Experimental apparatus and experimental method for filtration and cake formation

Abstract

The application discloses an experimental device and an experimental method for filtration loss measurement and mud cake formation. The experimental device for filtration loss measurement and mud cake formation comprises a pressure-bearing cylinder and a pressurizing assembly. The pressure-bearing cylinder comprises a lower cylinder body and an upper cylinder body which are detachably and sealingly connected. A seepage hole is formed in the bottom wall of the lower cylinder body. A first pressurizing hole is formed in the top wall of the upper cylinder body. The pressurizing assembly comprises an X-axis pressurizing assembly, a Y-axis pressurizing assembly and a Z-axis pressurizing assembly. The Z-axis pressurizing assembly comprises a pressurizing cylinder, a pressurizing piston and a pressurizing pump. The pressurizing cylinder is connected with the lower cylinder body. The pressurizing inner cavity of the pressurizing cylinder is in communication with the pressurizing hole. A second pressurizing hole is formed in the top of the pressurizing cylinder. A liquid injection valve port is arranged at the bottom of the pressurizing cylinder. The pressurizing piston is arranged in the pressurizing inner cavity. The pressurizing pump is used for injecting a pressurizing medium into the pressurizing inner cavity through the second pressurizing hole to drive the pressurizing piston to move downward. The device can more accurately simulate the formation environment and improve the reliability of experimental results.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas well drilling engineering technology, specifically relating to an experimental device and method for measuring filtration loss and forming mud cake. Background Technology

[0002] During oil and gas well drilling, drilling fluid is lost from the wellbore into formation pores or fractures under differential pressure, depositing as mud cake on the wellbore surface. The amount of fluid lost, as well as parameters such as the thickness, tightness, permeability, and mechanical properties of the mud cake, directly affect wellbore stability, wellbore cleanliness, differential pressure stuck pipe risk, and the degree of reservoir damage. Especially in sensitive formations such as shale or in high-temperature, high-pressure, and deep complex geostress environments, the behavior of fluid loss and mud cake is more complex, easily leading to engineering problems such as wellbore reduction, collapse and blockage, lost circulation, increased torque friction, and reduced production capacity. Therefore, conducting experiments on fluid loss and mud cake formation under near-original formation conditions is of great significance for optimizing drilling fluid systems, improving wellbore stability, and evaluating reservoir protection.

[0003] Existing drilling fluid filtration loss testing devices mostly adopt unidirectional pressure structures such as API filtration loss meters or HTHP filtration loss meters, and mostly use filter paper or filter screen as the filter medium. They measure the filtration loss over a certain period of time and make filter cake under unidirectional pressure difference. However, the seepage boundary conditions are still different from the actual wellbore-formation interface, making it difficult to reflect the coupling law between mud cake compaction and seepage channel evolution under actual geostress. Summary of the Invention

[0004] To address the aforementioned deficiencies or shortcomings, this invention provides an experimental apparatus and method for filtration loss measurement and cake formation, aiming to solve the technical problem that existing filtration loss measurement and cake formation experimental devices cannot accurately reflect the true changes in the formation.

[0005] To achieve the above objectives, the first aspect of the present invention provides an experimental apparatus for measuring filtration loss and forming cake, comprising a pressure cylinder and a pressurization assembly. The pressure cylinder includes a lower cylinder and an upper cylinder arranged sequentially from bottom to top. The lower and upper cylinders are detachably and sealed together to form the inner cavity of the pressure cylinder. The inner cavity of the lower cylinder is used to accommodate core specimens of equal height. A seepage hole is provided on the bottom wall of the lower cylinder, and a first pressurization hole is provided on the top wall of the upper cylinder. The pressurization assembly includes an X-axis pressurization component, a Y-axis pressurization component, and a Z-axis pressurization component. The X-axis pressurization component is used to apply pressure to the core specimen along the horizontal direction of the X-axis, and the Y-axis pressurization component is used to apply pressure along the horizontal direction of the Z-axis. The Y-axis applies pressure to the core specimen in the horizontal direction. The Z-axis pressurization assembly includes a pressurization cylinder, a pressurization piston, and a pressurization pump. The pressurization cylinder is located on the top wall of the upper cylinder body. The pressurization cavity of the pressurization cylinder is connected to the first pressurization hole. The pressurization piston is located in the pressurization cavity. The pressurization cylinder has a second pressurization hole and a liquid injection valve port on the upper and lower sides of the pressurization piston. The liquid injection valve port is used to inject drilling fluid. The pressurization pump is used to inject pressurization medium into the pressurization cavity through the second pressurization hole to drive the pressurization piston downward.

[0006] In this embodiment of the invention, the lower cylinder includes a main body and a pressure plate. The main body is used to accommodate the core specimen. A pressure opening is formed on the side of the main body facing the X-axis pressure assembly and the Y-axis pressure assembly. The pressure plate is embedded in the pressure opening. The upper end of the pressure plate is sealed and abuts against the upper cylinder. The pressure plate and the upper cylinder are detachably connected.

[0007] In this embodiment of the invention, an upper cylinder latching part is formed on the bottom outer extension of the upper cylinder body, and a lower cylinder latching part is formed on the top outer extension of the pressure plate. The upper cylinder latching part and the lower cylinder latching part are correspondingly assembled. The experimental device for filtration loss measurement and mud cake formation also includes a locking plate, which has a locking groove for the upper cylinder latching part and the lower cylinder latching part to be inserted.

[0008] In this embodiment of the invention, the upper cylinder latching part is bent upward to form an upper locking groove, the lower cylinder latching part is bent downward to form a lower locking groove, and the locking plate has an upper locking part embedded in the upper locking groove and a lower locking part embedded in the lower locking groove. The width of the lower locking groove is greater than the width of the lower locking part to form an adjustment gap for horizontal adjustment of the pressure plate.

[0009] In this embodiment of the invention, one end of the upper locking part extending out of the upper locking groove and one end of the lower locking part extending out of the lower locking groove form a locking hole that is configured to communicate with each other. The experimental equipment for filtration loss measurement and mud cake formation also includes a locking bolt assembly, which is inserted into the locking hole.

[0010] In this embodiment of the invention, the lower cylinder body also includes a support platform and a filter plate. The support platform has a material inlet, and the filter plate is detachably disposed in the material inlet and forms a seepage hole. The main body is disposed on the support platform around the material inlet, and the size of the material inlet is greater than or equal to the inner cavity size of the main body.

[0011] In this embodiment of the invention, the experimental apparatus for measuring filtration loss and forming cake further includes a level gauge and a data processing unit. The level gauge is used to measure the change in liquid level in the upper cylinder. The data processing unit communicates with the level gauge and is configured to: establish a filtration loss volume-time curve based on the monitoring data of the level gauge, and calculate the instantaneous filtration loss rate, cumulative filtration loss, and stable filtration loss rate.

[0012] In this embodiment of the invention, the X-axis pressurizing assembly includes an X-axis bracket and an X-axis hydraulic cylinder. The lower end of the X-axis bracket is fixedly installed, and the upper end of the X-axis bracket is bent and abuts against the upper cylinder body. The X-axis hydraulic cylinder is mounted on the X-axis bracket and is used to apply pressure to the lower cylinder body along the horizontal direction of the X-axis. The Y-axis pressurizing assembly includes a Y-axis bracket and a Y-axis hydraulic cylinder. The lower end of the Y-axis bracket is fixedly installed, and the upper end of the Y-axis bracket is bent and abuts against the upper cylinder body. The Y-axis hydraulic cylinder is mounted on the Y-axis bracket and is used to apply pressure to the lower cylinder body along the horizontal direction of the Y-axis.

[0013] In this embodiment of the invention, an exhaust valve port is provided at the bottom of the pressurized cylinder.

[0014] In this embodiment of the invention, a drain valve is provided at the bottom of the upper cylinder.

[0015] To achieve the above objectives, a second aspect of the present invention provides an experimental method for filtration loss measurement and cake formation, comprising: The prepared core specimen is loaded into the lower cylinder and the upper and lower cylinders are sealed together. Preload stress was applied to the core specimens using the X-axis pressurization assembly and the Y-axis pressurization assembly, respectively. Drilling fluid is injected through the injection valve until the pressurizing piston moves to its highest position. Record the initial liquid level and increase the X, Y, and Z axial pressures to the initial target values ​​according to the preset loading path; After the pressure fluctuation in any direction is less than the preset threshold and continues for a preset duration, the pressure in the Z direction is controlled to the working value, so that the drilling fluid enters the core. Under the pressure-holding condition, the change of fluid level over time is recorded at the preset sampling frequency, and the filtration volume-time curve is plotted.

[0016] In this embodiment of the invention, increasing the X, Y, and Z axial pressures to the initial target value according to a preset loading path includes: coordinating the X, Y, and Z axial pressures to the initial target value using a graded incremental method according to the preset loading path. Each loading stage gradually increases the pressure at a preset loading rate, which is set to a constant loading rate of 0.1–2 MPa / min. When the pressure fluctuation amplitude in each direction is less than 0.1–0.5 MPa and lasts for 5–10 minutes, it is determined that the loading stage has reached a stable state, and the next loading stage begins.

[0017] Through the above technical solutions, the experimental equipment for filtration loss measurement and cake formation provided by the embodiments of the present invention has the following beneficial effects: When using the aforementioned experimental equipment for filtration loss measurement and mud cake formation, the operator first places the prepared core specimen into the lower cylinder, then closes the upper cylinder and seals the connection between the two. After the upper and lower cylinders are assembled, drilling fluid is injected through the injection valve until the pressure piston floats to its highest position. Finally, the pressure pump injects pressure medium into the pressure chamber to drive the pressure piston downward. The pressure piston pushes the drilling fluid downward and applies vertical pressure to the core specimen. At the same time, the X-axis pressure assembly and Y-axis pressure assembly apply horizontal pressure to establish a confining pressure environment that can accurately simulate the formation. As the pressure pump continues to work, the drilling fluid begins to penetrate the pore structure of the core specimen. The liquid phase component is discharged from the seepage hole through the core specimen under the pressure difference. At the same time, a mud cake is formed on the upper surface of the core specimen. After the experiment, the upper cylinder is disassembled and the mud cake is directly removed. This equipment can achieve high-precision simulation of drilling fluid filtration behavior and mud cake formation mechanism under deep formation conditions, thereby improving the reliability of experimental results.

[0018] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0019] The accompanying drawings are provided to illustrate the invention and form part of the specification. They are used together with the following detailed description to explain the invention, but do not constitute a limitation thereof. In the drawings: Figure 1 This is a front view of the experimental apparatus according to an embodiment of the present invention; Figure 2 This is a cross-sectional view of the experimental apparatus according to an embodiment of the present invention along the X-axis. Figure 3 This is a cross-sectional view of the experimental apparatus according to an embodiment of the present invention along the Y-axis. Figure 4 This is a side view of a locking plate according to an embodiment of the present invention; Figure 5 This is a top view of the experimental apparatus according to an embodiment of the present invention.

[0020] Explanation of reference numerals in the attached figures Detailed Implementation

[0021] 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 present invention.

[0022] The experimental apparatus and method for measuring filtration loss and forming cake according to the present invention are described below with reference to the accompanying drawings.

[0023] like Figures 1 to 5 As shown, the present invention provides an experimental apparatus for measuring filtration loss and forming cake, comprising: The pressure cylinder 1 includes a lower cylinder body 12 and an upper cylinder body 11 arranged sequentially from bottom to top. The lower cylinder body 12 and the upper cylinder body 11 are detachably and sealedly connected and assembled to form the inner cavity of the pressure cylinder 1. The inner cavity of the lower cylinder body 12 is used to accommodate core specimens of the same height. A seepage hole 121 is provided on the bottom wall of the lower cylinder body 12, and a first pressurization hole 111 is provided on the top wall of the upper cylinder body 11. The pressurization assembly 2 includes an X-axis pressurization component 21, a Y-axis pressurization component 22, and a Z-axis pressurization component 23. The X-axis pressurization component 21 is used to apply pressure to the core specimen in the horizontal direction of the X-axis. The Y-axis pressurization component 22 is used to apply pressure to the core specimen in the horizontal direction of the Y-axis. The Z-axis pressurization component 23 includes a pressurization cylinder 231, a pressurization piston 232, and a pressurization pump. The pressurization cylinder 231 is located on the top wall of the upper cylinder 11. The pressurization cavity of the pressurization cylinder 231 is connected to the first pressurization hole 111. The pressurization piston 232 is located in the pressurization cavity. The pressurization cylinder 231 has a second pressurization hole 233 and a liquid injection valve port 234 on the upper and lower sides of the pressurization piston 232, respectively. The liquid injection valve port 234 is used to inject drilling fluid. The pressurization pump is used to inject pressurization medium into the pressurization cavity through the second pressurization hole 233 to drive the pressurization piston 232 downward.

[0024] When using the aforementioned experimental equipment for filtration loss measurement and mud cake formation, the operator first places the prepared core specimen into the lower cylinder 12, then closes the upper cylinder 11 and seals the connection between the two. After the upper cylinder 11 and lower cylinder 12 are assembled, drilling fluid is injected through the injection valve 234 until the pressure piston 232 floats to the highest position. Finally, the pressure pump injects the pressure medium into the pressure chamber to drive the pressure piston 232 downward. The pressure piston 232 pushes the drilling fluid downward and applies vertical pressure to the core specimen. At the same time, the X-axis pressure assembly 21 and the Y-axis pressure assembly 22 apply horizontal pressure to establish a confining pressure environment that can accurately simulate the formation. As the pressure pump continues to work, the drilling fluid begins to penetrate the pore structure of the core specimen. The liquid phase component is discharged from the seepage hole 121 through the core specimen under the pressure difference. At the same time, a mud cake is formed on the upper surface of the core specimen. After the experiment, the upper cylinder 11 is disassembled and the mud cake is directly removed. This equipment can achieve high-precision simulation of drilling fluid filtration behavior and mud cake formation mechanism under deep formation conditions, thereby improving the reliability of experimental results.

[0025] Specifically, the second pressurization port 233 is located at the top of the pressurization cylinder 231, and the liquid injection valve port 234 is located at the bottom of the pressurization cylinder 231, so as to obtain the maximum stroke of the pressurization piston 232.

[0026] In this embodiment of the invention, the lower cylinder 12 includes a main body 122 and a pressure plate 123. The main body 122 is used to accommodate the core specimen. A pressure opening is formed on the side of the main body 122 facing the X-axis pressure assembly 21 and the Y-axis pressure assembly 22. The pressure plate 123 is embedded in the pressure opening. The upper end of the pressure plate 123 is in sealed contact with the upper cylinder 11, and the pressure plate 123 is detachably connected to the upper cylinder 11. The pressure plate 123 increases the stress-bearing area of ​​the core specimen, making the pressure distribution more uniform and more realistically simulating the actual stress state in the formation.

[0027] Specifically, to prevent drilling fluid from leaking from the gap between the pressure plate 123 and the main body 122, a sealing sleeve is provided in the inner cavity of the lower cylinder 12. The sealing sleeve is made of elastic material, and the core specimen is placed inside the sealing sleeve. The outer peripheral wall of the sealing sleeve is tightly fitted with the inner peripheral wall of the main body 122 and the pressure plate 123, thereby forming a complete sealing barrier around the pressure plate 123.

[0028] Furthermore, an annular sealing groove is provided around the pressure plate 123, and an elastic sealing ring is embedded in the annular sealing groove. When the pressure plate 123 comes into contact with the main body 122, the elastic sealing ring is deformed under pressure to form a sealing interface.

[0029] Furthermore, a clearance fit can be used between the pressure plate 123 and the sidewall of the pressure opening, with the clearance range controlled between 0.05 mm and 0.15 mm. This ensures that the pressure plate 123 can undergo slight displacement with the core specimen to transmit pressure when under horizontal pressure, while preventing drilling fluid from seeping into the pressure opening through the lateral gap. The pressure plate 123 is made of high-strength alloy steel, and its surface is hardened to improve wear resistance, ensuring that it maintains dimensional accuracy and sealing reliability even under repeated disassembly and high-pressure cycling. The surface of the pressure plate 123 facing the core specimen is precision ground to ensure a good fit with the end face of the core specimen and reduce stress concentration.

[0030] Furthermore, the shape of the pressure plate 123 can be adaptively designed according to the end face shape of the core specimen to meet the testing requirements of core specimens of different specifications. When the core specimen is a cylindrical standard sample, the pressure plate 123 is designed to match the arc shape; for square core specimens, the pressure plate 123 can be adjusted to a rectangle accordingly.

[0031] Furthermore, a heating device can be integrated inside the pressure plate 123 to simulate a high-temperature environment.

[0032] In this embodiment of the invention, an upper cylinder latching part 112 is formed on the bottom outer extension of the upper cylinder body 11, and a lower cylinder latching part 124 is formed on the top outer extension of the pressure plate 123. The upper cylinder latching part 112 and the lower cylinder latching part 124 are correspondingly fitted together. The experimental device for filtration loss measurement and mud cake formation also includes a locking plate 3. The locking plate 3 has a locking groove 31 for the upper cylinder latching part 112 and the lower cylinder latching part 124 to be inserted. The locking plate 3 is inserted horizontally at the joint of the upper cylinder latching part 112 and the lower cylinder latching part 124. The side wall of the locking groove 31 forms a vertical limit on the upper cylinder latching part 112 and the lower cylinder latching part 124, thereby fixing the upper cylinder body 11 and the pressure plate 123 together. This latching and locking plate 3 connection method ensures the sealing reliability between the upper cylinder body 11 and the pressure plate 123, and facilitates quick disassembly after the experiment, making it convenient to remove the core specimen and clean the mud cake.

[0033] In this embodiment of the invention, the upper cylinder latching part 112 is bent upward to form an upper locking groove, and the lower cylinder latching part 124 is bent downward to form a lower locking groove. The locking plate 3 has an upper locking part 32 embedded in the upper locking groove and a lower locking part 33 embedded in the lower locking groove. The width of the lower locking groove is greater than the width of the lower locking part 33 to form an adjustment gap for horizontal adjustment of the pressure plate 123. The adjustment gap allows the pressure plate 123 to have a certain displacement margin in the horizontal direction, enabling adaptive fine-tuning according to the actual size of the core specimen, ensuring that the pressure plate 123 is fully in contact with the end face of the core specimen. When the X-axis pressure assembly 21 and the Y-axis pressure assembly 22 apply horizontal pressure to the pressure plate 123 from both sides, the pressure plate 123 can slide slightly within the adjustment gap range, automatically finding the optimal contact position with the core specimen, thereby making the pressure transmitted to the core specimen more evenly distributed.

[0034] In this embodiment of the invention, one end of the upper locking part 32 extending from the upper locking groove and the other end of the lower locking part 33 extending from the lower locking groove form a through locking hole. The experimental equipment for filtration loss measurement and cake formation also includes a locking bolt assembly 4, which passes through the locking hole. The locking bolt assembly 4 is used to fasten the upper locking part 32 and the lower locking part 33, so that the locking plate 3 simultaneously presses the upper cylinder latching part 112 and the lower cylinder latching part 124, thereby achieving reliable locking between the upper cylinder body 11 and the pressure plate 123. The locking bolt assembly 4 typically includes a bolt body, a washer, and a locking nut. After the bolt body passes through the locking holes of the upper locking part 32 and the lower locking part 33 in sequence, the locking nut is tightened to generate a preload, causing the locking plate 3 to undergo elastic deformation and fit tightly against the outer surface of the latching part. Specifically, the locking plate 3 is a metal part with a certain elastic deformation capability.

[0035] In this embodiment of the invention, the lower cylinder 12 further includes a support platform 125 and a filter plate 126. The support platform 125 has a material inlet, and the filter plate 126 is detachably disposed within the material inlet, forming a seepage hole 121. The main body 122 is disposed around the material inlet on the support platform 125, and the size of the material inlet is greater than or equal to the inner cavity size of the main body 122. Generally, after the experiment, the upper cylinder 11 can be opened to remove the core sample from the lower cylinder 12. For core samples that are difficult to grasp, the filter plate 126 can be removed, and the core sample can be taken out from the bottom through the material inlet. The detachable design of the filter plate 126 not only facilitates the removal of the core sample but also allows for the replacement of filter plates 126 with different pore sizes according to experimental needs, to adapt to the testing requirements of drilling fluids with different particle sizes or cores with different permeability.

[0036] Specifically, a connecting part is provided around the periphery of the filter plate 126. The connecting part extends downward from the filter plate 126 and has a connecting hole for bolts to pass through and connect to the support platform 125.

[0037] Furthermore, the filter plate 126 can be configured as a frustum shape, with the diameter of the upper surface of the filter plate 126 being smaller than the diameter of the lower surface, thus forming a conical structure that gradually slopes outward from top to bottom. The feed inlet is correspondingly configured as a conical hole adapted to the conical structure, with the taper of the conical hole matching the taper of the filter plate 126. The conical structure can automatically center the filter plate 126 during installation, reducing assembly accuracy requirements and improving installation efficiency. Moreover, the conical structure facilitates the disassembly of the filter plate 126; simply removing the bolts allows the filter plate 126 to be taken out of the feed inlet, eliminating the jamming problem caused by impurities adhering or pressure deformation in traditional planar mating structures.

[0038] Furthermore, the support platform 125 has a sealing groove circumferentially formed on the inner wall of the conical hole, and an elastic sealing ring is embedded in the sealing groove. The elastic sealing ring is in close contact with the conical surface of the filter plate 126. The elastic sealing ring is made of oil-resistant and heat-resistant fluororubber or polytetrafluoroethylene, which can maintain stable sealing performance under high temperature and high pressure experimental environments.

[0039] Furthermore, the lower surface of the support platform 125 is usually provided with a guide groove or a collection chamber for collecting the filtrate filtered through the seepage hole 121. The guide groove is connected to an external filtrate metering device to realize real-time monitoring and accurate measurement of filtrate loss.

[0040] In this embodiment of the invention, the experimental equipment for measuring fluid loss and forming mud cake further includes a level gauge 5 and a data processing unit. The level gauge 5 is used to measure the change in liquid level within the upper cylinder 11. The data processing unit communicates with the level gauge 5 and is configured to: establish a fluid loss volume-time curve based on the monitoring data from the level gauge 5, and calculate the instantaneous fluid loss rate, cumulative fluid loss, and stable fluid loss rate. Through real-time monitoring by the level gauge 5, the data processing unit can dynamically track the volume change pattern of the drilling fluid during the fluid loss process, thereby accurately characterizing the phased features of the fluid loss behavior.

[0041] Specifically, high-frequency sampling was used in the initial stage of the experiment, and low-frequency sampling was used in the subsequent stages to improve the data resolution during the rapid formation of the mud cake.

[0042] Furthermore, the data processing unit is connected to the pressurization assembly 2 to synchronously record the corresponding three-dimensional pressure fluctuations for comparative analysis.

[0043] In this embodiment of the invention, the X-axis pressurizing assembly 21 includes an X-axis bracket 211 and an X-axis hydraulic cylinder 212. The lower end of the X-axis bracket 211 is fixedly installed, and the upper end of the X-axis bracket 211 is bent and abuts against the upper cylinder body 11. The X-axis hydraulic cylinder 212 is mounted on the X-axis bracket 211 and is used to apply pressure to the lower cylinder body 12 along the horizontal direction of the X-axis. The Y-axis pressurizing assembly 22 includes a Y-axis bracket 221 and a Y-axis hydraulic cylinder 222. The lower end of the Y-axis bracket 221 is fixedly installed, and the upper end of the Y-axis bracket 221 is bent and abuts against the upper cylinder body 11. The Y-axis hydraulic cylinder 222 is mounted on the Y-axis bracket 221 and is used to apply pressure to the lower cylinder body 12 along the horizontal direction of the Y-axis. The X-axis bracket 211 and the Y-axis bracket 221 serve two purposes: firstly, to accommodate the hydraulic cylinder, and secondly, to limit the movement of the upper cylinder body 11, preventing horizontal displacement or deflection of the upper cylinder body 11 during pressurization, thus ensuring the accuracy and stability of the triaxial stress application.

[0044] In this embodiment of the invention, an exhaust valve 235 is provided at the bottom of the pressurized cylinder 231. Through the exhaust valve 235, air inside the upper cylinder 11 can be discharged during drilling fluid injection, thus avoiding errors in liquid level measurement and interference from pressurized gas passing through the core specimen with filtration loss measurement results. When drilling fluid is injected into the pressurized cylinder 231, opening the exhaust valve 235 allows air inside the upper cylinder 11 to be discharged smoothly, ensuring that the drilling fluid fills the entire upper cylinder 11 space and eliminating liquid level measurement errors caused by air bubbles. The location of the exhaust valve 235 at the bottom of the pressurized cylinder 231 facilitates the complete discharge of air accumulated at the top. This design also facilitates cleaning and purging of the cylinder interior after the experiment. A corresponding valve control device can be configured at the exhaust valve 235 to achieve precise control of the venting process and reliable maintenance of the sealing state.

[0045] In this embodiment of the invention, a drain valve 113 is provided at the bottom of the upper cylinder 11. After the experiment, the residual drilling fluid in the upper cylinder 11 can be completely drained by opening the drain valve 113, which facilitates cleaning and maintenance of the cylinder interior and also allows for quick replacement with drilling fluids of different properties for subsequent comparative experiments. The drain valve 113 is located at the bottom of the upper cylinder 11, which allows for complete drainage of the liquid by gravity, preventing residual liquid from contaminating the next experiment or causing measurement errors.

[0046] To achieve the above objectives, a second aspect of the present invention provides an experimental method for filtration loss measurement and cake formation, comprising: S100, the prepared core specimen is loaded into the lower cylinder 12 and the upper cylinder 11 and the lower cylinder 12 are sealed together.

[0047] Specifically, the preparation parameters for core specimens include core dimensions, bedding orientation, and initial water-bearing state; other experimental parameters include drilling fluid system parameters, triaxial stress combination, Z-axis fluid pressure, test temperature, and treatment time. Before the experiment, the core specimens are cut, shaped, cleaned, dried, or saturated, and their initial mass, dimensions, porosity, and permeability are measured. Drilling fluid is prepared according to a standardized formula, and its density, apparent viscosity, plastic viscosity, dynamic shear force, and basic filtration loss parameters are measured to ensure comparability between different groups of tests.

[0048] S200, preload stress is applied to the core specimen through the X-axis pressure assembly 21 and the Y-axis pressure assembly 22 respectively.

[0049] Specifically, preload stress is applied in the X and Y axes to achieve horizontal positioning and clamping of the core. The preload stress is the minimum stable load that can ensure that the core specimen does not slip laterally or loosen during subsequent pressurization.

[0050] S300, drilling fluid is injected through injection valve port 234 to pressurize piston 232 to the highest position.

[0051] Specifically, before executing step S300, it is necessary to determine the position of the pressurizing piston 232. If the pressurizing piston 232 is not in the lowest injection position, the pressurizing piston 232 is first moved down to the injection position, and drilling fluid is injected into the pressurizing cylinder 231 through the injection valve port 234. The air in the system is discharged by opening the vent valve port 235. After the vent valve port 235 continuously discharges fluid and no continuous bubbles escape within a preset time, the vent valve port 235 is closed. Fluid is then replenished through the injection valve port 234 to return the pressurizing piston 232 to the highest position.

[0052] S400 records the initial liquid level and increases the X, Y, and Z axial pressures to the initial target values ​​according to the preset loading path.

[0053] Specifically, the X-axis hydraulic cylinder 212 and the Y-axis hydraulic cylinder 222 are kept in a preloaded state, and the X, Y, and Z-axis stresses are synchronously or progressively increased to the target values ​​according to the preset loading path.

[0054] S500: After the pressure fluctuation in any direction is less than the preset threshold and continues for a preset duration, the Z-axis pressure is increased to the working value, causing the drilling fluid to penetrate the core.

[0055] Specifically, when the pressure fluctuations in each direction are less than the preset threshold and continue for a preset duration, the pressure stabilization is determined to be complete, and a controllable pressure is formed on the drilling fluid in the Z-axis direction, so that the drilling fluid can penetrate the core under the set pressure conditions. The timing of the filtration loss and mud cake formation process is started, and the change of liquid level over time is recorded at the preset sampling frequency under the pressure holding conditions, and the filtration loss volume-time curve is plotted.

[0056] Specifically, high-frequency sampling was used in the initial stage of the experiment, and low-frequency sampling was used in the subsequent stages to improve the data resolution during the rapid formation of the mud cake; and the corresponding triaxial stress values, temperature and pressure fluctuations were recorded simultaneously for comparative analysis. When the preset action time is reached, or the liquid level change per unit time is less than the preset threshold and continues for the preset duration, the test ends; then, in the reverse order of loading, the triaxial stress is gradually unloaded to zero or the safe unloading value, the drain valve 113 is opened, the residual drilling fluid in the system is discharged and the cleaning is completed.

[0057] In this embodiment of the invention, step S400, increasing the X, Y, and Z triaxial pressures to the initial target value according to a preset loading path, includes: coordinating the X, Y, and Z triaxial pressures to the initial target value using a graded incremental loading method according to the preset loading path. Each loading stage gradually increases the pressure at a preset loading rate, which can be a constant loading rate of 0.1–2 MPa / min or adaptively adjusted based on the sample deformation response. At each loading stage, the pressure deviation in each direction is controlled within ±0.5%–±2%, and pressure fluctuations are monitored in real time. When the amplitude of the pressure fluctuation in each direction is less than 0.1–0.5 MPa and lasts for 5–10 minutes, the loading stage is determined to have reached a stable state, and the next loading stage begins, until the initial target value is reached.

[0058] In the description of this invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0059] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0060] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0061] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. An experimental apparatus for measuring filtration loss and forming cake, characterized in that, The experimental equipment for filtration loss measurement and cake formation includes: The pressure cylinder (1) includes a lower cylinder body (12) and an upper cylinder body (11) arranged sequentially from bottom to top. The lower cylinder body (12) and the upper cylinder body (11) are detachably and sealed together to form the inner cavity of the pressure cylinder (1). The inner cavity of the lower cylinder body (12) is used to accommodate core specimens of equal height. A seepage hole (121) is provided on the bottom wall of the lower cylinder body (12), and a first pressurization hole (111) is provided on the top wall of the upper cylinder body (11). The pressurization assembly (2) includes an X-axis pressurization component (21), a Y-axis pressurization component (22), and a Z-axis pressurization component (23). The X-axis pressurization component (21) is used to apply pressure to the core specimen along the horizontal direction of the X-axis. The Y-axis pressurization component (22) is used to apply pressure to the core specimen along the horizontal direction of the Y-axis. The Z-axis pressurization component (23) includes a pressurization cylinder (231), a pressurization piston (232), and a pressurization pump. The pressurization cylinder (231) is located on the top wall of the upper cylinder body (11). The pressurized inner cavity of the cylinder (231) is connected to the first pressurized hole (111). The pressurized piston (232) is located in the pressurized inner cavity. The pressurized cylinder (231) has a second pressurized hole (233) and an injection valve port (234) on the upper and lower sides of the pressurized piston (232). The injection valve port (234) is used to inject drilling fluid. The pressurized pump is used to inject pressurized medium into the pressurized inner cavity through the second pressurized hole (233) to drive the pressurized piston (232) downward.

2. The experimental apparatus for measuring filtration loss and forming cake according to claim 1, characterized in that, The lower cylinder (12) includes a main body (122) and a pressure plate (123). The main body (122) is used to accommodate the core specimen. The main body (122) has a pressure opening on one side facing the X-axis pressure assembly (21) and the Y-axis pressure assembly (22). The pressure plate (123) is embedded in the pressure opening. The upper end of the pressure plate (123) is sealed and abutted against the upper cylinder (11). The pressure plate (123) is detachably connected to the upper cylinder (11).

3. The experimental apparatus for filtration loss measurement and cake formation according to claim 2, characterized in that, The bottom of the upper cylinder body (11) extends to form an upper cylinder latching part (112), and the top of the pressure plate (123) extends to form a lower cylinder latching part (124). The upper cylinder latching part (112) and the lower cylinder latching part (124) are correspondingly fitted together. The experimental device for filtration loss measurement and mud cake formation also includes a locking plate (3). The locking plate (3) has a locking groove (31) for the upper cylinder latching part (112) and the lower cylinder latching part (124) to be embedded.

4. The experimental apparatus for measuring filtration loss and forming cake according to claim 3, characterized in that, The upper cylinder latch (112) is bent upward to form an upper locking groove, the lower cylinder latch (124) is bent downward to form a lower locking groove, the locking plate (3) has an upper locking part (32) embedded in the upper locking groove and a lower locking part (33) embedded in the lower locking groove, the width of the lower locking groove is greater than the width of the lower locking part (33) to form an adjustment gap for the horizontal adjustment of the pressure plate (123).

5. The experimental apparatus for measuring filtration loss and forming cake according to claim 4, characterized in that, The upper locking part (32) extends out of the upper locking groove and the lower locking part (33) extends out of the lower locking groove to form a locking hole. The experimental equipment for filtration loss measurement and mud cake formation also includes a locking bolt assembly (4), which is inserted into the locking hole.

6. The experimental apparatus for measuring filtration loss and forming cake according to claim 2, characterized in that, The lower cylinder body (12) also includes a support platform (125) and a filter plate (126). The support platform (125) has a material inlet. The filter plate (126) is detachably disposed in the material inlet and forms the seepage hole (121). The main body (122) is disposed on the support platform (125) around the material inlet. The size of the material inlet is greater than or equal to the inner cavity size of the main body (122).

7. The experimental apparatus for filtration loss measurement and cake formation according to any one of claims 1 to 6, characterized in that, The experimental apparatus for measuring filtration loss and forming cake also includes a level gauge (5) and a data processing unit. The level gauge (5) is used to measure the change in liquid level within the upper cylinder (11). The data processing unit communicates with the level gauge (5) and is configured to: Based on the monitoring data of the level gauge (5), establish the filtration volume-time curve and calculate the instantaneous filtration rate, cumulative filtration volume, and stable filtration rate.

8. The experimental apparatus for filtration loss measurement and cake formation according to any one of claims 1 to 6, characterized in that, The X-axis pressurizing assembly (21) includes an X-axis bracket (211) and an X-axis hydraulic cylinder (212). The lower end of the X-axis bracket (211) is fixedly installed, and the upper end of the X-axis bracket (211) is bent and abuts against the upper cylinder body (11). The X-axis hydraulic cylinder (212) is mounted on the X-axis bracket (211) and is used to apply pressure to the lower cylinder body (12) in the horizontal direction of the X-axis. The Y-axis pressurizing assembly (22) includes a Y-axis bracket (221) and a Y-axis hydraulic cylinder (212). The cylinder (222) is fixedly installed at the lower end of the Y-axis bracket (221), and the upper end of the Y-axis bracket (221) is bent and abuts against the upper cylinder body (11). The Y-axis hydraulic cylinder (222) is installed on the Y-axis bracket (221) and is used to apply pressure to the lower cylinder body (12) in the horizontal direction of the Y-axis; and / or, the bottom of the pressurized cylinder (231) is provided with an exhaust valve port (235); and / or, the bottom of the upper cylinder body (11) is provided with a drain valve port (113).

9. An experimental method for measuring filtration loss and forming cake, characterized in that, The experimental method for filtration loss measurement and cake formation uses the experimental apparatus for filtration loss measurement and cake formation according to any one of claims 1 to 8, and includes: The prepared core specimen is loaded into the lower cylinder and the upper and lower cylinders are sealed together. Preload stress was applied to the core specimens using the X-axis pressurization assembly and the Y-axis pressurization assembly, respectively. Drilling fluid is injected through the injection valve until the pressurizing piston moves to its highest position. Record the initial liquid level and increase the X, Y, and Z axial pressures to the initial target values ​​according to the preset loading path; After the pressure fluctuation in any direction is less than the preset threshold and continues for a preset duration, the pressure in the Z direction is increased to the working value to allow the drilling fluid to invade the core. Under pressure-holding conditions, the change in fluid level over time is recorded at a preset sampling frequency, and the filtration volume-time curve is plotted.

10. The experimental method for filtration loss measurement and cake formation according to claim 9, characterized in that, The step of increasing the X, Y, and Z axial pressures to the initial target value according to the preset loading path includes: coordinating the X, Y, and Z axial pressures to the initial target value using a graded incremental method according to the preset loading path. Each loading stage gradually increases the pressure at a preset loading rate, which is set to a constant loading rate of 0.1 to 2 MPa / min. When the pressure fluctuation amplitude in each direction is less than 0.1 to 0.5 MPa and lasts for 5 to 10 minutes, it is determined that the loading stage has reached a stable state, and the next loading stage begins.

Images