Pred fluid circulating flushing type drilling fluid mud cake flushing efficiency evaluation device and method

Abstract

The invention discloses a prepad fluid circulation flushing type drilling fluid mud cake flushing efficiency evaluation device and method. The device comprises a spring measurement assembly, a dial assembly, a power assembly, a transmission assembly, a mud cake flushing assembly and detailed parts of all the assemblies. According to the scheme, the flushing effect of the drilling fluid mud cake under different displacements can be simulated, the interference of centrifugal force on the flushing efficiency evaluation of the drilling fluid mud cake is solved, the flushing effect of the prepad fluid on the drilling fluid mud cake can be accurately evaluated, and the prepad fluid hydraulic shear force borne by the drilling fluid mud cake on the rock core surface under different displacements can be accurately tested in real time; meanwhile, the concentration dynamic balance of the prepad fluid in the flushing process is guaranteed, the relation between the well cementation displacement and the drilling fluid mud cake flushing efficiency is quantified, and the well cementation prepad fluid system and displacement design are guided.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas well cementing, and in particular to a device and method for evaluating the flushing efficiency of a pad fluid circulation flushing drilling fluid mud cake. Background Art

[0002] During drilling, the pressure differential between the drilling fluid column and the formation causes the drilling fluid to lose water, forming a mud cake on the wellbore. Because the drilling fluid cake itself contains no cementing materials, it is difficult to solidify, which in turn impairs the bond between the cementing slurry and the formation rock. This can easily become a weak link in cementing quality and seriously affect the cement sheath isolation and cementing quality. Therefore, industry experts generally believe that ensuring the efficient flushing of the drilling fluid cake from the wellbore is key to improving the bond strength between the cement slurry and the formation rock, the cement sheath isolation capability, and ensuring the lifespan of oil and gas wells and the effective development of oil and gas resources. Furthermore, the flushing efficiency of the drilling fluid cake is an important factor guiding the formulation, performance, and dosage of cementing pre-pad fluids. Therefore, in order to improve cementing quality, ensure the efficient removal of the drilling fluid cake, and enhance the bond strength between the cementing slurry and the formation rock and the cement sheath isolation capability, it is imperative to develop a device and method that can accurately evaluate the flushing efficiency of the drilling fluid cake.

[0003] Currently, those skilled in the art have developed various drilling fluid cake flushing efficiency evaluation devices and methods based on theoretical and practical engineering conditions. However, the main factors affecting the experimental results in flushing experiments include: the quality testing method of the drilling fluid cake before and after flushing, the flushing rate and the hydraulic shear force on the mud cake at this flushing rate, centrifugal force, etc. Existing technical solutions have different solutions to each of these influencing factors, but none of them consider that the concentration of the effective component of the prepad fluid is also a significant factor affecting the flushing test results. In actual cementing operations, the prepad fluid flows continuously within the gap between the casing and the wellbore, so that the concentration of the effective component of the prepad fluid flushing the drilling fluid cake on the wellbore is in dynamic equilibrium, thereby ensuring that the flushing efficiency is not affected by changes in the prepad fluid concentration. However, when conducting flushing experiments, the above-mentioned equipment only uses an initial limited volume of prepad fluid near the drilling fluid cake for continuous flushing. As a result, the concentration of the effective component in the prepad fluid in this local area decreases continuously with the increase in flushing time, and it cannot be replenished in a timely manner, resulting in a low drilling fluid cake flushing efficiency evaluation result. Therefore, the displacement efficiency of the pre-fluid during the flushing experiment is also an important factor in ensuring the evaluation results of the drilling fluid mud cake flushing efficiency. Summary of the Invention

[0004] In response to the above technical problems, the present invention provides a device and method for evaluating the flushing efficiency of a pre-flushing drilling fluid mud cake.

[0005] The present invention is achieved by adopting the following technical solutions: First, a pre-flushing drilling fluid mud cake flushing efficiency evaluation device includes a spring measuring assembly, a dial assembly, a power assembly, a transmission assembly and a mud cake flushing assembly; wherein, the spring measuring assembly includes a spring, an inner cylinder shaft, an inner cylinder shaft bearing and a connector; the dial assembly includes a dial, a pointer and a magnifying glass; the power assembly includes a stepless speed motor and a speed control knob; the transmission assembly includes a transmission bearing, an active synchronous pulley, a synchronous belt, a driven synchronous pulley, a rotor and a rotating bearing; the mud cake flushing assembly includes a rotating drum, a core barrel, a pre-fluid cup, a support plate, a round handle and a core; the device as a whole also includes a supporting base and a column, as well as a metal shield for protecting the entire device.

[0006] Specifically, in the spring measuring assembly: the torque generated by the spring directly reflects the hydraulic shear force exerted on the core containing the mud cake; the inner cylinder shaft is used to suspend the core barrel; the inner cylinder shaft bearing is used to support the inner cylinder shaft and reduce its wear; the connector is used to connect the spring, the inner cylinder shaft and the dial of the dial assembly; when the rotating cylinder of the mud cake flushing assembly is working, the disturbance pre-fluid begins to circulate in the slurry cup, and at the same time, the core barrel fixed on the inner cylinder shaft is prompted to start rotating. Under the constraints of the connector and the spring, the core barrel only deflects at a certain angle, and after stabilization, the specific value of the hydraulic shear force exerted on the drilling fluid mud cake is read through a magnifying glass in conjunction with the dial and pointer.

[0007] Specifically, in the dial assembly: the dial is used to mark the hydraulic shear force value corresponding to the mechanical properties of the spring; the pointer is used to indicate the value on the dial; and the magnifying glass is used to read the hydraulic shear force.

[0008] Specifically, in the power assembly: the stepless speed-variable motor provides a power source for the device, and the speed regulating knob controls the rotation speed of the drum in the mud cake flushing assembly, and different flushing rates are set to meet different displacement requirements.

[0009] Specifically, in the transmission assembly: the transmission bearing is used to support the active synchronous pulley, the active synchronous pulley is directly connected to the stepless speed motor in the power assembly, and is then connected to the driven synchronous pulley by a synchronous belt, forming the main body of the transmission assembly; the rotor is used to connect the transmission assembly and the rotating drum in the mud cake washing assembly; the rotating bearing protects the rotor and reduces wear.

[0010] Specifically, in the mud cake flushing assembly: the drum is screwed onto the rotor in the transmission assembly by means of threads, and the rotation speed is controlled by the stepless speed motor in the power assembly; in the rigid connection between the drum and the rotor, the drum wall is composed of three circumferentially evenly distributed curved blades, each blade having an airfoil-shaped cross-section design, with the edge concave inward to form a fluid capture area and the center convex outward to generate a pressure gradient; when the drum rotates, the concave surface captures the fluid outside the front liquid cup, and through the diversion effect of the convex surface, the fluid is accelerated and pumped radially into the gap between the drum and the core barrel, simulating actual working conditions.

[0011] Specifically, the core barrel is used to load the core, and the top of the core barrel is provided with a freely removable metal cover. After the core with the drilling fluid mud cake is loaded, the top cover is directly grabbed by hand and fixed on the inner barrel shaft during the flushing experiment; the pre-fluid cup is used to hold the pre-fluid to be evaluated, and the inner wall of the pre-fluid cup is marked with a liquid level scale line; the support plate and the round handle are used to control the height of the pre-fluid cup so that the core barrel is completely submerged in the pre-fluid.

[0012] On the other hand, a method for evaluating the flushing efficiency of drilling fluid mud cake using a pre-pad circulating flushing method is implemented based on the aforementioned pre-pad circulating flushing method. A core sample with a drilling fluid mud cake is prepared under cementing temperature and pressure conditions, and the core sample is subjected to a flushing experiment. The method includes the steps of preparing a drilling fluid mud cake sample and a pre-pad sample, and conducting a drilling fluid mud cake flushing experiment and evaluation. The steps of preparing a drilling fluid mud cake sample and a pre-pad sample specifically include: Step A1: Take a certain standard core and blow the surface clean with nitrogen. At the same time, take the drilling fluid used on site and stir it evenly. Step A2: Using a high-temperature and high-pressure viscosifier and a high-pressure filter loss tester, pour drilling fluid to the container scale line, place the core in the drilling fluid, and cure at the required temperature and pressure for a predetermined time; Step A3: Prepare the pre-pad solution according to the pre-pad solution formula required for the experiment.

[0013] Specifically, in the drilling fluid mud cake flushing test and evaluation steps, the flushing test specifically includes: Step B1: Take the core sample with the drilling fluid cake from the thickening slurry cup, place the core steadily on a clean glass plate with tweezers, and remove the drilling fluid cake from the upper and lower surfaces of the core with a blade; Step B2: Use tweezers to place the processed core with the drilling fluid cake on the bottom of the core barrel, install the core barrel cover and tighten the screws; fix the core barrel on the inner barrel shaft, pour the pre-fluid into the pre-fluid cup until it submerges the scale line, and place the pre-fluid cup steadily on the support plate. Use the support plate and round handle to raise the pre-fluid cup until the pre-fluid submerges the core barrel. After standing for 30 seconds without rotating, remove the core barrel and weigh the total mass of the core barrel and the core with the drilling fluid cake, which is recorded as ; Step B3: After weighing, re-fix the core barrel on the inner barrel shaft, place the pre-fluid cup on the support plate, raise the pre-fluid cup to submerge the core barrel, turn on the power of the stepless speed motor, and determine the experimental flushing speed and rotation speed according to the flushing displacement of the cementing. After the rotation speed stabilizes, read the hydraulic shear force on the core surface from the dial through a magnifying glass; after the required flushing time is reached, stop the motor, remove the core barrel, weigh and record the total mass of the core barrel and the core with drilling fluid mud cake after flushing. ; Step B4: Rinse the remaining drilling fluid cake on the surface of the core thoroughly with clean water, weigh it, and record the initial mass of the core. .

[0014] Specifically, in the drilling fluid mud cake flushing experiment and evaluation step, the evaluation step is to calculate the flushing efficiency of the drilling fluid mud cake, and the specific calculation formula is: ; Wherein, η is the flushing efficiency, unit is %; is the total mass of the core barrel and the core with mud cake before flushing, in g; is the total mass of the core barrel and the residual mud cake core after flushing, in g; is the total mass of the core barrel and core, in g.

[0015] The beneficial effects of the present invention are as follows: the present invention provides a pre-flushing type drilling fluid mud cake flushing efficiency evaluation device, which can simulate the flushing effect of drilling fluid mud cake at different displacements, solve the interference of centrifugal force on the evaluation of drilling fluid mud cake flushing efficiency, and can accurately evaluate the flushing effect of the pre-flushing fluid on the drilling fluid mud cake. It can also accurately test the pre-flushing fluid hydraulic shear force exerted on the drilling fluid mud cake on the core surface at different displacements in real time, quantify the relationship between cementing displacement and drilling fluid mud cake flushing efficiency, and guide the cementing pre-flushing fluid system and displacement design. At the same time, the present invention can also drive the circulation and renewal of the pre-flushing fluid through the rotating drum blades, simulate the dynamic equilibrium of concentration in the experiment, and solve the problem of concentration attenuation caused by the flushing process. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0017] Figure 1 This is a structural diagram of a pad fluid circulation flushing drilling fluid mud cake flushing efficiency evaluation device according to an embodiment of the present invention; Among them, 1-spring, 2-magnifying glass, 3-pointer, 4-dial, 5-connector, 6-driven synchronous pulley, 7-rotating bearing, 8-inner cylinder shaft bearing, 9-inner cylinder shaft, 10-rotating cylinder, 11-core cylinder, 12-front liquid cup, 13-support plate, 14-base, 15-power switch, 16-round handle, 17-core, 18-column, 19-rotor, 20-synchronous belt, 21-transmission bearing, 22-active synchronous pulley, 23-stepless speed motor, 24-speed control knob, 25-metal shield. DETAILED DESCRIPTION

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

[0019] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings.

[0020] The following is combined with Figure 1 , some embodiments of the present invention are described in detail. In the absence of conflict, the following embodiments and features in the embodiments can be combined with each other.

[0021] The present invention proposes a device and method for evaluating the efficiency of mud cake flushing by circulating pre-flushing drilling fluid. First, the device and method for evaluating the efficiency of mud cake flushing by circulating pre-flushing drilling fluid are as follows: Figure 1As shown, it includes a spring measuring assembly, a dial assembly, a power assembly, a transmission assembly and a mud cake flushing assembly; wherein, the spring measuring assembly includes a spring 1, an inner cylinder shaft 9, an inner cylinder shaft bearing 8 and a connector 5; the dial assembly includes a dial 4, a pointer 3 and a magnifying glass 2; the power assembly includes a stepless speed motor 23 and a speed control knob 24; the transmission assembly includes a transmission bearing 21, an active synchronous pulley 22, a synchronous belt 20, a driven synchronous pulley 6, a rotor 19 and a rotating bearing 7; the mud cake flushing assembly includes a rotating drum 10, a core barrel 11, a front liquid cup 12, a support plate 13, a round handle 16 and a core 17; the entire device also includes a supporting base 14 and a column 18, as well as a metal shield 25 for protecting the entire device.

[0022] In this embodiment, the torque generated by the spring 1 in the spring measuring assembly directly reflects the hydraulic shear force exerted on the core containing the mud cake; the inner cylinder shaft 9 is used to suspend the core barrel 11; the inner cylinder shaft bearing 8 is used to support the inner cylinder shaft 9 and reduce its wear; the connector 5 is used to connect the spring 1, the inner cylinder shaft 9 and the dial 4 of the dial assembly; when the rotating drum 10 of the mud cake flushing assembly is working, the disturbance pre-fluid begins to circulate in the slurry cup, and at the same time, the core barrel 11 fixed on the inner cylinder shaft 9 is prompted to start rotating. Under the constraints of the connector 5 and the spring 1, the core barrel 11 only deflects at a certain angle, and after stabilization, the specific value of the hydraulic shear force exerted on the drilling fluid mud cake is read through the magnifying glass in conjunction with the dial 4 and the pointer 3.

[0023] In this embodiment, the dial 4 in the dial assembly is used to mark the hydraulic shear force value corresponding to the mechanical properties of the spring 1; the pointer 3 is used to indicate the value on the dial 4; and the magnifying glass 2 is used to read the hydraulic shear force.

[0024] In this embodiment, the stepless speed-variable motor 23 in the power assembly provides the power source for the device, and the speed knob 24 controls the rotation speed of the drum 10 in the mud cake flushing assembly, setting different flushing rates to meet different displacement requirements.

[0025] In this embodiment, the transmission bearing 21 in the transmission assembly is used to support the active synchronous pulley 22, which is directly connected to the stepless speed motor 23 in the power assembly, and then connected to the driven synchronous pulley 6 by the synchronous belt 20, forming the main body of the transmission assembly; the rotor 19 is used to connect the transmission assembly and the rotating drum 10 in the mud cake washing assembly; the rotating bearing 7 protects the rotor and reduces wear.

[0026] In this embodiment, the drum 10 in the mud cake flushing assembly is screwed onto the rotor 19 in the transmission assembly by means of threads, and the rotation speed is controlled by the stepless speed motor 23 in the power assembly; in the rigid connection between the drum 10 and the rotor 19, its drum wall is composed of three circumferentially evenly distributed curved blades, each blade having an airfoil-shaped cross-section design, with the edge concave inward to form a fluid capture area and the center convex outward to generate a pressure gradient; when the drum 10 rotates, the concave surface captures the fluid outside the front liquid cup 12, and through the diversion effect of the convex surface, the fluid is accelerated and pumped radially into the gap between the drum 10 and the core barrel 11, simulating actual working conditions. The core barrel 11 is used to load the core 17. The top of the core barrel 11 is provided with a removable metal cover. After the core with drilling fluid cake is loaded, the top cover is directly grabbed by hand and fixed to the inner barrel shaft 9 during the flushing test. The pre-fluid cup 12 is used to hold the pre-fluid to be evaluated. The inner wall of the pre-fluid cup 12 is marked with a liquid level scale line. The support plate 13 and the round handle 16 are used to control the height of the pre-fluid cup so that the core barrel 11 is completely submerged in the pre-fluid.

[0027] The present invention also provides a drilling fluid mud cake flushing efficiency evaluation method, which is applied to the pre-flushing type drilling fluid mud cake flushing efficiency evaluation device provided by the present invention. The method is based on preparing a core sample with a drilling fluid mud cake under cementing temperature and pressure conditions, and the core is subjected to a flushing experiment using the pre-flushing type drilling fluid mud cake flushing efficiency evaluation device and method. This method has the advantages of simple operation, no damage to the mud cake, and small error in the results, making the evaluation results of the flushing efficiency of the drilling fluid mud cake more accurate. The evaluation results include: the influence trend of the pre-flushing type, displacement, and flushing time on the flushing efficiency, and after determining the performance evaluation results of the flushing fluid, the formulation and performance of the pre-flushing fluid to be analyzed are optimized. It includes the following steps: 1. Preparation of drilling fluid mud cake samples and pre-pad samples (1) Take a standard core with a height of 50 mm and a diameter of 25 mm, blow the surface clean with nitrogen, and take 1000 ml of the drilling fluid used on site and stir it evenly; (2) Use a high-pressure container such as a high-temperature and high-pressure viscometer or a high-pressure filtration tester to pour drilling fluid to the container scale line, place the core in the drilling fluid, and maintain it at the required temperature and pressure for a predetermined time; (3) Prepare the pre-fluid according to the pre-fluid formula required for the experiment.

[0028] 2. Drilling fluid mud cake flushing test steps (1) Take the core sample with drilling fluid cake from the thickening slurry cup, place the core steadily on the surface of a clean glass plate with tweezers, and then use a blade to remove the drilling fluid cake on the upper and lower ends of the core.

[0029] (2) Use tweezers to place the processed core with the drilling fluid cake on the bottom of the core barrel, install the core barrel cover, and tighten the screws. Fix the core barrel on the inner barrel shaft, pour the pre-fluid into the pre-fluid cup until it submerges the scale line, then place the pre-fluid cup steadily on the support plate, use the support plate and the round handle to raise the pre-fluid cup until the pre-fluid submerges the core barrel. After standing for 30 seconds without rotating, remove the core barrel and weigh the total mass of the core barrel and the core with the drilling fluid cake, which is recorded as .

[0030] (3) After weighing, re-fix the core barrel on the inner barrel shaft, place the pre-fluid cup on the support plate, raise the pre-fluid cup to submerge the core barrel, turn on the power of the stepless speed motor, and determine the experimental flushing speed and rotation speed according to the flushing displacement of the cementing. Turn on the motor, wait for the speed to stabilize, and read the hydraulic shear force on the core surface from the dial through a magnifying glass. When the flushing time required for the experiment is reached, stop the motor, remove the core barrel, weigh and record the total mass of the core barrel and the core with drilling fluid mud cake after flushing. .

[0031] (4) Rinse the remaining drilling fluid cake on the core surface thoroughly with clean water, weigh it, and record the initial mass of the core. ; (5) The calculation formula for the flushing efficiency of drilling fluid cake is as follows: Where η is the flushing efficiency (%); is the total mass of the core barrel and the core with mud cake before flushing (g); is the total mass of the core barrel and the residual mud cake core after flushing (g); is the total mass of the core barrel and core (g).

[0032] In this embodiment, after the same core is flushed under low rotation speed conditions, the flushing experiment can be continued under higher rotation speed conditions, and the test steps are as described above.

[0033] Because the surface of the core cake will be stained with pre-fluid which cannot be cleaned directly after flushing, the total mass before flushing should be weighed. When measuring the core, the core barrel containing the mud cake core must be immersed in the pre-fluid for 30 seconds and then taken out and weighed.

[0034] During the formation of drilling fluid mud cake, drilling fluid filtrate will invade the internal pores of the core. This part of the intrusion cannot be completely removed in the subsequent cleaning. The total mass of the core barrel and the core after flushing and completely removing the surface mud cake is selected as the , which can reduce the weighing error caused by the non-removable objects inside the core to a certain extent, making the evaluation results more accurate.

[0035] In this embodiment, each set of experimental conditions needs to be repeated three times, and the average value of the flushing efficiency is taken as the final evaluation result.

[0036] In another embodiment, the pre-fluid flushing device mainly includes: a spring measuring assembly, a dial assembly, a power assembly, a transmission assembly, and a mud cake flushing assembly.

[0037] The spring measuring assembly is composed of a spring 1, a connector 5, an inner cylinder shaft bearing 8, and an inner cylinder shaft 9; the dial assembly is composed of a magnifying glass 2, a pointer 3, and a dial 4; the specific connector is used to connect the spring, the inner cylinder shaft, and the dial; the power assembly and the transmission assembly are composed of a driven synchronous pulley 6, a rotating bearing 7, a rotor 19, a synchronous belt 20, a transmission bearing 21, an active synchronous pulley 22, an infinitely variable speed motor 23, and a speed control knob 24; specifically, the stepless motor can control the speed through the speed control knob within the set range, thereby controlling the flushing rate; turn on the power switch 15, set a certain speed and the motor starts working, the active synchronous pulley and the transmission bearing start rotating, and the driven synchronous pulley rotates through the synchronous belt, and then the rotor and the rotating bearing start working; the mud cake flushing assembly is composed of a rotating drum 10, a core barrel 11, a pre-liquid cup 12, a support plate 13, a round handle 16, and a core 17; specifically, the core size is 50 mm in height and 25 in diameter. mm standard core, the core barrel is fixed on the inner barrel shaft with screws, the rotating barrel is screwed on the rotor with threads, the pre-fluid is poured into the liquid level line in the pre-fluid cup, and the support plate and round handle can lift the pre-fluid cup.

[0038] The top of the drum 10 is provided with threads, and its wall is composed of three metal blades with a convex center and an inward concave edge. The three blades are evenly distributed along the circumference (at intervals of 120 degrees). When the drum rotates, it can drive the peripheral pre-fluid to flow into the annular gap between the drum 10 and the core barrel 11, achieving a continuous displacement effect on the pre-fluid near the core barrel surface, simulating the flow state of the pre-fluid in the annulus during actual cementing operations, and helping to maintain the concentration of the effective components of the pre-fluid in the mud cake action area.

[0039] In the pre-flushing type drilling fluid mud cake flushing efficiency evaluation device, such as Figure 1 The base 14 and the column 18 play a supporting role for the entire device; the metal shield 25 is used to protect the safety of the entire device and the experimenters.

[0040] In this embodiment, the evaluation of the flushing efficiency of the drilling fluid mud cake by the pre-pad circulation flushing method specifically includes: 1. Drilling fluid cake preparation (1) Prepare the drilling fluid used at the Changqing site as the experimental slurry; (2) The present invention uses a core to simulate the well wall, and uses a pressure instrument that can create a pressure difference, such as a high-temperature and high-pressure viscosifier and a filter loss meter, to compress the mud cake. The drilling fluid retrieved on site is poured into the thickening slurry cup, covering the core, and sealed. The slurry cup is then placed in the high-temperature and high-pressure viscosifier, and the pressure and temperature conditions are set. (3) After removing the mud cakes on the upper and lower sections of the core with drilling fluid mud cakes, the core is loaded into the core barrel and fixed on the inner barrel shaft.

[0041] 2. Evaluation of pre-fluid performance (1) Soak the core barrel containing the mud cake in the pre-fluid to be evaluated for 30 seconds, then wipe off the excess pre-fluid on the surface of the core barrel, and weigh the total weight of the core, mud cake, and core barrel before the flushing test. ; (2) Fix the core barrel on the inner barrel shaft, tighten the rotating barrel, pour the pre-fluid to be evaluated into the pre-fluid cup, raise the pre-fluid cup to submerge the entire core barrel, turn on the motor, set the speed according to the annular return speed, and flush according to the experimental time; (3) After flushing, remove the core barrel and wipe off the excess pre-fluid attached to the surface of the core barrel with a clean paper towel. Weigh the total weight of the flushed core, remaining mud cake, and core barrel. ; (4) Rinse the remaining mud cake around the core with clean water, wipe the water on the surface of the core barrel, and weigh the total weight of the core and core barrel. ; (5) Calculate flushing efficiency , compare the influence trends of prepad fluid, annular return velocity and flushing time on flushing efficiency, and evaluate the prepad fluid performance; where η is the flushing efficiency (%); is the total mass of the core barrel and attached mud cake before flushing (g); is the total mass of the core barrel and the residual mud cake after flushing (g); is the total mass (g) of the core barrel and core after all residual mud cake is cleaned out.

[0042] For the sake of simplicity, the aforementioned embodiments are described as a series of actions. However, those skilled in the art should be aware that this application is not limited by the order of the actions described, because according to this application, some steps can be performed in other orders or simultaneously. Secondly, those skilled in the art should also be aware that the embodiments described in this specification are preferred embodiments, and the actions involved are not necessarily required by this application.

[0043] The above embodiments describe the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Without departing from the spirit and scope of the present invention, modifications and variations made by those skilled in the art without departing from the spirit and scope of the present invention should be within the scope of protection of the appended claims.

Claims

1. A device for evaluating the efficiency of drilling fluid cake flushing using a pre-flushing fluid circulation method, characterized in that: The invention comprises a spring measuring assembly, a dial assembly, a power assembly, a transmission assembly and a mud cake flushing assembly; wherein the spring measuring assembly comprises a spring (1), an inner cylinder shaft (9), an inner cylinder shaft bearing (8) and a connector (5); the dial assembly comprises a dial (4), a pointer (3) and a magnifying glass (2); the power assembly comprises a stepless speed-changing motor (23) and a speed regulating knob (24); the transmission assembly comprises a transmission bearing (21), an active synchronous pulley (22), a synchronous belt (20), a driven synchronous pulley (6), a rotor (19) and a rotating bearing (7); the mud cake flushing assembly comprises a rotating drum (10), a core barrel (11), a front liquid cup (12), a support plate (13), a round handle (16) and a core (17); the device as a whole further comprises a supporting base (14) and a column (18), a metal shield (25) for protecting the entire device, and a power switch (15).

2. The pad fluid circulation flushing drilling fluid mud cake flushing efficiency evaluation device according to claim 1, characterized in that: In the spring measuring assembly: the torque generated by the spring (1) directly reflects the hydraulic shear force exerted on the core containing the mud cake; the inner cylinder shaft (9) is used to suspend the core barrel (11); the inner cylinder shaft bearing (8) is used to support the inner cylinder shaft (9) and reduce its wear; the connector (5) is used to connect the spring (1), the inner cylinder shaft (9) and the scale plate (4) of the scale plate assembly; when the rotating cylinder (10) of the mud cake flushing assembly is working, the disturbance pre-fluid starts to circulate in the slurry cup, and at the same time, the core barrel (11) fixed on the inner cylinder shaft (9) starts to rotate. Under the constraints of the connector (5) and the spring (1), the core barrel (11) only deflects at a certain angle, and after stabilization, the specific value of the hydraulic shear force exerted on the drilling fluid mud cake is read through a magnifying glass in conjunction with the scale plate (4) and the pointer (3).

3. The pad fluid circulation flushing drilling fluid mud cake flushing efficiency evaluation device according to claim 1, characterized in that: In the scale plate assembly: the scale plate (4) is used to mark the hydraulic shear force value corresponding to the mechanical properties of the spring (1); the pointer (3) is used to indicate the value on the scale plate (4); and the magnifying glass (2) is used to read the hydraulic shear force.

4. The pre-flushing type drilling fluid mud cake flushing efficiency evaluation device according to claim 1, characterized in that: In the power assembly: the stepless speed-variable motor (23) provides a power source for the device, and the speed regulating knob (24) controls the rotation speed of the drum (10) in the mud cake flushing assembly, and sets different flushing rates in accordance with different displacement requirements.

5. The pre-flushing type drilling fluid mud cake flushing efficiency evaluation device according to claim 1, characterized in that: In the transmission assembly: the transmission bearing (21) is used to support the active synchronous pulley (22), the active synchronous pulley (22) is directly connected to the stepless speed motor (23) in the power assembly, and is then connected to the driven synchronous pulley (6) via a synchronous belt (20), forming the main body of the transmission assembly; the rotor (19) is used to connect the transmission assembly and the rotating drum (10) in the mud cake washing assembly; the rotating bearing (7) protects the rotor and reduces wear.

6. The pad circulation flushing drilling fluid mud cake flushing efficiency evaluation device according to claim 1, characterized in that: In the mud cake flushing assembly: the rotating drum (10) is screwed onto the rotor (19) in the transmission assembly by means of a thread, and the rotation speed is controlled by the stepless speed-variable motor (23) in the power assembly; in the rigid connection between the rotating drum (10) and the rotor (19), the drum wall is composed of three circumferentially evenly distributed curved blades, each blade having an airfoil-shaped cross-section design, with the edge concave inwardly curved to form a fluid capture zone, and the center convex outwardly convex to generate a pressure gradient; when the rotating drum (10) rotates, the concave surface captures the peripheral fluid of the front liquid cup (12), and through the diversion effect of the convex surface, the fluid is accelerated and pumped radially into the gap between the rotating drum (10) and the core barrel (11), simulating actual working conditions.

7. The pad circulation flushing drilling fluid mud cake flushing efficiency evaluation device according to claim 6, characterized in that: The core barrel (11) is used to load the core (17). The top of the core barrel (11) is provided with a freely removable metal cover. After the core with the drilling fluid cake is loaded, the top cover is directly grabbed by hand and fixed on the inner barrel shaft (9) during the flushing experiment. The pre-fluid cup (12) is used to hold the pre-fluid to be evaluated. The inner wall of the pre-fluid cup (12) is marked with a liquid level scale line. The support plate (13) and the round handle (16) are used to control the height of the pre-fluid cup so that the core barrel (11) is completely submerged in the pre-fluid.

8. A method for evaluating the efficiency of mud cake flushing in a pad circulation flushing drilling fluid, implemented based on the device for evaluating the efficiency of mud cake flushing in a pad circulation flushing drilling fluid according to any one of claims 1 to 7, characterized in that: A core sample with a drilling fluid cake is prepared under cementing temperature and pressure conditions, and the core sample is subjected to a flushing experiment, including a drilling fluid cake sample and a pre-pad sample preparation step and a drilling fluid cake flushing experiment and evaluation step. The drilling fluid cake sample and pre-pad sample preparation step specifically include: Step A1: Take a certain standard core and blow the surface clean with nitrogen. At the same time, take the drilling fluid used on site and stir it evenly. Step A2: Using a high-temperature and high-pressure viscosifier and a high-pressure filter loss tester, pour drilling fluid to the container scale line, place the core in the drilling fluid, and cure at the required temperature and pressure for a predetermined time; Step A3: Prepare the pre-pad solution according to the pre-pad solution formula required for the experiment.

9. The method for evaluating the flushing efficiency of a pre-pad circulating flushing drilling fluid mud cake according to claim 8, wherein: In the drilling fluid mud cake flushing test and evaluation steps, the flushing test specifically includes: Step B1: Take the core sample with the drilling fluid cake from the thickening slurry cup, place the core steadily on a clean glass plate with tweezers, and remove the drilling fluid cake from the upper and lower surfaces of the core with a blade; Step B2: Use tweezers to place the processed core with the drilling fluid cake on the bottom of the core barrel (11), install the core barrel top cover and tighten the screws; fix the core barrel (11) on the inner barrel shaft (9), pour the pre-fluid into the pre-fluid cup (12) until it submerges the scale line, and place the pre-fluid cup (12) stably on the support plate (13). Use the support plate (13) and the round handle (16) to raise the pre-fluid cup (12) until the pre-fluid submerges the core barrel (11). After standing for 30 seconds without rotating, remove the core barrel (11) and weigh the total mass of the core barrel (11) and the core with the drilling fluid cake, which is recorded as ; Step B3: After weighing, the core barrel (11) is re-fixed on the inner barrel shaft (9), the pre-liquid cup (12) is placed on the support plate (13), the pre-liquid cup (12) is raised to submerge the core barrel (11), the power of the stepless speed motor (23) is turned on, and the experimental flushing speed and rotation speed are determined according to the flushing displacement of the cementing. After the rotation speed stabilizes, the hydraulic shear force on the core surface is read from the dial (4) through a magnifying glass; after the flushing time required for the experiment is reached, the motor is stopped, the core barrel (11) is removed, and the total mass of the core barrel (11) and the core with drilling fluid mud cake after flushing is weighed and recorded. ; Step B4: Rinse the remaining drilling fluid cake on the surface of the core thoroughly with clean water, weigh it, and record the initial mass of the core. .

10. The method for evaluating the flushing efficiency of a pre-pad circulating flushing drilling fluid cake according to claim 9, wherein: In the drilling fluid mud cake flushing experiment and evaluation step, the evaluation step is to calculate the flushing efficiency of the drilling fluid mud cake. The specific calculation formula is: ； Wherein, η is the flushing efficiency, unit is %; is the total mass of the core barrel and the core with mud cake before flushing, in g; is the total mass of the core barrel and the residual mud cake core after flushing, in g; is the total mass of the core barrel and core, in g.

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