Experimental device and method for characterizing the thixotropy of thixotropic fluids

Abstract

The present invention discloses an experimental device and method for characterizing the thixotropy of thixotropic fluids, belonging to the technical field of reservoir profile control experiments. The experimental device includes a piston container, a simulated flow channel, an image acquisition device and a computer. The inlet of the piston container is connected to a delivery pump, and the outlet is connected to the simulated flow channel. A standard liquid inlet pipe is provided at the top of the outlet end of the piston container, and a drain port is provided at the bottom. The piston container and the simulated flow channel are horizontally placed and on the same horizontal line. The image acquisition device on the track can observe the fluid flow in the simulated flow channel. The present invention uses the piston container to hold the thixotropic fluid to be tested, uses the simulated flow channel to simulate different flow channel sizes, and records and analyzes various data during the experiment through the computer to test the rheological properties and thixotropic properties of the thixotropic fluid. Using the present invention can quantitatively characterize the properties of thixotropic fluids, and at the same time simulate the flow of thixotropic fluids in pipelines and reservoirs, providing technical support for thixotropic fluid profile control.

Description

Technical Field

[0001] The present invention belongs to the technical field of reservoir profile control experiments, and particularly relates to an experimental device and method for characterizing the thixotropy of thixotropic fluids. Background Art

[0002] During the oil extraction process, reservoir heterogeneity is a common problem. Due to the permeability differences in different regions, the injected displacement fluid (such as water) often flows rapidly along the high-permeability channels. Profile control technology can block these high-permeability channels, forcing the injected fluid to change its flow direction and enter the low-permeability regions, thereby increasing the swept volume of crude oil. Thixotropic fluid is a fluid system acting on heterogeneous reservoirs. Its thixotropy is mainly manifested as low viscosity when the fluid is under high pressure / high-speed migration / high shear, and high viscosity when the fluid is in a low-pressure environment / low-speed flow / low shear. At the same time, this thixotropic property is reversible, and within a certain range of pressure / flow rate / shear, its viscosity can change repeatedly. However, the current research equipment and methods cannot accurately quantitatively characterize this thixotropic effect. Therefore, the present invention has developed an experimental device and method capable of quantitatively characterizing the thixotropy of thixotropic fluids. Through indoor experiments, the thixotropic effect of thixotropic fluids is quantitatively characterized, and the thixotropic range and its effective boundaries of thixotropic agents are clarified. Summary of the Invention

[0003] The purpose of the present invention is to provide an experimental device and method for characterizing the thixotropy of thixotropic fluids, aiming to solve the technical problem that the thixotropy of thixotropic fluids cannot be quantitatively characterized through simulation experiments in the prior art.

[0004] To solve the above technical problems, the technical solutions adopted by the present invention are as follows:

[0005] An experimental device for characterizing the thixotropy of thixotropic fluids, the experimental device comprising a piston container, a simulated flow channel for simulating different flow channel sizes, an image acquisition device and a computer. The inlet side of the piston in the piston container can accommodate the fluid, and distilled water is transported to the inlet side of the piston container through a delivery pump. The outlet side of the piston in the piston container can accommodate a standard fluid or a thixotropic fluid to be measured. The outlet of the piston container is connected to the simulated flow channel. At the top of the outlet end of the piston container, there is a liquid inlet pipe for injecting the standard fluid or the thixotropic fluid to be measured, and at the bottom, there is a drain port. The inlet of the piston container is connected to the delivery pump, and the delivery pump is used to pump the fluid to the inlet end of the piston container and push the standard fluid or the thixotropic fluid to be measured on the other side of the piston through the piston. Valves are provided at both the inlet and outlet of the piston container and the simulated flow channel. The piston container and the simulated flow channel are horizontally placed and on the same horizontal line. The image acquisition device is arranged on a track for observing the flow of the standard fluid or the thixotropic fluid to be measured at different positions in the simulated flow channel. Both the delivery pump and the image acquisition device are connected to the computer.

[0006] Preferably, the delivery pump is a constant-speed and constant-pressure pump. The inlet end of the piston container is connected to the constant-speed and constant-pressure pump, and a pump outlet valve is provided at the outlet of the constant-speed and constant-pressure pump. The outlet end of the piston container is connected to the simulated flow channel, and a flow channel valve is provided at the inlet of the simulated flow channel. At the bottom of the inlet end of the piston container, there is a rear drain port.

[0007] Preferably, an observation window is provided on the side of the piston container. The simulated flow channel is made of a transparent material, and a scale is provided on the side of the simulated flow channel.

[0008] Preferably, there are two piston containers, namely a No. 1 container and a No. 2 container. At the top of the outlet end of the No. 1 container, there is a No. 1 liquid inlet pipe, and at the bottom, there is a No. 1 drain port. A No. 1 liquid inlet valve is provided at the lower part of the No. 1 liquid inlet pipe. At the top of the outlet end of the No. 2 container, there is a No. 2 liquid inlet pipe, and at the bottom, there is a No. 2 drain port. A No. 2 liquid inlet valve is provided at the lower part of the No. 2 liquid inlet pipe. At the bottom of the inlet end of the No. 1 container, there is a rear drain port of the No. 1 container, and at the bottom of the inlet end of the No. 2 container, there is a rear drain port of the No. 2 container.

[0009] The constant-speed and constant-pressure pump comprises a No. 1 pump and a No. 2 pump. The No. 1 pump is connected to the No. 1 container through a No. 1 pump inlet pipeline, and a No. 1 pump outlet valve and a No. 1 container pump inlet valve are respectively provided at both ends of the inlet and outlet of the No. 1 pump inlet pipeline. The No. 2 pump is connected to the No. 2 container through a No. 2 pump inlet pipeline, and a No. 2 pump outlet valve and a No. 2 container pump inlet valve are respectively provided at both ends of the inlet and outlet of the No. 2 pump inlet pipeline.

[0010] Preferably, there are two simulation channels, namely the first channel and the second channel. The first channel and the second channel are arranged in parallel. Both ends of the first channel are connected to the first container and the second container through the first container-first channel connection valve and the second container-first channel connection valve respectively. Both ends of the second channel are connected to the first container and the second container through the first container-second channel connection valve and the second container-second channel connection valve respectively. The first channel and the second channel are opened simultaneously to test the splitting effect of the thixotropic fluid, and the first channel or the second channel is opened separately to test the rheological properties of the thixotropic fluid;

[0011] The image acquisition device includes a first camera and a second camera. The first camera and the second camera are respectively arranged on two parallel tracks and are respectively used to observe the flow of the standard fluid or the to-be-tested thixotropic fluid at different positions in the first channel and the second channel.

[0012] Preferably, the simulation channel is a porous medium simulation channel, which is used to test the thixotropic properties of the thixotropic fluid during the seepage process in the porous medium.

[0013] Preferably, the porous medium simulation channel is a visual porous medium simulation channel, which can observe and analyze the seepage flow characteristics of the thixotropic fluid in the porous medium and the thixotropic properties in the microscopic pores.

[0014] An experimental method for characterizing the thixotropy of a thixotropic fluid includes the following steps:

[0015] Prepare the to-be-tested thixotropic fluid and the standard fluid of Newtonian fluids with different viscosities (whose viscosities do not change with the flow rate and pressure) according to the experimental requirements;

[0016] Assemble the above experimental device. The simulation channel is one or more, which can be adjusted according to the specific test items;

[0017] Set the flow rate of the distilled water injected into the piston container by the delivery pump, and measure the injection pressure values during the injection process at different flow rates. The standard fluid enters the piston container through the liquid inlet pipe and then enters the simulation channel;

[0018] Replace the standard fluid with different viscosities, measure the injection pressures at different flow rates of different standard fluids, and obtain the corresponding relationship between the viscosity-pressure-flow rate of the standard fluid. The fitting equation is as follows:

[0019]

[0020] In the formula, n is the flow rate of the standard fluid; x is the viscosity of the standard fluid; y is the injection pressure of the standard fluid;

[0021] Each curve in the obtained relationship curve represents the viscosity-pressure relationship under a flow rate condition;

[0022] Clean the experimental device, replace the thixotropic fluid to be measured, set the injection speed, measure the change in the injection pressure of the thixotropic fluid at different flow rates, substitute the flow rate and pressure data of the thixotropic fluid into the above formula, calculate the change in the viscosity of the measured thixotropic fluid, and finally obtain the thixotropic effect of the thixotropic fluid.

[0023] Further, when there is one simulated flow channel,

[0024] According to the pressure changes measured at different flow rates in the experiment, substitute the pressure values into the above fitting equation respectively, calculate the changes in the viscosity of the thixotropic fluid with the flow rate and pressure, and obtain the thixotropy of the thixotropic fluid to be measured;

[0025] Using the thixotropy index TI, dynamic thixotropy index DTI, and thixotropic loop area A t , to characterize the degree of viscosity change of the fluid at different shear rates, and quantify the viscosity change rate and recovery ability of the thixotropic fluid under shear action:

[0026]

[0027] In the formula, Δη: the amplitude of viscosity change caused by thixotropy, which is the difference between the viscosity values of the thixotropic fluid at the maximum and minimum flow rates during the first speed-up process, mPa·s;

[0028] η0: the viscosity of the thixotropic fluid in the initial static state, referring to the reference standard liquid or the measured value at low speed, mPa·s;

[0029] η min , η max : the viscosity of the thixotropic fluid at the minimum / maximum flow rate, mPa·s;

[0030]

[0031]

[0032] In the formula, Δt is the shear action time, s;

[0033] γ crit is the critical shear rate, and the flow in the simulated flow channel is calculated according to the circular pipe flow;

[0034] v is the average flow rate of the thixotropic fluid in the flow channel, m / s;

[0035] R is the radius of the simulated flow channel, m;

[0036]

[0037] v max is the highest flow rate of the thixotropic fluid during the test;

[0038] v min is the minimum flow rate of the thixotropic fluid during the test;

[0039] η 升 η(v) is the viscosity change of the thixotropic fluid during the test as the flow rate increases from low to high;

[0040] η 降 η(v) is the viscosity change of the thixotropic fluid during the test as the flow rate decreases from high to low;

[0041] The thixotropic loop area A t reflects the hysteresis effect of thixotropic recovery. The larger the area, the weaker the thixotropy and the weaker the recoverability of the fluid.

[0042] Furthermore, when there are two simulated flow channels, the two simulated flow channels are the first flow channel and the second flow channel, and the first flow channel and the second flow channel are installed in parallel between two piston containers;

[0043] Start the transfer pump and set the pressure / flow rate value to inject the thixotropic fluid to be tested into the piston container at a constant pressure and constant speed. Open the image acquisition device and record the flow state of the thixotropic fluid to be tested in the two simulated flow channels, and finally obtain the flow / seepage law of the thixotropic fluid in porous media with different flow radii / different permeabilities;

[0044] When the two simulated flow channels are circular tube simulated flow channels, the following data of the fluid flow in the two simulated flow channels are obtained from the experiment:

[0045] The pressure of the first flow channel: P a (t), MPa;

[0046] The liquid production per unit time at the outlet of the first flow channel: D a (t), ml;

[0047] The flow rate of the first flow channel: V a (t)=D a (t) / t, ml / min;

[0048] The cumulative liquid volume at the outlet of the first flow channel: , ml;

[0049] The pressure of the second flow channel: P b (t), MPa;

[0050] The liquid production per unit time at the outlet of the second flow channel: D b (t), ml;

[0051] The flow rate of the second flow channel: V b (t = i)=D b (t) / t, ml / min;

[0052] Accumulated liquid volume at the outlet of the second flow channel: , ml;

[0053] Diversion rate of the first flow channel ;

[0054] Diversion rate of the second flow channel ;

[0055] And draw a diversion curve graph;

[0056] When the two simulated flow channels are porous medium simulated flow channels, the first flow channel is a high-permeability porous medium, and the second flow channel is a low-permeability porous medium. The profile control ability of the thixotropic fluid is characterized by the profile control efficiency coefficient ECPC as follows:

[0057] ;

[0058] In the formula, S high : Diversion rate of the first flow channel;

[0059] S low : Diversion rate of the second flow channel;

[0060] The closer ECPC is to 1, the better the profile control effect, and the more the fluid tends to flow in the low-permeability reservoir.

[0061] Preferably, when there are two simulated flow channels, the two simulated flow channels are the first flow channel and the second flow channel respectively, and the first flow channel and the second flow channel are installed in parallel between two piston containers;

[0062] The first flow channel is a circular tube simulated flow channel, and the second flow channel is a porous medium simulated flow channel;

[0063] Porous media usually have strong shear effects. When thixotropic fluids pass through porous media, they will be subjected to strong shear effects and their properties will change. The following experiment is to test the thixotropy changes of thixotropic fluids before and after strong shear effects.

[0064] Start the transfer pump, turn on the image acquisition device, and test the thixotropy of the thixotropic fluid through the first flow channel;

[0065] Then inject the thixotropic fluid into the second flow channel at the same injection speed so that it passes through the porous medium;

[0066] Inject the thixotropic fluid sheared by the porous medium back into the first flow channel and test the thixotropy at this time;

[0067] Record the pressure changes during the experiment, and finally obtain the thixotropy changes of the measured fluid before and after the shear action of the porous medium.

[0068] The thixotropy change data before and after shearing are measured experimentally. The effect of the porous medium shearing effect on the thixotropic fluid is characterized by the thixotropic loss rate L and the thixotropic recovery rate R:

[0069]

[0070] TLpre: Thixotropic index of the thixotropic fluid before shearing;

[0071] TLpost: Thixotropic index of the thixotropic fluid after shearing;

[0072]

[0073] η post1 : Viscosity at the lowest flow rate during the rising speed test of the thixotropic fluid after shearing, mPa·s;

[0074] η post2 : Viscosity at the lowest flow rate during the falling speed test of the thixotropic fluid after shearing, mPa·s;

[0075] η pre1 : Viscosity at the lowest flow rate during the rising speed test of the thixotropic fluid before shearing, mPa·s;

[0076] η pre2 : Viscosity at the lowest flow rate during the falling speed test of the thixotropic fluid before shearing, mPa·s;

[0077] The thixotropic loss rate L and the thixotropic recovery rate R evaluate the degree of damage to thixotropy caused by the shearing effect and the self-healing ability of the fluid.

[0078] Compared with the prior art, the beneficial effects produced by the present invention are as follows:

[0079] The present invention uses a piston container to hold the thixotropic fluid to be measured, uses a simulated flow channel to simulate different flow channel sizes, observes the fluid flow conditions at different positions in the simulated flow channel through an image acquisition device, and records and analyzes various data during the experiment by a computer to test the rheological properties and thixotropic properties of the thixotropic fluid. By adopting the present invention, the properties of the thixotropic fluid can be quantitatively characterized, and at the same time, the flow of the thixotropic fluid in pipelines and reservoirs is simulated, providing technical support for the profile control of the thixotropic fluid. Brief Description of the Drawings

[0080] The drawings are used to provide a further understanding of the present invention, and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation to the present invention.

[0081] In the drawings:

[0082] Figure 1Schematic structural diagram of an experimental device for characterizing the thixotropy of thixotropic fluids provided by an embodiment of the present invention;

[0083] Figure 2 Viscosity-pressure standard curve graph of thixotropic fluid at different flow rates;

[0084] Figure 3 Viscosity change curve graph of thixotropic fluid during the process of changing with velocity;

[0085] Figure 4 Flow splitting curve graph of thixotropic fluid in two parallel simulated flow channels;

[0086] Figure 5 Thixotropy change graph of thixotropic fluid before and after being sheared by a porous medium:

[0087] Figure 6 Schematic diagram of the movement of fluid in the piston container and the simulated flow channel;

[0088] In the figure:

[0089] 1 - First observation window; 2 - Second observation window; 3 - First container; 4 - Second container; 5 - First drain port; 6 - Second drain port; 7 - First inlet pipe; 8 - Second inlet pipe; 9 - First inlet valve; 10 - Second inlet valve; 11 - First container first flow channel connection valve; 12 - Second container first flow channel connection valve; 13 - First container second flow channel connection valve; 14 - Second container second flow channel connection valve; 15 - First flow channel; 16 - Second flow channel; 17 - Scale; 18 - First container pumping valve; 19 - Second container pumping valve; 20 - First pumping pipeline; 21 - Second pumping pipeline; 22 - First pump outlet valve; 23 - Second pump outlet valve; 24 - First pump; 25 - Second pump; 26 - First camera; 27 - Second camera; 28 - Cable; 29 - Track; 30 - Computer; 31 - First container rear drain port; 32 - Second container rear drain port. Detailed implementation manner

[0090] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In the following detailed description of the present invention, some specific details are described in detail. However, those skilled in the art can also fully understand the present invention for the parts that are not described in detail.

[0091] In addition, those of ordinary skill in the art should understand that the accompanying drawings provided are only for illustrating the purpose, features and advantages of the present invention, and the drawings are not actually drawn to scale.

[0092] Meanwhile, unless the context clearly requires otherwise, the words such as "comprising", "including" and the like in the whole specification and claims shall be construed in an inclusive sense rather than an exclusive or exhaustive sense; that is to say, it means "including but not limited to".

[0093] As Figure 1 , 6 shown, an experimental device for characterizing the thixotropy of a thixotropic fluid, the experimental device comprising a piston container, a simulated flow channel for simulating different flow channel sizes, an image acquisition device and a computer 30. The inlet side of the piston in the piston container can accommodate the fluid, and distilled water is transported to the inlet side of the piston container through a delivery pump. The outlet side of the piston in the piston container can accommodate a standard fluid or a to-be-tested thixotropic fluid. The outlet of the piston container is connected to the simulated flow channel. An inlet pipe for injecting the standard fluid or the to-be-tested thixotropic fluid is provided at the top of the outlet end of the piston container. The fluid is sucked into the piston container by the movement of the internal piston. A drain port is provided at the bottom of the outlet end of the piston container for discharging the fluid in the piston container. The inlet of the piston container is connected to the delivery pump, and the delivery pump is used to pump the fluid to the inlet end of the piston container and push the standard fluid or the to-be-tested thixotropic fluid on the other side of the piston through the piston. Valves are provided at both the inlet and outlet of the piston container and the simulated flow channel for controlling the opening and closing of the flow channel. The piston container and the simulated flow channel are horizontally placed and on the same horizontal line to avoid affecting the fluid due to large changes in the flow state. And the simulated flow channel is made of a hydrophobic / oil-repellent material or has a hydrophobic / oil-repellent coating on the inner wall, and the material is changed according to the properties of the experimental fluid to reduce the obstruction of the flow channel material to the fluid flow. The image acquisition device is arranged on the track 29 for observing the flow of the standard fluid or the to-be-tested thixotropic fluid at different positions in the simulated flow channel. The delivery pump and the image acquisition device are respectively connected to the computer 30 through cables 28, and the fluid flow is controlled by the computer and various data during the experiment are recorded. The movement process of the fluid in the piston container is as Figure 6 shown.

[0094] In specific design, the simulated flow channel is one or more. When multiple flow channels are opened, it is used to test the splitting effect of the thixotropic fluid. When a single flow channel is opened, it is used to test the rheological properties of the thixotropic fluid. And the size of the simulated flow channel is smaller than the outlet size of the container to ensure that the simulated flow channel is the smallest flow channel in the whole system and ensure the accuracy of the test results. At the same time, the simulated flow channel with different lengths and diameters can be disassembled and replaced according to the test requirements. In specific production, the inner cavity of the piston container is divided into two spaces by the piston. The fluid is pumped into one end space through the delivery pump to squeeze the piston to move, and then push the fluid on the other side of the piston. Both ends of the piston container are detachable to facilitate the cleaning of the piston container and ensure the purity of the test fluid. Figure 1In the illustrated embodiment, the piston container has two outlet ends, and two simulated flow channels are connected between the two piston containers. When only one simulated flow channel experiment is required, the other simulated flow channel can be closed by a valve.

[0095] As a preferred structure, the delivery pump is a constant-speed and constant-pressure pump. The inlet end of the piston container is connected to the constant-speed and constant-pressure pump, and a pump outlet valve is provided at the outlet of the constant-speed and constant-pressure pump; the outlet end of the piston container is connected to the simulated flow channel, and a flow channel valve is provided at the inlet of the simulated flow channel; a rear drain port is provided at the bottom of the inlet end of the piston container.

[0096] In a specific embodiment of the present invention, as Figure 1 shown, there are two piston containers, namely the first container 3 and the second container 4. At the top of the outlet end of the first container 3, there is a first liquid inlet pipe 7, and at the bottom, there is a first liquid discharge port 5. At the lower part of the first liquid inlet pipe 7, there is a first liquid inlet valve 9. At the top of the outlet end of the second container 4, there is a second liquid inlet pipe 8, and at the bottom, there is a second liquid discharge port 6. At the lower part of the second liquid inlet pipe 8, there is a second liquid inlet valve 10; at the bottom of the inlet end of the first container 3, there is a rear drain port 31 of the first container, and at the bottom of the inlet end of the second container 4, there is a rear drain port 32 of the second container. Among them, chamfers are provided at the connection points of the first container and the second container with the first flow channel and the second flow channel to avoid a large shear effect during fluid flow, thereby changing the fluid properties and ensuring the accuracy of the test results. At the same time, a first observation window 1 and a second observation window 2 are respectively provided on the sides of the first container 3 and the second container 4; the simulated flow channel is made of a transparent material, and a scale 17 is provided on the side of the simulated flow channel.

[0097] Among them, the constant-speed and constant-pressure pump includes a first pump 24 and a second pump 25. The first pump 24 is connected to the first container 3 through a first pump inlet pipeline 20, and a first pump outlet valve 22 and a first container pump inlet valve 18 are respectively provided at both ends of the inlet and outlet of the first pump inlet pipeline 20; the second pump 25 is connected to the second container 4 through a second pump inlet pipeline 21, and a second pump outlet valve 23 and a second container pump inlet valve 19 are respectively provided at both ends of the inlet and outlet of the second pump inlet pipeline 21.

[0098] Meanwhile, there are two simulation channels, namely the first channel 15 and the second channel 16. The first channel 15 and the second channel 16 are arranged in parallel. Both ends of the first channel 15 are connected to the first container 3 and the second container 4 through the first container-first channel connection valve 11 and the second container-first channel connection valve 12 respectively. Both ends of the second channel 16 are connected to the first container 3 and the second container 4 through the first container-second channel connection valve 13 and the second container-second channel connection valve 14 respectively. The first channel 15 and the second channel 16 are opened simultaneously to test the splitting effect of the thixotropic fluid, and the first channel 15 or the second channel 16 is opened separately to test the rheological properties of the thixotropic fluid.

[0099] The piston container and the constant-speed and constant-pressure pump are placed in two corresponding sets for repeatedly testing the thixotropic effect of the thixotropic fluid and verifying the reversibility of the thixotropic effect of the measured thixotropic fluid.

[0100] To correspond to the two simulation channels, the image acquisition device includes a first camera 26 and a second camera 27. The first camera 26 and the second camera 27 are respectively arranged on two parallel tracks 29 for observing the flow of the standard fluid or the to-be-tested thixotropic fluid at different positions in the first channel 15 and the second channel 16.

[0101] In another embodiment of the present invention, the simulation channel can be replaced with a porous medium simulation channel. A porous medium (core) can be placed inside the porous medium simulation channel for testing the thixotropic properties of the thixotropic fluid during the seepage process in the porous medium and measuring the thixotropic change of the thixotropic fluid after being subjected to a shear action.

[0102] Meanwhile, the porous medium simulation channel is a visual porous medium simulation channel for observing and analyzing the seepage flow characteristics of the thixotropic fluid in the porous medium and the thixotropic properties in the microscopic pores. The visual porous medium simulation channel can be made by 3D printing with a fully transparent resin.

[0103] The present invention also provides an experimental method for characterizing the thixotropy of a thixotropic fluid, including the following steps:

[0104] Prepare the to-be-tested thixotropic fluid and the standard fluid of Newtonian fluids with different viscosities according to the experimental requirements;

[0105] Assemble the above experimental device, connect the liquid inlet and outlet, and open / close the corresponding valves;

[0106] Through the suction movement of the first piston container, suck the standard fluid into the first piston container through the liquid inlet pipe, close the liquid inlet, and open the simulation channel valve. At this time, the liquid inlet of the second piston container is closed and the drain hole is opened, and it is in an empty state;

[0107] Set the flow rate of the distilled water injected into the piston container of the transfer pump, and measure the injection pressure values during the injection process at different flow rates; replace the standard liquids with different viscosities, and measure the corresponding relationship between the viscosity, pressure, and flow rate of the fluid under this flow environment (pipe diameter, material). Figure 2 Each curve in it represents the viscosity-pressure relationship under a flow rate condition.

[0108] According to the injection pressures of the standard liquid fluid measured at different flow rates in the experiment, the following viscosity-pressure relationship fitting equation is obtained:

[0109]

[0110] In the formula, n is the flow rate of the standard liquid fluid; x is the viscosity of the standard liquid fluid; y is the injection pressure of the standard liquid fluid.

[0111] Clean the experimental device, replace the thixotropic fluid, set the injection speed, measure the changes in the injection pressure of the thixotropic fluid at different flow rates, substitute the flow rate-pressure data into the above formula, calculate the viscosity changes of the measured fluid, and finally obtain the thixotropic effect of the measured thixotropic fluid (viscosity changes under different pressures and flow rates).

[0112] When there is one simulated flow channel, measure the pressure changes at flow rates of 1, 2, 3, 4, 3, 2, and 1 ml / min respectively during the experiment, substitute the pressure values into the above fitting equation respectively, and obtain the thixotropy of the test liquid, as Figure 3 shown.

[0113] Use the thixotropy index TI, dynamic thixotropy index DTI, and thixotropic loop area At to characterize the degree of viscosity change of the fluid at different shear rates, and quantify the viscosity change rate and recovery ability of the thixotropic fluid under shear action:

[0114]

[0115] In the formula, Δη: the amplitude of viscosity change caused by thixotropy, which is the difference between the viscosity values at the maximum and minimum flow rates during the first speed increase process, mPa·s;

[0116] η0: the viscosity of the thixotropic fluid in the initial static state, referring to the measured value of the standard liquid or at low speed, mPa·s;

[0117] η min ,η max : the viscosity of the thixotropic fluid at the minimum / maximum flow rate, mPa·s;

[0118]

[0119]

[0120] where Δt is the shearing time, in s;

[0121] γ crit is the critical shear rate, and the flow in the simulated flow channel is calculated according to the flow in a circular pipe;

[0122] v is the average flow velocity of the thixotropic fluid in the flow channel, in m / s;

[0123] R is the radius of the simulated flow channel, in m;

[0124]

[0125] v max is the highest flow velocity of the thixotropic fluid during the test;

[0126] v min is the lowest flow velocity of the thixotropic fluid during the test;

[0127] η 升 (v) is the viscosity change of the thixotropic fluid during the process of increasing the flow velocity from low to high during the test;

[0128] η 降 (v) is the viscosity change of the thixotropic fluid during the process of decreasing the flow velocity from high to low during the test;

[0129] The thixotropic loop area A t reflects the hysteresis effect of thixotropic recovery. The larger the area, the weaker the thixotropy and the weaker the recoverability of the fluid.

[0130] When there are two simulated flow channels, the two simulated flow channels are the first flow channel and the second flow channel respectively, and the experimental device is assembled; the first flow channel and the second flow channel are installed in parallel between two piston containers, the liquid inlet and outlet are connected, and the corresponding valves are opened / closed.

[0131] Start the transfer pump, turn on the first camera and the second camera, and set the pressure / flow velocity value, so that the thixotropic fluid to be measured is injected into the piston container at a constant pressure and constant speed, record the flow state of the thixotropic fluid to be measured in the two simulated flow channels, and finally obtain the flow / seepage law of the thixotropic fluid in porous media with different flow radii / different permeabilities.

[0132] When the two simulated flow channels are circular pipe simulated flow channels, the following data of the fluid flow in the two simulated flow channels are obtained through experiments:

[0133] The pressure of the first flow channel: P a (t), in MPa;

[0134] The liquid production per unit time at the outlet of the first flow channel: D a (t), in ml;

[0135] The flow velocity of the first flow channel: V aD(t)= a D(t) / t, ml / min;

[0136] Cumulative liquid volume at the outlet of the first flow channel: , ml;

[0137] Pressure of the second flow channel: P b (t), MPa;

[0138] Liquid production per unit time at the outlet of the second flow channel: D b (t), ml;

[0139] Flow velocity of the second flow channel: V b V(t = i)=D b D(t) / t, ml / min;

[0140] Cumulative liquid volume at the outlet of the second flow channel: , ml;

[0141] Diversion rate of the first flow channel ;

[0142] Diversion rate of the second flow channel ;

[0143] And draw a diversion curve graph, as Figure 4 shown.

[0144] When the two simulated flow channels are porous medium simulated flow channels, the first flow channel is a porous medium with higher permeability, and the second flow channel is a porous medium with lower permeability. The profile control ability of the thixotropic fluid is characterized by the profile control efficiency coefficient ECPC as follows:

[0145] ;

[0146] In the formula, S high : Diversion rate of the first flow channel;

[0147] S low : Diversion rate of the second flow channel;

[0148] The closer ECPC is to 1, the better the profile control effect, and the more the fluid tends to flow in the low-permeability reservoir.

[0149] Porous media usually have strong shear effects. When thixotropic fluids pass through porous media, they will be subjected to strong shear effects and their properties will change. The following experiment is to test the thixotropy changes of thixotropic fluids before and after strong shear effects.

[0150] When there are two simulated flow channels, the two simulated flow channels are the first flow channel and the second flow channel respectively, and the first flow channel and the second flow channel are installed in parallel between two piston containers;

[0151] The first flow channel is a circular tube simulated flow channel, and the second flow channel is a porous medium simulated flow channel.

[0152] Start the transfer pump, turn on the image acquisition device, and test the thixotropy of the thixotropic fluid through the first flow channel. The specific process is the same as the operation when there is one simulated flow channel;

[0153] Then inject the thixotropic fluid into the second flow channel at the same injection speed so that it passes through the porous medium;

[0154] Inject the thixotropic fluid sheared by the porous medium back into the first flow channel and test the thixotropy at this time;

[0155] Record the pressure change during the experiment, and finally obtain the change in the thixotropy of the measured fluid before and after the shear action of the porous medium.

[0156] The experimentally measured change in thixotropy before and after shear is as Figure 5 shown.

[0157] The effect of the shear effect of the porous medium on the thixotropic fluid is characterized by the thixotropic loss rate L and the thixotropic recovery rate R:

[0158]

[0159] TLpre: Thixotropy index of the thixotropic fluid before shear;

[0160] TLpost: Thixotropy index of the thixotropic fluid after shear;

[0161]

[0162] η post1 : Viscosity at the lowest flow rate during the rising speed test of the thixotropic fluid after shear, mPa·s;

[0163] η post2 : Viscosity at the lowest flow rate during the falling speed test of the thixotropic fluid after shear, mPa·s;

[0164] η pre1 : Viscosity at the lowest flow rate during the rising speed test of the thixotropic fluid before shear, mPa·s;

[0165] η pre2 : Viscosity at the lowest flow rate during the falling speed test of the thixotropic fluid before shear, mPa·s;

[0166] The thixotropic loss rate (L) and the thixotropic recovery rate (R) evaluate the degree of damage to thixotropy caused by the shear action and the self-repair ability of the fluid.

[0167] In summary, the present invention simulates the flow of thixotropic fluids in flow channels of different sizes and seepage channels of different permeabilities, quantitatively characterizes the thixotropic effect of thixotropic fluids, clarifies the flow / seepage laws of thixotropic fluids, better corresponds to different flow environments in the reservoir, and can quantitatively characterize the viscosity change of thixotropic fluids under different pressures / flow rates through the simulation of flow channels. The seepage characteristics of thixotropic fluids under the action of different pressures / flow rates / shearing forces can be quantitatively characterized through the seepage simulation channel. At the same time, the thixotropic change of the fluid before and after shearing can be simulated, and then the effective action range of thixotropic fluids in the reservoir porous medium can be obtained. Through the parallel simulation of the double channels, the flow / seepage laws of thixotropic fluids under heterogeneous conditions can be obtained, and the profile control effect of thixotropic fluids can be clarified. This provides accurate theoretical and technical guidance for field applications.

[0168] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the scope of protection of the claims of the present invention.

Claims

1. An experimental device for characterizing the thixotropy of thixotropic fluids, characterized in that: The experimental device includes a piston container, a simulated flow channel for simulating different flow channel sizes, an image acquisition device, and a computer. The inlet side of the piston in the piston container can accommodate fluid, and distilled water is transported to the inlet side of the piston container through a delivery pump. The outlet side of the piston in the piston container can accommodate standard fluid or the thixotropic fluid to be measured. The outlet of the piston container is connected to the simulated flow channel. At the top of the outlet end of the piston container, there is a liquid inlet pipe for injecting standard fluid or the thixotropic fluid to be measured, and at the bottom, there is a liquid discharge port. The inlet of the piston container is connected to the delivery pump, and the delivery pump is used to pump the fluid to the inlet end of the piston container and push the standard fluid or the thixotropic fluid to be measured on the other side of the piston through the piston. Valves are provided at both the inlet and outlet of the piston container and the simulated flow channel. The piston container and the simulated flow channel are placed horizontally and on the same horizontal line. The image acquisition device is arranged on a track and is used to observe the flow of the standard fluid or the thixotropic fluid to be measured at different positions in the simulated flow channel. Both the delivery pump and the image acquisition device are connected to the computer. There are two piston containers, namely the first container and the second container. At the top of the outlet end of the first container, there is a first liquid inlet pipe, and at the bottom, there is a first liquid discharge port. At the lower part of the first liquid inlet pipe, there is a first liquid inlet valve. At the top of the outlet end of the second container, there is a second liquid inlet pipe, and at the bottom, there is a second liquid discharge port. At the lower part of the second liquid inlet pipe, there is a second liquid inlet valve. At the bottom of the inlet end of the first container, there is a first container rear drain port, and at the bottom of the inlet end of the second container, there is a second container rear drain port. The delivery pump includes a first pump and a second pump. The first pump is connected to the first container through a first pump inlet pipeline, and at both ends of the inlet and outlet of the first pump inlet pipeline, there are a first pump outlet valve and a first container pump inlet valve respectively. The second pump is connected to the second container through a second pump inlet pipeline, and at both ends of the inlet and outlet of the second pump inlet pipeline, there are a second pump outlet valve and a second container pump inlet valve respectively. There are two simulated flow channels, namely the first flow channel and the second flow channel. The first flow channel and the second flow channel are arranged in parallel. Both ends of the first flow channel are connected to the first container and the second container through a first container - first flow channel connection valve and a second container - first flow channel connection valve respectively. Both ends of the second flow channel are connected to the first container and the second container through a first container - second flow channel connection valve and a second container - second flow channel connection valve respectively. The first flow channel and the second flow channel are opened simultaneously to test the splitting effect of the thixotropic fluid, and the first flow channel or the second flow channel is opened separately to test the rheological properties of the thixotropic fluid. The image acquisition device includes a first camera and a second camera. The first camera and the second camera are respectively arranged on two parallel tracks and are respectively used to observe the flow of the standard fluid or the thixotropic fluid to be measured at different positions in the first flow channel and the second flow channel.

2. The experimental device for characterizing the thixotropy of a thixotropic fluid according to claim 1, characterized in that: The transfer pump is a constant-speed and constant-pressure pump. The inlet end of the piston container is connected to the constant-speed and constant-pressure pump, and a pump outlet valve is provided at the outlet of the constant-speed and constant-pressure pump; the outlet end of the piston container is connected to the simulated flow channel, and a flow channel valve is provided at the inlet of the simulated flow channel; a rear drain port is provided at the bottom of the inlet end of the piston container.

3. An experimental device for characterizing the thixotropy of a thixotropic fluid according to claim 1, characterized in that: The simulated flow channel is a porous medium simulated flow channel, which is used to test the thixotropic properties of the thixotropic fluid during the seepage process in the porous medium.

4. An experimental device for characterizing the thixotropy of a thixotropic fluid according to claim 3, characterized in that: The porous medium simulated flow channel is a visual porous medium simulated flow channel, which can observe and analyze the seepage flow characteristics of the thixotropic fluid in the porous medium and the thixotropic properties in the microscopic pores.

5. An experimental method for characterizing the thixotropy of a thixotropic fluid, characterized in that, It includes the following steps: Prepare the fluid with thixotropy to be measured and the standard fluid of Newtonian fluids with different viscosities according to the experimental requirements; Assemble the experimental device according to any one of claims 1-4, and the simulated flow channel is one or more; Set the flow rate of the distilled water injected into the piston container by the transfer pump, and measure the injection pressure values during the injection process at different flow rates; suck the standard fluid in the inlet pipe into the piston container through the transfer pump and then into the simulated flow channel; Replace the standard fluid with different viscosities, measure the injection pressures at different flow rates of different standard fluids, obtain the corresponding relationship between the viscosity-pressure-flow rate of the standard fluid, and the fitting equation is as follows: y = k n *x In the formula, n is the flow rate of the standard fluid; x is the viscosity of the standard fluid; y is the injection pressure of the standard fluid; Each curve in the obtained relationship curve represents the viscosity-pressure relationship under a flow rate condition; Clean the experimental device, replace the thixotropic fluid to be measured, set the injection speed, measure the change of the injection pressure of the thixotropic fluid at different flow rates, substitute the flow rate and pressure data of the thixotropic fluid into the above formula, calculate the viscosity change of the measured thixotropic fluid, and finally obtain the thixotropic effect of the thixotropic fluid.

6. An experimental method for characterizing the thixotropy of a thixotropic fluid according to claim 5, characterized in that: When the simulated flow channel is one, according to the pressure changes measured at different flow rates in the experiment, substitute the pressure values into the above fitting equation respectively, calculate the change of the thixotropic fluid viscosity with the flow rate and pressure, and obtain the thixotropy of the thixotropic fluid to be measured; Use the thixotropy index TI, dynamic thixotropy index DTI, and thixotropic loop area At to characterize the viscosity change degree of the fluid at different shear rates, and quantify the viscosity change rate and recovery ability of the thixotropic fluid under the shear action: ; In the formula, Δη: the viscosity change amplitude caused by thixotropy, which is the difference between the viscosity values at the maximum flow rate and the minimum flow rate during the first speed-up process, mPa·s; η0: the viscosity of the thixotropic fluid in the initial static state, mPa·s; η min , η max : Viscosity of thixotropic fluid at minimum / maximum flow rate, mPa·s; ； ； In the formula, Δt is the shear action time, s; γcrit is the critical shear rate, and the flow in the simulated flow channel is calculated according to the circular pipe flow; v is the average flow rate of the thixotropic fluid in the flow channel, m / s; R is the radius of the simulated flow channel, m; ； v max is the highest flow rate of the thixotropic fluid during the test; v min is the minimum flow rate of the thixotropic fluid during the test; η 升 (v) is the viscosity change during the thixotropic fluid flow rate increasing from low to high in the test process; η 降 (v) is the viscosity change during the process of the thixotropic fluid flow rate decreasing from high to low during the test; Thixotropic loop area A t It reflects the hysteresis effect of thixotropic recovery. The larger the area, the weaker the thixotropy and the weaker the recoverability of the fluid.

7. An experimental method for characterizing the thixotropy of a thixotropic fluid according to claim 5, characterized in that: When the simulated flow channels are two, the two simulated flow channels are the first flow channel and the second flow channel respectively, and the first flow channel and the second flow channel are installed in parallel between the two piston containers; Start the transfer pump and set the pressure / flow rate value so that the thixotropic fluid to be measured is injected into the piston container at a constant pressure and constant speed. Turn on the image acquisition device and record the flow state of the thixotropic fluid to be measured in the two simulated flow channels, and finally obtain the flow / seepage law of the thixotropic fluid in porous media with different flow radii / different permeabilities; When the two simulated flow channels are circular tube simulated flow channels, the following data of the fluid flow in the two simulated flow channels are obtained through experiments: Pressure of the first flow channel: P a (t), MPa; Liquid production volume per unit time at the outlet of the first flow channel: D a (t), ml; Flow velocity of the first flow channel: V a (t) = D a (t) / t, ml / min; Cumulative liquid volume at the outlet of the first flow channel: , ml; Pressure of the second flow channel: P b (t), MPa; Liquid production volume per unit time at the second flow channel outlet: D b (t), ml; Flow velocity of the second channel: V b (t = i) = D b (t) / t, ml / min; Cumulative liquid volume at the outlet of the second flow channel: , ml; Diversion ratio of the first flow channel ; Flow rate of the second flow channel ; And draw a flow splitting curve graph; When the two simulated flow channels are porous media simulated flow channels, the first flow channel is a porous medium with high permeability, and the second flow channel is a porous medium with low permeability. The profile control ability of the thixotropic fluid is characterized by the profile control efficiency coefficient ECPC as follows: ； Where S high : the diversion ratio of the first flow channel; S low : The flow rate splitting ratio of the second flow channel; The closer the ECPC is to 1, the better the profile control effect, and the more the fluid tends to flow in the low-permeability reservoir.

8. An experimental method for characterizing the thixotropy of a thixotropic fluid according to claim 6, characterized in that: When there are two simulated flow channels, the two simulated flow channels are the first flow channel and the second flow channel respectively, and the first flow channel and the second flow channel are installed in parallel between the two piston containers; The first flow channel is a circular tube simulated flow channel, and the second flow channel is a porous medium simulated flow channel; Start the transfer pump, turn on the image acquisition device, and test the thixotropy of the thixotropic fluid through the first flow channel; Then inject the thixotropic fluid into the second flow channel at the same injection speed so that it passes through the porous medium; Inject the thixotropic fluid sheared by the porous medium back into the first flow channel and test the thixotropy at this time; Record the pressure change during the experiment, and finally obtain the change in the thixotropy of the measured fluid before and after the shearing effect of the porous medium; The change data of the thixotropy before and after shearing are measured in the experiment. The effect of the porous medium shearing effect on the thixotropic fluid is characterized by the thixotropy loss rate L and the thixotropy recovery rate R: ； TLpre: Thixotropy index of the thixotropic fluid before shearing; TLpost: Thixotropy index of the thixotropic fluid after shearing; ； η post1 : Viscosity at the lowest flow rate during the ascending speed test of the thixotropic fluid after shearing, mPa·s; η post2 : Viscosity at the lowest flow rate during the deceleration test of the thixotropic fluid after shearing, mPa·s; η pre1 : Viscosity at the lowest flow rate during the ascending rate test of the thixotropic fluid before shearing, mPa·s; η pre2 : Viscosity at the lowest flow rate during the deceleration test of the thixotropic fluid before shearing, mPa·s; The thixotropy loss rate L and the thixotropy recovery rate R evaluate the degree of damage to the thixotropy by the shearing effect and the self-repair ability of the fluid.

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