Patent Application
20130161007
Formation fracturing is becoming an important tool for hydrocarbon production. There is an increasing need to produce hydrocarbons from wells in subterranean formations that contain a sufficient volume of hydrocarbon fluids, but have low permeability or restricted flow near the wellbore so that production is slow or difficult and, thus, not economical. In addition to oil and/or gas producing wells, formation fracturing is also an important tool for injection wells, storage wells, brine or water production wells, and disposal wells.
Flow of a fluid, such as oil or gas, through a porous medium, i.e. a subterranean formation, is directly related to the permeability of the formation. A formation with low permeability can occur naturally due to the geological conditions of the formation. Low permeability can also be caused by damage to the formation from drilling, cementing and perforating operations. Further, mature wells can incur damage from the buildup of fine particulates and contaminants. If permeability can be increased in these formations, more fluid can be recovered.
It is known that one way to increase production and permeability within a formation is artificial stimulation through “well fracturing.” Various fracturing procedures have been introduced and used, including: (1) hydraulic fracturing; (2) explosive fracturing; (3) various chemical treatments (usually acids); (4) high energy gas fracturing or controlled pulse fracturing; and (5) combinations of the above.
Originally, devices and materials such as nitroglycerin, dynamite or other high energy materials that produce “explosive” events were used to increase fluid flow around the wellbore of an oil or gas production well. This method of formation fracturing is called explosive fracturing and is associated with a rapid pressure rise over a short time period. The success of this method has been limited, however, due to safety hazards and because frequently the explosive compaction of the formation opposite to the explosion fracture causes formation and wellbore damage, which results in a decrease rather than increase of permeability.
Currently, the most common method of formation fracturing is hydraulic fracturing. Hydraulic fracturing increases formation permeability by slowly pumping a fluid into the formation, which in turn creates a slow pressure rise in the formation. Fluid pressure is steadily increased until the tensile strength of the rock formation is exceeded. At that point, a fracture will be initiated that propagates from opposite sides of the wellbore into the formation. Because the increased fluid pressure flows to the point of least resistance, a single bidirectional fracture typically is formed. Although this method is successful, the equipment and labor involved in hydraulic fracturing is extensive and expensive. There are also growing concerns regarding the environmental consequences associated with hydraulic fracturing due, in part, to the huge amounts of water that are required and the variety of chemicals that are used in connection with hydraulic fracturing.
The third type of well fracturing used in lieu of hydraulic fracturing or explosive fracturing is called “high energy gas fracturing” or “propellant fracturing.” This method employs propellant deflagration technology to create a more rapid pressure rise than that seen in hydraulic fracturing, but less rapid than during an explosive fracturing regime. “Deflagration” refers to the rapid burning of a material at faster rate than normal combustion, but at a rate slower than detonation. Propellant deflagration produces a good distribution of radial fractures around a wellbore and can be employed in lieu of hydraulic fracturing techniques as a more cost effective manner to create and propagate fractures. The resulting radial fractures, however, do not penetrate deep enough into the formation (i.e only 50-75 feet) and thus it is often necessary to combine them with, for example, hydraulic fracturing or chemical treatments.
Each of the current methods of formation fracturing thus have drawbacks. Pulse detonation devices, in general, are known and have been considered for use in jet aircrafts for propulsion, coal gasification, impulsive cleaning systems and medical cleaning devices. A pulse detonation device is an apparatus which produces high pressure exhaust from a series of repetitive detonations within a detonation chamber. The process is a constant volume heat addition process. The gaseous fuel is detonated within a chamber, causing a pulse detonation wave which propagates at supersonic speeds. The detonation wave compresses the fluid within the chamber, increasing its pressure, temperature and density, and producing a series of high-intensity, high-decibel blasts.
In pulse detonation combustors, a mixture of fuel and oxidizer, such as air, is ignited and either transitioned from deflagration to detonation, or detonated via direction initiation (DI), so as to produce detonation waves. The deflagration to detonation transition (DDT) or DI of detonation typically occurs in a tube or pipe structure.
In one aspect of the invention, a pulse detonation tool for fracturing subterranean formations is adapted to be lowered into a production tubing disposed within a wellbore and comprises a first and 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 a 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 tool; 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.
Another aspect of the invention includes 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.
In another aspect of the invention, a method of fracturing subterranean formations comprises 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 further extend the fractures until at least one hydrocarbon fluid fracture is intersected.
Another aspect of the invention includes 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 repeated, supersonic pulses within the interior of the wellbore with a total number of pulses to produce multiple fractures in the subterranean formation and further extend the fractures until at least one hydrocarbon fluid fracture is intersected.
The nature and various additional features of the invention will appear more fully upon consideration of the illustrative embodiments of the invention which are schematically set forth in the figures. Like reference numerals represent corresponding parts.
Embodiments of the present invention will be explained in further detail by making reference to the accompanying drawings, which do not limit the scope of the invention in any way.
Turning now to
Embodiments of PDCs include a means of igniting a fuel/oxidizer mixture, for example a fuel/air mixture, and a detonation chamber, in which pressure wave fronts initiated by the ignition process coalesce to produce a detonation wave. Each detonation or quasi-detonation is initiated either by external ignition, such as spark discharge or laser pulse, or by gas dynamic processes, such as shock focusing, autoignition or by another detonation (i.e. cross-fire). Pulse detonation may be accomplished in a number of types of chambers including detonation tubes, shock tubes, resonating detonation cavities and annular detonation chambers, for example. In addition, a PDC can include one or more detonation chambers. The structure and construction of the pulse detonation combustor 101 is that of any known pulse detonation combustor type device, and the present invention is not limited in this regard.
In one or more embodiments, pulse detonation combustor 101 includes an ignition chamber 110 and a combustion region, or detonation chamber, 120. The ignition chamber 110 and the detonation chamber 120 can be formed as a contiguous region, as in
In the embodiment shown in
As used herein, “wellbore”, “borehole” and “well” are used interchangeably and should not be considered of varying scope.
Tubular housing 102 is preferably fabricated from a steel or like material having sufficient wall thickness and strength that it will not be destroyed during the pulse detonation cycle. Similarly, each of the components of tool 100 described herein should be formed from strong, durable materials and securely mounted so as to withstand the high pressures, repeated shock waves and thermal deformations from the repeated detonations and to resist fluid pressure in the wellbore during the pulse detonation cycle.
In the embodiment shown in
Configured as a shock tube, tubular housing 102 contains and isolates the flammable mixture from production tubing 300 so as to confine combustion, or detonation, waves 20 generated by the repeating detonations to within tubular housing 102. Tubular housing 102 further comprises a plurality of spaced nozzles 80 along the length of the circular side wall 105. Nozzles 80 are located at spaced intervals. Each nozzle 80 extends radially outward and is configured to direct or aim the shock waves 30 generated by the repeating detonations in a substantially axial direction into the subterranean formation 305. Nozzles 80 are adapted so that tubular housing 102 can be lowered into and subsequently removed from wellbore 304. For example, in one embodiment, nozzles 80 can be telescoping.
In the embodiment shown here, fuel inlet port 50 is also configured to supply a buffer to pulse detonator combustor 101, wherein the buffer is any nonflammable fluid. In this embodiment, the buffer is different from the fuel and oxidant and introduced separately. One of ordinary skill in the art would recognize, however, that a buffer and buffer inlet is not required if there is sufficient time between detonation cycles to allow the combustion products remaining in the pulse detonation combustor 101 to cool below autoignition temperature of the fuel-oxidizer mixture for the next detonation cycle. Furthermore, even if a buffer is required, one of ordinary skill in the art would recognize that either the fuel or oxidizer could be used as the buffer by configuring and adjusting valve assembly 80, thereby eliminating the need for a separate buffer and buffer inlet.
Referring now to
First sealing mechanism 200 has at least one first inlet port 50 configured to allow a fuel, an oxidizer and a buffer to flow into pulse detonation combustor 101 disposed within isolated zone 210. In the embodiment shown in
Additionally, in the embodiment shown in
Referring again to
Tool 100 also comprises at least one valve assembly disposed within tubular housing 102. The at least one valve assembly is configured to achieve controlled delivery of the fuel, oxidizer and buffer to tool 100. In the embodiment shown in
As used herein, the term “valve” or “valve assembly” is intended to describe any device that turns on and off a flow at a high frequency, namely, faster than or equal to the time scale of one pulse detonation combustion cycle. Valves 80a-c are configured in accordance with pulse detonation technology known to one of ordinary skill in the art, and may be either a passive check valve or active valve, or a combination of both. Furthermore, one of ordinary skill in the art could configure a single valve to achieve controlled delivery of the fuel, oxidizer and/or buffer. As shown in
Although not shown, in other embodiments, the valve assembly is located outside of tubular housing 102 but within isolated zone 210. In still further embodiments, the valve assembly is located upstream of the isolated zone 210 defined by sealing mechanisms 200/201. For example, in these embodiments, fuel valve 51 a is disposed between the fuel source and inlet port 51a, and oxidizer valve 51b is disposed between the oxidizer source and inlet port 51b. In exemplary embodiments, tool 100 also comprises means for preventing backflow of the fuel or flammable mixture towards the surface within the production tubing 300.
Pulse detonation combustor 101 is detonated by suitable detonation means connected to ignition device 10. In this embodiment, ignition device 10 is located within ignition chamber 110 and is arranged downstream from the fuel and oxidizer inlets. Ignition device 10 comprises at least one ignition point, as shown in
In further embodiments, ignition device 10 comprises an external power source, timing device and remote signaler configured to remotely ignite the flammable mixture exiting mixing chamber 130, wherein the timing of ignition is predetermined and controlled via one of ordinary by one skill in the art. In an embodiment where there is no separate mixing chamber, the location of the ignition device 10 is arranged based upon the optimum ignition location for fuel-oxidizer mixing. For example, the ignition device 10 can be placed downstream of the fuel inlet port to provide time for the fuel to mix with the oxidizer. Ignition device 10 should also be placed upstream of any detonation-creating obstacles that may be located in the detonation chamber.
Ignition chamber 110 and detonation chamber, or combustion region, 120 define a fluid flow path in flow communication with mixing chamber 130, as illustrated in
Pulse detonator combustor 101 also comprises means for initiating a series of repeating detonations that in turn generate a series of repeating supersonic, high impulse shock waves 30. In one embodiment, as shown in
It is to be noted that the invention is not limited to the use of a particular DDT geometry. Any suitable DDT geometry can be used to increase turbulence. Similarly, detonation chamber 120 can be arranged without DDT geometry or with other means for initiating a series of repeating supersonic shock waves known to those skilled in the art. For example, in alternate embodiments, the means for initiating a series of repeating detonations comprises direct initiation (DI) detonation methods, such as a high energy laser, spark, or other shock-to-detonation methods suitable for achieving direction initiation (DI) of detonation. In practicing the invention, one of ordinary skill in the art would recognize that DI of detonation is preferable over DDT if circumstances allow for lower frequency requirements, high pressure in the well bore, and the appropriate fuel-oxidizer mixtures. In addition, the fuel-oxidizer ratio can be supplied so that there is a slightly fuel-rich mixture in the ignition chamber 110 to improve the selected means for initiating a series of repeating detonations . This can be accomplished by controlling the flow of fuel and oxidizer into the ignition chamber 110 via valve assembly 80.
Referring to
In practice, and referring again to
Tool 100, which includes sealing mechanism 200/201, is then lowered into the wellbore 304 to a depth adjacent to the particular section of subterranean formation 305 to be fractured. In the example shown in
Prior to lowering the tool 100 into the wellbore 304, the location, distance and direction of the at least one natural hydrocarbonaceous fluid fracture is determined. Furthermore, the characteristics of the subterranean formation 305 are determined and used to construct a pulse detonation combustor 101 with the desired pulse detonation characteristics for the particular formation such that optimum radial fractures can be achieved within the subterranean formation 305. These determinations can be made by geologists and others skilled in the art.
Once tool 100 is properly positioned within the well to create an isolated zone 210 adjacent to both the perforations 306 and the portion of the formation to be fractured, the pulse detonation cycle is commenced. A controlled amount of fuel from fuel source 302 located on the surface, and a controlled amount of oxidizer from oxidizer source 303 located on the surface, are injected into mixing chamber 130 via fuel supply line 308, oxidizer supply line 309, and the respective inlet ports, to create a flammable mixture comprised of a predetermined fuel and oxidant mixture in the pulse detonation combustor 101.
The flammable mixture flows from the mixing chamber 130 to the ignition chamber 110 and is ignited. The flame then propagates into the detonation chamber and detonates within the detonation chamber 120, which in turn generates a supersonic shockwave. In the embodiment shown in
As illustrated in
These same steps are repeated at a predetermined, calculated time and frequency sufficient to generate a series of repeating, high impulse supersonic shock waves that cause propagation of multiple fractures 400 to extend further and further into the formation with each cycle. In practice, the precise number of repeated detonation “pulses”, or cycles, required to reach the desired fracture length will depend on the nature and characteristics of the formation. More specifically, in one example rock formation, the propagation of a fracture 1 cm in length requires 1000 detonation cycles. Therefore, in order to extend the fracture out 100 m into the formation, the pulse detonation cycle will require 10,000,000 pulses or cycles.
The repeating, high impulse shock waves have a pressure above the maximum fracture extension pressure but below that which would cause casing, wellbore or formation damage. In other words, the shock waves create a pressure loading rate sufficient to fracture the rock and create multiple radial fractures at the wellbore and extending into the formation, but low enough to avoid crushing the formation or casing adjacent to the wellbore. As such, the repeated “pulses” will allow fractures to continue their extension into the formation to obtain the required distances to reach the hydrocarbons in the formation.
In another embodiment, shown in
In this embodiment, both the combustion waves 20 and shock waves 30 generated by the repeating detonations extend into the fractures 400. More specifically, the flammable mixture is pushed into perforations 306 and thus into the subterranean formation. In one embodiment (not shown), combustion can be initiated in the production tubing and then transition into the fueled perforations or fractures within the formation. Alternatively, and as shown in
As shown in
As used herein, the terms “tubular housing” and “concentric liner” include tubes having a circular or alternatively non-circular cross-section. Exemplary hollow carriers or concentric liners include cylindrical tubes and tubes having polygonal cross-sections, such as, for example, hexagonal tubes. Each of the circular and non-circular cross-sections identified above may have a continuous cross sectional area, or the cross sectional area may vary. For example, in the exemplary embodiments shown in
In further embodiments, tool 100 comprises means to introduce a proppant into the fractures. Fractures have a tendency to close or collapse once the pressure in the formation is relieved. To prevent such closing when the fracturing pressure is relieved, fracturing techniques often employ a granular or particulate material, referred to as a “proppant,” that is left behind in the fractures. The proppant is used to keep the fracture open and thus provide a flow path through which hydrocarbons can flow. In one or more of the embodiments disclosed herein, the means to introduce proppants include mixing the proppant with the fuel, the oxidizer or both and the introduction of the proppant would start with the deflagration event pushing the proppant into the formation. In other embodiments, proppants could be entrained with the fracturing fluid or introduced via other means as is known in the art. A variety of proppants can be used depending on the geological conditions of the formation, including particulate materials, such as sand, glass beads and ceramic pellets, which create a porous structure.
It is noted that the above embodiments have been shown with respect to a single pulse detonation combustor. However, the concept of the present invention is not limited to single pulse detonation combustor. Furthermore, it should be expressly understood that any desired number of pulse detonation combustors could be employed in series, and that the dimensions, configurations, and compositions of tool 100 is within the discretion of the skilled artisan to meet the needs of a particular well.
Finally, in exemplary embodiments, a computer program can be used to model the pulse detonation cycle to predict the resulting generation of fracture propagation, and thereby determine a suitable configuration of tool 100 for fracture propagation in the surrounding formation. Tool 100 may also be equipped with remote pressure and temperature sensors, transducers, acoustic sensors, accelerometers (vibration sensors), chemical sensors such as oxygen sensor to confirm presence or absence of oxidizer] or other means known in the art to accurately monitor the pulse denotation cycle within the wellbore.
Although the apparatus and method of the invention is disclosed with examples that incorporate a cased well with production tubing that has been perforated, the apparatus and method of the invention are equally applicable to an open hold completion of a well.
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
