Patent Publication Number: US-10316616-B2

Title: Dissolvable bridge plug

Description:
PRIORITY CLAIM/CROSS REFERENCE TO RELATED APPLICATIONS 
     The present document Ser. No. 11/427,233 is a continuation in part of U.S. Pat. No. 8,211,247, entitled “Degradable Compositions, Apparatus Comprising Same, and Method of Use,” which was filed on Jun. 28, 2006, which claims the benefit of U.S. Provisional patent application Ser. No. 60/771,627, which was filed on Feb. 9, 2006, the disclosures of which are incorporated herein by reference in their entireties. 
    
    
     FIELD 
     Embodiments described relate to a bridge plug configured for use in cased well operations. More specifically, embodiments of the plug are described wherein metal-based anchoring and support features may be dissolvable in a well environment, particularly following fracturing applications. 
     BACKGROUND 
     Exploring, drilling and completing hydrocarbon and other wells are generally complicated, time consuming and ultimately very expensive endeavors. In recognition of these expenses, added emphasis has been placed on efficiencies associated with well completions and maintenance over the life of the well. Over the years, ever increasing well depths and sophisticated architecture have made reductions in time and effort spent in completions and maintenance operations of even greater focus. 
     Perforating and fracturing applications in a cased well, generally during well completion, constitute one such area where significant amounts of time and effort are spent, particularly as increases in well depths and sophisticated architecture are encountered. These applications involve the positioning of a bridge plug downhole of a well section to be perforated and fractured. Positioning of the bridge plug may be aided by pumping a driving fluid through the well. This may be particularly helpful where the plug is being advanced through a horizontal section of the well. 
     Once in place, equipment at the oilfield surface may communicate with the plug assembly over conventional wireline so as to direct setting of the plug. Such setting may include expanding slips and a seal of the assembly for anchoring and sealing of the plug respectively. Once anchored and sealed, a perforation application may take place above the bridge plug so as to provide perforations through the casing in the well section. Similarly, a fracturing application directing fracture fluid through the casing perforations and into the adjacent formation may follow. This process may be repeated, generally starting from the terminal end of the well and moving uphole section by section, until the casing and formation have been configured and treated as desired. 
     The presence of the set bridge plug in below the well section as indicated above keeps the high pressure perforating and fracturing applications from affecting well sections below the plug. Indeed, even though the noted applications are likely to generate well over 5,000 psi, the well section below the plug is kept isolated from the section thereabove. This degree of isolation is achieved largely due to the use of durable metal features of the plug, including the above noted slips, as well as a central mandrel. 
     Unfortunately, unlike setting of the bridge plug, wireline communication is unavailable for releasing the plug. Rather, due to the high pressure nature of the applications and the degree of anchoring required of the plug, it is generally configured for near permanent placement once set. As a result, removal of a bridge plug requires follow on drilling out of the plug. Once more, where the plug is set in a horizontal section of the well, removal of the plug may be particularly challenging. Unlike the initial positioning of the bridge plug, which may be aided by pumping fluid through the well, no significant tool or technique is readily available to aid in drillably removing the plug. Indeed, due to the physical orientation of the plug relative the oilfield surface equipment, each drill-out of a plug in a horizontal well section may require hours of dedicated manpower and drilling equipment. 
     Depending on the particular architecture of the well, several horizontal bridge plug drill-outs, as well as dozens of vertical drill-outs may take place over the course of conventional perforating and fracturing operations for a given cased well. All in all, this may add up to several days and several hundred thousand dollars in added manpower and equipment expenses, solely dedicated to bridge plug drill-out. Furthermore, even with such expenses incurred, the most terminal or downhole horizontal plugs are often left in place, with the drill-out application unable to achieve complete plug removal, thus cutting off access to the last several hundred feet of the well. 
     Efforts have been made to reduce expenses associated with time, manpower, and equipment that are dedicated to bridge plug drill-outs as described above. For example, many bridge plugs today include parts made up of fiberglass based materials which readily degrade during drill-out. However, use of such materials for the above noted slips and/or mandrel may risk plug failure during high pressure perforating or fracturing. Such failure would likely require an additional clean out application and subsequent positioning and setting of an entirely new bridge plug, all at considerable time and expense. Thus, in order to avoid such risks, conventional bridge plugs generally continue to require time consuming and labor intensive drill-out for removal, particularly in the case of horizontally positioned plugs. 
     SUMMARY 
     A bridge plug is disclosed for use in a cased well during a pressure generating application. The plug provides effective isolation during the application. However, the plug is also configured of a solid structure that is dissolvable in the well. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side, partially-sectional view of an embodiment of a dissolvable bridge plug. 
         FIG. 2  is an overview of an oilfield accommodating a well with the bridge plug of  FIG. 1  employed therein. 
         FIG. 3  is an enlarged view of a downhole area taken from  3 - 3  of  FIG. 2  and revealing an interface of the bridge plug with a casing of the well. 
         FIG. 4A  is the enlarged view of  FIG. 3  now revealing the dissolvable nature of a slip of the bridge plug and the changing interface as a result. 
         FIG. 4B  is the enlarged view of  FIG. 4A  now depicting a drill-out application as applied to the substantially dissolved bridge plug. 
         FIG. 5  is a flow-chart summarizing an embodiment of employing a dissolvable bridge plug in a well. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments are described with reference to certain downhole operations employing a bridge plug for well isolation. For example, embodiments herein focus on perforating and fracturing applications. However, a variety of applications may be employed that take advantage of embodiments of a dissolvable bridge plug as detailed herein. For example, any number of temporary isolations, for example to run an isolated clean-out or other application, may take advantage of bridge plug embodiments described below. Regardless, embodiments described herein include a bridge plug configured for securably anchoring in a cased well for a high-pressure application. This may be followed by a substantial dissolve of metal-based parts of the plug so as to allow for a more efficient removal thereof. 
     Referring now to  FIG. 1 , a side, partially-sectional view of an embodiment of a dissolvable bridge plug  100  is shown. The bridge plug  100  is referred to as ‘dissolvable’ in the sense that certain features thereof may be configured for passive degradation or dissolution upon exposure to downhole well conditions as detailed further below. As used herein, the term passive degradation is meant to refer to degradation upon exposure to downhole conditions, whether or not such conditions are pre-existing or induced. 
     In the embodiment of  FIG. 1 , the plug  100  includes slips  110  and a mandrel  120  which, while ultimately dissolvable, are initially of substantially high strength and hardness (e.g. L80, P110). Thus, maintaining isolation and anchoring to a casing  380  during a high pressure application may be ensured (see  FIG. 3A ). In one embodiment, the slips  110  and mandrel  120  are configured to withstand a pressure differential of more than about 8,000 psi to ensure structural integrity of the plug  100 . Thus, a standard perforating or fracturing application which induces a pressure differential of about 5,000 psi is not of significant concern. Due to the anchoring and structural integrity afforded the plug  100 , the slips  110  and mandrel  120  may be referred to herein as integrity components. 
     In spite of the high strength and hardness characteristics of the slips  110  and mandrel  120 , their degradable or dissolvable nature allows for subsequent drill-out or other plug removal techniques to be carried out in an efficient and time-saving manner (see  FIG. 3B ). Incorporating a degradable or dissolvable character into the slips  110  and mandrel  120  may be achieved by use of reactive metal in construction. Namely, as detailed to a greater degree below, the slips  110  and mandrel  120  may be made up of a reactive metal such as aluminum with an alloying element incorporated thereinto. For example, as detailed in U.S. application Ser. No. 11/427,233, incorporated herein, the alloying element may be elements such as lithium, gallium, indium, zinc and/or bismuth. Thus, over time, particularly in the face of exposure to water, fracturing fluid, high temperatures, and other downhole well conditions, the material of the slips  110  and mandrel  120  may begin to degrade or dissolve. 
     Continuing with reference to  FIG. 1 , with added reference to  FIG. 2 , the plug  100  may also include a seal  150  for isolation upon deployment in a well  280 . The seal  150  may be of conventional polymer seal material. Additionally, in the embodiment shown, the plug  100  is configured for wireline deployment and equipped with a coupling  175  for securing to the wireline. The plug  100  also includes other body portions  160  which may house underlying components and/or serve as structural interfaces between the slips  110 , seal  150 , head  175  and other plug features. 
     Unlike the slips  110  and mandrel  120 , none of the body portions  160 , the seal  150 , or the head  175  is responsible for anchoring or maintaining structural integrity of the plug  100  during a perforating, fracturing or other high pressure applications in the well  280 . Thus, at the very outset material choices for these features  150 ,  160 ,  175  may be selected based on other operational parameters. For example, the polymer seal material of the seal  150  may be an elastomer selected based on factors such as radial expansiveness and likely well conditions. Similarly, the body portions  160  of the plug  100  may be a conventional polymer or fiberglass composite that is selected based on its ease of drill-out removal following a high pressure application (see  FIG. 4B ). 
       FIG. 2  is an overview of an oilfield  200  accommodating a well  280  with the bridge plug  100  of  FIG. 1  employed therein. More specifically, the bridge plug  100  is employed for isolation in a terminal lateral leg  285  of the well  280 . Nevertheless, in spite of the challenging architecture and potentially significant depth involved, a follow on drill-out of the plug  100  may be achieved and in a time-efficient manner as detailed below. 
     In the embodiment shown, a rig  210  is provided at the oilfield surface over a well head  220  with various lines  230 ,  240  coupled thereto for hydraulic access to the well  280 . More specifically, a high pressure line  230  is depicted along with a production line  240 . The production line  240  may be provided for recovery of hydrocarbons following completion of the well  280 . However, more immediately, this line  240  may be utilized in recovering fracturing fluids. That is, the high pressure line  230  may be coupled to large scale surface equipment including fracturing pumps for generating at least about 5,000 psi for a fracturing application. Thus, fracturing fluid, primarily water, may be driven downhole for stimulation of a production region  260 . 
     In the embodiment of  FIG. 2 , the well  280 , along with production tubing  275 , is shown traversing various formation layers  290 ,  295  and potentially thousands of feet before reaching the noted production region  260 . Perforations  265  penetrating the formation  295  may be pre-formed via a conventional fracturing application. Additionally, the production tubing  275  may be secured in place uphole of the region  260  by way of a conventional packer  250 . Thus, a high pressure fracturing application as directed through the production tubing  275  may be effectively directed at the region  260 . 
     As to deployment and setting of the bridge plug  100 , a variety of techniques may be utilized. For example, as noted above, wireline coupled to the head  175  may be used to drop the plug  100  down the vertical portion of the well  280 . Upon reaching the lateral leg  285 , hydraulic pressure may be employed to position the plug  100  therein. Once in place, the slips  110  may be wireline actuated for anchoring as described below. Similarly, the seal  150  may be compressibly actuated for sealing. In other embodiments slickline, jointed pipe, or coiled tubing may be used in deployment of the plug  100 . In such embodiments, setting may be actuated hydraulically or though the use of a separate setting tool which acts compressibly upon the plug  100  for radial expansion of the slips  110  and seal  150 . 
     Continuing with reference to  FIG. 2 , the bridge plug  100  may be deployed as indicated so as to isolate more downhole, most likely uncased, portions of the lateral leg  285  from the remainder of the well  280 . Indeed, with the bridge plug  100  in place as shown, the fracturing application may be focused at the area of the well  280  between the plug 100  and the packer  250 . Thus, high pressure targeting of the perforations  265  of the production region  260  may be achieved. As noted above, subsequent recovery of fracturing fluid may follow through the production tubing  275  and line  240 . 
     Continuing with reference to  FIG. 3 , an enlarged view of the downhole area taken from  3 - 3  of  FIG. 2  is shown. The well  280  is defined by conventional casing  380  which extends at least somewhat into more uphole portions of the lateral leg  285 . In this view, the interface  375  of the plug  100  with casing  380  defining the well  280  is depicted. It is at this interface  375  where teeth  350  of the visible slip  110  are shown digging into the casing  380 , thereby anchoring the plug  100  in place. Indeed, in spite of differential pressure potentially exceeding about 5,000 psi during the noted fracturing application, or during the preceding perforating, the slips  110  help keep the plug  100  immobilized as shown. Similarly, with added reference to  FIG. 1 , the internal mandrel  120  helps to ensure structural integrity of the plug  100  in the face of such high pressures. Indeed, as noted above, the mandrel  120  may be rated for maintaining structural integrity in the face of an 8,000-10,000 psi or greater pressure differential. 
     Referring now to  FIG. 4A , the enlarged view of  FIG. 3  is depicted following a dissolve period with the bridge plug  100  in the well  280 . Noticeably, the visible slip  110  has undergone a degree of degradation or dissolve over the dissolve period. Indeed, the underlying support structure for the teeth  350  of the slip  110  as shown in  FIG. 3  has eroded away. Thus, the teeth  350  are no longer supported at the casing  380 . This leaves only an eroded surface  400  at the interface  375 . As a result, the plug  100  is no longer anchored by the slips  110  as described above. The internal support structure of the mandrel  120  of  FIG. 1  is similarly degraded over the dissolve period. As a result, a follow-on drill-out application as depicted in  FIG. 4B  may take place over the course of less than about 30 minutes, preferably less than about 15 minutes. This is a significant reduction in drill-out time as compared to the several hours or complete absence of drill-out available in the absences of such dissolve. 
     The dissolve rate of the plug  100  may be tailored by the particular material choices selected for the reactive metals and alloying elements described above. That is, material choices selected in constructing the slips  110  and mandrel  120  of  FIG. 1  may be based on the downhole conditions which determine the dissolve rate. For example, when employing reactive metals and alloying element combinations as disclosed herein and in the &#39;233 Application, incorporated herein by reference as detailed above, the higher the downhole temperature and/or water concentration, the faster the dissolve rate. 
     Continuing with reference to  FIG. 4A , with added reference to  FIG. 1 , downhole conditions which affect the dissolve rate may be inherent or pre-existing in the well  280 . However, such conditions may also be affected or induced by applications run in the well  280  such as the above noted fracturing application. That is, a large amount of fracture fluid, primarily water, is driven into the well  280  at high pressure during the fracturing operation. Thus, the exposure of the slips  110  and mandrel  120  to water is guaranteed in such operations. However, if the well  280  is otherwise relatively water-free or not of particularly high temperature, the duration of the fracturing application may constitute the bulk of downhole conditions which trigger the dissolve. Alternatively, the well  280  may already be water producing or of relatively high temperature (e.g. exceeding about 75° C.). In total, the slips  110  and mandrel  120  are constructed of materials selected based on the desired dissolve rate in light of downhole conditions whether inherent or induced as in the case of fracturing operations. Further, where the conditions are induced, the expected duration of the induced condition (e.g. fracturing application) may also be accounted for in tailoring the material choices for the slips  110  and mandrel  120 . 
     While material choices may be selected based on induced downhole conditions such as fracturing operations, such operations may also be modulated based on the characteristics of the materials selected. So, for example, where the duration of the fracturing application is to be extended, effective isolation through the plug  100  may similarly be extended through the use of low temperature fracturing fluid (e.g. below about 25° C. upon entry into the well head  220  of  FIG. 2 ). Alternatively, where the fracture and dissolution periods are to be kept at a minimum, a high temperature fracturing fluid may be employed. 
     Compositions or material choices for the slips  110  and mandrel  120  are detailed at great length in the noted &#39;233 Application. As described, these may include a reactive metal, which itself may be an alloy with structure of crystalline, amorphous or both. The metal may also be of powder-metallurgy like structure or even a hybrid structure of one or more reactive metals in a woven matrix. Generally, the reactive metal is selected from elements in columns I and II of the Periodic Table and combined with an alloying element. Thus, a high-strength structure may be formed that is nevertheless degradable. 
     In most cases, the reactive metal is one of calcium, magnesium and aluminum, preferably aluminum. Further, the alloying element is generally one of lithium, gallium, indium, zinc, or bismuth. Also, calcium, magnesium and/or aluminum may serve as the alloying element if not already selected as the reactive metal. For example, a reactive metal of aluminum may be effectively combined with an alloying element of magnesium in forming a slip  110  or mandrel  120 . 
     In other embodiments, the materials selected for construction of the slips  110  and mandrel  120  may be reinforced with ceramic particulates or fibers which may have affect on the rate of degradation. Alternatively, the slips  110  and mandrel  120  may be coated with a variety of compositions which may be metallic, ceramic, or polymeric in nature. Such coatings may be selected so as to affect or delay the onset of dissolve. For example, in one embodiment, a coating is selected that is itself configured to degrade only upon the introduction of a high temperature fracturing fluid. Thus, the dissolve period for the underlying structure of the slips  110  and mandrel  120  is delayed until fracturing has actually begun. 
     The particular combinations of reactive metal and alloying elements which may be employed based on the desired dissolve rate and downhole conditions are detailed at great length in the noted &#39;233 Application. Factors such as melting points of the materials, corrosion potential and/or the dissolvability in the presence of water, brine or hydrogen may all be accounted for in determining the makeup of the slips  110  and mandrel  120 . 
     In one embodiment, the dissolve apparent in  FIG. 4A  may take place over the course of between about 5 and 10 hours. During such time, a perforating application may be run whereby the perforations  265  are formed. Further, a fracturing application to stimulate recovery from the formation  295  through the perforations  265  may also be run as detailed above. Additionally, to ensure that the plug  100  maintains isolation throughout the fracturing application, the dissolve rate may be intentionally tailored such that the effective life of the plug  100  extends substantially beyond the fracturing application. Thus, in one embodiment where hydrocarbon recovery is possible downhole of the plug  100 , the plug  100  may be actuated via conventional means to allow flow therethrough. This may typically be the case where the plug  100  is employed in a vertical section of the well  280 . 
     Referring now to  FIG. 4B , the enlarged view of  FIG. 4A  is depicted, now showing a drill-out application as applied to the substantially dissolved bridge plug  100 . That is, once sufficient dissolve has taken place over the dissolve period, a conventional drill tool  410  with bit  425  may be used to disintegrate the plug  100  as shown. Indeed, in spite of the potential excessive depth of the well  280  or the orientation of the plug in the lateral leg  285 , a drill-out as shown may be completed in a matter of less than about 15 minutes (as opposed to, at best, several hours). This, in spite of the durability, hardness and other initial structural characteristics of the slips  110  and mandrel  120  which allowed for effective high pressure applications uphole thereof (see  FIGS. 1 and 2 ). 
     Referring now to  FIG. 5 , a flow-chart is shown summarizing an embodiment of employing a dissolvable bridge plug in a well. The bridge plug is delivered and set at a downhole location as indicated at  515  and described hereinabove. Thus, as shown at  535 , a high pressure application may be run uphole of the location while isolation is maintained by the plug (see  555 ). However, by the same token, as indicated at  575 , downhole conditions, whether introduced by the high pressure application or otherwise, may be used to effect dissolve of metal-based components of the plug. As a result, the plug may be effectively removed from the well as indicated at  595 . This may be achieved by way of fishing, drill-out as described hereinabove, or even by bluntly forcing the plug remains to an unproductive terminal end of the well. Regardless the manner, the removal may now take a matter of minutes as opposed to hours (or failed removal altogether). 
     Embodiments described hereinabove provide a bridge plug and techniques that allow for effective isolation and follow on removal irrespective of the particular architecture of the well. That is, in spite of the depths involved or the lateral orientation of plug orientation, drill-out or other removal techniques may effectively and expediently follow an isolated application uphole of the set plug. The degree of time savings involved may be quite significant when considering the fact that completions in a given well may involve several bridge plug installations and subsequent removals. This may amount to several days worth of time savings and hundreds of thousands of dollars, particularly in cases where such installations and removals involve a host of horizontally oriented plugs. 
     The preceding description has been presented with reference to presently preferred embodiments. Persons skilled in the art and technology to which these embodiments pertain will appreciate that alterations and changes in the described structures and methods of operation may be practiced without meaningfully departing from the principle, and scope of these embodiments. Furthermore, the foregoing description should not be read as pertaining only to the precise structures described and shown in the accompanying drawings, but rather should be read as consistent with and as support for the following claims, which are to have their fullest and fairest scope.