Magnets-based tool for pulsing injected liquid
The pulse-tool is used when injecting liquid into a borehole in the ground. When a pulse-valve of the tool opens, liquid passes through from an accumulator to the ground formation, whereby the accumulator pressure falls and the formation pressure rises. When the pulse-valve closes, the accumulator pressure rises and the formation pressure falls. The pulse-valve is driven to open when the pressure differential (PDAF) reaches a high-threshold, at which the PDAF overcomes a biasing force acting to hold the pulse-valve closed. The biasing force is provided by a pair of magnets, in attraction mode. When the PDAF reaches its high-threshold, and the magnets separate, the magnetic attraction force decreases rapidly. This characteristic helps the pulse-valve to open very rapidly, e.g explosively, creating an energetic penetrative shock-wave out into the formation.
1. Tool for pulse-injecting liquid from a borehole out into the surrounding ground-formation, wherein:
the tool includes a pulse-valve;
the pulse-valve includes a valve-seat and a relatively-movable valve-member;
the tool includes a pair of magnet-elements, one connected to the valve-seat, the other to the valve-member;
the magnet-elements are arranged in the tool for magnetic attraction;
the magnet-elements urge the pulse-valve closed;
the tool is so configured that the two magnet-elements are close together when the pulse-valve is closed, and apart from each other when the pulse-valve is open;
whereby, when the pulse-valve opens, the magnetic attraction between the two magnet-elements decreases;
the tool includes a supply of liquid, stored in an accumulator at accumulator-pressure;
liquid in the ground formation is at formation-pressure;
the pressure differential between accumulator-pressure and formation-pressure is termed the PDAF;
the tool is so configured that, during operation:
(a) when the pulse-valve is closed, the PDAF is increasing towards a high-threshold at which the Pulse-valve opens; and
(b) when the pulse-valve is open, the PDAF is decreasing towards a low-threshold at which the pulse-valve closes;
the movable valve-member is a component of a movable-unit, which is movable relative to a fixed housing of the tool;
one of the magnet-elements is integral with the movable-unit, and the other is integral with the fixed housing;
the tool is so configured that, during operation, the PDAF urges the movable-unit in the direction to open the pulse-valve with a force termed the PDAF-force;
the PDAF-force is termed the closed-PDAF-force when the Pulse-valve is closed;
the PDAF-force is termed the open-PDAF-force when the Pulse-valve is open;
the magnet-elements bias the valve-member in the direction to close the pulse-valve with a force termed the magnet-force;
the magnet-force is termed the closed-magnet-force when the pulse-valve is closed;
the magnet-force is termed the open-magnet-force when the Pulse-valve is open;
the high-threshold of the PDAF is the magnitude of the increasing PDAF at which the closed-PDAF-force equals the closed-magnet-force;
the low-threshold of the PDAF is the magnitude of the decreasing PDAF at which the open-magnet-force equals the open-PDAF-force;
whereby the pulse-valve cycles automatically between open and closed.
2. As in claim 1 , wherein at least one of the two magnet-elements of the pair is a permanent magnet.
3. As in claim 1 , wherein:
the two magnet-elements are respective permanent magnets;
each magnet is a rare-earth magnet, of grade N-52 or higher.
4. As in claim 3 , wherein each magnet is annular-cylindrical.
5. As in claim 1 , wherein:
a moving-magnet of the pair of magnets is fixedly mounted in the movable-unit;
the other of the pair of magnets, termed the fixed-magnet, is fixedly mounted in the fixed housing.
6. As in claim 5 , wherein:
the tool includes two or more pairs of magnets, each pair comprising a moving-magnet and a fixed-magnet;
all the moving-magnets are fixedly mounted in the movable-unit;
all the fixed-magnets are fixedly mounted in the fixed housing.
7. As in claim 1 , wherein:
the movable-unit includes a hammer, and the valve-member is integral with the hammer;
the one of the magnet-elements that is integral with the movable-unit is integral with the hammer;
the valve-seat is mounted for movement relative to the fixed-housing;
the hammer and the valve-seat are formed with respective accumulator-areas, which are exposed to the accumulator pressure, and with respective opposed formation-areas, which are exposed to formation-pressure, the hammer and the valve-seat being thus exposed to the PDAF;
the tool is so structured that, when the PDAF reaches its high-threshold:
(a) the valve-seat and the hammer at first move in unison for a small distance, and the magnet-elements separate;
(b) then the movement of the valve-seat is arrested;
(c) and the hammer continues to move, and the moving hammer drives the valve-member away from the valve-seat.
8. As in claim 1 , wherein:
the movable valve-member is a component of a movable-unit, which is movable relative to a fixed housing of the tool;
the movable-unit includes a hammer;
the one of the magnet-elements that is integral with the movable-unit is integral with the hammer;
the hammer and the valve-member are relatively movable;
the tool is so structured that, when the PDAF reaches its high-threshold:
(a) the hammer moves in the direction to open the pulse-valve, and the magnet-elements separate;
(b) at first, the valve-member does not move, while the hammer moves a small distance;
(c) and then, the moving hammer collects the valve-member, and the moving hammer drives the valve-member away from the valve-seat.
9. As in claim 8 , wherein the tool is so structured that, when the pulse-valve is closed, the PDAF acts over a small area of the valve-member to bias the valve-member against the valve-seat.
10. As in claim 1 , wherein:
the tool is so structured and arranged that:
(a) the closed-PDAF-force is substantially larger than the open-PDAF-force, for a given magnitude of the PDAF; or
(b) the closed-magnet-force is substantially larger than the open-magnet-force; or
(c) both.
11. Tool for pulse-injecting liquid from a borehole out into the surrounding ground-formation, wherein:
the tool includes a pulse-valve;
the pulse-valve includes a valve-seat and a relatively-movable valve-member;
the tool includes a pair of magnet-elements, one connected to the valve-seat, the other to the valve-member;
the magnet-elements are arranged in the tool for magnetic attraction;
the magnet-elements urge the pulse-valve closed;
the tool is so configured that the two magnet-elements are close together when the pulse-valve is closed, and apart from each other when the pulse-valve is open;
whereby, when the pulse-valve opens, the magnetic attraction between the two magnet-elements decreases;
the movable valve-member is a component of a movable-unit, which is movable relative to a fixed housing of the tool;
the tool includes an oil-bath;
the oil-bath includes a sealed chamber defined between upper and lower oil-seals, which seal the movable-unit to the fixed housing;
the two magnet-elements are located inside the sealed chamber, and are immersed in oil therein;
the tool is so configured that the volume of the enclosed chamber remains constant during movement of the movable-unit relative to the fixed housing.