Heavy oil well dilution gas injection production tubing, methods and downhole mixing devices

Abstract

This invention provides a heavy oil well dilution and gas injection production tubing string, method, and downhole mixing device, belonging to the field of oil production engineering. The mixing device includes a shell, a lift pipe, an acceleration mechanism, and a flow guiding mechanism. The lift pipe is disposed inside the shell and has a formation heavy oil inlet at the bottom, a production heavy oil outlet at the top, and a mixing chamber in the middle. The mixing chamber is used to uniformly mix the light oil and natural gas mixture with the formation heavy oil to produce production heavy oil. The acceleration mechanism is disposed in the annular space formed by the shell and the lift pipe, and can accelerate the injection of the light oil and natural gas mixture into the mixing chamber. The flow guiding mechanism is disposed inside the lift pipe, and can guide the formation heavy oil into the mixing chamber in a turbulent state. The mixing device provided by this invention can help improve the uniformity of mixing heavy oil, light oil, and natural gas, thereby improving the mixing viscosity reduction efficiency.

Description

Technical Field

[0001] This invention relates to the field of oil production engineering technology, specifically to a heavy oil well dilution gas injection production string, a heavy oil well dilution gas injection production method, and a downhole mixing device. Background Technology

[0002] Developing efficient, environmentally friendly, and low-cost new technologies for heavy oil extraction is an inevitable trend. However, heavy oil extraction is extremely difficult, and heavy oil has the following main characteristics compared to conventional light crude oil:

[0003] ① Heavy oil has high viscosity, high density, and poor fluidity. This not only increases the difficulty and cost of extraction but also reduces the ultimate recovery rate of the oil field. The key to heavy oil extraction is to improve its flowability in the reservoir, wellbore, and gathering and transportation pipelines. ② Heavy oil has a low content of light components but a high content of gums and asphaltenes. ③ Heavy oil viscosity is sensitive to temperature; as the temperature of heavy oil increases, its viscosity decreases significantly, which is the main mechanism of thermal recovery of heavy oil.

[0004] Since the development of heavy oil in the 1960s, various technologies have been developed, including thermal recovery technologies such as steam injection and steam flooding, and cold recovery technologies such as alkaline flooding, polymer flooding, and miscible flooding, achieving good results. Due to the high viscosity, high density, and poor fluidity of heavy oil, reducing its viscosity and improving its fluidity are key to solving the problems in heavy oil extraction.

[0005] Currently, one heavy oil extraction technology involves injecting a certain amount of thin oil into the well to mix with the heavy oil in the wellbore, reducing the viscosity of the heavy oil, and then extracting it using conventional methods. However, this method requires a large amount of thin oil, and the price of the produced crude oil is sold at the same level as medium crude oil, which is significantly lower than the price when heavy oil and thin oil are sold separately, resulting in an overall unsatisfactory outcome. To reduce the amount of thin oil used and improve the economic efficiency of heavy oil extraction, the oilfield has proposed mixing natural gas with thin oil before using it for heavy oil extraction. This would reduce the viscosity of heavy oil by mixing it with natural gas, thus reducing the amount of thin oil used, and would also increase the wellbore lift energy through gas injection. However, the large differences in density and viscosity between natural gas and thin oil compared to heavy oil lead to uneven mixing when they meet at the fluid surface in the wellbore annulus, resulting in slugging in the fluid within the tubing and failing to achieve the optimal effect of thinning and gas injection to reduce viscosity.

[0006] There is an urgent need for a downhole tool that specifically enhances the uniformity of mixing of heavy oil, light oil and natural gas in heavy oil-liquid gas injection wells, in order to solve the problem of uniform mixing of natural gas, light oil and heavy oil below the dynamic fluid level. Summary of the Invention

[0007] To address the technical problem of uneven mixing of natural gas, light oil, and heavy oil after they meet at the fluid surface in the wellbore annulus, this invention provides a downhole mixing device. This device can improve the uniformity of mixing of heavy oil, light oil, and natural gas in the well, and improve the mixing and viscosity reduction efficiency.

[0008] To achieve the above objectives, a first aspect of the present invention provides a downhole mixing device, which is connected to a downhole tubing and includes a housing, a lift pipe, an acceleration mechanism, and a flow guiding mechanism. The housing is a hollow cylinder with an outer diameter equal to that of the tubing. The lift pipe is disposed inside the housing and has a formation heavy oil inlet at the bottom, a production heavy oil outlet at the top, and a mixing chamber in the middle. The mixing chamber is used to uniformly mix a light oil-natural gas mixture and formation heavy oil to produce production heavy oil. The acceleration mechanism is disposed in the annular space formed by the housing and the lift pipe, and can accelerate the injection of the light oil-natural gas mixture into the mixing chamber. The flow guiding mechanism is disposed inside the lift pipe, and can guide the formation heavy oil into the mixing chamber in a turbulent flow state.

[0009] In an exemplary embodiment of the present invention, the flow guiding mechanism may consist of two flow guiding plates, and the angle between each flow guiding plate and the horizontal direction may be 30° to 60°.

[0010] In an exemplary embodiment of the present invention, the guide plate may be a semi-elliptical straight plate.

[0011] In an exemplary embodiment of the present invention, the pressure in the annular space may be greater than the pressure in the mixing chamber.

[0012] In an exemplary embodiment of the present invention, 4 to 8 sets of acceleration mechanisms may be provided along the axial direction of the housing.

[0013] In an exemplary embodiment of the present invention, each acceleration mechanism may consist of multiple variable-diameter channels arranged circumferentially along the lifting tube, wherein the variable-diameter channels have a gradually narrowing and expanding structure.

[0014] In an exemplary embodiment of the present invention, the side wall of the housing may have multiple sets of oil and gas inlets that communicate with the acceleration mechanism and are arranged along the axis of the housing; the side wall of the lifting pipe may have multiple sets of oil and gas outlets corresponding to the oil and gas inlets.

[0015] In an exemplary embodiment of the present invention, the oil and gas outlet may be tangent to the wall of the lifting pipe.

[0016] A second aspect of the present invention provides a production tubing string for heavy oil wells with dilution and gas injection. The production tubing string includes a casing, tubing, a pump, and a mixing device as described above. The casing is disposed outside the tubing, and the casing and tubing are coaxial and form an annulus. The pump and the mixing device are disposed inside the tubing, and the mixing device is located below the pump.

[0017] The third aspect of the present invention provides a method for heavy oil well dilution and gas injection, which uses the production tubing as described above to complete the heavy oil viscosity reduction process. During the production process, the mixture of thin oil and natural gas enters the mixing device through the annulus of the casing and is uniformly mixed with the formation heavy oil before being lifted to the surface by a pump.

[0018] The present invention has at least the following technical effects through the technical solution provided by the present invention:

[0019] (1) The mixing device of the present invention can help improve the uniformity of mixing of heavy oil, light oil and natural gas, thereby improving the mixing viscosity reduction efficiency;

[0020] (2) The mixing device of the present invention is a downhole tool specifically applied to the thick oil dilution and viscosity reduction process in the form of positive dilution, which helps to achieve the best dilution and gas injection viscosity reduction effect.

[0021] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0022] The accompanying drawings are provided to further illustrate embodiments of the present invention and form part of the specification. They are used together with the following detailed description to explain the embodiments of the present invention, but do not constitute a limitation thereof. In the drawings:

[0023] Figure 1 This is a schematic diagram of the downhole mixing device provided in an embodiment of the present invention;

[0024] Figure 2 This is a schematic diagram of the acceleration mechanism provided in an embodiment of the present invention;

[0025] Figure 3 This is a schematic diagram of the structure of the Laval nozzle provided in an embodiment of the present invention;

[0026] Figure 4 This is a schematic diagram of the flow guiding mechanism provided in an embodiment of the present invention;

[0027] Figure 5 A schematic diagram of the process of a heavy oil well dilution gas injection production tubing provided in an embodiment of the present invention;

[0028] Figure 6 This is a schematic diagram of the heavy oil well dilution gas injection extraction method provided in an embodiment of the present invention.

[0029] Explanation of reference numerals in the attached figures

[0030] 1-Shell, 2-Acceleration mechanism, 3-Lifting pipe, 4-Flow guiding mechanism, 5-Casing, 6-Oil pipe, 7-Oil pump, 8-Mixer. Detailed Implementation

[0031] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the scope of the present invention.

[0032] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0033] In this invention, unless otherwise stated, directional terms such as "upper," "lower," "top," and "bottom" are generally used to describe the relative positions of components in relation to the directions shown in the accompanying drawings or in relation to the vertical, perpendicular, or gravitational directions.

[0034] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integrated connection; they can refer to a direct connection or an indirect connection; they can refer to a wired connection or a wireless connection. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0035] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0036] Example 1

[0037] The first embodiment of the present invention provides a downhole mixing device, which includes a housing, a lifting pipe, an acceleration mechanism, and a flow guiding mechanism.

[0038] The casing is connected to the downhole tubing. The casing is a hollow cylinder with an outer diameter equal to that of the tubing. Furthermore, the connection point between the casing and the tubing should be below the annular fluid level in the wellbore.

[0039] The lift pipe is located inside the shell and has a formation heavy oil inlet at the bottom, a production heavy oil outlet at the top, and a mixing chamber in the middle. The mixing chamber is used to uniformly blend the light oil and natural gas mixture with the formation heavy oil to produce production heavy oil. The light oil and natural gas mixture consists of light oil spray and natural gas, and its function is to reduce the viscosity of the formation heavy oil.

[0040] An acceleration mechanism is disposed within the annular space formed by the housing and the lift pipe, and is used to accelerate the injection of the thin oil and natural gas mixture into the mixing chamber. The function of the acceleration mechanism is to increase the entry velocity of the thin oil and natural gas mixture so that the droplets can be further broken up and enter the lift pipe in a wide-range diffusion manner. Exemplarily, the acceleration mechanism may consist of multiple variable-diameter channels arranged circumferentially along the lift pipe. The variable-diameter channels may be a tapered structure or a tapered-expanding structure.

[0041] A flow guiding mechanism is installed inside the lift pipe to guide the formation heavy oil into the mixing chamber in a turbulent state. The function of the flow guiding mechanism is to induce a swirling flow field at the formation heavy oil inlet. In this swirling flow field, the formation heavy oil undergoes turbulent motion due to the pressure field, making it less likely to form slugs within the lift pipe. For example, the flow guiding mechanism can consist of two guide vanes, each with an angle of 30° to 60° with the horizontal direction. Preferably, the angle between each guide vane and the horizontal direction can be 45°. The guide vanes can be semi-elliptical straight plates, arc blades, helical blades, etc.

[0042] Furthermore, the sidewall of the shell can have multiple sets of oil and gas inlets connected to the acceleration mechanism and arranged along the shell axis; the sidewall of the lift pipe can have multiple sets of oil and gas outlets corresponding to the oil and gas inlets; and multiple sets of acceleration mechanisms can be arranged along the axial direction of the shell. For example, 4 to 8 sets of oil and gas inlets can be arranged along the axial direction on the sidewall of the shell, and correspondingly, 4 to 8 sets of acceleration mechanisms connected to the oil and gas inlets can be arranged, with each set of acceleration mechanisms having 2 to 8 variable diameter channels. The variable diameter channels can accelerate the injection speed of the light oil and natural gas mixture, and setting multiple sets of acceleration mechanisms is beneficial to increasing the distribution space of high-speed oil and gas inside the lift pipe, providing more possibilities for the uniform mixing of heavy oil, light oil and natural gas.

[0043] Example 2

[0044] Please refer to Figure 1 Regarding the downhole blending process in heavy oil blending wells for natural gas viscosity reduction, a second embodiment of the present invention provides a downhole blending device for heavy oil blending wells. This blending device (hereinafter referred to as the blender) includes a shell 1, an acceleration mechanism 2, a lift pipe 3, and a flow guiding mechanism 4. The entire device adopts a passive downhole blender design combining open-hole and swirling flow types. The upper part is a side-opening natural gas atomized thin oil inlet, and the lower part is a swirling flow heavy oil inlet. It should be noted that natural gas atomized thin oil refers to a mixture of thin oil and natural gas composed of thin oil spray and natural gas.

[0045] The housing 1 is a hollow cylinder, with a lifting tube 3 inside. The acceleration mechanism 2 is located in the annular space between the housing 1 and the lifting tube 3, and the flow guiding mechanism 4 is fixedly connected to the lower part of the lifting tube 3.

[0046] As shown Figure 2 in the figure, the acceleration mechanism 2 can be composed of multiple variable-diameter channels arranged circumferentially along the lifting pipe, and the cross-sectional shape of the variable-diameter channel is a spline curve shape. The side wall of the housing 1 is provided with 4 rows of lateral opening type natural gas atomized thin oil inlets in the vertical direction, and each row of lateral opening type natural gas atomized thin oil inlets consists of 4 tangential openings arranged evenly along the circumferential direction of the housing. Correspondingly, the side wall of the lifting pipe 3 is provided with 4 rows of natural gas atomized thin oil outlets in the vertical direction, and each row of natural gas atomized thin oil outlets consists of 4 variable-diameter openings arranged evenly along the circumferential direction of the lifting pipe. Designed based on the principle of the Laval nozzle, the variable-diameter channel connecting the natural gas atomized thin oil inlet and the natural gas atomized thin oil outlet adopts a Laval nozzle structure in a gradually shrinking and then expanding form.

[0047] Figure 3 The schematic diagram of the Laval nozzle structure is given. When high-speed gas flows through the pipe, if the pipe length is not large, the influence of wall friction is not significant and the friction force influence can be ignored. Under ideal conditions, ignoring the influence of wall friction and heat exchange, this adiabatic and frictionless motion is isentropic. The gas undergoes one-dimensional isentropic motion in the nozzle, and the continuity equation and momentum differential equation are obtained as follows:

[0048]

[0049]

[0050] Solving dA / A gives:

[0051]

[0052] Because where a is the speed of sound and M is the Mach number, thus it can be obtained that

[0053]

[0054] When M = 0, that is, when a is infinite, at this time the decrease or increase of the area will lead to the increase or decrease of the speed, and the changed values are equal, which is the case of incompressible fluid; when 0 < M < 1, v < a < ∞, the gas is in the subsonic range, and the signs of dv / v and dA / A are opposite, and the decrease of the area leads to the increase of the speed; when M > 1, that is, v > a, at this time the area increases, the speed increases, and the pressure decreases, and vice versa, and the larger M is, the less sensitive the speed is to the change of the area; when M = 1, that is, v = a, at this time dA = 0, indicating that the maximum or minimum value is reached at M = 1, indicating that the pipe reaches the speed of sound at the minimum cross-section.

[0055] Therefore, the Laval nozzle structure used in this embodiment is a contraction-expansion type. Under certain pressure conditions, the compressible fluid first contracts within the nozzle, gradually increasing in velocity. At the critical cross-section, the fluid velocity reaches the speed of sound, also known as the critical velocity. After passing the critical cross-section, the fluid enters the expansion section. At the instant it passes the critical cross-section, it undergoes adiabatic expansion into the surrounding environment, and its velocity continues to increase, reaching supersonic speed.

[0056] Therefore, the variable-diameter channel in this embodiment, which converges first and then expands, accelerates the atomization of natural gas into thin oil, facilitating further droplet breakup and diffusion, and allowing the liquid to enter the lift pipe for mixing. The pressure on the outer side of the lift pipe is greater than on the inner side, preventing the mixed liquid inside the lift pipe from flowing out. Considering the turbulent swirling effect, the variable-diameter orifice is tangential to the wall of the lift pipe, increasing the tangential force and enhancing disturbance during initial startup.

[0057] The lower part of the lift pipe is configured as a vortex-type heavy oil inlet. Axial vortex initiation can be used to allow the heavy oil produced from the reservoir to enter the main pipeline flow field axially at the bottom of the well, forming vortices under the induction of the guide vanes. For example... Figure 4 As shown, the flow guiding mechanism can be a straight-plate guide vane, which consists of two semi-elliptical straight plates with an angle of 45° between the two plates and the horizontal direction. The straight-plate guide vane creates a swirling flow field with a high pressure drop and a long development section, resulting in more chaotic flow near the outlet of the guiding zone. Furthermore, because the straight-plate guide vane has no shaft, it has a large flow area and is less prone to blockage.

[0058] Example 3

[0059] Please refer to Figure 5 and Figure 6 The third embodiment of the present invention provides a heavy oil well dilution gas injection production string and its production method. Figure 5 The symbol AA represents the dynamic liquid level, the arrow corresponding to the symbol x indicates the flow direction of the natural gas atomized thin oil, the arrow corresponding to the symbol y indicates the flow direction of the formation crude oil, and the arrow corresponding to the symbol z indicates the flow direction of the production crude oil after blending and viscosity reduction.

[0060] like Figure 5 As shown, the heavy oil well dilution gas injection production string in this embodiment includes a casing 5, tubing 6, a pump 7, and a mixer 8. The casing 5 is located outside the tubing 6, and the casing 5 and tubing 6 are coaxial and form an annulus. The pump 7 and mixer 8 are located inside the tubing 6, and the mixer 8 is installed below the pump 7. The lower part of the mixer 8 is connected to a tailpipe of a certain length.

[0061] During the production process, the thin oil spray formed by natural gas atomization flows into the acceleration mechanism of the mixer along with the natural gas and then enters the internal lifting pipe. It is then uniformly mixed with the formation heavy oil induced to swirl by the straight guide plate and lifted to the ground by the pump.

[0062] The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the specific details of the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0063] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0064] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A downhole mixing device, characterized in that, The mixing device is used in a positive-blending heavy oil dilution gas injection extraction process. The mixing device is connected to the downhole tubing and includes a shell, lift pipe, acceleration mechanism, and flow guiding mechanism. The shell is in the shape of a hollow cylinder, and the outer diameter of the shell is equal to the outer diameter of the oil pipe; The lift pipe is located inside the housing and has a formation heavy oil inlet at the bottom, a production heavy oil outlet at the top, and a mixing chamber in the middle. The mixing chamber is used to uniformly mix the light oil and natural gas mixture with the formation heavy oil to produce heavy oil. The acceleration mechanism is set in the annular space formed by the housing and the lifting pipe, and can accelerate the injection of the mixture of thin oil and natural gas into the mixing chamber; each acceleration mechanism consists of multiple variable diameter channels arranged along the circumference of the lifting pipe, the variable diameter channels have a gradually narrowing and expanding structure, and the variable diameter orifice is tangent to the wall of the lifting pipe. The flow guiding mechanism is located inside the lifting pipe and can guide the formation heavy oil into the mixing chamber in a turbulent state. The flow guiding mechanism consists of two guide vanes, which are semi-elliptical straight plates with an angle of 30° to 60° between each guide vane and the horizontal direction.

2. The downhole mixing device of claim 1, wherein, The pressure in the annular space is greater than the pressure in the mixing chamber.

3. The downhole mixing device of claim 1, wherein, Four to eight sets of acceleration mechanisms are arranged along the axial direction of the shell.

4. The downhole mixing device of claim 1, wherein, The side wall of the housing has multiple sets of oil and gas inlets that are connected to the acceleration mechanism and arranged along the axis of the housing; the side wall of the lifting pipe has multiple sets of oil and gas outlets that correspond to the oil and gas inlets.

5. A heavy oil well mixed thinning gas injection production string, characterized in that, The extraction string includes a casing, tubing, a pump, and a mixing device as described in any one of claims 1 to 4. The casing is disposed outside the tubing, and the casing and tubing are coaxial and form an annulus. The pump and the mixing device are disposed inside the tubing, and the mixing device is located below the pump.

6. A method for exploiting heavy oil wells by mixing thinning and injecting gas, characterized in that, The heavy oil viscosity reduction process is completed using the extraction tubing described in claim 5. During the production process, the mixture of light oil and natural gas enters the mixing device through the annulus of the casing and is uniformly mixed with the formation heavy oil. Then, it is lifted to the surface by a pump.

Images