Patent Publication Number: US-2017370153-A1

Title: Piston assembly to reduce annular pressure buildup

Description:
TECHNICAL FIELD 
     A wellbore can include multiple annuli having trapped fluids. Pressure can build up in the annuli because of heating of these fluids, which can cause damage to wellbore components if the pressure is not reduced. A piston assembly can be used to reduce the amount of pressure in the annuli. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The features and advantages of certain embodiments will be more readily appreciated when considered in conjunction with the accompanying figures. The figures are not to be construed as limiting any of the preferred embodiments. 
         FIG. 1  is cross-sectional view of a well system showing multiple annuli and a piston assembly. 
         FIG. 2A  is an enlarged cross-sectional view of the piston assembly prior to movement of the piston. 
         FIG. 2B  is an enlarged cross-sectional view of the piston assembly after movement of the piston. 
     
    
    
     DETAILED DESCRIPTION 
     Oil and gas hydrocarbons are naturally occurring in some subterranean formations. In the oil and gas industry, a subterranean formation containing oil and/or gas is referred to as a reservoir. A reservoir can be located under land or off shore. Reservoirs are typically located in the range of a few hundred feet (shallow reservoirs) to a few tens of thousands of feet (ultra-deep reservoirs). In order to produce oil or gas, a wellbore is drilled into a reservoir or adjacent to a reservoir. The oil, gas, or water produced from a reservoir is called a reservoir fluid. 
     As used herein, a “fluid” is a substance having a continuous phase that tends to flow and to conform to the outline of its container when the substance is tested at a temperature of 71° F. (22° C.) and a pressure of one atmosphere “atm” ( 0 . 1  megapascals “MPa”). A fluid can be a liquid or gas. 
     A well can include, without limitation, an oil, gas, or water production well, or an injection well. As used herein, a “well” includes at least one wellbore. A wellbore can include vertical, inclined, and horizontal portions, and it can be straight, curved, or branched. As used herein, the term “wellbore” includes any cased, and any uncased, open-hole portion of the wellbore. A near-wellbore region is the subterranean material and rock of the subterranean formation surrounding the wellbore. As used herein, a “well” also includes the near-wellbore region. The near-wellbore region is generally considered to be the region within approximately 100 feet radially of the wellbore. As used herein, “into a well” means and includes into any portion of the well, including into the wellbore or into the near-wellbore region via the wellbore. 
     A portion of a wellbore can be an open hole or cased hole. In an open-hole wellbore portion, a tubing string can be placed into the wellbore. The tubing string allows fluids to be introduced into or flowed from a remote portion of the wellbore. In a cased-hole wellbore portion, a casing is placed into the wellbore that can also contain a tubing string. It is also common for more than one casing and tubing string to be installed within a wellbore. The multiple casings can be placed inside of one another and may not extend the same distance within the wellbore. A wellbore can contain an annulus. Examples of an annulus include, but are not limited to: the space between the wellbore and the outside of a tubing string in an open-hole wellbore; the space between the wellbore and the outside of a casing in a cased-hole wellbore; and the space between the inside of a casing and the outside of a tubing string in a cased-hole wellbore. When there are multiple casings and/or tubing strings, there can also be multiple annuli. 
     A wellbore can be separated into one or more wellbore intervals. One way to create wellbore intervals is by bringing the top of a cement column from a subsequent tubing string up inside the annulus above the previous casing shoe. However, annular pressure buildup can occur. Annular Pressure Buildup (APB) is one of many challenging issues in the oil and gas industry. APB occurs when annular fluids that are trapped between the column of cement and the surface of the land become heated due to production or higher formation temperatures. The annular fluids then expand and can exert pressure on the casing. This condition is present in all producing wells, but is most evident in deep water wells. Deep water wells are likely to be vulnerable to annular pressure buildup because of the cold temperature of the displaced fluid, in contrast to elevated temperature of the production fluid during production. This big change in temperature during production can increase the pressure in the annulus rather rapidly. Sometimes the pressure can become so great as to collapse the inner string or even rupture the outer string or casings, thereby destroying the well. 
     A wellhead can provide access to some or all of the wellbore annuli, and an observed pressure increase can be quickly bled off via the wellhead. However, most subsea wellhead installations do not have access to each wellbore annulus. In order to overcome the lack of access to each annulus, other attempts to solve the problem of annular pressure build up include: use of a syntactic crushable foam wrap; leaving the cement column short of previous casings; providing a leak path or bleed port; use of a compressible fluid in the inaccessible annulus; different casing designs; and full column height cementing. However, these attempts have some shortcomings, for example, cement channeling can occur due to poor mud displacement in the case of cement column short of previous casings, very high costs can be incurred in the case of enhanced casing design and full column height cementing, and a foam wrap can only be used one time to bleed off the excess pressure. 
     Therefore, there is a need for improved means to reduce the amount of pressure that builds up in wellbore annuli. It has been discovered that a piston assembly can be used to bleed off the excess pressure from one or more wellbore annuli. The one or more annuli can be connected via a common tubular that is connected to the piston assembly. Any excess pressure would be exerted on a piston of the piston assembly to prevent the pressure from building up within the annuli. 
     According to certain embodiments, a system for preventing annular pressure buildup comprises: a wellbore; two or more annuli located within the wellbore; a piston assembly located adjacent to a wellhead of the wellbore; and a pipe system that connects the two or more annuli in parallel to the piston assembly, wherein when the amount of pressure in the pipe system exceeds a predetermined amount, then a piston of the piston assembly moves whereby the movement reduces the amount of pressure in the two or more annuli. 
     According to other embodiments, a method of reducing the amount of pressure in two or more annuli of a wellbore comprises: connecting the two or more annuli in parallel to a piston assembly via a pipe system, wherein the piston assembly is located adjacent to a wellhead of the wellbore; and allowing a piston of the piston assembly to move when the amount of pressure in the pipe system exceeds a predetermined amount, wherein the movement reduces the amount of pressure in the two or more annuli. 
     Any discussion of the embodiments regarding the well system or any component related to the well system is intended to apply to all of the apparatus, system, and method embodiments. 
     Turning to the Figures,  FIG. 1  depicts a well system  10 . The well system  10  can include at least one wellbore  21 . The wellbore  21  can penetrate a subterranean formation  20 . The subterranean formation  20  can be a portion of a reservoir or adjacent to a reservoir. The well system  10  can be an off-shore system. The off-shore system can include, for example, an off-shore platform  100  that is located within a body of water  11 . The well system  10  can include a wellhead  13  that is located on the sea floor  12 . In off-shore drilling, a production tubing  22  is inserted into the body of water  11  and extends through the water to the sea floor  12  of the body of water. The sea floor  12  is the surface of the sub-water land. The body of water and the wellbore can be several hundred to several thousands of feet deep. As used herein, the term “body of water” includes, without limitation, either formed by nature or man-made, a river, a pond, a lake, a gulf, a canal, a reservoir, a retention pond, or an ocean. As used herein, the term “water” means the water located within the body of water. The water can be freshwater, salt water, effluent, produced or flowback water, or brackish water. The well system  10  can also include other components not depicted in the drawings or described herein that are commonly included in an off-shore drilling system. 
     The wellbore  21  can include one or more wellbore intervals. The wellbore intervals can correspond to one or more zones of the subterranean formation  20 . The wellbore intervals can be formed via the use of isolation devices, for example, packers  24 , cement  31 , balls and seats, etc. (not shown). 
     The well system  10  also includes two or more annuli. The well system  10  can include two or more casing strings  23  installed within the wellbore  21 . The casing strings  23 , for example as depicted in  FIG. 1 , can be various lengths. The well system  10  can include a first annulus  25  located between the outside of the tubing string  22  and the inside of a first casing string. A second annulus  26  can be located between the outside of the first casing string and the inside of a second casing string. A third annulus  27  can be located between the outside of the second casing string and the inside of a third casing string. Of course there can be more than three annuli in the well system as well as a multitude of casing strings or tubing strings. The casing strings  23  can be partially or wholly cemented in the wellbore  21  via cement  31 . Partially cemented means that the cement composition does not completely fill the annulus in which the cement is placed; whereas, wholly cemented means that the cement composition does completely fill the annulus in which the cement is placed. According to certain embodiments, at least two annuli are not completely filled with the cement  31 . 
     Some or all of the two or more annuli (e.g., the first, second, and third annuli  25 ,  26 ,  27 ) can contain a wellbore fluid  32 . The two or more annuli can contain the wellbore fluid  32  in addition to the cement  31 . The wellbore fluid  32  can be a fluid that is introduced by an operator or a reservoir fluid. According to certain embodiments, the wellbore fluid  32  can exert a certain amount of pressure within the two or more annuli. The amount of pressure can be exerted on the outside and inside of the casing strings  23  and/or tubing string  22  making up the annuli. The amount of pressure can also increase over time. By way of example, the amount of pressure can increase due to an increase in temperature of the wellbore fluid  32  via production of a reservoir fluid or the surrounding subterranean formation temperature. 
     The well system  10  includes a pipe system that connects the two or more annuli in parallel to a piston assembly  200 . The pipe system can include two or more pipes that are connected to a common pipe  40 . The two or more pipes can correspond to the two or more annuli. According to certain embodiments, the two or more annuli are accessible from the sea floor  12  for being able to connect a pipe to the accessible annulus. By way of example, a first pipe  41  can be connected to the first annulus  25 , a second pipe  42  can be connected to the second annulus  26 , and a third pipe  43  can be connected to the third annulus  27 . The pipes can be connected to each annulus in any manner that is known to those skilled in the art. It is to be understood that as used herein, reference to a pipe means any tubular object that allows fluids to flow through the object and does not imply a particular shape. A pipe can be any shape so long as fluids are able to flow through the pipe. The pipes of the pipe system can also be made out of a variety of materials including, but not limited to, metals, metal alloys, plastics, non-corrodible materials, etc. 
     The amount of pressure in each annulus of the well system can be the same or different. The initial amount of pressure from each of the pipes is the initial amount of pressure from the respective annuli that are connected to the pipes. By way of example and as depicted in  FIG. 1 , the initial amount of pressure in the first pipe  41  will be the amount of pressure from the first annulus  25 , the initial amount of pressure in the second pipe  42  will be the amount of pressure from the second annulus  26 , etc. Each of these pressures in the pipes of the pipe system will feed into the common pipe  40 . By connecting the annuli with the common pipe  40 , the pressure will become the same in the annuli  25 ,  26 ,  27 , corresponding pipes  41 ,  42 ,  43 , and the common pipe  40  of the network because of the continuity of fluids. 
     The well system  10  can also include one or more annuli that are inaccessible (not shown) from the sea floor. Any of the annuli can include a rupture disk  28  or other fluid flow restriction device that restricts fluid flow past the device but fails above a certain pressure rating. The rupture disk can block fluid flow past the disk when the pressure of the wellbore fluid  32  is below a certain value. Then, when the pressure equals or exceeds the certain value, the disk can rupture, thus allowing the wellbore fluid to flow out of the annulus and into an adjacent annulus. Generally, the pressure at which the disk ruptures is below the pressure at which damage to the casing strings or tubing strings forming the annulus would occur. In this manner, the strings do not become damaged by the pressure from the wellbore fluid. Preferably, any inaccessible annuli contain the rupture disk  28  or similar device. When the pressure in the inaccessible annulus equals or exceeds the pressure rating of the rupture disk, then the disk will rupture and allow the fluid within that annulus to flow into an adjacent annulus. The amount of pressure in the inaccessible annulus will then decrease as the fluid flows into the adjacent annulus. The adjacent annulus can be an accessible annulus that is connected to a pipe of the pipe system. 
     The common pipe  40  of the pipe system is connected to the piston assembly  200 . The piston assembly  200  is located adjacent to the wellhead  13  of the wellbore. Accordingly, the piston assembly  200  can be located on the sea floor  12 . Turning to  FIGS. 2A and 2B , the piston assembly  200  includes a housing  201 . The housing  201  can be made of a variety of materials and can be a variety of shapes. For example, the housing  201  can be made out of metals, metal alloys, plastics, non-corrodible materials, etc. The piston assembly  200  also includes a piston  202 . The piston  202  can define two chambers within the housing  201 . The common pipe  40  can feed into a first chamber  204  on one side of the piston  202 . A second chamber  205  can be located on the other side of the piston  202  opposite of the first chamber. The second chamber  205  can be filled with a compressible gas  203  or mixtures of compressible gases. Compressibility is a measure of the relative volume change of a fluid or solid as a response to a pressure (or mean stress) change. The compressibility of a gas or mixture is dependent on the pressure, temperature, and molar volume. The compressible gas  203  or mixture can be selected from air (which generally comprises about 80% nitrogen and about 20% oxygen), oxidizer gases such as oxygen, or inert gases such as helium, and combinations thereof. Preferably the compressible gas does not include a flammable gas. 
     The piston  202  can move within the housing  201 . Movement of the piston  202  can inversely change the dimensions of the first and second chambers  204 / 205 . As the piston movement increases the dimensions of the first chamber  204  the dimensions of the second chamber  205  are reduced and vice versa. The compressible gas  203  within the second chamber  205  will compress as the piston moves to reduce the dimensions of the second chamber  205 , for example as depicted in  FIG. 2B . 
     When the pressure in the pipe system via the pressure from the two or more annuli increases and exceeds a predetermined amount, then the piston  202  of the piston assembly  200  moves. The pressure moves the piston  202  to reduce the dimensions of the second chamber  205  via compression of the compressible gas  203 . This movement of the piston  202  reduces the amount of pressure in the common pipe  40 , each of the pipes making up the pipe system, and each annulus connected to a pipe of the pipe system. In this manner, movement of the piston reduces the total amount of pressure in the two or more annuli. 
     The predetermined amount of pressure at which the piston  202  moves within the housing  201  can be based on anticipated conditions of the oil and gas operation. By way of example, the casing strings  23  can have a pressure rating at which above that pressure then damage could occur to the casing strings. In this example, the predetermined amount of pressure can be less than the pressure rating of the casing strings so the piston would move to reduce the pressure in the annuli prior to the casing strings becoming damaged. The predetermined amount of pressure can also be a pressure less than the amount of pressure at which wellbore components become damaged. 
     The amount of movement of the piston, thereby increasing the dimensions of the first chamber  204 , causes a certain amount of pressure in the pipe assembly and the two or more annuli to decrease. The amount of reduction in the pressure in the two or more annuli can be calculated based on a variety of factors including, but not limited to, the temperature of the wellbore fluid  32  within the annuli, the size of the piston assembly  200  including the size of the housing  201  making up the first chamber  204  and second chamber  205 , the compressibility of the compressible gas  203 , and the initial amount of pressure in the two or more annuli prior to reduction. 
     The size of the housing  201  and the second chamber  205  can be adjusted to provide a desired pressure decrease in the two or more annuli. By way of example, the larger the dimensions of the housing  201  and second chamber  205  prior to movement of the piston  202 , the greater amount of pressure decrease will occur in the two or more annuli. The type of compressible gas  203  can also be selected to provide the desired pressure decrease in the two or more annuli. According to certain embodiments, the desired pressure decrease is at least sufficient such that damage to wellbore components, such as the casing or tubing strings, does not occur. In this manner, the excess pressure within the annuli of the wellbore can be bled off into the piston assembly before any damage can occur. 
     After the amount of pressure in the two or more annuli is reduced or decreased, the piston  202  can move back towards the inlet into the first chamber  204 . This movement decreases the dimensions of the first chamber  204  and increases the dimensions of the second chamber  205 . Should the pressure in the pipe system increase again above the predetermined amount, then the piston  202  would move again to reduce the pressure in the two or more annuli. 
     It should be noted that the well system  10  is illustrated in the drawings and is described herein as merely one example of a wide variety of well systems in which the principles of this disclosure can be utilized. It should be clearly understood that the principles of this disclosure are not limited to any of the details of the well system  10 , or components thereof, depicted in the drawings or described herein. Furthermore, the well system  10  can include other components not depicted in the drawing. 
     Therefore, the present system is well adapted to attain the ends and advantages mentioned as well as those that are inherent therein. The particular embodiments disclosed above are illustrative only, as the principles of the present disclosure can be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is, therefore, evident that the particular illustrative embodiments disclosed above can be altered or modified and all such variations are considered within the scope and spirit of the principles of the present disclosure. 
     As used herein, the words “comprise,” “have,” “include,” and all grammatical variations thereof are each intended to have an open, non-limiting meaning that does not exclude additional elements or steps. While compositions and methods are described in terms of “comprising,” “containing,” or “including” various components or steps, the compositions and methods also can “consist essentially of” or “consist of” the various components and steps. It should be understood that, as used herein, “first,” “second,” “third,” etc., are arbitrarily assigned and are merely intended to differentiate between two or more annuli, casing strings, wellbore intervals, etc., as the case may be, and does not indicate any particular orientation or sequence. Furthermore, it is to be understood that the mere use of the term “first” does not require that there be any “second,” and the mere use of the term “second” does not require that there be any “third,” etc. Whenever a numerical range with a lower limit and an upper limit is disclosed, any number and any included range falling within the range is specifically disclosed. In particular, every range of values (of the form, “from about a to about b,” or, equivalently, “from approximately a to b”) disclosed herein is to be understood to set forth every number and range encompassed within the broader range of values. Also, the terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee. Moreover, the indefinite articles “a” or “an,” as used in the claims, are defined herein to mean one or more than one of the element that it introduces. If there is any conflict in the usages of a word or term in this specification and one or more patent(s) or other documents that can be incorporated herein by reference, the definitions that are consistent with this specification should be adopted.