Abstract:
A centralizer including hollow structural components. In at least one embodiment, the hollow structural component is sealed by at least one valve or rupture disk. When unacceptable overpressures occur, the valve or rupture disks break to allow influx into the hollow element, thereby relieving pressure and avoiding damage that might otherwise occur. In other embodiments, the hollow structural component collapses to expand available volume.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to systems and methods for controlling pressure in wellbores.  
       BACKGROUND AND SUMMARY OF THE INVENTION  
       [0000]     Background: Pressure in Well  
         [0002]     Annular pressure buildup within wellbores has been recognized in the oil and gas industry for many years as a serious problem. Fluids trapped in a wellbore or annular space in a wellbore will expand with a corresponding increase in temperature leading to a volume increase and increase in the force they exert upon the surrounding area. This pressure has been known to be a significant factor in the failure of subsea wells, including Well A-2 of British Petroleum 1999 Marlin development program in the deepwater program off the Gulf of Mexico. One relevant article is  Practical and Successful Prevention of Annular Pressure Buildup on the Marlin Project,  SPE International 77473, 2002, Richard F. Vargo, Jr., et al, and which is hereby incorporated by reference in its entirety.  
         [0000]     Background: Annular Pressure Build Up  
         [0003]     Annular pressure buildup (“APB”) is the pressure generated by thermal expansion of trapped fluids as they are heated. When wellbore fluids heat up and expand in a closed system, the expansion causes high induced pressures. Most land and many offshore locations may be able to bleed this pressure through surface-accessible wellhead equipment. In subsea completions, the primary annulus between the tubing and production casing may be the only accessible annulus. Consequently, bleeding the outer annuli may not be possible. Therefore, when the risk of subsea APB exists, well designers should give serious consideration to appropriate mitigation as part of the fundamental well design.  
         [0004]     Offshore hydrocarbon recovery operations are increasingly moving into deeper water and more remote locations. Often satellite wells are completed at the sea floor and are tied to remote platforms or other facilities through extended subsea pipelines. Some of these pipelines extend through water that is thousands of feet deep, where temperatures of the water near the sea floor are in the range of about 40° F. The hydrocarbon fluids, usually produced along with some water, reach the sea floor at much higher temperatures, characteristic of depths thousands of feet below the sea floor.  
         [0005]     In order for a well to experience APB, two conditions are generally known to be present. First, there must be a sealed region, typically an annulus, wherein pressure may build. Second, a temperature rise is generally associated with the increase in pressure.  
         [0000]     Background: General APB Mitigation Techniques  
         [0006]     Several existing solutions have been presented in past literature. These solutions include: 
        cement shortfall (leave cement short of previous casing);     providing a leak path or bleed port;     syntactic, crushable foam wrap;     compressible fluids placed in the trapped annulus to absorb volume;     heavyweight and/or high-yield casing (enhanced casing design); and     full-height cementing (cement filling the entire annulus).        
 
         [0013]     These can be incorporated into drilling plans to mitigate APB risks in some circumstances. A good starting point is to try to ensure that the annulus does not become trapped. Whenever possible, cement shortfall is usually designed. This assumes that cement heights will be below the previous casing shoe and that a trapped annulus condition may not occur. However, cement can still channel because of poor mud displacement. Such displacement problems are caused by poor casing eccentricity or poor erodibility of the wellbore fluids during the primary cementing operation. In addition, barite sag following drilling can cause a trapped condition. A trapped condition can occur either by cementitious materials or due to the settling of weighting materials from the mud. In many cases, subsea wells are drilled and left to be completed at a later date because of the lead time required for other components of the production infrastructure, i.e. pipelines, etc. Over time, the solids in the mud can settle out, creating a trapped condition. Later when the well is completed, the trapped annulus condition and the resulting APB may not show up until a failure occurs.  
         [0014]     A second APB prevention technique consists of attaching syntactic crushable-foam wrap to the casing. The syntactic foam contains small, hollow glass spheres filled with air at atmospheric pressure. When ABP reaches a certain level, the hollow spheres collapse. This collapse results in a correspondent increase in available volume to thereby decrease pressure. Data demonstrate that the volume required for an effective solution is about 2% to about 8% of the annular volume.  
         [0015]     Another way of prevention of APB is the use of compressible fluids in the trapped annulus to absorb volume increases as the heat up occurs.  
         [0016]     A final way of mitigating APB is by using enhanced casing products. Increased casing capacities can accommodate a higher degree of pressure buildup without detrimental effects to the casing or well. Extensive work has been applied here also involving advanced, probabilistic performance properties of the subject casings.  
         [0000]     Pressure Responsive Centralizer System  
         [0017]     The present inventions describe methods and systems for controlling pressure and volume variations in boreholes. For example, in one embodiment an innovative centralizer comprises a centralizing structure with at least one sealed hollow structural component where a rupture disk is capable of breaking in response to sufficient pressure. The present innovations further teach a method of effecting a volumetric change in response to overpressure within a wellbore comprising at least one hollow structural component. The present innovative systems and methods can be used to avoid production loss due to wellbore damage or the need to restrict hydrocarbon flow in an effort to keep production temperature below danger levels.  
         [0018]     Another advantage of the disclosed centralizer is the ability to be connected to the drilling and production equipment in a number of ways. The centralizer can be fitted with a rupture component made part of the centralizer, screwed into the bottom of the centralizer by means of threads within the centralizer, or connected by some other means.  
         [0019]     It should, of course, be understood that the description is merely illustrative and that various modifications and changes can be made in the structure disclosed without departing from the spirit of the invention.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]     The disclosed inventions will be described with reference to the accompanying drawings, which show important sample embodiments of the invention and which are incorporated in the specification hereof by reference, wherein:  
         [0021]      FIGS. 1   a  and  1   b  show a preferred embodiment of a centralizer.  
         [0022]      FIG. 2  shows a preferred embodiment of a centralizer.  
         [0023]      FIG. 3  shows a preferred embodiment of a centralizer configuration using a ‘hinged’ arrangement within a bore.  
         [0024]      FIG. 4  shows a production system using a centralizer with hollow rupture components.  
         [0025]      FIG. 5  shows a preferred embodiment of a centralizer with multiple rupture components.  
         [0026]      FIG. 6  shows a preferred embodiment of a pressure responsive system with a centralizer and multiple rupture components.  
         [0027]      FIG. 7  shows a preferred embodiment of a hollow rupture component.  
         [0028]      FIG. 8  shows a preferred embodiment of a centralizer where an empty rupture component is affixed to the main chamber of the centralizer.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0029]     The numerous innovative teachings of the present application will be described with particular reference to the presently preferred embodiment (by way of example, and not of limitation).  
         [0030]     The disclosed inventions take advantage of a new way in which the pressure in boreholes can be controlled. In one embodiment, a centralizer is combined with a rupture disk to allow for the release of excess pressure from a wellbore. The hollow components in this embodiment contain a burst disk or rupture disk, which are selected to rupture at a predetermined pressure as required by well hydrostatic pressure and other factors. The inside and outside diameters of the centralizer preferably provide effective centering of the casing in the borehole or outer casing. The number of struts and rupture and burst disks may be adjusted in such a way as to meet the specific pressure and volume needs of a specific project. For instance, in one embodiment, there may be six struts with one rupture disk in each strut. In another embodiment, there may be four struts with two rupture disks in each strut.  
         [0031]     In another embodiment, a centralizer is combined with a relief valve in order to allow for the release of excess pressure from a wellbore. The hollow components in this embodiment contain a relief valve that is selected to open at a predetermined pressure as required by well hydrostatic pressure and other factors. A relief valve is something that is not destroyed when it opens. A hollow structural component is a prefabricated rigid structure capable of allowing for volumetric expansion.  
         [0032]     In yet another embodiment, the rupture disk is sealed in such a way as to ‘burst’ at a predetermined pressure to facilitate the production of hydrocarbons. This invention avoids production loss due to wellbore damage due to overpressures and the need to restrict hydrocarbon flow in an effort to keep production temperature below danger levels.  
         [0033]     In a further embodiment, the centralizer may also comprise at least one centralizing structure and include at least one breakable structural component that can respond to pressure increase surges. The breakable structural component can collapse, burst, or rupture to provide a volume change in response to overpressure.  
         [0034]     One advantage of this embodiment is that pressures build up within boreholes can be alleviated. Another advantage is that the volume in a well can be controlled in such a manner as to optimize the production within a well.  
         [0035]      FIG. 1   a  shows a sample preferred embodiment of the centralizer unit  100 . This is a side view of the centralizer unit itself, not showing the casing which, once the centralizer  100  has been installed, would normally pass through the axial central cavity  130 . The struts  110  of the centralizer  100 , in this embodiment, run parallel with the wellbore  140 . One or more rupture disks (not shown in this figure) are located in one or more of the struts. These struts are hollow structural components. In this embodiment, the centralizer is made of stainless steel. Carbon steel, chrome-moly, or titanium or other materials can be used instead.  
         [0036]      FIG. 1   b  shows a sample preferred embodiment of one of the struts  110  of the centralizer unit  100 . This is a formed shape of tubular steel, having a hollow center (not visible in this figure). A rupture disk  112  blocks the sole opening into the hollow center of strut  110 . (Preferably a hole is drilled and tapped in the strut  110 .) In this embodiment, the end of strut  110  is attached to circumferential element  120  by a weld  114 , which also serves to close off the hollow within the strut  110 . In this embodiment the centralizer is made of stainless steel. Carbon steel, chrome-moly, or titanium or other materials can be used instead.  
         [0037]      FIG. 2  shows a sample preferred embodiment of the pressure responsive system using centralizer unit  200 . This is a side view of the centralizer unit itself, not showing the casing which, once the centralizer  200  has been installed, would normally pass through the axial central cavity  230 . The struts  210  of the centralizer, in this embodiment, run parallel with the wellbore  240 . One or more rupture disks (not shown in this figure) are located in one or more of the struts. In this embodiment, the centralizer is made of stainless steel. Carbon steel, chrome-moly, or titanium or other materials can be used instead. In this embodiment, a centralizer is attached to the rupture component using threads  260 .  
         [0038]      FIG. 3  shows a sample preferred embodiment of the centralizer unit  300 . This is a side view of the centralizer unit itself, not showing the casing which, once the centralizer  300  has been installed, would normally pass through the axial central cavity  330 . The struts  310  of the centralizer, in this embodiment, run parallel with the wellbore  340 . One or more rupture disks (not shown in this figure) are located in one or more of the struts. In this embodiment, the centralizer is made of stainless steel, but or course carbon steel or chrome-moly or titanium or other materials can be used instead. In this embodiment, a centralizer is attached to the rupture component using hinges  360 .  
         [0039]      FIG. 4  shows a production system  400  using a centralizer  410  with hollow rupture component  420  surrounded by wellbore  440 . A casing used to move the desired hydrocarbons or other material is illustrated by  470  in which hydrocarbons or other desired products may be moved from the well to some kind of recovery equipment located at  480 .  
         [0040]      FIG. 5  shows a centralizer system  500  with multiple rupture components  510 ,  520 , and  530 . Rupture components  510 ,  520 , and  530  are attached to the centralizer component  540 . Centralizer component  540  is attached to hollow struts  550 . Rupture components  510 ,  520 , and  530  may be of different sizes and pressure sensitivities.  
         [0041]      FIG. 6  shows a casing combination with centralizer and hollow rupture components. A hollow component  600  contains multiple rupture components  610  and  630 . Within said hollow component walls  640  a hole is drilled and the first rupture component is placed at  610 . A second rupture component  630  is held in place by elements within the hollow component at  620 .  
         [0042]      FIG. 7  shows a hollow rupture component  700 . A ring  710  separates the sealed disc components  720  and  730 . Hinges  740  can attach hollow rupture component to the centralizer system. Hollow rupture component can also be attached by means of threads found at  750 .  
         [0043]      FIG. 8  shows a centralizer system  800  with a rupture component  810  located at either end of the centralizer system  850  or  860 . Additional rupture components may be placed at  820 ,  830 , and  840 . The structural centralizer support struts  850  are placed along the bore.  
         [0044]     In one example, the present innovations are enabled as a method for avoiding overpressure in a borehole, comprising the actions of opening a sealed hollow structural component within the borehole to thereby relieve overpressure by volumetric expansion into the hollow structural component is claimed.  
         [0045]     In another example, the present innovations are enabled as a method for avoiding overpressure in a borehole, comprising the actions of relieving overpressure within a borehole by collapsing at least part of a hollow structural component and creating volumetric expansion is also claimed.  
         [0046]     In another example, the present innovations are enabled as a method of relieving overpressure in a borehole comprising of inserting a hollow structural component into a borehole and increasing pressure within the borehole and relieving overpressure in the borehole by increasing the available volume in the borehole through a change in the hollow structural component is also claimed.  
         [0047]     None of the description in the present application should be read as implying that any particular element, step, or function is an essential element which must be included in the claim scope: THE SCOPE OF PATENTED SUBJECT MATTER IS DEFINED ONLY BY THE ALLOWED CLAIMS.  
         [0000]     Modifications and Variations  
         [0048]     As will be recognized by those skilled in the art, the innovative concepts described in the present application can be modified and varied over a tremendous range of applications, and accordingly the scope of patented subject matter is not limited by any of the specific exemplary teachings given.  
         [0049]     The pressure responsive system may be made out of any number of materials, including, but not limited to, stainless steel, carbon steel, titanium, or any number of other materials. In addition, the number of struts, rupture disks, and relief valves may vary from embodiment to embodiment. The downhole string may be in different forms, including, but not limited to a tubular string or casing string.  
         [0050]     One variation includes replacing the rupture disks with relief valves or other structures that will allow the enclosed volume to open at a predetermined pressure.  
         [0051]     A particular advantage of the hollow chamber (at atmospheric pressure or pressurized) to be transported to a downhole location with a rupture disk is that it can be designed to rupture at a predetermined stage of operations.  
         [0052]     Note that the pressure required for rupture will correspond directly with the internal design of the centralizer and the pressure with which it is sealed at.  
         [0053]     The hollow structural component may be physically part of the centralizer, or be attached thereto, or may be separate from the centralizer itself.  
         [0054]     None of the description in the present application should be read as implying that any particular element, step, or function is an essential element which must be included in the claim scope: THE SCOPE OF PATENTED SUBJECT MATTER IS DEFINED ONLY BY THE ALLOWED CLAIMS.