System for pulse-injecting fluid into a borehole

• US 8,544,552 B2
• Filed: 04/30/2009
• Issued: 10/01/2013
• Est. Priority Date: 04/30/2008
• Status: Active Grant

• Current Assignee: Wavefront Reservoir Technologies Ltd.
• Original Assignee: Wavefront Reservoir Technologies Ltd.
• Inventors: Davidson, Brett Charles
• Primary Examiner(s): Bomar, Shane
• Assistant Examiner(s): MICHENER, BLAKE E
• Application Number:
  US12/989,719
• Publication Number:
  US 20110036581A1
• Time in Patent Office: 1,615 Days
• Field of Search: 166/373, 166/386, 166/319, 166/320, 166/321, 166/177.1, 166/177.7, 137/494
• US Class Current: 166/373
• CPC Class Codes: E21B 43/168 Injecting a gaseous medium
• CPC Class Codes: E21B 43/255 including the injection of a gaseous medium as treatment fluid into the formation

Abstract

For injecting e.g. water into ground formation around a borehole, and for superimposing pulses onto the outflow of the injected water, it is important that the pulses have a rapid rise-time. A piston is connected to a pulse-valve of the tool. A bias spring urges the piston towards its closed position. The piston is urged towards the open position by a differential PDAF between the supplied accumulator-pressure and the in-ground formation-pressure. When the pulse-valve is open, the PDAF is falling, until the force of the spring closes the pulse-valve. Then the PDAF rises, but now the PDAF acts over only a small area of the piston. When the PDAF is high enough to ease the pulse-valve open, suddenly the whole area of the piston is exposed to the PDAF, whereby the pulse-valve opens violently.

Claims

1. Tool having an operational capability to superimpose pulses onto a pressurized stream of fluid being injected into a ground formation, wherein:

the tool includes a pulse-valve, having a pulse-valve-member that is movable between a valve-closed position and a valve-open position;

the tool includes an accumulator, in which fluid is stored at accumulator-pressure;

the tool includes a piston, which is connected to the pulse-valve-member;

the tool includes an area-divider, relative to which the piston is movable between a contact-position and a clear-position;

the piston has an accumulator-surface and an opposed formation-surface, and the tool is so structured that, the pulse-valve being open;

(a) accumulator-pressure acting on the accumulator-surface urges the piston to its clear-position; and

(b) formation-pressure acting on the formation-surface urges the piston to its contact-position;

the tool includes structure that exerts a biassing-force on the piston in the direction to urge the piston towards the contact-position;

the tool is so structured that, the piston being in the contact-position;

(a) the accumulator-surface of the piston now makes sealing contact with the area-divider, thereby creating a divider-seal;

(b) the divider-seal sealingly divides the area of the accumulator-surface of the piston into two sub-areas, being area-A and area-B;

(c) the divider-seal, and the tool as a whole, are so structured as to enable the pressure to which area-A is exposed to be substantially different from the pressure to which area-B is exposed;

(d) only area-A of the accumulator-surface , and not area-B, is exposed to accumulator-pressure;

(e) when the pressure differential between accumulator-pressure and formation-pressure (PDAF) exceeds an upper trigger level, forces on the piston due to the PDAF acting over the area-A now exceed the biassing-force on the piston, whereby the piston now moves clear of the area-divider, towards the clear-position;

the tool is so structured that, the piston being in the clear-position;

(a) area-A and area-B are not now sealingly separated by the area-divider, but are now connected;

(b) whereby the accumulator-pressure now suddenly acts over the sum of area-A and area-B together;

(c) whereupon the piston now is subjected to a sudden force of sufficient magnitude to move the piston and to move the valve-member to the valve-open position.

2. As in claim 1, wherein the tool is so structured that, in use:

(a) when the pulse-valve is open;

—

(i) a charge-volume of fluid now passes from the accumulator, through the open pulse-valve, and out into the formation;

(ii) whereby now the accumulator-pressure decreases, and the formation-pressure increases; and

(iii) whereby now the PDAF decreases;

(b) when the pulse-valve is closed;

(i) the accumulator now is re-charged with fluid from a reservoir, whereby the accumulator-pressure increases;

(ii) the just-injected fluid leaks away into the formation, whereby the formation-pressure decreases;

(iii) whereby now the PDAF increases;

(c) the tool cycles between the valve-open position, in which the PDAF is decreasing towards a lower-trigger-level, and the valve-closed position, in which the PDAF is increasing towards the upper-trigger-level.

3. As in claim 2, wherein:

the fluid is liquid;

the structure of the tool is such that;

(a) when the pulse-valve is open, the PDAF exerts a pressure-force, PFopen, on the piston in the direction to open the pulse-valve, of magnitude

PFopen=PDAF*(area-A+area-B);

(b) when the pulse-valve is closed, the PDAF exerts a pressure-force, PFclosed, on the piston in the direction to open the pulse-valve, of magnitude

PFclosed=PDAF*area-A;

(c) throughout pulsing operation of the tool, the biasing-force BF acts on the piston in the direction to close the pulse-valve;

the upper-trigger-level of the PDAF is defined as the PDAF at which, the pulse-valve being closed, PFclosed=BF;

the lower-trigger-level of the PDAF is defined as the PDAF at which, the pulse-valve being open, PFopen=BF;

the charge-volume is the volume of liquid injected from the tool, per pulse, through the pulse-valve while the pulse-valve is open, and while the PDAF falls from the upper-trigger-level to the lower-trigger-level.

4. As in claim 1, wherein the tool is so structured that, in use:

(a) the magnitude of the biassing-force is;

(i) so large that, when the PDAF is at a relatively low level, the biassing-force provides sufficient force to drive the piston into the contact-position, against the PDAF;

(ii) so small that, when the PDAF is at a relatively high level, the PDAF provides sufficient force to drive the piston to the clear-position, against the biassing force;

(b) when the piston is in the contact-position;

(i) only area-A of the accumulator-surface of the piston is now exposed to the accumulator-pressure, not area-B;

(ii) when, the pulse-valve being closed and the accumulator having been re-charged, the rising PDAF has increased to the upper-trigger-level, the PDAF, acting over the area-A of the accumulator-surface of the piston, now exerts enough force on the piston to overcome forces biassing the piston into the contact-position, whereby the piston now moves to the clear-position;

(c) when the piston moves to the clear-position;

(i) the accumulator-surface of the piston being now clear of the area-divider, an area of the piston that is the sum of area-A and area-B of the accumulator-surface of the piston now becomes exposed to the PDAF;

(ii) whereupon the piston now is subjected to a sudden large force, acting to move the piston in the direction to open the pulse-valve.

5. Tool of claim 1, wherein the tool is operable to produce pulses in response to the tool being supplied with accumulator-pressure that is higher than the formation-pressure by an amount greater than the upper-trigger-level of the PDAF.

6. Tool of claim 1, wherein:

the piston being in the contact-position;

only area-A of the accumulator-surface is exposed to the accumulator-pressure, area-B being exposed to a lower pressure;

in that, either;

(a) the divider-seal is leak-proof;

or

(b) the area-B is vented to the formation;

or

(c) both.

7. Tool of claim 1, wherein:

the piston is connected to the pulse-valve-member at a lost-motion connection;

in the lost-motion connection, the piston and the valve-member are able to move relatively over a lost-distance;

the tool is so structured that, the PDAF having reached the upper-trigger-level, and the piston having moved clear of the area-divider;

(a) the valve-member at first does not move;

(b) upon the lost-distance being taken up, the piston picks up the valve-member, and the two then move in unison; and

(c) the lost-distance is of sufficient magnitude to enable the piston to acquire momentum before the piston picks up the valve-member.

8. Tool of claim 1, wherein:

the tool includes a piston-seal;

the piston-seal seals the piston to a housing of the tool, between the accumulator-surface of the piston and the formation surface of the piston, both when the pulse-valve is open and when the pulse-valve is closed; and

the area-B is the area enclosed between the divider-seal and the piston-seal when the pulse-valve is closed.

9. Tool of claim 1, wherein:

the pulse-valve includes a valve-seat, which is formed in a housing of the tool;

when the pulse-valve is closed, the valve-member lies pressed sealingly against the valve-seat;

when the pulse-valve is open, the open pulse-valve defines a window through the housing, through which fluid under pressure from the accumulator can pass outwards, in a radial direction;

and thence out into the formation.

10. Tool of claim 9, wherein:

the housing of the tool has a basically cylindrical overall configuration;

the tool is free from protrusions outside of the cylindrical configuration;

the tool is suitable, as a physical structure, to be lowered down into a cylindrical borehole in the ground; and

the tool is operable while physically located down the said borehole.

11. Tool of claim 10, in combination with the borehole, wherein the borehole includes a tubular casing, and the injected fluid passes out of the borehole into the formation through perforations formed radially in the casing.

12. As in claim 1, wherein the fluid is liquid.

13. As in claim 12, wherein:

the accumulator includes structure that resiliently applies compressive force to a stored-volume of liquid in the accumulator;

the tool is so structured that;

(a) the stored-volume is located close to the pulse-valve; and

,

(b) when the pulse-valve opens, the stored-volume is available for rapid discharge through the pulse-valve.

14. As in claim 12, wherein:

the tool includes an equalization-hole, through which, the piston being in its contact-position, area-B of the accumulator-surface of the piston communicates with formation-pressure;

whereby, area-B being exposed to the lower pressure, the lower pressure equals formation-pressure.