Abstract:
Acid-soluble plugs may be employed within telescoping devices to connect a reservoir face to a production liner without perforating. Such technology eliminates formation damage and debris removal associated with perforating, as well as reducing risk and time. The plugs may provide enough resistance to enable the telescoping devices to extend out from the production liner under hydraulic pressure. The plugs may then be dissolved in an acidic solution, which may also be used as the hydraulic extension fluid. After the plugs are substantially removed from the telescoping devices, the reservoir may be hydraulically fractured using standard fracturing processes.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a Divisional application and claims priority to U.S. application Ser. No. 12/723,983, filed on Mar. 15, 2010; which is incorporated by reference herein in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to methods and compositions for temporarily blocking a flow pathway, and more particularly relates, in one embodiment, to methods and compositions for temporarily blocking a flow pathway to subterranean formations during hydrocarbon recovery operations. 
       BACKGROUND 
       [0003]    There are a number of procedures and applications that involve the formation of a temporary seal or plug while other steps or processes are performed, where the seal or plug must be later removed. Often such seals or plugs are provided to temporarily block a flow pathway or inhibit the movement of fluids or other materials, such as flowable particulates, in a particular direction for a short period of time, when later movement or flow is desirable. 
         [0004]    The recovery of hydrocarbons from subterranean formations often involves applications and/or procedures employing coatings or plugs. In instances where operations must be conducted at remote locations, namely deep within the earth, equipment and materials can only be manipulated at a distance. One such operation concerns perforating and/or well completion operations incorporating filter cakes and the like as temporary coatings. 
         [0005]    Generally, perforating a well involves a special gun that shoots several relatively small holes in the casing. The holes are formed in the side of the casing opposite the producing zone. These perforations, or communication tunnels, pierce the casing or liner and the cement around the casing or liner. The perforations go through the casing and the cement and a short distance into the producing formation. Formations fluids, which include oil and gas, flow through these perforations and into the well. 
         [0006]    The most common perforating gun uses shaped charges, similar to those used in armor-piercing shells. A high-speed, high-pressure jet penetrates the steel casing, the cement, and the formation next to the cement. Other perforating methods include bullet perforating, abrasive jetting, or high-pressure fluid jetting. 
         [0007]    The characteristics and placement of the communication tunnels can have significant influence on the productivity of the well. Technology has been developed which eliminates the need for perforating guns and enables significantly more controlled perforation through the use of fluid conduits installed within casings. These fluid conduits may be extended out from the casing to contact a formation wall, thereby forming “perforations” at desired locations along the length of the casing. Temporary plugs in the conduits form fluid barriers, and the conduits are pushed out from the casing via fluid pressure. The plugs may be made of a porous filter structure on which a degradable barrier material is coated. After the fluid conduits are extended, the degradable material may be removed, thereby allowing the flow of fluids through the filter structure. This technology, known as TELEPERF™ from Baker Hughes Inc, is described in more detail in U.S. Pat. Nos. 7,527,103 and 7,461,699, each incorporated by reference herein its entirety. 
         [0008]    In some instances, it may be necessary or desirable to fracture a formation to enable or promote the flow of fluids therethrough. For example, in low-permeability reservoirs, it may be beneficial to fracture the well formation and inject proppants into the fractures to stimulate the flow of fluids (such as oil, gas, water, and the like) through the formation. When hydraulic fracturing is performed, the viscous fracturing fluids mixed with proppant are flowed into the formation through the casing and associated perforations. However, filters in the above-described TELEPERF™ devices may obstruct or impede the high-viscosity fluids and proppants utilized in hydraulic fracturing from entering the formation. 
         [0009]    Accordingly, it may be desirable to temporarily block, fill, or plug the fluid conduits without employing a filter structure in the conduits while still enabling the conduits to telescope outward via fluid pressure. 
       SUMMARY 
       [0010]    There is provided, in one non-limiting form, a method for hydraulic fracturing which includes drilling a wellbore through a subterranean reservoir and positioning a pipe within the wellbore. The pipe has orifices through at least a region of its wall, and flow conduits, pathways, channels, passages, outlets, or the like are situated within the orifices in a retracted position within the pipe. The flow conduits have temporary plugs which block, inhibit, or prevent the flow of fluid through the conduits. The hydraulic fracturing method further involves applying hydraulic pressure to the temporary plugs by pumping an extension fluid into the pipe and the flow conduits. The hydraulic pressure extends the flow conduits radially outward from the pipe in the direction of the wellbore wall. The temporary plugs may then be removed from the flow conduits via an acidic solution. In an exemplary non-limiting embodiment, the extension fluid may be an acidic solution which serves to both extend the flow conduits out from the pipe and to dissolve the temporary plugs. Hydraulic fracturing fluid may then be injected into the subterranean reservoir via the pipe and the flow conduits. 
         [0011]    In another non-limiting embodiment of the present disclosure, a plug may be provided for use in a conduit, pathway, channel, passage, or the like that is radially extensible from a pipe. The plug may be made of a material that has an acid solubility greater than 70% and permeability of less than 10 mD. The plug may additionally have a compressive Young&#39;s modulus of at least 5,000 MPa. For example, the plug may be made of a natural, low cost material, like Indiana limestone, other natural limestones with similar properties, or another material. In addition, the plug may have a matrix formation that is augmented with nanoparticles disposed within the matrix. 
         [0012]    In a further non-limiting embodiment, the present disclosure provides a pipe for use in well completions. The pipe may have flow conduits, pathways, channels, passages, outlets, or the like which provide fluid communication between the interior and the exterior of the pipe. The flow conduits may be at least partially disposed within the pipe and extensible from the pipe in a direction relatively perpendicular to a longitudinal axis of the pipe. Additionally, fluid flow through the flow conduits may be temporarily blocked, inhibited, or prevented by acid-soluble plugs disposed within the flow conduits. In an exemplary embodiment, the acid-soluble plugs may be made of a material having an acid solubility greater than 70%, permeability of less than 10 mD, and/or a compressive Young&#39;s modulus of at least 5,000 MPa. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a cross-section schematic view of an oil well casing or conduit in a borehole having two sleeves or tubes, one on either side of the casing, each in a retracted position in an orifice in the casing and having a dissolvable plug therein; 
           [0014]      FIG. 2  is a cross-section schematic view of the oil well casing in the wellbore of  FIG. 1  having two flow pathways on either side thereof, where the sleeves or tubes have been extended or expanded in the direction of the wellbore wall; and 
           [0015]      FIG. 3  is a cross-section schematic view of the oil well casing in the wellbore of  FIG. 1  where the dissolvable plugs in the flow pathways have been removed, and hydrocarbons may flow from the reservoir into the casing. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    In accordance with a present embodiment, an oil well casing or liner may contain pre-formed perforations, or holes, therethrough. Further, installed in each perforation may be a moveable fluid conduit or pathway which enables fluid communication between the interior and the exterior of the casing or liner. Although illustrated as a one-piece pipe which moves relative to the casing or liner, the fluid conduit or pathway may be made up of multiple pieces which move relative to each other. For example, the fluid conduit may be several generally cylindrical conduits arrange coaxially with a limited range of motion relative to each other along the commonly shared axis, e.g. in a telescoping configuration. 
         [0017]    The flow conduits or pathways may further contain temporary plugs which inhibit or prevent the flow of fluid through the conduits. The moveable flow conduits or pathways may be telescoped out from the casing or liner into the wellbore annulus via fluid pressure within the casing or liner. That is, as fluid is pumped into the casing, the temporary plugs inhibit the fluid from exiting the casing via the flow conduits. Rather, as the pressure inside the casing increases, the flow conduits are pushed outward from the casing. Optimally, the flow conduits contact the wellbore wall, thereby forming a flow pathway through the annulus from the interior of the casing to the formation. In this manner, the described structure may be used as a completion tubular to avoid using a cementing and perforation process. After the assembly is in place across the producing zone location, the temporary plugs may be dissolved using an acidic solution. 
         [0018]    The invention will now be described more specifically with respect to the figures, where in  FIG. 1  there is shown a cross-section of a vertically oriented, cylindrical casing or liner  10  having multiple orifices  12  therethrough. The orifices  12  may be created by machining or other suitable technique. The casing  10  is placed in a borehole or wellbore  14  through a subterranean reservoir  16 . The subterranean reservoir  16  may be a flow source from which gas and/or oil is extracted or, alternatively, a flow target into which gas or water is injected. The wellbore  14  has a wall  18  coated with a filter cake  20  deposited by a drilling fluid or, more commonly, a drill-in fluid  22 . In some non-limiting embodiments, the filter cake  20  may be optional. The casing  10  and the wall  18  define an annulus  24  there between. 
         [0019]    Fluid conduits  26  are disposed within the orifices  12 . These fluid conduits  26  are shown in  FIG. 1  in a retracted position within the casing  10 . The flow conduits  26  may be generally hollow structures open on opposing ends having an enveloping wall defining their shape. It is expected that in most cases the flow conduits  26  will have a cylindrical shape, but there is no particular requirement that they have such a shape. The fluid conduits  26  contain a temporary plug  28  made of a soluble substance having low permeability and high strength. For example, the plug  28  may have an acid solubility greater than 70% and permeability of less than 10 mD. An exemplary substance is Indiana limestone, which is a relatively inexpensive material that is readily available in the United States and has permeability of less than 3 mD in laboratory studies. Indiana limestone is generally composed of greater than 98% calcite, which has high acid solubility. Additionally, literature data has shown that the compressive Young&#39;s modulus of Indiana limestone is approximately 30,600 MPa, which is comparable to high strength concrete. Limestone with similar properties is also easily available in other countries and on other continents. Although the present disclosure refers to the soluble substance of the plugs  28  as limestone, it should be understood that other materials having similar solubility, permeability, and strength may be utilized in the disclosed methods and systems. 
         [0020]    In a non-limiting embodiment, the plugs  28  may be pre-formed and secured at an end of the conduits  26  via a threaded hollow cap. In other embodiments, the plugs  28  may be force fit into the conduits  26  or inserted into the conduits  26  and abutted against the inside of a flange (not shown) on an end of the conduit  26 . The permeability of the plugs  28  may be further reduced by filling the limestone matrix with another acid-soluble substance, such as a nanoparticle slurry. For example, nanoparticle slurry may be optionally used to fill in the limestone matrix to make the acid-soluble plug  28  tighter, further reducing the permeability of the plug  28 . The nanoparticles may have relatively large surface charges per volume, thereby permitting the crystal particles to associate, link, connect, group, or otherwise relate together to further reduce the permeability of the plug  28 . Exemplary acid-soluble nanoparticle slurries include, in non-limiting embodiments, ConFINE™, available from Baker Hughes, or a high-concentration slurry of approximately 35 nm magnesium oxide (MgO). 
         [0021]    Once the casing  10  is placed or positioned in the wellbore  14 , a fluid  30  may be pumped through the casing  10  and the conduits  26 , as shown in  FIG. 2 . As noted above, the plugs  28  within the conduits  26  have a very low permeability; accordingly, the fluid  30  does not flow through the plugs  28  or flows through the plugs  28  very slowly. As the fluid  30  is pumped into the casing  10 , high enough hydraulic pressure is built up to radially extend the flow conduits  26  out from the casing  10  into the annulus  24  to contact the producing formation  16 . That is, the conduits  26  may be extended out from the casing  10  in a direction generally perpendicular to a longitudinal axis  32  of the casing  10 . In a non-limiting embodiment, the conduits  26  may be several generally cylindrical coaxial conduits which telescope outward from the casing  10  as pressure is applied to the plug  28 . The hydraulic pressure of the fluid  30  typically causes the conduits  26  to extend to a position in which the conduits  26  touch the wall  18 . 
         [0022]    An acidic solution may then be pumped into the casing  10  to dissolve the plugs  28 , thereby forming flow paths  34  through the annulus  24  between the casing  10  and the formation  16 , as shown in  FIG. 3 . The acidic solution may also dissolve the portions of the filter cake  20  (if present) with which it comes into contact. Fracturing fluids containing proppants may then be flowed through the casing  10  at high pressure to fracture the formation  16  in accordance with techniques well known in the art. Because the limestone plugs  28  may be substantially removed and do not leave behind a porous substrate to act as a filter, the proppants, such as grains of sand or the like, are not hindered from flowing into the fractures (not shown) created in formation  16 . After the well is fractured, the well may be produced or injected. For instance, hydrocarbons may flow through the pathways  34  from the formation  16  into the casing  10 , or water may be injected into the casing  10 , through the flow pathways  34 , and into the formation  16 . 
         [0023]    In a non-limiting embodiment, the fluid  30  used to extend the conduits  26  may also be utilized to dissolve the plugs  28 . That is, the fluid  30  may be an acidic solution having a low enough chemical reaction rate with the limestone plugs  28  that the plugs  28  begin slowly dissolving while the hydraulic pressure of the extension fluid  30  pushes the conduits  26  outward toward the wellbore wall  18 . After the conduits  26  are extended out to touch the face of the reservoir  16 , the acidic fluid  30  may continue to be pumped into the casing  10  to substantially dissolve the plugs  28 . It should be understood that the method herein is considered successful if the plugs  28  dissolve sufficiently to open up the flow conduits  26  enough to enable flow of viscous fracturing fluids and proppants therethrough. 
         [0024]    An exemplary acidic solution for use as the extension and dissolving fluid  30  may be a dicarboxylic acid, as described in U.S. Pat. No. 6,805,198, incorporated by reference herein in its entirety. Dicarboxylic acid, also known as HTO (high temperature organic) acid, has a very low corrosion rate on metal components used in well production, such as tubing, casing, and downhole equipment. Exemplary dicarboxylic acids include, but are not necessarily limited to, oxalic acid (ethanedioic acid), malonic acid (propanedioic acid), succinic acid (butanedioic acid), glutaric acid (pentanedioic acid), adipic acid (hexanedioic acid), pimelic acid (heptanedioic acid), and mixtures thereof. In a non-limiting embodiment, the extension and dissolving fluid  30  may be dibasic acid composed of 51-61 weight percent glutaric acid, 18-28 weight percent succinic acid, and 15-25 weight percent adipic acid. Suitable solvents or diluents for the acidic fluid  30  may include, but are not limited to, water, methanol, isopropyl alcohol, alcohol ethers, aromatic solvents, and mixtures thereof. Laboratory tests show that the solubility of Indiana limestone in 10 weight percent HTO acid is about 98.86 percent. Accordingly, given enough time to contact all of the limestone plugs  28 , essentially all of the acid-soluble plugs  28  will be removed. 
         [0025]    In another non-limiting embodiment, a stronger acid, such as, for example, 15 weight percent hydrochloric acid (HCl), may be pumped into the casing  10  to dissolve the plugs  28  more quickly after the conduits  26  are extended out to touch the face of the reservoir  16 . Laboratory tests show that the solubility of Indiana limestone in 15 weight percent HCl is about 99.01 percent. Further exemplary acids which may be used in the present disclosure include, but are not limited to, sulfuric acid (H 2 SO 4 ), hydrofluoric acid (HF), formic acid (HCOOH), acetic acid (CH 3 COOH), fluoroboric acid (HBF 4 ), phosphoric acid (H 3 PO 4 ), citric acid, sulfonic acid, glycolic acid, and other acids. In addition, the plugs  28  may be dissolved with chelating agents, such as, for example, ethylenediaminetetriacetic acid (EDTA), disodium EDTA (Na 2 EDTA), hydroxyethylethylenediaminetriacetic acid (HEDTA), docosatetraenoic acid (DTA), nitrilotriacetic acid (NTA), hydroxyaminopolycarboxylic acid (HACA), diethylenetriaminepentaacetic acid (DTPA), hydroxyethyliminodiacetic acid (HEIDA), polyaspartic acid (PASP), and the like. 
       CONCLUSION 
       [0026]    It will be evident that various modifications and changes may be made to the foregoing specification without departing from the broader spirit or scope of the invention as set forth in the appended claims. Accordingly, the specification is to be regarded in an illustrative rather than a restrictive sense. For example, specific materials, fluids, acidic solutions, and combinations thereof falling within the claimed parameters, but not specifically identified or tried in a particular composition, are anticipated to be within the scope of this invention. Additionally, various components and methods not specifically described herein may still be encompassed by the following claims. 
         [0027]    The words “comprising” and “comprises” as used throughout the claims is to be interpreted as “including but not limited to”. The present invention may suitably comprise, consist of, or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. For example, in one non-limiting embodiment, a pipe used in well completions may consist of or alternatively consist essentially of an interior space, an outer surface, at least one flow conduit and an acid-soluble plug disposed within the flow conduit, as described in the claims.