Abstract:
A combination liquid and gas separator and jetting tool includes a housing containing a rotatable drum, a stator in the inlet end of the housing for swirling a liquid/gas mixture, a rotor attached to the drum for rotation by the mixture; whereby the gas and liquid are separated. The liquid and gas are discharged through separate restricted orifices downstream of the drum. Orifices can be located in a rotating head for cleaning, cutting or other downhole operations.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application claims benefit of PCT Patent Application No. PCT/CA2005/001439, filed Sep. 20, 2005, which claims benefit of U.S. Provisional Patent Application No. 60/611,111, filed Sep. 20, 2004, the contents of each incorporated herein by reference in their entirety. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to a gas separator and in particular to a gas separator for use as an inline, downhole tool for oil and gas well drilling and servicing. 
   2. Brief Description of the Prior Art 
   As described in the Latos et al U.S. Pat. No. 6,138,757, there are occasions in the oil and gas industry when a gas is pumped down a well with a liquid. Coiled tubing deployed jetting services are commonly performed in depleted wells using energized fluids—typically nitrogen and water. Underbalanced operation with energized fluids reduces the potential for well damage and helps to transport fluids and cuttings to surface. When nitrogen and water are jetted as a two-phase fluid, the jet expands as it leaves the nozzle, reducing the jet impact pressure. Two-phase flow in the jet nozzle may also be sonically choked—limiting the jet discharge velocity and effectiveness. Moreover, fluid jets dissipate rapidly in the surrounding wellbore fluid. All these factors combine to reduce the effectiveness of a two-phase jet. 
   Removal of the gas from the fluid stream would enhance the performance of jetting for well servicing. A single phase water jet has higher density and stagnation pressure than a mixed-phase jet and would be more effective than a two-phase jet. Under conditions found in oil and gas well service operations, the gas cut in the fluid discharge from the separator should be less than 1 vol % to ensure effective jetting. 
   Shrouding the jets with the separated gas would reduce jet dissipation and increase the effective range of the jet. Many well service operations required that the jetting tools pass through small diameter tubing and obstructions before cleaning larger diameter tubing, downhole equipment in side-pocket mandrels or openhole wellbores; increased jetting range will increase the effectiveness of jetting tools compared to single-phase fluid jetting for these applications. 
   The use of energized fluid with a gas separator will also boost the differential pressure and hydraulic power of the jet by reducing bottomhole circulating pressure. Increased pressure and power will allow erosion of harder material such as mineral scale, cement and rock, while increased power will improve erosion rates. 
   An effective gas separator would maintain high efficiency over a relatively high range of inlet gas fractions. In a common application, sufficient nitrogen is added to reduce the bottomhole pressure to 50% of hydrostatic. Under these conditions compressed gas makes up 20 to 60% of the volume fraction of the flow inside the coil. The volume fraction of gas entering the separator may vary substantially during a single run due to changes in pressure and temperature as the operating depth of the tool increases. 
   The Latos et al patent (supra) describes a downhole phase separator for coiled tubing using a cyclonic separator design. This tool provides less than 5% gas cut for a supply fluid with 30% to 40% gas content. Cyclonic separators are used to swirl fluid flow through a set of vanes. This approach generates very high radial accelerations, which provide the separation forces. In small diameter tools, the high flow rate generates high turbulent mixing forces that overcome the separation forces and limit separation performance. 
   Rotary gas separators are commonly used in two-phase production to prevent gas from entering electric submersible pumps. The rotary gas separator is powered by the pump shaft and spins at 3500 or 1750 rpm depending on the electric motor and power supply. The system includes an inducer to pressurize the two-phase flow entering the separator. The flow enters a shrouded vane section where the flow spins and the water or oil moves to the outside due to centrifugal forces. The shroud rotates with the vanes reducing turbulence in the separator. A crossover manifold at the top directs the fluid flow to the pump and the gas flow back into the well annulus. The claimed gas cut is less than 10% for a wide range of flow rates and gas/liquid flow ratios, 
   Inline rotary gas separators are also used in pipelines to remove small volumes of condensate from the gas flow. This style of separator uses a stator to induce swirling flow inside of a drum which includes rotor vanes in the gas flow. The rotor provides power to spin the drum. This type of separator is designed to remove all fluid from the gas stream as opposed to providing a low gas cut in the fluid. 
   Yahiro et al in U.S. Pat. No. 4,047,580 disclose a method for shrouding a submerged jet by introducing compressed air through the outer annular ring of a concentric jet nozzle. The air shroud increased the range of the jet by a factor of four. The construction of annular gas nozzles is complex, particularly for high-pressure fluid jetting. 
   SUMMARY OF THE INVENTION 
   A need still exists for an inline separator for efficiently separating a gas from a liquid. An object of the present invention is to meet this need by providing a relatively simple, compact separator for removing gas from a gas/liquid mixture. 
   Another object of the invention is to provide an apparatus combining a separator for separating gas from liquid and a jetting tool for inline, downhole operations. 
   Accordingly, the invention relates to an apparatus for separating a gas from a liquid under pressure comprising: 
   a tubular housing having an inlet end and an outlet end; 
   a stator in said inlet end of the housing for causing swirling of gas-containing liquid introduced into said inlet end; 
   a drum rotatably mounted in said housing downstream of said stator in the direction of liquid flow between said inlet and outlet ends of the housing; 
   a rotor in an inlet end of said drum for causing the drum to rotate in the housing; 
   an end wall in a downstream end of said drum in the direction of fluid flow through the housing; 
   liquid outlet ports in the periphery of said end wall for discharging liquid from the drum; 
   a gas outlet port in the centre of said end wall for discharging gas from the drum; 
   a liquid outlet passage in said housing for receiving liquid from said liquid outlet port and discharging liquid from said housing; 
   a gas outlet passage in said housing for receiving gas from said gas outlet port and discharging gas from said housing; 
   a first flow restriction in said liquid outlet for restricting liquid flow during discharge from the apparatus; and 
   a second flow restriction in said gas outlet for restricting gas flow during discharge from the apparatus. 
   In another embodiment, the invention relates to a method of jetting comprising the steps of passing a two-phase fluid stream through a jetting tool, removing gas from the two-phase fluid stream thereby producing a gas-rich phase and a liquid phase containing less than 1 vol % gas. In a further embodiment, the gas-rich phase and the liquid phase are discharged from the tool and the gas-rich phase shrouds the discharge of the liquid phase. 
   In yet another embodiment, the invention relates to a method of pumping a two phase fluid containing a gas and a liquid into a wellbore and separating the gas phase phase from the liquid phase whereby the resulting liquid phase contains less than 1 vol % gas. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic, longitudinal sectional view of a combination separator and jetting apparatus in accordance with the present invention; 
       FIG. 2  is a schematic, longitudinal sectional view of a second embodiment of a combination separator and jetting tool in accordance with the present invention; 
       FIG. 3  is a schematic, longitudinal sectional view of a combination separator and rotary jetting tool in accordance with the invention; 
       FIG. 4  is a schematic, longitudinal sectional view of a second embodiment of a combination separator and rotary jetting tool in accordance with the invention; 
       FIG. 5  is a schematic, longitudinal sectional view of a third embodiment of a combination separator and rotary jetting tool in accordance with the invention; 
       FIG. 6  is a schematic, longitudinal sectional view of a fourth embodiment of the combination separator and rotary jetting tool in accordance with the present invention; 
       FIG. 7  is a schematic, longitudinal sectional view of a fifth embodiment of a combination separator and rotary cutting tool in accordance with the invention; 
       FIG. 8  is an end view of the separator and cutting tool of  FIG. 7 ; 
       FIG. 9  is an isometric view of a stator used in the tool of  FIG. 7 ; and 
       FIG. 10  is an isometric view of a rotor used in the tool of  FIG. 7 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIG. 1 , a separator in accordance with the invention includes an elongated tubular housing  1  containing a rotatable drum  2 . A gas-containing liquid is introduced into the inlet end  3  of the housing  1  via a narrow diameter throat  4 . The liquid passes around the conical end  5  of a stator  6 , which is fixedly mounted in the housing. The stator  6  includes vanes  7  connected to the housing  1  for causing the fluid entering the housing  1  to swirl. The swirling flow causes a rotor  9  to spin. The rotor  9 , which is connected to the drum  2 , includes straight vanes  10  extending parallel to the longitudinal axis of the drum to ensure that the tangential flow of fluid in the drum  2  is small. The rotor  9  is rotatably supported in the stator  6  by a bearing  12 . The flow of fluid through the rotor  9  causes rotation of both the rotor and the drum  2 . 
   An end wall  25  of the drum  2  is rotatably connected to a discharge end of the housing  1  by a bearing  14  which has a restriction. The bearings  12  and  14  are formed of low friction materials and have a small diameter to limit bearing torque. The bearing  14  is a combined journal and thrust bearing, while the bearing  12  is a plain journal bearing. A clearance seal  15  is provided between the trailing end of the drum  2  and the trailing end  16  of the housing  1 . Gas in the liquid entering the drum  1  via the stator  6  and the rotor  9  is separated from the mixture flowing past the conical trailing end  18  of the rotor  9  by centripetal acceleration, which forces the liquid  19  to the outside and the gas  20  to the center of the drum  2 . Since the tangential component of fluid velocity is small, the total flow velocity is minimized which minimizes turbulent mixing forces opposing separation. 
   Preferably a balance pressure port  21  is provided in the rotor  9  for venting a balance pressure chamber  22  between the stator and the rotor. Reduced pressure in the chamber  22  reduces the thrust load imparted by the rotating drum  2  on the thrust bearing  12 . Ports  23  can also be provided in the drum  2  near the trailing end thereof. The ports  23  are located in a region of low velocity liquid flow, which is at a higher pressure than the high velocity region between the stator  6  and the rotor  9 . The ports  23  result in reverse circulation of fluid which counteracts the leakage of gas through the space between the housing  1  and the drum  2 . 
   Liquid  19  is discharged from the drum  2  through ports  24  in the periphery of the end wall  25  of the drum  2 . The ports  24  define sections of an annulus. The liquid flows through a passage  26  in the trailing end  16  of the housing  1  to a restriction in the form of a nozzle  28 . The gas is discharged through a central, axially extending siphon tube  30  connected to the trailing end wall  25  of the drum  2 , and a passage  31  and an orifice  32  in the trailing end  16  of the housing  1 . Multiple gas outlets can be provided. 
   The gas orifice at the inlet end of the passage  31  is preferably sized as a sonic nozzle which will pass the maximum volumetric flow rate of gas anticipated in a given operation. The gas dynamics equations for sizing a gas orifice for a given pressure, temperature and flow rate are well known to those skilled in the art. The liquid nozzles  28  are sized to provide the maximum hydraulic jetting power taking into account frictional pressure losses in the coil. If the liquid flow rate increases and the gas fraction decreases, the differential pressure and flow rate across the liquid jet nozzles and gas orifice increases. Liquid entering the gas orifice causes it to choke, which reduces the gas flow capacity. The gas orifice therefore provides a simple and robust means of limiting liquid loss from the gas separator while maintaining pressure and hydraulic power of the liquid jets as the gas flow rates decrease. 
   The trailing end of the housing  1  in the direction of fluid flow is closed by a jetting assembly  34 , which contains parts of the passages  26  and  31 , the nozzle  28  and the orifices  32 . The jetting assembly  34  is representative of a variety of more complex tools including rotary jetting tools, drilling motors and other tools relying on a restriction to fluid flow. 
   In a preferred embodiment of the invention, the gas orifice  32  is sized to be slightly larger than required for the maximum flow rate of gas anticipated in a given operation. The gas dynamics equations for sizing a gas orifice for a given pressure, temperature and flow rate are well known to those skilled in the art. The liquid nozzles  28  are sized for the pumped fluid flow rate at the desired jetting pressure, taking into account frictional pressure losses in the coil. If the gas fraction decreases, fluid will start to enter the siphon tube  30  and the orifice  32 . The two-phase flow capacity of the gas orifice  32  is much smaller than the gas flow capacity. The gas orifice  32  therefore provides a simple and robust means of limiting liquid loss from the gas separator due to variations in inlet gas fraction that may occur during operation. Gas separator bench tests show that the liquid loss is 0.6% or smaller while the inlet gas fraction ranges from 29% to 52%. 
   The embodiment of the invention shown in  FIG. 2  is similar to that of  FIG. 1  except that the rotor  9  is cylindrical with no conical trailing end, and the upstream end  36  of the drum end wall  25  is conical to accelerate the flow of liquid into the outlet ports  24  without introducing sudden changes in flow direction which could trigger turbulent remixing of gas and liquid. The axes of the nozzle  28  and the orifice  32  intersect outside of the jetting assembly  34  so that a gas shroud is formed around the liquid jet. The orifice  32  in the embodiment of  FIG. 2  is restricted rather than bearing  14  as in the embodiment of  FIG. 1 . 
     FIG. 3  shows an apparatus for applications requiring rotary jetting of liquid leaving the apparatus. The apparatus of  FIG. 3  is similar to that of  FIG. 1  except that liquid discharged from the drum  2  via the siphon tube  30  passes through passages  38  in the trailing end of the housing  1 , and central axial passages  39  and  40  via a brake assembly  42  and a head  43 , respectively. The brake assembly  42 , which includes a tube  46  carrying the head  43 , is rotatably mounted on bearings  47  in the housing  1 . The passage of liquid through the nozzles  44 , which are offset from the longitudinal axis of the head  43 , i.e. inclined with respect to radii of the head  43 , causes the brake assembly  42  and the head  43  to spin in the housing. The nozzles  44  are located beyond the trailing end of the housing  1 , so that when deployed in a oil or gas production tube  49 , the fluid jets will remove scale deposits  50 . It will be appreciated that any rotary motor with an axial flow passage sufficiently large to accommodate the siphon tube  30  can be used in combination with the separator. For example, the Marvin et al US Patent Application 2005/0109541 discloses a reaction turbine jet rotor with a large diameter, unobstructed axial flow passage. 
   The siphon tube  30  conveys gas from the drum  2  to a central outlet orifice  51  in the head  43 . The inlet end of the siphon tube  30  is freely rotatable in the end wall  25  of the drum  2 . The outlet end of the tube  30  is fixed in the rotatable head  43 , which rotates at a different speed from the drum  2 . Thus, a gas bubble forms at the outlet end of the head  51  and the outlet end of the housing  1 , so that the liquid jets from the nozzles  44  into gas. 
   The apparatus of  FIG. 4  is similar to that of  FIG. 3  except that gas discharged through the siphon tube  30  passes through passage  54  and is discharged via a cylindrical passage  55  between the housing  1  and the discharge end  56  of the head  43 . The liquid discharged through the ports  24  in the end wall  25  of the drum  2  passes through a passage  57  in the trailing end of the housing  1  into the passages  39  and  40 , and through the brake assembly  42  and the head  42  to exit through the nozzle  44 . 
   Referring to  FIG. 5 , another embodiment of the rotary jetting apparatus includes all of the elements of the apparatus of  FIG. 3 , except that the conical trailing end  18  of the rotor  9  and the brake assembly  42  have been omitted, and the cylindrical end wall  25  of the drum has been replaced with an end wall having a conical inlet or upstream end  36 . 
   Moreover, in the apparatus of  FIG. 5 , the head  43  itself is rotatably mounted in the trailing end of the housing  1 . Liquid is discharged through passages  38  and  40 , and a plurality of inclined nozzles  44  in the trailing end of the head  43 . The gas is discharged through the end wall  25  of the drum  2  via the siphon tube  30 , a passage  58  in the trailing end of the head  43  and inclined nozzles  59 . The trailing end of the siphon tube  30  includes a restriction  60 . The axes of the nozzles  44  and  59  intersect outside of the head  43  so that the liquid jets are shrouded in gas. 
   The apparatus of  FIG. 6  is used for cutting through a formation  60 . The apparatus is similar to that of  FIG. 4 , except that the rotor  9  is cylindrical with no conical trailing end, the trailing end wall  25  of the drum  2  has a conical leading end  36 , and the brake assembly  42  is omitted. Liquid is discharged via ports  24  in the drum end wall  25 , a passage  57  in the trailing end of the housing  1 , a central passage  40  in the head  43  and orifices  44 . The gas passage  54  defining a siphon tube contains a restriction  62 . 
   With reference to  FIG. 7 , another embodiment of the combination separator jetting apparatus includes a separator including the housing  1  with internally threaded inlet and outlet ends  64  and  65 , respectively for receiving couplings  67  and  68 . A stator  70  is fixedly mounted in the inlet end  64  of the housing  1 . As best shown in  FIG. 9 , the stator  70  includes a cylindrical body  71  with a generally hemispherical leading end  72 . Arcuate vanes  74  extending outwardly from the body  71  connect the stator to a sleeve  75 , which connects the stator to the housing  1 . 
   A cylindrical rotor  77  is rotatably mounted on a bearing  78  on the trailing end of the stator. The rotor  77  ( FIG. 10 ) includes a cylindrical body  80  with radially extending vanes  81 . 
   The end wall  25  of the drum  2  is rotatably mounted on a bearing  14  at the inlet end of a sleeve  83  on the siphon tube  30 . The bearing  14  is connected to the inlet end of the coupling  68  by a sleeve  84 . The downstream end of the coupling  68  is connected to a second housing  85  containing a speed governor  87 . The speed governor  87  includes a central, tubular shaft  88 , which is rotatably mounted on bearings  89  in the coupler  68  and bearings  91  in a coupler  92 . Centralizers  93  in the shaft  88  center the siphon tube  30  in the speed governor. Segmented weights  94  around the shaft  88  govern the speed of rotation of the shaft by sliding outwardly against the housing  85 . 
   A jetting assembly indicated generally at  96  is rotatably supported on the end of the coupling  92  by bearings  97 ,  98 ,  99 ,  100  and  101 . The assembly  96  includes a housing  102  carrying a rotatable head  43 . The bearing  97  includes a mid-face vent  104 , which vents to the rotatable head  43  and forms a mechanical face seal with the bearing  98 . The bearing  100  is fixed to the rotatable head  43 . The bearing  100  forms a mechanical face seal with the bearing  101 . The diameters of the bearing contact surfaces are sized to minimize the mechanical contact load on the mechanical face seals while maintaining effective sealing under high pressures. 
   Liquid discharged from the drum  2  through the ports  24  in the end wall  25  flows through three jet nozzles  106  (one shown) in a cap  107  on the rotating head  43 . Gas discharged from the drum  2  travels through the siphon tube  30  and is discharged through a gas orifice  109  in the end of the siphon tube  30  and through three discharge ports  110  (one shown) in the cap  107  to form shrouds around the liquid jets.