500,000; the polymer is a water soluble, carboxylate containing acrylamide, and the crosslinking agent is a chromium (III) carboxylate complex; the filter aid is diatomaceous earth; the filter aid is pearlite; the reinforcing material selected from the group consisting of hydrophilic fibers, hydrophobic fibers, and comminuted plant material; and/or various weight percentages are in the range of about 4 to about 35 weight percent polymer, in the range of about 1 to about 10 weight percent cross linking agent, and in the range of about 55 to about 95 weight percent filter aid, based on the total weight of the polymer, cross linking agent and filter aid.

[0053] These and other embodiments of the present invention will become apparent to those of skill in the art upon review of this specification and claims.

DETAILED DESCRIPTION OF THE INVENTION

[0054] The lost circulation additive of the present invention includes polymer, cross-linking agent, filter aid, and optionally a reinforcing material, preferably either fibers or comminuted particles of plant materials, and optionally any other materials that are known in the art. It is to be understood that the lost circulation additive of the present invention may be in the form of a dry mixture or a slurry. In a preferred embodiment of the present invention, the lost circulation additive is a dry mixture.

[0055] A well fluid of the present invention comprises the additive of the invention. In a method of modifying a lost circulation fluid to form a modified lost circulation fluid, the lost circulation fluid to be modified is contacted the additive or well fluid of the present invention.

[0056] Any suitable relative amounts of the polymer, cross-linking agent, filter aid and the optional reinforcing materials may be utilized in the present invention provided that the desired lost circulation results are achieved. Generally, the relative amounts of each will be determined based on the particular application to which the additive is to be subjected. A suitable amount of crosslinking agent is provided to reach the desired amount of crosslinking. The amount of optional reinforcing material is selected to provide desired physical properties.

[0057] Any suitable types of filter aid materials as are known in the filtration art may be utilized as the filter aid component in the present invention. All that is necessary is that the filter aid will function to be “squeezed” and allow migration of the solution of polymer and crosslinking agent into the formation, and will form a plug of the filter aid that will hold the solution in place until it sufficiently crosslinks. Non-limiting examples of which include diatomaceous earth (“DE” or diatomite), perlite (or pearlite), glass beads, magnesium silicate, solid thermoplastic or thermoset polymers generally in powder form, talc (naturally occuring form of hydrous magnesium silicate containing varying proportions of such associated minerals as alpha-quartz, calcite, chlorite, dolomite, kaolin, magnesite, and phlogopite), and calcium silicate (for example, see, U.S. Pat. No. 5,750,038, issued May 12, 1998, to Tsunematsu, for “Method for the preparation of acid-resistant calcium silicate,” incorporate herein by reference), and any combination of two or more of the above. Preferably, the filter aid is selected from the group consisting of diatomaceous earth perlite (or pearlite), magnesium silicate, and talc. More preferably, the filter aid is a mineral based type of filter aid, non-limiting examples of which include diatomaceous earth, pearlite, magnesium silicate, talc and calcium silicate, and any combination of two or more of the above. Even more preferably, the filter aid comprises pearlite and/or diatomaceous earth. Still more preferably, the filter aid comprises diatomaceous earth.

[0058] The amount of filter aid to be utilized is generally not dependent upon the amount of polymer or crosslinking agent, but rather, is that amount sufficient to form a plug to retain the polymer in place until it crosslinks sufficiently to remain in place on its own. However, in an effort to quantify the amount of filter aid, a weight ratio of filter aid to polymer is provided for convenience.

[0059] Generally, the weight ratio of filter aid:polymer in the additive is in the range of about 100:1 to about 1:100, preferably in the range of about 50:1 to about 1:50, more preferably in the range of about 15:1 to about 1:15, even more preferably in the range of about 5:1 to about 1:5, and still more preferably in the range of about 5:1 to about 1:1.

[0060] Commercially, it is envisioned that the additive will be packaged in a single bag, to promote ease of use and eliminate the necessity of any measuring and/or mixing at the well site. As a non-limiting example of a commercial embodiment, a 40 pound bag might contain any where from about 1.5 to about 17.5 lbs. polymer, from about 0.4 to about 5 lbs. crosslinking agent, and the balance of from about 17.5 to about 38.1 lbs. filter aid.

[0061] In weight percentage terms, examples of weight percentage ranges include from about 4 to about 35 weight percent polymer, from about 1 to about 10 weight percent cross linking agent, and from about 55 to about 95 weight percent filter aid, based on the total weight of the polymer, cross linking agent and filter aid. Specific non-limiting examples of useful compositions include 4% polymer, 1% cross linker, 95% DE, or 24% polymer, 6% cross linker, 70% DE, or 35% polymer, 10% cross linker, 55% DE.

[0062] The particle size distribution of the filter aid is selected to allow dewatering of the filter aid (i.e., the solution containing polymer and crosslinking agent will separate from the filter aid), and to allow formation of a plug of the filter aid that retains the polymer and crosslinking agent in the reservoir during crosslinking. It is believed that the particle size distribution will be determined by the reservoir conditions.

[0063] Other additives as are known in the well fluid art may be utilized, non limiting examples of which include surfactants, dispersants, retarders, accelerants, weighting agents (such as hematite, barite or calcium carbonate), lost circulation materials and other additives may be provided as necessary or desired.

[0064] The polymer utilized in the practice of the present invention is preferably water soluble and must be capable of being pumped as a liquid and subsequently crosslinked in place to form a substantially non-flowing crosslinked polymer which has sufficient strength to withstand the pressures exerted on it. Optionally, when reinforcing materials are utilized, it would have a network structure capable of incorporating reinforcing materials.

[0065] While any suitable water soluble polymer may be utilized, the preferred polymer utilized in the practice of the present invention is a water soluble carboxylate-containing polymer, more preferably a water soluble partially hydrolyzed carboxylate-containing polymer. This carboxylate-containing polymer may be any crosslinkable, high molecular weight, water-soluble, synthetic polymer or biopolymer containing one or more carboxylate species.

[0066] For an example of polymers and crosslinking agents suitable for use herein and details regarding their making and use, please see any of the above listed patents to Boyce D. Burts, Jr. all herein incorporated by reference, or please see U.S. Pat. Nos. 4,683,949, 4,723,605, 4,744,418, 4,770,245, 4,844,168, 4,947,935, 4,957,166 and 4,989,673, 5,377,760, 5,415,229, 5,421,411, all herein incorporated by reference.

[0067] The average molecular weight of the carboxylate-containing polymer utilized in the practice of the present invention is in the range of about 10,000 to about 50,000,000, preferably in the range of about 100,000 to about 20,000,000, more preferably in the range of about 200,000 to about 15,000,000, and still more preferably in the range of about 200,000 to about 10,000,000.

[0068] In some instances, a blend of two polymers, a lower molecular weight polymer and a higher molecular weight polymer may be utilized. For example, in some instances where high fluid loss is encountered, such as a hole in the casing, a fault zone, loose sand, unconsolidated zones, or vugular formations, higher molecular weight polymer must be utilized. However, this higher molecular weight polymer causes problems in mixing, pumping and total polymer load. Thus, this higher molecular weight polymer is mixed with a lower molecular weight polymer to provide mixing, pumping and loading as desired.

[0069] Generally, this lower molecular weight polymer has a molecular weight less than 1,000,000, preferably less than 500,000, and more preferably less than 200,000. Generally the lower molecular weight polymer will have a molecular weight in the range of about 20,000 to less than 1,000,000, preferably in the range of about 20,000 to less than 500,000, and more preferably in the range of about 200,000 to less than 500,000. The higher molecular weight polymer generally has a molecular weight of at least 1,000,000, preferably from about 1,000,000 to about 50,000,000, more preferably from about 5,000,000 to about 20,000,000, and even more preferably from about 6,000,000 to about 12,000,000.

[0070] Biopolymers useful in the present invention include polysaccharides and modified polysaccharides. Non-limiting examples of biopolymers are xanthan gum, guar gum, carboxymethylcellulose, o-carboxychitosans, hydroxyethylcellulose, hydroxypropylcellulose, and modified starches. Non-limiting examples of useful synthetic polymers include acrylamide polymers, such as polyacrylamide, partially hydrolyzed polyacrylamide and terpolymers containing acrylamide, acrylate, and a third species. As defined herein, polyacrylamide (PA) is an acrylamide polymer having substantially less than 1% of the acrylamide groups in the form of carboxylate groups. Partially hydrolyzed polyacrylamide (PHPA) is an acrylamide polymer having at least 1%, but not 100%, of the acrylamide groups in the form of carboxylate groups. The acrylamide polymer may be prepared according to any conventional method known in the art, but preferably has the specific properties of acrylamide polymer prepared according to the method disclosed by U.S. Pat. No. Re. 32,114 to Argabright et al incorporated herein by reference.

[0071] Any crosslinking agent suitable for use with the selected polymer may be utilized in the practice of the present invention. Non limiting examples of suitable crosslinking agents includes chromium (III) carboxylate complexes, aldehydes, dialdehydes, formaldehydes, glutaraldehyde, dichromates, titanium chelates, phenols, substituted phenols, ethers, aluminum citrate, and is aluminates.

[0072] Preferably, the crosslinking agent utilized in the present invention is a chromic carboxylate complex.

[0073] The term “complex” is defined herein as an ion or molecule containing two or more interassociated ionic, radical or molecular species. A complex ion as a whole has a distinct electrical charge while a complex molecule is electrically neutral. The term “chromic carboxylate complex” encompasses a single complex, mixtures of complexes containing the same carboxylate species, and mixtures of complexes containing differing carboxylate species.

[0074] The chromic carboxylate complex useful in the practice of the present invention includes at least one or more electropositive chromium III species and one or more electronegative carboxylate species. The complex may advantageously also contain one or more electronegative hydroxide and/or oxygen species. It is believed that, when two or more chromium III species are present in the complex, the oxygen or hydroxide species may help to bridge the chromium III species. Each complex optionally contains additional species which are not essential to the polymer crosslinking function of the complex. For example, inorganic mono- and/or divalent ions, which function merely to balance the electrical charge of the complex, or one or more water molecules may be associated with each complex. Non-limiting representative formulae of such complexes include:

[Cr3(CH3CO2)6(OH)2]1+;

[Cr3(CH3CO2)6(OH)2]NO3·6H2O;

[Cr3 (CH3CO2)6(OH)2]3+; and

[Cr3 (CH3CO2)6(OH)2](CH3CO2)3·H2O.

[0075] “Trivalent chromium” and “chromic ion” are equivalent terms encompassed by the term “chromium III” species as used herein.

[0076] The carboxylate species are advantageously derived from water-soluble salts of carboxylic acids, especially low molecular weight mono-basic acids. Carboxylate species derived from salts of formic, acetic, propionic, and lactic acid, substituted derivatives thereof and mixtures thereof are preferred. The preferred carboxylate species include the following water-soluble species: formate, acetate, propionate, lactate, substituted derivatives thereof, and mixtures thereof. Acetate is the most preferred carboxylate species. Examples of optional inorganic ions include sodium, sulfate, nitrate and chloride ions.

[0077] A host of complexes of the type described above and their method of preparation are well known in the leather tanning art. These complexes are described in Shuttleworth and Russel, Journal of the Society of Leather Trades' Chemists, “The Kinetics of Chrome Tannage Part I.,” United Kingdom, 1965, v. 49, p. 133-154; “Part III.,” United Kingdom, 1965, v. 49, p. 251-260; “Part IV.,” United Kingdom, 1965, v. 49, p. 261-268; and Von Erdman, Das Leder, “Condensation of Mononuclear Chromium (III) Salts to Polynuclear Compounds,” Eduard Roether Verlag, Darmstadt Germany, 1963, v. 14, p. 249; and incorporated herein by reference. Udy, Marvin J., Chromium. Volume 1: Chemistry of Chromium and its Compounds. Reinhold Publishing Corp., New York, 1956, pp. 229-233; and Cotton and Wilkinson, Advanced Inorganic Chemistry 3rd Ed., John Wiley and Sons, Inc., New York, 1972, pp. 836-839, further describe typical complexes which may be within the scope of the present invention and are incorporated herein by reference. The present invention is not limited to the specific complexes and mixtures thereof described in the references, but may include others satisfying the above-stated definition.

[0078] Salts of chromium and an inorganic monovalent anion, e.g., CrCl3, may also be combined with the crosslinking agent complex to accelerate gelation of the polymer solution, as described in U.S. Pat. No. 4,723,605 to Sydansk, which is incorporated herein by reference.

[0079] The molar ratio of carboxylate species to chromium III in the chromic carboxylate complexes used in the process of the present invention is typically in the range of 1:1 to 3.9:1. The preferred ratio is range of 2:1 to 3.9:1 and the most preferred ratio is 2.5:1 to 3.5:1.

[0080] The optional reinforcing material of the present invention may comprise fibers or comminuted particles of plant materials, and preferably comprises comminuted particles of one or more plant materials.

[0081] Fibers suitable for use in the present invention are selected from among hydrophilic and hydrophobic fibers. Incorporation of hydrophobic fibers will require use of a suitable wetting agent. Preferably, the fibers utilized in the present invention comprise hydrophilic fibers, most preferably both hydrophilic and hydrophobic fibers.

[0082] With respect to any particular fiber employed in the practice of the present invention, it is believed that the longer the fiber, the more difficult it is to be mixed uniformly in solution. It is believed that fibers as long as 12,500 microns may tend to aggregate and form clumps. The shorter the fiber, it is believed the easier it is to mix in solution. On the other hand, the shorter the fiber, the greater the quantity necessary to provide the desired level of strength in a reinforced mature gel. In general, the fibers utilized in the present invention will have a length in the range of 100 microns to 3200 microns, preferable 100 microns to 1000 microns.

[0083] Non-limiting examples of suitable hydrophobic fibers include nylon, rayon, hydrocarbon fibers and mixtures thereof.

[0084] Non-limiting examples of suitable hydrophilic fibers include glass, cellulose, carbon, silicon, graphite, calcined petroleum coke, cotton fibers, and mixtures thereof.

[0085] Non-limiting examples of comminuted particles of plant materials suitable for use in the present invention include any derived from: nut and seed shells or hulls such as those of peanut, almond, brazil, cocoa bean, coconut, cotton, flax, grass, linseed, maize, millet, oat, peach, peanut, rice, rye, soybean, sunflower, walnut, wheat; various portions of rice including the rice tips, rice straw and rice bran; crude pectate pulp; peat moss fibers; flax; cotton; cotton linters; wool; sugar cane; paper; bagasse; bamboo; corn stalks; various tree portions including sawdust, wood or bark; straw; cork; dehydrated vegetable matter (suitably dehydrated carbonhydrates such as citrus pulp, oatmeal, tapioca, rice grains, potatoes, carrots, beets, and various grain sorghams); whole ground corn cobs; or various plant portions the corn cob light density pith core, the corn cob ground woody ring portion, the corn cob coarse or fine chaff portion, cotton seed stems, flax stems, wheat stems, sunflower seed stems, soybean stems, maize stems, rye grass stems, millet stems, and various mixtures of these materials.

[0086] Optionally a dispersant for the comminuted plant material in the range of about 1 to about 20 pounds, preferably in the range of about 5 to about 10 pounds, and more preferably in the range of about 7 to about 8 pounds of dispersant may be utilized per pound of comminuted plant material. A non-limiting example of a dispersant would be NaCl.

[0087] Preferred comminuted materials useful in the practice of the present invention include those derived from peanuts, wood, paper any portion of rice seed or plant, and any portion of corn cobs.

[0088] These various materials can be comminuted to very fine particle sizes by drying the products and using hammer mills, cutter heads, air control mills or other comminution methods as is well known to those of skill in the comminution art. Air classification equipment or other means can be used for separation of desired ranges of particle sizes using techniques well-known in the comminution art.

[0089] Any suitable size of comminuted material may be utilized in the present invention, along as such size produces results which are desired. Of course, the particle size will be a function of diameter of the porosity passages. While the present invention will find utility for passages on the order of microns in diameter, it will also find utility on larger passages, for example, those with diameters greater than {fraction (1/64)}, {fraction (1/16)} or event ⅛ of an inch.

[0090] In most instances, the size range of the comminuted materials utilized herein will range from below about 8 mesh (“mesh” as used herein refers to standard U.S. mesh), preferably from about −65 mesh to about −100 mesh, and more preferably from about −65 mesh to about −85 mesh. Specifically preferred particle sizes for some materials are provided below.

[0091] Preferred mixtures of comminuted materials useful in the practice of the present invention include a rice fraction and peanut hulls; a rice fraction and wood fiber and/or almond hulls; a rice fraction and a corn cob fraction, preferably a chaff portion; and a corn cob fraction, preferably a pith or chaff portion, a rice fraction, and at least one of wood fiber, nut shells, paper and shredded cellophane.

[0092] Rice is commercially available in the form of rice hulls, rice tips, rice straw and rice bran, as these various parts of the rice plant are separated commercially and are widely available from rice mills. Preferably, the size range of the rice fraction utilized herein will range from below about 8 mesh (“mesh” as used herein refers to standard U.S. mesh), preferably from about −65 mesh to about −100 mesh, and more preferably from about −65 mesh to about −85 mesh.

[0093] After the corn kernals are removed, corn cobs consist of four principle parts that are arranged concentrically. The central portion is a very light density pith core, that is surrounded by a woody ring, that in turn is surrounded by a coarse chaff portion, that in turn is covered by a fine chaff portion. The coarse and fine chaff portions form the sockets for ancoring the corn kernels to the corncob. The normal methods of grinding corncobs produce a mixture of all four parts enumerated above. It is possible, however, to separate the woody ring material from the remainder of the cob. The chaff portion of the corncob remaining after removal of the woody ring material is known as “bees wings”. In the present invention, any of the pith or chaff portions (“BPC”) are the preferred portions of the corn cob, with the chaff portions being more preferred. A range of particle sizes of pith and chaff can be obtained from comminution, but the size range smaller than about 8 mesh is suitable for this invention. Preferably, a particle size distribution ranging from smaller than 8 mesh to smaller than 100 mesh is utilized.

[0094] Preferred woods for use as comminuted materials in the present invention include any type of hard wood fiber, including cedar fiber, oak fiber, pecan fiber and elm fiber. Preferably the wood fiber comprises cedar fibers.

[0095] Preferred nut shells for use in the present invention include pecan, walnut, and almond. Preferably, the nut shells comprise at least one of pecan or walnut shells.

[0096] Preferred particle sizes for the wood fibers, nut shells, paper and cellophane will generally range from about +10 mesh to −100 mesh. An illustration of a non-limiting particle size distribution for these materials would include particles of +10 mesh, +20 mesh, +30 mesh, +50 mesh, +60 mesh, +100 mesh, and −100 mesh.

[0097] For one of the preferred comminuted plant mixtures comprising a corn cob fraction, a rice fraction, and at least one of wood fiber, nut shells, paper and shredded cellophane, the mixture will generally comprise in the range of about 5 to about 95 weight percent rice, in the range of about 5 to about 95 weight percent corncob pith or chaff, with the total of ground wood fiber, ground nut shells, ground paper and shredded cellophane comprising in the range of about 5 to about 95 weight percent (weight percent based on the total weight of plant material in the mixture. Preferred ranges are about 20 to about 75 weight percent rice, about 5 to about 35 weight percent corncob pith or chaff, with the total of ground wood fiber, ground nut shells, ground paper and shredded cellophane comprising in the range of about 20 to about 75 weight percent. More preferred ranges are about 30 to about 50 weight percent rice, about 10 to about 30 weight percent corncob pith and chaff, with the total of ground wood fiber, ground nut shells, ground paper and shredded cellophane comprising in the range of about 25 to about 50 weight percent.

[0098] As these comminuted materials are to be added to a water base lost circulation fluid, a small amount of oil may optionally added to the mixture. This optional oil is preferably added while the plant materials are being mixed together. This mixing may take place in a ribbon blender, where the oil in the required amount is applied by a spray bar. The oil wets the particles and adds to their lubricity while at the same time helping to control dust produced by the mixing operation. A variety of oils may be utilized in the practice of the present invention in concentrations generally ranging from about 1 percent to about 5 percent by weight based on the total weight of the mixture of comminuted materials, more preferably ranging from about 1 percent to about 2 percent. A non-limiting example of a commercially available oil suitable for use in the present invention includes ISOPAR V, available from Exxon Corporation.

[0099] In the method of the present invention for forming a lost circulation additive, the various components of polymer, crosslinking agent and filter aid, may be mixed in any form (dry form, liquid form, or slurry form) in any suitable order utilizing mixing techniques as known to those in the art.

[0100] Specifically, a dry lost circulation additive may be formed by mixing solid polymer, solid crosslinking agent and solid filter aid to form a solid (dry) lost circulation additive.

[0101] In the practice of the present invention, liquid lost circulation additive may be formed by mixing the various components in any form (dry form or liquid or slurry form) in any suitable order utilizing mixing techniques as know to those in the art. If the various components are mixed in dry form, this dry mixture may subsequently may be contacted with water or aqueous solution to form a liquid lost circulation additive.

[0102] Lost circulation fluids are known to those of skill in the art, and in the overwhelming number of cases would generally be of the category of well fluid known as drilling fluids, although in few instances, lost circulation fluids can be a completion fluid. Generally such lost circulation drilling fluids include a solid phase and a liquid phase in which a density agent has been included to increase the density of the fluid, and of course, lost circulation materials.

[0103] In a method of treating a lost circulation fluid, the lost circulation fluid to be treated is contacted with a liquid or solid form of the lost circulation additive of the present invention. Preferably, the lost circulation fluid is contacted with a dry mixture (i.e., solid form) of the lost circulation additive.

[0104] A well fluid of the present invention comprises a traditional lost circulation fluid and the lost circulation additive of the present invention.

[0105] In a method of operating a well of the present invention in which a well fluid is circulating down from the surface of the well, through the drill string positioned in a wellbore, and out through openings in the drill bit such that the well fluid is then circulated upwardly in the annulus between the side of the wellbore and the rotating drill string, the present invention includes circulating such a well fluid comprising the lost circulation additive. The lost circulation additive can be added in liquid or solid form to the circulating fluid. Alternatively, the lost circulation additive may be added to the fluid prior to it being circulated.

[0106] In well operation, it is also known to define a vertically limited zone into which a slurry is then pumped and subsequently squeezed by application of pressure (either from the formation itself, or by application of pressure to the zone). In a method of performing a well operation of the present invention, the lost circulation fluid of the present invention is pumped into a desired vertically defined zone in the well, and then “squeezed” to dewater the fluid such that a plug of the filter aid remains behind and the solution of polymer and crosslinking agent migrates into the formation. The filter aid plug remains in place to prevent or slow down the escape of the solution back into the well allowing time for the solution to form a gel plug.

EXAMPLES

[0107] The following examples are provided merely to illustrate some but not all of the embodiments of the present invention, and are not intended to, nor do they, limit the scope of the claims.

[0108] DE

[0109] The DE utilized in this example was that produced by Eagle Picher Minerals, Inc., and sold under the trademark CELATOM® Diatomite ET-905. As measured, the particle size distribution was:

[0110] 8% +200 mesh

[0111] 92% −200 mesh

[0112] Polymer

[0113] The polymers utilized were obtained from Ciba and a water-soluble, crosslinkable, carboxylate-containing acrylamide polymers, CIBA 254 (MW from 300,000 to less than 500,000) and CIBA 935 (MW from 6 to 9 million).

[0114] Crosslinking Agent

[0115] The crosslinking agent was chromium acetate. 1 Formulations Formulation No. 1 17.5 grams 254   5 grams CrIII Acetate 27.5 grams DE Formulation No. 2   12 grams 254   3 grams CrIII Acetate   25 grams DE Formulation No. 1   5 grams 935   3 grams 254  1.2 grams CrIII Acetate 30.8 grams DE

[0116] Filter Press Test

[0117] This test was run to simulate the dewatering of the DE in a subterranean formation, and subsequent formation of a plug of DE and separate crosslinked polymer.

[0118] 30 ml. of plain tap water was added to a beaker and subjected to mixing at 10,000 rpm in a Hamilton Beach commercial drink mixer with a solid agitator. To this blending water was added the above formulations (three separate runs). The sample was allowed to blend for 5 minutes at 10,000 rpm. After the 5 minutes of blending, this mixture was placed into the cylinder of a filter press in which substantial dewatering of the DE slurry occured without any pressure applied. Subsequently, 80 psi of pressure was applied to further dewater and consolidate the DE. Finally, heat was applied to the filter press to heat the consolidated DE and liquid run off. Both the filter press cylinder and collected run off (water soluble crosslinkable polymer and crosslinking agent—no visible DE) were placed into a 160 deg. F water bath and allowed to crosslink. Without being limited in theory, applicant believes that residual polymer remaining in the DE after dewatering crosslinks and serves to promote the consolidation of the DE. Once crosslinked, the collected run off for all of the formulations promotes a rigid ringing gel.

[0119] While the illustrative embodiments of the invention have been described with particularity, it will be understood that various other modifications will be apparent to and can be readily made by those skilled in the art without departing from the spirit and scope of the invention. Accordingly, it is not intended that the scope of the claims appended hereto be limited to the examples and descriptions set forth herein but rather that the claims be construed as encompassing all the features of patentable novelty which reside in the present invention, including all features which would be treated as equivalents thereof by those skilled in the art to which this invention pertains.

Claims

1. A lost circulation additive comprising a dry mixture of water soluble crosslinkable polymer, a crosslinking agent, and a filter aid.

2. The additive of claim 1, wherein the filter aid is selected from the group consisting of diatomaceous earth, perlite, glass beads, magnesium silicate, solid thermoplastic or thermoset polymers, talc, and calcium silicate.

3. The additive of claim 2, wherein the polymer is an a carboxylate-containing polymer, and the crosslinking agent is selected from the group consisting of chromium (III) carboxylate complexes, aldehydes, dialdehydes, formaldehydes, glutaraldehyde, dichromates, titanium chelates, phenols, substituted phenols, ethers, aluminum citrate, and aluminates.

4. The additive of claim 3, wherein the filter aid comprises at least one of diatomaceous earth or pearlite.

5. The additive of claim 4, wherein the polymer comprises a low molecular weight polymer having a molecular weight less than 200,000, and a high molecular weight polymer having a molecular weight of at least 200,000.

6. The additive of claim 4, wherein the polymer is a water soluble, carboxylate containing acrylamide, and the crosslinking agent is a chromium (III) carboxylate complex.

7. The additive of claim 6, wherein the filter aid is diatomaceous earth.

8. The additive of claim 6, wherein the filter aid is pearlite.

9. The additive of claim 6, further comprising reinforcing material selected from the group consisting of hydrophilic fibers, hydrophobic fibers, and comminuted plant material.

10. A well fluid comprising a lost circulation fluid, water soluble crosslinkable polymer, a crosslinking agent, and a filter aid.

11. The well fluid of claim 10, wherein the filter aid is selected from the group consisting of diatomaceous earth, perlite, glass beads, magnesium silicate, solid thermoplastic or thermoset polymers, talc, and calcium silicate.

12. The well fluid of claim 11, wherein the polymer is an a carboxylate-containing polymer, and the crosslinking agent is selected from the group consisting of chromium (III) carboxylate complexes, aldehydes, dialdehydes, formaldehydes, glutaraldehyde, dichromates, titanium chelates, phenols, substituted phenols, ethers, aluminum citrate, and aluminates.

13. The well fluid of claim 12, wherein the filter aid comprises at least one of diatomaceous earth or pearlite.

14. The well fluid of claim 13, wherein the polymer comprises a low molecular weight polymer having a molecular weight less than 200,000, and a high molecular weight polymer having a molecular weight of at least 200,000.

15. The well fluid of claim 13, wherein the polymer is a water soluble, carboxylate containing acrylamide, and the crosslinking agent is a chromium (III) carboxylate complex.

16. The well fluid of claim 15, wherein the filter aid is diatomaceous earth.

17. The well fluid of claim 15, wherein the filter aid is pearlite.

18. The well fluid of claim 15, further comprising reinforcing material selected from the group consisting of hydrophilic fibers, hydrophobic fibers, and comminuted plant material.

19. A method of modifying a lost circulation fluid comprising:

(a) contacting the lost circulation fluid with water soluble crosslinkable polymer, a crosslinking agent, and a filter aid to form a modified lost circulation fluid.

20. The method of claim 19, wherein the filter aid is selected from the group consisting of diatomaceous earth, perlite, glass beads, magnesium silicate, solid thermoplastic or thermoset polymers, talc, and calcium silicate.

21. The method of claim 20, wherein the polymer is an a carboxylate-containing polymer, and the crosslinking agent is selected from the group consisting of chromium (III) carboxylate complexes, aldehydes, dialdehydes, formaldehydes, glutaraldehyde, dichromates, titanium chelates, phenols, substituted phenols, ethers, aluminum citrate, and aluminates.

22. The method of claim 21, wherein the filter aid comprises at least one of diatomaceous earth or pearlite.

23. The method of claim 22, wherein the polymer comprises a low molecular weight polymer having a molecular weight less than 200,000, and a high molecular weight polymer having a molecular weight of at least 200,000.

24. The method of claim 22, wherein the polymer is a water soluble, carboxylate containing acrylamide, and the crosslinking agent is a chromium (III) carboxylate complex.

25. The method of claim 24, wherein the filter aid is diatomaceous earth.

26. The method of claim 24, wherein the filter aid is pearlite.

27. The method of claim 19, wherein water soluble crosslinkable polymer, a crosslinking agent, and a filter aid.

28. A method for decreasing fluid loss from a borehole into a subterranean formation comprising:

(a) providing a lost circulation fluid comprising water or an aqueous solution, water soluble crosslinkable polymer, a crosslinking agent, and a filter aid;

(b) injecting the lost circulation fluid into the wellbore; and

(c) dewatering the lost circulation fluid to force the polymer and crosslinking agent into the formation, and to form the filter aid into a plug.

29. The method of claim 28, wherein the filter aid is selected from the group consisting of diatomaceous earth, perlite, glass beads, magnesium silicate, solid thermoplastic or thermoset polymers, talc, and calcium silicate.

30. The method of claim 29, wherein the polymer is an a carboxylate-containing polymer, and the crosslinking agent is selected from the group consisting of chromium (III) carboxylate complexes, aldehydes, dialdehydes, formaldehydes, glutaraldehyde, dichromates, titanium chelates, phenols, substituted phenols, ethers, aluminum citrate, and aluminates.

31. The method of claim 30, wherein the filter aid comprises at least one of diatomaceous earth or pearlite.

32. The method of claim 31, wherein the polymer comprises a low molecular weight polymer having a molecular weight less than 200,000, and a high molecular weight polymer having a molecular weight of at least 200,000.

33. The method of claim 31, wherein the polymer is a water soluble, carboxylate containing acrylamide, and the crosslinking agent is a chromium (III) carboxylate complex.

34. The method of claim 33, wherein the filter aid is diatomaceous earth.

35. The method of claim 33, wherein the filter aid is pearlite.

36. The method of claim 33, further comprising reinforcing material selected from the group consisting of hydrophilic fibers, hydrophobic fibers, and comminuted plant material.

37. A method for decreasing fluid loss from a borehole into a subterranean formation comprising:

(a) providing a lost circulation fluid comprising water or an aqueous solution, water soluble crosslinkable polymer, a crosslinking agent, and a filter aid;

(b) injecting the lost circulation fluid into the formation and into the opening to be plugged; and

(c) applying pressure to dewater the lost circulation fluid to force the polymer and crosslinking agent into the formation, and to form the filter aid into a plug.

38. The method of claim 37, wherein the filter aid is selected from the group consisting of diatomaceous earth, perlite, glass beads, magnesium silicate, solid thermoplastic or thermoset polymers, talc, and calcium silicate.

39. The method of claim 38, wherein the polymer is an a carboxylate-containing polymer, and the crosslinking agent is selected from the group consisting of chromium (III) carboxylate complexes, aldehydes, dialdehydes, formaldehydes, glutaraldehyde, dichromates, titanium chelates, phenols, substituted phenols, ethers, aluminum citrate, and aluminates.

40. The method of claim 39, wherein the filter aid comprises at least one of diatomaceous earth or pearlite.

41. The method of claim 40, wherein the polymer comprises a low molecular weight polymer having a molecular weight less than 200,000, and a high molecular weight polymer having a molecular weight of at least 200,000.

42. The method of claim 40, wherein the polymer is a water soluble, carboxylate containing acrylamide, and the crosslinking agent is a chromium (III) carboxylate complex.

43. The method of claim 42, wherein the filter aid is diatomaceous earth.

44. The method of claim 42, wherein the filter aid is pearlite.

45. The method of claim 42, further comprising reinforcing material selected from the group consisting of hydrophilic fibers, hydrophobic fibers, and comminuted plant material.

46. A method of circulating a lost circulation fluid in a welbore penetrating a subterranean formation, comprising:

(a) providing a lost circulation fluid comprising water or an aqueous solution, water soluble crosslinkable polymer, a crosslinking agent, and a filter aid;

(b) circulating the lost circulation fluid in the wellbore.

47. The method of claim 46, wherein the filter aid is selected from the group consisting of diatomaceous earth, perlite, glass beads, magnesium silicate, solid thermoplastic or thermoset polymer beads, talc, and calcium silicate.

48. The method of claim 47, wherein the polymer is an a carboxylate-containing polymer, and the crosslinking agent is selected from the group consisting of chromium (III) carboxylate complexes, aldehydes, dialdehydes, formaldehydes, glutaraldehyde, dichromates, titanium chelates, phenols, substituted phenols, ethers, aluminum citrate, and aluminates.

49. The method of claim 48, wherein the filter aid comprises at least one of diatomaceous earth or pearlite.

50. The method of claim 49, wherein the polymer comprises a low molecular weight polymer having a molecular weight less than 500,000, and a high molecular weight polymer having a molecular weight of at least 500,000.

51. The method of claim 49, wherein the polymer is a water soluble, carboxylate containing acrylamide, and the crosslinking agent is a chromium (III) carboxylate complex.

52. The method of claim 51, wherein the filter aid is diatomaceous earth.

53. The method of claim 51, wherein the filter aid is pearlite.

54. The method of claim 51, further comprising reinforcing material selected from the group consisting of hydrophilic fibers, hydrophobic fibers, and comminuted plant material.

55. A method of modifying a lost circulation fluid circulating in a wellbore penetrating a subterranean formation, comprising:

(a) introducing a water soluble crosslinkable polymer, crosslinking agent, and filter aid to the circulating lost circulation fluid.

56. The method of claim 55, wherein the filter aid is selected from the group consisting of diatomaceous earth, perlite, glass beads, magnesium silicate, solid thermoplastic or thermoset polymer beads, talc, and calcium silicate.

57. The method of claim 56, wherein the polymer is an a carboxylate-containing polymer, and the crosslinking agent is selected from the group consisting of chromium (III) carboxylate complexes, aldehydes, dialdehydes, formaldehydes, glutaraldehyde, dichromates, titanium chelates, phenols, substituted phenols, ethers, aluminum citrate, and aluminates.

58. The method of claim 57, wherein the filter aid comprises at least one of diatomaceous earth or pearlite.

59. The method of claim 58, wherein the polymer comprises a low molecular weight polymer having a molecular weight less than 500,000, and a high molecular weight polymer having a molecular weight of at least 500,000.

60. The method of claim 58, wherein the polymer is a water soluble, carboxylate containing acrylamide, and the crosslinking agent is a chromium (III) carboxylate complex.

61. The method of claim 60, wherein the filter aid is diatomaceous earth.

62. The method of claim 60, wherein the filter aid is pearlite.

63. The method of claim 55, wherein the water soluble crosslinkable polymer, crosslinking agent, and filter aid, are all in solid form.