SYSTEM FOR PULSE-INJECTING FLUID INTO A BOREHOLE

• US 20110036581A1
• Filed: 04/30/2009
• Published: 02/17/2011
• 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
• Granted Patent: US 8,544,552 B2
• Time in Patent Office: Days
• US Class Current: 166/305.1
• 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 for pulse-injecting fluid 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, for storing pressurized fluid that is to be pulse-injected into the ground formation;

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

the piston has an accumulator-surface and an opposed formation-surface, and the tool is so structured that, in operation, the accumulator-surface is exposed to accumulator-pressure, and the formation-surface is exposed to formation-pressure;

the pressure differential between the accumulator-pressure and the formation-pressure is termed the PDAF;

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

the tool includes a biasing-means, which exerts a biasing-force on the piston in the direction to urge the piston towards its contact-position;

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

—

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

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

(c) the area-divider keeps area-A sealingly separated from area-B, to the extent that fluid pressure in area-A of the accumulator-surface of the piston can be substantially different from fluid pressure in area-B;

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

(e) when the PDAF exceeds an upper trigger level, forces on the piston due to the PDAF acting over the area-A now exceed forces on the piston due to the biasing-means, whereby the piston now moves clear of the area-divider, towards its clear-position;

the tool is so structured that, the piston having moved to its clear-position;

—

(a) area-A and area-B are not now sealingly separated by the area-divider, but are 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 large force that acts to move the piston and to move the valve-member to its open-position.

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

—

(a) when the pulse-valve is open;

—

(i) 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 low-trigger-level, and the valve-closed position, in which the PDAF is increasing towards a high-trigger-level.

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

—

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

—

(i) large enough that, when the PDAF is at a relatively low level, the biasing-force drives the piston forcefully into its contact-position, against the PDAF;

(ii) small enough that, when the PDAF is at a relatively high level, the PDAF drives the piston forcefully to its clear-position, against the biasing force;

(b) when the piston is in its 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 its 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 biasing the piston into its contact-position, whereby the piston now moves to its clear-position;

(c) when the piston moves to its 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.