MX2007002155A - Dry blend fracturing fluid additives - Google Patents

Abstract

A method and compositiona for crosslinking a polymer based fluid includes providing a dry blend of crosslinker and delay agent. The crosslinker and delay agent are mixed and granulated in a dry form prior to addition to the polymer fluid.

Description

ADDITIVES OF FRACTURATION FLUID OF DRY MIXTURE BACKGROUND OF THE INVENTION Field of the Invention The present invention relates generally to additives for fracturing fluids. More specifically, the invention is a dry granulated mixture consisting of a crosslinker and a delay agent. Description of the Prior Art In the recovery of hydrocarbons from underground formations, it is common practice, particularly in low permeability formations, to fracture the hydrocarbon carrier formation, providing flow channels. These flow channels allow oil or gas to reach the well bore so that oil or gas can be pumped from the well. Water-based hydraulic fracturing fluids usually contain a hydratable polymer that acts to swell the fracture and can be thickened further by chemical cross-linking. Such a polymer is usually presented in a powder form, or in the form of a pasty mixture in a hydrocarbon such as diesel, and is hydrated on the surface of the earth, for example in a batch mixing operation in large mixing tanks by a significant period of time, and then mixed with other liquid additives of various types using high cost equipment. After hydration, the polymer is typically crosslinked to increase the thickness of the fluid and improve its viscosity at elevated temperatures often found in the fracture, so that it can transport proppant into the fracture once it is pumped into the borehole. of well below the earth's surface. The Natural polymers include polysaccharides such as guar and guar derivatives such as guar hydroxypropyl (HPG), carboxymethylhydroxypropyl guar (CMHPH), carboxymethyl guar (CMG). , or hydrophobically modified guar. Crosslinking agents containing borate, zirconium and titanium are typically used. Both borate and organometallic crosslinking agents offer advantages depending on fluid performance and treatment cost requirements. Numerous chemical additives such as anti-foaming agents, acids or bases, or other chemicals can be added to provide the proper properties to the fluid after it is hydrated. Other additives commonly included in fracturing fluids include viscosity stabilizers, activators for crosslinking, shear recovery agents, hydration-enabling agents and clay stabilizers. Generally, a viscosity stabilizer is an additive used to retard polymer degradation from the effects of temperature, cut and exposure to iron. A clay stabilizer prevents the expansion or migration of clays in the formation. Pole-based hydraulic fracturing fluids are well known in the oilfield service industry. These fluids are routinely used to treat and fracture underground formations to increase production from them. Typically, the fluid is prepared or mixed on the surface by combining a number of flow rates of liquid additives with a hydrated polymer fluid. The fluid is then pumped down the orifice with sufficient pressure to achieve the treatment. In certain cases, The fluid can be used to transport proppant or other additives into the formation. The viscosity of the fluid is often an important consideration in the design of the work. The fluid must have sufficient viscosity to carry any included fluids, such as proppant; however, it can not be so viscous that it can not be economically pumped down the orifice. Crosslinkers are commonly used to increase the viscosity of polymer-based fracturing fluids. The crosslinker chemically connects or bonds the polymer chains in the fluid, in order to increase the viscosity. Well-known polymer crosslinkers include compounds containing boron, zirconium, and titanium. In many cases, the use of a crosslinker only causes a very rapid increase in the viscosity of the fluid and can present significant problems in terms of handling and pumping the viscosified fluid (ie, the amount of horsepower required to pump the highly viscous fluid). is greater than that typically provided in the workplace). To alleviate this problem, the crosslinking of the polymer can be delayed for a predetermined time. In this way, the fluid does not reach its full viscosity until it is down in the hole. Delay agents are commonly combined with the crosslinker before mixing the crosslinker with the polymer fluid. The delay of the polymer crosslinking mechanism can be achieved using different means. One method is to physically trap or sequester the crosslinker within a capsule that will dissolve over time under certain conditions of temperature, pH, pressure, etc. Alternatively, the crosslinker may be bound to or reacted with another chemical (i.e., a delay agent). The release from this chemical delay agent will also be a function of time, temperature and relative concentrations of the crosslinker and the delay agent. The delay in the crosslinker reaction is due to an exchange of ligands between the crosslinker, the delay agent and the polymer. In simplified terms, the delay is determined by the time required by the crosslinker to "escape" from the delay agent and crosslink the polymer. Although the fluid additives, including the crosslinker and the delaying agent, are typically provided in liquid form, it is known that some of these additives or in some cases the additives and the polymer can be provided in dry form. For example, Patent E.U.A. No. 5,372,732 (Harris) teaches a dry, granulated and delayed cross-linking agent. A borate crosslinker is combined with a liquid polysaccharide solution to produce a fluid containing a high crosslinking polymer. This solution is then dried and granulated and can then be added to a polymer fluid. Another example of the use of a dry mixture of polymers and additives is described in the patent E.U.A. No. 5,981,446 (Qiu). A dry mixed particulate composition is prepared which includes the polymer as well as a number of other additives and added to the water to produce a fracturing fluid. The specific composition of the fluid must be predetermined and generally can not be changed at the well site. This loss of flexibility can present significant problems in terms of termination of work. Decreased flexibility can also be a significant concern during job design. For example, in a typical fracturing job, fracture initiation is achieved by using a linear fluid (not crosslink) that does not contain proppant. Once the fracture is formed, the fluid is crisscrossed and the proppant is added. Clearly, two different mixtures would be necessary in this case, one that contains a crosslinker, the other that does not contain the crosslinker.

SUMMARY OF THE INVENTION The present invention is directed to a dry, granular mixture or composition for swelling or crosslinking polymer-based fracturing fluids. The mixture is composed of a cross-linker and a delay agent. The invention also discloses a method for adding this granulated mixture in dry form to a polymer-based fracturing fluid typically upstream of the proppant. The number of extra additive flows is reduced as the mixture combines in a simple additive two or more products that were typically provided separately. This decreases the complexity of preparing or mixing the fluid, in order to thus reduce the cost and time required to produce the fluid and perform a fracturing or other treatment of the formation. In addition, the concentration of the crosslinker and the delay agent in the mixture are often linked to the concentration of the chelating agent. Therefore, the quality control of the work is better because the two critical additives are added in a fixed proportion (the mixture is made in advance to work in a controlled environment the opposite of mixing at the place of the fracturing operation) . The granulated mixture is prepared by the provision of a dry cross-linker and a dry-delay agent. The crosslinker and the delay agent are typically combined or mixed completely in a dry form to produce a mixed crosslinker / delay agent compound. The compound can then be formed into granules. Depending on the nature of the components (Le., the between and the delay agent) it may be necessary to include a binder to aid in the formation and stability of the granules. The relative proportions of crosslinker and delay agent as well as the size of the granules can be adjusted to vary the length of the delay, as necessary. The dry, mixed compound is useful both in batch mixing and in fluids that are "mixed on the fly." At no point during the preparation of this dry blend are the individual components combined or provided in a liquid form. Similarly, the dry mixture is not dissolved or otherwise reduced to a liquid form before being shaped or formed into granules. This dry, granulated compound can be stored and transported easier to the well site. In addition, the preparation of the fracturing fluid is simplified, since the dry mix provides two additives in simple form, thus reducing the number of additive flows within the fluid. In addition, the number of operations in situ is reduced due to the reduced number of flows. A dry compound is not prone to freezing, thus facilitating use in cold climates. In addition, the concentration of the components in the dry mix will not change due to the evaporation of the solvent. This is particularly beneficial in warmer climates. Yet another advantage of the dry mix is a reduction in the volume and weight of the product, when compared to a liquid additive. Furthermore, it has been shown that the crosslinking activity, particularly that of the zirconium and titanium crosslinkers, decreases with time in the solution. The dry blend of the present invention reduces the time that the crosslinker is in solution before being combined in the polymer, thus maintaining a novel of higher activity and consistent. Depending on the specific application in which the compound will be used, it may be desirable to include any number of additional additives in the compound. As previously mentioned, a binder can be included to aid in the manufacture of the dry compound. In addition, the compounds may also include a viscosity stabilizer, particularly a high temperature stabilizer, an activator or a clay stabilizer. Using principles similar to those described above for a crosslinker / delaying agent compound, other fluid additives may be combined in dry form to produce a dry additive and / or simple granulate. For example, the crosslinker may be combined with an activator, a viscosity stabilizer, a cutting recovery agent, a hydration enabling agent, instead of the delay agent. Similarly, the delay agent may be combined with any number of suitable additives, including activators, stabilizers, shear recovery agents, hydration enablement agent and the like.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a graph showing the delay time as a function of the concentration of the delay agent. Figure 2 is a graph showing the viscosity over time for a polymer fluid. Figure 3 is a graph showing the effect of the size of the granule on the delay time.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is a crosslinker and a delay agent provided in a dry form. Preferably, the crosslinker / delaying agent is provided in a granular form. In contrast to the dry additives, particularly the crosslinkers and delaying agents, which have been developed in the past, the present invention does not require that the individual components (Le, the crosslinker and the delay agent) be mixed or complexed in liquid form before being dried. The crosslinker and the delay agent can both be combined in dry form to produce a dry compound. The crosslinkers useful in the present invention are those that are capable of crosslinking a polymer. In a preferred embodiment, the crosslinker contains boron. More preferably, the crosslinker is boric acid, borax, earthy alkali metal borates, borates of alkali earth metals or mixtures thereof. Alternatively, the crosslinker may be a zirconium or titanium compound, or a combination or mixture of any of the above-mentioned compounds. Similarly, any number of delay agents can be used in the present invention. Examples of suitable delay agents include, but are not limited to, polyols, sodium gluconate, sorbitol, a carbonate salt or a combination of the foregoing. In addition to the crosslinker and the delay agent, any number of additional suitable additives may be included in the dry mix material. In a preferred embodiment, a binder may be included to physically stabilize the dry mix and aid in granulation. Others Additives include, but are not limited to, a crosslinker activator, a high temperature stabilizer, a breaker, a shear recovery agent and a clay stabilizer. In a preferred embodiment, the stabilizer can be an oxygen scavenger, a polyol or a carbonate salt. The clay stabilizer may be any suitable composition, but preferably it is a salt such as potassium chloride. In a preferred embodiment, the breaker may be composed of an encapsulated or non-encapsulated oxidant. The specific delay time provided by the product of the present invention can be adjusted or modified through a number of parameters. The specific type and the relative amount of crosslinker and delay agent are the two primary factors. Nevertheless, the granule size, the pH of the fluid, temperature, the relative size of the particles being mixed and the presence of an external delay agent, crosslinker or activator can all be used to affect the delay time provided by the product granulated. The method of the present invention is to provide a polymer fluid, wherein the fluid can be totally or partially hydrated. A dry fluid additive is then mixed with the polymer fluid. The fluid additive consists of a granular compound that includes a crosslinker and a delay agent. In a first embodiment, the method of the present invention consists in mixing the polymer fluid and the additive in a simple tank (i.e., mixed by batches). The polymer is combined with a liquid and allowed to hydrate at least partially. The additive is then combined with the polymer fluid. Once the fluid and the additive are combined, the fluid can be pumped hole down. In a second embodiment, the method consists of mixing the components "on the fly." In other words, the components are mixed as the fluid is pumped down orifice. It is important to note that the crosslinker / delaying agent additive is provided in a dry form prior to the combination or addition to the polymer fluid. In an alternate embodiment, the crosslinking additive / dry delay agent can be added to or combined with a dry polymer. The combined additive and polymer can then be mixed with a suitable liquid flow rate to produce a polymer-based fluid. EXAMPLE The following examples illustrate certain embodiments of the present invention. Figure 1 shows the delay obtained as a function of the concentration of the delay agent in the dry mix. The samples were prepared with a polymer fluid with a charge of 4.2 grams per liter of fluid (35 pounds per 1000 gallons (ppt)). The polymer was completely hydrated in this example; however, in certain applications, it may be possible to add the crosslinker / delay agent before the polymer is fully hydrated. The polymer used in the experiment was guar. It should be completely clear that although in this example guar was used, any polymer or chelating agent can be used. Preferably, the polymer is guar or guar derivative. Preferred guar derivatives include hydroxypropyl guar, carboxymethyl hydropropyl guar, carboxymethyl guar or any combination thereof. The polymer fluid can be allowed to hydrate for approximately 30 minutes before the crosslink. The dry mixture of crosslinker and agent of Delay was added to the fluid while it was in a mixer at 2000 rpm. The crosslinker was present in an amount of 0.8 grams per liter of fluid (1.5 pounds per thousand gallons (ppt).) The amount of delay agent ranged from 0% by weight to about 1.1 grams per liter of fluid Following the addition of the crosslinker / delaying agent, 4.5 liters per thousand liters of caustic solution (28% solution of caustic soda) were added and the fluid was mixed again for 10 seconds. Final embouchure time was recorded for each sample The initial embosure time indicates the time required for a polymer fluid to develop an initial viscosity The final embosure time indicates the time required for the polymer to reach full viscosity. was boric acid and the delay agent was sodium gluconate, both were added simultaneously in the form of a powder.These results show that the crosslinker and the delay agent can to be added in dry form, without reaction or previous dissolution, to crosslink a polymer fluid. The following procedure was used to determine the embouchure times: the prepared fluid is poured from a container until a tongue of approximately 1.9 cm is formed and can be retracted back to the container. This is the initial embouchure time. The final embouchure time is the time at which a two-inch (5 cm) tongue can be poured and retracted. In addition to the use of guar base fluids, the crosslinker / retarder of the present invention was also tested with a CMHPG based fluid. A CMHPG fluid of 4.2 grams per liter was prepared and hydrated. The pH of the fluid was adjusted to approximately 9.46 with a soda solution caustic to 5%. A 200 ml sample of the CMHPG fluid was then cross-linked with a dry mixture containing sodium zirconium lactate and sodium gluconate at a molecular ratio of 40: 1. The dry mix was mixed in the fluid for approximately 45 seconds, indicating that the cross-linking was delayed by the dry mix. For comparison purposes, a typical polymer fluid CMHPG under the same conditions without a delay agent would have an intercross time of less than 10 seconds. Figure 2 shows the stability of a fluid prepared using a crosslinker / dry granulation delay agent. A base fluid consisting of 4, 2 grams per liter (35 ppt) of dry guar was hydrated in a mixer for approximately 30 minutes. The fluid was then crosslinked by the addition of a granulated mixture of 0.56 grams per liter, corresponding to 0.18 grams per liter of boric acid and 0.36 grams per liter of sodium gluconate, and also including binding agents and anti-cake in an approximate amount of 2% by weight. The activator was a liquid solution of 28% caustic soda used in 0.45 liters per thousand liters. The viscosity of the crosslinked fluid was then measured and recorded over time at 93 ° C in a Fann 50 rheometer. As can be seen, the fluid remained stable and maintained a viscosity adequate to the temperature for about 2 hours, at which point they were not taken other measurements. Figure 3 shows the difference in the delay time when the crosslinker / delaying agent is added in ground or pulverized form and in granulated form. A polymer-based fluid with a polymer charge of 4.2 grams per liter was prepared. The fluid was hydrated in a mixer for approximately 30 minutes. Following hydration, the fluid was crosslinked with 0.05 grams per liter of a 28% caustic soda solution and a crosslinker / delaying agent combination having 0.18 grams per liter of boric acid and 0.36 grams per liter of sodium gluconate. The crosslinking / delaying agent was added in a ground dry form and a first granular form (10/20 mesh size (ie, average particle diameter of 1.26 mm)) and a second granular form (mesh size 4 / 10 (ie, average particle diameter of 3.38 mm)). The results show that the larger the diameter of the particle, the longer the delay of the crossing, since the delay is a function of the surface area of the granule subject to dissolution. In addition, the result shows that the granular dry mix additive effectively crosslinks the polymer fluid and provides adequate delay. In addition to the combination of a crosslinker and a delay agent in a dry blend, as previously described, the present invention can include any additional number of dry components combined in a set to form a simple, dry additive. For example, magnesium oxide, an activator, and sodium gluconate, a delay agent, can be combined in dry form to produce a dry mixture to delay the crosslinking of a polymer fluid. To illustrate this, a solution of 4.2 grams per liter of guar and hydrated was prepared. An equivalent of 0.24 grams per liter of boric acid and 0.6 grams per liter of magnesium oxide, in the form of 0.42 grams of a dry mixture containing magnesium oxide and boric acid in a ratio of 2.5 : 1, was added to 500 mL of the hydrated guar solution and the resulting fluid was mixed for approximately 10 seconds. Following this, the fluid was added. The first embouchure appeared at 1 minute and the final intercross time was approximately 2 minutes. A similar experiment was then conducted with a similar guar base fluid. An equivalent solution of 4.2 grams per liter of guar was prepared and treated. An equivalent of 0.24 grams per liter of boric acid was added to 500 mL of the hydrated guar solution and the resulting fluid was mixed for approximately 30 seconds. A dry mixture of MgO and sodium gluconate, in a ratio of 1: 1, was then added in place of the MgO / boric acid mixture. The final intercross time was approximately 4 minutes.

Claims (10)

1. CLAIMS 1. A fluid additive consisting of: • a cross-linker; and • a delaying agent, in which the crosslinker and the delaying agent are combined in dry form to produce a dry granulated compound. The additive of Claim 1, wherein the crosslinker consists of at least one of the following: a boron containing compound, a titanium containing compound and a zirconium containing compound. 3. The additive according to any of the preceding Claims, wherein the crosslinker consists of boric acid, borax, alkali earth metal borates, borates of alkali earth metals or mixtures thereof. 4. The additive according to any of the preceding claims, wherein the delay agent consists of sodium gluconate, sorbitol or a combination of the foregoing. 5. The additive according to any of the preceding claims, which further comprises a viscosity stabilizer. 6. The additive according to any of the preceding claims, which further comprises an activator. 7. A fluid additive consisting of: • a first dry component; and • one second of delay, wherein the first and second components are combined in dry form to produce a simple compound. 8. The fluid additive of Claim 7, wherein the first dry component is a delay agent, an activator, a crosslinker, a cutting recovery agent, a viscosity stabilizer or a hydration enablement agent, and wherein the second dry component is different from the first dry component, the second component being dry a delay agent, a crosslinker, a cutting recovery agent, a viscosity stabilizer or a hydration enablement agent. 9. A method for crosslinking a polymeric fracturing fluid that consists of: • providing a fluid consisting of a polymer; and · provide a fluid additive consisting of a cross-linker and a delay agent, where the cross-linker and the delay agent are combined in dry form to produce a dry, granular compound. 10. The method of Claim 9, wherein the polymer is guar, a guar derivative. eleven . The method of Claim 10, wherein the guar derivative is guar hydroxypropyl, carboxymethylhydroxypropyl guar, carboxymethyl guar, and combinations thereof. 12. The method according to any of Claims 9-1, wherein the fluid additive is batch mixed with the fluid. 13. The method according to any of Claims 9-1, wherein the fluid additive and the fluid are mixed on the fly. The method according to any of Claims 9-1, wherein the fluid additive provides a delay to the crosslinker from about 30 seconds to about 15 minutes.