Downhole pressure wave generating device

1. A device for generating pressure waves in a well or a wellbore, the device comprising:

a housing containing an impact-generating mechanism for generating the pressure waves, wherein the impact-generating mechanism comprises a piston contained within a cylinder, the piston configured to impact an upper surface of an anvil;

a pressure wave outlet located below the anvil, the pressure wave outlet defined by a plurality of openings permitting propagation of the pressure waves from inside the device into fluid contained in the well or wellbore, wherein the upper surface of the anvil is located above the pressure wave outlet and a bottom surface of the anvil is located within a cavity of the pressure wave outlet; and

a connector for connecting the housing to a conveyor for transporting the device to any desired location within the well or the wellbore.

2. The device of claim 1 , wherein the cylinder is configured to provide a piston stroke which is longer than half of the length of the piston.

3. The device of claim 2 , wherein the piston stroke is at least about twice as long as the length of the piston.

4. The device of claim 3 , wherein the piston stroke is about three times as long as the length of the piston.

5. The device of claim 1 , wherein the anvil comprises a constricted middle portion and a flared bottom portion.

6. The device of claim 5 , further comprising one or more seals between an outer sidewall of the anvil above the constricted middle portion and an inner sidewall of the pressure wave outlet, wherein working fluid contacts the anvil below the one or more seals.

7. The device of claim 1 , wherein the anvil further comprises an upper radial extension below the upper surface of the anvil, wherein a lower surface of the radial extension is adjacent to an upper surface of the pressure wave outlet.

8. The device of claim 1 , wherein the plurality of openings is at least one set of three radially aligned elliptical or stadium-shaped openings.

9. The device of claim 1 , wherein the conveyor is a coiled tubing conveyor.

10. The device of claim 1 , which is configured for operation by a pneumatic control system, the device including a plurality of valves configured to fire the piston and to return the piston to a firing position and vent air from the device.

11. The device of claim 10 , wherein the pneumatic control system is further configured to purge the device with an airflow to remove fluid and/or contaminants from the device when the impact-generating mechanism is not operating.

12. The device of claim 10 , wherein the pneumatic control system is further configured to provide a gas spring between a lower surface of an upper radial extension of the anvil and an upper surface of the pressure wave outlet.

13. The device of claim 10 , wherein the plurality of valves are located in a control system housing located above the impact generating mechanism.

14. The device of claim 13 , further comprising one or more pneumatic pilot circuits extending between the cylinder and at least one of the valves of the plurality of valves to provide switching between a purge mode and an operational mode by only controlling an air pressure conveyed into the device past a pre-set pressure threshold.

15. The device of claim 14 , wherein the plurality of valves includes:

a purge valve to switch between the purge mode and the operational mode;

a vent check valve to provide a path to vent air from the device;

an outlet valve to provide a path to vent air from the device and to prevent ingress of fluids into the device; and

a primary control valve to switch between a piston firing mode and a piston return mode.

16. The device of claim 13 , further comprising a filter housing located between the control system housing and the connector, the filter housing provided to filter air entering the device via the conveyor.

17. The device of claim 10 , wherein the plurality of valves includes:

a vent check valve to provide a path to vent air from the device;

an outlet valve to provide a path to vent air from the device and to prevent ingress of fluids into the device;

a primary control valve to switch between a piston firing mode and a piston return mode; and

a pair of solenoid-actuated spool valves under electronic control to actuate the outlet valve and the primary control valve.

18. A system for generating downhole pressure waves, the system comprising:

the device of claim 1 wherein the connector is connected to the conveyor, wherein the conveyor is a coiled tubing conveyor; and

a pressure-controllable air supply unit for conveying pressurized air to the device via the coiled tubing, wherein the device is configured to switch between a low-pressure purge mode and a cycling operating sequence when the air supply unit is controlled to provide an air pressure in the device which is above a pre-determined threshold pressure.

19. A process for cleaning plugged perforations in a well, the process comprising:

conveying the device of claim 1 into the well and positioning the device adjacent to a set of casing perforations; and

operating the device to generate a series of impacts of the piston on the anvil, thereby generating pressure waves which propagate through the openings and horizontally into the fluid, the pressure waves subsequently impacting and dislodging material plugging the perforations, thereby cleaning the perforations and improving production of hydrocarbons therefrom.