Apparatus and method

Abstract

The present invention includes methods and apparatuses to pump fluids from a well bore using a hydraulically actuated reciprocating pump to pump fluids from a well to the surface. In one embodiment the weight of the pumped fluid is utilised to return the piston in one direction and preferably the pressure within the well is utilised to urge the piston in the opposite direction thus reducing the amount of force required to reciprocate the piston and consequently reducing the amount of power required to operate the pump.

Description

RELATED APPLICATIONS

This application is related to and claims priority from U.S. Provisional Application No. 60/567036, filed Apr. 30, 2004 and U.S. Provisional Application No. 60/609538, filed Sep. 13, 2004, the disclosures of which are incorporated herein by reference in their entirety.

FIELD OF THE INVENTION

This invention relates to an apparatus and method to recover fluids from a well and particularly but not exclusively to pump fluids from a gas well where fluid, such as water, hinders the release of the gas. However embodiments of the present invention may also be used to recover oil, particularly in low-producing wells with insufficient natural pressure to produce oil of their own accord.

BACKGROUND OF THE INVENTION

Production of hydrocarbon gas from wells is frequently prevented by the hydrostatic pressure of fluids, water and hydrocarbons which have entered the well bore. To cope with this, fluid is removed from the well using artificial lift methods including but not restricted to electric submergible pumps, progressive cavity pumps and beam-operated pumps.

Because of the tight confines of wellbores, it is often not feasible to deploy certain traditional pumping apparatuses to their subterranean depths. Prior artificial lift systems have employed downhole pumps that are actuated by a reciprocating rod. The rod typically extends to the surface where a motor assembly reciprocates the rod, thereby oscillating the downhole pump and bringing the fluids to the surface. While effective, systems of this type usually require the permanent installation of a motor assembly (one having structural support) and the manufacture of a long lift rod to extend down the hole to the subterranean pump. Therefore these systems are costly and require considerable power supply facilities for their operation, making them uneconomical for wells having low levels of production.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided a hydraulically powered pump, adapted to be placed in a well and pump fluids from the well to the surface.

Preferably the pump is a reciprocating pump.

Preferably the pump comprises a reciprocating piston and a cylinder, the cylinder having a bore, wherein the piston is adapted to move within at least a portion of the bore of the cylinder.

Preferably the pump is adapted to allow fluid within the well to bias the piston in a first direction.

More preferably the pump is adapted to allow pumped fluid within the well to bias the piston in the first direction.

Preferably the piston is biased towards an upper direction. More preferably the pumped fluid biases the piston towards the upper direction.

Preferably the pump is adapted to allow fluid in a separate part of the well to urge the piston in a second direction. Preferably the second direction is opposite the first direction.

Preferably the piston is urged by the well bore pressure below the pump in the second direction. Preferably the second direction is a lower direction.

‘Upper’ and ‘lower’ above refer to the general orientation of the pump in use.

Preferably a hydraulic chamber is provided which, when pressurised, is adapted to urge the piston in the second direction, the second direction being the opposite direction to the first direction.

The hydraulic chamber may comprise, for example, an annular space and a conduit leading to the annular space.

Preferably a portion of the bore of the cylinder is shaped to receive well bore fluids.

Preferably the cylinder comprises a first valve to allow or prevent fluid communication between the well and the bore of the cylinder.

Preferably the piston has a central bore. Preferably a second valve is provided between the central bore of the piston and the cylinder in order to allow or prevent fluid communication between the central bore of the piston and the bore of the cylinder.

Preferably the first and second valves are ball and seat type valves.

Preferably the portion of the cylinder which can communicate with the bore of the piston via the second valve is the same portion of the cylinder which can communicate with the well via the first valve.

Preferably the pump comprises a resilient seal adapted to seal the pump within a tube, such as a portion of production tubing.

Preferably a second piston is adapted to compress the resilient seal in order to form a seal between the pump and the tube. Preferably retraction of the second piston causes the seal to decompress and, in use, disengage from the tube.

Preferably the second piston is adapted to move following pressurisation of a second hydraulic chamber.

The second hydraulic chamber may comprise, for example, an annular space and a conduit leading to the annular space. Preferably a third valve is provided between the second hydraulic chamber and the first hydraulic chamber.

Preferably the third valve is adapted to allow hydraulic fluid to flow from the first hydraulic chamber to the second hydraulic chamber when a certain pressure level is reached and preferably resist flow of hydraulic fluid from the second hydraulic chamber to the first hydraulic chamber, preferably regardless of the pressure level.

Preferably a radially extendable grip is also provided on an external face of the pump in order to grip a tube such as the production tubing.

Preferably a breakable seal is provided between a portion of the pump which, in use and once broken, allows fluid communication between the production tubing and the well below the seal of the pump and the production tubing.

Preferably a moveable housing is provided on the outside of the pump and is adapted to engage, and typically move with, the second piston; all with respect to a main body of the pump. Preferably shear pins are provided to resist movement of the housing with respect to the main body of the pump.

Preferably a third hydraulic chamber is provided which, when pressurised, urges the housing away from the main body of the pump. Therefore, in use, sufficient pressurisation of the third hydraulic chamber can cause the shear pins to break and can cause the housing typically along with the second piston to move with respect to the main body of the pump which preferably, in turn, allows the seal to decompress and disengage from the production tubing.

According to a second aspect of the present invention there is provided an apparatus for recovering fluids from a well comprising a hydraulically powered pump and a hydraulic conduit.

Preferably the pump according to the second aspect of the invention is the pump according to the first aspect of the invention.

Preferably the pump is, in use, suspended in a well by the hydraulic conduit.

Preferably the hydraulic conduit is a flexible conduit, that is, it is not rigid enough to transfer a compressing force along its elongate axis.

Preferably the apparatus comprises a system at the surface which is adapted to pressurise the hydraulic conduit and in turn the pump.

Preferably the system comprises a timing device in order to repeatedly pressurise and depressurise the hydraulic conduit in order to cause the piston in the pump to reciprocate.

According to a third aspect of the present invention there is provided a method for removing fluid from a well, the method including the steps of lowering a hydraulically activated pump into a well; the pump being connected to the surface via a hydraulic conduit; and hydraulically activating the pump to pump fluid from the well to the surface.

Preferably the method according to the third aspect of the invention is performed with the pump according to the first aspect of the invention and more preferably the apparatus according to the second aspect of the invention.

Preferably a portion of the pump is secured in production tubing within the well. Preferably the pump is sealed within said production tubing. For certain embodiments of the invention, particularly where the production tubing is above a point where hydrocarbons may enter the well, a portion of the pump is secured in the production tubing whilst the piston and cylinder are spaced away therefrom such that the piston and cylinder are lower than said point where hydrocarbons may enter the well.

Preferably the fluid within the production tubing biases the piston of the pump in a first direction.

Preferably the pressure within the well, outside the production tubing and preferably below said seal between the pump and production tubing, urges the piston of the pump in a second direction. Preferably the first direction is opposite the second direction.

Preferably the hydraulic line is pressurised to a sufficient pressure in order to pass the first valve and urge the second piston down, preferably causing the seal to engage with the production tubing and form a seal therebetween.

Preferably the hydraulic line is activated to move the piston from its biased position to the opposite position.

Preferably the hydraulic line is repeatedly pressurised and depressurised in order to reciprocate the piston.

The hydraulic line may be provided substantially within the production tubing and can be generally concentric with the production tubing.

Optionally further pressure may be applied to the production tubing at the surface in order to increase the pressure therein.

In order to remove the pump, the production tubing pressure may be increased by a surface facility to break the breakable seal, thereby equalising the pressure above and below the seal between the production tubing and the pump.

The pressure in the hydraulic conduit may be increased in order to break the shear pins and move the second piston along with the housing both with respect to the main body of the pump, thereby allowing the seal to decompress and disengage from the production tubing.

The present invention also provides a downhole pump to remove fluids from a wellbore, the pump comprising:

• • a first power transmission line and a second power transmission line;
  • a piston, said piston configured to be displaced within a cylinder from a first upward position to a second downward position;
  • said piston within said housing defining a first fluid chamber and a second fluid chamber;
  • said piston urged into said first downward position when pressure within said first power transmission line is increased;
  • said piston urged into said second upward position when pressure within said second power transmission line is increased; and
  • a fluid return line connected to outlets of said first and second fluid chambers.

Pressure within said first and said second power transmission lines may be controlled by a surface pump.

The pump may be powered by solar energy.

The said first and said second power transmission lines and said fluid return line may extend through a hydraulic pack-off isolating the wellbore from the atmosphere.

Gas may be produced from the wellbore simultaneously with the production of fluids through the fluid return line.

The first and said second power transmission lines may extend down the wellbore in a parallel arrangement.

The first and said second power transmission lines may extend down the wellbore in a coaxial arrangement.

A working fluid used within said first and said second power transmission lines may be the same as the fluids produced through said fluid return line.

The first power transmission line may include an injection valve, wherein said injection valve is configured to allow the bleeding of gas from the first power transmission line and the injection of a chemical substance therethrough.

The second power transmission line may include an injection valve to allow the bleeding of a chemical substance therethrough.

The present invention also provides a method to produce fluids from a wellbore, the method including the steps of:

• • installing a hydraulically actuated pump to a desired depth within the wellbore;
  • operating the hydraulically actuated pump with a surface power pump, wherein the surface power pump pressurizes power transmission lines extending from the surface of the wellbore to the depth within the wellbore;
  • reciprocating a piston within the hydraulically actuated pump with a surface control system, the surface control system configured to alternate pressure to the power transmission lines to oscillate the piston from a first position to a second position; and
  • pumping the fluids from the wellbore up a fluid return line when the piston is oscillated between the first and the second position.

Chemicals may be injected to the desired depth through an injection valve located within the power transmission lines.

Gas may be bled from the power transmission lines through an injection valve mounted thereupon

To recover production fluids, a well is normally drilled cased, and cemented. The casing is then preferably connected to a wellhead valving system and the well is preferably perforated at a depth to produce fluids. One embodiment of the present invention preferably includes deploying a pump assembly through the cemented casing or production tubing. The pump assembly for said one embodiment preferably includes a system having three hydraulic lines with a hydraulically actuated pump disposed thereupon. Two of the hydraulic lines preferably transmit hydraulic power to the pump and the third hydraulic line preferably carries the fluids to be produced and discharged from the wellbore.

Preferably, fluids are produced through the production line on both strokes (up and down) of the hydraulic pump, but a separate line for each stroke may be desired and used instead. Preferably, the production hydraulic line includes a standing valve or check valve in it to keep fluids from “falling” back down the hydraulic line and returning back to the pump assembly downhole after discharge.

BRIEF DESCRIPTION OF THE DRAWING

Embodiments of the invention will now be described by way of example only with reference to the accompanying figures, in which:

FIG. 1 is a schematic sketch of a hydraulically actuated downhole pump assembly in accordance with an embodiment of the present invention;

FIG. 2 is a schematic sketch of the hydraulically actuated downhole pump assembly of FIG. 1 and a surface control scheme in accordance with the FIG. 1 embodiment of the present invention;

FIG. 3 is a schematic diagram of a valving configuration of a pumping method and apparatus for the FIG. 1 embodiment of the present invention;

FIG. 4a is a representation of a gas production well completion including a reciprocating pumping apparatus of an alternative embodiment of the invention, before pumping has begun;

FIG. 4b is a representation of the gas production well completion and reciprocating pumping apparatus of FIG. 4a, after pumping has begun;

FIG. 5a is a simplified front sectional view of the reciprocating pumping apparatus of FIG. 4a with its piston positioned at the upper end of its stroke;

FIG. 5b is a simplified front sectional view of the reciprocating pumping apparatus of FIG. 4a with its piston positioned towards the lower end of its stroke;

FIGS. 6a-6c are detailed upper, middle and lower front section views of the reciprocating pumping apparatus of FIG. 4a;

FIGS. 7a-7e are front sectional views of the reciprocating pumping apparatus of FIG. 4a showing its piston in a variety of different positions;

FIGS. 8a-8e are front sectional views of the reciprocating pumping apparatus of FIG. 4a showing a mechanism for securing and sealing the reciprocating pump within production tubing;

FIG. 9 is a simplified front sectional view of a reciprocating pumping apparatus used in an oil production well completion;

FIG. 10 is a simplified front sectional view of the reciprocating pumping apparatus of FIG. 4a showing the main bearing surfaces within the apparatus; and,

FIG. 11 is a representation of a gas production well completion including a reciprocating pumping apparatus of a further alternative embodiment of the invention, before pumping has begun;

FIG. 12 is a representation of the gas production well completion and reciprocating pumping apparatus of FIG. 11, after pumping has begun.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring initially to FIG. 1, a schematic hydraulic pump assembly 200 is shown. Pump assembly 200 preferably includes three hydraulic lines, L1, L2, and L3. L1 is shown as a hydraulic down-stroke operation line, L2 is shown as a hydraulic up-stroke operation line, and L3 is shown as a production fluid return line. While the lines are shown as three distinct lines, it should be understood by one of ordinary skill in the art that lines L1, L2, and L3 may be constructed as a single co-axial line having three distinct fluid flow passages. Pump assembly 200 includes a pump 201 with a hydraulic piston assembly P that reciprocates up and down within a housing of pump assembly 200. Piston P defines two pumping chambers, 211 and 212 and two pressure actuation surfaces U and D. Pressure from line L1 engages surface D and drives piston P down. As piston P is driven down, chamber 211 fills with production fluids through inlet valve I1 and production fluids within chamber 212 are forced through outlet valve O2 to line L3. Next, pressure from line L2 engages surface U and drives piston P upward. As piston P is driven upward, chamber 212 fills with production fluids through inlet valve I2 and production fluids within chamber 211 are forced through outlet valve O1 to line L3. The upward and downward movement of piston P is alternated at a desired frequency to allow production fluids to flow from the wellbore, through line L3, and up to the surface. Valves, I1, I2, O1, and O2 are preferably one-way check valves that only allow flow of production fluids in a single direction. Injection valves IV1, IV2 allow for elevated pressures within lines L1, L2 respectively to be released therefrom.

Once the apparatus is in location, the hydraulic lines L1, L2 are connected to a surface hydraulic power system 220 that includes a series of valves V1, V2, V3 & V4 and a surface pump 221.

Referring briefly to FIG. 2, a schematic of the surface hydraulic power system 220 can be described with reference to the hydraulic pump assembly provided in a wellbore 230.

The wellbore 230 has casing 231 with perforations 232. A wellhead 233 is provided at the top of the well and the lines L1, L2, L3 are sealed therein by packers (not shown). The line L3 (which recovers the hydrocarbons) is directed to a holding tank 229. A line L4 is provided at the top of the well to recover gas for sale. A further gas line L5 may be provided to recover gas to be used as a power source for the surface pump 221.

The surface power system 220 comprises a solar panel 222, batteries 223, a controller 224 and an RTV 225. The controller 224 controls valves V1, V2, V3 and V4. Pressure monitors 226, 227 are provided on the lines L1 and L2. The surface pump 221 has a pump reservoir 228.

To operate the downhole pump 201, fluids are preferably pumped down line L1 with all valves closed except for valve V1. This forces fluid out of injection valve IV1 to purge line L1. This step is capable of removing air bubbles or gas from line L1. Next, valve V1 is closed and valve V2 opened and air is similarly bled through injection valve IV2 to purge line L2. Next the surface pressure required for the surface pump 221 to operate piston P is preferably set on the surface control logic such that the operating pressure to function the downhole pump 201 is less than the pressure required to open injection valves IV1, and IV2. In addition to their use in purging lines L1 and L2 from air or gas bubbles, injection valves IV1 and IV2 can also be used as chemical injection ports for wells that require the addition of chemicals downhole. Next, by switching the surface valves in an appropriate sequence, the surface pump 221 oscillates piston P upward and downward to deliver fluids from the wellbore 230 up line L3. The surface power system 220 provides the switching and logic for activating the downhole pump assembly 200. The surface power system 220 powers the downhole pump assembly 200. Using the apparatus and method gas fluids are capable of being simultaneously produced from the well with gas production. Using a three-line wellhead packoff, fluid pressure (gas or liquid) can be maintained with lines L1, L2, and L3 extending therefrom and continuing to operate downhole pump 201. The weight of hydrostatic pressure within lines L1 and L2 allow minimal power input from the surface pump to operate piston P of downhole pump 200. Furthermore, lines L1, L2, and L3 can be manufactured of continuous hydraulic line (or hose), or jointed sections of line or pipe, depending on preferences of the well operator.

Referring to FIG. 3A, a method of operating a downhole pump like the pump 201 disclosed in FIGS. 1-2 can be described. The method preferably includes opening line L1 and valves V1 and V4 and closing valves V2, V3 and V5. Next, when pressure within line L1 reaches a set pressure, V3, V5 are opened, V1, V4 are closed and line L1 is vented to the pump reservoir tank 228 via valve V3.

Next, valves V1, V4 and V5 are closed, valve V2 and V3 are opened and fluid is pumped down line L2. When L1 reaches the set pressure, V3 is closed, V5 is opened and V2 is then closed. V5 is then closed and V4 opened allowing L2 to be vented via valve V4 to the pump reservoir 228. When pumping down line L1, valves V4 and V1 are opened by the surface controller and valves V2, V3, and V5 are closed. When pressure in line L1 reaches the set pressure, valve V4 is closed, valve V5 is opened, and valve V1 is closed. Next, valve V5 is closed, valve V3 is opened, and valve V2 is opened. When pumping down line L2, valves V3 and V2 are open and valves V1, V4, and V5 are closed. When pressure in line L2 reaches the set pressure, valve V3 is closed, valve V5 is opened, and valve V2 is then closed. Next, valve V5 is closed, valve V4 is opened and valve V1 is opened. The process is then repeated, preferably with computer control of valves V1, V2, V3, V4, and V5 to maximize the speed of operation of downhole pump 201.

Optionally, the system can include the use of a gas operated surface pump using the well pressure for power as part of the system. The system can include powering the surface pump with chemical energy from gas. The system can include powering the surface pump with solar power. The lines in the system can extend downhole in parallel or concentrically. The system can include running multiple fluid conduits to transmit the power fluid and a separate fluid conduit to transmit the produced fluids to the surface. The system can include timing and switching the hydraulic power fluid at the surface between the hydraulic power conduits running from surface to the depth of the well. The system can include having a downhole injection valve built into each of the hydraulic control lines down at the bottom end in the well to be opened by applying sufficiently high pressure to open them and allow fluid to discharge into the well therethrough. The system can include the hydraulic power fluid being the same as the produced fluid. The system can include the power fluid as a separate fluid from the produced fluid, for example, a fluid with lubricating qualities. The system can include a power fluid having corrosion inhibitors, scale inhibitors, hydrate inhibitors, paraffin inhibitors, and wax inhibitors. The piston of the downhole pump of the system can optionally be biased with springs.

FIG. 4a shows a reciprocating pump 1 secured and sealed within production tubing 2 suspended within a well bore 4 and hydraulically connected, via a hydraulic conduit 3, to a hydraulic pumping system 24 located at the surface. Water within the well bore 4 prevents gas entrained in a formation 5 from entering the well bore 4 and being recovered. As described below, production of water to the surface via the reciprocating pump 1 and production tubing 2 reduces the height of the water column in the well bore 4 as shown in FIG. 4b, allowing the gas entrained within the formation 5 to enter the well bore 4 and flow to surface for recovery.

The conduit 3 can be made from any suitable material such as stainless steel, inconel or titanium. A first annular space 81 is formed above the pump 1 between the hydraulic conduit 3 and production tubing 2. The outer diameter of the conduit 3 is around ¼″.

One typical outer diameter of production tubing is 2⅜″, with an inner diameter or bore of 2″. The diameter of the pump 1 suitable for operation in such a size of production tubing is 1.905″. However, pumps in accordance with the present invention may be larger or smaller in order to be operable with production tubing of correspondingly different sizes or for other reasons.

FIGS. 5a and 5b diagrammatically represent the reciprocating pump 1 which comprises a piston 18 having an axial bore 23, a cylinder 50 enclosing the piston 18, a manifold 30 and a pack-off assembly 6 for securing and sealing the pump 1 within the production tubing 2.

The piston 18 has a head 60 at its lower end, an end face 64 at its upper end and a bearing flange 62 extending radially outwards around its centre. The head 60 and bearing flange 62 each have upper and lower bearing faces 60u & 60l, 62u & 62l respectively.

The cylinder 50 has a bore 16 which encloses the piston 18. A seal 69 seals the piston head 60 in the bore 16. The portion of the bore between the seal 69 and the end of the cylinder 50 is hereinafter referred to as the bore 16′.

A finger 70 from the manifold 30 extends into the bore 23 of the piston 18. A second annular space 82 is defined within the bore 16 of the cylinder 50 between the finger 70 and the end face 64 of the piston 18.

The diameter of the bore 16 is slightly less at its upper end than its lower end. A step 54 separates these areas of differing diameter and defines a third annular space 83 between the piston 18, step 54 and bearing flange 62 of the piston 18.

An inwardly extending flange 66 is provided on the bore side of the cylinder 50 and has a seal 68 to seal the piston 18 between the piston's head 60 and the piston bearing flange 62. The flange 66, piston 18 and the piston bearing flange 62 define a fourth annular space 84 above the flange 66; and a fifth annular space 85 below the flange 66, between the flange 66, the piston 18 and the piston head 60.

The forth annular space 84 is in fluid communication with the first annular space 81 via drillings 8, 9 and bore 23. Therefore the pressure within the production tubing 2 acts on the lower face 62l of the flange 62 of the piston 18 urging the piston 18 in an upwards direction.

The hydraulic conduit 3 is connected, via a drilling 11, to the second annular space 82 in the bore 16 between the finger 70 and the upper end of the piston 18. Therefore the pressure within the conduit 3 acts on an upper face 64 of the piston 18 urging it in a downwards direction. The hydraulic fluid within the conduit 3 has a specific gravity less than that of the water contained within the first annular space 81 and thus exerts less force than the water in the first annular space 81, unless pressurised.

The well bore 4 below the reciprocating pump 1 is connected via passages 12 and 13 to the fourth and fifth annular spaces 84 and 85 and to the bore 16′ within the reciprocating pump 1. Therefore the pressure within the well bore 4 acts on the upper face 62u of the bearing flange 62, via the fourth annular space 84, to urge the piston 18 downwards. Also, the pressure within the well bore 4 acts on the upper face 60u of the piston head 60, via the fifth annular space 85, also to urge the piston 18 downwards.

The bore 16′ will also be exposed to well bore pressure in use and thus urges the piston 18 in an upwards direction. The pressure within the bore 23 (equalised with the production tubing pressure) of the piston 18 will urge the piston 18 downwards.

Thus to summarise the various forces acting on the piston 18:

• • The hydrostatic pressure from water present in the production tubing 2 (via the fourth annular space 84) along with the pressure within the well bore 4 (via bore 16′) act to urge the piston 18 in an upwards direction.
  • The hydrostatic pressure from water present in the production tubing 2 (via the bore 23), the hydrostatic pressure (and any applied pressure) in the hydraulic conduit 3 (via the second annular space 82) and the well bore pressure (via the third and fifth annular spaces 83, 85) act to urge the piston 18 in downwards direction.

By selection of the sizing of the reciprocating pump 1, and the various bearing surfaces, the piston 18 is biased to the upper extent of its allowed movement. The piston 18 may be moved toward the lower extent of its allowed movement by pressurising the hydraulic conduit 3 which increases the pressure in the second annular space 82 to a sufficient extent to overcome the bias of the piston to its upper extent and therefore lower the piston 18. When the applied pressure within the hydraulic conduit 3 is released, the piston 18 will again be biased and therefore move toward the upper extent of its allowed movement.

The hydraulic fluid used in the hydraulic conduit 3—even when no pressure is applied—will also affect the movement of the piston 18 due to its weight. However the specific gravity of hydraulic fluid is less than that of water and thus the pressure caused by the weight of the water in the production tubing 2 overcomes the pressure caused by the weight of the hydraulic fluid in the hydraulic conduit 3.

FIG. 10 is a further view of the simplified pump 1 highlighting the annular spaces and other areas which act on the piston 18. In the following calculation:

• • A82-A85=Surface area of bearing faces acting to move the piston within the annular spaces 82-85 respectively
  • B16′=Surface area of bearing face acting to move the piston within the bore 16′
  • B23=Surface area of bearing face acting to move the piston within the bore 23
  • Pw=Well Pressure
  • Pt=Production tubing pressure
  • Pc=Pressure in conduit 3

Thus,

• • Pt(A84-B23)=Force acting to raise the piston 18
  • Pw(A85+A83-B16′)+A82Pc=Force acting to lower piston 18

The net effect of the production tubing pressure is to urge the piston 18 upwards whilst the net effect of the well pressure is to urge the piston 18 downwards.

The weight of the hydraulic fluid in the conduit 3 urges the piston 18 downwards.

The force acting to raise the piston 18:
=(B16′×Pw)+(A84×Pt)

The force acting to lower the piston 18:
=(A85×Pw)+(A83×Pw)+(A82×Pc)+(B23×Pt)

Exemplary data are as follows:

• • Setting Depth 10,000 feet.
  • Tubing Fluid—Water S.G.=1.00
  • Pressure in Tubing (Pt)=4330 psi.
  • Conduit Fluid—Hydraulic Oil S.G.=0.92
  • Pressure in Conduit (Pc) without any applied force=3984 psi.

The dimensions of the various bearing faces on the piston 18 areas are as follows:

• • B16′=2.074 sq.in.
  • A85=1.473 sq.in.
  • A84=1.169 sq.in.
  • A83=0.881 sq.in.
  • A82=0.690 sq.in.
  • A6=0.196 sq.in.

Well Bore Pressure (Pw) can vary. In this example it is taken to be 50 psi.

• • Upward Force on Piston=(2.074×50)+(1.169×4330)=5165 lbf.
  • Downward Force on Piston=(1.473×50)+(0.881×0.50)+(0.690×3984)+(0.196×4330)=3715 lbf (pounds of force).
  • Resulting Upward Force on Piston=1450 lbf.

Applied pressure required on A82 via hydraulic conduit 3 to equalise the forces on the piston: $\begin{array}{c}=\mathrm{Force}/\mathrm{Area}\\ =1450/0.69\\ =2100\mathrm{lb}\text{/}\mathrm{sq}\mathrm{inch}\end{array}$

In another example where the Well Bore Pressure (Pw)=1200 psi.

• • Upward Force on Piston=(2.074×1200)+(1.169×4330)=7550 lbf.
  • Downward Force on Piston=(1.473×1200)+(0.881×1200)+(0.690×3984)+(0.196×4330)=6422 lbf.
  • Resulting Upward Force on Piston=1128 lbf.

Applied pressure required on A82 via hydraulic conduit 3 to equalise the forces on the piston: $\begin{array}{c}=\mathrm{Force}/\mathrm{Area}\\ =1128/0.69\\ =1635\mathrm{lb}\text{/}\mathrm{sq}\mathrm{inch}\end{array}$

Therefore allowing the well pressure (below the pump) to act on the piston 18 to urge the piston downwards reduces the pressure which is required to be applied to the hydraulic conduit 3, thus saving power.

In alternative embodiments the piston 18 may be biased in the opposite direction by, for example, directing the pressure within the production tubing and/or conduit 3 to the to the 3^rd and 5^th annular spaces 83, 85—although this is less preferable. Optionally the size of the various bearing faces may be adjusted in order to bias the piston in a downwards direction.

Referring back to FIGS. 5a, 5b, the head 60 of the piston 18 includes a first ball valve 19 in a seat 20. The ball 19 is adapted to lift from its seat thereby opening the valve when the piston 18 is moved in a downwards direction due to the pressure rise in the bore 16′ because of the reduction in volume of the bore 16′ between the seal 69 of the piston head 60 and the end of the cylinder 50. When open, the valve 19 allows communication between the bore 16′ of the cylinder and the bore 23 of the piston 18.

A second ball valve 21 is provided in a seat 22 at the lower end of the cylinder 50. The ball 21 is adapted to lift from its seat thereby opening the valve when the piston 18 is moved in an upwards direction due to the pressure drop in the bore 16′ because of the increase in volume of the bore 16′ between the seal 69 of the piston head 60 and the end of the cylinder 50. When open, the valve 21 allows communication between the bore 16′ and the well bore 4. FIGS. 7a-7e show more detailed views of the pump 1 at various point in the piston cycle.

Thus in use, the pressure of the hydraulic fluid in the second annular space 82 is increased by control of the hydraulic conduit 3 and the piston 18 moves in a downwards direction. The ball 21 is firmly pressed against its seat 22 preventing water within the bore 16′ from egress into the well bore 4 whilst the ball 19 is lifted from a seat 20 allowing the water in the bore 16 to egress into the bore 23 of the piston 18 (see FIG. 7b). The water can thereafter proceed via drillings 8 into the first annular space 81 between the production tubing 2 and the conduit 3. When the piston 18 reaches the bottom of its stroke (see FIG. 7c) the applied pressure in the hydraulic conduit 3 is removed causing a drop in pressure in the second annular space 82 and the resulting return of the piston 18 to the upper extent of its movement (since it is biased in this direction by the hydrostatic pressure of the fluid within the production tubing 2). During the piston's upward stroke, the ball 19 is firmly pressed onto the seat 20 whilst the ball 21 is lifted from the seat 22 and water from the well bore 4 is drawn into the bore 16 of the reciprocating pump 1 (see FIG. 7d).

The piston 18 can then be returned to the lower position (as shown in FIG. 7c) which expels the water into the bore 23 as described above.

By sequential manipulation of the pressure of the hydraulic fluid in the hydraulic conduit 3 using a timing device of known technology in the hydraulic pumping system 24, the piston 18 of the reciprocating pump 1 may be repeatedly moved between the upper and lower extents of its allowed movement and water from the well bore 4 lifted via the first annular space 81 between the production tubing 2 and the conduit 3 to surface.

In the absence of the water, well bore gas is then allowed to expand and flow up the annulus between the production tubing 2 and casing 7.

An advantage of certain embodiments of the present invention is that heavy rods between the pump and the surface are not required to reciprocate the piston. The weight of these rods in known systems adds drag to the pump and thus require more power to operate.

A further advantage of certain embodiments of the present invention is that the fluid produced by the pump aids the return of the piston, thus reducing the amount of power required to operate the pump.

A yet further benefit of embodiments of the invention is that the power required to move the piston in the opposite direction is less since the well pressure urges the piston in this direction.

The features required to mount, seal and disengage the pump 1 from the production tubing 2 will now be described with reference to FIGS. 6a-6c which show a more detailed view of the reciprocating pump 1.

The pack-off assembly 6 comprises serrated slips 37 (FIG. 6b) for securing the pump 1 within the production tubing 2 and above the slips 37, a resilient seal 43 for sealing the pump 1 within said production tubing 2. The serrated slips 37 are mounted on slidable support sleeves 38, 39 and are retained by retaining cups 40, 41; each above and below the slips 37.

An outer annular space 36 is defined by the outer face of the cylinder 50, an outer jacket 45 provided around the cylinder 50, a slidable sleeve 42 and a second piston 44. The outer annular space 36 can be pressurised to move the slidable sleeve 42 and piston 44.

The slidable sleeve 42 extends downwards from the outer annular space 36, past the resilient seal 43, to the upper support sleeve 39 of the serrated slips 37 and is adapted to move the serrated slips 37 radially outward when the sleeve 42 is moved downwards.

The resilient seal 43 is mounted on said slidable sleeve 42. The second piston 44 holds the resilient seal 43 in place and is adapted to compress the seal 43 when the piston 44 is moved with respect to the sleeve 42, causing the seal to move radially outwards and form a seal between the pump 1 and the production tubing 2.

A one-way pressure relief valve 33 is connected to the drilling 11 and is adapted to allow passage of hydraulic fluid above a certain predetermined pressure level. This pressure level is greater than the normal operating pressure of the pump 1 and so in normal use, the valve 33 is closed. The valve 33 leads, via drilling 35 and annular gallery 34, to the outer annular space 36.

Thus in order to set the pump 1 in the production tubing 2, the pump 1 is lowered via the hydraulic conduit 3 below the gas formation into the water which is blocking the flow of gas. Sufficient hydraulic pressure is applied via the conduit 3 and drilling 11 to pass the check valve 33 and pressurise the outer annular space 36 via the drilling 35. (A side effect is that the piston 18 moves to its lowermost position, but this does not affect the operation of securing the pump 1 to the production tubing 2.)

Pressure within the annular space 36 moves the piston 44 and slidable sleeve 42 (carrying the resilient seal 43) downwards. The sleeve 42 engages the support sleeve 39 of the serrated slips 37 and drives it together with the lower support sleeve 38 forcing the serrated slips 37 radially outwards to engage with the production tubing 2, see FIG. 8b. Continual pressure applied to the outer annular space 36 forces the piston 44 downwards further (with respect to the sleeve 42 which can move no further and is now stationary), compressing the length of the resilient seal 43 causing it to expand radially to seal against the production tubing 2, see FIG. 8c. The pressure applied within the annular space 36 is maintained by the valve 33 after the hydraulic pressure applied via the conduit 3 is removed, leaving the reciprocating pump 1 secured and sealed within the production tubing 2.

Pumping operations can then be conducted as described above with respect to FIGS. 5a, 5b.

Referring back to FIGS. 6a-6c, the components involved in the disconnection procedure will now be described. The outer jacket 45 is rigidly connected to a housing or ‘fishing neck’ 29 which is connected to the top of the manifold 30 of the pump 1. A stop pin 25 is provided generally within the bore of the housing 29 and connects to the manifold 30 of the pump 1. The stop pin 25 has a threaded connector 26 for connection to the hydraulic conduit 3 (not shown in FIGS. 6a-6c) and a drilling 27 which links the threaded connector 26 of the stop pin 25 to the hydraulic fluid input drilling 11 of the manifold 30.

When the pump 1 is to be removed from the well, the outer jacket 45 and connected housing 29 move together with respect to the stop pin 25 and manifold 30 as described further below.

Shear pins 28 extend through the housing 29 and connect to the manifold 30 to resist relative movement of the housing 29 with respect to the manifold 30. A drilling 32 from the drilling 27 in the stop pin 25 leads to a further annular space 31 between the stop pin 25, manifold 30 and housing 29. When pressurised the annular space 31 urges the housing 29 and manifold 30 apart. The shear pins 28 are adapted to break when the pressure is increased above operating and setting pressure and allow the disengagement of the pump from the production tubing 2 before recovery, as described further below.

Before disengagement, the pressure differential on either side of the seal 43 needs to be equalised. To provide for this, a fragile disk 46 is provided in the piston 18 and is adapted to rupture at a predetermined pressure level. When ruptured a communication is formed between the bore 23 of the piston 18 via third annular space 83 and passage 12 to the well bore 4 below the reciprocating pump 1. This equalises the pressure in the first annular space 81 between the production tubing 2 and conduit 3 and that in the well bore 4.

Thus, on completion of pumping operations a high pressure is applied to the first annular space 81 and consequently to the drilling 8 and bore 23 of the piston 18 via a surface facility (not shown). The pressure is of sufficient magnitude to rupture the fragile disc 46 which then provides communication between the well bore 4 and the first annular space 81 between the production tubing 2 and the conduit 3, allowing equalisation of the pressures on either side of the resilient seal 43. Then, hydraulic pressure is applied via the conduit 3 to the drilling 32, check valve 33 and drilling 35 to annular space 31 (and outer annular space 36). As stated above, pressure within the annular space 31 urges the housing 29 and manifold 30 apart. The pressure is increased until the shear pins 28 break, see FIG. 8d, causing the housing 29 with attached outer jacket 45 to move upwards with respect to the manifold 30.

The pressure within the annular space 36 ensures that the slidable sleeve 42 does not, at this stage, move with the jacket 45 and housing 29. However a connection between the lower end of the jacket 45 and the piston 44 causes the piston 44 to move upwards with the housing 29. The piston 44 thus disengages from the resilient seal 43 which returns to its former geometry and disengages from the production tubing 2.

After the seal has disengaged from the production tubing 2, continued movement of the housing 29 with respect to the manifold 30 causes the slidable piston 44 to engage with a step 72 of the slidable sleeve 42, FIG. 8d, and move the support sleeve 42 along with the piston 44 and housing 29 all with respect to the manifold 30.

Movement of the slidable sleeve 42 causes it to move the upper support sleeve 39 of the serrated slips 37 which disengages the serrated slips 37 from the production tubing 2.

The pump 1 can then be winched to the surface by the hydraulic conduit 3.

In an alternative embodiment shown in FIGS. 11 and 12, a pump 101 has the piston and cylinder components of the pump 1 separate from the manifold and pack-off components. A tube 14 (around ⅜″ diameter) joins them together whilst a hydraulic line (not shown) of around ¼″ is provided to power the piston. Other features are similar with the features already described with respect to the pump 1. This embodiment has particular application where the lowermost end of production tubing 2 in a given well is above the perforated interval in the casing 7 which receives the hydrocarbon gas from the formation 5. The pack-off assembly 106 secures the manifold into the production tubing 2 whilst the tube 14 spaces the pump 101 including the piston and cylinder to below said perforated interval. The pump 101 operates in a similar fashion to the previous embodiment of the pump 1—fluid in the well is produced through the conduit 14 and thereafter through the production tubing 2 to the surface. The weight of the fluid in the production tubing 2 (now combined with tube 14) continue to act on the piston as described for the pump 1.

In a further alternative embodiment, a hydraulic pumping system may be provided at the surface to pressurise the production tubing, thus increasing the force acting to bias the piston in an upwards direction. Manipulation of the pressure within the production tubing 2 may therefore be utilised to optimise the sequential time of the stroke of the reciprocating pump and hence control the rate at which fluid is removed from the well. This option is particularly beneficial when producing liquid hydrocarbons from the well rather than removing water to allow gaseous hydrocarbons to escape.

FIG. 9 demonstrates a method for producing oil from a well using the reciprocating pump 1. In this embodiment the first annular space 81 between the production tubing 2 and the conduit 3 is maintained at a pre-determined pressure by a hydraulic pumping system 47 incorporating a pressure relief valve 48. Said pre-determined pressure providing bias to move the piston 18 of the reciprocating pump 1 to the upper extent of its allowable movement whilst hydraulic pressure provided via the conduit 3 provides bias to return the piston 18 of the reciprocating pump 1 to the lower extent of its allowable movement. By repeatedly sequencing the application of the hydraulic pressure applied via the conduit 3 the piston 18 may therefore be reciprocated and oil produced to surface via the annular space 81 between the production tubing 2 and the conduit 3. In a further alternative the bearing faces within the pump 1 can be altered in order to overcome the lower specific gravity of the produced oil compared with the hydraulic conduit fluid. The piston can therefore be biased towards the upper direction and liquid hydrocarbons recovered through the production tubing as described previously without having to pressurise the production tubing. Thus the dimensions of the pump may be sized to produce water or oil. Nonetheless, a pump with bearing faces sized to produce water may still be used to produce oil by manipulation of the pressure within the production tubing.

Improvements and modifications may be made without departing from the scope of the invention.

Claims

1. A hydraulically powered pump, adapted to be placed in a well and pump fluids from the well to the surface.

2. A pump as claimed in claim 1, comprising a reciprocating piston and a cylinder, the cylinder having a bore, wherein the piston is adapted to move within at least a portion of the bore of the cylinder.

3. A pump as claimed in claim 2, wherein the pump is adapted to allow fluid within the well to bias the piston in a first direction.

4. A pump as claimed in claim 3, wherein the piston, in use, is biased towards an upper direction.

5. A pump as claimed in claim 3, wherein fluid in a separate part of the well is adapted to urge the pump in a second direction, preferably opposite the first direction.

6. A pump as claimed in claim 1, comprising a resilient seal adapted to seal the pump within a tube, such as a portion of production tubing.

7. An apparatus for recovering fluids from a well comprising a hydraulically powered pump and a hydraulic conduit.

8. Apparatus as claimed in claim 7, wherein the hydraulic conduit is a flexible conduit.

9. Apparatus as claimed in claim 7, comprising a hydraulic power source which is adapted to pressurise the hydraulic conduit and in turn the pump.

10. A method for removing fluid from a well, the method comprising the steps of:

lowering a hydraulically powered pump into a well;

the pump being connected to the surface via a hydraulic conduit; and

hydraulically activating the pump to pump fluid from the well to the surface.

11. A method as claimed in claim 10, wherein a portion of the pump is secured in production tubing within the well.

12. A method as claimed in claim 11, wherein fluid within the production tubing biases the piston of the pump in a first direction.

13. A method as claimed in claim 10, wherein pressure within the well, outside the production tubing, urges the piston of the pump in a second, preferably opposite, direction.

14. A method as claimed in claim 10, wherein the hydraulic line is repeatedly pressurised and depressurised in order to reciprocate a piston of the pump.

15. A method as claimed in claim 10, wherein the fluid includes water and the method includes the step of recovering gaseous hydrocarbons from a formation proximate to the well.

16. A method as claimed in claim 10, wherein pressure is applied to the production tubing at the surface in order to increase the pressure therein.

17. A method as claimed in claim 10, wherein the pump is operated from a point below where hydrocarbons may enter the well.

18. A downhole pump to remove fluids from a wellbore, the pump comprising:

a first power transmission line and a second power transmission line;

a piston, said piston configured to be displaced within a cylinder from a first upward position to a second downward position;

said piston within said housing defining a first fluid chamber and a second fluid chamber

said piston urged into said first downward position when pressure within said first power transmission line is increased;

said piston urged into said second upward position when pressure within said second power transmission line is increased; and

a fluid return line connected to outlets of said first and second fluid chambers.

19. The downhole pump of claim 18 wherein pressure within said first and said second power transmission lines are controlled by a surface pump.