Drilling fluid plugging performance evaluation device and method based on improved sand filling pipe

Abstract

The invention belongs to the field of oil and gas field development of petroleum engineering, and discloses a drilling fluid plugging performance evaluation device and method.The evaluation device comprises a displacement pump, a fluid tank and the sand-filled pipe, an outlet of the displacement pump is connected with an inlet of the fluid tank, and an outlet of the fluid tank is connected with an inlet of the sand-filled pipe; a zero pressure measuring point is arranged at an inlet of the sand filling pipe, and a plurality of pressure measuring points are arranged on the sand filling pipe at intervals in the direction from the inlet to the outlet of the sand filling pipe. Drilling fluid can be displaced through the displacement pump to conduct dynamic plugging in the sand filling pipe, the multiple pressure measuring points are arranged on the sand filling pipe in the direction from the inlet to the outlet of the sand filling pipe at intervals, in this way, the formation depth of a plugging layer can be judged according to the pressure sudden change positions of the pressure measuring points, and the smaller the depth is, the better the plugging performance is; and if the plugging fails, namely the seepage at the outlet end continues, judging the plugging performance of the plugging agent according to the permeability damage rate of the clear water and the drilling fluid.

Description

Technical Field

[0001] The invention belongs to the field of oil and gas field development in petroleum engineering, and in particular relates to a drilling fluid plugging performance evaluation device and method based on an improved sand-filled pipe. Background Art

[0002] Loss of circulation during drilling is directly related to well control safety and drilling efficiency. To reduce or even prevent the adverse effects of lost circulation, various plugging materials are often added to the drilling fluid to seal the leakage channels. However, due to the strong heterogeneity of the formation, the sealing effect of the drilling fluid containing plugging agents often varies significantly under different geological conditions. This necessitates indoor experimental evaluation of the sealing performance before drilling.

[0003] Current methods for evaluating drilling fluid plugging performance primarily include the fracture plate method, the simulated formation core method, and the mudcake test. While these methods have considerable practical value, they also have limitations. The fracture plate method can rapidly assess the plugging performance of drilling fluid against fracture-type lost circulation, but due to technological limitations, it cannot simulate microfractures smaller than 0.1 mm. The simulated formation core test uses natural or artificial cores to more realistically simulate formation characteristics, but this is expensive and complex. The mudcake test primarily evaluates the plugging capacity of drilling fluids under static conditions but overlooks the impact of dynamic lost circulation environments. Therefore, accurately testing the plugging performance of drilling fluids remains a pressing issue. Summary of the Invention

[0004] To address the shortcomings of current drilling fluid plugging performance testing methods, the present invention proposes a drilling fluid plugging performance evaluation device and method based on an improved sand-filled pipe. The present invention can accurately evaluate the plugging performance of drilling fluid under different formation conditions (fracture leakage and permeability leakage), thereby improving on-site plugging capacity and efficiency.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions: A drilling fluid plugging performance evaluation device based on an improved sand-filling pipe includes a displacement pump, a liquid tank and a sand-filling pipe. The outlet of the displacement pump is connected to the inlet of the liquid tank, and the outlet of the liquid tank is connected to the inlet of the sand-filling pipe. The inlet of the sand-filling pipe is provided with a zero pressure measuring point, and the sand-filling pipe is provided with multiple pressure measuring points at intervals from its inlet to its outlet.

[0006] Preferably, the inlet of the sand filling pipe adopts a gradually expanding pipe, the small end of the gradually expanding pipe is connected to the outlet of the liquid tank, the large end of the gradually expanding pipe is connected to the sand filling pipe body of the sand filling pipe, and the end of the large end of the gradually expanding pipe is provided with a filter screen; The outlet of the sand filling pipe adopts a convergent pipe with the same structure as the gradually expanding pipe. The large end of the convergent pipe is connected to the sand filling pipe body of the sand filling pipe. The front end of the large end of the convergent pipe is provided with a filter screen.

[0007] Preferably, the inner diameter of the small end of the gradually expanding tube is 6-8 mm, the inner diameter of the large end is 10-12 mm, the cone angle of the inner diameter expansion from the small end to the large end of the gradually expanding tube is 14°-16°, the inner diameter of the sand-filled tube body is 23-27 mm; the aperture of the filter screen is 0.8-0.9 times the minimum particle size of the sand particles.

[0008] Preferably, the intervals between the multiple pressure measuring points are 4-6 cm.

[0009] The present invention also provides a method for evaluating the plugging performance of drilling fluid based on an improved sand-filled pipe. The method is performed using the drilling fluid plugging performance evaluation device based on the improved sand-filled pipe of the present invention, and comprises the following steps: Determine the target block loss type; Determine the equivalent permeability of each leakage type; Screening the sand particle size to be filled according to the relevant parameters of the target block; the relevant parameters include the porosity and permeability of the target block; Fill the sand filling pipe with the screened sand; Using clean water as the displacement medium and the equivalent permeability as the target permeability, constant pressure displacement conditions are set to measure the initial permeability of the sand filling pipe filled with sand particles. The filling is considered qualified when the relative error between the permeability measured by clean water in the sand filling pipe and the target permeability is less than 10%; After the sand filling pipe is filled to the required standard, a plugging performance test experiment is carried out using drilling fluid as the displacement medium and setting the net pressure during drilling of the lost-gas layer section in the target block as a constant pressure displacement condition. During the plugging performance test experiment, the pressure data of each pressure measuring point and the liquid volume data at the sand filling pipe outlet are monitored. The plugging depth and plugging capacity of the plugging agent are determined based on the pressure data of each pressure measuring point and the equivalent permeability, thereby realizing performance evaluation of the plugging agent.

[0010] Preferably, the process of determining the target block loss type includes the following steps: When the target block leakage velocity is less than 5m 3 / h and the pump-stop pressure drop rate is less than 0.2MPa / min, the target block leakage type is determined to be permeability leakage; When the leakage velocity is ≥5m 3 / h and the pressure drop rate is ≥0.2MPa / min, the leakage type of the target block is determined to be fracture leakage.

[0011] Preferably, if the target block leakage type is permeability leakage, the equivalent permeability is the permeability of the leakage layer of the block, which is determined by the permeability test of the target block core; If the target block leakage type is fracture leakage, it is necessary to perform scanning electron microscopy analysis on the core of the leakage layer. According to the scanning electron microscopy results, the width of micro fractures is counted and the average fracture width is calculated. Then, the equivalent permeability is calculated based on the following formula: :

[0012] Where, is the width of micro cracks, in units of ; is the permeability, in units of ; is the correction coefficient, which is the porosity of the target block in %.

[0013] Preferably, the particle size of the sand to be filled is calculated by the following formula:

[0014] Where, d is the sand particle diameter, in units of ; is the porosity of the target block, in %; is the permeability of the target block, in D; is the correction coefficient, the value for sandstone is 0.2, the value for coal rock is 0.1, and the value for shale is 0.15.

[0015] Preferably, the method uses clean water as the displacement medium, the equivalent permeability as the target permeability, sets a constant pressure displacement condition, and measures the initial permeability of the sand-filled pipe filled with sand particles. When the relative error between the permeability measured by the clean water in the sand-filled pipe and the target permeability is less than 10%, the filling is considered qualified, including the following steps: Using clean water as the displacement medium and the equivalent permeability as the target permeability, a constant pressure displacement condition is set, and the initial permeability of the sand filling pipe filled with sand is measured. When the relative error between the tested initial permeability and the target permeability is ≥10%, the pressure of the sand filling compactor is increased at a pressure interval of 0.1 MPa to refill the sand filling pipe until the relative error between the tested initial permeability and the target permeability is less than 10%, and the filling is completed.

[0016] Preferably, during the plugging performance test experiment, the pressure data of each pressure measuring point and the liquid volume data at the sand filling pipe outlet are monitored, and the plugging depth and plugging capacity of the plugging agent are determined based on the pressure data of each pressure measuring point and the equivalent permeability to achieve performance evaluation of the plugging agent, including the following steps: During the plugging performance test, the pressure data of each pressure measuring point and the liquid volume data at the sand filling pipe outlet are monitored. The distance between the test point where the pressure mutation occurs and the sand filling pipe inlet is the plugging depth of the drilling fluid. The plugging performance of the plugging agent is evaluated by comparing the plugging depth formed by different drilling fluids containing different plugging agents. The shorter the plugging depth, the better the plugging performance. If the drilling fluid cannot form an effective seal in the sand filling pipe, drilling fluid will flow out of the sand filling pipe outlet. When the flow rate at the sand filling pipe outlet stabilizes, measure the sand filling pipe outlet flow rate and calculate the permeability K2. Combined with the permeability K1 measured by clean water, the permeability reduction degree is calculated using the formula :

[0017] Where: is the permeability of the sand-filled pipe measured with clean water, in D; is the permeability of the sand filling pipe measured by drilling fluid, the unit is D; is the experimental time, which is used as a correction factor to take into account the influence of the plugging time on the plugging performance of the plugging agent. The unit is min.

[0018] The present invention has the following beneficial effects: The present invention is based on an improved drilling fluid plugging performance evaluation device for a sand-filled pipe. A displacement pump can displace drilling fluid within the sand-filled pipe to dynamically plug the pipe. Multiple pressure measuring points are spaced apart on the sand-filled pipe from its inlet to its outlet. This allows the depth of the plugging layer to be determined based on the location of the pressure change at the pressure measuring points; the smaller the depth, the better the plugging performance. If the plugging fails, i.e., continuous seepage occurs at the outlet, the plugging performance of the plugging agent is determined by comparing the permeability damage ratio of clean water to the drilling fluid. Furthermore, in this application, by providing a sand-filled pipe, sand can be filled according to the target block's leakage type. Once the filling is satisfactory, drilling fluid is then used for displacement, resulting in a more accurate final evaluation. Therefore, the present invention can accurately evaluate the plugging performance of drilling fluid under different formation conditions (fracture leakage and permeability leakage), thereby improving on-site plugging capacity and efficiency and providing guidance for the design of drilling fluid plugging systems during on-site drilling. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Flowchart of the method for evaluating the plugging performance of drilling fluid based on the improved sand filling pipe in the embodiment; Figure 2 Schematic diagram of the overall structure of a drilling fluid plugging performance evaluation device based on an improved sand-filled pipe in an embodiment of the present invention; FIG3(a) is a front view of a gradually expanding tube (or gradually converging tube) used in an embodiment of the present invention; FIG3(b) is a left side view of a gradually expanding tube (or gradually converging tube) used in an embodiment of the present invention; FIG3(c) is a top view of a gradually expanding tube (or gradually converging tube) used in an embodiment of the present invention; FIG3(d) is a perspective view of a gradually expanding tube (or gradually converging tube) used in an embodiment of the present invention; FIG4(a) is a front view of the filter screen used in the embodiment of the present invention; FIG4(b) is a left side view of the filter screen used in the embodiment of the present invention; FIG4(c) is a top view of the filter screen used in the embodiment of the present invention; FIG4(d) is a perspective view of the filter screen used in the embodiment of the present invention; Figure 5 This is a diagram showing changes in pressure with the position of the sand filling pipe in Example 1 of the present invention; Figure 6 This is a diagram showing the change in pressure with the position of the sand filling pipe in Example 2 of the present invention.

[0020] Among them, 1-displacement pump, 2-displacement pipeline, 3-liquid tank, 4-pressure measuring point No. 0, 5-pressure measuring point No. 1, 6-pressure measuring point No. 2, 7-pressure measuring point No. 3, 8-pressure measuring point No. 4, 9-pressure measuring point No. 5, 10-pressure measuring point No. 6, 11-pressure measuring point No. 7, 12-pressure measuring point No. 8, 13-pressure measuring point No. 9, 14-pressure measuring point No. 10, 15-sand filling pipe body, 16-sand particles, 17-gradual expansion pipe, 18-filter screen, 19-signal transmission line, 20-computer. DETAILED DESCRIPTION

[0021] The present invention will be described clearly and completely below with reference to the accompanying drawings and embodiments of the present invention. The described embodiments are only a part of the embodiments of the present invention, not all embodiments.

[0022] See also Figure 2 This embodiment is based on an improved drilling fluid plugging performance evaluation device for a sand-filled pipe, comprising a displacement pump 1, a liquid tank 3, and a sand-filled pipe. The outlet of the displacement pump 1 is connected to the inlet of the liquid tank 3 via a displacement pipeline 2, and the outlet of the liquid tank 3 is connected to the inlet of the sand-filled pipe. A zero pressure measuring point 4 is provided at the inlet of the sand-filled pipe, and a plurality of pressure measuring points are provided on the sand-filled pipe at intervals from its inlet to its outlet.

[0023] As a preferred embodiment of the present invention, see Figure 3 (a) to Figure 3 (d), and combine Figure 2Because the bentonite and plugging agent particles in the drilling fluid are large and easily accumulate at the inlet, a diverging pipe is installed at the inlet of the sandfill pipe. The inlet of the sandfill pipe adopts a diverging pipe 17. The small end of the diverging pipe 17 is connected to the outlet of the liquid tank 3, and the large end of the diverging pipe 17 is connected to the sandfill pipe body 15. This prevents sudden changes in flow rate from causing particle accumulation. A filter 18 is installed at the end of the large end of the diverging pipe 17. The outlet of the sandfill pipe adopts a converging pipe with the same structure as the diverging pipe 17. The large end of the converging pipe is connected to the sandfill pipe body 15. The converging pipe can collect the liquid at the sandfill pipe outlet, which facilitates the observation of the flow rate and flow rate changes at the sandfill pipe outlet. The filter 18 is installed at the front end of the large end of the converging pipe. The diverging pipe and the diverging pipe 17 can actually be of the same structure, just with different installation locations. The filters 18 are installed on the inlet and outlet of the sandfill pipe to prevent sand leakage while allowing the plugging agent particles to pass through.

[0024] As a further preferred embodiment of the present invention, in this embodiment, the inner diameter of the small end of the gradually expanding tube 17 is 6-8 mm (specifically, 6 mm, 7 mm, or 8 mm, which can be selected by those skilled in the art according to actual conditions), and the inner diameter of the large end is 10-12 mm (specifically, 10 mm, 11 mm, or 12 mm, which can be selected by those skilled in the art according to actual conditions). The cone angle of the inner diameter expansion from the small end to the large end of the gradually expanding tube 17 is 14°-16° (specifically, 14°, 15°, or 16°, which can be selected by those skilled in the art according to actual conditions). The inner diameter of the sand filling tube body 15 is 23-27 mm (specifically, 23 mm, 24 mm, 25 mm, 26 mm, or 27 mm, which can be selected by those skilled in the art according to actual conditions). The pore size of the filter screen 18 is 0.8-0.9 times the minimum sand particle size (specifically, 0.8 times, 0.85 times, or 0.9 times, which can be selected by those skilled in the art according to actual conditions).

[0025] like Figure 1 As shown, combined with Figure 2 The present embodiment of the drilling fluid plugging performance evaluation method based on the improved sand filling pipe specifically includes the following steps: Step 1: Determine the target block loss type. When the target block loss rate is less than 5m 3 / h and the pump stop pressure drop rate is less than 0.2MPa / min, it is judged as permeability leakage. 3 / h and the pressure drop rate ≥0.2MPa / min is judged as fracture leakage.

[0026] Step 2: Determine the equivalent permeability. If the leakage is caused by permeability, the equivalent permeability is the permeability of the leakage layer in the block. The permeability of the core of the leakage layer is tested through indoor core flooding experiments. If the leakage is caused by fracture, it is necessary to perform scanning electron microscopy analysis on the core of the leakage layer. According to the scanning electron microscopy results, the width of microcracks is counted, the average fracture width is calculated, and then the equivalent permeability is calculated based on the following formula: :

[0027] Where, is the width of micro cracks, in units of ; is the permeability, in units of ; is the correction coefficient, which is the porosity of the target block in %.

[0028] Step 3: Select the filling sand. Based on Step 1, select the sand type according to the experimental conditions. The sand mesh size is calculated using the formula. Specifically, the sand selection includes the sand type and sand particle size. In conventional drilling, the net pressure of the drilling fluid acting on the target layer is less than 10 MPa, which is far lower than the fracture pressure of all currently used sand particles. Therefore, the sand type can be selected based on the existing experimental conditions. The sand particle size is calculated based on the following formula:

[0029] Where, d is the particle diameter, in units of ; is the porosity of the target block, in %; is the permeability, unit is D; is the correction coefficient, the value for sandstone is 0.2, the value for coal rock is 0.1, and the value for shale is 0.15.

[0030] After selecting the filling sand, before filling the sand pipe, first use the standard screening method to screen the sand, remove the oversized particles, wash the sand to remove clay and dust (rinse with clean water until the water is clear), and then dry it for use.

[0031] Step 4: Fill the sand tube. Fix the sand tube vertically and fill it with sand in multiple times (each filling height is 1 cm). After each filling, use a sand compactor to compact the sand (need to set the compaction pressure and time, specifically 1 MPa and 30 seconds) to eliminate gaps between layers. Repeat the above process until the sand tube is full.

[0032] Step 5: Permeability test. After the sand filling tube is completed, connect the displacement device (such as Figure 2), using clean water as the displacement medium and setting constant pressure displacement conditions, measure the initial permeability of the sand-filled pipe until the relative error between the permeability measured with clean water and the target permeability (i.e., the equivalent permeability determined in step 2) is less than 10%, and the filling is considered qualified. In this step, connect displacement pump 1, liquid tank 3, and the sand-filled pipe in sequence. Add distilled water to the liquid tank as the displacement fluid. Open the valves of the displacement pump, liquid tank 3, and the intermediate liquid tank. Measure flow rate Q1 under constant pressure differential displacement conditions. Calculate permeability using Darcy's law. The sand-filled pipe is considered qualified when the relative error between the measured permeability K1 and the target permeability is less than 10%. If the relative error exceeds 10%, increase the pressure of the sand compactor in 0.1 MPa increments to refill the pipe until the relative error between the measured permeability and the target permeability is less than 10%.

[0033] Step 6: Plugging performance test. After the sand filling pipe permeability test is qualified, connect the experimental device (such as Figure 2 ) and the clean water drilling fluid in the liquid tank 3, open the pressure test system, displacement pump and valves on the pipeline, set the constant pressure displacement condition (the pressure is the net pressure during the drilling process of the lost layer section of the target block), and conduct the plugging performance test experiment. In the specific operation of this step, the distilled water in the liquid tank is replaced with the drilling fluid for testing, and the plugging performance test is started under constant pressure conditions. The experimental device is connected as follows Figure 2 As shown, the displacement pressure is determined based on the net pressure in the target well's lost circulation zone—the difference between the static pressure of the drilling fluid column and the formation pore pressure. During the experiment, pressure values ​​are monitored and recorded in real time by a computer. Simultaneously, the experimenter monitors and records the flow rate at the sand packing pipe outlet. The test is complete when the pressure at each pressure measuring point and the outlet flow rate remain stable.

[0034] Step 7: Analyze the experimental data. During the experiment, the pressure data and the liquid volume data of the measuring cylinder are monitored in real time. The plugging depth and plugging ability of the plugging agent are determined based on the pressure data and the calculated permeability, so as to realize the performance evaluation of the plugging agent. During the specific operation of this step, the pressure value of each pressure test point is analyzed according to the recorded pressure data, where the test point of the pressure mutation is the plugging depth of the drilling fluid. The plugging performance can be evaluated by comparing the plugging depths formed by different plugging agents. The shorter the plugging depth, the better the plugging performance. If the drilling fluid cannot form an effective plugging in the sand filling pipe, drilling fluid will flow out of the outlet of the sand filling pipe. When the flow rate stabilizes, the flow rate is measured and the permeability K2 is calculated. Combined with the permeability K1 measured by clean water, the degree of permeability reduction is calculated using the formula. :

[0035] Where: is the permeability of the sand-filled pipe measured with clean water, in D; is the permeability of the sand filling pipe measured by drilling fluid, the unit is D; is the experimental time, which is used as a correction factor to take into account the influence of the plugging time on the plugging performance of the plugging agent. The unit is min.

[0036] The sand filling pipe used in steps 5 and 6 of the improved sand filling pipe drilling fluid plugging performance evaluation method of the above embodiment of the present invention is an improved sand filling pipe. The sand filling pipe body is made of pressure-resistant stainless steel with an inner diameter of 25 mm. In order to monitor the plugging position of the plugging agent in real time, pressure test points are set at 5 cm intervals on the sand filling pipe body (such as Figure 2 As shown in Figures 0, 4, ..., and 10, 14, respectively. Because the bentonite and plugging agent particles in the drilling fluid are large and easily accumulate at the inlet, a gradually expanding tube with a wall thickness of 1.5 mm and a taper angle of 15° is installed at the inlet of the sand filling pipe. This tube gradually expands from the conventional 6 mm inner diameter to 12 mm at the sand filling pipe entrance to prevent particle accumulation caused by sudden changes in flow rate. A gradually converging tube is used at the outlet (Figures 3(a)-3(d)). To prevent sand leakage and allow plugging agent particles to pass through, a filter with a matching pore size is installed between the gradually expanding (converging) tube and the sand filling pipe. The filter is connected to the sand filling pipe via conventional threads. The filter has an outer diameter of 12 mm and an inner diameter of 10 mm. The width of the fixed ring in the middle of the filter is 1.5 mm, as shown in Figures 4(a)-4(d). The filter pore size is 0.9 times the minimum sand particle size.

[0037] Example 1: The present invention was used to evaluate the X1 and Y1 plugging agents used in a shale block in Liaohe Oilfield. The specific steps are as follows: Step (1) Determine the type of leakage. Collecting field data revealed that the leakage rate of the target well was 8.6m 3 / h, after stopping the pump, the wellhead pressure is 4MPa, and the falling rate is 0.28MPa / min. Therefore, the target block belongs to fracture leakage.

[0038] Step (2) Determine the equivalent permeability. Scanning electron microscopy testing of the core of the leaking zone and counting the width of the microcracks revealed an average value of 4 μm. Combining this with conversion formula 1, the equivalent permeability was calculated to be K = 1.33D.

[0039] Step (2) Select the sand type. Based on step 1, quartz sand was selected as the filling medium. The average porosity of the block was 5%. Combining formula 2, the required sand particle size was calculated to be d = 197.1 μm, corresponding to 70 / 80 mesh sand. Therefore, 70 / 80 mesh quartz sand was selected for this test. The required sand particle size was sieved and washed and dried for later use.

[0040] Step (3) Filling the sand filling tube. Fix the sand filling tube vertically and fill it with sand particles in batches (1 cm each time). After each sand filling, apply 1 MPa pressure with a sand filling compactor for 30 seconds to eliminate the gaps between layers. Repeat until the tube is filled.

[0041] Step (4) Permeability test. After the sand filling tube is completed, connect the displacement device (such as Figure 2 ), using clean water as the displacement medium, displacement was carried out under a certain pressure difference ΔP=1MPa (constant pressure difference), and the measured flow rates Q1 were 1.37mL / s, 1.27mL / s and 1.32mL / s respectively. The permeability was calculated based on the Darcy's law formula. The permeability was repeated three times and the average value K1=1.35D was calculated. The relative error between this value and the target permeability K=1.33D was 1.5%<10%, so the filling was considered qualified.

[0042] Step (5) Plugging performance test. The plugging agents used for micro-fractures in the target block are mainly X2 and X5 plugging agents of a certain company. Among them, 90% of the particles of X1 plugging agent and Y1 plugging agent are distributed below 0.9mm. The two plugging agents are prepared into drilling fluid according to the on-site formula. Before the experiment begins, the experimental device is first connected: the inlet of the sand filling pipe is connected to the liquid tank and the displacement pump through a gradually expanding pipe (cone angle 15°), and the outlet is connected to the measuring cylinder for flow testing through a gradually converging pipe (cone angle 15°); secondly, the displacement pressure is set to the net pressure of the target well leakage layer. In this embodiment, the target leakage layer drilling static pressure is 4MPa; finally, the displacement pump is turned on to inject the drilling fluid containing the plugging agent at a constant pressure of 4MPa, and the pressure data of each pressure measuring point and the outlet flow are recorded in real time until the pressure and flow are stable.

[0043] Step (6) Analyze the experimental data. In this embodiment, there is no flow at the outlet, so it is necessary to determine the plugging depth and plugging performance of the plugging agent based on the pressure mutation point. The pressure changes with the position of the sand filling pipe as shown in the following figure. Figure 5 As shown in the figure, combined with the experimental data, it was found that the pressure of the two plugging agents, X1 plugging agent, dropped sharply at the pressure measuring point 2, while the pressure of Y2 plugging agent dropped sharply at the pressure measuring point 4. Combined with the distribution of the pressure test points of the sand filling pipe, it can be seen that the plugging depth of X1 plugging agent is 0.410cm, while the plugging depth of Y2 plugging agent is 20cm. Therefore, the plugging performance of X1 plugging agent is better than that of Y2 plugging agent. Example 2 The present invention was used to evaluate T1 and F1 plugging agents used in a sandstone block of Yanchang Oilfield. The specific steps are as follows: Step (1) Determine the leakage type and equivalent permeability. Based on the geological data of the target block and related experimental research, it is found that the target block is a fracture leakage, and its micro-fracture width is mainly distributed around 6μm. Combined with the conversion formula, its equivalent permeability is calculated as K=3D, and the calculation formula is Equation 1.

[0044] Step (2) Select the sand type. Based on Step 1, quartz sand was selected as the filling medium. The average porosity of the block was 4.2%. Combining Formula 2, the required sand particle size was calculated to be d = 517 μm, corresponding to 30 / 32 mesh sand. Therefore, 30 / 32 mesh quartz sand was selected.

[0045] Step (3) Filling the sand filling tube. Fix the sand filling tube vertically and fill it with sand in batches (about 1 cm each time). After each sand filling, vibrate it with a vibrator (frequency 60 Hz, amplitude 1.2 mm) for 8 seconds to eliminate the gaps between layers. Repeat until it is filled.

[0046] Step (4) Permeability test. After the sand filling tube is completed, connect the displacement device (such as Figure 2 ), using clean water as the displacement medium, displacement was carried out under a certain pressure difference ΔP=1MPa (constant pressure difference). The flow rates Q1 were measured three times and were 3.14mL / s, 3.04mL / s and 3.14mL / s respectively. The permeability was calculated based on the Darcy's law formula. The permeability was repeated three times and the average value K1=3.17D was calculated. The relative error between this value and the target permeability K=3D was 5.7%<10%, so the filling was considered qualified.

[0047] Step (5) Plugging performance test. The plugging agents used for micro-fractures in the target block are mainly T1 and F1 plugging agents. 90% of the particles of T1 and F plugging agents are distributed below 0.5 mm. The two plugging agents are prepared into drilling fluid according to the on-site formula. Before the experiment begins, the experimental device is first connected: the inlet of the sand filling pipe is connected to the liquid tank and the displacement pump through a gradually expanding pipe (cone angle 15°), and the outlet is connected to the measuring cylinder for flow testing through a gradually contracting pipe (cone angle 15°); secondly, the displacement pressure is set to the net pressure of the target well leakage layer. In this embodiment, the target leakage layer drilling static pressure is 2.6 MPa; finally, the displacement pump is turned on to inject the drilling fluid containing the plugging agent at a constant pressure of 2.6 MPa, and the pressure data of each pressure measuring point and the outlet flow are recorded in real time until the pressure and flow are stable.

[0048] Step (6) Analyze the experimental data. During this experiment, drilling fluid flow was detected at the outlet of the sand filling pipe during the plugging process of the T1 plugging agent. After stabilization, the flow rate Q2 = 0.51 mL / s was recorded, and the permeability was calculated to be 0.2D. During the plugging process of the F1 plugging agent, there was no flow at the outlet of the sand filling pipe, that is, the permeability was 0D. Figure 6As shown in the figure, monitoring the pressure revealed a sudden drop in pressure at pressure point 4. Combined with the distribution of pressure test points in the sand filling pipe, it can be seen that the plugging depth of type T1 plugging agent is 20cm. Comparing the plugging depth, type F1 plugging agent has a plugging depth of 20cm, while type T1 plugging agent has a plugging depth of more than 50cm. Comparing the permeability damage rate, type Y2 plugging agent has a damage rate of 100% to permeability, while type Y1 plugging agent has a damage rate of 93%. Therefore, type Y2 plugging agent has better plugging performance than type Y1.

[0049] As can be seen from the above scheme of the present invention, the experimental method proposed in the present invention realizes the dynamic evaluation of the plugging performance of the plugging agent under different leakage types, improves the accuracy of the results, and reduces the experimental cost to a certain extent. The experimental method proposed in the present invention can provide guidance for the design of drilling fluid plugging systems during on-site drilling.

[0050] Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0051] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered by the scope of protection of the claims of the present invention.

Claims

1. A drilling fluid plugging performance evaluation device based on an improved sand filling pipe, characterized in that: The invention comprises a displacement pump (1), a liquid tank (3) and a sand filling pipe, wherein the outlet of the displacement pump (1) is connected to the inlet of the liquid tank (3), and the outlet of the liquid tank (3) is connected to the inlet of the sand filling pipe. The inlet of the sand filling pipe is provided with a zero pressure measuring point (4), and the sand filling pipe is provided with a plurality of pressure measuring points at intervals from the inlet to the outlet.

2. The drilling fluid plugging performance evaluation device based on the improved sand filling pipe according to claim 1, characterized in that: The inlet of the sand filling pipe adopts a gradually expanding pipe (17), the small end of the gradually expanding pipe (17) is connected to the outlet of the liquid tank (3), the large end of the gradually expanding pipe (17) is connected to the sand filling pipe body (15) of the sand filling pipe, and the end of the large end of the gradually expanding pipe (17) is provided with a filter screen (18); The outlet of the sand filling pipe adopts a converging pipe with the same structure as the gradually expanding pipe (17), the large end of the converging pipe is connected to the sand filling pipe body (15) of the sand filling pipe, and the front end of the large end of the converging pipe is provided with a filter screen (18).

3. The drilling fluid plugging performance evaluation device based on the improved sand filling pipe according to claim 2, characterized in that: The inner diameter of the small end of the gradually expanding tube (17) is 6-8 mm, and the inner diameter of the large end is 10-12 mm. The cone angle of the inner diameter expansion from the small end to the large end of the gradually expanding tube (17) is 14°-16°. The inner diameter of the sand filling tube body (15) is 23-27 mm. The aperture of the filter screen (18) is 0.8-0.9 times the minimum particle size of the sand particles.

4. The drilling fluid plugging performance evaluation device based on the improved sand filling pipe according to claim 1, characterized in that: The intervals between the multiple pressure measuring points are 4-6 cm.

5. A drilling fluid plugging performance evaluation method based on an improved sand-filled pipe, characterized in that: The method is carried out using the drilling fluid plugging performance evaluation device based on the improved sand-filled pipe according to any one of claims 1 to 4, and comprises the following steps: Determine the target block loss type; Determine the equivalent permeability of each leakage type; Screening the sand particle size to be filled according to the relevant parameters of the target block; the relevant parameters include the porosity and permeability of the target block; Fill the sand filling pipe with the screened sand; Using clean water as the displacement medium and the equivalent permeability as the target permeability, constant pressure displacement conditions are set to measure the initial permeability of the sand filling pipe filled with sand particles. The filling is considered qualified when the relative error between the permeability measured by clean water in the sand filling pipe and the target permeability is less than 10%; After the sand filling pipe is filled to the required standard, a plugging performance test experiment is carried out using drilling fluid as the displacement medium and setting the net pressure during drilling of the lost-gas layer section in the target block as a constant pressure displacement condition. During the plugging performance test experiment, the pressure data of each pressure measuring point and the liquid volume data at the sand filling pipe outlet are monitored. The plugging depth and plugging capacity of the plugging agent are determined based on the pressure data of each pressure measuring point and the equivalent permeability, thereby realizing performance evaluation of the plugging agent.

6. The method for evaluating the plugging performance of drilling fluid based on an improved sand-filled pipe according to claim 5, characterized in that: The process of determining the target block loss type includes the following steps: When the target block leakage velocity is less than 5m 3 / h and the pump-stop pressure drop rate is less than 0.2MPa / min, the target block leakage type is determined to be permeability leakage; When the leakage velocity is ≥5m 3 / h and the pressure drop rate is ≥0.2MPa / min, the leakage type of the target block is determined to be fracture leakage.

7. The method for evaluating the plugging performance of drilling fluid based on an improved sand-filled pipe according to claim 6, characterized in that: If the target block has a permeability loss, the equivalent permeability is the permeability of the block's leakage interval, which is determined by a permeability test of the target block's core. If the target block leakage type is fracture leakage, it is necessary to perform scanning electron microscopy analysis on the core of the leakage layer. According to the scanning electron microscopy results, the width of micro fractures is counted and the average fracture width is calculated. Then, the equivalent permeability is calculated based on the following formula: : Where, is the width of micro cracks, in units of ; is the permeability, in units of ; is the correction coefficient, which is the porosity of the target block in %.

8. The method for evaluating the plugging performance of drilling fluid based on an improved sand-filled pipe according to claim 6, wherein: The particle size of the sand to be filled is calculated by the following formula: Where, d is the sand particle diameter, in units of ; is the porosity of the target block, in %; is the permeability of the target block, in D; is the correction coefficient, the value for sandstone is 0.2, the value for coal rock is 0.1, and the value for shale is 0.

15.

9. The method for evaluating the plugging performance of drilling fluid based on an improved sand-filled pipe according to claim 5, characterized in that: The method uses clean water as the displacement medium, the equivalent permeability as the target permeability, sets a constant pressure displacement condition, and measures the initial permeability of the sand-filled pipe filled with sand particles. When the relative error between the permeability measured by the clean water in the sand-filled pipe and the target permeability is less than 10%, the filling is considered qualified, including the following steps: Using clean water as the displacement medium and the equivalent permeability as the target permeability, a constant pressure displacement condition is set, and the initial permeability of the sand filling pipe filled with sand is measured. When the relative error between the tested initial permeability and the target permeability is ≥10%, the pressure of the sand filling compactor is increased at a pressure interval of 0.1 MPa to refill the sand filling pipe until the relative error between the tested initial permeability and the target permeability is less than 10%, and the filling is completed.

10. The method for evaluating the plugging performance of drilling fluid based on an improved sand-filled pipe according to claim 5, wherein: During the plugging performance test experiment, the pressure data of each pressure measuring point and the liquid volume data at the sand filling pipe outlet are monitored, and the plugging depth and plugging capacity of the plugging agent are determined based on the pressure data of each pressure measuring point and the equivalent permeability to achieve performance evaluation of the plugging agent, including the following steps: During the plugging performance test, the pressure data of each pressure measuring point and the liquid volume data at the sand filling pipe outlet are monitored. The distance between the test point where the pressure mutation occurs and the sand filling pipe inlet is the plugging depth of the drilling fluid. The plugging performance of the plugging agent is evaluated by comparing the plugging depth formed by different drilling fluids containing different plugging agents. The shorter the plugging depth, the better the plugging performance. If the drilling fluid cannot form an effective seal in the sand filling pipe, drilling fluid will flow out of the sand filling pipe outlet. When the flow rate at the sand filling pipe outlet stabilizes, measure the sand filling pipe outlet flow rate and calculate the permeability K2. Combined with the permeability K1 measured by clean water, the permeability reduction degree is calculated using the formula : Where: is the permeability of the sand-filled pipe measured with clean water, in D; is the permeability of the sand filling pipe measured by drilling fluid, the unit is D; is the experimental time, which is used as a correction factor to take into account the influence of the plugging time on the plugging performance of the plugging agent. The unit is min.

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