Acoustic inhibition of hydrates, scales and paraffins

Abstract

Devices and methods for inhibiting the deposition of methane or natural gas hydrates, as well as scales, paraffins and other undesirable deposits within a wellbore using acoustic energy. An acoustic inhibitor is associated with a wellbore proximate the wellhead and is used to generate a low frequency acoustic energy signal that is propagated axially through the wellbore. The acoustic inhibitor preferably comprises a magneto-restrictive element that is pulsed in accordance with a predetermined frequency to generate acoustic waves in fluid that is located within the flowbore of wellbore production tubing or in a pipeline. The tubing string or pipeline is used as a waveguide to propagate the acoustic energy axially.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to the use of acoustic energy to retard and prevent deposits of hydrates, scales and paraffins within a wellbore or pipeline and the components associated therewith.

2. Description of the Related Art

Multiphase flow in deep sea oil and gas wells and pipelines is an environment conducive to the formation of methane or natural gas hydrates, which consist of gas trapped within an ice matrix. These hydrates can choke off or entirely plug off fluid flow through a wellbore or pipeline. Typically, hydrates tend to form in specific temperature and pressure regimes. As pressure increases, the hydrate formation temperature also increases. For pressures typically seen in deep water wells, this places the hydrate formation temperature in the range of temperatures seen at the mud line of a sea-based well (i.e., around the ocean floor). Thus, hydrate formation generally occurs proximate the ocean floor.

Removing hydrate deposits is a difficult and lengthy process. Presently, hydrate formation is often inhibited using chemicals and, in some case, heaters, for remediation of a plugged conduit. The use of inhibition chemicals and/or heaters is logistically complex and expensive. In addition to hydrates, scales and paraffins also become deposited on wellbore and pipeline components during operation. These also are detrimental to operation of valves and other components within the flowbore or pipeline.

Some arrangements are known to try to clean hydrates, scales or other matter from wellbores using acoustic energy. However, these arrangements generally rely primarily upon transmitting acoustic energy through the walls of the flowbore or pipeline itself rather than through the fluid within the flowbore. The vibratory transducers used in these earlier approaches are typically operated at high vibration frequencies, i.e., 20 kHz or higher. These high frequency vibrations are used to shatter the matrix of an already formed hydrate plug or to remove an existing deposit of hydrates or other matter. It is believed, however, that these higher frequencies are not effective in preventing the initial deposition of hydrates and other deposits within portions of a wellbore or pipeline. Thus, these prior approaches have not been effective in preventing the build-up of hydrates, scales or paraffins within the flowbore.

U.S. Pat. No. 4,280,557, issued to Bodine, is one example of a prior acoustic energy cleaning arrangement. Bodine describes a system for remedial cleaning of foreign matter from tubular members wherein a mechanical oscillator, is secured within a wellbore casing and rotationally driven to create whirling vibratory pressure action in annulus fluid. Rotation speed of the oscillator is on the order 20-100 cycles per second.

U.S. Pat. No. 5,595,243, issued to Maki, Jr. et al. describes an acoustic well cleaning system wherein a sonde is lowered into a wellbore. The sonde contains a number of transducers that are powered to generate a high frequency sonic signal in the range of 20 kHz to 100 kHz. Cleaning occurs as the tool is moved upwardly through a producing zone. U.S. Pat. No. 5,727,628, issued to Patzner describes a similar system wherein an ultrasonic cleaning unit is lowered into a wellbore by cable. The cleaning unit includes a number of magneto-restrictive ultrasonic oscillator transducers that are pulsed to produce ultrasonic waves that are intended to clean proximate portions of the wellbore. The transducers are operated at a frequency in the range of 18 to 25 kHz, and preferably, at around 20 kHz.

U.S. Pat. No. 5,948,171, issued to Grothaus, teaches an electro-hydraulic transducer device for cleaning the inner surface of pipelines. The typical operating parameters for the device include a pulse frequency of 1-25 Hz.

U.S. Pat. No. 6,405,796, issued to Meyer et al., describes an ultrasonic device that is suspended within a borehole by a cable and used to improve production by breaking up particle agglomeration. The method of use requires that an acoustic slow wave, or the point at which the motion of solid and liquid are 180 degrees out of phase, be calculated. This calculation is a function of specific reservoir characteristics, such as reservoir permeability and aggregate porosity.

U.S. Pat. No. 6,418,960, to Mintz et al. describes a liquid delivery system that is configured for purging cycles between pumping cycles of process fluids. Ultrasonic transducers are mounted on fluid transmission lines and operated during the purge cycle to help remove mixed purge and process fluids. The preferred operating frequency range for the transducers is from 25 kHz to 200 kHz.

U.S. Pat. No. 6,467,542, issued to Kostrov et al. illustrates a system for stimulation of fluid-bearing formations using resonant vibration. In Kostrov's system, a wave generator is disposed into a wellbore suspended on wireline. A vibration sensor detects the eigen frequency or bandwidth of the production formation, and the wave generator is then operated at the eigen frequency or bandwidth.

U.S. Pat. No. 6,474,349, issued to Laker, describes an ultrasonic tool for the cleaning of tubular members. The tool is run into a wellbore on a cable. Operation of an acoustic vibrator within the tool causes cavitation that is intended to remove scales and asphaltenes in the wellbore. Laker provides no specifics with regard to the preferred frequencies of operation for his vibrator.

U.S. Pat. No. 6,619,394, issued to Soliman et al., is directed to a well cleaning tool that subjects substantially the same portion of a wellbore to vibratory waves produced by a plurality of vibratory wave generators. The vibratory waves may have about the same frequency or a plurality of frequencies that may overlap or be modulated across a range. This type of system utilizes a piston pulser and a vibrating pipe to try to remove already deposited mudcake from the inside of a wellbore.

The present invention addresses the problems of the prior art.

SUMMARY OF THE INVENTION

The invention provides devices and methods for inhibiting the deposition of methane or natural gas hydrates, as well as scales, paraffins and other undesirable deposits within a wellbore using acoustic energy. In a preferred embodiment, an acoustic inhibitor is associated with a wellbore proximate the wellhead and is used to generate a low frequency acoustic energy signal that is propagated axially through the wellbore. The acoustic inhibitor preferably comprises a transducive element that is pulsed in accordance with a predetermined frequency to generate acoustic waves in fluid located within the flowbore of wellbore production tubing or in a pipeline. The tubing string or pipeline is used as a waveguide to propagate the acoustic energy axially.

In preferred embodiments, the acoustic waves are generated at a frequency in a relatively low frequency range that is generally from about 1000 Hz to about 2200 Hz. Particularly effective frequencies for inhibiting the growth and formation of a hydrate matrix are 1130 Hz and 2000 Hz. This pulsing will prevent the agglomeration of hydrate particles that would lead to the formation of a hydrate deposit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side, cross-sectional view depicting an exemplary hydrocarbon production wellbore that includes an acoustic inhibitor arrangement constructed in accordance with the present invention.

FIG. 2 is a schematic diagram depicting the components of a currently preferred acoustic inhibitor, in accordance with the present invention.

FIG. 3 is a schematic operational diagram illustrating an exemplary vibratory element used with the acoustic inhibitor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates an offshore hydrocarbon production well 10 that includes an offshore platform 12 located within the sea 14 and resting on the sea floor 16. An upper portion of the platform 12 extends above the surface 18 of the sea 14 and supports a production Christmas tree 20, of a type known in the art for connection of suitable production piping and valving to a hydrocarbon production well. A riser 22 extends downwardly from the Christmas tree 20 and to a wellhead 24 located on the sea floor 16. A wellbore 26 extends downwardly from the wellhead 24 through the earth 28 to a hydrocarbon-bearing formation 30. The wellbore 26 includes exterior casing 32 that runs along at least a portion of the length of the wellbore 26. A string 34 of production tubing is disposed within the riser 22 and the casing 32. An annulus 36 is defined between the production tubing string 34 and the casing 32. During production of hydrocarbons from the production zone 30, the interior flowbore of the production tubing string 34 is filled with production fluid. The interior flowbore of the production tubing string 34 is, therefore, prone to deposits of scales, paraffins, and hydrates (hereinafter “harmful deposits”) along its length. The primary area of concern, particularly for the creation of harmful deposits is the portion of the production string 34 that is generally proximate mud line, or sea floor 16.

In a preferred embodiment, the Christmas tree 20 and wellhead 24 include portions of an acoustic inhibitor 40 that is associated with the flowbore 42 of the production tubing string 34, as depicted schematically in FIG. 2. The acoustic inhibitor 40 preferably includes a transducive vibratory element 44 that is formed of electro-ceramic material. Applying a voltage across the element 44 causes it to expand proportionally to an expanded state (see position 44a in FIG. 2). When voltage is removed, the element 44 returns to unexpanded state. If a voltage signal is applied at a given frequency expansion and contraction occurs in concert with the provided frequency. The vibratory element 44 is actuated by an actuator that includes a signal generator 46 to generate a sine wave electrical signal that is provided to an amplifier 48 and then to the vibratory element 44 so that the vibratory element 44 will be pulsed in accordance with a particular voltage and frequency. The amplifier 48 is used to boost the signal provided to the vibratory element 44.

The vibratory element 44 may be constructed in a number of ways. FIG. 2 depicts a first embodiment wherein the element 44 is a monolithic rod-shaped member that is formed of magnetostrictive material, of a known type. In this embodiment, a magnetic coil (not shown) used to selectively actuate the element 44 between expanded and unexpanded conditions in response to the electrical signal provided from the amplifier 48. The element 44 might also be formed as an annular member with a central opening that allows fluid flow through its central opening. In addition, the element 44 might be formed of piezoelectric material, of a known type, that will deform as a function of applied voltage from the amplifier 48.

FIG. 3 depicts one currently preferred construction for a vibratory element 44′. A number of circular electro-ceramic, magnetostrictive or piezoelectric members, i.e., disks, 50 are glued or otherwise secured together in a stacked configuration with the electrical signal from the amplifier 48 applied to expand each of the individual members 50. The use of a stack of individual members 50 to form the element 44′ is advantageous because the stacked device will require a lower voltage to achieve a maximum expansion of the members 50. The stack of circular members 50 is preferably encapsulated in a fluid-resistant membrane 52. The stack of circular members 50 is preferably secured to a base 54. The base 54 may be incorporated into or attached to the wellhead 24 and is used to position the vibratory element 44 relatively centrally within the flowbore 42. The function generator 46 and amplifier 48 meanwhile are preferably located at or near the Christmas tree 20 so that they may be controlled and monitored by rig personnel.

In operation, vibration of the vibratory element 44 or 44′ generates cyclical acoustic waves, depicted at 56 in FIG. 2, within fluid in the flowbore 42. The flowbore 42 acts as a waveguide to provide axial propagation of sonic energy. The vibratory element 44, 44′ is operated to pulse at a frequency that is intended to inhibit growth of hydrates within the flowbore 42 particularly proximate the wellhead 24. The acoustic waves 56 are generated in a relatively low frequency range that is generally from about 1000 Hz to about 2200 Hz. Particularly effective frequencies for inhibiting the growth and formation of a hydrate matrix are around 1130 Hz and around 2000 Hz. In testing, these low frequencies have been shown to be particularly effective in preventing the growth of hydrates within a tubular member. It is believed that these lower range frequencies are particularly suited to preventing and retarding the initial growth of hydrates rather than in shattering an existing matrix of already-deposited hydrates. Similarly, these frequencies are effective in preventing initial deposits and slowing the growth of scales and paraffin deposits within a tubular member.

The frequencies used and the configuration of the acoustic inhibitor 40 is designed to optimally prevent the initial agglomeration of particles of hydrates, scales, paraffins and other undesirable deposits rather than remedially cleaning deposits from a tubular member. Thus, to provide maximum effectiveness in inhibiting deposits and growth of hydrates, scales and paraffins, it is suggested that the signal generator 46 be operated to vibrate the vibratory element 44, 44′ in a substantially continuous manner during production operations. It is noted that use of the acoustic inhibitor 40 will not preclude the additional use of chemical inhibitors in the flowbore 42.

Although shown here used with a sea-based well, those of skill in the art will understand that the acoustic inhibitor 40 and methods of operation thereof may also be used with land-based wells or with pipelines.

Those of skill in the art will recognize that numerous modifications and changes may be made to the exemplary designs and embodiments described herein and that the invention is limited only by the claims that follow and any equivalents thereof.

Claims

1. An acoustic inhibitor for inhibiting harmful deposits within the flowbore of a tubular member containing fluids, the acoustic inhibitor comprising:

a vibratory element capable of inducing an acoustic wave within the flowbore;

an actuator for operating the vibratory element at a frequency that inhibits deposits of hydrates within the flowbore.

2. The acoustic inhibitor of claim 1 wherein the actuator operates the vibratory element at a frequency that is from about 1000 Hz to about 2200 Hz.

3. The acoustic inhibitor of claim 2 wherein the actuator operates the vibratory element at a frequency that is about 1130 Hz.

4. The acoustic inhibitor of claim 2 wherein the actuator operates the vibratory element at a frequency that is about 2000 Hz.

5. The acoustic inhibitor of claim 1 wherein the actuator comprises a signal generator that produces a sine wave signal of particular frequency.

6. The acoustic inhibitor of claim 5 wherein the actuator further comprises a signal amplifier.

7. The acoustic inhibitor of claim 1 wherein the vibratory element is formed of electro-ceramic material.

8. The acoustic inhibitor of claim 1 wherein the vibratory element is formed of magnetostrictive material.

9. The acoustic inhibitor of claim 1 wherein the vibratory element is covered with a fluid-resistant membrane.

10. The acoustic inhibitor of claim 1 wherein the vibratory element comprises a plurality of stacked members.

11. A system for inhibiting deposits and growth of harmful deposits within a tubular member, the system comprising:

a vibratory element capable of inducing an acoustic wave within the flowbore, the vibratory element comprising: a member fashioned from a material fro the group of materials consisting essentially of electroceramic, magnetostrictive and piezoelectric; and

an actuator for operating the vibratory element at a frequency that inhibits deposits of hydrates within the flowbore.

12. The system of claim 11 wherein the actuator operates the vibratory element at a frequency that is from about 1000 Hz to about 2200 Hz.

13. The system of claim 11 wherein the actuator operates the vibratory element at a frequency that is about 1130 Hz.

14. The system of claim 11 wherein the actuator operates the vibratory element at a frequency that is about 2000 Hz.

15. The system of claim 11 wherein the vibratory element is covered with a fluid-resistant membrane.

16. The system of claim 11 wherein the vibratory element comprises a plurality of stacked members.

17. A method for inhibiting deposits and growth of harmful deposits within a tubular member comprising the step of:

actuating a vibratory element within the flowbore of a tubular member at a frequency that is from about 1000 Hz to about 2200 Hz.

18. The method of claim 17 wherein the actuator operates the vibratory element at a frequency that is about 1130 Hz.

19. The method of claim 17 wherein the actuator operates the vibratory element at a frequency that is about 2000 Hz.