Buoyancy assist tool with overlapping membranes

A downhole apparatus has a casing string and a degradable plug positioned in the casing string to block flow therethrough. An upper membrane covers an upper end of the degradable plug. The upper membrane is made up of a plurality of separable membranes. A lower membrane covers a lower end of the degradable plug and is comprised of a plurality of separable membranes.

BACKGROUND

The length of deviated or horizontal sections in well bores is such that it is sometimes difficult to run well casing to the desired depth due to high casing drag. Long lengths of casing create significant friction and thus problems in getting casing to the toe of the well bore. Creating a buoyant chamber in the casing utilizing air or a fluid lighter than the well bore fluid can reduce the drag making it easier to overcome the friction and run the casing to the desired final depth.

DESCRIPTION

The following description and directional terms such as above, below, upper, lower, uphole, downhole, etc., are used for convenience in referring to the accompanying drawings. One who is skilled in the art will recognize that such directional language refers to locations in the well, either closer or farther from the wellhead and the various embodiments of the inventions described and disclosed here may be utilized in various orientations such as inclined, deviated, horizontal and vertical.

Referring to the drawings, a downhole apparatus10is positioned in a well bore12. Well bore12includes a vertical portion14and a deviated or horizontal portion16. Apparatus10comprises a casing string18which is made up of a plurality of casing joints20. Casing joints20may have inner diameter or bore22which defines a central flow path24therethrough. Well casing18defines a buoyancy chamber26with upper end or boundary28and lower end or boundary30. Buoyancy chamber26will be filled with a buoyant fluid which may be a gas such as nitrogen, carbon dioxide, or air but other gases may also be suitable. The buoyant fluid may also be a liquid such as water or diesel fuel or other like liquid. The important aspect is that the buoyant fluid has a lower specific gravity than the well fluid in the well bore12in which casing18is run. The choice of gas or liquid, and which one of these is used is a factor of the well conditions and the amount of buoyancy desired.

Lower boundary30may comprise a float device such as a float shoe or float collar32. As is known, such float devices will generally allow fluid flow downwardly therethrough but will prevent flow upwardly into the casing. The float devices are generally a one-way check valve. The float device32is thus a fluid barrier that will be configured such that it will hold the buoyant fluid in the buoyancy chamber26until additional pressure is applied after the release of the buoyancy fluid from the buoyancy chamber. The upper boundary28is defined by a buoyancy assist tool as described herein.

Buoyancy assist tool34includes an outer case36defining flow path37therethrough that is connectable in casing string18. Buoyancy assist tool34comprises a plug assembly38that is connected to and positioned in outer case36. Buoyancy assist tool34has upper end40and lower end42. Buoyancy assist tool34is connectable in the casing string at the upper and lower ends40and42thereof and forms a part of the casing string18lowered into well bore12.

Outer case36comprises an upper outer case44and a lower outer case46. A connecting shield48is connected to and extends between upper outer case44and lower outer case46. Outer case36and plug assembly38define an annular space50therebetween.

Plug assembly38has upper end52and lower end54. Plug assembly38is connected to upper outer case44at the upper end52thereof and to lower outer case46at the lower end54thereof. The plug assembly may be threadedly connected or connected by other means known in the art. Plug assembly38may comprise a plug housing56with upper and lower ends52and54which are the upper and lower ends of the plug assembly38. A degradable plug or degradable core58is fixed in housing56. Degradable core58has upper end57and lower end59, which may be for example coincident with the upper and lower ends52and54of plug housing56. The degradable core may be a matrix of sand and salt but can be other degradable substances that can be degraded with fluids or other means once the casing string18is lowered into the well bore to a desired location in the well. Plug housing56has a plurality of housing ports60defined through the wall thereof. Housing ports60communicate the annular space50with the degradable plug or core58so that fluid passing therethrough can contact degradable plug58and can degrade the plug to remove it from plug housing56to create a full bore flow path therethrough.

Buoyancy assist tool34may include an upper impermeable membrane62positioned across upper end57of degradable plug58and a lower impermeable membrane63positioned across the lower end59of degradable plug58. Impermeable membranes62and63, as described in more detail below, comprise a plurality of separable membranes configured to prevent the premature contact of fluid with degradable plug58. Membranes62and63will prevent fluid thereabove from contacting the degradable plug at the upper end of the plug assembly38prior to the time casing string18is placed at the desired location in well bore12. Likewise, the impermeable membrane63will prevent fluid in the buoyancy chamber26from contacting the degradable plug58until such time as degradation of the plug is desired. Upon degradation of the plug58the membranes62and63will be easily ruptured by fluid flowing through the casing string18, including outer case36.

Plug housing56has an inner surface64defining a diameter66and has an outer surface68. In the embodiment described diameter66is a diameter that is no smaller than an inner diameter of casing string18such that upon the degradation of plug58buoyancy assist tool34provides no greater restriction to the passage of well tools therethrough than that which already exists as a result of the inner diameter of the casing string18.

Upper end40of buoyancy assist tool34is likewise the upper end of upper outer case44. Upper outer case44has a lower end70. Plug assembly38is connected at its upper end52to the lower end70of upper outer case44. Outer surface68of plug housing56may have a groove67with an O-ring seal69therein to sealingly engage an inner surface of upper outer case44. Upper outer case44has inner surface72which defines an inner diameter74that is a minimum inner diameter of upper outer case44. Upper outer case44has a port76therethrough. Inner diameter74is a diameter that is no smaller than an inner diameter of casing string18such that upon the degradation of plug58buoyancy assist tool34provides no greater restriction to the passage of well tools therethrough than that which already exists as a result of the inner diameter of the casing string18.

A rupture disc or other rupturable membrane78is positioned in port76in upper outer case44. Rupture disc78will prevent flow through port76until a desired or predetermined pressure is reached in casing string18. Upon reaching the predetermined pressure the rupture disc78will rupture and fluid will be communicated from casing string18through port76into annular space50. Fluid will pass from annular space50through housing ports60and will contact the degradable plug58. The fluid passing therethrough may be referred to as a degrading fluid. The degrading fluid may be any fluid utilized to degrade the degradable plug and may be water or other degrading fluid.

The degrading fluid is in fluid chamber84, which has upper end86and lower end88. Upper membrane62prevents the fluid in fluid chamber84from contacting degradable plug58prior to the rupturing of rupture disc78. Upper outer case44may be a two-piece outer case comprising an upper portion80that is threadedly and sealingly connected to lower portion82. Lower portion82connects to plug assembly38as shown in the figures. Upper outer case44may define fluid chamber84which is a closed fluid chamber84. Fluid chamber84has an upper seal85that extends across upper end88thereof. Fluid in fluid chamber84is thus trapped between seal85and the upper membrane62. There are certain formations in which it is not desirable to pump water. In those instances oil or another fluid other than water may be utilized to fracture or otherwise treat the formation. Where, for example, water is the degrading fluid, but not the treatment fluid, water will be contained in the fluid chamber84such that upon reaching the appropriate position in the well oil or other fluid may be pumped through the casing string18so that the water in fluid chamber84will contact the degradable plug58a further described herein. The water in fluid chamber84passes into and from annular space50through ports60in plug housing56and will contact the degradable plug58until it is degraded or dissolved.

Lower outer case46has upper end90and a lower end which is the lower end42of buoyancy assist tool34. Upper end90of lower outer case46is connected to lower end54of plug assembly38. Outer surface68of plug housing56may have a groove91with an O-ring seal93therein to sealingly engage lower outer case46. Lower outer case46has inner surface92defining an inner diameter94. Inner diameter94is a diameter that is no smaller than an inner diameter of casing string18such that upon the degradation of plug58buoyancy assist tool34provides no greater restriction to the passage of well tools therethrough than that which already exists as a result of the inner diameter of the casing string18.

Connecting sleeve48has upper end102and lower end104. Connecting sleeve48is connected at its upper end102to an outer surface of upper outer case44and is connected at its lower end104to an outer surface of lower outer case46. O-ring seals105may be positioned in grooves in the outer surfaces of the upper and lower outer cases44and46respectively to sealingly engage an inner surface106of connecting shield48. Inner surface106of connecting shield48defines an inner diameter108. An annular passageway110is defined by and between upper outer case44and connecting shield48. Annular passageway110communicates fluid delivered through port76into annular space50. Fluid is communicated through ports60so that it will contact degradable plug58to dissolve or degrade the plug.

Upper and lower membranes62and63may be multiple layer membranes in which at least some of the multiple layers are dissimilar materials. In the embodiment described the multiple layer membrane62covers the upper end57of degradable plug58and has a first or inner membrane120adjacent upper end57of the degradable core58. Inner membrane120will cover the upper end of the degradable core58. Multiple layer membrane62likewise includes a second or outer member adjacent to and covering the first inner membrane120. First and second membranes120and122are of dissimilar materials and are not bonded to one another in any way. First and second membranes120and122are thus separable membranes. Thus, upon degradation of the plug58first and second membranes120and122will not adhere to one another and will break into pieces that will pass through casing string18and eventually through float equipment32at the end thereof. Outer membrane122is bonded to the upper end52of plug housing56. In the embodiment described the inner membrane120is a membrane of a first material which may be, for example a silicone membrane and the outer membrane122is a membrane of a second material, which may be, for example, a nitrile rubber membrane. Utilizing a multiple layer membrane as described herein will alleviate the risk of a premature rupture of membrane. When a nitrile rubber membrane is directly in contract with the degradable core, it is possible that imperfections and rough areas in the degradable core could puncture the nitrile rubber and allow degrading fluid to contact and begin to prematurely degrade the core58. Silicone inner membrane120described herein is far less likely to rupture and will provide separation between the upper end57of degradable core58and the nitrile rubber membrane.

Membrane63is generally identical to membrane62and multiple layer63membrane acts in the same way as does membrane62. Thus, multiple layer membrane63covers the lower end59of the degradable core58. First or inner membrane128of lower membrane63is adjacent lower end59and second or outer member130is adjacent first inner membrane128and covers membrane128. Outer membrane130is bonded to the lower end54of plug housing56. First and second membranes128and130are not bonded to one another and are separable membranes. Multiple layer membrane63will prevent the premature contact of any fluid in buoyancy chamber26from contacting and prematurely beginning to degrade plug core58. First membrane128may be a silicone membrane and second membrane130may be a nitrile rubber membrane. The first and second membranes of multiple layer membranes62and63are not connected to one another in any way and are not bonded so that upon degradation of the degradable plug58both will tear into pieces small enough to pass through the casing18such that no restriction to any flow therethrough or to the passage of tools therethrough is provided.

In operation casing string18is lowered into well bore12to a desired location. Running a casing such as casing18in deviated wells and long horizontal wells often results in significantly increased drag forces and may cause a casing string to become stuck before reaching the desired location in the well bore. For example, when the casing produces more drag forces than the available weight to slide the casing down the well, the casing may become stuck. If too much force is applied to the casing string18damage may occur. The buoyancy assist tool34as described herein alleviates some of the issues and at the same time provides for a full bore passageway so that other tools or objects such as, for example production packers, perforating guns and service tools may pass therethrough without obstruction after well casing18has reached the desired depth. When well casing18is lowered into well bore12buoyancy chamber26will aid in the proper placement since it will reduce friction as the casing18is lowered into horizontal portion16to the desired location.

Once the casing string18has reached the desired position in the well bore, pressure is increased and fluid pumped through the casing string18. The pressure will burst the seal85and will push the degradable fluid contained in fluid chamber84. Pressure will be increased until the rupture disc78bursts. Once that occurs degrading fluid from fluid chamber84will pass through port76into passageway110and into annular space50. Fluid will pass from annular space50through ports60and will contact the degradable plug58. A sufficient quantity of the degrading fluid will be utilized to degrade degradable plug58so that it will be completely removed from plug housing56. Typically, once the degradation process reaches a certain level, the degradable plug58will break up, and at that point both of upper and lower membranes62and63will likewise be broken, and the pieces thereof will pass through casing string18.

The choice of degrading fluid will be dependent on the plug material, but in many cases water will be used to degrade a plug formed of a sand and salt matrix. Once the degradable plug58is dissolved or degraded service tools may be passed through plug assembly38, and more particularly through plug housing56. As described herein, buoyancy assist tool34provides no size restriction on the tools that can be passed therethrough that does not already exist due to the size of the inner diameter of casing18. In other words, diameters66,74and94are of a size that will not limit the passage of tools beyond the limitation that results from the casing inner diameter thereabove.

A downhole apparatus comprises a casing string. A degradable plug is positioned in the casing string to block flow therethrough. An upper membrane covers an upper end of the degradable plug. The upper membrane comprises a plurality of separable membranes. In one embodiment a lower membrane covers a lower end of the degradable plug. The lower membrane may also comprise a plurality of separable membranes. A flexible fluid barrier is positioned in the casing string above the upper end of the degradable plug. The fluid barrier and the upper end of the degradable plug define a fluid chamber containing a degrading fluid. In one embodiment upper and lower membranes of the downhole apparatus the upper and lower membranes comprise a first membrane of a first material and a second membrane of a second material. The first membrane of the upper and lower membranes is positioned adjacent the upper and lower ends of the degradable plug and the second membrane covers the first membrane. The upper and lower membranes are configured to separate and tear upon degradation of the degradable plug. In one embodiment an outer case is connected in the casing string, and the fluid chamber is defined in the outer case. A plug housing is connected in the outer case, and the outer case and plug housing define an annular space therebetween. The plug housing has a plurality of ports communicating the annular space with the degradable plug. A rupture disk is positioned in a port in the outer case and configured to burst at a predetermined pressure. The port in the outer case is positioned to communicate fluid in the fluid chamber with the annular space. In one embodiment the membranes in the upper and lower membranes comprise a silicone membrane adjacent the upper and lower ends of the degradable plug and a rubber membrane covering the silicone membrane.

A downhole apparatus comprises an outer case connected at upper and lower ends in a casing string. A degradable plug is positioned in the outer case to block flow therethrough. An upper multiple layer impermeable membrane is positioned across an upper end of the degradable plug, and a lower multiple layer impermeable membrane is positioned across a lower end of the degradable plug. The upper and lower membranes each comprise membranes of dissimilar materials. The upper and lower multiple layer membranes comprise a first membrane adjacent the degradable plug and a second membrane covering the first membrane and the first and second membranes are not bonded to one another.

In one embodiment the upper and lower multiple layer membranes comprise a silicone membrane adjacent the upper and lower ends respectively of the degradable plug and a rubber layer covering the silicone layer. A flow barrier is connected in the casing string, and the flow barrier and degradable plug define a buoyancy chamber therebetween. A fluid chamber containing a degrading fluid is defined in the casing above the degradable plug. The degrading fluid in an embodiment comprises water, and an outer layer of the multiple layer membranes comprises a rubber membrane.

A downhole apparatus comprises a casing string lowered in a well. A buoyancy assist toll is connected in the casing string. A flow barrier is connected in the casing string and the buoyancy assist tool and the flow barrier define a buoyancy chamber therebetween. The buoyancy assist tool in one embodiment comprises an outer case with a plug housing positioned in the outer case. A degradable plug is fixed in the plug housing and an upper multiple layer impermeable membrane covers an upper end of the degradable plug. At least some layers of the upper multiple layer membrane comprise dissimilar materials. A fluid barrier in the casing positioned above the degradable plug barrier and the multiple layer membrane define a fluid chamber continuing a degrading fluid. A lower multiple layer impermeable membrane covers a lower end of the degradable plug, at least some of the layers of the lower multiple layer impermeable membrane comprising dissimilar materials. The upper multiple layer impermeable membrane comprises in one embodiment a first membrane adjacent the upper end of the degradable plug and a second membrane adjacent the first membrane. The first and second membranes are not bonded to one another and the second membrane is being bonded to the plug housing. The first membrane comprises a silicone membrane and the second membrane a nitrile rubber membrane.

Thus it is seen that the apparatus and methods of the present invention readily achieve the ends and advantages mentioned as well as those inherent therein. While certain preferred embodiments of the invention have been illustrated and described for purposes of the present disclosure, numerous changes in the arrangement and construction of parts and steps may be made by those skilled in the art, which changes are encompassed within the scope and spirit of the present invention.