A. Field of the Invention
This invention relates to remote-controlled tubing safety valves and more particularly to a tubing safety valve having a check valve and remote-control means for maintaining the check valve in open position.
B. The Prior Art
Remote-controlled tubing safety valves utilized in well installations are well known. Such valves are normally biased towards a closed position and are held open hydraulically. Although the valve is positioned in the tubing string, the hydraulic conduit controls are often at the surface. Having the controls at the surface permits the valve to be opened or closed regardless of the conditions at the valve. Such remote-controlled valves have the disadvantage that if it is desired to operate the valve in response to conditions at the valve, means must be provided for sensing these conditions at the surface and then means must be provided to operate in response to the sensed conditions. The remote sensing of conditions followed by the remote operation of the valve takes time. During this time period equipment and personnel at the surface may be damaged and/or injured. The remote sensing and controlled operation of the valve is simply not fast enough in all circumstances.
Sometimes remote-controlled tubing safety valves are opened without the use of the hyrdraulic control means. To open the valve, fluid is pumped downward into the tubing string until a sufficient pressure differential exists across the valve for the valve member to move to slightly open position. (See Composite Catalogue of Oil Field Equipment and Services 1974-75 pages 3997 and 3998 and U.S. Pat. No. 3,870,101 to Helmus). To partially open the valve by pumping through it, the force exerted by the main biasing means which urges the valve member closed and which is normally overcome by the hydraulic means, must be overcome by the pressure differential across the valve. When the valve member is opened in this manner it is only partially opened and a high velocity flow results. This high velocity flow can erode the valve member and the valve seat. If the valve becomes eroded it will leak and must be replaced. U.S. Re. Pat. No. 26,149 discloses a remote control subsurface tubing safety valve. One form of the valve has a flapper valve member. However, even this flapper valve can not be pumped through without overcoming the force of the main spring biasing the valve member to a closed position and thus cannot operate as a check valve responsive to conditions at the valve.
U.S. Pat. No. 3,860,066 to Pearce et al discloses a remote-controlled tubing safety valve having two springs. The springs acts against an operating sleeve to bias it to a first position where the valve member is in a valve closing position while hydraulic means move the operating sleeve to a second position so that the valve member is in a valve opening position. One spring is disposed above the valve member while the second spring is disposed below the valve member. In the first form of the valve the valve member is a rotating ball valve confined between two valve seats. To close the safety valve, the springs overcome the hydrostatic head of fluid in the hydraulic control conduit. Generally one heavy spring is provided to do this; however, as illustrated in the aforementioned patent to Pearce, two springs may be provided. The upper spring may be stronger than the lower so that it alone can move the valve member operator to valve closing position. The second spring operates in conjunction with the first spring to assist in moving the operator and to maintain the valve member tightly confined between its seats. The lower and upper springs may be of equal stength but is preferable to have the lower spring be weaker than the upper spring. This is because if the valve member is forced upward by the lower spring, the pivot of the valve member can become worn causing the valve to malfunction. Again if the valve disclosed in the aforementioned patent to Pearce was attempted to be opened by pumping through the valve rather than by utilizing the hydraulic control means, a high pressure differential would have to be created across the valve, high velocity flow through the valve would result thereby causing erosion of the valve member and valve seat surfaces.
There are valves having valve members that respond quickly to conditions at the location of the valve for movement between valve opening and closing positions. Such valves may be ambient-type (e.g. the valve closes when the ambient pressure around the valve drops below a predetermined level), a pressure-differential type (e.g. the valve automatically closes when there is an abnormal increase of pressure through the valve) or injection safety valves. (See Composite Catalogue of Oil Field Equipment & Services 1974-75 pages 3995, 4008 to 4011, and 4014). However, such valves only close in response to the predetermined condition and cannot be controlled to open or close from the surface.
Injection safety valves do respond quickly to close the tubing string whenever a backkick occurs. However, present injection safety valves have no means to maintain the valve in an open position if it is desired to have a high back flow rate through the valve because they are urged towards a close position by such back flow. In addition they may have biasing means to constantly urge the valve member to a closed position.
It is sometimes desirable to inject fluids in a well equiped with a subsurface safety valve. In doing so, it is desirable that a check valve be present down in the tubing to protect personnel and equipment at the well. Equipment has not been available for this purpose without running additional equipment in to the well.