PULSED COMBUSTION DEVICE AND METHOD

摘要

1. A pulsed combustion device (1, 22) for use in an underground borehole (3, 20), the device comprising a substantially tubular combustion chamber (10, 27) having an upstream (11) and a downstream end (12), separate fuel and oxidant supply conduits (2, 23, 6, 24) for supplying fuel and oxidant to the combustion chamber, one of said conduits having a fluid discharge port (9, 29) debouching into the combustion chamber between the upstream and downstream ends (11, 12) thereof, the other of said conduits (2, 24) having a fluid discharge port (11) located at the upstream end of the chamber (10, 27), which discharge port is equipped with return flow limitation means (13, 28) which limit flow of combustion fluids from the combustion chamber (10, 27) into the fluid supply conduit (2, 24) and wherein the combustion chamber is shaped as a Helmholz resonator having a tailpipe section (15, 30) near the downstream end (12), the tailpipe has a smallest cross-sectional area which is between 0.15 and 0.30 times the average cross-sectional area of the other parts of the combustion chamber. 2. The pulsed combustion device of claim 1 wherein the tailpipe (10, 27) and the other parts of the combustion chamber (10, 27) have a cylindrical or conical shape. 3. The pulsed combustor device of claim 2 wherein the tailpipe (10, 27) has a tapered divergent conical shape and the other parts of the combustion chamber (10, 27) have a substantially cylindrical shape. 4. The pulsed combustor device of claim 1 wherein the return flow limitation means comprise one or more discharge or non-return valves (13). 5. The pulsed combustor device of claim 1 wherein the return flow limitation means comprise one or more aerovalves (28) which do not have movable parts. 6. A method of enhancing fluid flow in a natural gas production well (3), the method comprising installing a pulsed combustor device (1) according to claim 4 in the well production tubing (2) such that a seal (5) is created between the outer surface of the combustion chamber (10) and the inner surface of the production tubing (2), injecting an oxidant through the supply conduit (6) which has a fluid discharge port (9) which debouches into the combustion chamber (10) between the upstream and downstream ends (11, 12) thereof, allowing the oxidant to react with a fraction of the natural gas present in the combustion chamber (10) thereby generating a high pressure wave front which is inhibited at the upstream end of the combustion chamber by the return flow limitation means (13) and which is enhanced at the downstream end (12) of the combustion chamber by the tailpipe section (15) thereby inducing the mixture and combustion gases to flow up through the production tubing (2), which high pressure wave front is followed by a low pressure wave front which induces natural gas to flow into the combustion chamber via the return flow limitation means (13). 7. A method of heating an underground formation, the method comprising lowering into a well (30) traversing the formation (21) at least one pulsed combustor device (22) according to claim 1 into the well, feeding fuel and oxidant to each pulsed combustor device via fuel and oxidant supply conduits (23, 24) which extend from the wellhead into the well and repeatedly allowing in each pulsed combustor device (23, 24) the oxidant to react with a fraction of the fuel fed into the combustion chamber (27) thereby generating a high pressure wave front which is inhibited at the upstream end of each combustion chamber by the return flow limitation means (28) and which is enhanced at the downstream end of said chamber by the tailpipe section (30), which high pressure wave front is followed by a low pressure wave front which induces oxidant and fuel to flow into the combustion chamber(27). 8. The method of claim 7 wherein a string of pulsed combustor devices is suspended from the wellhead from the oxidant and fuel supply conduits (23, 24) such that the devices (22) are axially spaced in the well (20). 9. The method of claim 8 wherein fuel in the form of methane is fed to each of the devices via a methane supply conduit (23) which passes through the centre of the combustion chamber (27) and tailpipe (30) of at least one pulsed combustor device (22) and methane is injected into the combustion chamber of each device via a methane discharge port (29) located between the upstream and downstream ends (27) of the chamber whereas oxidant is supplied via an oxidant discharge port (26) at the upstream end of the combustion chamber (27). 10. The method of claim 7 wherein the underground formation (21) contains shale oil and the pulsed combustor devices (22) are operated such that the shale oil containing formation in the region of the well is between 600 and 800 K.