Measurement Device and Method for Permeability of Ultra-Narrow Fractures Supported by Microfluidics

Abstract

An embodiment of the present invention discloses a measurement device and method for the permeability of an ultra-narrow propped fracture based on microfluidic technology. The measurement device includes: a propped fracture model, including a tube body formed with a fluid channel, and an ultra-narrow prefabricated fracture paved with proppants is formed on its side wall; a fluid supply unit for supplying a fluid with preset flow parameters to the fluid channel; a fluid collection unit for collecting the fluid flowing out through the outlet end; a monitoring and measurement unit for measuring the parameters of the fluid flowing through the inlet end and the outlet end; the fracture width of the ultra-narrow prefabricated fracture is not greater than 1 mm. Based on microfluidic technology, the present invention can effectively simulate the flow behavior of fluids in ultra-narrow real fracture channels by fabricating fracture or core models with millimeter-level or even micron-level precision, and further can measure the effective permeability of fractures affected by viscous shear action, providing accurate formation reference information for the optimization design in actual operations.

Description

Technical Field

[0001] The embodiments of the present invention relate to the technical field of oil and gas exploration and development, and particularly to a measuring device and method for the permeability of ultra-narrow propped fractures based on microfluidic technology. Background Art

[0002] In recent years, with the increase in the proven reserves of unconventional oil and gas fields, in order to improve the production efficiency, the fracturing technology in the stimulation measures has been widely applied, which has also promoted the development of proppants. During the hydraulic fracturing process, the sand-carrying fluid composed of solids such as proppants and sand and the fracturing fluid is injected into the casing and flows through the casing perforations to the fractures, forming a channel with a certain conductivity, thereby improving the oil and gas production effect.

[0003] During the fracturing process, for a fully propped fracture, if the fracture width is large enough, the viscous resistance from the fracture wall can be ignored. However, in the actual production process, as the production progresses, the stress between the proppant and the fracture wall will gradually increase, resulting in the embedding of the proppant, thereby reducing the contact area between the fluid and the proppant surface. If the embedding degree is large enough, the contact area between the fluid and the fracture wall will be greater than the contact area between the fluid and the proppant surface. In this case, the viscous shear from the fracture wall surface cannot be ignored, resulting in the emergence of Brinkman flow. However, there is currently no rigorous test device to measure the effective permeability of ultra-narrow propped fractures below 1 mm, which will seriously affect the evaluation accuracy of unconventional oil and gas field exploration and the formulation of production systems.

[0004] For this, the above problems currently proposed have no corresponding solutions as can also be reflected from the solutions in the prior art. For example, Chinese Patent CN216594692U discloses "a device for testing the permeability of acid-etched fractures in rock", which solves the technical problems in the prior art that it is impossible to accurately obtain acid-etched fractures in rock and it is difficult to study the permeability of acid-etched fractures; Chinese Patent CN113670793B discloses "a device and method for real-time monitoring of the permeability of hydraulic fractures", which discloses a device and method for real-time monitoring of the permeability of hydraulic fractures. Using this device, the formation creep effect and the stress interference phenomenon between fractures in unconventional oil and gas development can be simulated, so as to accurately detect the change of the permeability of hydraulic fractures over time and be used for unconventional oil and gas production capacity prediction; Chinese Patent CN109426673B discloses "a method and device for determining the conductivity of an inclined support area in a shale reservoir", which determines the conductivity of the inclined support area through the permeability and the first height of this fracture area, the permeability and the second height of this proppant-filled area, the permeability and the third height of this self-supporting area, and the fracture width of this inclined support area, so as to provide a basis for the transformation of the shale reservoir and further ensure the recovery rate of shale gas in the shale reservoir; Chinese Patent CN210003265U discloses "a permeability measurement device based on the coupling of artificial fractures and natural fractures", which adopts a square flow guide chamber and an HXDL-2C type proppant fracture evaluation system, effectively reducing the complexity of the connection of the equipment system and improving the accuracy of the measurement data record. It can reasonably optimize the fractures under indoor conditions so as to reasonably fracture the tight reservoir, improve the effectiveness of on-site operations, and be able to accurately measure the permeability of the tight reservoir containing natural fractures after fracturing, overcoming the limitations of the core holder structure and measurement method in the prior art.

[0005] Based on this, considering the actual situation of artificial fracturing fractures in the reservoir, if the above methods are referred to for experiments, the following problems and difficulties still exist: The width of the fractures in the reservoir is mostly in millimeters or even microns. In this case, the influence of the viscous shear effect on the fracture wall on the conductivity cannot be ignored. However, the existing test devices mentioned above are still unable to reach this precision due to the size limitation of the prefabricated fracture model. Therefore, the influence of viscous shear cannot be considered during the experiment, resulting in the inability to accurately measure the effective permeability under the condition of ultra-narrow propped fractures. Summary of the Invention

[0006] Therefore, the embodiments of the present invention provide a measurement device and a measurement method for the permeability of ultra-narrow propped fractures based on microfluidic technology. Based on microfluidic technology, by fabricating a fracture or core model with millimeter-level or even micron-level precision, the flow behavior of fluids in an ultra-narrow real fracture channel can be effectively simulated, and further, the effective permeability of the fracture affected by the viscous shear effect can be measured, providing accurate formation reference information for the optimization design in actual operations.

[0007] To achieve the above object, the embodiments of the present invention provide the following technical solutions:

[0008] In one aspect of the embodiments of the present invention, a measurement device for the permeability of an ultra-narrow supported fracture based on microfluidic technology is provided, including:

[0009] A supported fracture model, including a tube body with a fluid channel formed therethrough, and both ends of the fluid channel are open to form an inlet end and an outlet end respectively. An ultra-narrow prefabricated fracture communicating with the fluid channel is formed through the side wall of the tube body, and a proppant is formed in a convex shape on the inner wall of the tube body;

[0010] A fluid supply unit, communicating with the inlet end of the fluid channel, for supplying a fluid with preset flow parameters to the fluid channel;

[0011] A fluid collection unit, communicating with the outlet end of the fluid channel, for collecting the fluid flowing out through the outlet end;

[0012] A monitoring and measuring unit, for measuring the parameters of the fluid flowing through the inlet end and the outlet end;

[0013] The fracture width of at least a part of the ultra-narrow prefabricated fracture is not greater than 1 mm.

[0014] As a preferred solution of the present invention, the monitoring and measuring unit includes a flow sensor connected between the fluid supply unit and the inlet end, and a pressure sensor connected between the fluid collection unit and the outlet end.

[0015] As a preferred solution of the present invention, the fluid supply unit includes a gas supply structure, a fluid pumping structure and a liquid storage structure arranged in sequence;

[0016] The gas supply structure is used to inject gas with corresponding parameters into the fluid pumping structure according to the preset flow parameters, and the fluid pumping structure is used to adjust the fluid in the liquid storage structure to the preset flow parameters and supply it to the supported fracture model after being measured by the flow sensor.

[0017] As a preferred solution of the present invention, the gas provided by the gas supply structure is a non-corrosive gas;

[0018] The fluid pumping structure is a microfluidic pressure pump.

[0019] As a preferred solution of the present invention, the fluid is a pressurized liquid with a preset pressure value.

[0020] In another aspect of the embodiments of the present invention, there is also provided a method for measuring the permeability of an ultra-narrow propped fracture based on microfluidic technology. Using the above-mentioned measuring device, the measuring method includes:

[0021] S100. Preset the parameters of the propped fracture model, and fabricate a propped fracture model with an inlet end and an outlet end and filled with proppant according to the preset parameters of the propped fracture model;

[0022] S200. After injecting fluid into the fluid supply unit, adjust the flow parameters of the fluid to preset flow parameters;

[0023] S300. Connect the adjusted fluid supply unit in step S200, a part of the monitoring and measuring unit on the side of the inlet end, the propped fracture model fabricated in step S100, another part of the monitoring and measuring unit on the side of the outlet end, and the fluid collection unit in sequence;

[0024] S400. Start the fluid supply unit, supply fluid with preset flow parameters into the propped fracture model, and measure the actual parameters of the fluid at the inlet end and the outlet end;

[0025] S500. Calculate the permeability of the ultra-narrow propped fracture according to the formula described in Formula I based on the measured data;

[0026]

[0027] Formula I; where

[0028] K is the permeability of the ultra-narrow propped fracture model, with the unit of D; Q is the flow rate of the fluid flowing in through the inlet end, with the unit of mL / s; μ is the fluid viscosity, with the unit of mPa·s; L is the length of the propped fracture model, with the unit of cm; A is the cross-sectional area of the propped fracture model, with the unit of cm 2 ; P1 is the absolute pressure of the fluid at the inlet end, with the unit of MPa; P2 is the absolute pressure of the fluid at the outlet end, with the unit of MPa.

[0029] As a preferred solution of the present invention, in step S100, the parameters of the propped fracture model further include the parameters of the proppant and the width of the ultra-narrow prefabricated fracture.

[0030] As a preferred solution of the present invention, in step S100, the propped fracture model is fabricated by the molding method, and the fabrication process specifically includes:

[0031] S101. Fabricate a male mold with protrusions matching the ultra-narrow prefabricated fracture and depressions matching the proppant;

[0032] S102. Pour a curing material on the male mold with protrusions and depressions;

[0033] S103. After the material to be cured is cured, the cured material is demolded from the male mold to obtain a propped fracture model with ultra-narrow propped fractures and proppants.

[0034] As a preferred solution of the present invention, in step S101, the recesses cooperating with the proppants are fabricated by photolithography.

[0035] The embodiments of the present invention have the following advantages:

[0036] The embodiments of the present invention can simulate the permeability of propped fractures with different widths at millimeter or even micron-level precision, making up for the shortcomings of the size limitation of prefabricated rock sample models in the prior art, effectively evaluating the Brinkman flow considering the viscous shear effect on the fracture walls, being able to effectively evaluate the flow behavior of fluids under the viscous shear effect, and providing technical support for accurately measuring the conductivity of propped fractures. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only exemplary, and for those of ordinary skill in the art, without creative efforts, other implementation drawings can also be obtained according to the provided drawings.

[0038] The structures, ratios, sizes, etc. shown in this specification are only used to cooperate with the content disclosed in the specification for those familiar with this technology to understand and read, and are not used to limit the limiting conditions for the implementation of the present invention. Therefore, they do not have a substantial technical meaning. Any modification of the structure, change of the proportional relationship, or adjustment of the size, without affecting the effects that the present invention can produce and the purposes that can be achieved, should still fall within the scope that can be covered by the technical content disclosed in the present invention.

[0039] Figure 1 It is a schematic structural diagram of the measuring device provided by the embodiment of the present invention;

[0040] Figure 2 It is a cross-sectional view of the propped fracture model provided by the embodiment of the present invention;

[0041] Figure 3 It is a schematic diagram of the flow direction of the fluid in the liquid storage structure provided by the embodiment of the present invention;

[0042] Figure 4 It is a flowchart of the measuring method provided by the embodiment of the present invention.

[0043] In the figure:

[0044] 1 - Gas supply structure; 2 - Microfluidic pressure pump; 3 - Liquid storage structure; 4 - Flow sensor; 5 - Supporting fracture model; 6 - Pressure sensor; 7 - Fluid collection unit; 8 - Proppant; 9 - Ultra-narrow prefabricated fracture. Detailed implementation manners

[0045] The following specific embodiments illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of them. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0046] The technical solution of the present invention will be described in detail through specific embodiments below.

[0047] As Figures 1-3 shown, the present invention provides a measurement device for the permeability of an ultra-narrow supported fracture based on microfluidic technology. Specifically, it includes: a gas supply structure 1 (a gas cylinder can be specifically selected), a microfluidic pressure pump 2, a liquid storage structure 3 (which can be any suitable liquid storage structure, and its shape can be selected according to needs, including but not limited to a bottle body, a tube body, etc. For example, in the present invention, a liquid storage tube can be selected), a flow sensor 4, a supporting fracture model 5, a pressure sensor 6, and a liquid collection unit 7 (similarly, the shape of the liquid collection unit 7 can be not limited. Specifically, a collection tube can be selected in the present invention). At the same time, it should be noted that the supported fracture in the supporting fracture model 5 is an ultra-narrow prefabricated fracture 9, and the width of the ultra-narrow prefabricated fracture 9 is not greater than 1 mm, thus providing a favorable guarantee for the effective measurement of the effective permeability of the ultra-narrow fracture under this size. A proppant 8 is formed on the inner wall of the supporting fracture model 5. It should be further explained that the proppant 8 here is a simulation structure, which is a similar attachment form that the proppant 8 can form during the conventional use process on the supporting fracture model 5, and it is a structural form formed after simulating the conventional attachment, rather than a material.

[0048] Among them, the function of the microfluidic pressure pump 2 is to apply an external pressure to the sealed liquid storage tube filled with fluid (it should be further noted that the way to apply the external pressure here is to pump in non-corrosive gas, and the non-corrosive gas here can be any type that those skilled in the art can understand and use. For example, it can be gases such as CO2 and N2), so as to utilize the pressure difference between the inlet and outlet of the liquid storage tube in the sealed state to pump the fluid into the propped fracture model 5. It should be further explained that the connection port of the liquid storage tube connected to the gas supply structure 1 and the microfluidic pressure pump 2 is the inlet, and the connection port of the liquid storage tube connected to the flow sensor 4 is the outlet. The directions of the inlet and outlet here are defined according to the flow direction of the fluid, and no more details will be elaborated here.

[0049] On this basis, the present invention further provides a method for measuring the effective permeability of an ultra-narrow propped fracture based on the above-mentioned measuring device, as Figure 4 shown. Specifically, it includes:

[0050] Step 1: Determine data such as the parameters of the proppant and the width of the ultra-narrow prefabricated fracture according to the experimental requirements, use the molding method to make a propped fracture model, and record the cross-sectional area and length of the obtained propped fracture model. Among them, the cross-sectional area of the propped fracture model is denoted as A, and the length of the propped fracture model (the length here refers to the length in the direction extending from its inlet end to the outlet end) is denoted as L. It should be further explained that the parameters of the proppant here include but are not limited to the morphology and particle size of the proppant, and other parameters of the proppant that those skilled in the art can understand and that have a certain influence on the propped fracture in the present invention are all included herein.

[0051] Step 2: After cleaning and drying the propped fracture model rock sample, connect its inlet end and outlet end to pipelines respectively. Among them, the outlet end is connected to a high-precision pressure sensor for recording the pressure at the outlet end, and the pressure at the outlet end is denoted as P2.

[0052] Step 3: Load the fluid into the liquid storage tube, connect the liquid storage tube filled with fluid to the microfluidic pressure pump and the flow sensor and make it sealed;

[0053] Step 4: Open the gas supply structure (in the specific embodiment of the present invention, a nitrogen cylinder is specifically used here) and the microfluidic pressure pump, adjust the pressure at the inlet end to a preset value and record it, denoted as P1.

[0054] Step 5: At this time, further observe the instrument of the flow sensor. After the value displayed on it is stable, record the data displayed on the flow sensor, which is the flow rate of the fluid (i.e., the fluid flowing in through the inlet end), denoted as Q.

[0055] Step 6: According to the data such as the pressures at the inlet end and the outlet end and the liquid flow rate, calculate using the formula described in Formula I, and the effective permeability of the ultra-narrow propped fracture model can be obtained. Formula I is specifically as follows:

[0056] Wherein,

[0057] K is the permeability of the ultra-narrow propped fracture model, with the unit of D; Q is the flow rate of the fluid flowing into through the inlet end, with the unit of mL / s; μ is the fluid viscosity, with the unit of mPa·s; L is the length of the propped fracture model, with the unit of cm; A is the cross-sectional area of the propped fracture model, with the unit of cm 2 ; P1 is the absolute pressure of the fluid at the inlet end, with the unit of MPa; P2 is the absolute pressure of the fluid at the outlet end, with the unit of MPa.

[0058] It should be further elaborated that due to the high standard of the fracture width of the ultra-narrow propped fracture here, a propped fracture with a size of millimeter level or even micron level needs to be obtained. Therefore, it is often impossible to obtain an ultra-narrow propped fracture with such high precision by using conventional methods in the art. Thus, in the present invention, the molding method is adopted here, and its specific manufacturing process further includes: first, a male mold is made by photolithography (the required channel part protrudes, and the required channel here is the place where the propped fracture is formed; further, the male mold also has depressions to adapt to the structural shape formed by the proppant), then a liquid polymer material is poured, and the cured polymer material is peeled off from the male mold, and a propped fracture model with micro-channels can be obtained.

[0059] It should be further noted that since the propped fracture itself has reached the micron level, the formation of the propped fracture and the proppant is obtained by etching on the template of the prefabricated male mold. Specifically, for the depressions that need to cooperate to form the proppant, photolithography can be used to obtain them, so as to better improve the controllability of the production of the proppant.

[0060] Although the present invention has been described in detail with general descriptions and specific embodiments above, based on the present invention, some modifications or improvements can be made, which are obvious to those skilled in the art. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection required by the present invention.

Claims

1. A method for measuring the permeability of ultra-narrow propped fractures based on microfluidic technology, characterized in that, The measuring device includes: A supported fracture model (5), including a pipe body with a fluid channel formed therethrough, and both ends of the fluid channel are open to form an inlet end and an outlet end. A ultra-narrow prefabricated fracture (9) communicating with the fluid channel is formed through the side wall of the pipe body, and a proppant (8) is formed in a convex shape on the inner wall of the pipe body; A fluid supply unit, communicating with the inlet end of the fluid channel, for supplying a fluid with preset flow parameters to the fluid channel; A fluid collection unit (7), communicating with the outlet end of the fluid channel, for collecting the fluid flowing out through the outlet end; A monitoring and measuring unit, for measuring the parameters of the fluid flowing through the inlet end and the outlet end; The crack width of at least part of the ultra-narrow prefabricated fracture (9) is not greater than 1 mm; The measuring method includes: S100. Preset the parameters of the supported fracture model, and use the molding method to fabricate a supported fracture model with an inlet end and an outlet end and formed with a proppant according to the preset parameters of the supported fracture model. The manufacturing process of the molding method at least includes: S101. Fabricate a male mold with protrusions matching the ultra-narrow prefabricated fractures and depressions matching the proppant, and the depressions are fabricated by photolithography; S200. After injecting fluid into the fluid supply unit, adjust the flow parameters of the fluid to the preset flow parameters; S300. Connect the adjusted fluid supply unit in step S200, a part of the monitoring and measuring unit on the side of the inlet end, the supported fracture model fabricated in step S100, another part of the monitoring and measuring unit on the side of the outlet end, and the fluid collection unit in sequence; S400. Turn on the fluid supply unit, supply a fluid with preset flow parameters to the supported fracture model, and measure the actual parameters of the fluid at the inlet end and the outlet end; S500. Calculate the permeability of the ultra-narrow supported fracture according to formula I based on the measured data; Formula I; wherein, K is the permeability of the ultra-narrow propped fracture model, with the unit of D; is the flow rate of the fluid flowing in through the inlet end, with the unit of mL / s; μ is the fluid viscosity, with the unit of mPa·s; L is the length of the propped fracture model, with the unit of cm; A is the cross-sectional area of the propped fracture model, with the unit of cm 2 ; is the absolute pressure of the fluid at the inlet end, with the unit of MPa; is the absolute pressure of the fluid at the outlet end, with the unit of MPa.

2. The method for measuring the permeability of ultra-narrow propped fractures based on microfluidic technology according to claim 1, characterized in that, The monitoring and measuring unit includes a flow sensor (4) connected between the fluid supply unit and the inlet end, and a pressure sensor (6) connected between the fluid collection unit (7) and the outlet end.

3. The method for measuring the permeability of ultra-narrow propped fractures based on microfluidic technology according to claim 2, characterized in that, The fluid supply unit includes a gas supply structure (1), a fluid pumping structure, and a liquid storage structure (3) arranged in sequence; The gas supply structure (1) is used to inject gas with corresponding parameters into the fluid pumping structure according to the preset flow parameters, and the fluid pumping structure is used to adjust the fluid in the liquid storage structure (3) to the preset flow parameters and supply it to the supported fracture model (5) after being measured by the flow sensor (4).

4. The method for measuring the permeability of ultra-narrow propped fractures based on microfluidic technology according to claim 3, characterized in that, The gas provided in the gas supply structure (1) is a non-corrosive gas; The fluid pumping structure is a microfluidic pressure pump (2).

5. The method for measuring the permeability of ultra-narrow propped fractures based on microfluidic technology according to any one of claims 1-4, characterized in that, The fluid is a pressurized liquid with a preset pressure value.

6. The method for measuring the permeability of ultra-narrow propped fractures based on microfluidic technology according to claim 1, characterized in that, In step S100, the parameters of the supported fracture model further include the parameters of the proppant and the width of the ultra-narrow prefabricated fracture.

7. The method for measuring the permeability of ultra-narrow propped fractures based on microfluidic technology according to claim 1, characterized in that, The manufacturing process of step S100 further includes: S102. Pour a curing material on the male mold with protrusions and depressions; S103. After the material to be cured is cured, the cured material is demolded from the male mold to obtain a support fracture model with ultra-narrow support fractures and proppants.

Images