Rough crack flowback sand discharging and residual flow conductivity testing device and method

Abstract

The invention relates to the technical field of reservoir transformation hydraulic fracturing, in particular to a rough fracture flowback sand discharge and residual flow conductivity testing device and method.The rough fracture flowback sand discharge and residual flow conductivity testing device comprises a hydraulic drive system and a flow guide system, the flow guide system comprises a flow guide chamber, and an upper piston and a lower piston which can move up and down are arranged in the flow guide chamber in the horizontal direction; a flow guide cavity is formed between the upper piston and the lower piston, pressure detection points are arranged at the positions, corresponding to the left end, the middle and the right end of the flow guide cavity, in the flow guide chamber, pressure detectors are fixedly arranged at the pressure detection points, and a laser range finder used for measuring the distance change between the upper piston and the lower piston is fixedly arranged at the left end of the upper piston. A temperature sensor is arranged on the left side of the flow guide chamber, and the hydraulic drive system comprises a constant-pressure constant-flow pump and a liquid storage tank. The device for testing the flowback sand discharge and residual flow conductivity of the rough crack, disclosed by the invention, has the advantages that the stratum adjustment is truly simulated, the distribution of residual phases in the crack is clearly tested, the accuracy of various data obtained in the backflow process after fracturing is high, and the device has important significance on researching the flowback after fracturing.

Description

Technical Field

[0001] The present invention relates to the technical field of hydraulic fracturing for reservoir stimulation, and is a device and method for testing sand production during the return of rough fractures and remaining conductivity. Background Art

[0002] Hydraulic fracturing is one of the main production methods for unconventional reservoirs. Hydraulic fracturing creates fractures of a certain size in the reservoir, and then proppants are filled in to support the fractures and prevent them from closing. Therefore, the more proppants there are, the better the permeability of the pores, the stronger the conductivity, and the lower the residual oil saturation in the fractures.

[0003] However, during the fracturing fluid return process, due to reasons such as flow rate and closure stress, the proppants that have entered the fractures will embed, break, and flow out. When the closure stress increases, the conductivity will decrease to varying degrees. When the proppants reach the ultimate bearing pressure, the conductivity will decrease significantly. When a large amount of proppants flow back, the sand concentration in the fractures will decrease, resulting in a significant decrease in conductivity. And when various factors are superimposed, there will be a significant difference between the conductivity after the return and the conductivity recognized before the return, and the production decline will be rapid. Therefore, clearly understanding the comprehensive impact of various factors on conductivity during the return process is of great significance for formulating fracturing plans.

[0004] During the return process, the residual phase saturation and permeability in the fractures will change. When the proppants flow back, the two-phase co-flow region of the oil-water relative permeability curve will decrease, and the equal-permeability point will shift to the left. This means that the flow situation of the crude oil in the fractures will change, and the residual oil saturation will increase. At the same time, at the same saturation, the relative permeability of oil and water will also change. Studying the changes in the oil-water relative permeability curve during the return process and understanding the flow situation of oil and water in the fractures have important guiding significance for oil and gas production.

[0005] Chinese patent document with publication number CN102183796A discloses a test device and method for simulating proppant return, which considers the influence of different temperatures, different closure stresses, different sand concentrations, etc. on the return, but cannot monitor the change in conductivity and does not consider rough fracture surfaces. Chinese patent document with publication number CN111103222A discloses a test device and method for the conductivity of self-supporting fractures under triaxial confining pressure conditions, which can simulate rough fracture surfaces formed under triaxial confining pressure conditions, but cannot simulate large closure stresses and cannot monitor the influence of return on conductivity. Chinese patent document with publication number CN104747182A discloses a method for testing fracture conductivity, which can change the fracture width, fracture corner support, and fracture width combination, but lacks dynamic fracture width monitoring and the simulated formation environment is not realistic.

[0006] None of the above patents simultaneously monitors the backflow situation and diversion capacity. Although some patents can detect changes in the slot width, they cannot explore the backflow situation and the changes in diversion capacity under the condition of dynamic slot width (constantly changing slot width). Some inventions can simulate different individual formation environments (such as rough slot surface, high closure stress, high temperature, etc.), but none of them comprehensively simulates all variables.

[0007] At the same time, none of the above inventions can conduct in-line tests on residual phase saturation and permeability to explore backflow and dynamic relative permeability changes.

[0008] The existing test methods for oil-water relative permeability curves include the steady-state method and the unsteady-state method. Due to disadvantages such as too long time in the steady-state method, the unsteady-state method is generally adopted. However, the traditional unsteady-state method calculates by measuring the amount of oil and liquid at the outlet end per unit time. Its method mainly calculates local data through overall average data and uses the local data for calculation. At the same time, the outlet end effect will also cause the liquid to accumulate at the outlet end, resulting in errors. When encountering heavy oil, this effect is more obvious, and the fractional flow at the end of the oil will increase within a very short time, resulting in a lack of data points in the middle section and a large error in the final result.

[0009] The existing devices cannot dynamically monitor the impact of backflow on diversion capacity under the condition of considering multiple variables. And none of them consider the impact of the oil-water relative permeability curve in the slot on development. There are still large errors in the traditional calculation method of the oil-water relative permeability curve, making its results inaccurate, the understanding of the oil and water production degree in the fracture unclear, and the practicability poor.

[0010] Therefore, there is an urgent need to establish a device and method for testing sand production during backflow and remaining diversion capacity in rough fractures, which can accurately understand the impact of proppant backflow on diversion capacity under different conditions and obtain the oil and water production situation in the fracture at the same time. Summary of the Invention

[0011] The present invention provides a device and method for testing sand production during backflow and remaining diversion capacity in rough fractures, which overcomes the deficiencies of the above prior art and can effectively solve the problems that the prior art cannot simultaneously simulate multiple formation conditions and cannot conduct real-time monitoring during the backflow process, resulting in an unclear understanding of the change in diversion capacity when backflow occurs under real formation conditions.

[0012] One of the technical solutions of the present invention is achieved by the following measures: A rough fracture sand backflow and remaining conductivity testing device, including a liquid drive system and a conductivity system. The conductivity system includes a conductivity chamber. Horizontally arranged in the conductivity chamber are an upper piston and a lower piston that can move up and down. A conductivity chamber is formed between the upper piston and the lower piston. Pressure detection points are arranged at the left end, middle, and right end of the conductivity chamber corresponding to the conductivity chamber. Pressure detectors are fixedly arranged at the pressure detection points. A laser rangefinder for measuring the change in distance between the upper piston and the lower piston is fixedly arranged at the left end of the upper piston. A temperature sensor is arranged on the left side of the conductivity chamber. The liquid drive system includes a constant pressure and constant flow pump and a liquid storage tank. A first liquid drive pipeline is fixedly connected between the constant pressure and constant flow pump and the liquid storage tank. A second liquid drive pipeline is fixedly connected between the liquid outlet of the liquid storage tank and the inlet of the conductivity chamber. The liquid outlet of the conductivity chamber is fixedly connected to a first drain pipe. A back pressure valve is fixedly arranged on the first drain pipe. A first liquid collection tank is arranged at the outlet of the first drain pipe.

[0013] The following is a further optimization or / and improvement of one of the above-mentioned technical solutions of the invention:

[0014] Filter loss holes are opened in the middle of the above-mentioned upper piston and lower piston. A second drain pipe is fixedly connected at the filter loss hole of the upper piston. A second liquid collection tank is arranged at the outlet of the second drain pipe. A third drain pipe is fixedly connected between the filter loss hole of the lower piston and the second drain pipe.

[0015] The above-mentioned rough fracture sand backflow and remaining conductivity testing device further includes a CT scanner. The conductivity chamber is arranged in the scanning area of the CT scanner.

[0016] A filter plug is arranged at the inlet of the above-mentioned conductivity chamber.

[0017] The above-mentioned liquid storage tank includes a water storage tank and a fracturing fluid storage tank. A first liquid drive pipeline is fixedly connected between the constant pressure and constant flow pump and the water storage tank. A second liquid drive pipeline is fixedly connected between the liquid outlet of the water storage tank and the inlet of the conductivity chamber. A third liquid drive pipeline is fixedly connected between the fracturing fluid storage tank and the first liquid drive pipeline. A fourth liquid drive pipeline is fixedly connected between the outlet of the fracturing fluid storage tank and the second liquid drive pipeline.

[0018] A heater for heating the conductivity chamber is arranged in the above-mentioned conductivity chamber. The heater is a detachable heating rod or heating pack.

[0019] The above-mentioned rough fracture sand backflow and remaining conductivity testing device further includes a data processing system. The pressure detector, temperature sensor, and laser rangefinder are all electrically connected to the data processing system.

[0020] One of the technical solutions of the present invention is achieved by the following measures: A rough fracture sand backflow and remaining conductivity testing method is carried out according to the following steps:

[0021] First step: subject the rock to true triaxial fracturing to simulate the rough fracture surface underground after fracturing;

[0022] Second step: make the fractured rock into two rock slabs (the size of the rock slabs matches the size of the diversion chamber cavity), and then apply glue to seal its perimeter;

[0023] Third step: after laying the two rock slabs and the proppant required for the experiment, load them into the diversion chamber, and assemble the rough fracture sand return and remaining diversion capacity test device;

[0024] Fourth step: adjust the closing stress applied to the upper piston and the lower piston through the press, and adjust the back pressure according to the experimental requirements. Inject the displacement fluid into the proppant in the diversion chamber at the injection pressure or flow rate required for the experiment to conduct the diversion test experiment. Collect the outflowing displacement fluid and the sand produced, and record the experimental data;

[0025] Fifth step: based on the displacement pressure difference, fracture width change, sand production volume, and displacement fluid outflow volume measured in the experiment, obtain the change in the proppant diversion capacity and the situation of the fracture width changing with the diversion capacity.

[0026] The following is a further optimization or / and improvement of the second technical solution of the above invention:

[0027] In the above fourth step, the specific operation of the diversion test experiment is as follows:

[0028] A41: Inject the water in the water storage tank into the proppant layer at the injection water flow rate required for the experiment in the constant flow mode, and record the pressure difference between the pressure sensors at the left end and the right end of the diversion chamber at this time. The water injection volume is 100PV to 150PV;

[0029] A42: After the water injection is completed, inject the fracturing fluid in the fracturing fluid storage tank into the diversion chamber in the constant flow mode. The injection flow rate of the fracturing fluid is 0.1 ml / min to 0.5 ml / min, and the injection volume of the fracturing fluid is 10PV;

[0030] A43: After the injection of the fracturing fluid is completed, set the injection water flow rate and inject the water in the water storage tank into the proppant layer again in the constant flow mode, and record the pressure difference between the pressure sensors at the left end and the right end of the diversion chamber at this time;

[0031] A44: Observe whether sand is produced at the current injection water flow rate. If sand is produced, record the current displacement time. This injection water flow rate is the critical sand production flow rate. If no sand is produced, increase the injection water flow rate and execute step A43 again.

[0032] In the above fifth step, the diversion capacity is calculated using the following formula:

[0033]

[0034] where \(k_w\) f is the conductivity of the proppant, μm 2 ·cm; \(q\) is the displacement rate (i.e., the flow rate of water injection into the proppant layer), ml / min; \(\Delta p\) is the pressure difference, kPa (KPa); \(\mu\) is the fluid viscosity at the test temperature, cP (cp).

[0035] The above-mentioned method for testing sand production during backflow and residual conductivity of rough fractures also includes the sixth step, measurement of the oil-water relative permeability curve. The specific operation is as follows: Inject white oil into the proppant layer at a low flow rate, and then displace it with water. At the same time, perform CT scanning on the diversion chamber through a CT scanner to obtain the oil-water relative permeability curve online.

[0036] In the above-mentioned fourth step, the experimental temperature of the displacement experiment is 0 to 150 degrees Celsius.

[0037] To solve the problems of unclear understanding of the fracture conductivity and unclear underground oil-water utilization during the pre-backflow, post-backflow, and process; the present invention provides a device and method for testing sand production during backflow and residual conductivity of rough fractures. The device can simulate various formation conditions such as roughness, high temperature, and high pressure, and can monitor the change of conductivity during the backflow process in real time. At the same time, a more accurate oil-water relative permeability curve can be obtained, so as to understand the oil-water utilization in the fracture more clearly. Brief Description of the Drawings

[0038] Att Figure 1 is a schematic diagram of Embodiment 1 of the present invention.

[0039] The codes in the drawings are as follows: 1 is the diversion chamber, 2 is the upper piston, 3 is the lower piston, 4 is the diversion cavity, 5 is the pressure detector, 6 is the laser rangefinder, 7 is the temperature sensor, 8 is the constant pressure and constant flow pump, 9 is the water storage tank, 10 is the fracturing fluid storage tank, 11 is the first liquid drive pipeline, 12 is the second liquid drive pipeline, 13 is the first drain pipe, 14 is the back pressure valve, 15 is the first liquid collection tank, 16 is the third liquid drive pipeline, 17 is the fourth liquid drive pipeline, 18 is the heater, 19 is the data processing system, 20 is the filtration hole, 21 is the second drain pipe, 22 is the second liquid collection tank, 23 is the third drain pipe, 24 is the filter plug, 25 is the valve, 26 is the press.

[0040] Att Figure 2 is the oil-water relative permeability curve before the backflow experiment in Embodiment 12 of the present invention.

[0041] Att Figure 3 is the oil-water relative permeability curve after the backflow experiment in Embodiment 12 of the present invention. Detailed Embodiments

[0042] The present invention is not limited by the following embodiments, and specific implementation manners can be determined according to the technical solution of the present invention and actual situations.

[0043] In the present invention, unless otherwise specified, the devices and apparatuses used are all well-known and commonly used devices and apparatuses in the art.

[0044] The present invention will be further described below in conjunction with embodiments:

[0045] Embodiment 1: As Figure 1 shown, the rough fracture sand backflow and remaining conductivity testing device includes a liquid drive system and a conductivity system. The conductivity system includes a conductivity chamber 1. In the horizontal direction of the conductivity chamber 1, an upper piston 2 and a lower piston 3 that can move up and down are arranged. A conductivity chamber 4 is formed between the upper piston 2 and the lower piston 3. Pressure detection points are arranged at the left end, middle, and right end of the conductivity chamber 4 in the conductivity chamber 1. Pressure detectors 5 are fixedly arranged at the pressure detection points. A laser rangefinder 6 for measuring the change in the distance between the upper piston 2 and the lower piston 3 is fixedly arranged at the left end of the upper piston 2. A temperature sensor 7 is arranged on the left side of the conductivity chamber 1. The liquid drive system includes a constant pressure and constant flow pump 8 and a liquid storage tank. A first liquid drive pipeline 11 is fixedly connected between the constant pressure and constant flow pump 8 and the liquid storage tank. A second liquid drive pipeline 12 is fixedly connected between the liquid outlet of the liquid storage tank and the inlet of the conductivity chamber 4. The liquid outlet of the conductivity chamber 4 is fixedly connected with a first drain pipe 13. A back pressure valve 14 is fixedly arranged on the first drain pipe 13. A first liquid collection tank 15 is arranged at the outlet of the first drain pipe 13.

[0046] When the rough fracture sand backflow and remaining conductivity testing device is used, two layers of rock plates are placed in the conductivity chamber 4, and the proppant required for the experiment is laid between the two layers of rock plates to form a proppant layer. The water or fracturing fluid provided by the liquid drive system enters the proppant layer between the rock plates in the conductivity chamber 4 through the second liquid drive pipeline 12. The rough fracture sand backflow and remaining conductivity testing device further includes a press 26. Both the upper piston 2 and the lower piston 3 are connected to the press 26. The closing stress required for the experiment is provided by the press 26. At the same time, in order to simulate the formation environment, the back pressure required for the experiment can be achieved by adjusting the back pressure valve 14 at the outlet of the first drain pipe 13 (a pressure gauge can be equipped at the outlet of the first drain pipe 13 for displaying the back pressure). By measuring the change in the distance between the upper piston 2 and the lower piston 3 with the laser rangefinder 6, the change in the thickness (i.e., the fracture width) of the proppant layer during the experiment can be obtained.

[0047] Embodiment 2: As Figure 1As shown in the figure, as an optimization of the above embodiments, filter loss holes 20 are provided in the middle of the upper piston 2 and the lower piston 3. A second drain pipe 21 is fixedly connected to the filter loss hole 20 of the upper piston 2, and a second liquid collecting tank 22 is provided at the outlet of the second drain pipe 21. A third drain pipe 23 is fixedly connected between the filter loss hole 20 of the lower piston 3 and the second drain pipe 21. When performing a displacement experiment using the rough fracture sand backflow and remaining conductivity testing device, the filter loss liquid flowing out of the filter loss hole 20 can be collected and measured, and thus the determination of the filter loss volume can be achieved.

[0048] Embodiment 3: As Figure 1 shown in the figure, as an optimization of the above embodiments, the rough fracture sand backflow and remaining conductivity testing device further includes a CT scanner, and the diversion chamber 1 is arranged in the scanning area of the CT scanner. When performing a displacement experiment using the rough fracture sand backflow and remaining conductivity testing device, white oil is injected into the proppant layer at a low flow rate, and then water is used for displacement. At the same time, the diversion chamber 1 is scanned by the CT scanner to obtain the oil-water relative permeability curve online.

[0049] Embodiment 4: As Figure 1 shown in the figure, as an optimization of the above embodiments, a filter plug 24 is provided at the inlet of the diversion cavity 4.

[0050] Embodiment 5: As Figure 1 shown in the figure, as an optimization of the above embodiments, the liquid storage tank includes a water storage tank 9 and a fracturing fluid storage tank 10. A first liquid displacement pipeline 11 is fixedly connected between the constant pressure and constant flow pump 8 and the water storage tank 9. A second liquid displacement pipeline 12 is fixedly connected between the liquid outlet of the water storage tank 9 and the inlet of the diversion cavity 4. A third liquid displacement pipeline 16 is fixedly connected between the fracturing fluid storage tank 10 and the first liquid displacement pipeline 11. A fourth liquid displacement pipeline 17 is fixedly connected between the outlet of the fracturing fluid storage tank 10 and the second liquid displacement pipeline 12.

[0051] Embodiment 6: As Figure 1 shown in the figure, as an optimization of the above embodiments, the diversion chamber 1 is provided with a heater 18 for heating the diversion cavity 4. The heater 18 is a detachable heating rod or heating pack. Specifically, there is a hole with a diameter of about 2 cm at the upper left corner and the upper right corner of the diversion chamber 1, and the heating rod is inserted into these two holes. A detachable heating pack is arranged on the side of the diversion chamber 1, and the detachable heating pack can also play a heat preservation role.

[0052] Embodiment 7: As Figure 1 shown in the figure, as an optimization of the above embodiments, the rough fracture sand backflow and remaining conductivity testing device further includes a data processing system 19. The pressure detector 5, the temperature sensor 7, and the laser rangefinder 6 are all electrically connected to the data processing system 19. The data processing system 19 can be a computer for storing and processing data.

[0053] In the present invention, according to requirements, valves 25 are provided on each pipeline of the rough fracture backflow sand production and remaining conductivity testing device as required.

[0054] Example 8: As Figure 1 shown, the rough fracture backflow sand production and remaining conductivity testing method is carried out according to the following steps:

[0055] The first step is to perform true triaxial fracturing on the rock to simulate the rough fracture surface underground after fracturing.

[0056] The second step is to make the fractured rock into two rock slabs (the size of the rock slabs matches the size of the cavity of the diversion chamber 1), and then apply glue to seal its periphery.

[0057] The third step is to load the two rock slabs and the proppant required for the experiment into the diversion cavity 4 after paving, and assemble the rough fracture backflow sand production and remaining conductivity testing device.

[0058] The fourth step is to adjust the closing stress applied to the upper piston 2 and the lower piston 3 through the press 26, and adjust the back pressure according to the experimental requirements, and inject the displacement fluid into the proppant in the diversion cavity 4 at the injection pressure or flow rate required for the experiment to conduct the conductivity testing experiment, collect the outflow displacement fluid and sand production, and record the experimental data.

[0059] The fifth step is to obtain the change in the conductivity of the proppant and the change in the fracture width with the change in conductivity according to the displacement pressure difference, fracture width change, sand production amount, and displacement fluid outflow amount measured in the experiment.

[0060] In the present invention, the proppant can be artificial ceramsite, quartz sand, metal aluminum balls, walnut shells, glass beads, plastic balls, steel balls, resin-coated sand, etc.

[0061] Example 9: As an optimization of the above example, in the fifth step, the conductivity is calculated using the following formula:

[0062]

[0063] In the formula, kw f is the conductivity of the proppant, μm 2 ·cm; q is the displacement (i.e., the flow rate of water injection into the proppant layer), ml / min; Δp is the pressure difference, kilopascal (kPa); μ is the fluid viscosity at the test temperature, centipoise (cp).

[0064] Example 10: As an optimization of the above example, the rough fracture sand backflow and remaining conductivity test method further includes a sixth step, measurement of the oil-water relative permeability curve. The specific operation is as follows: Inject white oil into the proppant layer at a low flow rate, and then displace it with water. At the same time, perform a CT scan on the flow-through cell 1 using a CT scanner to obtain the oil-water relative permeability curve online.

[0065] Example 9: As an optimization of the above example, in the fourth step, the specific operation of the conductivity test experiment is as follows:

[0066] A41, Inject the water in the water storage tank 9 into the proppant layer at the injection water flow rate required for the experiment in the constant flow mode, and record the pressure difference between the pressure sensors at the left and right ends of the flow-through cell 1 at this time. The injected water volume is 100 PV to 150 PV;

[0067] A42, After the water injection is completed, inject the fracturing fluid in the fracturing fluid storage tank 10 into the flow-through cell 1 in the constant flow mode. The injection flow rate of the fracturing fluid is 0.1 ml / min to 0.5 ml / min, and the injected volume of the fracturing fluid is 10 PV;

[0068] A43, After the injection of the fracturing fluid is completed, set the injection water flow rate and inject the water in the water storage tank 9 into the proppant layer again in the constant flow mode, and record the pressure difference between the pressure detectors 5 at the left and right ends of the flow-through cell 1 at this time;

[0069] A44, Observe whether sand production occurs at the current injection water flow rate. If sand production occurs, record the current displacement time. This injection water flow rate is the critical sand production flow rate. If no sand production occurs, increase the injection water flow rate and perform step A43 again.

[0070] Using the rough fracture sand backflow and remaining conductivity test device of the present invention, the damage ability of the proppant can also be tested. The damage ability is also the comparison before and after the damage. The experimental process is to first measure the conductivity 1 with clean water, inject the fracturing fluid, and then inject clean water under the same conditions. At this time, measure the conductivity 2. Since there will be residues in the fracturing fluid, which will affect the conductivity, as long as the fracturing fluid flows through, the conductivity will decrease. Clean water is used before and after injecting the fracturing fluid, and measured at the same flow rate, and the comparison before and after the damage can be obtained. The test steps are the same as steps A41 to A43. The injection water flow rates in steps A41 and A43 are the same. Substitute the experimental data measured in step A41 into Equation 1 to calculate the conductivity 1 kw f1 , Substitute the experimental data measured in step A43 into Equation 1 to calculate the conductivity 2 kw f2 , Further calculate the damage ability η according to the following

[0071] Equation 2.

[0072]

[0073] Example 10: As an optimization of the above embodiments, in the fourth step, the experimental temperature of the displacement experiment is 0 to 150 degrees Celsius.

[0074] To solve the problems of unclear understanding of the fracture conductivity and unclear underground oil and water utilization before, after, and during the backflow, the present invention provides a rough fracture sand production during backflow and remaining conductivity testing device and method. This device can simulate various formation conditions such as roughness, high temperature, and high pressure, and can monitor the change of conductivity in real time during the backflow process. At the same time, a more accurate oil-water relative permeability curve can be obtained, so as to understand the oil and water utilization in the fracture more clearly.

[0075] Example 11: The experimental test is carried out using the rough fracture sand production during backflow and remaining conductivity testing device of the present invention. The test process is as follows:

[0076] In the first step, true triaxial fracturing is carried out on the rock to simulate the rough fracture surface underground after fracturing.

[0077] In the second step, after the fractured rock is processed into two rock slabs with a length of 17.8 cm, a width of 3.8 cm, and a thickness of 2 cm using a cutting machine, silicone rubber adhesive is applied to seal its periphery.

[0078] In the third step, after laying two rock slabs and 38.712 g of 40 / 70 mesh proppant, they are loaded into the diversion cavity 4, and the rough fracture sand production during backflow and remaining conductivity testing device is assembled. A detachable heating pack is added, the heating rod is inserted, the heating temperature is set through the computer, and at the same time, the temperature sensor 7 is turned on.

[0079] In the fourth step, displacement fluid is injected into the proppant in the diversion cavity 4 at the injection pressure or flow rate required for the experiment for displacement experiment, and the outflow displacement fluid and sand production are collected, and the experimental data are recorded:

[0080] ① After the device reaches the expected temperature, check whether the expected pressure exceeds the range of the pressure sensor. If it does not exceed the range, turn on all pressure sensors.

[0081] ② Through the computer, adjust the pressure of the press 26 to the specified pressure of 1 MPa; manually adjust the backpressure valve 14 to set the backpressure to the specified pressure of 1 MPa.

[0082] ③ Open the valves 25 before and after the water storage tank 9, and close the valves 25 before and after the water storage tank 9 for storing fracturing fluid; set the pump to the constant flow mode for displacement, and initially set the injection flow rate to 3 ml / min, and the displacement fluid volume is 100 PV (PV refers to the pore volume, and 100 PV means 100 times the void volume. In the experimental process, it is generally considered that the porosity is 30%, that is, 100 cm 3The proppant with a volume of 30 cm in the middle pore volume 3 ) The displacement time is 100 PV liquid volume divided by the current flow rate, and record the pressure difference between the pressure detectors 5 at the left and right ends of the diversion chamber 1 at this time.

[0083] ④ Close the constant flow pump, close the valves 25 before and after the water storage tank 9, and open the valves 25 before and after the water storage tank 9 for storing pressure.

[0084] ⑤ Set the flow rate of the constant flow pump to 0.1 ml / min, and the displacement liquid volume is 10 PV (the time is 10 PV liquid volume divided by the current flow rate).

[0085] ⑥ Close the constant flow pump, open the valves 25 before and after the water storage tank 9, and close the valves 25 before and after the water storage tank 9 for storing fracturing fluid; set the pump to the constant flow mode for displacement, initially set the injection flow rate to 3 ml / min, and the injection volume is 100 PV (the time is 100 PV liquid volume divided by the current flow rate).

[0086] ⑦ Observe whether sand production occurs at the current flow rate. If no sand is produced, adjust the flow rate to 5 ml / min; the displacement liquid volume is 100 PV (the time is 100 PV liquid volume divided by the current flow rate). If sand is produced, record the current displacement time, and this flow rate is the critical sand production flow rate.

[0087] ⑧ Adjust the injection flow rate to 5 ml / min, 7 ml / min, 10 ml / min, 15 ml / min, and 20 ml / min in sequence. In the case of no sand production, the displacement time is 100 PV liquid volume divided by the current flow rate. If sand is produced, after the time of 100 PV displacement liquid volume, reduce the flow rate to the critical sand production flow rate for displacement (specifically, if 7 ml / min is used as the critical flow rate, 1 PV volume is 7.74 cm 3 , and the 100 PV volume is 774.24 cm 3 . The experimental time at a flow rate of 7 ml / min is 111 min. At 112 min, the flow rate is adjusted to 10 ml / min, the displacement time for 100 PV is 77 min, and at the 78th min, the flow rate is adjusted to 7 ml / min for displacement for 33 min (the total time is 111 min), and so on). The total time is the time required for displacing 100 PV at the critical sand production flow rate.

[0088] Record the sand production amount at each flow rate (expressed as the sand production percentage. After drying the proppant flowing out during the experiment, measure the weight, and the weight of the flowing out proppant divided by the total weight of the laid proppant is the sand production percentage), and the reading after the pressure difference between the pressure sensors at the left and right ends of the diversion chamber 1 stabilizes. Calculate the diversion capacity of the rough fracture under different sand production amounts, and the results are shown in Table 1.

[0089] Example 12: The rough fracture sand backflow and remaining conductivity testing device is used to test the oil-water relative permeability curve:

[0090] In this experiment, outcrop rocks were processed into rock slabs for the experiment. Before the reflux experiment started, the diversion chamber 1 was placed in the scanning area of the CT scanner to measure its oil-water relative permeability curve (as Figure 2 shown). Then the reflux experiment was carried out. After the reflux experiment ended, the diversion chamber 1 was scanned by CT again to measure its oil-water relative permeability curve (as Figure 3 shown). It can be Figure 3 observed that after the proppant backflows, the amount of proppant between the rock slabs decreases and the conductivity drops. The intersection point of Kro and Krw (hereinafter referred to as the isosmotic point) moves to the left as the proppant flows out. Before the proppant backflows, within the water saturation range of 0 to 1, both oil and water have relative permeability and there is no residual oil in the fracture. After the proppant backflows, the water saturation is greater than 0.65, Kro is 0, indicating that the oil phase cannot move in the fracture, and the residual oil saturation is 35%. After the proppant backflows, the conductivity drops; the amount of residual oil increases; the isosmotic point moves to the left, and at the same water saturation, the relative permeability of the oil phase is lower.

[0091] In summary, the present invention fully considers the problems of single simulation variables and unrealistic simulated formation conditions in previous experimental processes, and introduces various devices such as true triaxial fracturing and laser rangefinders into the device. At the same time, in order to better understand the residual phase distribution in the fracture at different stages, CT scanning is also introduced to measure the oil-water relative permeability curve. The rough fracture sand backflow and remaining conductivity testing device of the present invention has a more realistic simulation of formation conditions, a better understanding of the residual phase distribution in the fracture, higher accuracy of various data obtained during the backflow process after fracturing, is of great significance for studying the backflow after fracturing, and can measure a variety of experimental data, with a wide range of applications.

[0092] The above technical features constitute the embodiments of the present invention, which have strong adaptability and implementation effects. Non-essential technical features can be increased or decreased according to actual needs to meet the requirements of different situations.

[0093] Table 1

[0094]

Claims

1. A rough fracture return sand discharge and residual conductivity testing device, characterized in that The invention comprises a liquid drive system and a flow diversion system. The flow diversion system comprises a flow diversion chamber. An upper piston and a lower piston which can move up and down are arranged horizontally in the flow diversion chamber. A flow diversion chamber is formed between the upper piston and the lower piston. Pressure detection points are arranged in the flow diversion chamber corresponding to the left end, the middle part and the right end of the flow diversion chamber. A pressure detector is fixedly arranged at the pressure detection point. A laser rangefinder for measuring the distance change between the upper piston and the lower piston is fixedly arranged at the left end of the upper piston. A temperature sensor is arranged on the left side of the flow diversion chamber. The liquid drive system comprises a constant pressure and constant flow pump and a liquid storage tank. A first liquid drive pipeline is fixedly connected between the constant pressure and constant flow pump and the liquid storage tank. A second liquid drive pipeline is fixedly connected between the liquid outlet of the liquid storage tank and the inlet of the flow diversion chamber. A first liquid discharge pipe is fixedly connected to the liquid outlet of the flow diversion chamber. A back pressure valve is fixedly arranged on the first liquid discharge pipe. A first liquid collecting tank is arranged at the outlet of the first liquid discharge pipe.

2. The rough fracture return sand discharge and residual conductivity testing device according to claim 1 is characterized in that A filtration hole is opened in the middle of the upper piston and the lower piston, a second drainage pipe is fixedly connected to the filtration hole of the upper piston, a second liquid collecting tank is arranged at the outlet of the second drainage pipe, and a third drainage pipe is fixedly connected between the filtration hole of the lower piston and the second drainage pipe; the rough fracture return sand discharge and residual conductivity testing device also includes a CT scanner, and the diversion chamber is arranged in the scanning area of ​​the CT scanner.

3. The rough fracture return sand discharge and residual conductivity testing device according to claim 1 or 2, characterized in that The inlet of the diversion cavity is provided with a filter plug; the diversion chamber is provided with a heater for heating the diversion cavity, and the heater is a detachable heating rod or a heating pack.

4. The rough fracture return sand discharge and residual conductivity testing device according to claim 1, 2 or 3, characterized in that The liquid storage tank includes a water storage tank and a fracturing fluid storage tank. A first liquid drive pipeline is fixedly connected between the constant pressure and constant flow pump and the water storage tank, a second liquid drive pipeline is fixedly connected between the liquid outlet of the water storage tank and the inlet of the diversion cavity, a third liquid drive pipeline is fixedly connected between the fracturing fluid storage tank and the first liquid drive pipeline, and a fourth liquid drive pipeline is fixedly connected between the outlet of the fracturing fluid storage tank and the second liquid drive pipeline.

5. The rough fracture return sand discharge and residual conductivity testing device according to any one of claims 1 to 4, characterized in that The rough fracture return sand discharge and residual conductivity testing device also includes a data processing system, and the pressure detector, the temperature sensor, and the laser rangefinder are all electrically connected to the data processing system.

6. A method for testing the rough fracture return sand discharge and residual conductivity testing device according to any one of claims 1 to 5, characterized in that Follow these steps: The first step is to perform true triaxial fracturing on the rock to simulate the rough fracture surface underground after fracturing; The second step is to make two rock plates from the fractured rock, and then apply glue to seal them all around; The third step is to install two rock plates and the proppant required for the experiment into the diversion cavity after paving, and assemble the rough fracture return sand discharge and residual conductivity test device; The fourth step is to adjust the closing stress applied to the upper piston and the lower piston by the press, and adjust the back pressure according to the experimental needs, inject the displacement fluid into the proppant in the diversion cavity at the injection pressure or flow rate required by the experiment to conduct a diversion test experiment, collect the outflowing displacement fluid and sand, and record the experimental data; The fifth step is to obtain the change of sand discharge and conductivity of rough fractures based on the displacement pressure difference, fracture width change, sand production and displacement fluid outflow measured in the experiment.

7. The testing method according to claim 6, characterized in that In the fourth step, the specific operations of the diversion test experiment are as follows: A41, in constant flow mode, inject water from the water storage tank into the proppant layer at the required water injection flow rate for the experiment, and record the pressure difference between the pressure sensors at the left and right ends of the diversion chamber at this time. The water injection volume is 100PV to 150PV; A42, after the water injection is completed, the fracturing fluid in the fracturing fluid storage tank is injected into the flow guide chamber in a constant flow mode, the injection flow rate of the fracturing fluid is 0.1ml / min to 0.5ml / min, and the injection volume of the fracturing fluid is 10PV; A43, after the injection of the fracturing fluid is completed, the water injection flow rate is set and the water in the water storage tank is injected into the proppant layer again in a constant flow mode, and the pressure difference between the pressure sensors at the left and right ends of the diversion chamber is recorded at this time; A44, observe whether sand is produced at the current water injection flow rate. If sand is produced, record the current displacement time. This water injection flow rate is the critical sand production flow rate. If no sand is produced, increase the water injection flow rate and execute step A43 again.

8. The method for testing sand discharge and residual conductivity of rough fractures according to claim 6 or 7, characterized in that In the fifth step, the flow conductivity is calculated using the following formula: In the formula, kw f is the conductivity of the proppant, μm 2 ·cm; q is the displacement, ml / min; Δp is the pressure difference, KPa; μ is the fluid viscosity at the test temperature, cp.

9. The method for testing sand return and residual conductivity of rough fractures according to any one of claims 6 to 8, characterized in that It also includes a sixth step, measuring the oil-water relative permeability curve. The specific operation is: inject white oil into the proppant layer at a low flow rate, then displace it with water, and at the same time perform a CT scan of the diversion chamber through a CT scanner to obtain the oil-water relative permeability curve online.

10. The method for testing sand return and residual conductivity of rough fractures according to any one of claims 6 to 9, characterized in that In the fourth step, the experimental temperature of the displacement experiment is 0 to 150 degrees Celsius.

Images