Title:
SONIC METHOD AND APPARATUS FOR AUGMENTING THE FLOW OF OIL FROM OIL BEARING STRATA
United States Patent 3578081
Abstract:
A source of sonic vibrational energy is tightly coupled to the walls of an oil well casing, this energy source being adapted to vibrationally distort the casing in an elliptical pattern. The casing is sonically energized in this manner, the sonic energy being transferred to the surrounding oil bearing strata to induce the migration of the oil particles therein into the well. The energy source may be two pairs of piezoelectric crystals oriented on axes normal to each other, or a pair of rollers driven around the longitudinal axis of the casing.
US Patent References:
Well flow stimulator
Brammer - December 1939 - 2184809
Piezoelectric motor
Williams et al. - April 1948 - 2439499
Recovery of hydrocarbons
Sherborne - March 1954 - 2670801
Means for loosening pipes in underground borings
Herbold - January 1956 - 2730176
Method for oscillating drilling
Herbold - August 1962 - 3049185
Well flow stimulator
Brammer - December 1939 - 2184809
Piezoelectric motor
Williams et al. - April 1948 - 2439499
Recovery of hydrocarbons
Sherborne - March 1954 - 2670801
Means for loosening pipes in underground borings
Herbold - January 1956 - 2730176
Method for oscillating drilling
Herbold - August 1962 - 3049185
Application Number:
04/825142
Publication Date:
05/11/1971
Filing Date:
05/16/1969
View Patent Images:
Export Citation:
Primary Class:
Other Classes:
367/180, 166/66.400, 181/106, 166/177.200
International Classes:
E21B43/00; E21B43/25
Field of Search:
166/249,286,65,177 181/(0.5),(EM) 340/8,10,17 259/1 (Bodine/ &/ Mech./ Vib./ Digests)/
US Patent References:
Primary Examiner:
Calvert, Ian A.
Claims:
I claim
1. A method for coupling vibrational energy to oil bearing strata to enhance the removal of oil therefrom comprising the steps of:
2. A method for coupling vibrational energy to oil bearing strata to enhance the removal of oil therefrom comprising the steps of:
3. Apparatus for sonically energizing oil bearing strata to induce the flow of oil therefrom comprising:
4. The apparatus of claim 3 wherein said first pair of transducers is sonically energized in phase opposition to said second pair of transducers.
5. The apparatus of claim 4 wherein said transducers are elongated, the longitudinal dimension thereof being oriented substantially parallel to the wall of said casing so as to provide a substantially uniform radial deformation force along the extent of said casing corresponding to the extent of said transducers.
6. Apparatus for sonically energizing oil bearing strata to induce the flow of oil therefrom comprising:
1. A method for coupling vibrational energy to oil bearing strata to enhance the removal of oil therefrom comprising the steps of:
2. A method for coupling vibrational energy to oil bearing strata to enhance the removal of oil therefrom comprising the steps of:
3. Apparatus for sonically energizing oil bearing strata to induce the flow of oil therefrom comprising:
4. The apparatus of claim 3 wherein said first pair of transducers is sonically energized in phase opposition to said second pair of transducers.
5. The apparatus of claim 4 wherein said transducers are elongated, the longitudinal dimension thereof being oriented substantially parallel to the wall of said casing so as to provide a substantially uniform radial deformation force along the extent of said casing corresponding to the extent of said transducers.
6. Apparatus for sonically energizing oil bearing strata to induce the flow of oil therefrom comprising:
Description:
This invention relates to a system for sonically augmenting the flow of oil from oil bearing strata, and more particularly to the technique and apparatus for efficiently coupling sonic energy to such strata. As described in my U.S. Pat. Nos. 2,667,932; 2,680,485; 2,700,422 and 3,322,196, the oil production of a well can be substantially augmented by coupling sonic energy into the strata surrounding the well, thereby effectively liberating the particles of oil from the strata and causing them to migrate to the well. This technique is particularly significant with wells that are nearing depletion where the yield can be increased by this technique so as to make further operations feasible.
In certain of the systems described in my aforementioned patents, the coupling of the sonic energy to the strata is implemented through a liquid medium contained in the well casing. This type of fluid coupling, while having certain impedance matching advantages, has a disadvantage in that it creates undesirable back pressure impeding the flow of oil. Further, in the case of gas bearing wells, the use of liquid as the coupling mediums is impracticable. The method and apparatus of this invention provides an improved technique for coupling sonic energy to the strata without the use of a liquid coupling medium, but in which an optimum impedance match between the energy source and the strata is achieved in a simple yet highly efficient manner. Further, by the technique and apparatus of this invention, the energy is transmitted into the ground radially outwardly from the casing enabling a relatively wide energy coupling area from the vertically oriented sonic energy generator.
It is therefore the principal object of this invention to increase the efficiency of coupling of sonic energy to petroleum bearing strata to induce the migration of the oil particles to a well.
Other objects of this invention will become apparent as the description proceeds in connection with the accompanying drawings, of which:
FIG. 1 is a cross-sectional view of a first embodiment of the device of the invention;
FIG. 2 is a cross-sectional view taken along the plane indicated by 2-2 in FIG. 1;
FIG. 3 is a cross-sectional view of second embodiment of the device of the invention, and;
FIG. 4 is a cross-sectional view taken along the plane indicated by 4-4 in FIG. 3.
It has been found most helpful in analyzing the technique of this invention to analogize the acoustically vibrating circuit utilized to an equivalent electrical circuit. This sort of approach to analysis is well known to those skilled in the art and is described, for example, in Chapter 2 of "Sonics" by Hueter and Bolt, published in 1955 by John Wiley and Sons. In making such an analogy, force F is equated with electrical voltage E, velocity of vibration u is equated with electrical current i, mechanical compliance C m is equated with electrical capacitance C e , mass M is equated with electrical inductance L, mechanical resistance (friction) R m is equated with electrical resistance R and mechanical impedance Z m is equated with electrical impedance Z e .
Thus, it can be shown that if a member is elastically vibrated by means of an acoustical sinusoidal force F o sinωt (ωbeing equal to 2π times the frequency of vibration), that
Where ωM is equal to 1/ωC , a resonant condition exists, and the effective mechanical impedance Z m m is equal to the mechanical resistance R m , the reactive impedance components ωM and 1 /ωC m cancelling each other out. Under such a resonant condition, velocity of vibration u is at a maximum, power factor is unity, and energy is more efficiently delivered to a load to which the resonant system may be coupled.
It is important to note the significance of the attainment of high acoustical Q in the resonant system being driven, to increase the efficiency of the vibration thereof and to provide a maximum amount of power. As for an equivalent electrical circuit, the Q of an acoustically vibrating circuit is defined as the sharpness of resonance thereof and is indicative of the ratio of an energy stored in each vibration cycle to the energy used in each such cycle. Q is mathematically equated to the ratio between ωM and R m . Thus, the effective Q of the vibrating circuit can be maximized to make for highly efficient, high-amplitude vibration by minimizing the effect of friction in the circuit and/or maximizing the effect of mass in such circuit.
In considering the significance of the parameters described in connection with equation (1), it should be kept in mind that the total effective resistance, mass, and compliance in the acoustically vibrating circuit are represented in the equation and that these parameters may be distributed throughout the system rather than being lumped in any one component or portion thereof.
It is also to be noted that orbiting-mass oscillators may be utilized in the implementation of the invention that automatically adjust their output frequency and phase to maintain resonance with changes in the characteristics of the load. Thus, in the face of changes in the effective mass and compliance presented by the load with changes in the conditions of the work material as it is sonically excited, the system automatically is maintained in optimum resonant operation by virtue of the "lock-in" characteristic of applicant's unique orbiting-mass oscillators. Furthermore in this connection the orbiting-mass oscillator automatically changes not only its frequency but its phase angle and therefore its power factor with changes in the resistive impedance load, to assure optimum efficiency of operation at all times.
Briefly described, the technique and apparatus of the invention involves the utilization of a sonic energy source, the output of which is tightly coupled to the walls of a well casing which has been sunk into oil bearing strata. The sonic energy source, which in one embodiment comprises two pairs of piezoelectric crystal transducers, and in another embodiment a pair of mechanically driven roller members, vibrationally distort the casing wall in an elliptical pattern in directions normal to the longitudinal axis thereof. This cyclical vibration distortion of the casing results in the transfer of sonic energy radially outwardly from the casing walls into the strata, there being a highly efficient impedance match between the high impedance sonic generator output and the high impedance load formed by the casing and the earthen material against which it abuts.
In the embodiment utilizing the two pairs of piezoelectric crystal transducers, one pair of such transducers is oriented along an axis normal to that along which the other pair is oriented, all of such transducers being of an elongated configuration with their longitudinal axes oriented substantially parallel to the longitudinal axis of the casing. The transducers are coupled tightly to the casing wall and the first transducer pair is excited in phase opposition to the second such that while one is in an outward expansion cycle portion, the other is moving inwardly, thereby resulting in the desired elliptical vibrational pattern.
In a second embodiment the same end result is achieved by means of a pair of roller members positioned opposite each other with their longitudinal axes substantially parallel to the longitudinal axis of casing, these rollers being rotated together to provide the desired elliptical vibrational pattern.
Referring now to FIGS. 1 and 2, a first embodiment of the device of the invention is illustrated. Casing member 11 is an oil well casing member sunk into strata 12 in normal fashion and has the usual perforations 14 formed therein to permit oil from the surrounding strata to enter the casing. Casing 11 is generally of a thin wall steel which can readily be elliptically distorted in response to the elliptical vibration pattern set up by the vibration generator.
The vibration generator is formed by a first pair of piezoelectric crystal transducers 15a and 15b, oriented opposite each other along a first transverse axis, and a second pair of similar transducers 16a and 16b oriented opposite each other along a second transverse axis normal to the first axis. Transducers 15a, 15b, 16a and 16b may be fabricated of a piezoelectric material such as barium titanate. The transducer members are elongated in form and are oriented so that their longitudinal axes are substantially parallel to the longitudinal axis of casing member 11. Transducers 15a, 15b, 16a and 16b are clamped between tubing string 18 and wedge-shaped clamp members 20 by means of bolts 21. Clamp members 20 and transducers 15a, 15b, 16a and 16b are thus attached to tubing string 18 to form an integrated unit.
The clamping members 20 are tightly coupled to the inner wall of casing 11 by means of wedge-shaped slip member 25 in the following manner: The tubing string 18 with the transducers 15a, 15b, 16a and 16b and clamp members 20 attached thereto, by means of bolts 21, is first carefully lowered into casing 11 with the slip members 25 suspended from the top edge of clamp members 20 on their rim portions 25a. The dimensions of the various elements involved must of course be such as to permit the easy passage of this assembly down into the casing. Care must also be taken in lowering these members to avoid any accelerations which might cause the clamp members 20 to slip downwardly relative to slip member 25. When the portion of casing 11 has been reached at which it is desired that acoustical energy be coupled to the strata, the units may be seated in position at this location by allowing the tubing string 18 to drop suddenly, this downward acceleration causing the clamp members 20 to move downwardly relative to slip members 25. By virtue of the wedge action between the clamps and the slip members, the serrated portions 25b of the slip members are caused to tightly grip the inner walls of the casing, the walls of clamp members 20 tightly engaging the slip members by virtue of this wedging action.
Crystal transducers 15a, 15b, 16a and 16b are vibrationally energized by means of an oscillating electrical signal fed thereto by means of cables 35, the frequency of such excitation being in the sonic range, i.e., typically of the order of 10,000 cycles. To achieve the desired elliptical distortion in an optimum manner, transducers 15a and 15b are excited with signals that are in phase opposition to those utilized for exciting transducers 16a and 16b, i.e., the signals fed to transducers 15a and 15b are 180° out of phase with those fed to transducers 16a and 16b. This results in a cyclical elliptical vibrational pattern which cyclically deforms flexible casing 11 as indicated by dotted lines 40 and 41 in FIG. 2. Thus, during the portions of the vibrational cycle when transducers 15a and 15b are in the portions of their vibrational cycle which involve an outward displacement, such as to deform the casing as indicated by dotted line 40, transducers 16a and 16b are in the portion of their vibrational cycle involving an inward displacement. Conversely, during the opposite halves of the vibrational cycle of the transducers when transducers 16a and 16b are experiencing an outward displacement, the casing is deformed as indicated by dotted lines 41. Thus, the two pairs of transducers operate cooperatively to cause the desired elliptical vibration pattern, this vibrational energy being transmitted radially outwardly into the strata 12 from the walls of the casing.
The vibrational energy, it is to be noted, is transmitted substantially uniformly to the casing along the entire longitudinal extent of the transducers, thus providing a fairly wide radiation area which includes the entire extent of the casing wall which corresponds to the longitudinal extent of the transducers. It is also to be noted that this type of vibrational pattern involves a maximum transfer of energy radially outwardly from the casing wall with a minimal transmission either up or down the tubing string and casing, thus minimizing the inefficient dissipation of the energy along these elements.
As already noted, for optimum efficiency, it is highly desirably to adjust the frequency at which the transducers are excited to one at which resonant vibration of the crystal, the mounting structure and the casing in the desired elliptical vibration mode is attained.
Referring now to FIGS. 3 and 4, a second embodiment of the device of the invention is illustrated. In this embodiment, the elliptical vibrational pattern is generated by a mechanical oscillator rather than through an electrical transducer, typically at lower frequency, but otherwise the same general operational results are achieved. Tubing string 18 has clamp members 20 attached thereto by welding and is inserted into casing 11 with slip members 25 suspended therefrom and clamped to the inner wall thereof at a desired location in the same manner as described for the first embodiment by means of the wedge-shaped slip members 25. Contained within tubing string 18 which is fabricated of an elastic material such as steel is an orbiting mass oscillator having roller members 46 and 47 which are oriented opposite each other and are rotatably driven around a raceway formed by the inner walls of tubing string 18. Drive shaft 45 is supported for rotation in sleeve bearing 50 formed in the bottom of the casing string and is rotatably driven by a motor (not shown) at a speed which determines the vibration frequency of the elliptical vibration pattern, typically 60°--400° c.p.s. Fixedly attached to shaft 45 are drive arms 51 and 52. These drive arms extend outwardly from the shaft and have elongated slot portions 51a and 52a which engage pin portions 46a and 47a which extend from the ends of the rollers.
Thus, as shaft 45 is rotated, rollers 46 and 47 are rotatably driven about the raceway formed by the inner wall of the tubing string. This results in a cyclical elliptical deformation of tubing string 18 as indicated by dotted lines 60, this deformation causing a like deformation of casing 11 as indicated by dotted pattern 62. This deformation pattern of course will follow the rotation of rollers 46 and 47 in a cyclical fashion in response to the outward force imparted to the portions of the tubing string wall against which the rollers abut as they rotate. As noted for the first embodiment, the rotation speed of rollers 46 and 47 is preferably adjusted for optimum resonant vibration at a low frequency mode of the vibration system including the tubing string and casing. The vibrational energy is radiated outwardly into the strata along the entire longitudinal extent of the roller members in the same manner as described for the first embodiment.
It is to be noted that the elliptical distortion of the casing produced by the technique of the invention results in an elastic motion of such casing without the center of gravity of the casing moving. That is to say, the casing is not being shaken sideways in a totally bodily movement as, for example, in situations where a single roller is rotated around the inside of a casing to loosen it from its anchored position.
The apparatus and technique of this invention thus enable the highly efficient coupling of sonic energy to the strata surrounding a well casing to engender the separation of oil particles from such strata and to cause the migration of such particles to the well. This end result is achieved by the direct coupling of a high impedance sonic energy source to the high impedance load formed by the strata, this end result being achieved by directly sonically energizing the casing in an elliptical vibration mode, such vibration being transmitted radially outwardly from the walls of the casing.
In certain of the systems described in my aforementioned patents, the coupling of the sonic energy to the strata is implemented through a liquid medium contained in the well casing. This type of fluid coupling, while having certain impedance matching advantages, has a disadvantage in that it creates undesirable back pressure impeding the flow of oil. Further, in the case of gas bearing wells, the use of liquid as the coupling mediums is impracticable. The method and apparatus of this invention provides an improved technique for coupling sonic energy to the strata without the use of a liquid coupling medium, but in which an optimum impedance match between the energy source and the strata is achieved in a simple yet highly efficient manner. Further, by the technique and apparatus of this invention, the energy is transmitted into the ground radially outwardly from the casing enabling a relatively wide energy coupling area from the vertically oriented sonic energy generator.
It is therefore the principal object of this invention to increase the efficiency of coupling of sonic energy to petroleum bearing strata to induce the migration of the oil particles to a well.
Other objects of this invention will become apparent as the description proceeds in connection with the accompanying drawings, of which:
FIG. 1 is a cross-sectional view of a first embodiment of the device of the invention;
FIG. 2 is a cross-sectional view taken along the plane indicated by 2-2 in FIG. 1;
FIG. 3 is a cross-sectional view of second embodiment of the device of the invention, and;
FIG. 4 is a cross-sectional view taken along the plane indicated by 4-4 in FIG. 3.
It has been found most helpful in analyzing the technique of this invention to analogize the acoustically vibrating circuit utilized to an equivalent electrical circuit. This sort of approach to analysis is well known to those skilled in the art and is described, for example, in Chapter 2 of "Sonics" by Hueter and Bolt, published in 1955 by John Wiley and Sons. In making such an analogy, force F is equated with electrical voltage E, velocity of vibration u is equated with electrical current i, mechanical compliance C m is equated with electrical capacitance C e , mass M is equated with electrical inductance L, mechanical resistance (friction) R m is equated with electrical resistance R and mechanical impedance Z m is equated with electrical impedance Z e .
Thus, it can be shown that if a member is elastically vibrated by means of an acoustical sinusoidal force F o sinωt (ωbeing equal to 2π times the frequency of vibration), that
Where ωM is equal to 1/ωC , a resonant condition exists, and the effective mechanical impedance Z m m is equal to the mechanical resistance R m , the reactive impedance components ωM and 1 /ωC m cancelling each other out. Under such a resonant condition, velocity of vibration u is at a maximum, power factor is unity, and energy is more efficiently delivered to a load to which the resonant system may be coupled.
It is important to note the significance of the attainment of high acoustical Q in the resonant system being driven, to increase the efficiency of the vibration thereof and to provide a maximum amount of power. As for an equivalent electrical circuit, the Q of an acoustically vibrating circuit is defined as the sharpness of resonance thereof and is indicative of the ratio of an energy stored in each vibration cycle to the energy used in each such cycle. Q is mathematically equated to the ratio between ωM and R m . Thus, the effective Q of the vibrating circuit can be maximized to make for highly efficient, high-amplitude vibration by minimizing the effect of friction in the circuit and/or maximizing the effect of mass in such circuit.
In considering the significance of the parameters described in connection with equation (1), it should be kept in mind that the total effective resistance, mass, and compliance in the acoustically vibrating circuit are represented in the equation and that these parameters may be distributed throughout the system rather than being lumped in any one component or portion thereof.
It is also to be noted that orbiting-mass oscillators may be utilized in the implementation of the invention that automatically adjust their output frequency and phase to maintain resonance with changes in the characteristics of the load. Thus, in the face of changes in the effective mass and compliance presented by the load with changes in the conditions of the work material as it is sonically excited, the system automatically is maintained in optimum resonant operation by virtue of the "lock-in" characteristic of applicant's unique orbiting-mass oscillators. Furthermore in this connection the orbiting-mass oscillator automatically changes not only its frequency but its phase angle and therefore its power factor with changes in the resistive impedance load, to assure optimum efficiency of operation at all times.
Briefly described, the technique and apparatus of the invention involves the utilization of a sonic energy source, the output of which is tightly coupled to the walls of a well casing which has been sunk into oil bearing strata. The sonic energy source, which in one embodiment comprises two pairs of piezoelectric crystal transducers, and in another embodiment a pair of mechanically driven roller members, vibrationally distort the casing wall in an elliptical pattern in directions normal to the longitudinal axis thereof. This cyclical vibration distortion of the casing results in the transfer of sonic energy radially outwardly from the casing walls into the strata, there being a highly efficient impedance match between the high impedance sonic generator output and the high impedance load formed by the casing and the earthen material against which it abuts.
In the embodiment utilizing the two pairs of piezoelectric crystal transducers, one pair of such transducers is oriented along an axis normal to that along which the other pair is oriented, all of such transducers being of an elongated configuration with their longitudinal axes oriented substantially parallel to the longitudinal axis of the casing. The transducers are coupled tightly to the casing wall and the first transducer pair is excited in phase opposition to the second such that while one is in an outward expansion cycle portion, the other is moving inwardly, thereby resulting in the desired elliptical vibrational pattern.
In a second embodiment the same end result is achieved by means of a pair of roller members positioned opposite each other with their longitudinal axes substantially parallel to the longitudinal axis of casing, these rollers being rotated together to provide the desired elliptical vibrational pattern.
Referring now to FIGS. 1 and 2, a first embodiment of the device of the invention is illustrated. Casing member 11 is an oil well casing member sunk into strata 12 in normal fashion and has the usual perforations 14 formed therein to permit oil from the surrounding strata to enter the casing. Casing 11 is generally of a thin wall steel which can readily be elliptically distorted in response to the elliptical vibration pattern set up by the vibration generator.
The vibration generator is formed by a first pair of piezoelectric crystal transducers 15a and 15b, oriented opposite each other along a first transverse axis, and a second pair of similar transducers 16a and 16b oriented opposite each other along a second transverse axis normal to the first axis. Transducers 15a, 15b, 16a and 16b may be fabricated of a piezoelectric material such as barium titanate. The transducer members are elongated in form and are oriented so that their longitudinal axes are substantially parallel to the longitudinal axis of casing member 11. Transducers 15a, 15b, 16a and 16b are clamped between tubing string 18 and wedge-shaped clamp members 20 by means of bolts 21. Clamp members 20 and transducers 15a, 15b, 16a and 16b are thus attached to tubing string 18 to form an integrated unit.
The clamping members 20 are tightly coupled to the inner wall of casing 11 by means of wedge-shaped slip member 25 in the following manner: The tubing string 18 with the transducers 15a, 15b, 16a and 16b and clamp members 20 attached thereto, by means of bolts 21, is first carefully lowered into casing 11 with the slip members 25 suspended from the top edge of clamp members 20 on their rim portions 25a. The dimensions of the various elements involved must of course be such as to permit the easy passage of this assembly down into the casing. Care must also be taken in lowering these members to avoid any accelerations which might cause the clamp members 20 to slip downwardly relative to slip member 25. When the portion of casing 11 has been reached at which it is desired that acoustical energy be coupled to the strata, the units may be seated in position at this location by allowing the tubing string 18 to drop suddenly, this downward acceleration causing the clamp members 20 to move downwardly relative to slip members 25. By virtue of the wedge action between the clamps and the slip members, the serrated portions 25b of the slip members are caused to tightly grip the inner walls of the casing, the walls of clamp members 20 tightly engaging the slip members by virtue of this wedging action.
Crystal transducers 15a, 15b, 16a and 16b are vibrationally energized by means of an oscillating electrical signal fed thereto by means of cables 35, the frequency of such excitation being in the sonic range, i.e., typically of the order of 10,000 cycles. To achieve the desired elliptical distortion in an optimum manner, transducers 15a and 15b are excited with signals that are in phase opposition to those utilized for exciting transducers 16a and 16b, i.e., the signals fed to transducers 15a and 15b are 180° out of phase with those fed to transducers 16a and 16b. This results in a cyclical elliptical vibrational pattern which cyclically deforms flexible casing 11 as indicated by dotted lines 40 and 41 in FIG. 2. Thus, during the portions of the vibrational cycle when transducers 15a and 15b are in the portions of their vibrational cycle which involve an outward displacement, such as to deform the casing as indicated by dotted line 40, transducers 16a and 16b are in the portion of their vibrational cycle involving an inward displacement. Conversely, during the opposite halves of the vibrational cycle of the transducers when transducers 16a and 16b are experiencing an outward displacement, the casing is deformed as indicated by dotted lines 41. Thus, the two pairs of transducers operate cooperatively to cause the desired elliptical vibration pattern, this vibrational energy being transmitted radially outwardly into the strata 12 from the walls of the casing.
The vibrational energy, it is to be noted, is transmitted substantially uniformly to the casing along the entire longitudinal extent of the transducers, thus providing a fairly wide radiation area which includes the entire extent of the casing wall which corresponds to the longitudinal extent of the transducers. It is also to be noted that this type of vibrational pattern involves a maximum transfer of energy radially outwardly from the casing wall with a minimal transmission either up or down the tubing string and casing, thus minimizing the inefficient dissipation of the energy along these elements.
As already noted, for optimum efficiency, it is highly desirably to adjust the frequency at which the transducers are excited to one at which resonant vibration of the crystal, the mounting structure and the casing in the desired elliptical vibration mode is attained.
Referring now to FIGS. 3 and 4, a second embodiment of the device of the invention is illustrated. In this embodiment, the elliptical vibrational pattern is generated by a mechanical oscillator rather than through an electrical transducer, typically at lower frequency, but otherwise the same general operational results are achieved. Tubing string 18 has clamp members 20 attached thereto by welding and is inserted into casing 11 with slip members 25 suspended therefrom and clamped to the inner wall thereof at a desired location in the same manner as described for the first embodiment by means of the wedge-shaped slip members 25. Contained within tubing string 18 which is fabricated of an elastic material such as steel is an orbiting mass oscillator having roller members 46 and 47 which are oriented opposite each other and are rotatably driven around a raceway formed by the inner walls of tubing string 18. Drive shaft 45 is supported for rotation in sleeve bearing 50 formed in the bottom of the casing string and is rotatably driven by a motor (not shown) at a speed which determines the vibration frequency of the elliptical vibration pattern, typically 60°--400° c.p.s. Fixedly attached to shaft 45 are drive arms 51 and 52. These drive arms extend outwardly from the shaft and have elongated slot portions 51a and 52a which engage pin portions 46a and 47a which extend from the ends of the rollers.
Thus, as shaft 45 is rotated, rollers 46 and 47 are rotatably driven about the raceway formed by the inner wall of the tubing string. This results in a cyclical elliptical deformation of tubing string 18 as indicated by dotted lines 60, this deformation causing a like deformation of casing 11 as indicated by dotted pattern 62. This deformation pattern of course will follow the rotation of rollers 46 and 47 in a cyclical fashion in response to the outward force imparted to the portions of the tubing string wall against which the rollers abut as they rotate. As noted for the first embodiment, the rotation speed of rollers 46 and 47 is preferably adjusted for optimum resonant vibration at a low frequency mode of the vibration system including the tubing string and casing. The vibrational energy is radiated outwardly into the strata along the entire longitudinal extent of the roller members in the same manner as described for the first embodiment.
It is to be noted that the elliptical distortion of the casing produced by the technique of the invention results in an elastic motion of such casing without the center of gravity of the casing moving. That is to say, the casing is not being shaken sideways in a totally bodily movement as, for example, in situations where a single roller is rotated around the inside of a casing to loosen it from its anchored position.
The apparatus and technique of this invention thus enable the highly efficient coupling of sonic energy to the strata surrounding a well casing to engender the separation of oil particles from such strata and to cause the migration of such particles to the well. This end result is achieved by the direct coupling of a high impedance sonic energy source to the high impedance load formed by the strata, this end result being achieved by directly sonically energizing the casing in an elliptical vibration mode, such vibration being transmitted radially outwardly from the walls of the casing.