Pulse detonation tool, method and system for formation fracturing

Abstract

According to one aspect of the invention, a pulse detonation tool is provided for fracturing subterranean formations. The pulse detonation tool includes a pulse detonation combustor and creates an isolated zone within a wellbore. The tool generate a series of repeating supersonic shock waves that are directed into the subterranean formation to cause propagation of multiple fractures into the formation. According to another aspect of the invention, a method and system for fracturing a subterranean formation using pulse detonation is provided.

What is claimed is: 
     
         1 . A pulse detonation tool for fracturing subterranean formations, adapted to be lowered into production tubing within a wellbore, and comprising:
 a first sealing mechanism and a second sealing mechanism configured to create an isolated zone having an axis parallel to and extending through the production tubing, wherein the first sealing mechanism has at least one inlet port configured to allow a fuel and an oxidizer to flow into a pulse detonation combustor disposed within the isolated zone and wherein the first sealing mechanism is further configured to connect to an oxidizer and fuel source by way of a fluid injection line extending from the surface through the tubing;   at least one valve assembly to achieve controlled delivery of the fuel and oxidizer to the pulse detonation combustor, the pulse detonation combustor comprising:   a combustion region defining a fluid flow path;   a mixing region for producing a flammable mixture comprising a controlled volume of fuel and oxidizer, wherein the mixing region is in fluid communication with the at least one inlet port and the combustion region;   an ignition device configured to periodically ignite the flammable mixture; and means for initiating a series of repeating detonations that generate a series of repeating supersonic shock waves, wherein the shock waves are directed into the subterranean formation to cause propagation of multiple fractures into the formation.   
     
     
         2 . The apparatus of  claim 1  wherein the first sealing mechanism and second sealing mechanism are positioned to align the isolated zone with perforations in the production tubing, a well casing, or both. 
     
     
         3 . The apparatus of  claim 1  wherein the shock waves are about 10 to about 16 times the initial pressure in the wellbore. 
     
     
         4 . The apparatus of  claim 3  wherein the shock waves are in the range of about 10,000 psi to 24,000 psi, and preferably 15,000 psi. 
     
     
         5 . The apparatus of  claim 1  wherein the frequency of operation of the pulse detonation combustor is at a frequency in the range from about 0.1 millihertz to 100 hertz, preferably 0.2 millihertz to 5 hertz, and more preferably 0.01-0.2 Hertz. 
     
     
         6 . The apparatus of  claim 1  wherein the means for initiating a series of repeating detonations comprise a series of obstacles disposed along the fluid flow path of the combustion region. 
     
     
         7 . The apparatus of  claim 1  wherein the at least one inlet port comprises a fuel inlet port and an oxidizer inlet port. 
     
     
         8 . The apparatus of  claim 1  wherein the at least one inlet port and the at least one valve assembly are further configured to introduce a buffer into the pulse detonation combustor after each detonation to purge the combustor of combustion products. 
     
     
         9 . The apparatus of  claim 8  wherein the buffer is non-flammable and selected from the group consisting of the oxidant, the fuel or air . 
     
     
         10 . The apparatus of  claim 8  wherein the at least one inlet port further comprises a buffer inlet port. 
     
     
         11 . The apparatus of  claim 1  wherein the at least one valve assembly comprises a plurality of valves and valve-actuating means. 
     
     
         12 . The apparatus of  claim 1  wherein the at least one valve assembly comprises a fuel valve disposed between the fuel source and inlet port, the fuel valve configured to only allow fuel to flow into the combustion chamber periodically. 
     
     
         13 . The apparatus of  claim 1  further comprising means for preventing backflow of the fuel or flammable mixture towards the surface within the tubing. 
     
     
         14 . The apparatus of  claim 1  wherein the pulse detonation combustor comprises a tubular housing having a first end and a second end and a circular side wall. 
     
     
         15 . The apparatus of  claim 14  wherein the tubular housing is formed by an elongated, cylindrical shock tube closed at both ends and disposed within the production tubing, wherein the shock tube has an outside diameter smaller than the inside diameter of the production tubing and is adapted to be lowered into and subsequently removed from the wellbore. 
     
     
         16 . The apparatus of  claim 15  wherein the shock tube contains and isolates the flammable mixture from the production tubing surrounding the shock tube so as to confine combustion waves generated by the repeating detonations to within the shock tube. 
     
     
         17 . The apparatus of  claim 15  wherein the shock tube further comprises a plurality of spaced nozzles along the length of the circular side wall, each nozzle extending radially outward and configured to aim the shock waves in a substantially axial direction into the formation. 
     
     
         18 . The apparatus of  claim 17  wherein the nozzles are adapted so that the shock tube can be lowered into and subsequently removed from the wellbore. 
     
     
         19 . The apparatus of  claim 14  wherein the circular side wall of the tubular housing is formed by the production tubing. 
     
     
         20 . The apparatus of  claim 19  wherein the first and second end of the tubular housing are formed by the first and second sealing mechanisms, respectively. 
     
     
         21 . The apparatus of  claim 20  wherein the flammable mixture is contained within the production tubing so as to confine combustion waves generated by the repeating detonations to the production tubing. 
     
     
         22 . The apparatus of  claim 20  further comprising a cylindrical tube with an outside wall, wherein the outside wall has a diameter smaller than the diameter of the production tubing, and wherein the first and second sealing mechanisms are adapted to be mounted to each end of the cylindrical tube to form an annular combustion region between the outside wall of the cylindrical tube and the production tubing. 
     
     
         23 . The apparatus of  claim 22  wherein the mixing region is disposed in fluid communication with the at least one inlet port and the annular combustion region, and wherein the annular combustion region is aligned with the perforations in the well casing to provide direct flow of the flammable mixture into the fractures of the subterranean formation. 
     
     
         24 . The apparatus of  claim 23  wherein the combustion wave generated by the repeating detonations extends into the fractures of the formation. 
     
     
         25 . The apparatus of  claim 1  wherein the structural components of the pulse detonation combustor are made of materials sufficient to withstand repeated shock waves and thermal deformations from the repeated detonations and to resist fluid pressure in the wellbore. 
     
     
         26 . The apparatus of  claim 1  wherein the ignition device comprises at least one ignition point. 
     
     
         27 . The apparatus of  claim 1  wherein the ignition device comprises multiple ignition points. 
     
     
         28 . The apparatus of  claim 1  wherein the ignition device comprises electrical ignition means or chemical ignition means. 
     
     
         29 . The apparatus of  claim 1  wherein the ignition device comprises a remote signaler to remotely ignite the flammable mixture. 
     
     
         30 . The apparatus of  claim 1  wherein the fuel is a liquid fuel or a gaseous fuel. 
     
     
         31 . The apparatus of  claim 1  adapted to be lowered into a wellbore on a wireline, production tubing, coiled tubing, or any combination thereof. 
     
     
         32 . The apparatus of  claim 1  wherein the at least one inlet port is configured to provide a continuous supply of air to the pulse detonation combustor during the operation of the combustor. 
     
     
         33 . The apparatus of  claim 1  wherein the first and second sealing mechanisms comprise a pair of expandable packers. 
     
     
         34 . The apparatus of  claim 1  further comprising means to introduce a proppant into the fractures. 
     
     
         35 . A method of fracturing subterranean formations comprising the steps of:
 (a) deploying at least one pulse detonation combustor into production tubing disposed within a wellbore;   (b) positioning the pulse detonation combustor in an isolated zone within the wellbore, wherein the isolated zone is adjacent to a portion of the formation to be fractured;   (c) commencing a pulse detonation cycle by,
 (i) creating a flammable mixture comprised of a fuel and oxidant mixture in the pulse detonation combustor by injecting a controlled amount of fuel from a fuel source and controlled amount of oxidant from an oxidant source into the pulse detonation combustor, wherein both the fuel source and oxidant source are located at the surface; 
 (ii) igniting the fuel and oxidant mixture to cause a detonation, wherein the detonation within the pulse detonation combustor generates a supersonic shockwave; and 
 (iii) purging combustion products of the detonation from the pulse detonation combustor; 
   (d) directing the shockwave into the subterranean formation; and   (e) repeating steps (i)-(iii) at a selected time and frequency sufficient to generate a series of repeating supersonic shock waves, thereby causing propagation of multiple fractures in the formation.   
     
     
         36 . The method according to  claim 35  wherein the isolated zone is formed by a first and second sealing mechanism secured within the wellbore. 
     
     
         37 . The method according to  claim 35  wherein the isolated zone is aligned with perforations in the production tubing, well casing, or both. 
     
     
         38 . The method according to  claim 35  wherein the pulse detonation combustor comprises:
 a combustion region defining a fluid flow path; 
 a mixing region for producing the flammable mixture comprising a controlled volume of fuel and oxidizer, wherein the mixing region is in fluid communication with the at least one inlet port and the combustion region; 
 an ignition device configured to periodically ignite the flammable mixture; and means for initiating a series of repeating detonations. 
 
     
     
         39 . The method of  claim 35  wherein the step of purging the pulse detonation combustor comprises introducing a buffer into the pulse detonation combustor after igniting a fuel and oxidant mixture from a previous cycle and before commencing a next pulse detonation cycle. 
     
     
         40 . The method of  claim 35  further comprising the step of introducing a proppant into the fractures. 
     
     
         41 . The method according to  claim 35  further comprising the step of controlling the time and frequency of the pulse detonation cycle by a programmable digital signal processor. 
     
     
         42 . The method according to  claim 35  wherein the pulse detonation combustor provides shockwaves at a frequency in the range from about 0.1 millihertz to 100 hertz, preferably 0.2 millihertz to 5 hertz, and more preferably 0.01-0.2 Hertz. 
     
     
         43 . The method according to  claim 35  wherein two or more pulse detonation combustors are connected in series. 
     
     
         44 . A method of fracturing subterranean formations comprising the steps of:
 establishing a wellbore extending to the subterranean formation; and   deploying a pulse detonation apparatus for generating repeating, supersonic shockwaves within the interior of the wellbore at a selected time and frequency sufficient to produce multiple fractures in the subterranean formation without causing damage to the wellbore and to further extend the fractures until at least one hydrocarbon fluid fracture is intersected.   
     
     
         45 . A system for fracturing a subterranean/subterranean/geologic formation, comprising:
 means for establishing a wellbore extending to the subterranean formation; and a pulse detonation apparatus for generating repeating, supersonic pulses within the interior of the wellbore with a total number of pulses sufficient to produce multiple fractures in the subterranean formation and further extend the fractures until at least one hydrocarbon fluid fracture is intersected.