A downhole distributed ultrasonic atomization method for wellbore crude oil viscosity reduction

Abstract

The application discloses a downhole distributed ultrasonic atomization method for reducing viscosity of crude oil in a wellbore, and relates to the technical field of oil and gas field development.The method comprises the following steps: S1, obtaining a distribution curve of the viscosity of crude oil along the depth in the wellbore, determining a viscosity inflection point depth Hc, and determining the installation position of a first ultrasonic wave emitting short section according to the viscosity inflection point depth Hc; the remaining at least two ultrasonic wave emitting short sections are determined to be positioned at a set distance along the vertical upward direction; and each ultrasonic wave emitting short section is fixed on an armored cable; S2, the assembled armored cable and each ultrasonic wave emitting short section are lowered into the annular space gap of the wellbore or the oil pipe, and are fixed after reaching the designed depth; S3, a ground control cabinet is started, and each ultrasonic wave emitting short section is driven to emit ultrasonic waves in a preset interval pulse mode, wherein each ultrasonic wave emitting short section works independently or in sequence; and the method realizes segmented viscosity reduction and step-by-step atomization of the crude oil in the oil pipe. The method can realize accurate and efficient viscosity reduction of the whole wellbore.

Description

Technical Field

[0001] This invention relates to the field of oil and gas field development technology, and in particular to a downhole distributed ultrasonic atomization method for reducing the viscosity of crude oil in wellbores. Background Technology

[0002] In deep oil and gas extraction, crude oil exhibits good fluidity under high temperature and pressure conditions in the formation. However, as crude oil rises along the wellbore, the temperature and pressure gradually decrease, causing light components to volatilize and heavy components to precipitate, leading to a sharp increase in crude oil viscosity and even solidification or gelation. In severe cases, this can cause wellbore blockage or lift failure. Existing viscosity reduction technologies mainly include chemical viscosity reduction (dosing chemicals), thermal viscosity reduction (electric heating, steam tracing), and mechanical shearing, but these methods suffer from problems such as high chemical costs, low heating efficiency, high energy consumption, and high requirements for downhole tools.

[0003] Existing ultrasonic viscosity reduction technologies mostly employ single-point transducer processing schemes. However, due to the long wellbore and large longitudinal viscosity gradient, the processing range of single-point transducers is limited and cannot cover long well sections. This can easily lead to a "processing blind zone" in the upper well section, where the crude oil viscosity rebounds and solidifies during the lifting process; or it can cause the crude oil in the lower well section to be repeatedly processed, resulting in energy waste. Summary of the Invention

[0004] The purpose of this invention is to provide a downhole distributed ultrasonic atomization method for reducing the viscosity of crude oil in wellbore, so as to solve the problems existing in the prior art and achieve accurate and efficient viscosity reduction throughout the well section.

[0005] To achieve the above objectives, the present invention provides the following solution: This invention provides a downhole distributed ultrasonic atomization method for reducing crude oil viscosity in wellbore, comprising the following steps: S1. Obtain the viscosity distribution curve of crude oil in the wellbore along the depth, determine the viscosity inflection point depth Hc, and determine the installation position of the first ultrasonic transmitting sub-section based on this; determine the position of the remaining at least two ultrasonic transmitting sub-sections vertically upward at a set distance; and fix each ultrasonic transmitting sub-section to the armored cable. S2, the assembled armored cable, along with each ultrasonic short section, is lowered into the annular space of the wellbore or into the tubing, and fixed after reaching the designed depth; S3, start the ground control cabinet, drive each ultrasonic transmitting segment to emit ultrasonic waves according to the preset interval pulse mode, where each ultrasonic transmitting segment works independently or takes turns in sequence; to achieve segmented viscosity reduction and step-by-step atomization of crude oil in the oil pipe.

[0006] Preferably, in S1, the first ultrasonic transmitting sub is installed 30m to 100m below the height of Hc, and the remaining ultrasonic transmitting subs are arranged every L meters along the upward direction of the wellbore until 200m below the wellhead.

[0007] Preferably, each of the ultrasonic transmitting sections encapsulates an ultrasonic transducer assembly; a monitoring cable is laid inside the tubing, and a downhole temperature, pressure, and viscosity sensing module is fixed on the monitoring cable at the position corresponding to each of the ultrasonic sections; the downhole temperature, pressure, and viscosity sensing module is used to collect crude oil temperature, pressure, and viscosity parameters in real time, which are transmitted back to the surface control cabinet via the monitoring cable.

[0008] Preferably, the ground control cabinet is communicatively connected to each of the ultrasonic transducer assemblies via an interval pulse drive module.

[0009] Preferably, the interval pulse driving module is used to generate periodic intermittent ultrasonic pulse signals, wherein the working duration ton and the sleep duration toff of the periodic intermittent ultrasonic pulse signals satisfy ton / toff≤0.3, and ton≤2s, toff≥3s.

[0010] Preferably, the interval pulse drive module is disposed in the ground control cabinet, or the interval pulse drive module includes multiple interval pulse drive sub-modules; the interval pulse drive sub-modules correspond one-to-one with the ultrasonic transmitting section and are encapsulated and integrated within the ultrasonic transmitting section.

[0011] Preferably, the ground control cabinet adjusts the transmission power and ton / toff data of each ultrasonic transducer assembly in real time based on the data returned by each of the downhole temperature, pressure and viscosity sensing modules and / or the ground production parameters.

[0012] Preferably, the interval distance L is determined based on the wellbore temperature gradient and / or crude oil viscosity profile; and L = 5m~50m.

[0013] Preferably, the outer sheath of the armored cable is an alloy or polymer composite sheath that is resistant to temperature ≥180℃, pressure ≥60MPa, and H2S / CO2 corrosion.

[0014] Preferably, the outer diameter of the ultrasonic transmitting section is ≤22mm and the length is ≤200mm.

[0015] The present invention achieves the following technical effects compared to the prior art: The downhole distributed ultrasonic atomization method for reducing crude oil viscosity in wellbore provided by this invention accurately locates the first ultrasonic transmitting sub-section at the viscosity inflection point depth Hc based on the actual distribution curve of crude oil viscosity along depth in the wellbore, and then sequentially arranges at least three sub-sections upwards at intervals, so that the sub-sections form a "segmented relay" arrangement along the longitudinal direction of the wellbore. This fundamentally eliminates the physical limitation of insufficient ultrasonic action distance in single-point solutions, and avoids the upper well section from becoming a treatment blind zone due to its distance from the sound source, which can lead to viscosity rebound and condensation. Each ultrasonic transmitting sub-section works independently or in rotation, so that each sub-section only emits ultrasonic waves in its local well section. This avoids repeated irradiation of treated sections, which would waste energy, and also avoids omitting untreated sections. It achieves precise energy delivery and uniform coverage of the entire well section, reducing the problems of high cost of chemical viscosity reduction and high energy consumption of thermal viscosity reduction in existing methods. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the overall structure of the downhole distributed ultrasonic atomization method for reducing crude oil viscosity in wellbore provided by the present invention.

[0018] In the diagram: 1-Casing; 2-Tubing; 3-Annular space; 4-Armored cable; 5-Surface control cabinet; 6-Wellhead; 7-Schematic diagram of crude oil rising upwards. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] The purpose of this invention is to provide a downhole distributed ultrasonic atomization method for reducing the viscosity of crude oil in wellbore, so as to solve the problems existing in the prior art and achieve accurate and efficient viscosity reduction throughout the well section.

[0021] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0022] Example 1 This embodiment provides a downhole distributed ultrasonic atomization method for reducing crude oil viscosity in wellbore, such as... Figure 1 As shown, it includes the following steps: S1, obtain the viscosity distribution curve of crude oil along the depth in the wellbore, determine the viscosity inflection point depth Hc, and determine the first ultrasonic transmitting sub-section (i.e., Figure 1 The installation position of the short section 1); at least two remaining ultrasonic emitting short sections (i.e. Figure 1 Short sections 2, 3, ... are positioned vertically upwards at predetermined distances; and each ultrasonic transmitting section is fixed to the armored cable 4. S2, the assembled armored cable 4 together with each ultrasonic short section is lowered into the annular space 3 of the wellbore. A monitoring cable is placed in the tubing 2. A downhole temperature, pressure and viscosity sensing module is fixed on the monitoring cable at the position of each ultrasonic short section corresponding to the armored cable 4. It is fixed after reaching the design depth. S3, start the ground control cabinet 5, drive each ultrasonic transmitting section to emit ultrasonic waves according to the preset interval pulse mode, where each ultrasonic transmitting section works independently or takes turns in sequence; to achieve segmented viscosity reduction and step-by-step atomization of crude oil in oil pipe 2 (in-situ atomization viscosity reduction: ultrasonic waves generate cavitation effect and acoustic flow in crude oil, breaking and dispersing high viscosity crude oil into micron-sized droplets (diameter 10~200μm), forming a three-phase atomized flow of oil-gas-liquid droplets, reducing the apparent viscosity of crude oil by more than 60%).

[0023] By accurately locating the first ultrasonic transmitting sub-section at the viscosity inflection point depth Hc based on the actual distribution curve of crude oil viscosity along the depth in the wellbore, and then sequentially arranging at least three sub-sections upwards at intervals, the sub-sections form a "segmented relay" arrangement along the longitudinal direction of the wellbore. This fundamentally eliminates the physical limitation of insufficient ultrasonic action distance in single-point solutions, and avoids the upper well section becoming a treatment blind zone due to its distance from the sound source, leading to viscosity rebound and solidification. Each ultrasonic transmitting sub-section works independently or in rotation, ensuring that each sub-section only emits ultrasonic waves within its designated local well section. This avoids repeated irradiation of already treated sections, preventing energy waste, and also ensures that untreated sections are not missed. This achieves precise energy delivery and uniform coverage of the entire well section, reducing the high cost of chemical viscosity reduction and the high energy consumption of thermal viscosity reduction in existing methods.

[0024] Regarding the original viscosity distribution curve along depth: Specifically, based on the wellbore structure, geothermal gradient, crude oil viscosity-temperature curve, and production dynamics of the target well, the distribution curve of crude oil viscosity along the depth in the wellbore is calculated; the viscosity at the position in the tubing corresponding to each short section is set with a threshold in the ground control cabinet, and if the viscosity measured in real time is not within the threshold, a signal is triggered to control the emission of acoustic waves to reduce viscosity.

[0025] The following are the relevant settings instructions for armored cable 4: Specifically, the armored cable 4 is lowered into the wellhead 6, serving both power transmission and load-bearing functions.

[0026] In the optional solutions of this embodiment, it is more preferred that the outer sheath of the armored cable 4 is an alloy or polymer composite sheath that is resistant to temperature ≥180℃, pressure ≥60MPa, and H2S / CO2 corrosion.

[0027] The following are the settings instructions for the ultrasonic transmitting sub: Specifically, N ultrasonic transmitting sections (N≥2) are fixed at intervals along the four axes of the armored cable.

[0028] In the optional schemes of this embodiment, it is more preferred that in S1, the first ultrasonic transmitting sub is installed 30m to 100m below the height of Hc, and the remaining ultrasonic transmitting subs are arranged every L meters along the upward direction of the well shaft until 200m below the wellhead.

[0029] In the optional schemes of this embodiment, the preferred method is to determine the interval distance L based on the wellbore temperature gradient and / or crude oil viscosity profile; and L = 5m~50m.

[0030] In the optional solutions of this embodiment, it is more preferred that the outer diameter of the ultrasonic transmitting section is ≤22mm and the length is ≤200mm.

[0031] In the optional schemes of this embodiment, it is more preferred that each ultrasonic transmitting section is encapsulated with an ultrasonic transducer assembly; a monitoring cable is laid down in the tubing 2, and a downhole temperature, pressure and viscosity sensing module is fixed on the monitoring cable at the position corresponding to each ultrasonic section; the downhole temperature, pressure and viscosity sensing module is used to collect crude oil temperature, pressure and viscosity parameters in real time, which are transmitted back to the surface control cabinet 5 via armored cable 4.

[0032] Specifically, the ultrasonic transducer assembly is encapsulated inside the sub-section, with its core component being a high-temperature resistant piezoelectric ceramic (Curie temperature ≥300℃) or magnetostrictive material, operating at a frequency of 15~100kHz. The transducer is surrounded by a pressure balancing chamber (filled with an insulating medium, balanced with the wellbore pressure via a flexible metal diaphragm) and an acoustic radiating head (made of metal, sealed to the sub-section shell). This part is existing technology and will not be elaborated further here.

[0033] The following are the settings instructions for the interval pulse drive module: Specifically, a monitoring cable is installed inside the tubing 2, and a downhole temperature, pressure and viscosity sensing module is fixed at the position of each ultrasonic short section on the monitoring cable. The downhole temperature, pressure and viscosity sensing module is used to collect crude oil temperature, pressure and viscosity parameters in real time, which are transmitted back to the surface control cabinet 5 via the monitoring cable.

[0034] In the optional schemes of this embodiment, it is more preferred that the ground control cabinet 5 is communicatively connected to each ultrasonic transducer assembly via an interval pulse drive module.

[0035] In the optional schemes of this embodiment, a preferred embodiment uses an interval pulse drive module to generate periodic intermittent ultrasonic pulse signals. The working duration ton and the sleep duration toff of the periodic intermittent ultrasonic pulse signals satisfy ton / toff≤0.3 (i.e., duty cycle≤30%), and ton≤2s, toff≥3s. This parameter range has been experimentally verified to control the transducer core temperature rise within ≤15℃ while ensuring viscosity reduction.

[0036] In the optional solutions of this embodiment, it is more preferred that the interval pulse drive module is disposed in the ground control cabinet 5, or the interval pulse drive module includes multiple interval pulse drive sub-modules; the interval pulse drive sub-modules correspond one-to-one with the ultrasonic transmitting sub-sections and are encapsulated and integrated in the ultrasonic transmitting sub-sections.

[0037] The following are the settings instructions for the downhole temperature, pressure, and viscosity sensing module: In the optional schemes of this embodiment, the more preferred method is that the ground control cabinet 5 adjusts the transmission power and ton / toff data (duty cycle) of each ultrasonic transducer assembly in real time based on the data returned by each downhole temperature, pressure and viscosity sensing module and / or ground production parameters.

[0038] The following are the settings instructions for ground control cabinet 5: Specifically, the ground control cabinet 5 includes a power supply, an interval pulse generator, a data acquisition and processing unit, and a human-machine interface, which can independently control the transmission parameters (start / stop, power, duty cycle) of each segment (i.e., ultrasonic transmitting segment).

[0039] Regarding other relevant explanations: Specifically, (1) Interval pulse emission strategy: Unlike existing technologies (such as continuous ultrasound), it adopts a "work-sleep" cycle mode. Experimental verification shows that, under the premise of comparable viscosity reduction, it can reduce the average temperature rise of the transducer by more than 70% and extend the theoretical lifespan to 5 to 8 times that of the continuous working mode. This is the first time that the lifespan bottleneck of ultrasonic transducers in long-term downhole operation has been solved.

[0040] (2) Ultra-small transducer packaging structure resistant to high temperature and high pressure corrosion: Through the combined design of pressure balance chamber, metal radiating head, corrosion resistant coating, and ultra-thin wall shell (wall thickness 1~2mm), it achieves engineering indicators such as outer diameter ≤20mm (can be placed in the annular space 3 between tubing 2 and casing 1), pressure resistance 60MPa, temperature resistance 180℃, and resistance to H2S / CO2 corrosion. It can directly pass through the annulus between standard 2-7 / 8″ tubing 2 and casing 1 (minimum gap of about 15mm).

[0041] (3) Distributed multi-point layout and independent control along the wellbore: Unlike existing single-point treatment solutions, this method optimizes the spacing and number of short sections based on the wellbore viscosity profile to achieve "segmented viscosity reduction and step-by-step atomization," thus avoiding viscosity rebound. Each short section can be started, stopped, and its power adjusted independently to adapt to the differences in crude oil properties in different well sections.

[0042] (4) Closed-loop feedback control: By combining real-time downhole viscosity / temperature monitoring, the surface control system automatically adjusts ultrasonic parameters to achieve "viscosity reduction on demand," further reducing energy consumption.

[0043] Specifically, the beneficial effects it achieves are further explained as follows: (1) Regarding the working life of transducers, existing continuous ultrasonic technology is prone to overheating failure when working continuously downhole, and the lifespan is usually no more than 3,000 hours. This embodiment adopts an intermittent and distributed working mode, which greatly reduces heat accumulation and can extend the transducer lifespan to more than 15,000 hours, achieving a several-fold improvement.

[0044] (2) Regarding the daily power consumption of a single well, existing technologies require continuous ultrasonic output, resulting in power consumption as high as 1.5 to 3 kW. This embodiment significantly reduces ineffective energy consumption through intermittent start-stop and distributed layout, requiring only 0.3 to 0.6 kW per day, achieving an energy saving of 70% to 80%.

[0045] (3) Regarding viscosity reduction rate, existing continuous ultrasonic technology can reduce crude oil viscosity by 60% to 75% under the same power. In this embodiment, under the same power conditions, by optimizing the excitation method and distribution position, the viscosity reduction rate reaches 65% to 80%, which is comparable or slightly superior.

[0046] (4) Regarding wellbore adaptability, existing technologies rely on single-point transducers, which are difficult to cover long well sections and have a limited range of application. This embodiment adopts a distributed multi-point deployment and excitation along the wellbore in segments, which can effectively handle the entire well section and achieve a qualitative improvement in adaptability.

[0047] Specific Case Studies In an indoor simulated wellbore (inner diameter 62mm, outer diameter 114mm, annular clearance 326mm), using heavy oil with a viscosity of 1800 mPa·s (60℃) as the medium, three ultrasonic transmitting sub-sections (spaced 1.5m apart) were installed. Simultaneously, monitoring cables carrying the corresponding number and positions of downhole temperature, pressure, and viscosity sensing modules were lowered into tubing 2. Operating parameters: 40kHz, 50W, ton=1s, toff=5s. After 72 hours of operation, a sample was taken 2m above the lowest sub-section, and the viscosity was measured to have decreased to 320 mPa·s, a viscosity reduction rate of 82.2%. The transducer casing temperature stabilized at 75~80℃ (ambient temperature 60℃), with a temperature rise ≤20℃. After 2000 hours of continuous operation, the transducer performance degradation was <3%.

[0048] Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this invention. Furthermore, those skilled in the art will recognize that, based on the ideas of this invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A downhole distributed ultrasonic atomization method for reducing crude oil viscosity in wellbore, characterized in that: Includes the following steps: S1. Obtain the viscosity distribution curve of crude oil in the wellbore along the depth, determine the viscosity inflection point depth Hc, and determine the installation position of the first ultrasonic transmitting sub-section based on this; determine the position of the remaining at least two ultrasonic transmitting sub-sections vertically upward at a set distance; and fix each ultrasonic transmitting sub-section to the armored cable. S2, lower the assembled armored cable along with each ultrasonic short section into the annular space of the well shaft, and fix it after reaching the designed depth; S3, start the ground control cabinet, drive each ultrasonic transmitting segment to emit ultrasonic waves according to the preset interval pulse mode, where each ultrasonic transmitting segment works independently or takes turns in sequence; to achieve segmented viscosity reduction and step-by-step atomization of crude oil in the oil pipe.

2. The downhole distributed ultrasonic atomization method for reducing crude oil viscosity in wellbore according to claim 1, characterized in that: In S1, the first ultrasonic transmitting sub is installed 30m to 100m below the height of Hc, and the remaining ultrasonic transmitting subs are arranged every L meters along the upward direction of the wellbore until 200m below the wellhead.

3. The downhole distributed ultrasonic atomization method for reducing crude oil viscosity in wellbore according to claim 1, characterized in that: Each of the ultrasonic transmitting sections contains an ultrasonic transducer assembly. A monitoring cable is laid inside the tubing, and a downhole temperature, pressure and viscosity sensing module is fixed on the monitoring cable at the position corresponding to each of the ultrasonic short sections. The downhole temperature, pressure and viscosity sensing module is used to collect crude oil temperature, pressure and viscosity parameters in real time, which are transmitted back to the ground control cabinet via the monitoring cable.

4. The downhole distributed ultrasonic atomization method for reducing crude oil viscosity in wellbore according to claim 3, characterized in that: The ground control cabinet is communicatively connected to each of the ultrasonic transducer components via an interval pulse drive module.

5. The downhole distributed ultrasonic atomization method for reducing crude oil viscosity in wellbore according to claim 4, characterized in that: The interval pulse driving module is used to generate periodic intermittent ultrasonic pulse signals. The working duration ton and the sleep duration toff of the periodic intermittent ultrasonic pulse signals satisfy ton / toff≤0.3, and ton≤2s, toff≥3s.

6. The downhole distributed ultrasonic atomization method for reducing crude oil viscosity in wellbore according to claim 4, characterized in that: The interval pulse drive module is located inside the ground control cabinet, or the interval pulse drive module includes multiple interval pulse drive sub-modules; each interval pulse drive sub-module corresponds one-to-one with the ultrasonic transmitting section and is encapsulated and integrated within the ultrasonic transmitting section.

7. The downhole distributed ultrasonic atomization method for reducing crude oil viscosity in wellbore according to claim 5, characterized in that: The ground control cabinet adjusts the transmission power and ton / toff data of each ultrasonic transducer assembly in real time based on the data returned by each downhole temperature, pressure and viscosity sensing module and / or ground production parameters.

8. The downhole distributed ultrasonic atomization method for reducing crude oil viscosity in wellbore according to claim 2, characterized in that: The interval distance L is determined based on the wellbore temperature gradient and / or crude oil viscosity profile; and L = 5m~50m.

9. The downhole distributed ultrasonic atomization method for reducing crude oil viscosity in wellbore according to claim 1, characterized in that: The armored cable has an outer sheath made of alloy or polymer composite material that is resistant to temperature ≥180℃, pressure ≥60MPa, and H2S / CO2 corrosion.

10. The downhole distributed ultrasonic atomization method for reducing crude oil viscosity in wellbore according to claim 1, characterized in that: The outer diameter of the ultrasonic transmitting section is ≤22mm and the length is ≤200mm.

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