Abstract:
A method of conditioning a compacted polymeric powder to a flowable and meterable state. The polymeric powder is compacted during transport such that the flowability is hindered. To increase flowability, gas is introduced into the polymeric powder to condition the same to an improved flowable and meterable state.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation of patent application Ser. No. 11/146,596, now U.S. Pat. No. 7,540,308, filed Jun. 7, 2005, and claims the benefit of the filing date thereof, the disclosure of which is hereby incorporated by reference in its entirety. 

   FIELD OF THE INVENTION 
   Background of the Invention 
   Chemical compositions are used in subterranean operations for such purposes as the development and completion of wellbores that penetrate subterranean formations, and the production of gaseous and liquid hydrocarbons from natural reservoirs. These operations include perforating subterranean formations, fracturing subterranean formations, modifying the permeability of subterranean formations, or even controlling the production of sand or water from subterranean formations. Some compositions employed in these oilfield operations are commonly known as drilling compositions, completion compositions, work-over compositions, packer compositions, fracturing compositions, stimulation compositions, conformance or permeability control compositions, consolidation compositions, and the like. Often such chemical compositions are additives, crosslinkers, or polymer compositions, and in the case of viscosifying agents, may be agents such as guar, guar-derived polymer compositions, cellulose, or cellulose-derived polymer compositions. These chemical compositions are generally transported to wellsites, where a wellbore is located, slurried in a fluid carrier, such as diesel fuel, or mineral oil, for example. 
   The use of a fluid carrier, however, has drawbacks. For example, the use of a fluid carrier increases the cost of the polymer composition. The fluid carrier to suspend the polymer composition must be purchased, along with any other agents required to aid in wetting the polymer composition upon mixing with water at the wellsite. Additionally, the use of a fluid carrier increases the weight of the polymer composition and thereby increases the transportation costs. Furthermore, depending on the type of fluid carrier used, there may be environmental regulations regarding exposure to the fluid carrier. Thus, it would be advantageous to avoid the use of a fluid carrier to transport chemical compositions to wellsites for subterranean treatment operations. 
   SUMMARY OF THE INVENTION 
   To alleviate one or more disadvantage associated with the use of a fluid carrier, the invention is directed toward supplying chemical compositions in substantially dry form (e.g. in powder form) for subterranean treatment operations. The inventors have discovered that some chemical compositions, such as viscosifying polymer compositions, crosslinkers, additives, chelants, surfactant, delay agents, proppants, breakers, and the like, in powder form can become compacted for various reasons and particularly tend to become compacted due to vibrations which occur during transport. Compacting can decrease the flowability and/or prevent the powder chemical composition from adequately flowing out of a container. Such a decrease in flowability also may lead to metering accuracy concerns. To improve the flowability of the powdered chemical composition, the inventors have discovered that introducing a gas into the powdered chemical composition improves the flowability. As flowability is improved, metering of the dry chemical composition may also be improved. 
   In one aspect of the invention, a method of supplying a powdered chemical composition to a wellsite for treating a subterranean formation is disclosed. The method includes the steps of (1) introducing a powdered chemical composition into a container at a first location; (2) transporting the container including the powdered chemical composition to a second location different than the first location; (3) introducing a gas flow into the powdered chemical composition within the container; and (4) discharging the powdered chemical composition from the container; whereby the metering of the powdered chemical composition after discharge is improved. 
   In another aspect of the invention, a method of increasing the flowability of a compacted powder chemical composition is disclosed. The method includes the steps of (1) retaining a compacted powder chemical composition having a bulk density of a first value in a container; and (2) altering the bulk density of the compacted polymeric powder composition within the container to a second value, the second bulk density value being less than the first bulk density value thereby resulting in an increased flowability of the polymeric powder composition upon discharge from the container. 
   In yet another aspect of the invention, a method of delivering a powdered polymer chemical composition is disclosed. The method includes the steps of (1) transporting a guar based powdered polymer chemical composition to a wellsite in a container; (2) aerating the powdered polymer chemical composition within the container with a plurality of air flows introduced into the container; (3) reducing the bulk density of the powdered polymer chemical composition with the introduced air flows; and (4) discharging the reduced bulk density powdered polymer chemical composition from the container. 
   In a further aspect of the invention, another method of delivering a powdered polymer chemical composition to a wellsite is disclosed. The method includes the steps of (1) transporting a guar based powdered polymer chemical composition to a wellsite in a container; (2) aerating the powdered polymer chemical composition within the container with a plurality of air flows introduced into the container; (3) discharging the powdered polymer chemical composition from the container; and, (4) metering the powdered polymer chemical composition after discharging from the container. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
       FIG. 1  is a schematic cross-sectional representation of a transport container including apparatus for introducing gas into a viscosifying polymer powder within the transport container; 
       FIG. 2  is a schematic representation of a gas supply system for use with the container of  FIG. 1  according to the principles of the present invention; and 
       FIG. 3  is a flowchart of a method of conditioning a compacted polymeric powder to a flowable state according to the principles of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The following description of the preferred embodiment is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. Illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation specific decisions must be made to achieve the developer&#39;s specific goals, such as compliance with system related and business related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time consuming but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. 
   Chemical compositions, such as viscosifying polymer compositions, crosslinkers, additives, chelants, surfactants, delay agents, proppants, breakers, and the like, in powder form can become compacted for various reasons and particularly tend to become compacted due to vibrations which occur during transport. Compacting of the powdered chemical composition can decrease the flowability and/or prevent the powdered chemical composition from adequately flowing out of a container. To improve the flowability of the powdered chemical composition, the inventors have discovered that introducing gas into the powdered chemical composition improves the flowability. As flowability is improved, metering of the powdered chemical composition may also be improved. As used herein, the term “viscosifying polymer compositions” means any suitable polymer compositions for treating a subterranean formation, such as, by non-limiting example, guar, guar-derived polymers, cellulose, cellulose-derived polymers, xanthan gum, or synthetic polymers such as polyacrylamides and polyacrylamide copolymers, and the like. 
   Referring to  FIG. 1 , a schematic cross-section of a container  20  suitable for supplying a powdered chemical composition to a desired location, such as a wellsite, is shown. Container  20  can be loaded with the powdered composition  32  at one location, such as a supply location, and preferably transported in the container to a wellsite for subsequent discharge of the powdered chemical composition  32 . Container  20  has an interior cavity  22  with a lower discharging/feeder portion  24 . Cavity  22  is defined by longitudinally extending sidewalls  26 ,  28  and a bottom surface  30 . Each sidewall  26 ,  28  has a tapering portion  26   a ,  28   a  that taper toward each other as they extend toward bottom surface  30 . Tapering portions  26   a ,  28   a  facilitate the flow of powdered composition  32  within cavity  22  toward discharge portion  24 . 
   A metering device/apparatus  40  is disposed within discharge portion  24  of cavity  22 . Metering device  40  controls the quantity and rate at which a powdered chemical composition  32  is discharged from container  20 . Metering device  40  includes a longitudinally extending metering screw  42  and a pair of longitudinally extending agitators  44 ,  46  that help feed the powdered chemical composition  32  into metering screw  42 . 
   A plurality of devices  50  for introducing gas to the powdered chemical composition  32  are located at various locations along the container  20 . As illustrated, the devices  50  are preferably located along sidewalls  26 ,  28  and in proximity to the discharge portion  24 . As will be discussed in more detail below, the introduction of gas, such as, by non-limiting example, air, nitrogen, carbon dioxide, and the like, into the powdered chemical composition  32  reduces the bulk density of the powdered chemical composition  32  within container  20  and increases the flowability of the composition at the time of discharge.  FIG. 1  also illustrates that during the discharge of a compacted powdered chemical composition  32 , in the absence of introduction of gas, the centrally located portion of the powdered composition  32  may have greater flowability than the outer portions, thus forming a central columnar cavity during the transfer. 
   The devices  50  can take a variety of forms. For example, the devices  50  can include one or more nozzles, one or more elastomeric cups attached to the interior of container  20  in which compressed air is injected under the cups, and one or more permeable membranes, such as a felt cloth or finely divided, consolidated metal particles (porous metal) or a finely perforated pad through which the gas can be injected into container  20 . Other examples of possible gas introduction devices include those disclosed in U.S. Pat. No. 4,172,539 to Botkin for “AERATOR NOZZLE,” issued Oct. 30, 1979; U.S. Pat. No. 4,556,173 to Pausch et al. for “BIN FLUIDIZER,” issued Dec. 3, 1985; U.S. Pat. No. 4,662,543 to Solimar for “AERATION DEVICE FOR ASSISTING IN AERATION OF MATERIAL FROM CONTAINERS,” issued May 5, 1987; and U.S. Pat. No. 6,170,976 to Sisk for “PREASSEMBLED FLUIDIZING DEVICE HAVING EXPANSIVE AIR PASSAGE STIMULATING ENHANCED FLOW OF GRANULAR MATERIALS IN TANK TRAILERS AND CONTAINERS,” issued Jan. 9, 2001. 
   Referring now to  FIG. 2 , a schematic of a gas supply system  60  for supplying gas flow to gas introduction devices  50  is shown. Gas supply system  60  includes a gas supply  64 . Gas supply  64  can be an integral part of container  20 , a vehicle for transporting the container, or a separate component attached to the container prior to discharge. Regardless of the location, gas supply  64  is operable to supply a gas flow to each gas device (1 st  to the N th )  50  via appropriate supply plumbing  66 . A selectively operable controller  68  controls the operation of gas supply  64  and/or each gas introduction device  50 . Controller  68  can also take a variety of forms. For example, controller  68  can be as simple as one or more manually operable open/close or proportional valve(s). Alternately, if greater control is desired, controller  68  can be an electrical or pneumatic controller that can automatically individually control gas supply  64  and/or each gas introduction device  50  via appropriate connections  70 ,  72 , respectively, therebetween. Regardless of the type of controller utilized, gas supply system  60  is operable to selectively supply gas flows to gas introduction devices  50  as needed. By the phrase “selectively supply,” it is meant that gas flows can be a steady stream of gas, pulsed flows of gas or a combination thereof, in patterned or random order. 
   The methods of the present invention are applicable to a variety of powdered chemical compositions, such as viscosifying polymer compositions for well treatment fluids by way of non-limiting example. Preferred types of viscosifying polymer compositions may include any suitable polymer compositions, such as, by non-limiting example, guar, guar-derived polymers, cellulose, and cellulose-derived polymers. The viscosifying polymer in substantially dry form (powder) is typically ground to very small dimensions. Preferably, the median particle size of the viscosifying polymer is in the range of from about 40 to about 60 microns. This small particle size aids in the rapid hydration and viscosification of the well treatment fluid, and facilitates continuously mixing a fluid. The bulk density of the viscosifying polymer is generally in the range of from about 500 to about 700 kilograms per cubic meter. 
   During transport of powdered chemical composition  32  from a supply location to the wellsite, vibrations of the container  20  can cause the powdered chemical composition  32  to become compacted. Specifically, the bulk density of the powdered chemical composition is increased due to the induced vibrations during movement of container  20  to the wellsite. Bulk density of the powdered chemical composition varies with the consolidating pressure. The permeability, as measured with air flow through the powdered chemical composition, varies inversely with the bulk density. It is believed that the increase in bulk density increases the consolidation strength of the powdered chemical composition such that flow of the powdered chemical composition at discharge, generally through a metering device  40  is reduced or ceases altogether. It has been found that the introduction of a gas, such as compressed air, into the powdered polymer composition, especially at the bottom of the compacted powdered chemical composition in container  20 , substantially reduces the bulk density and improves the flowability of the powdered chemical composition. 
   Referring to  FIG. 3 , the transporting and delivery of a powdered polymer composition from a supply location to a wellsite is shown. The powdered polymer composition is packed into transport container  20 , as indicated in block  100 . Container  20  is then transported from the supply site to the wellsite, as indicated in block  102 . Container  20  can be transported over the roadway and/or railways or other suitable means of transport. During transport vibrations are induced into the powdered polymer composition in container  20 . The vibrations cause the bulk density of the powdered polymer composition to become compacted within container  20  which increases the bulk density of the powdered polymer composition. Optionally, as indicated in block  104 , gas flows can be introduced into the powdered polymer composition during transport via gas devices  50 . When the gas is introduced into container  20  during transport, a suitable gas supply  64  is included either with container  20  and/or the vehicle transporting container  20 . 
   Upon arriving at the wellsite, gas can also be introduced into the powdered polymer composition in container  20 , as indicated in block  106 . If needed, a local gas supply  64  is connected to supply plumbing  66 . Controller  68  is then operated to cause gas supply  64  to supply gas flows to gas devices  50  which then flow into container  20 . The gas flows flow through the powdered polymer composition therein and decreases the bulk density of the powdered polymer composition. This operation thereby conditions the compacted powdered polymer composition to an improved flowable state. 
   Once the powdered polymer composition is flowable, metering device  40  can be operated to discharge the powdered polymer composition from the container at the wellsite, as indicated in block  108 . Optionally, as indicated in block  110 , the gas flows can continue to be introduced into the powdered polymer composition during the discharging operation. 
   Accordingly, the present invention facilitates the use of a viscosifying powdered polymer composition in dry form at a wellsite. The transport of the polymer composition in dry form eliminates the cost of purchasing and disposing of a liquid carrier. Additionally, the injection of gas flow into the polymer composition within container  20  conditions the polymer composition to a flowable state. The use of such gas flows thereby minimizes the concern of vibrational compacting that occurs to the polymer composition during transport. 
   Methods of the invention are useful in subsurface operations, including such operations as fracturing subterranean formations, modifying the permeability of subterranean formations, fracture or wellbore cleanup, acid fracturing, matrix acidizing, gravel packing or sand control, and the like. Another application includes the placement of a chemical plug to isolate zones or to assist an isolating operation. 
   When used in fracturing operations, techniques for hydraulically fracturing a subterranean formation will be known to persons of ordinary skill in the art, and will involve pumping a fracturing composition, often including a powdered chemical composition, into the borehole and out into the surrounding formation. The fluid pressure is above the minimum in situ rock stress, thus creating or extending fractures in the formation. See Stimulation Engineering Handbook, John W. Ely, Pennwell Publishing Co., Tulsa, Okla. (1994), U.S. Pat. No. 5,551,516 (Normal et al.), “Oilfield Applications”, Encyclopedia of Polymer Science and Engineering, vol. 10, pp. 328-366 (John Wiley &amp; Sons, Inc. New York, N.Y., 1987). In the fracturing treatment, the compositions delivered by methods of the invention fluids may be delivered in the pad treatment stage, the proppant stage, or both. The fracturing materials are preferably mixed on the surface. Alternatively, the materials may be mixed downhole. 
   Methods of the invention may be useful for delivering powdered chemical compositions for cleanup operations. The term “cleanup” or “fracture cleanup” refers to the process of removing the fracture fluid (without the proppant) from the fracture and wellbore after the fracturing process has been completed. Techniques for promoting fracture cleanup traditionally involve reducing the viscosity of the fracture fluid as much as practical so that it will more readily flow back toward the wellbore. The invention may also be useful when gravel packing a wellbore. 
   The following example is presented to illustrate the methods of conditioning compacted powdered chemical compositions, and should not be construed to limit the scope of the invention, unless otherwise expressly indicated in the appended claims. All percentages, concentrations, ratios, parts, etc. are by weight unless otherwise noted or apparent from the context of their use. 
   EXAMPLE 
   The following example illustrates the invention, as described herein above. 
   A sample of a powdered viscosifying polymer composition was subjected to vibrations to determine the compaction that can be expected to occur when being transported. In the test, 100 grams of guar gum, powdered polymer composition, was placed in a 500 ml graduated cylinder. The cylinder with the sample therein was subjected to vibrations having an amplitude of 5 mm and a frequency of 10,000 Hz. The initial bulk density of the polymer composition sample was about 520 kilograms per cubic meter. After being subjected to the vibrations for a duration of two minutes, the bulk density was found to have increased to about 660 kilograms per cubic meter. The graduated cylinder was then inverted and no flow was observed from the polymer composition at the bulk density of about 660 kilograms per cubic meter. 
   Compressed air at a pressure of about 0.7 MPa was introduced into the bottom of the graduated cylinder through a 3.2 mm diameter tubing for 5 seconds. The introduction of the compressed air reduced the bulk density to about 590 kilograms per cubic meter. The graduated cylinder was then again inverted and the bulk density was adequate to allow the polymer composition to flow from the cylinder upon inversion. 
   While the present invention has been described with reference to specific embodiments, it should be appreciated that the above description is merely exemplary in nature and variations that do not depart from the gist of the invention are intended to be within the scope of the invention. For example, while metering device  40  is shown as including a metering screw  42  and two agitators  44 ,  46 , it should be appreciated that other types of metering devices could be employed. Additionally, while container  20  is shown as having a specific configuration, it should be appreciated that the configuration of transport container  20  can take a variety of forms and still be within the scope of the present invention. Moreover, while a specific polymer composition having specific physical properties is disclosed, it should be appreciated that other powdered polymeric compositions, or powdered chemical compositions can also be employed and utilized with the methods of the present invention. Thus, such variations are not to be regarded as a departure from the spirit and scope of the invention.