Patent Publication Number: US-6655475-B1

Title: Product and method for treating well bores

Description:
This application claims the benefit of the filing date of U.S. provisional application Ser. No. 60/263,969, filed Jan. 23, 2001, entitled “Product and Method for Treating Well Bores.” 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to oil, gas and water wells and, more particularly, but without limitation, to products and methods for treating well bores during drilling and completion. 
     BACKGROUND OF THE INVENTION 
     Oil and gas well bores typically are made by drilling down into a formation using rotary-driven drill bits. This process generates cuttings that must be flushed or swept from the well to maximize efficiency of the drilling operation. Conventionally, this sweeping process has been carried out by pouring a liquefied polymer composition down through the drill string. Other well treatments involve the introduction of a treatment composition into the well bore from the surface. For example, sometimes during the drilling process, it is desirable to introduce agents to act as preservatives, caustics, and/or corrosion inhibitors. 
     Where these treatment chemicals and compositions are liquid, the introduction of the liquid through the drill pipe is often problematic. For example, in the case of liquid polymers, spillage frequently occurs around the rig floor and near the mud pits and the mud pump. This makes the work area hazardous because the liquid is so slippery. Moreover, spillage results in waste. Still further, most of the treatment compositions are introduced using water or other solvents, which reduces the concentration and the efficiency of the compositions. 
     SUMMARY OF THE INVENTION 
     The present invention comprises a well treatment product for use in a well bore with a treatment solvent. The product comprises a concentrated well treatment composition. The composition is soluble in the solvent to form a circulating solution. The circulating solution formed is characterized by the ability to circulate through the well bore. The product further comprises a container enclosing the composition. The container is sized to be received in the well bore and is at least partially soluble in the solvent to release the composition. 
     Further, the present invention comprises a method for treating a well bore. The method comprises depositing in the well bore from the surface an effective amount of a treatment composition. The treatment composition is soluble in a selected solvent to form a circulating solution characterized by the ability to circulate through the well bore. When it is deposited, the treatment composition is enclosed in a container that is at least partially soluble in the selected solvent. An effective amount of the selected solvent is deposited in the well bore to dissolve the treatment composition and form the circulating solution. The circulating solution is circulated through the well bore, and a significant portion of the circulating solution is recovered at the surface. 
     Still further, the present invention includes a system for treating a well bore. The system comprises an elongate conduit sized to be inserted down the well bore. Also included in the system are a solvent, and a container enclosing a treatment composition. The container is sized to be received in the conduit and is characterized by being at least partially soluble in the solvent. The treatment composition is soluble in the solvent to form a circulating solution characterized by the ability to circulate through the well bore. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a semi-schematic view of a system comprising the well treatment product of the present invention. 
     FIG. 2 is a longitudinal sectional view of a product made in accordance with the present invention and comprising a treatment composition in particulate form. 
     FIG. 3 is a longitudinal sectional view of a product made in accordance with the present invention and comprising a liquid as the treatment composition. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Turning now to the drawings in general and to FIG. 1 in particular, there is shown therein a well treatment system  10  in accordance with one embodiment of the present invention. The system  10  services a well  12  comprising a well bore  14 . As used herein, “well” refers to any subterranean well including but not limited to oil and gas wells. As shown, the system  10  includes an elongate conduit, such as the drill string  16 . A rotary bit  18  is operatively attached at the end of the drill string  16 , and the drill string is driven by a rig (not shown). 
     The system  10  preferably includes a fluid circulation assembly  20  for circulating fluid, such as drilling mud  22 , down the drill string  16  and up through the well bore  14  outside the drill string. The fluid circulation assembly  20  preferably includes a pump  24  fluidly connected to the drill string  16  by a conduit  26  to pump the fluid being circulated down the drill string  16 . A Kelly  28  and a swivel  30  usually are included. Because the fluid  22  returning from the bottom of the well bore  14  near the bit  18  is likely to contain cuttings and other solids, it will usually be desirable to include in the fluid circulation assembly  20  a filtering device, such as a mud tank  32 . The fluid  22  returning from the well bore  14  is directed through the flow line  34  to the mud tank  32 . From the mud tank  32 , the fluid  22  is returned to the pump  24  through the conduit  36 , and cycle is repeated. Now it will be seen that in this system  10 , drilling mud  22  or other fluids can be continuously circulated through the bottom of the well bore  14 . 
     In the practice of the present invention, the system  10  further comprises a well treatment product  40  for use in the well bore  14 . As shown in FIG. 2, to which attention now is directed, the product  40  comprises a treatment composition  42  inside a container  44 . The treatment composition  42  is selected depending on the nature of the treatment to be applied to the well bore  14 . For example, the treatment may be sweeping the well bore or introducing an anti-corrosive or caustic agent, and the treatment composition will vary accordingly. 
     Where the selected treatment is sweeping the well bore  14 , a preferred treatment composition  42  is a polymer agent. Preferably, the polymer used in this application is a partially hydrolyzed polyacrylamide (“PHA”) concentrated in a powdered or particulate form. One suitable composition is a copolymer of sodium acrylate and acrylamide, such as the composition sold under the brand name ALCOMER 110RD by Allied Colloids, Inc. (Suffolk, Va.). This polymer also acts as a bentonite extender or viscosifier in low solids, nondispersed muds or floculate, and settles solids in clear water drilling. The polymer used in this invention may also aid in minimizing bit and stabilizer balling in soft or gumbo shales. When liquified, this polymer is a relatively viscous fluid capable of encapsulating drill cuttings and stabilizing shale in a well bore, and yet is fluid enough to be circulated repeatedly through the well bore  14 . “Shale stabilization” means the ability of the polymer to adsorb onto cuttings and clays clinging to the borehole, thus preventing dispersion. 
     It will be appreciated that the system  10  includes a solvent. In the sweeping system illustrated herein, the solvent is the water-based drilling mud  22  (FIG.  1 ). Alternately, the solvent could be water, as the polymer agent is soluble in both. However, the solvent may vary widely depending on the selected treatment composition. 
     In the preferred system  10 , the composition  42  is soluble in the drilling mud  22  to form a circulating solution characterized by the ability to circulate through the well bore  14 . As used herein, “circulate” used in reference to the circulating solution denotes a fluid of a character and viscosity that it can flow freely down the drill string  16  and back up through the well bore  14  for recycling through the fluid circulating assembly  20 . While this encompasses a variety of composition/solvent combinations, it excludes swellable compositions designed to swell down hole in the presence of mud or water for the purpose of plugging a well or borehole, instead of circulating through the well bore. It is understood, of course, that a certain amount of the circulating solution necessarily will remain in the well bore in order to have the desired effect. However, the amount effective for treating the well bore in accordance with this invention is not sufficient to block or plug the well bore. 
     As used herein, “solution” and “solvent” are not limited to the strict chemical definitions of the terms. Rather, these terms are used herein to denote any fluid composition, including a suspensions, emulsions, and mixtures as well as a true solutions, capable of being circulated through the well bore. 
     Referring still to FIG. 2, the container  44  is sized to be received in the well bore  14  and to contain an effective amount of the treatment composition  42 . The container may be rigid or flexible and may take various shapes and sizes. For example, the container may be one or more spheres, capsules or tubes, and may be circular or non-circular in cross-section. In the preferred form shown in the drawings, the container  44  is an elongate, cylindrical tube. 
     The container  44  is formed at least partially of material that is soluble in the selected solvent to release the treatment composition  42  down hole. For example, the container may be made entirely of a soluble material or be formed with openings or pores filled with soluble plugs. Thus, “soluble” when used to describe the container  44  means at least partially soluble when exposed to the selected solvent. 
     In the embodiment described herein for sweeping a well bore during drilling, the container  44  preferably is an elongate tube formed of a soluble polymer soap composition that dissolves entirely in the presence of drilling mud or water down hole. Such soluble tubes are available under the brand name “DI” tube from Hydro Foam Technology (Stillwater, Okla.). The DI brand tube is about 15 inches long and about 1 inch in diameter. It comes with one open end and one end closed by a salt plug  46 . The open end may be closed by a soap plug  48 , or in some other suitable manner, after the container  44  is filled with the treatment composition  42 . 
     Turning now to FIG. 3, there is shown therein an alternate embodiment of the well treatment product designated by the reference numeral  40 A. The product  40 A comprises a container  44  similar to the container  44  of the embodiment of FIG.  2 . However, the composition  42 A is in a concentrated liquid form instead of a powdered or particulate form, as in FIG.  2 . 
     In accordance with the method of the present invention, a well bore can be treated. First, returning to FIG. 1, an effective amount of a treatment composition  42  is deposited in the well bore  14  from the surface of the well  12 . The treatment composition, such as a polymer agent for sweeping as well as described previously, is soluble in a selected solvent, such as the drilling mud  22 . When mixed with the solvent, the combined solvent and composition form a circulating solution, such as a drilling mud mixed with diluted, liquefied polymer agent, that is characterized by the ability to be circulated through the well bore. 
     In the practice of this method, when the treatment composition is deposited in the well bore, it is enclosed in a container that is at least partially soluble in the solvent. A preferred container, as described above, is DI brand tube formed of soap. 
     Having deposited the composition-filled container in the well bore, an effective amount of the selected solvent, such as drilling mud or water, is deposited in the well bore to dissolve the composition and form the circulating solution. It will be understood that the well bore may already contain fluid, such as drilling mud, that is to be used as the solvent. 
     Where the application is sweeping a well bore during the early phase (e.g., the first 5000 feet), the composition-filled container comprising the treatment product  40  may be introduced by simply dropping it down the drill string  16  (FIG.  1 ), and it will sink to the bottom of the well bore  14 . Once the product  40  reaches the drill bit  18  it will be dissolved in the drilling mud  22 . The liquefied polymer or other treatment composition is forced through the orifices in the drill bit and is flushed back up hole by continued circulation of the drilling mud  22  in which it becomes diluted. 
     While in the embodiment described herein the treatment product  40  is introduced into the well bore  14  through the drill string  16 , other methods may be used to deposit the product. It may be dropped loose into an empty well bore, or it may be lowered at the end of a cable, or deposited in any other suitable manner. 
     The circulating solution is circulated through the well bore to expose the well bore to the solution to produce the desired effect. For this purpose, the circulating assembly  20  described herein will suffice. After the treatment is completed, a significant portion of the circulating solution is recovered from the well at the surface. 
     Now it will be appreciated that the present invention provides an improved product, system and method for the treatment of well bores during the drilling phase with circulating solutions. A treatment product comprising a powdered or concentrated liquid form of a treatment composition is placed inside a soluble container that will dissolve down hole to allow the treatment composition to escape through the drill bit into the well bore and form a diluted circulating solution. Thus, the process of introducing the composition is simplified and made safer and more efficient and consequently less costly. Because the treatment composition is introduced in a container, there is no spillage of slippery or hazardous materials. Because the treatment composition may be in a powdered or concentrated form, efficiency of the composition is improved; that is, a greater concentration per volume of material is provided. 
     Changes can be made in the combination and arrangement of the various parts and steps described herein without departing from the spirit and scope of the invention.