A METHOD FOR RECOVERING FLUID USED IN POWERING AN

UNDERWATER APPARATUS SUBMERGED IN DEEP WATER The present invention relates to a method for recovering fluid used in powering an underwater apparatus submerged in deep water. Preferably but not exclusively, the fluid is a hydraulic or power fluid.

Deepwater accumulators provide pressurized working fluid for the control and operation of equipment, for example for blowout preventer operators ; gate valves for the control of flow of oil or gas to the surface or to other subsea locations ; hydraulically actuated connectors ; and similar devices . The fluid to be pressurized is typically an oil based product or a water based product with added lubricity and corrosion protection, for example, but not limited to hydraulic fluid.

Certain prior art accumulators are precharged with pressurized gas to a pressure at or slightly below an anticipated minimum pressure required to operate equipment. Fluid can be added to the accumulator, increasing the pressure of the pressurized gas and the fluid. The fluid introduced into the accumulator is stored at a pressure at least as high as the precharge pressure and is available for doing hydraulic work. Such prior art accumulators include: a bladder type with a bladder to separate the gas from the fluid; a piston type having a piston sliding up and down a seal bore to separate the fluid from the gas; and a float type with a float providing a partial separation of the fluid from the gas and for closing a valve when the float approaches the bottom to prevent the escape of gas .

In one particular example, a prior art system has accumulators that provide typical 3000 psi (207 bars)

working fluid to surface equipment has a 5000 psi (345 bars) working pressure and contain fluid which raises the precharge pressure from 3000 psi (207 bars) to 5000 psi

(345 bars) The efficiency of accumulators is decreased in deepwater; for example, 1000 feet (305m) of seawater the ambient pressure is approximately 465 psi (32 bars) and, for an accumulator to provide a 3000 psi (207 bars) differential at 1000 ft. (305m) depth, it is precharged to 3000 psi (207 bars) plus 465 psi (32 bars) , or 3465 psi (239 bars) At slightly over 4000 ft. (1220m) water depth, the ambient pressure is almost 2000 psi (138 bars) , so the precharge is required to be 3000 psi (207 bars) plus 2000 psi (138 bars) , or 5000 psi (345 bars) , i.e., the precharge equals the working pressure of the accumulator. Any fluid introduced for storage causes the pressure to exceed the working pressure, rendering the accumulator non functional .

In the deepwater use of accumulators the ambient temperature can decrease to about 35 degrees F. (275K) For an accumulator precharged to 5000 psi (345 bars) at a surface temperature of 80 degrees F. (300K) , about 416 psi (29 bars) precharge is lost simply because the temperature was reduced to 35 degrees F (275K) . The rapid discharge of fluids from accumulators and the associated rapid expansion of the pressurizing gas causes a natural cooling of the gas so that an accumulator is quickly reduced in pressure from, for example, 5000 psi (345 bars) to 3000 psi (207 bars) without heat coming into the accumulator (adiabatic) , experiences a pressure drop to 2012 psi (139 bars) .

U.S. Patents 7,108,006; 6,202,753; 4,777,800; 4,649,704; and 3,677,001 are illustrative of various prior art subsea power fluid systems and are mentioned

here not by way of limitation nor as exhaustive of the available prior art; and all said patents are incorporated fully herein for all purposes .

There has long been a need, recognized by the present inventor, for an effective method and system for preventing exhausted power fluids from polluting a body of water.

According to the present invention, there is provided a method for recovering fluid used in power ing an underwater apparatus submerged in deep water, the method comprising the steps of flowing fluid to the underwater apparatus to power the underwater apparatus characterised in that the method further comprises the step of flowing recovered fluid from the underwater apparatus to a fluid recovery apparatus submerged in deep water to move the fluid to the surface of the deepwater. Preferably, the recovered fluid is moved to above the surface . Deep water may be of any depth in which offshore oil well drilling is carried out. Deep water can be as little as many metres to ultra deep water which may be several thousand metres deep. Powering can include activating an underwater apparatus where there is enough fluid used to be worth recovering same .

Advantageously, the fluid recovery apparatus comprises a pump apparatus for selectively pumping recovered fluid to the surface of the water, the pump apparatus comprising at least one pump, and a valve apparatus, the valve apparatus controlling the at least one pump, and pumping recovered fluid to above a surface of the water with the at least one pump. Preferably, the underwater apparatus is at least in part powered by hydraulic actuation; the fluid is a liquid; the fluid is substantially incompressible; the fluid is a hydraulic

fluid. Advantageously, the recovered fluid is a liquid; the fluid is substantially incompressible; the fluid is a hydraulic fluid.

Preferably, the at least one pump comprises a first pump and a second pump, the method further comprising the step of the valve apparatus controlling the first pump and the second pump to allow only one of the first and second pumps to pump recovered power fluid to the surface of the deep water. Preferably, the at least one pump may comprise three, four, five, six or more pumps. In certain embodiments, two (or more) pumps are used to pump exhausted power fluid to the surface. The pumps' action is timed so that, when one pump is pumping fluid, the other pump is in the process of receiving fluid to be pumped. Thus fluid can be continuously pumped without the downtime associated with a single pump system's fluid reception by the single pump. In certain aspects, using more than one pump results in a reduced requirement for reserve capacity and/or provides a relatively constant flow rate of fluid to the surface. In certain aspects, pilot signals are provided from each pump to a valve assembly of the other pump so that only one pump at a time is pumping fluid to the surface.

Advantageously, the pump apparatus comprises pilot signal apparatus for supplying a pilot signal to the at first pump and to the second pump signalling when one of the first pump and the second pump is pumping recovered power fluid to the surface of the deep water so that the pump receiving the pilot signal is then prevented from pumping recovered power fluid to the surface of the deep water, the method further comprising the steps of sending the pilot signal to one of the first pump or the second pump and inhibiting the pump receiving the pilot signal

from pumping recovered power fluid to the surface of the deep water.

Preferably, the method further comprises the step of continuously pumping recovered power fluid to the surface of the deep water by alternately using the first pump the second pump.

Preferably, the first and second pumps each comprise a piston movably disposed in a piston housing, the piston and piston housing defining a piston chamber, the piston housing having an input flow channel through the piston housing, the method further comprising the step of allowing recovered fluid to flow therethrough into the piston chamber. Preferably, the recovered fluid fills the piston chamber completely before the piston is activated to pump the recovered fluid to the surface of the water. Preferably, the input is provided with a non-return valve to inhibit recovered fluid from exiting through the input flow channel .

Advantageously, the first and second pumps each comprise an output flow channel in the piston housing, the method further comprising the step of allowing recovered fluid to flow therethorugh to the surface of the deepwater. Preferably, the output flow channel is provided with a shuttle valve to selectively allow recovered fluid to be pumped from one of the chamber of the respective first or second pump.

Preferably, the first and second pumps each comprises a maintenance flow channel therethrough in fluid communication with a chamber for providing fluid under pressure from a surface fluid apparatus into the piston housing above the piston, the method further comprising the steps of introducing fluid under pressure into the piston chamber through the maintenance flow

channel to maintain a pressure within the piston housing less than a pressure of fluid exterior to the at least one pump. Advantageously, the maintenance flow channel is connected to a compensation piston. Preferably, the compensation piston comprises a tube connected to the piston housing and a recess in the piston, the method comprising the step of allowing the tube to move within the recess in the piston when the piston strokes within the piston housing. Preferably, there is a gap between the tube and the recess through which fluid can flow. Advantageously, a seal is provided between the tube and the recess in the piston, preferably, to inhibit ingress of high pressure (such as 3000 psi) fluid pumped from the surface, into the piston chamber. In certain aspects , in such a apparatus a negative internal pressure is maintained on a pump apparatus (with a pump or pumps) , for example with a line leading to the pump system maintained at a pressure lower than a pressure in an input line to a system providing reserve capacity so that the reserve capacity system remains evacuated of all power fluid and filled or substantially filled with water (for example seawater) exterior to the system. This insures that, in certain aspects, all power fluid to be pumped to the surface is indeed pumped to the surface. Optionally this is achievable using a switch that turns the pump(s) off when the reserve capacity system is empty of pushing fluid. In certain aspects, in system in accordance with the present invention, the pressure at which power fluid is supplied to an underwater device or apparatus is equalized to the pressure of the water on the underwater device or apparatus . Due to the difference in density between the power fluid and, for example, seawater at depth, a

density pressure differential occurs. Without pressure equalization, seawater could flow into the system, for example via check valves , resulting in the pumping of seawater with power fluid to the surface. In one aspect a relief valve in line from the pump system to the surface provides for the equalization of pressure due to the density differential. Such systems with pumps with pistons having an internal compensation apparatus to facilitate piston movement and/or to assist in maintaining a negative pressure in a piston housing

Preferably, the force of the fluid under pressure flows in through the maintenance flow channel to facilitate downward movement of the piston and thus filling of the piston chamber with recovered fluid. Advantageously, the first and second pumps each further comprise a piston rod arranged on an opposing side of the piston to the piston chamber and a further chamber about or within the piston rod, the method further comprising the step of introducing fluid into the further chamber to pump the recovered fluid from the piston chamber .

Preferably, each of the first pump and the second pump further comprise an associated mechanically- activated valve, the method further comprising the step of moving the piston of first pump or the piston of the second pump to contact a corresponding mechanically- actuated valve to close the mechanically-activated valve allowing the piston to move down so that a chamber in which the piston is movable can fill with recovered fluid to be pumped to the surface of the deep water.

Advantageously, each piston of the first pump and the second pump has an activation member connected thereto for contacting the corresponding mechanically-

activated valve and the activation member is spring loaded with a spring device to provide snap action for facilitating contact with and actuation of the mechanically-activated valve, the method further comprising the step of facilitating actuation of the activation member to actuate the corresponding mechanically-activated valves .

Preferably, each of the first pump and the second pump commences pumping of recovered power fluid to the fluid container only upon complete filling of it corresponding pump chamber with recovered fluid.

Advantageously, a definite amount of fluid powers the underwater apparatus , the method further comprising the step of automatically shutting off the pump apparatus when the definite amount of fluid has been pumped by the pump apparatus to the fluid container. In certain aspects, in system in accordance with the present invention the pump or pumps are automatically shut off once all the exhausted fluid has been pumped to the surface. Such systems with automatic pump shut-off.

Preferably, the fluid recovery apparatus further comprises a reserve capacity apparatus in the deep water, the method further comprising the step of allowing the reserve tank to fill with recovered fluid. Pr eferably, the reserve capacity apparatus acts as buffer storage between the output of the underwater apparatus and the at least one pump. Advantageously, the reserve capacity apparatus comprises a tank having an expandable membrane therein, with ambient water on one side of the membrane. In certain aspects, such an apparatus has reserve capacity apparatus for receiving the exhausted power fluid so that a pump (or pumps) pumping the fluid is not overloaded or rendered inefficient. In certain

embodiments of the present invention, a pump or pumps (and, if present, a reserve capacity apparatus) are controlled by the pressure of exhausted power fluid and require no control or intervention by either subsea controls or devices or by surface controls or devices . This results in a simpler, less complex system. Upon complete evacuation of an amount of exhausted power fluid, the pump(s) stop. In certain aspects by employing a reserve capacity apparatus in systems in accordance with the present invention, the flow in a line or lines in which exhausted power fluid is pumped to the surface is minimized, reducing required discharge pressures and, thus reducing the power required to pump fluid to the surface. This reduced power requirement translates to a lower flow required on a pump system piston, i.e., the piston's bottom area can be reduced in size while the system still effectively pumps the fluid to the surface.

Preferably, the fluid recovery apparatus further comprises check valves between the underwater apparatus and the fluid recovery apparatus, the check valves open to ambient deep water. Preferably, the check valves inhibit ingress of ambient water into the recovered fluid. In certain aspects, a pumping system useful in embodiments of the present invention has both high pressure and low pressure protection, for example one or more relief valves (for example "cracking" check valves) so that the line leading to a pump system is not at too high a pressure, i.e., to protect a pump system enclosure or housing from undesirable pressures (either too high or too low) .

Preferably, the fluid is a hydraulic fluid and most preferably, the recovered fluid is a hydraulic fluid.

Preferably, the recovered fluid is re-used to power

the underwater apparatus. Preferably, the recovered fluid is pumped into a fluid container above the surface of the water .

The present invention, in certain aspects, discloses a fluid recovery system in which power fluid used by and exhausted from a subsea apparatus, for example, but not limited to a blowout preventer operator, is recovered and pumped from beneath the water back to the surface.

Such Apparatus with two pumps in which only one pump at time is allowed to pump fluid to the surface. Such systems with power-fluid/water pressure equalization.

For a better understanding of the present invention, reference will now be made, by way of example, to the accompanying drawings , in which :

Figure 1 is a schematic view of a system in accordance with the present invention comprising a power fluid system and a fluid recovery system;

Figure 2A is a perspective view of an apparatus in accordance with the present invention;

Figure 2B is a rear perspective view of the apparatus shown in Figure 2A;

Figure 2C is a top view of the apparatus shown in Figure 2A;

Figure 3A is a perspective view of part of the apparatus shown in Figure 2A; Figure 3B is a side view of the part shown in Figure 3A;

Figure 4A is a cross-section view of the part shown in Figure 3A;

Figure 4B is an enlargement of a portion of the view of Figure 4A;

Figure 4C is an enlargement of a portion of the view of Figure 4A;

Figure 4D is an enlargement of a portion of the view of Figure 4A; Figure 5 is a cutaway perspective view of a valve used in an apparatus in accordance with the present invention ;

Figure 6A is a perspective view of a reserve capacity apparatus used in the apparatus in accordance with the present invention;

Figure 6B is a cross-section view of the reserve capacity apparatus shown in Figure 6A;

Figure 7 illustrates schematically a system in

accordance with the present invention for equalizing pressure between power fluid and seawater.

Figure 8 is a schematic view of a system in accordance with the present invention; Figure 8A is an enlargement in cross-section of part of a pump of an apparatus in accordance with the present invention, for example, a pump shown in Figure 4A, 8, or 9A;

Figure 8B is a cross-section view of a compensator piston of the pump shown in Figure 8A;

Figure 9A illustrates schematically apparatus in a step in a method in accordance with the present invention ;

Figure 9B illustrates apparatus used in the step shown in Figure 9A;

Figure 9C is an enlargement of a portion of the view of Figure 9B;

Figure 9D is an enlargement of a portion of the view of Figure 9B; Figure 9E is an enlargement of a portion of the view of Figure 9B;

Figure 9F is an enlargement of a portion of the view of Figure 9B;

Figure 1OA illustrates schematically apparatus in a step in a method in accordance with the present invention ;

Figure 1OB illustrates apparatus used in a step shown in Figure 1OA;

Figure 1OC is an enlargement of a portion of the view of Figure 1OB;

Figure 1OD is an enlargement of a portion of the view of Figure 1OB;

Figure 1OE is an enlargement of a portion of the

view of Figure 1OB;

Figure 1OF is an enlargement of a portion of the view of Figure 1OB;

Figure HA illustrates schematically apparatus in a step in a method in accordance with the present invention;

Figure HB illustrates apparatus used in a step shown in Figure HA;

Figure HC is an enlargement of a portion of the view of Figure HB;

Figure HD is an enlargement of a portion of the view of Figure HB;

Figure HE is an enlargement of a portion of the view of Figure HB; Figure HF is an enlargement of a portion of the view of Figure HB;

Figure 12A illustrates schematically a step in a method in accordance with the present invention;

Figure 12B illustrates apparatus used in a step shown in Figure 12A;

Figure 12C is an enlargement of a portion of the view of Figure 12B;

Figure 12D is an enlargement of a portion of the view of Figure 12B; Figure 12E is an enlargement of a portion of the view of Figure 12B; and

Figure 12F is an enlargement of a portion of the view of Figure 12B.

Figure 1 shows a system S in accordance with the present invention in which power fluid from a hydraulic power unit is provided to a subsea apparatus , such as , but not limited to, a blowout preventer operator ("BOP

OPERATOR") . Hydraulic power fluid is pumped from a

reservoir ("TANK") by a pump ("PUMP") through a check valve ("CHECK VALVE") to a bank of accumulator containers at the surface ("ACCUMULATOR SYSTEM") . This fluid is then provided beneath a water level L through a check valve ("CHECK VALVE"), then optionally, to an accumulator system, for example, with one or more depth compensated containers or bottles ("ACCUMULATOR SYSTEM") (for example a conventional bladder or piston accumulator or with depth compensated bottles as disclosed in U.S. Application Ser. No. 11/594,012 filed 11/07/2006 and co- owned with the present invention) . A control valve ("DIRECTIONAL CONTROL VALVE") selectively provides the power fluid from the depth compensated accumulator containers to operate a subsea device or apparatus, for example the BOP operator shown. Fluid exhausted from the BOP operator either flows into the water ("VENT") or to a fluid recovery system ("FLUID RECOVERY SYSTEM") in accordance with the present invention (any disclosed herein) with any pump or pumps disclosed herein. The power fluid is pumped to the surface, for example to a fluid reservoir ("TANK") or to other containers and/or conditioning systems. The accumulator system may be any suitable accumulator system including, for example, those disclosed in U.S. Application Ser. No. 11/594,012 filed on 11/07/2006.

Figures 2A to 2C show a fluid recovery system 10 in accordance with the present invention which has two reserve bottles 20 and 30 secured to a base, enclosure (or pod) 12 in which valves, etc. are located and to which are secured structural members 22 and 32 (which can serve as guide tubes for guide wires that allow the system to be retrieved) . Two pump systems 40 and 50, secured on the base 12 , receive power fluid from the

reserve bottles 20 and 30. The fluid (for example, but not limited to, hydraulic fluid, for example, but not limited to, from a device powered by the power fluid, for example, but not limited to, an operator for a blowout preventer) is conveyed to the reserve bottles 20 and 30 through a line A (see also line a, Figure 8) . The system 10 has check valves X and Y (as in Figure 8) .

A typical hydraulic manifold box 14 houses hydraulic controls. Power fluid is pumped from the pump systems 40 and 50 to the surface in a return line B (see also line b, Figure 8) . Via a line C, (see also line C, Fig 8) a constant flow of fluid under pressure is pumped from a surface system to the pump systems so that a negative internal pressure is maintained. A suction/discharge manifold 80 houses the check valves X and Y and check valves M and N for the lines A and B (these check valves shown in dotted line in Fig 2C); for example like the valves P and Q, Figure 8; the valve P which may be a check valve or as shown) . Each pump system 40, 50 has a corresponding valve system 41, 51 (respectively) (see, for example the valves Vl, V2 , Figure 9A and the valve system of Figure 5) .

Figure 6A and 6B show one possible embodiment of the reserve bottle 20 (the bottle 30 is like the bottle 20) . The bottle 20 has an outer housing 22 in which is mounted an inflatable bladder 24. Water exterior to the bottle 20 can enter the bladder 24 through a hole 26 in the housing 22. Power fluid exhausted from a subsea apparatus or device enters the housing 22 through a hole 28. As power fluid enters the housing 22 at a pressure greater than the pressure of the water exterior to the housing, water is exhausted from the bladder 24 out from the housing 22.

Alternatively, the bladder 24 is used to contain exhausted power fluid and water is introduced around the bladder 24. In certain particular embodiments, each bottle 20 and 30 can contain about 300 litres (80 gallons) of power fluid.

As shown in Figures 4A to 4D, the pump systems 40, 50 have valve systems 41 and 51 (respectively) including main bodies 42, 52 with valves Vl, V2 (body 42) and valves V3, V4 (body 52) . The valve Vl includes a mechanical actuator 43 and the valve V4 includes a mechanical actuator 53. As described in detail below, movement of pistons 44, 54 (respectively) results in movement of actuators 45, 55 (respectively) which in turn results in movement of the mechanical actuators 43, 53 during a sequence of operation of the pump systems 40, 50. Optional springs 46 56 provide a "snap open" or "snap close" feature for the valves Vl, V4 (respectively) . As shown in Figure 9A, for example, the lines A, B, C (as in Figure 2A and Figure 8) are in communication with the pump systems 40, 50. When the piston 54 is pumped up, a pilot signal is sent from the valve system 51 (from the valve V4) to the valve system 41 (to the valve V2) which vents a pressure chamber CR around a main piston 44 (or vice-versa regarding the chamber CR around the piston 54 when the main piston 44 is pumped up) so that the piston 44 is not pumped up, i.e., so that both pistons do not pump fluid to the surface simultaneously. When a valve system's mechanical activator 45 or 55 is moved up (for example when a piston 44 or 54 pulls up on an activator 45 or 55) , a line is opened by action of a valve Vl or V4 and a line is closed so that a chamber CR around a main piston 44 or 54 is vented in the line B to tank. When one of the activators

45 or 55 pushes down on an activator 43 or 53, this chamber CR (one chamber CR around each of the pistons 44, 54) fills with pressurized fluid pressurizing the chamber to push that piston up, pushing the fluid on the top that piston out of the pump into the line B back to the surface .

As shown in Figure 5 the valve V2 is hydraulically actuated for closing and actuated open by the force of springs 47, 48. As shown in Figure 5 the valve V2 is open by pilot pressure (for example from the outlet of the valve V4 as seen in Figure 12A) . The valve Vl is mechanically actuated via the mechanical actuator 43

(both to open and to close the valve Vl) . As shown in

Figure 5 the valve Vl is open. The other valve systems herein, for example the valve system 51 and those of Figures 9A to 12A, may be like the valve system 41 shown in Figure 5.

Figure 7 illustrates the equalization of the pressure of power fluid in a line LN from a fluid recovery system FRS in accordance with the present invention with the pressure of seawater at depth (for example, but not limited to, at a depth of 3,000m (10,000 feet) ) . The power fluid (for example to power an apparatus 23) in this instance is slightly less dense than is the seawater, resulting in a pressure differential of about 8 bars (120 psi) . So that seawater is not sucked into the Line LN via a "Low Pressure Protect" check valve W and pumped to the surface, a relief valve VL is placed in the line LN between a reserve system 20 (with a bottle or bottles 21, if any) and a surface reservoir ("Return tank"). For example, the relief valve VL is set at 8 bars (120 psi) (the pressure differential) and, if the pressure in the line

LN drops below the setting of the valve VL (for example 8 bars (120 psi) ) the relief valve VL closes the line LN to flow (for example until more power fluid is to be pumped to the surface by the system FRS in a line LE leading to the system FRS) . The system FRS has a pump system PS (or pump systems) (for example like any pump system in accordance with the present invention, for example like the pump systems 40, 50 or those shown in Figures 8A, 9A to 12A) . A check valve V (like the check valve X, above) provides high pressure protection. Check valves G and H (like the check valves P and Q, above) provide a check valve function on either side of a line LE to the system FRS.

Figure 8A illustrates part of the interior structure of a pump system 40 (and of a pump system 50; and of the pumps in Figures 9A to 12A) . A fluid recovery system with such a pump system ("PUMP SYSTEM") is shown schematically in Figure 8. An embodiment of the system 10 ("POWER FLUID RECOVERY SYSTEM") has a reserve capacity apparatus (as may any embodiment of the present invention) which equalizes pressure between the exterior water (for example sea water outside) and the hydraulic fluid returns, for example, but not limited to (as is the case for any embodiment herein) bottles like the bottles 20, 30, Figure 2A ("RESERVE CAPACITY BOTTLES") which recover hydraulic fluid from a blowout preventer operator ("BOP OPERATOR"), flow to which is controlled by a control valve ("CONTROL VALVE") which itself is controlled by a drive control ("VALVE DRIVE CONTROL") . The pump system ("PUMP SYSTEM") (for example like the systems 40, 50) with a valve system VS (like the systems 41, 51) receives fluid from the blowout preventer operator (in a line A) and pumps it in a line B back to a

surface reservoir ("TANK"). An optional relief valve

("RELIEF VALVE") provides for equalization of pressure due to the density differential discussed above. The pump system may have any desired number of pumps (like those of the systems 40, 50) .

Check valves as indicated in the various lines provide a check valve function. The two check valves labeled X and Y provide high pressure protection (valve X) and low pressure protection (valve Y) (for example like the valves V and W, Figure 7) . Accumulator containers at the surface ("SURFACE BOTTLES") serve as containers for fluid pumped from the tank; and optional subsea containers ("ACCUMULATOR SYSTEM") provide an accumulator function at the level of the Power Fluid Recovery System.

As shown in Figure 8A, via the line C, a constant flow of fluid under pressure is provided to the Pump System's pump which maintains the negative internal pressure in the pump as discussed above. Via the line A (like line A, Figure 2A) , the pump receives fluid exhausted from the BOP operator and, via the line B (like line B, Figure 2A) , the pump pumps the fluid back to the surface. The piston 44 movably disposed in the housing 44h is movable (downwardly as shown in Figure 8A) in response to exhausted power fluid being introduced into the housing 44h and the piston 44 is movable (upwardly as shown in Figure 8A) to pump the fluid into the line B and to the surface. In such movement, the piston 44 overcomes any friction drag due to a seal 45 that seals the piston/housing interface. As shown in Figures 9A to 12A, the piston 44 is movable to contact and move a valve actuator of a valve system 41 or 51.

The piston 44 has a central member 42a with a hollow

channel 42b therein. Releasably secured to the housing 44h is a compensator piston CP (shown in Figure 8B) with a hollow channel 49a therethrough. Fluid under pressure flowing through the line C flows into, down, and through the compensator piston CP and up into the hollow channel or annulus 42b. The pressure of this fluid pushes against the piston 44 pushing the piston 44 away from the top inner surface of the housing 44h. The pressure in the line A is maintained less than the pressure of water exterior to the housing 44h. The force applied to the main piston 44 through the compensator piston CP assists the main piston 44 in overcoming friction drag due to the seal 45. The compensator piston CP is connected to the housing 44h, for example with a threaded coupling 49b. A snap ring 48a holds a gland 48b in place around the compensator piston CP. The gland 48b includes a seal 48c which seals the gland/housing interface. A seal 48d on the interior of the gland seals the gland/compensator- piston interface. In certain aspects, several interchangeable compensator pistons are provided with different effective diameters permitting fine tuning of the suction characteristics of the pump ("fine tuning" - referring to the ability to select the negative pressure level desired by selecting a particular compensator piston (so the line

A is maintained at a negative pressure so the reserve capacity bottles remain fully evacuated of all power fluid and the bladders therein remain full of water

(water from exterior to the bottles) until the BOP operator functions and power fluid used to operate the BOP operator which is exhausted from the BOP operator is to be pumped to the surface.

Figure 8B shows the compensator piston CP. The

compensator piston CP is secured to the housing 44h with the threaded coupling 49b. Since the piston CP is fixed to the housing 44h, fluid entering in the line C and flows down through the piston CP and up into the space around the piston CP, resulting in a force pushing the piston 44 downward. Thus, as this piston tries to draw fluid in the pump via the check valve Q, a negative pressure is maintained in the return line A and movement of the piston 44 is facilitated. Figures 9A to 12F illustrate steps in methods in accordance with the present invention using a fluid recovery system in accordance with the present invention which has two pumps (for example, like the pumps of the systems of Figures 2A, 3A, 8A) . One pump is a "Left Pump" (with a "Left Piston") and one pump is a "Right Pump" (with a "Right Piston") (see Figure 9A) .

The line labelled "FLUID RETURNS BACK TO SURFACE" is the line through which the pumps pump power fluid back to the surface and corresponds to line B, Figure 8 and Figure 8A. The line labelled "POD RETURNS" is the line through which the pumps receive exhausted fluid, corresponding to line A, Figure 8 and Figure 8A. In the line labelled "3000 PSI PRESSURE" fluid is supplied from the accumulator system, corresponding to the line C, Figure 8A (of course the pressure in this line is not limited to 3000 psi (approximately 200 bars) and may, in accordance with the present invention, be any suitable pressure) .

As shown in Figures 9A, 1OA, HA and 12A, systems in accordance with the present invention may have a series of valves Vl, V2 , V3, V4 (for example within a body like the body 12 , Figure 2A) for controlling fluid flow to and from the pumps to effect efficient and continuous pumping

of fluid from a powered downhole apparatus or device to the surface . In one aspect the valves Vl to V4 are as indicated in Figures 4A to 4D . Valves Vl and V4 are mechanically operated by movement of the Left Piston and Right Piston moving corresponding mechanical valve actuators Al and A2 (like the mechanical actuators 43, 53, Figure 4A) .

Figure 9A illustrates a first step in the method of pumping power fluid to the surface, wherein fluid pressure from the line C pushing the Left Piston up to pump power fluid (previously supplied through line A) into the line B from above the Left Piston. The Left Piston has previously moved down, pushing the valve actuator Al down to activate the valve Vl to allow fluid under pressure in the line C to enter below the Left Piston.

Also as shown in Figure 9A, as the Left Piston is pumping fluid into the line B, the housing of the Right Piston is beginning to receive exhausted power fluid via the line A (through the check valve Q) which is flowing into the space above the Right Piston for eventual pumping to the surface. The Right Piston has previously moved the mechanical valve actuator A2 to operate the valve V4 to close the valve V4 (so that no further power fluid enters below the Right Piston and the fluid from beneath the Right Piston is allowed to vent to the line A) . In Figure 9A, valve V2 is opened by the spring force of its spring so that fluid under pressure is allowed to flow to the valve Vl from the line C. Also, as shown in Figure 9A, fluid under pressure in the line C flows to the compensator piston Cl (like the compensator piston CP, Figure 8B) of the Left Pump and to the compensator piston C2 (like the compensator piston CP, Figure 8B) of

the Right Pump. Valve V3 closes off flow from the line C to the Right Pump (thereby venting fluid to line A from the bottom of the Right Piston) . The dotted line in Figure 9A (and in subsequent figures) indicates a pilot line for providing a pilot signal to the valve V3 to insure that fluid from the bottom of the Right Piston is vented to the line A regardless of the position of the valve V4 (so that in certain positions, for example as in Figure 9A, the Right Piston cannot pump exhausted power fluid to the surface; i.e., so that only one pump pumps exhausted power fluid to the surface at a time) . "Mech SPM" refers to a mechanically actuated valve (for example Vl, V4) and "Hyd SPM" refers to a hydraulically actuated valve (for example V2 , V3) . "Work Port" refers to a port from the chambers CR.

As shown in Figure 1OA illustrates a second step in the method of pumping power fluid to the surface, wherein the Left Piston is in the process of pumping fluid to the surface and the Right Piston is in the process of moving the actuator A2 down to actuate the valve V4 ("firing") to stop further power fluid "POD RETURNS" from flowing to the Right Piston. The valve V2 is still permitting fluid under pressure to flow beneath the Left Piston as it continues to pump fluid to the surface and the valve V3 is receiving the pilot signal which keeps the valve V3 shifted to a closed position (as in Figure 9A) while fluid from the line C is provided to the bottom of the Left Piston. As shown in Figures 9A and 1OA, no pressure from the line C is applied beneath the Right Piston so the Right Piston cannot go up when the Left Piston is going up. (Thus only one pump pumps power fluid to the surface at a time) .

Figure HA illustrates a third step in the method of

pumping power fluid to the surface, wherein the Left Piston approaching the upper limit of its travel, still pumping fluid into the line B, and almost at the point of pulling the mechanical actuator Al up to the required extent to activate the valve Vl to shut off the flow of fluid under pressure in the line C to the space beneath the Left Piston. No exhausted fluid is flowing into the space above the Left Piston. The space above the Right Piston is filled with exhausted power fluid and the Right Piston as shown is static. The reserve capacity bottles

("Reserve Bottles") are in the process of receiving more power fluid exhausted from the power-fluid-operated downhole device (for example a BOP operator) . The space above the Left Piston will be substantially evacuated before any more exhausted power fluid is introduced above the Left Piston.

As shown in Figure HA, the valve V2 is in the same position as in Figures 9A and 1OA allowing fluid from the line C to go to the valve Vl. The Right Piston, shown as static, is ready to pump fluid above it to the surface via the line B; and the Left Piston is in the process of finishing the pumping of fluid into the line B and of moving ("firing") the valve Vl.

Figure 12A illustrates a fourth step in the method of pumping power fluid to the surface, wherein, exhausted power fluid is flowing into the space above the Left Piston while the Right Piston is moving up and pumping exhausted power fluid to the surface in line B. The valve Vl has been activated to permit fluid from beneath the Left Piston allowing the Left Piston to move down so that the space above the Left Piston can receive exhausted power fluid to flow to the line A. The valve V2 is insuring that fluid from the bottom of the Left

Piston can flow to the line A. The valve V4 has been activated to permit fluid under pressure from line C to flow into the space beneath the Right Piston to move it up to pump exhausted power fluid above the Right Piston to the surface in the line B. The pilot signal from the valve Vl is vented to the line A, hence the valve V3 is vented allowing the spring of the valve V3 to shift the valve V3 open allowing fluid through the line C to go to the valve V4 and then to the space below the Right Piston.

In all of the steps, fluid under pressure from the line C is constantly applied to the compensator pistons Cl and C2 to assist in moving the Left and Right Pistons down when the spaces above them are receiving exhausted power fluid.

The present invention, therefore, provides in at least certain embodiments, a method for recovering power fluid used to power a device under water and for pumping the recovered power fluid to a fluid container above a surface of the water, the method including: flowing fluid from a subsurface apparatus to a subsurface recovery system, the fluid initially provided to the subsurface apparatus to power the subsurface apparatus ; and the subsurface recovery system including a pump system for selectively pumping recovered power fluid to a fluid container above a surface of the water; the pump system including at least one pump, and a valve system, the valve system controlling the at least one pump, and pumping recovered power fluid to the fluid container with the at least one pump. In such a method the at least one pump may have a main piston movably disposed in a main piston chamber in a main piston housing, the main piston housing having a flow channel therethrough in fluid

communication with the main piston chamber for providing fluid under pressure from a surface fluid system into the main piston housing above the main piston, the method further including introducing fluid under pressure into the main piston chamber through the flow channel to maintain a pressure within the main piston housing less than a pressure of fluid exterior to the at least one pump.

The present invention, therefore, provides in at least certain embodiments, a method for recovering power fluid used to power a device under water and for pumping the recovered power fluid to a fluid container above a surface of the water, the method including: flowing fluid from a subsurface apparatus to a subsurface recovery system, the fluid initially provided to the subsurface apparatus to power the subsurface apparatus; and the subsurface recovery system including a pump system for selectively pumping recovered power fluid to a fluid container above a surface of the water, the pump system including a first pump, a second pump, and a valve system, the valve system controlling the first pump and the second pump to allow only one pump of the first pump and the second pump to pump recovered power fluid to the fluid container above the surface of the water, the method further including pumping recovered power fluid to the fluid container with only one pump at a time of the first pump and the second pump. Such a method may have one or some, in any possible combination, of the following: wherein the pump system includes pilot signal apparatus for supplying a pilot signal to the first pump and to the second pump signalling when one of the first pump and the second pump is pumping recovered power fluid to the fluid container so that the pump receiving said

pilot signal is then prevented from pumping recovered power fluid to the fluid container, the method further including sending said pilot signal to one of the first pump or the second pump and then preventing said pump receiving said pilot signal from pumping recovered power fluid to the fluid container; continuously pumping recovered power fluid to the fluid container with the pump system using alternately the first pump then the second pump; wherein a definite amount of power fluid powers the subsurface apparatus, the method further including automatically shutting off the pump system when the definite amount of power fluid has been pumped by the pump system to the fluid container; wherein the recovered power fluid is re-used to power the subsurface apparatus; wherein each of the first pump and the second pump has a main piston and an associated mechanically-activated valve actuatable by contact by a corresponding main piston, the method further including moving a main piston of the first pump or of the second pump to contact a corresponding mechanically-actuated valve to close said valve allowing said main piston to move down so that a chamber in which said piston is movable can fill with recovered power fluid to be pumped to the fluid container; wherein each main piston of the first pump and the second pump has an activation member connected thereto for contacting a corresponding mechanically- activated valve and said activation member is spring loaded with a spring device to provide snap action for facilitating contact with and actuation of the mechanically-activated valve, the method further including facilitating actuation with said spring device of the mechanically-activated valves ; wherein each pump has a main piston movably disposed in a main piston

chamber in a main piston housing, each main piston housing having a flow channel therethrough in fluid communication with a main piston chamber for providing fluid under pressure from a surface fluid system above a main piston, the method further including introducing fluid under pressure into each main piston chamber through the flow channel to maintain a pressure within each main piston housing less than a pressure of fluid exterior to the pump system; wherein each of the first pump and the second pump has a main piston movably disposed in a main piston chamber in a main piston housing, each main piston having main a piston body with a central hollow member extending down within the main piston body, each of the first pump and the second pump having a compensation member connected to a main piston housing, the compensation member extendable into the central hollow member of the main piston body, the compensation member having a flow channel therethrough from top to bottom, said flow channel in fluid communication with a channel providing fluid under pressure from a surface fluid system, the method further including introducing fluid under pressure into the central hollow member of the main piston body through the flow channel of the compensation member to maintain a pressure within the main piston housing less than a pressure of fluid exterior to the pump; wherein force of said fluid under pressure flowed in the central hollow member of the main piston facilitates downward movement of the main piston, the method further including facilitating downward movement of the main piston with the force of fluid introduced into the central hollow member of the main piston and which flows therefrom into the main piston housing; wherein each of the first pump

and the second pump includes a corresponding pump housing which receives recovered power fluid to be pumped to the surface, the method further including each of the first pump and the second pump commencing pumping recovered power fluid to the fluid container only upon complete filling of it corresponding pump housing with recovered power fluid; and/or while the first pump is pumping recovered power fluid to the fluid container, providing recovered power fluid to the second pump for the second pump, in turn, to pump to the fluid container.

The present invention, therefore, provides in at least certain embodiments, a method for recovering power fluid used to power a device under water and for pumping the recovered power fluid to a fluid container above a surface of the water, the method including: flowing fluid from a subsurface apparatus to a subsurface recovery system, the fluid initially provided to the subsurface apparatus to power the subsurface apparatus; and the subsurface recovery system including a pump system for selectively pumping recovered power fluid to a fluid container above a surface of the water, the pump system including a first pump, a second pump, and a valve system, the valve system controlling the first pump and the second pump to allow only one pump of the first pump and the second pump to pump recovered power fluid to the fluid container above the surface of the water, the method further including pumping recovered power fluid to the fluid container with only one pump at a time of the first pump and the second pump, wherein the pump system includes pilot signal apparatus for supplying a pilot signal to the first pump and to the second pump signalling when one of the first pump and the second pump is pumping recovered power fluid to the fluid container

so that the pump receiving said pilot signal is then prevented from pumping recovered power fluid to the fluid container, the method further including sending said pilot signal to one of the first pump or the second pump and then preventing said pump receiving said pilot signal from pumping recovered power fluid to the fluid container, continuously pumping recovered power fluid to the fluid container with the pump system using alternately the first pump then the second pump, and while the first pump is pumping recovered power fluid to the fluid container, providing recovered power fluid to the second pump for the second pump, in turn, to pump to the fluid container.

The present invention, therefore, provides in at least certain embodiments, a system for recovering power fluid used to power a device under water and for pumping the recovered power fluid to a fluid container above a surface of the water, the system including: subsurface recovery system for receiving power fluid exhausted subsurface from a subsurface apparatus, the power fluid initially provided to the subsurface apparatus to power the subsurface apparatus; a pump system for selectively pumping recovered power fluid to a fluid container above a surface of the water, the pump system including at least one pump for pumping recovered power fluid to the fluid container, a valve system, and the valve system for controlling the at least one pump. Such a system may have one or some, in any possible combination, of the following: wherein the at least one pump is a first pump and a second pump, the valve system for controlling the first pump and the second pump to allow only one pump at a time of the first pump and the second pump to pump recovered power fluid to the fluid container above the

surface of the water; the pump system including pilot signal apparatus for supplying a pilot signal to the first pump and to the second pump signalling when one of the first pump and the second pump is pumping recovered power fluid to the fluid container so that the pump receiving said pilot signal is then prevented from pumping recovered power fluid to the fluid container; the pump system for continuously pumping recovered power fluid to the fluid container; wherein a definite amount of power fluid powers the subsurface apparatus, the system further including the pump system including shut off apparatus for automatically shutting off the pump system when the definite amount of power fluid has been pumped by the pump system to the fluid container; wherein each of the first pump and the second pump has a main piston and an associated mechanically-activated valve actuatable by contact by a corresponding main piston so that moving a main piston of the first pump or of the second pump to contact a corresponding mechanically- activated valve to close said valve allows said main piston to move down so that a chamber in which said piston is movable can fill with recovered power fluid to be pumped to the fluid container; wherein each main piston of the first pump and the second pump has an activation member connected thereto for contacting a corresponding mechanically-activated valve and said activation member is spring loaded with a spring device to provide snap action for facilitating contact with and actuation of the mechanically-activated valve; wherein the at least one pump has a main piston movably disposed in a main piston chamber in a main piston housing, the main piston housing having a flow channel therethrough in fluid communication with the main piston chamber for

providing fluid under pressure from a surface fluid system above the main piston so that introducing fluid under pressure into the main piston chamber through the flow channel maintains a pressure within the main piston housing less than a pressure of fluid exterior to the at least one pump; wherein each of the first pump and the second pump has a main piston movably disposed in a main piston chamber in a main piston housing, each main piston having a main piston body with a central hollow member extending down within the main piston body, each of the first pump and the second pump having a compensation member connected to a main piston housing, the compensation member extendable into the central hollow member of the main piston body, the compensation member having a flow channel therethrough from top to bottom, said flow channel in fluid communication with a channel providing fluid under pressure from a surface fluid system so that introducing fluid under pressure into the central hollow member of the main piston body through the flow channel of the compensation member maintains a pressure within the main piston housing less than a pressure of water exterior to the pump system; wherein force of said fluid under pressure flowed in the central hollow member of the main piston facilitates downward movement of the main piston; wherein each of the first pump and the second pump includes a corresponding pump housing which receives recovered power fluid to be pumped to the surface, each of the first pump and the second pump controlled so that said pump is able to commence pumping recovered power fluid to the fluid container only upon complete filling of a corresponding pump housing with recovered power fluid; and/or fluid provision apparatus for providing recovered power fluid to the

second pump for the second pump while the first pump is pumping recovered power fluid to the fluid container.