Patent Application
20080073079
In a preferred embodiment, in situ stimulation of a hydrocarbon-containing material, particularly heavy oil (otherwise known as low-API oil), is provided that includes the following operations:
Many of the world's heavy oil deposits are located at relatively shallow depths (less than 2,000 feet) while others are much deeper. Shallow formations are problematic for conventional water flooding and steam injection stimulation production owing to poor ground competence and fracturing and channeling, all of which result in a very low net oil recovery. At greater depths, hot fluid injection techniques must suffer high energy losses on the downhole passage and other stimulation techniques, such as electrical and acoustic stimulation, are disadvantaged by power losses in connecting cables, breakage of cables, and actuator units, including electrical components, difficulty in precise placement and frequent inability to recover hardware.
In both the shallow and deep formation scenarios, nearly all of the attendant engineering and production difficulties can be eliminated if direct access can be gained to the hydrocarbon-bearing formation. Accordingly, the present invention creates an underground excavation, such as a tunnel, to provide access to the hydrocarbon-bearing formation from the ground surface. The excavation enables formation stimulation to substantially the entire hydrocarbon-bearing formation region of interest and, in doing so, enables a high net recovery of hydrocarbon-containing materials from the region, thereby depleting substantially the formation region. The excavation, in conjunction with the stimulation techniques disclosed herein, enables the sequential and systematic drainage of the hydrocarbon-bearing formation, section-by-section, without the need to stimulate simultaneously the entire formation region as is the case with other stimulation methods. Because of the relative inability of the natural high-viscosity hydrocarbon-containing materials to flow freely throughout the formation, there is little opportunity for the untapped hydrocarbon-containing materials in one region to backflow into an adjacent depleted region. Hydrocarbon recovery is, in one configuration, by means of a directionally drilled horizontal well placed at or near the bottom of the hydrocarbon-bearing formation “pay zone” and which essentially follows the tunnel direction.
As can be appreciated, the present invention is entirely compatible with conventional, surface-mounted, enhanced drive processes, such as gas injection, for the purpose of driving the liberated oil downward toward the producing well.
Referring now to
The system 108 includes a lined access excavation 112, a lined stimulation excavation 116, an electromagnetic radiation generation, transmission, and irradiation assembly 120 extending a length of the stimulation excavation 116, surfactant injection wells 124a-c positioned at intervals along the length of the excavation 116, and acoustic energy emitters 128a-c also positioned at intervals along the length of the excavation 116.
The lined access excavation 112 may be any suitable excavation providing access from the surface 132. Examples include shafts, declines, and inclines.
The lined stimulation excavation 116 extends from the lined access excavation 112, is substantially sealed from fluids in the surrounding formations, and can be any suitable excavation that generally follows the strike and/or dip of the hydrocarbon-bearing formation 100. Examples of suitable excavations 116 include tunnels, stopes, adits, and winzes. The excavation 116 may be positioned above (as shown), in, or below the hydrocarbon-bearing formation 100. Preferably, the excavation 116 is placed along the top of the formation 100 so that the formation 100 is directly accessible at the excavation floor. The excavation is typically relatively small (e.g., from about 4 to about 15 feet and more typically from about 6 to about 8 feet in diameter), is lined with a liner such as concrete or cement, and is suitably reinforced and fitted with apertures in the liner to expose the formation 100 to radiation emitters.
The electromagnetic radiation generation, transmission, and irradiation assembly 120 imparts one or more selected wavelength bands of electromagnetic radiation to a selected portion or region of the hydrocarbon-bearing formation 100. As will be appreciated, the higher the frequency of the electromagnetic radiation the higher the attenuation and lower the penetration depth in the formation, and the lower the frequency the lower the attenuation and higher the penetration depth in the formation. The frequency of the radiation preferably ranges from about Direct Current (DC) to about 10 GHz, more preferably in a power frequency band of from about DC to about 60 Hz Alternating Current (AC), in the short wave band of from about 100 kHz to about 100 MHz, and/or in the microwave band of from about 100 MHz to about 10 GHz, with the microwave band in the range of from about 100 MHz to about 3 GHz being particularly preferred.
When the radiation is in the microwave band, the assembly 120 includes a waveguide 136 having multiple, regularly spaced antenna or radiating elements 140a-k, a generator 144, and timer 148. The waveguide 136 can have any suitable configuration for the set of radiation frequencies to be transported by the waveguide 136. For example, an exemplary waveguide could include a metal cylinder having any desired cross sectional shape, which is commonly rectangular. Likewise, the particular configuration of the antenna elements depends on the particular set of radiation frequencies to be emitted. For example, each element can be configured as a resonant slot. In one configuration, the emitted electromagnetic radiation (shown as arcs emanating from each element 140) is a set of different frequencies having differing penetration depths into the formation to heat the formation to differing degrees. As will be appreciated, lower frequencies travel with less attenuation than higher frequencies in the formation. The generator 144 can be any suitable generating device, such as a magnetron or klystron. Finally, the tuner 148 can be any suitable tuning device to provide propagation characteristics in the waveguide that reduce substantially, or minimize, reflected electromagnetic radiation. The tuner 148, for example, may be a tunable dielectric material, such as a thin or thick film or bulk ferrite, ferromagnetic, or non-ferrous metallic material.
Each of the antenna elements 140a-k has a corresponding impedance transformer 152a-k positioned in the excavation liner to match the waveguide field impedance to the impedance of the formation 100 and couple the electromagnetic radiation to the adjacent formation. Because the formation 100 is directly accessible through the liner of the excavation, there is no need to drill holes for placement of the antenna elements within the formation, as is the case with all other RF or microwave stimulation methods. Furthermore, the assembly 120 is completely removable at the completion of the stimulation process.
Although any suitable impedance matching material or materials may be used, a preferred impedance transformer 152a-k is a “pillow” block of a special material, such as a ceramic material, that interfaces between the waveguide and the formation 100. The principal property of the impedance transformer is its intrinsic impedance, which must be designed to fall at approximately the average value of the two impedances being “matched”, in this case the typically air-filled waveguide (having an intrinsic impedance of about 377 ohms) and the formation 100 whose intrinsic impedance is given by:
η=√(jωμ)/(σ+jωε)
where
The permittivity value is dependent on temperature, frequency, and the relative soil/water ratio, which, for a typical heavy oil formation, yields an impedance of approximately 80 ohms. A preferable transformer therefore has a stepped or graded impedance from about 377 ohms to about 80 ohms. Alternatively, the impedance transformation may be incorporated into the antenna element by designing the radiating slots in the waveguide to have a low near-field impedance, i.e., a ratio of electric to magnetic field magnitudes of the order of about 80. In this manner, the electromagnetic energy may be coupled efficiently to the formation 100.
The antenna elements 140a-k preferably intermittently emit radiation into the hydrocarbon-bearing formation. Beam steering or scanning techniques may be employed to direct the radiation into selected areas but not in others and/or to direct differing amounts of radiation into differing areas. By way of example, rather than irradiating in a 180 degree arc as shown beam steering may be used to irradiate in a 90 degree arc. In another example, the radiation may be beam steered so that it emanates from the antenna element in the same manner as a windshield wiper moving across a car's windshield.
As will be appreciated, a system of sensors (not shown) embedded in the hydrocarbon-bearing formation 100 and computer (not shown) can be used to control generation and emission of electromagnetic radiation from the assembly 120. The computer receives control feedback signals from an interface that is connected to telemetering lines (not shown). The telemetering lines are in turn connected to the sensors. Each sensor monitors the amount of radiation reaching the underground location where that sensor is located and/or the formation temperature at that location. Preferably, the formation temperature in the selected formation region is maintained from about 200 to about 350 degrees Celsius and even more preferably from about 250 to about 300 degrees Celsius. At these temperatures, the heavy oil and bitumen normally has a viscosity of no more than about 10 Cp and even more normally of from about 1 to about 5 Cp.
In one operational configuration, the generator 144 is turned on and off to emit radiation into the formation 100 only during selected, discrete time periods. The time periods may of uniform length or differing lengths depending on the application. It is believed that intermittent irradiation of the selected region of the formation 100 can produce a flow of hydrocarbon-containing material that is greater than that produced by continuous irradiation of the region. Intermittent irradiation of the deposit further represents a lower consumption of thermal energy to recover a selected volume of hydrocarbon-containing material and prevents overheating near the antenna elements, thereby allowing the deposited heat energy to dissipate through the selected formation region and making maximum use of the available microwave power.
In one operational configuration, the radiation is emitted, at least initially, at incrementally increasing radiation power. As in the prior embodiment, the radiation may be emitted intermittently.
In one operational configuration, alternate sets of antenna elements are energized at different times. In other words, a first set of antenna elements are energized at a first time while a second set of antenna elements are energized at a second, normally nonoverlapping, time. This permits the emitted microwave energy to affect a larger portion of the formation and allows the heat to dissipate into the formation between alternating cycles.
The action of the radiated electromagnetic radiation heats the fluids within the formation 100 (water and asphaltenes are good receptors), thereby substantially reducing fluid viscosity. For a single waveguide, the affected heated region will be the angular bandwidth directly beneath the waveguide, being approximately +/−60 degrees from the vertical (normal) direction. Given the relatively small thickness of the typical formation “pay zone”, the use of microwave frequencies is beneficial since there is no need to transmit high power densities over long distances as is the case with all other RF and microwave heating techniques. This makes it possible to take advantage of the high absorption of receptive oil and water molecules at these frequencies.
The surfactant injection wells 124a-c introduce, under pressure (via pump 200), an aqueous solution including one or more surfactants into the formation 100. The primary purpose of the aqueous fluid is not to effect a bulk fluid displacement of the hydrocarbon-containing material but rather, in synergistic combination with the acoustic and microwave stimulation, to reduce effectively the hydrocarbon-containing material viscosity and enhance its release from the formation matrix. This may, for example, result from the creation of fluid flow channels through the thickness of the pay zone, which are known to enhance the effectiveness of acoustic stimulation. Unlike most other fluid transport enhancement techniques, the occurrence of “channeling” is not detrimental in the present invention and the fluid flow direction is downward under the force of gravity instead of laterally between vertical wells. In this respect, the invention is somewhat similar to gravity drainage.
The surfactant can be any substance that reduces surface tension in the hydrocarbon-containing material or water containing the material, or reduces interfacial tension between the two liquids or one of the liquids and the surrounding formation. For example, the surfactant can be a detergent, wetting agent or emulsifier. Preferred surfactants include aqueous alkaline solutions (formed from hydroxides, silicates, and/or carbonates), oxygen-containing organic products of the oxidation of organic compounds (e.g., oxygen-containing functional groups, such as aldehydes, ketones, alcohols, and carboxylic acids, that are more soluble and polar than the original organic compound), demulsifiers (such as pine oil and other terpene hydrocarbon derivatives), and mixtures thereof.
The concentration of surfactant required is lowered due to the synergistic combination of surfactant with acoustic energy.
The acoustic energy emitters 128a-c introduce acoustic energy (shown by arcs emanating from emitters) into the formation 100 to disperse the surfactant and effect viscosity reduction of the hydrocarbon-containing material. While not wishing to be bound by any theory, it is believed that a sound wave passing through a viscous liquid, such as water, causes a vibration pattern that sets the liquid in motion. Acoustic vibration patterns form water molecule layers that stretch, compress, bend, and relax. Interacting layers generate tiny vacuum spaces called cavitations within the liquid. Imploding cavitations scrub surfaces and pull away foreign matter.
It is postulated that when acoustic energy is applied to a hydrocarbon-bearing formation one or more of the following changes in formation properties is realized: alteration of reduction in adherence of wetting films to the rock matrix due to nonlinear acoustic effects (such as in-pore turbulence, acoustic streaming, cavitation, and perturbation in local pressures), reduction in surface tension, density, and viscosity from heating by acoustic energy, increased solubility of surfactants and reduction of adsorption of surface-acting components, deposition of paraffin wax and asphaltenes, permeability and porosity increase due to deformation of pores and removal of fine particles or increase in the flow by reduced boundary layer of immobile phase, reduction of capillary forces due to the destruction of surface films, coalescence of hydrocarbon-containing material drops due to the Bjerknes forces that cause a continuous stream of water, oscillation and excitation of capillary trapped hydrocarbon-containing material drops due to forces generated by cavitating bubbles and acoustic/mechanical vibration in the rock and fluids, emulsification generated by intense sound vibration and the presence of natural or introduced surfactants, sonocapillary effects, and/or peristaltic transport caused by the deformation of the pore walls.
Which effect(s) predominates depends on the frequency and intensity of the acoustic energy. At higher intensity, mechanical stresses increase markedly and therefore temperature increases. Frequency can play an important role in wave dispersion, attenuation, and heat dissipation.
Although acoustic energy frequencies in the subsonic and lower and upper sonic bands may be employed, the preferred frequency of acoustic energy is in the ultrasonic or supersonic frequency spectrum and the intensity of the energy is at least about 10 watts per square inch and more preferably ranges from about 50 to about 100 watts per square inch in the immediate vicinity of the acoustic transducer. The acoustic energy can be in analog (sinusoidal) or digital (pulsed) form. Digital acoustic energy permits adjustment of the cavitation response for the specific application.
In one configuration, multiple acoustic energy frequencies are intermixed to use multiple of the effects noted above. In this configuration, complex or modulated vibrational waves are derived from the combination of multiple sinusoidal waves of dissimilar frequencies. The wave components of the complex wave may bear a harmonic relationship to one another, i.e., the frequency of all but one (the fundamental wave) of the component waves may be an integral multiple of the frequency of the one fundamental wave. Such complex waves may be formed by the use of multiple wave generators.
Each emitter 128 includes a power source 204, a wave generator 208, a transducing medium 216, and a coupler 212 between the power source 204 and generator 208. Although the emitters 128 are depicted as being positioned in a drilled hole, it is to be understood that the emitters 128 can be in the form of flat plate transducers that are bolted or otherwise secured to the formation. The use of flat plates is permitted because the formation 100 is accessible through the liner. Upon completion of the stimulation procedure, the emitters are dismounted and reused elsewhere.
The power source 204 can be mechanical (e.g., an engine or motor) or electrical (e.g., a generator, battery, capacitor bank, etc.).
The generator 208 can be mechanically or electrically driven and capable of introducing large amounts of acoustic energy into the formation 100.
Suitable mechanical generators 208 include, for example, sonic pump and motor assembly. In one example of a mechanical wave generator, a motor and generator assembly is located at in the stimulation excavation. The motor (or power source 204) rotates a cam (not shown) to effect vertical movement of a roller bearing resting on the cam. The roller bearing is fastened to a rod that is pivoted about a point and is counterbalanced by an adjustable weight. A further coupling rod is attached to the rod by a pivot. The rotation of the cam produces a reciprocating motion of the rod through the bearing. The motion is transmitted by the coupling rod to the transducing medium in the drilled hole, which releases acoustic energy into the formation 100. The preceding exemplary generator, and other possible mechanical generator designs, are discussed in U.S. Pat. No. 2,670,801, which is incorporated herein by this reference.
Suitable electrical generators 208 include sonic and supersonic horns, piezo-electric crystals coupled with low or high frequency oscillating electrical currents, magneto-restrictive devices positioned in an alternating magnetic field, and the like.
The transducer or transducing medium 216 is preferably a solid or liquid medium. Under certain conditions, such as those prevailing in high pressure formations, gaseous media may be used. The transducing medium 216 may be, for example, water and other liquids, cement or concrete, plastic, melted or solidified alloys, or some other material lodged within or in the vicinity of the formation 100.
The relative timing of surfactant injection and acoustic energy emission depends on the application. The surfactant may be injected before and/or during acoustic energy emission. In one configuration, the surfactant is injected at a point called the acoustic slow wave point at which the motion of the solid and pore liquid is 180 degrees out of phase. At this point, the pore liquid and solid have the maximum amount of relative motion. When excited at the slow wave frequency, on alternate sound wave half cycles, the maximum amount possible of pore fluid is moved from previously inaccessible pores adjacent to the percolation flow path into the flow path for removal and collection. On intervening acoustic wave half cycles, fluid containing surfactants from the percolation flow path is injected into the surrounding pores in the rock, thus increasing the size of the percolation flow domain. Accordingly, both ultrasound half cycles perform useful functions for secondary oil recovery; that is, removing previously inaccessible oil from rock surrounding the percolation flow path and enlarging the area of the oil reservoir accessible to surfactants and percolation flow. Regardless of the particular timing of surfactant injection and acoustic energy emission, viscosity reduction can be substantial, with a reduction of at least four orders of magnitude being possible.
The hydrocarbon material, after exposure to the electromagnetic radiation and acoustic energy and contact with the surfactant, flows to a production well 170 positioned in proximity to the excavation 116 and generally having a bearing parallel to the bearing of the excavation 116. The production well 170 is preferably formed by directional drilling techniques and located within the stimulated region, or irradiated region, of the formation 100. When the formation 100 comprises multiple zones, the well 170 is placed beneath the lowermost zone. The production well 170 is cased with a well casing (not shown) which extends from the surface to a position proximal to the formation 100, and a perforated liner 51 containing perforations (not shown) through which the hydrocarbon-containing material flows and is collected by the well 170. Pump tubing (not shown) extends into the well 170 and is fitted with a standing valve (not shown) that permits an upward liquid flow and prevents reverse flow. The upward flow is maintained by a traveling valve (not shown) which is actuated by a sucker rod (not shown). The sucker rod is in turn actuated by a motor (not shown) at the surface 132. The well casing is sealed with a casing head (not shown). The casing head is fitted with a packing gland (not shown) through which the pump tubing passes. The collected hydrocarbon-bearing material is stored at the surface 132 in a storage tank (not shown).
With reference to
To facilitate a more efficient electromagnetic heating effect and substantially minimize the unrecovered portion of the pay zone, the electromagnetic beam is steered laterally (in a cross-excavation direction) by incorporating a second waveguide (not shown) along the excavation floor alongside the first waveguide and separated from the first by a distance of at least about 4 inches (or about one-quarter wavelength at the microwave frequency of 915 MHz). By adjusting the relative phase of the microwave signals in the adjacent waveguides, one may effectively steer the radiation beam so as to increase the lateral coverage and enable a wider tunnel separation, with only a substantially minimal amount of unrecoverable pay zone. As will be more fully disclosed below, net hydrocarbon-containing material recoveries approaching 80% may be realized, and in much shorter time periods, than is possible with other stimulation methods.
As will be understood by one familiar with the prior art, there is considerable advantage to the simultaneous combination of electromagnetic, acoustic, and fluid stimulation techniques as disclosed herein.
Extensive computer reservoir modeling analyses were conducted for several heavy oil scenarios in Cold Lake, Alberta, Canada to evaluate the expected performance of microwave stimulation. The reservoir parameters are as follows:
A single vertical microwave (915 MHz) emitter was located in the center of a cylindrical test area with diameter 150 meters. Oil “recovery” was modeled as oil which reached the bottom of the test cylinder. The cylinder bottom coincided with the bottom of the pay zone. The simulation was run with 100 kW of microwave power for the first 150 days and 70 kW thereafter. Microwave power was switched on and off according to a set thermostat temperature of 300 degrees (max) to 280 degrees Celsius (minimum). The simulation run time was three years (
For the same Cold Lake reservoir parameters as in Example 1, a single microwave emitter (100 kW at 915 MHz) was located at the center of a 150 m by 150 m area directly above a horizontal recovery well, which was located at the bottom of the pay zone. The microwave power supply was thermostatically controlled as in Example 1. The simulation time was 10 years (
For the same Cold Lake reservoir arrangement as in Example 2, an arrangement of four vertical microwave emitters were positioned 25 m apart and along a horizontal recovery well. Each injector antenna provided 25 kW of microwave power at 915 MHz and the sources were thermostatically controlled as in Example 1. The simulation time was 10 years (
A number of variations and modifications of the invention can be used. It would be possible to provide for some features of the invention without providing others.
For example in one alternative embodiment, the surfactant is not injected into the formation 100 but is generated in situ by hydrous pyrolysis/partial oxidation of constrained organics, such as petroleum and petroleum products, including fuel hydrocarbons, polycyclic aromatic hydrocarbons, chlorinated hydrocarbons, and other volatile materials. The materials are contained in groundwater in the formation 100. When oxidized, the organic material produces intermediate oxygenated organic compounds, e.g., surfactants and precursors thereof. The intermediate oxygenated organic compounds, as noted above, have oxygen-containing functional groups, such as aldehydes, ketones, alcohols, and carboxylic acids. The surfactants are formed in situ by introducing into the formation 100 an oxidant, such as steam (or air) and/or mineral oxidants, a catalyst of the organic partial oxidation (such as manganese dioxide or ferric oxide), and thermal energy in the form of electromagnetic radiation.
In another alternative embodiment, the various elements noted above, namely electromagnetic radiative heating, acoustic energy stimulation, and surfactant injection are used alone or in any combination to stimulate the reservoir.
The present invention, in various embodiments, includes components, methods, processes, systems and/or apparatus substantially as depicted and described herein, including various embodiments, subcombinations, and subsets thereof. Those of skill in the art will understand how to make and use the present invention after understanding the present disclosure. The present invention, in various embodiments, includes providing devices and processes in the absence of items not depicted and/or described herein or in various embodiments hereof, including in the absence of such items as may have been used in previous devices or processes, e.g., for improving performance, achieving ease and\or reducing cost of implementation.
The foregoing discussion of the invention has been presented for purposes of illustration and description. The foregoing is not intended to limit the invention to the form or forms disclosed herein. In the foregoing Detailed Description for example, various features of the invention are grouped together in one or more embodiments for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the following claims are hereby incorporated into this Detailed Description, with each claim standing on its own as a separate preferred embodiment of the invention.
Moreover, though the description of the invention has included description of one or more embodiments and certain variations and modifications, other variations and modifications are within the scope of the invention, e.g., as may be within the skill and knowledge of those in the art, after understanding the present disclosure. It is intended to obtain rights which include alternative embodiments to the extent permitted, including alternate, interchangeable and/or equivalent structures, functions, ranges or steps to those claimed, whether or not such alternate, interchangeable and/or equivalent structures, functions, ranges or steps are disclosed herein, and without intending to publicly dedicate any patentable subject matter.
The present application claims the benefits of U.S. Provisional Application Ser. No. 60/827,012, filed Sep. 26, 2006, entitled “Means for the Stimulation and Recovery of Heavy Hydrocarbon Fluids”, and 60/867,537, filed Nov. 28, 2006, of the same title, each of which are incorporated herein by this reference.
| Number | Date | Country | |
|---|---|---|---|
| 60827012 | Sep 2006 | US | |
| 60867537 | Nov 2006 | US |
