Patent Publication Number: US-6702025-B2

Title: Hydraulic control assembly for actuating a hydraulically controllable downhole device and method for use of same

Description:
TECHNICAL FIELD OF THE INVENTION 
     The present invention relates, in general, to controlling the actuation of a downhole device and, in particular, to a hydraulic control assembly for actuating a hydraulically controllable downhole device using subsea intensification of a hydraulic fluid. 
     BACKGROUND OF THE INVENTION 
     Without limiting the scope of the present invention, its background will be described with reference to subsurface safety valves as an example. 
     Subsurface safety valves are commonly used to shut in oil and gas wells in the event of a failure or hazardous condition at the well surface. Such safety valves are typically fitted into the production tubing and operate to block the flow of formation fluid upwardly therethrough. The subsurface safety valve provides automatic shutoff of production flow in response to a variety of out of range safety conditions that can be sensed or indicated at the surface. For example, the safety conditions include a fire on the platform, a high or low flow line temperature or pressure condition or operator override. 
     During production, the subsurface safety valve is typically held open by the application of hydraulic fluid pressure conducted to the subsurface safety valve through an auxiliary control conduit which extends along the tubing string within the annulus between the tubing and the well casing. For example, flapper type subsurface safety valves utilize a closure plate which is actuated by longitudinal movement of a hydraulically actuated, tubular or rod type piston. The flapper valve closure plate is maintained in the valve open position by an operator tube which is extended by the application of hydraulic pressure onto the piston. Typically, a pump at the surface pressurizes hydraulic fluid from a hydraulic fluid reservoir that is also at the surface. The high pressure hydraulic fluid is then delivered through the control conduit to a variable volume pressure chamber of the subsurface safety valve to act against the crown of the piston. When, for example, the production fluid pressure rises above or falls below a preset level, the hydraulic control pressure is relieved such that the piston and operator tube are retracted to the valve closed position by a return spring. The flapper plate is then rotated to the valve closed position by, for example, a torsion spring or tension member. 
     It has been found, however, that as oil and gas wells are being drilled in deeper water, the hydrostatic pressure of the column of hydraulic fluid in the control conduit approaches the closing pressure of typical subsurface safety valves. Accordingly, stronger springs are required to generate the necessary closing pressure such that a subsurface safety valve installed in a deep water well may be operated to the closed position. It has been found, however, that use of these stronger springs increases the opening pressure required to operate the subsurface safety valve from the closed position to the open position as well as the pressure required to hold the subsurface safety valve in the open position. This in turn requires that the entire hydraulic system used to control these deep water subsurface safety valves must be operated at a higher pressure. 
     Therefore, a need has arisen for an apparatus and method for actuating subsurface safety valves installed in deep water wells wherein the hydrostatic pressure of the column of hydraulic fluid in the control conduit does not approach the closing pressure of the subsurface safety valves. A need has also arisen for such an apparatus and method that does not require the use of stronger springs in the subsurface safety valve to generate high closing pressures. Further, a need has arisen for such an apparatus and method that does not require the use of hydraulic systems having higher operating pressures to generate the higher opening and holding pressures required to overcome the higher spring forces of stronger springs. 
     SUMMARY OF THE INVENTION 
     The present invention disclosed herein comprises a hydraulic control assembly and method for actuating a hydraulically controllable downhole device that is installed in a deep water well. Using the hydraulic control assembly of the present invention, the hydrostatic pressure of the column of hydraulic fluid in the control conduit does not approach, for example, the closing pressure of the subsurface safety valve. Accordingly, subsurface safety valves installed in deep water wells using the hydraulic control assembly of the present invention do not require stronger springs for closure and do not require higher hydraulic opening pressures. 
     The hydraulic control assembly of the present invention includes a hydraulic fluid source located on a surface installation that is used to supply low pressure hydraulic fluid. An umbilical assembly is coupled to the hydraulic fluid source. The umbilical assembly provides a supply fluid passageway for the low pressure hydraulic fluid. A subsea intensifier that is operably associated with a subsea wellhead is coupled to the umbilical assembly. The subsea intensifier receives the low pressure hydraulic fluid from the umbilical assembly and pressurizes the low pressure hydraulic fluid into a high pressure hydraulic fluid suitable for actuating the hydraulically controllable device. The subsea intensifier may have one of several power sources. A surface hydraulic power source may be coupled to the subsea intensifier via the umbilical assembly or a surface electric power source may be coupled to the subsea intensifier via the umbilical assembly. 
     In another embodiment of the present invention, the hydraulic control assembly of the present invention includes a subsea hydraulic fluid source. A subsea intensifier is operable to convert the low pressure hydraulic fluid from the subsea hydraulic fluid source into a high pressure hydraulic fluid suitable for actuating the hydraulically controllable downhole device. An umbilical assembly may be coupled between the surface installation and the subsea intensifier to provide electrical power to the subsea intensifier. Alternatively, a subsea battery may provide electrical power, in which case the subsea intensifier may be controlled via wireless telemetry. 
     The method of the present invention includes storing a hydraulic fluid in a reservoir located on a surface installation, supplying low pressure hydraulic fluid from the reservoir via an umbilical assembly to a subsea intensifier which is operably associated with a subsea wellhead and converting the low pressure hydraulic fluid into high pressure hydraulic fluid suitable to actuate the hydraulically controllable downhole device. Alternatively, the method includes storing the hydraulic fluid in a subsea reservoir, pressurizing the hydraulic fluid with a subsea intensifier and actuating the hydraulically controllable downhole device. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the features and advantages of the present invention, reference is now made to the detailed description of the invention along with the accompanying figures in which corresponding numerals in the different figures refer to corresponding parts and in which: 
     FIG. 1 is a schematic illustration of an offshore production platform operating a hydraulic control assembly of the present invention; 
     FIG. 2 is a side elevation view of an umbilical assembly of a hydraulic control assembly of the present invention; 
     FIG. 3 is a fluid circuit diagram illustrating one embodiment of a hydraulic control assembly of the present invention wherein the hydraulic fluid source is positioned at a surface installation; 
     FIG. 4 is a fluid circuit diagram illustrating another embodiment of a hydraulic control assembly of the present invention wherein the hydraulic source is positioned at a surface installation; 
     FIG. 5 is a fluid circuit diagram illustrating a further embodiment of a hydraulic control assembly of the present invention wherein the hydraulic source is positioned subsea; 
     FIG. 6 is a fluid circuit diagram illustrating yet another embodiment of a hydraulic control assembly of the present invention wherein the hydraulic source is positioned subsea; and 
     FIG. 7 is a fluid circuit diagram illustrating still a further embodiment of a hydraulic control assembly of the present invention wherein the hydraulic fluid source is positioned subsea. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     While making and using of various embodiments of the present invention are discussed in detail below, it should be appreciated that the present invention provides many applicable inventive concepts which can be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative of specific ways to make and use the invention, and do not delimit the scope of the present invention. 
     Referring initially to FIG. 1, a hydraulic control assembly in use during an offshore production operation is schematically illustrated and generally designated  10 . A semi-submergible production platform  12  is positioned generally above a submerged oil and gas formation  14  located below a sea floor  16 . An umbilical assembly  18  extends from control unit  20  on platform  12  to a subsea wellhead  22  at sea floor  16 . Umbilical assembly  18  is flexible and able to adopt to the ocean currents as well as any drift of the surface installation  12 . A subsea intensifier  24  is operably associated with subsea wellhead  22  and is in fluid communication with umbilical assembly  18 . 
     A wellbore  26  extends from wellhead  22  through various earth strata including formation  14 . A casing  28  is cemented within wellbore  26  by cement  30 . A production tubing  32  is positioned within casing  28 . Tubing string  32  includes a subsurface safety valve  34 . In addition, tubing string  32  has a sand control screen  36  positioned proximate formation  14  such that production fluids may be produced through perforations  38  and into tubing string  32 . A pair of packers  40 ,  42  isolate the production interval between tubing string  32  and casing  28 . A hydraulic control line  44  extends from subsea intensifier  24  to subsurface safety valve  34 . Even though FIG. 1 depicts a vertical well, it should be noted by one skilled in the art that the hydraulic control assembly of the present invention is equally well-suited for use in deviated wells, inclined wells, horizontal wells and other types of well configurations. In addition, even though FIG. 1 depicts a production well, it should be noted by one skilled in the art that the hydraulic control assembly of the present invention is equally well-suited for use in injection wells. 
     Referring now to FIG. 2 therein is depicted an umbilical assembly  50  used in the hydraulic control assembly of the present invention. The umbilical assembly  50  includes an outer tube  52 . Outer tube  52  may, for example, have an axial component with a Young&#39;s modulus of elasticity preferably in the range of 500,000 to 10,500,000 psi, may be non-isotropic and may have a modulus of elasticity is not the same in all axes nor is it linear. Outer tube  52  may be constructed of fibers such as nonmetallic fibers, metallic fibers, or a mixture of nonmetallic and metallic fibers. Outer tube  52  may be constructed from a helically wound or braided fibers reinforced with a thermoplastic or a thermosetting polymer or epoxy. Outer tube  52  is preferably made of a material having a density with a specific gravity approximately in the range of about 0.50 grams per cubic centimeter to about 3.25 grams per cubic centimeter. The composition of outer tube  52  allows umbilical assembly  50  to flex and bend with the horizontal and vertical movement of the ocean water and the drift of platform  12 . It should be appreciated that the exact characteristics of umbilical assembly  50  such as Young&#39;s modulus, composition and specific gravity will be determined by a number of factors including the depth of sea floor  16 , the horizontal and vertical currents of the ocean waters and the desired fluid capacity of umbilical assembly  50 . 
     Umbilical assembly  50  preferably has a wear layer  54 , an impermeable fluid liner  56  and a load carrying layer  58 . Wear layer  54  is preferably braided around impermeable fluid liner  56 . Wear layer  54  is a sacrificial layer that engages outer tube  52  to protect the underlying impermeable fluid liner  56  and load carrying layer  58 . One preferred wear layer  54  is constructed from Kevlar™. Although only one wear layer  54  is shown, there may be additional wear layers as required. 
     Impermeable fluid liner  56  is an inner tube preferably made of a polymer, such as polyvinyl chloride or polyethylene. Impermeable fluid liner  56  can also be made of a nylon, other special polymer or elastomer. In selecting an appropriate material for impermeable fluid liner  56 , consideration is given to the underwater environment in which umbilical assembly  50  will be deployed. The primary purpose of impermeable fluid liner  56  is to provide an impervious fluid barrier since fibers, such as the metallic fibers of outer tube  52  or a Kevlar™ wear layer  54  are not impervious to fluid migration after repeated contortions. 
     Load carrying layer  58  includes a sufficient number of fiber layers to sustain the load of umbilical assembly  50  in a fluid. Preferably, load carrying layer  58  is a plurality of resin layers wound into a thermal setting or a hybrid of glass and carbon fibers. The composition of load carrying layer  58  will depend upon the particular characteristics of the well such as the depth of the well. It should be appreciated that the exact composition of umbilical assembly  50  including the number and types of layers, such as outer layer  52 , wear layer  54  and impermeable fluid liner  56 , may vary. Umbilical assembly  50  however, must have all the properties required to enable the recovery of hydrocarbons from subsea wells. In particular, umbilical assembly  50  must have sufficient strength, flexibility and longevity when suspended in an oceanic environment. 
     A plurality of passageways  60  are housed within load carrying layer  58 . Passageways  60  may be fluid passageways  62 , such as hydraulic fluid passageways  64 ,  66  or production fluid passageways  68 ,  70 . Fluid passageways  62  comprise a protective sheath defining a fluid cavity that is compatible with a variety of fluids, including hydraulic fluids, salt water and hydrocarbons. Such fluid passageways  62  are well known in the art. In addition, some passageways, such as passageway  76  may house electrical power conduits or electrical signal conduits. Electrical power conduits and electrical signal conduits preferably include one or more copper wires, multi-conductor copper wires, braided wires, or coaxial woven conductors bounded in a protective sheath. Additionally, any number of electrical conductors, data transmission conduits, sensor conduits, additional fluid passageways, or other types of systems may be positioned within load carrying layer  58 . 
     Of particular importance in the present invention, umbilical assembly  50  is designed to carry low pressure hydraulic fluid and/or electrical power from the control unit  20  to subsea intensifier  24 . Specifically, as explained in detail below, umbilical assembly  50  may be used to carry low pressure hydraulic fluid from a hydraulic fluid source on platform  12  to subsea intensifier  24  wherein the hydraulic fluid is pressurized to a suitably high pressure in order to operate a downhole hydraulically controllable device such as subsurface safety valve  34 . The low pressure hydraulic fluid may be used not only as the supply fluid that is pressurized, but also, as the power source for operating a hydraulic pump or other pressurizing system that pressurizes the portion of the low pressure hydraulic fluid that serves as the supply fluid. The supply portion and power portion of the low pressure hydraulic fluid may travel together in the same passageway, for example fluid passageway  64  or may travel in separate passageways, for example fluid passageways  66  and  68 . Alternatively, the power source for pressurizing the low pressure hydraulic fluid may be electricity carried in an electrical power conduit housed in a passageway  70 . 
     Referring now to FIG. 3, therein is depicted one embodiment of a hydraulic control assembly that is generally designated  80 . Hydraulic control assembly  80  includes a hydraulic fluid source  82  that is positioned at a surface installation, such as platform  12  of FIG.  1 . Hydraulic fluid source  82  houses a hydraulic fluid. A pump  84  in fluid communication with hydraulic fluid source  82  via fluid line  86  pumps the hydraulic fluid in a supply fluid passageway  88  at a relatively low pressure. 
     Supply fluid passageway  88  may, for example, be a passageway of the umbilical assembly. Supply fluid passageway  88  conveys the low pressure hydraulic supply fluid to a subsea intensifier  90 . At subsea intensifier  90 , low pressure line  92  conveys the low pressure hydraulic supply fluid from supply fluid passageway  88  to pump  94  where the low pressure hydraulic supply fluid is converted into high pressure hydraulic supply fluid. High pressure hydraulic supply fluid is conveyed via high pressure line  96  and control line  98  to hydraulically actuate a hydraulically controllable downhole device such as subsurface safety valve  100 . Although subsurface safety valve  100  is being used as an example of a hydraulically actuatable downhole device, it should be appreciated by one skilled in the art that the hydraulically actuatable downhole device could alternatively be other downhole devices such as sliding sleeves, globe valves, downhole chokes or the like. 
     Pump  94  is driven by hydraulic motor  102 . Power source  104 , which is a hydraulic pump in this embodiment, provides hydraulic motor  102  with hydraulic power fluid via power fluid passageway  106 , which is a passageway of an umbilical assembly. A fluid power line  108  couples the fluid passageway  106  to the hydraulic motor  102  at intensifier  90 . In an alternative embodiment, the hydraulic supply fluid and hydraulic power fluid may be combined and carried in the same fluid passageway. For example, supply fluid passageway  88  may provide both low pressure hydraulic supply fluid to pump  94  and hydraulic power fluid to hydraulic motor  102 . 
     Even though FIG. 3 has been described utilizing hydraulic motor  102  to drive hydraulic pump  94  in intensifier  90 , it should be understood by those skilled in the art that other types of pressure intensifiers could alternatively be utilized. For example, a pressure intensifier utilizing one or more reciprocating pistons operating in response to area imbalances could be utilized. 
     Hydraulic control assembly  80  of the present invention allows high pressure hydraulic fluid to be generated from low pressure hydraulic fluid at a subsea location eliminating the need for a high pressure hydraulic line to run from the surface to the hydraulically controllable downhole device. Instead, the present invention utilizes an umbilical assembly to provide the fluid passageway for the low pressure hydraulic fluid. More specifically, the positioning of the subsea intensifier at the subsea wellhead and use of the umbilical assembly to traverse the distance between the surface installation and the subsea wellhead, which may be several thousand feet, greatly reduces the hydrostatic head in the column of hydraulic fluid in the control line that runs only from the subsea wellhead to the hydraulically controllable downhole device. 
     Referring now to FIG. 4, therein is depicted another embodiment of a hydraulic control assembly of the present invention that is generally designated  120 . Hydraulic control assembly  120  includes a hydraulic fluid source  122  that is positioned at a surface installation, such as platform  12  of FIG.  1 . Hydraulic fluid source  122  houses a hydraulic fluid. A pump  124  in fluid communication with hydraulic fluid source  122  via fluid line  126  powers the hydraulic fluid at low pressure into a supply fluid passageway  128 . 
     Supply fluid passageway  128  conveys the low pressure hydraulic fluid to a subsea intensifier  130 . At subsea intensifier  130 , low pressure line  132  conveys the low pressure hydraulic supply fluid from supply fluid passageway  128  to pump  134  where the low pressure hydraulic supply fluid is converted into high pressure hydraulic supply fluid. The high pressure hydraulic supply fluid is conveyed via high pressure line  136  and control line  138  to hydraulically actuate a hydraulically controllable downhole device such as subsurface safety valve  140 . 
     Pump  134  is driven by electrical motor  142 . Electrical power source  144 , which is an electrical generator in this embodiment, provides electrical motor  142  with electrical power via electrical conduit  146 , which is disposed in a passageway of the umbilical assembly. A power line  148  couples the electrical conduit  146  to the electrical motor  142  at intensifier  130 . Electrical motor  142  is any motor hereto known or unknown in the art, such as a three-phase electrical induction motor that is energized by three-phase electrical power from the surface. 
     Referring now to FIG. 5, therein is depicted another embodiment of a hydraulic control assembly of the present invention that is generally designated  150 . Hydraulic control assembly  150  includes a hydraulic fluid source  152  that is positioned at a subsea location, such as at subsea wellhead  22  of FIG.  1 . Hydraulic fluid source  152  houses a hydraulic fluid. 
     A supply fluid passageway  154  conveys the low pressure hydraulic supply fluid to a subsea intensifier  156 . At subsea intensifier  156 , low pressure line  158  conveys low pressure hydraulic supply fluid from supply fluid passageway  154  to pump  160  where the low pressure hydraulic supply fluid is converted into high pressure hydraulic supply fluid. The high pressure hydraulic fluid is conveyed via high pressure line  162  and control line  164  to hydraulically actuate a hydraulically controllable downhole device such as subsurface safety valve  166 . As with the previous embodiments, although subsurface safety valve  166  is being used as an example of a hydraulically controllable downhole device, it should be appreciated by one skilled in the art that any hydraulically controllable downhole device could alternatively be actuated using the hydraulic control assembly of the present invention. 
     Pump  160  is driven by electrical motor  168 . Electrical power source  170 , which is an electrical generator in this embodiment, provides electrical motor  168  with electrical power via electrical conduit  172 , which is housed within a passageway of the umbilical assembly. A power line  174  couples the electrical conduit  172  to the electrical motor  168  at intensifier  156 . 
     Yet another embodiment of the invention is shown in FIG.  6  and generally designated as hydraulic control assembly  200 . Hydraulic control assembly  200  includes a hydraulic fluid source  202  that is positioned at a subsea location, such as at subsea wellhead  22  of FIG.  1 . Hydraulic fluid source  202  houses a hydraulic fluid. 
     A supply fluid passageway  204  conveys the low pressure hydraulic supply fluid to a subsea intensifier  206 . At subsea intensifier  206 , low pressure line  208  conveys the low pressure hydraulic supply fluid from supply fluid passageway  204  to pump  210  where the low pressure hydraulic supply fluid is converted into high pressure hydraulic supply fluid. The high pressure hydraulic supply fluid is conveyed via high pressure line  212  and control line  214  to hydraulically actuate a hydraulically controllable downhole device such as subsurface safety valve  216 . 
     Pump  210  is driven by electrical motor  218 . Electrical power source  220 , which is a battery in this embodiment, provides electrical motor  218  with electrical power via electrical conduit  222 . Electrical power source  220  is located subsea, for example, coupled to subsea wellhead  22  of FIG.  1 . 
     A power line  224  couples the electrical conduit  222  to the electrical motor  218  at intensifier  206 . A signal source  226  positioned at the surface, at for example, surface installation  12  of FIG. 1, signals electrical power source  220  ON and OFF via signal conduit  228 , which may be housed in a passageway of the umbilical assembly. 
     A further embodiment of the present invention is illustrated in FIG.  7  and generally designated hydraulic control assembly  250 . Hydraulic control assembly  250  includes a hydraulic fluid source  252  that is positioned at a subsea location, such as subsea wellhead  22  of FIG.  1 . Hydraulic fluid source  252  houses a hydraulic fluid. 
     A supply fluid passageway  254  conveys the low pressure hydraulic supply fluid to a subsea intensifier  256 . At subsea intensifier  256 , low pressure line  258  conveys the low pressure hydraulic supply fluid from supply fluid passageway  254  to pump  260  where the low pressure hydraulic supply fluid is converted into high pressure hydraulic supply fluid. The high pressure hydraulic supply fluid is conveyed via high pressure line  262  and control line  264  to hydraulically actuate a hydraulically controllable downhole device such as subsurface safety valve  266 . 
     Pump  260  is driven by electrical motor  268 . Electrical power source  270 , which is a battery in this embodiment, provides subsea intensifier  256  with electrical power via electrical conduit  272 . Electrical power source  270  is located subsea, for example, coupled to subsea wellhead  22  of FIG. 1. A power line  274  couples the electrical conduit  272  to the electrical motor  268  at intensifier  256 . A signal source  276  positioned at the surface, at for example, surface installation  12  of FIG. 1, signals electrical power source  270  ON and OFF via a wireless telemetry. Transceiver units  278 ,  280  are positioned at the signal source  276  and electrical power source  270 , respectively, to generate and receive wireless signals. Wireless telemetry is well known in the art and could utilize, for example, acoustic signal and acoustic modems for such communications. 
     It should be appreciated by those skilled in the art that the hydraulic control assembly of the present invention advantageously overcomes the various limitations of the existing subsea actuator solutions. By employing a subsea intensifier at a subsea wellhead and conveying a low pressure hydraulic fluid through an umbilical assembly, a hydraulically controllable downhole device may be actuated efficiently and with greatly reduced cost. 
     Moreover, the hydraulic control assembly of the present invention provides an apparatus and method for actuating subsurface safety valves installed in wells located in deep water thereby overcoming the problems caused by the hydrostatic pressure of the column of hydraulic fluid in a control conduit running from a surface installation to the hydraulically controllable downhole device that is installed in deep water. 
     While this invention has been described with a reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to the description. It is, therefore, intended that the appended claims encompass any such modifications or embodiments.