Abstract:
Hydraulic well fluid vented from a hydraulically controlled actuating device is disposed of by pumping the fluid via a pump and a valve into a production flowline of the well.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a national stage application under 35 U.S.C. §371(c) of prior-filed, co-pending PCT patent application serial number PCT/GB2009/051477, filed on Nov. 3, 2009, which claims priority to British patent application serial number 0820326.7, filed on Nov. 7, 2008, each of which is hereby incorporated by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    Embodiments of the present invention relate to the disposal of well control fluids. 
         [0004]    2. Description of the Prior Art 
         [0005]    During the operation of a subsea well, hydraulic fluid is expelled from hydraulic control actuating devices, such as valve and choke actuators. Typically, in the past, this fluid has been exhausted to the sea. The fluid is, typically, ethylene glycol based and is now considered to be a pollutant. Environmental legislation now prompts well operators to stop exhausting such fluids into the sea, particularly on new installations, which presents well equipment suppliers with the problem of finding a solution to the new requirements. Embodiments of the present invention resolve the problem, removing the need to exhaust such fluids into the sea. 
       SUMMARY OF THE INVENTION 
       [0006]    According to an embodiment of the present invention, there is provided a method of disposing of hydraulic well control fluid, comprising pumping the fluid into a production flowline of the well. 
         [0007]    The fluid typically comprises hydraulic fluid vented from a hydraulically controlled actuating device of a control system of the well. 
         [0008]    Preferably, the fluid is pumped into the production flowline via a valve, which preferably opens at a pressure greater than the pressure of fluid in the flowline. 
         [0009]    The well could be a subsea hydrocarbon production well. 
         [0010]    According to an alternate embodiment of the present invention, there is provided a well control system, which includes means for disposing of hydraulic well control fluid by pumping the fluid into a production flowline of the well. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a schematic diagram of a system according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0012]    Referring to  FIG. 1 , for simplicity a single hydraulic actuator  1  of a subsea hydrocarbon well, is shown. The hydraulic actuator  1  is operated by hydraulic fluid, under pressure, fed to it through feed pipes  2  and  3  via an electrically operated directional control valve (DCV)  4 . The actuator  1  typically operates a valve as part of the control of the production fluid from the well. The actuator  1  is released, by de-energising the DCV  4 , which then shuts off the hydraulic fluid feed from the hydraulic fluid source via the feed pipe  2  and connects the actuator  1  to a vent pipe  5 . The hydraulic fluid exhausted from the actuator is fed via the vent pipe  5  into a pump  6 , which could be electrically or hydraulically powered. 
         [0013]    The production fluid pressure from the well in a production fluid flowline  7  (shown in section view) is at a much higher pressure than the hydraulic control fluid pressure and is typically as high as 3000 psi. The pump  6  has, therefore, to raise the pressure of the vented hydraulic control fluid to a pressure that is greater than the production fluid flowline pressure in order to be able to inject it into the flowline. The high pressure vented hydraulic fluid from the pump  6  is fed via a relief valve  8  to a feed pipe  9 , and injected into the flowline  7 , through a nozzle  10 . A typical relief valve  8  is illustrated in the inset sectioned diagrammatic view in  FIG. 1  and primarily consists of a steel ball  11 , held against a valve seat  12  by a spring  13 . The compression of the spring is arranged to allow the valve to open only when the inputted hydraulic fluid pressure is significantly greater than the pressure in the flowline  7 , that is the “cracking pressure” of the relief valve  8  is significantly greater than the pressure in the flowline  7 . 
         [0014]    Although the principle of the invention as shown in  FIG. 1  is applied to a single actuator, in practice, well hydraulic control systems employ several hydraulic actuators and the vented fluids from all the actuators would all be fed to the single pump  6 . 
         [0015]    Thus vented hydraulic control fluid, at a relatively low pressure, is pressurised by a pump, allowing it to be injected into the production fluid flowline, thus avoiding the pollution which results from such fluid being injected into the sea in existing systems. 
         [0016]    The above embodiment of the invention injects the exhausted hydraulic fluid from hydraulic operated devices into a production fluid pipeline, using a pump to achieve this function. Compared to the production fluid flow rate, the quantity of exhausted hydraulic fluid injected is negligible in terms of contamination of the production fluid and is, anyway, likely to be extracted by the water extraction process, typical of most installations, remote from the subsea well. 
         [0017]    The invention avoids disposal of vented hydraulic fluids from the control systems of wells into the environment, thus enabling well operators to meet new environmental requirements. 
         [0018]    In alternative systems that employ containers to store vented hydraulic fluid, the containers can be dispensed with and the costly process of emptying them avoided.